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The Zettabyte Era Trends and Analysis Cisco Enhanced PDF Este documento faz parte do Cisco Reg Visual Networking Index (VNI), uma iniciativa contínua para rastrear e prever o impacto das aplicações de redes visuais. O documento apresenta algumas das principais descobertas da previsão de tráfego global de IP da Ciscos e explora as implicações do crescimento do tráfego de IP para os prestadores de serviços. Para uma visão mais detalhada da previsão e da metodologia por trás, visite Cisco VNI: Forecast and Methodology, 20152020. O tráfego global anual de IP passará o limite zettabyte (ZB 1000 exabytes EB) até o final de 2016 e atingirá 2,3 ZB por ano até 2020. Até o final de 2016, o tráfego global de IP atingirá 1,1 ZB por ano, ou 88,7 EB por mês, e, até 2020, o tráfego global de IP atingirá 2,3 ZB por ano, ou 194 EB por mês. O tráfego IP global aumentará quase três vezes nos próximos 5 anos. Em geral, o tráfego de IP crescerá a uma taxa de crescimento anual composta (CAGR) de 22 por cento de 2015 a 2020. O tráfego mensal de IP chegará a 25 GB per capita até 2020, acima de 10 GB per capita em 2015. O tráfego de Internet ocupado é de Crescendo mais rapidamente do que o tráfego médio na Internet. A hora ocupada (ou o período mais movimentado de 60 minutos em um dia) aumentou 51 por cento em 2015, em comparação com o crescimento de 29 por cento no tráfego médio. O tráfego da Internet de horas ocupadas aumentará em 4,6 entre 2015 e 2020, e o tráfego médio da Internet aumentará em 2,0. O tráfego de smartphones excederá o tráfego de PC até 2020. Em 2015, as PCs representaram 53% do tráfego total de IP, mas, até 2020, as PCs representarão apenas 29% do tráfego. Os smartphones representarão 30 por cento do tráfego IP total em 2020, acima de 8 por cento em 2015. O tráfego originado pelo PC crescerá em um CAGR de 8 por cento, e os módulos de TV, tablets, smartphones e máquina-a-máquina (M2M) Terá taxas de crescimento do tráfego de 17%, 39%, 58% e 44%, respectivamente. O tráfego de dispositivos sem fio e móveis representará dois terços do tráfego IP total até 2020. Até 2020, os dispositivos com fio representarão 34% do tráfego de IP, e Wi-Fi e dispositivos móveis representarão 66% do tráfego de IP. Em 2015, os dispositivos com fio representavam a maior parte do tráfego de IP, em 52%. As redes de entrega de conteúdo (CDNs) terão quase dois terços do tráfego de Internet até 2020. Sessenta e quatro por cento de todo o tráfego da Internet irão cruzar os CDNs até 2020 globalmente, ante 45% em 2015. O número de dispositivos conectados às redes IP será mais de três vezes a população global até 2020. Haverá 3,4 dispositivos em rede per capita até 2020, em relação a 2,2 dispositivos em rede per capita em 2015. Haverá 26,3 bilhões de dispositivos em rede em 2020, ante 16,3 bilhões em 2015. A velocidade da banda larga quase dobrará até 2020. Até 2020, as velocidades globais de banda larga fixas chegarão a 47,7 Mbps, acima de 24,7 Mbps em 2015. Destaques globais de vídeos e jogos da Internet Levarão mais de 5 milhões de anos para assistir a quantidade de vídeo que cruzará as redes IP globais por mês em 2020. A cada segundo, um milhão de minutos de conteúdo de vídeo atravessará a rede até 2020. Globalmente, o tráfego de vídeo IP será de 82% de todo o tráfego de IP (empresas e consumidores) em 2020, ante 70% em 2015. O tráfego global de vídeo IP crescerá três vezes de 2015 a 2020, um CAGR de 26%. O tráfego de vídeo na Internet crescerá quatro vezes de 2015 a 2020, um CAGR de 31%. O tráfego de videovigilância na Internet quase duplicou em 2015. De 272 petabytes por mês no final de 2014 para 516 petabytes por mês em 2015. O tráfego de vigilância de Internet aumentará dez vezes entre 2015 e 2020. Globalmente, o tráfego de vídeo na Internet será de 3,9 por cento em 2020, a partir de 1,5 por cento em 2015. O tráfego de realidade virtual quadruplicou em 2015. De 4,2 petabytes (PB) por mês em 2014 para 17,9 PB por mês em 2015. Globalmente, o tráfego de realidade virtual aumentará 61 vezes entre 2015 e 2020, um CAGR de 127%. O vídeo na Internet para TV cresceu 50% em 2015. Este tráfego continuará a crescer a um ritmo acelerado, aumentando 3,6 vezes até 2020. O vídeo da Internet para a TV será de 26% do tráfego fixo de vídeo na Internet do consumidor em 2020. O tráfego de video-on-demand (VoD) do consumidor quase dobrará até 2020 . A quantidade de tráfego VoD em 2020 será equivalente a 7,2 bilhões de DVDs por mês. O tráfego de jogos na Internet crescerá sete vezes de 2015 a 2020. Um CAGR de 46%. Globalmente, o tráfego de jogos na Internet será de 4% do tráfego de Internet do consumidor em 2020, ante 2% em 2015. Global Mobile Highlights Globalmente, o tráfego de dados móveis aumentará oito vezes entre 2015 e 2020. O tráfego de dados móveis crescerá em um CAGR de 53% entre 2015 e 2020, chegando a 30,6 exabytes por mês até 2020. O tráfego global de dados móveis crescerá quase três vezes mais rápido que o tráfego IP fixo de 2015 a 2020. O tráfego fixo de IP crescerá em um CAGR de 19 por cento entre 2015 e 2020, enquanto o tráfego móvel cresce em um CAGR de 53 por cento. O tráfego global de dados móveis foi de 5% do tráfego IP total em 2015 e será de 16% do tráfego total de IP até 2020. O tráfego IP está crescendo mais rápido no Oriente Médio e África, seguido pela Ásia-Pacífico. O tráfego no Oriente Médio e África crescerão em um CAGR de 41% entre 2015 e 2020. Resumo das taxas de crescimento regional: o tráfego de IP na América do Norte atingirá 59,1 EB por mês até 2020, crescendo a uma CAGR de 19%. O tráfego de IP na Europa Ocidental atingirá 28,0 EB por mês até 2020, crescendo a uma CAGR de 20%. O tráfego de IP na Ásia-Pacífico atingirá 67,8 EB por mês até 2020, crescendo a CAGR de 22%. O tráfego de IP na América Latina atingirá 11,6 EB por mês até 2020, crescendo em um CAGR de 21%. O tráfego de IP na Europa Central e Oriental atingirá 17,0 EB por mês até 2020, crescendo a uma CAGR de 27%. O tráfego de IP no Oriente Médio e África atingirá 10,9 EB por mês até 2020, crescendo a uma CAGR de 41%. Nota: várias ferramentas interativas estão disponíveis para permitir que você crie destaques personalizados e gráficos de previsão por região, por país, por aplicativo e por segmento de usuário final (consulte a ferramenta Cisco VNI Forecast Highlights e a ferramenta Cisco VNI Forecast Widget). Destaques do Negócio Global O tráfego de IP de negócios crescerá em um CAGR de 18% de 2015 para 2020. A adoção crescente de comunicações de vídeo avançadas no segmento empresarial causará o crescimento do tráfego de negócios por um fator de 2 entre 2015 e 2020. O tráfego de Internet de negócios crescerá a um ritmo mais rápido do que o IP WAN. O tráfego IP WAN crescerá em um CAGR de 6 por cento, em comparação com um CAGR de 21 por cento para Internet de negócios fixos e 47 por cento para tráfego de internet de negócios móveis. O tráfego IP de negócios crescerá mais rápido no Oriente Médio e na África. O tráfego de IP empresarial no Oriente Médio e África crescerá em um CAGR de 21 por cento, um ritmo mais rápido do que a média global de 18 por cento. Em volume, a Ásia-Pacífico terá a maior quantidade de tráfego IP comercial em 2019, em 11,4 EB por mês. A América do Norte será em segundo lugar, com 9,1 EB por mês. O atual índice de rede visual da Cisco (VNI) projeta o tráfego global de IP para quase triplicar entre 2015 e 2020. O apêndice A oferece um resumo detalhado. O tráfego global de IP deverá crescer para 194 EB por mês até 2020, acima de 72,5 EB por mês em 2015, um CAGR de 22% (Figura 1). Esse crescimento representa apenas um ligeiro declínio da taxa de crescimento projetada de 2014 para 2019, que foi de 23%. Parece que o crescimento do tráfego IP global está se estabilizando no intervalo de porcentagem de 2025. Figura 1. Previsões da Cisco VNI 194 EB por Mês de tráfego de IP até 2020 Fonte: Previsão de tráfego de IP global da Cisco VNI, 20152020 Para obter mais detalhes sobre a metodologia de previsão Ciscos, consulte o artigo Cisco VNI: Previsão e metodologia, 20152020. Para entender a magnitude Dos volumes de tráfego IP, ajuda a examinar os números em termos mais familiares: até 2020, o gigabyte (GB) equivalente a todos os filmes já realizados passará a Internet global a cada 2 minutos. Globalmente, o tráfego de IP atingirá 511 terabits por segundo (Tbps) em 2020, o equivalente a 142 milhões de pessoas que transmitem o vídeo de alta definição (HD) da Internet simultaneamente, o dia todo, todos os dias. O tráfego global de IP em 2020 será equivalente a 504 bilhões de DVDs por ano, 42 bilhões de DVDs por mês, ou 58 milhões de DVDs por hora. O tráfego total na Internet experimentou um crescimento dramático nas últimas duas décadas. Mais de 20 anos atrás, em 1992, as redes globais de Internet carregavam aproximadamente 100 GB de tráfego por dia. Dez anos depois, em 2002, o tráfego global da Internet era de 100 gigabytes por segundo (GBps). Em 2015, o tráfego global da Internet atingiu mais de 20 mil GBps. A Tabela 1 fornece uma visão dos benchmarks históricos para o tráfego total da Internet. Tabela 1. O contexto Cisco VNI ForecastHistorical Internet Source: Cisco VNI, 2016 IP per capita e crescimento do tráfego da Internet seguiram uma curva de crescimento igualmente íngreme na última década. Globalmente, o tráfego mensal de IP atingirá 25 GB per capita até 2020, acima de 10 GB per capita em 2015, e o tráfego da Internet atingirá 21 GB per capita até 2020, acima de 7 GB per capita em 2015. Não há muito tempo, em 2008 , O tráfego per capita de Internet era de 1 GB por mês. Em 2000, o tráfego per capita na Internet era de 10 megabytes (MB) por mês. As seções a seguir exploram as tendências que contribuem para o crescimento contínuo do tráfego IP global. Tendência 1: Mudanças contínuas na mistura de dispositivos e conexões A Figura 2 mostra que globalmente, dispositivos e conexões (CAGR de 10%) estão crescendo mais rápido do que a população (CAGR de 1,1%) e usuários de Internet (CAGR de 6,5%). Essa tendência está acelerando o aumento na média de dispositivos e conexões por lar e por usuário da Internet. Todos os anos, vários novos dispositivos em diferentes fatores de forma com capacidades e inteligência aumentadas são introduzidos e adotados no mercado. Um número crescente de aplicativos M2M, como medidores inteligentes, videovigilância, monitoramento de cuidados de saúde, transporte e rastreamento de pacotes ou ativos, estão contribuindo de forma importante para o crescimento de dispositivos e conexões. Até 2020, as conexões M2M serão 46 por cento do total de dispositivos e conexões. Figura 2. Figuras de crescimento de dispositivos e conexões globais (n) referem-se ao compartilhamento de dispositivo 2015, 2020. Fonte: Previsão Global de tráfego IP da Cisco VNI, 20152020 As conexões M2M serão a categoria de crescimento mais rápido, crescendo quase 2,5 vezes durante o período de previsão, em 20 por cento CAGR, para 12,2 bilhões de conexões até 2020. Os smartphones crescerão o segundo mais rápido, às 13 - CAGR por cento (aumentando em um fator de 1,8). As TVs conectadas (que incluem TVs de tela plana, set-top boxes, adaptadores de mídia digital DMAs, leitores de discos Blu-ray e consoles de jogos) crescerão próximo ao mais rápido em 12 por cento CAGR, para 3.1 bilhões até 2020. Os PCs continuarão Para diminuir (cerca de um declínio de 2 por cento) durante o período de previsão. No entanto, haverá mais PCs do que comprimidos no final de 2020 (1,35 bilhões de PCs versus 785 milhões de comprimidos). Em 2020, a participação dos consumidores nos dispositivos totais, incluindo dispositivos fixos e móveis, será de 74 por cento, com negócios alegando os 26 por cento restantes. A parcela do consumidor crescerá a uma taxa ligeiramente mais lenta, com CAGR de 9,5% em relação ao segmento de negócios, que crescerá em 12% da CAGR. Para obter mais detalhes sobre o crescimento em dispositivos e conexões em segmentos residenciais, móveis de consumo e de negócios, consulte a ferramenta Cisco VNI Service Adoption Forecast Highlights. Globalmente, o número médio de dispositivos e conexões per capita passará de 2 em 2015 para 3,2 até 2020 (Tabela 2). Tabela 2. Número médio de dispositivos e conexões por habitante Fonte: Cisco VNI, 2016 Entre os países que terão a maior média de dispositivos e conexões per capita até 2020, estão os Estados Unidos (12,3), a Coréia do Sul (12,2) e o Japão (11,9). A mudança de mix de dispositivos e conexões eo crescimento da propriedade multidevice afetam o tráfego e podem ser vistos na troca de contribuição do dispositivo para o tráfego IP total. No final de 2015, 47 por cento do tráfego de IP e 37 por cento do tráfego de Internet do consumidor eram originários de dispositivos que não eram PC. Até 2020, 71 por cento do tráfego de IP e 71 por cento do tráfego de Internet do consumidor serão originados a partir de dispositivos não-PC (Figura 3). Figura 3. Tráfego IP global por dispositivos Figuras (n) referem-se ao compartilhamento de dispositivo 2015, 2020. Fonte: Cisco VNI Global IP Traffic Forecast, 20152020 Como no caso das redes móveis, os dispositivos de vídeo podem ter um efeito multiplicador no tráfego. Uma televisão HD habilitada para Internet que desenha 45 minutos de conteúdo por dia da Internet geraria tanto tráfego na Internet quanto toda a família hoje. Com o crescimento da visualização de vídeos em smartphones e tablets, o tráfego desses dispositivos está crescendo como uma porcentagem do tráfego total na Internet. As tabelas representarão 15% do tráfego global global de Internet até 2020, ante 9% em 2015. Os smartphones representarão 37% do tráfego global global da Internet até 2020, ante 11% em 2015 (Figura 4). Figura 4. Tráfego global da Internet por tipo de dispositivo Figuras (n) referem-se a 2015, compartilhamento de dispositivos 2020. Fonte: Previsão de tráfego de IP global Cisco VNI, 20152020 O impacto de vídeo dos dispositivos no tráfego é mais pronunciado devido à introdução de transmissão de vídeo ultra-alta (UHD) ou 4K. Essa tecnologia tem um impacto, pois a taxa de bits para o vídeo de 4K em cerca de 18 Mbps é mais que o dobro da taxa de bits de vídeo em HD e nove vezes mais do que a taxa de bits de vídeo de definição padrão (SD). Nós estimamos que até 2020, 40 por cento dos aparelhos de TV instalados instalados serão UHD, acima de 8 por cento em 2015 (Figura 5). Figura 5. Aumento da definição de vídeo: até 2020, mais de 40 por cento dos conjuntos de TV de painel plano conectados serão 4K Fonte: Cisco VNI Global IP Traffic Forecast, 20152020 UHD (ou 4K) IP VoD representará 21% do tráfego global VoD Em 2020 (Figura 6). Figura 6. Dados globais de tráfego de vídeo 4K (n) referem-se a 2015, partes de tráfego de 2020. Fonte: Previsão de tráfego IP global da Cisco VNI, 20152020 Tendência 2: A adoção de IPv6 permite a conexão da Internet de tudo A transição de um ambiente IPv4 para um ambiente IPv6 está fazendo um excelente progresso, com aumentos nos recursos do dispositivo IPv6, ativação de conteúdo e operadores implementando IPv6 em Suas redes. Esses desenvolvimentos são particularmente importantes porque a Ásia, a Europa, a América do Norte e a América Latina já esgotaram suas atribuições de IPv4, e espera-se que a África esvazie sua colocação até 2018. A Tabela 3 mostra as datas de exaustão projetadas até maio de 2016, de acordo com a Região Registos da Internet (RIR). Tabela 3. Datas de exaustão do endereço IPv4 Registros regionais da Internet Com base na análise de dispositivos VNI IPv6, a previsão prevê que, em todo o mundo, haverá cerca de 13 bilhões de dispositivos fixos e móveis IPv6apapáveis ​​até 2020, em comparação com quase 4 bilhões em 2015, um CAGR de 27 por cento. Em termos de porcentagens, 48 ​​por cento de todos os dispositivos fixos e móveis em rede serão compatíveis com IPv6 até 2020, acima de 23 por cento em 2015 (Figura 7). Essa estimativa é baseada na capacidade do dispositivo e na conexão de rede para suportar o IPv6 e não é uma projeção de conexões IPv6 ativas. O recurso IPv6 do dispositivo móvel é avaliado com base no suporte do sistema operacional do IPv6 e estimativas dos tipos de infraestrutura de rede móvel a que o dispositivo pode se conectar (3.5-geração 3.5G ou posterior). A capacidade IPv6 do dispositivo fixo é avaliada com base no suporte do dispositivo IPv6 e uma estimativa da capacidade do equipamento residencial de instalações do cliente (CPE) ou roteadores empresariais para suportar IPv6, dependendo do segmento de usuário final do dispositivo. Figura 7. Previsões globais de dispositivos e conecções compatíveis com IPv6 20152020 Fonte: Previsão de tráfego global de IP Cisco VNI, 20152020 Globalmente, 90% dos smartphones e tablets serão compatíveis com IPv6 até 2020, acima de 60% em 2015. Globalmente, haverá 5,8 bilhões de smartphones e tablets compatíveis com IPv6 até 2020, contra 2.1 bilhões em 2015. Em 2020, 30% das conexões M2M serão compatíveis com IPv6, chegando a 3,7 bilhões, um CAGR de 67%. De acordo com a World IPv6 Launch Organization em maio de 2016, operadores de rede fixa e móvel em todo o mundo estão implantando IPv6 e começando a reportar a geração de tráfego IPv6 notável. Romania RCS ampère RDS relatou cerca de 12 por cento, Frances Free Telecom informou que 22 por cento, KDDI relatou cerca de 28 por cento, Comcast relatou 45 por cento, ATampT relatou 59 por cento, e Verizon Wireless relatou 69 por cento de implantação. De acordo com o Google, em maio de 2016, a porcentagem de usuários que acessam o Google através do IPv6 é de cerca de 11%. Em meio a esses desenvolvimentos da indústria, a previsão do VNI está tentando estimar o potencial tráfego de rede IPv6 que poderia ser gerado se uma porcentagem de dispositivos compatíveis com IPv6 se conectar ativamente a uma rede IPv6, dada a média global estimada para tráfego mensal por tipo de dispositivo . Olhando para 2020, se 60 por cento dos dispositivos compatíveis com IPv6 estiverem ativamente conectados a uma rede IPv6, a previsão estima que o tráfego global de IPv6 seria de 55 EB por mês, ou 34 por cento do tráfego total na Internet (Figura 8). Figura 8. Previsão de tráfego IPv6 fixo e móvel projetado 20152020 Fonte: Previsão de tráfego IP global da Cisco VNI, 20152020 Esta estimativa inicial do potencial tráfego IPv6 é baseada nas premissas de que a capacidade do dispositivo IPv6, a ativação do conteúdo IPv6 e a implantação da rede IPv6 manterão o ritmo Com tendências atuais, e pode até acelerar durante o período de previsão. Considerando a interdependência dessas variáveis, os pressupostos de previsão podem ser sujeitos a aprimoramento à medida que nossa análise continua. Os provedores de conteúdo também estão se movendo para aumentar a habilitação do IPv6 de seus sites e serviços. De acordo com os laboratórios Cisco IPv6. Até 2020, o conteúdo disponível em relação ao IPv6 será de cerca de 35%. Pode haver, no entanto, variação dependendo da popularidade dos sites em regiões e países. Além disso, as iniciativas específicas do país e as implantações de provedores de conteúdo afetaram positivamente a acessibilidade local do conteúdo IPv6. Em geral, a probabilidade de que uma parcela significativa do tráfego da Internet seja gerada através de redes IPv6 representa uma oportunidade considerável para operadores de rede, provedores de conteúdo e usuários finais que buscam obter a escalabilidade e os benefícios de desempenho do IPv6 e permitir a Internet de tudo (IoE). Tendência 3: Aplicações M2M em muitas indústrias aceleram o crescimento do IoE O fenômeno do Internet of Everything (IoE), no qual as pessoas, os processos, os dados e as coisas se conectam à Internet e entre si, está mostrando um crescimento tangível. Globalmente, as conexões M2M crescerão quase 2,5 vezes, passando de 4,9 bilhões em 2015 para 12,2 bilhões até 2020 (Figura 9). Haverá 1.6 conexões M2M para cada membro da população global até 2020. Figura 9. Crescimento Global da Conexão M2M Fonte: Previsão Global de Tráfego IP Cisco VNI, 20152020 Aplicativos domésticos conectados, como automação residencial, segurança doméstica e vigilância por video, branco conectado Bens e aplicações de rastreamento, representarão 47 por cento, ou quase metade, das conexões M2M totais até 2020, mostrando a omnipresença do M2M em nossas vidas (Figura 10). Os cuidados de saúde conexos, com aplicações como monitores de saúde, dispensadores de medicamentos, conectividade de primeiro respondente e telemedicina, serão o segmento da indústria de mais rápido crescimento, com CAGR de 49%. As aplicações de automóveis conectados terão o segundo crescimento mais rápido, com CAGR de 37%. Chips para animais de estimação e gado, monitores digitais de saúde e muitos outros serviços M2M de próxima geração estão promovendo esse crescimento. Figura 10. Crescimento Global da Conexão M2M por Indústrias Outro inclui Agricultura, Construção e Serviços de Emergência. Fonte: Previsão de tráfego de IP global da Cisco VNI, 20152020 Embora o número de conexões cresça três vezes, o tráfego global de M2M IP crescerá seis vezes ao longo desse mesmo período, de um EB por mês em 2015 (1,4 por cento do tráfego IP global) para 6.3 EB por 2020 (3,2 por cento do tráfego IP global referem-se à Figura 11). A quantidade de tráfego está crescendo mais rápido do que o número de conexões devido ao aumento da implantação de aplicativos de vídeo em conexões M2M e ao aumento do uso de aplicativos, como a telemedicina e sistemas de navegação inteligentes, que requerem maior largura de banda e baixa latência. Figura 11. Crescimento global do tráfego M2M: Exabytes por mês Fonte: Previsão global de tráfego de IP da Cisco VNI, 20152020 Tendência 4: Tendências de adoção de serviços: serviços residenciais residenciais, móveis para consumidores e comerciais Serviços residenciais globais: o vídeo continua a crescer entre 2014 e 2015 O crescimento mais alto ocorreu no lado da Internet em jogos online, com crescimento de 15 por cento do ano-ano (ano). A rede social foi o serviço de Internet residencial mais amplamente adotado, com crescimento de 8,5% em termos homólogos, passando de 1,3 bilhão de usuários em 2014 para 1,4 bilhões de usuários em 2015. Em 2020, a TV digital e as redes sociais serão os dois serviços com as maiores taxas de penetração , Com 87% e 76%, respectivamente. O crescimento mais rápido virá de serviços de TV atrasados, como o gravador de vídeo pessoal (PVR) e os serviços de gravador de vídeo digital (DVR), com CAGR de 7%. O jogo online (5,5 por cento do CAGR) será o serviço de Internet residencial de mais rápido crescimento. O crescimento do jogo online é acelerado principalmente por aprimoramentos tecnológicos em PCs, como gráficos, detecção de movimento, reconhecimento de gestos, etc. (Figura 12). Figura 12. Nota de Adoção e Crescimento de Serviços Residenciais Globais. Em 2020, a população residencial fixa residencial global será de 2,4 bilhões, o número de famílias de TV global será de 1,8 bilhão. Fonte: Previsão de Adopção do Serviço Cisco VNI, 20152020 Serviços Móveis Globais do Consumidor Entre 2014 e 2015, todos os serviços móveis de consumo, exceto um, cresceram em mais de 10%. O maior crescimento foi nos serviços baseados em localização do consumidor (LBS), com crescimento de 38%, de uma base de 585 milhões de usuários em 2014 para 807 milhões em 2015. Outro crescimento significativo em relação ao período homólogo foi no banca móvel e no comércio (37%) , Seguido de vídeo móvel (35 por cento). Regiões como a América Latina (62 por cento do crescimento interanual) e Oriente Médio e África (crescimento de 52 por cento em relação ao período anterior) tiveram o crescimento mais rápido no LBS móvel de consumo. O banco móvel e o comércio também cresceram mais rapidamente na América Latina, com crescimento de 49%. O crescimento do vídeo móvel foi liderado pelo Oriente Médio e África, com crescimento de 43%. De 2015 a 2020, seis dos oito serviços móveis de consumo crescerão em mais de 14% de CAGR, três crescerão em mais de 20% de CAGR, e um diminuirá. O crescimento mais rápido será no consumidor LBS (3,9 por cento), seguido pelo comércio móvel (22,7 por cento). As regiões com taxas de crescimento especialmente elevadas nos serviços de comércio móvel são o Oriente Médio e África, Europa Central e Oriental, América Latina e Ásia-Pacífico, que historicamente foram desatendidas (ou não alcançadas) pelas instituições financeiras tradicionais de tijolos e argamassa (Figura 13 ). Figura 13. Nota de Adoção e Crescimento dos Serviços Móveis Globais de Consumidores. Até 2020, a população móvel global de consumidores será de 5 bilhões. Fonte: Previsão de Adopção do Serviço Cisco VNI, 20152020 Serviços Empresariais Globais Entre 2014 e 2015, o maior crescimento do período homólogo foi no negócio LBS, com um aumento de 32%, de 92 milhões de usuários em 2014 para 121 milhões em 2015. Outro crescimento significante do período homólogo foi Em videoconferência de mesa (25 por cento referem-se à Figura 14). Business LBS inclui serviços utilizados por assinantes corporativos em que a subscrição é geralmente paga pelo empregador. Esses serviços incluem automação de força de vendas e campo, gerenciamento de frotas, etc. Vemos que a videoconferência pessoal ou de mesa está substituindo cada vez mais a conferência baseada em sala, à medida que o vídeo se torna mais simples e mais integrado nas ofertas de serviços de comunicações unificadas. De 2015 a 2020, espera-se que o serviço de negócios de mais rápido crescimento seja uma videoconferência pessoal ou de área de trabalho. O crescimento da videoconferência pessoal, especificamente comunicações de videoconferência comunicativas unificadas, recentemente acelerou devido à maior qualidade e menor preço de novos serviços e produtos. Também é causada pela disponibilidade de ofertas de videoconferência no desktop, que podem ser autônomas ou integradas. Além disso, o crescimento em clientes móveis suportará o crescimento de videoconferência. Por outro lado, o uso de web conferencing sem vídeo mostrará um declínio de 4 por cento CAGR durante o período de previsão (Figura 14). Figura 14. Nota de Adoção e Crescimento dos Serviços de Negócios Globais. Até 2020, a população mundial de negócios na Internet será de 2,2 bilhões, o número de usuários empresariais será de 577 milhões. Fonte: Previsão de Adopção do Serviço Cisco VNI, 20152020 Para obter detalhes sobre todos os aspectos do estudo de adoção de serviços, use a ferramenta Cisco VNI Service Adoption Highlights. Tendência 5: crescimento do tráfego de aplicativos A soma de todas as formas de vídeo IP, que inclui vídeo na Internet, IP VoD, arquivos de vídeo trocados através de compartilhamento de arquivos, jogos de vídeo e videoconferência, continuará a variar entre 80 e 90 Por cento do tráfego IP total. Globalmente, o tráfego de vídeo IP representará 82% do tráfego até 2020 (Figura 15). Figura 15. Tráfego de IP Global por Categoria de Aplicação Números (n) referem-se a 2015, partes de tráfego de 2020. Fonte: Cisco VNI Global IP Traffic Forecast, 20152020 As implicações do crescimento do vídeo são difíceis de exagerar. Com o crescimento do vídeo, o tráfego da Internet está evoluindo a partir de um fluxo de tráfego relativamente estável (característica do tráfego P2P peer-to-peer) para um padrão de tráfego mais dinâmico. No ano passado, os prestadores de serviços observaram um aumento pronunciado no tráfego associado aos downloads de jogos. Os consoles mais recentes, como o Xbox One e o PlayStation 4, têm armazenamento onboard suficiente para permitir que os jogadores baixem novos jogos em vez de comprá-los no disco. Esses jogos graficamente intensos são arquivos grandes, e os downloads de jogos já são 2 por cento do tráfego de Internet fixo para o consumidor e alcançarão 4 por cento do tráfego fixo de Internet fixo para o consumidor em 2020. Além disso, esses downloads tendem a ocorrer durante períodos de pico de uso, com downloads de jogos atingindo Até 10% do tráfego de horas ocupadas. Impacto do vídeo na simetria de tráfego Com a exceção do vídeo curto e vídeo chamada, a maioria das formas de vídeo na Internet não tem um grande componente a montante. Como resultado, o tráfego não está se tornando mais simétrico, uma situação que muitos esperavam quando o conteúdo gerado pelo usuário se tornou popular. O surgimento de assinantes como produtores de conteúdo é um fenômeno social, econômico e cultural extremamente importante, mas os assinantes ainda consomem muito mais vídeos do que produzem. O tráfego a montante tem diminuído ligeiramente em porcentagem por vários anos. Parece provável que o tráfego residencial na Internet permaneça assimétrico nos próximos anos. No entanto, vários cenários podem resultar em um movimento em direção a uma maior simetria, por exemplo: fornecedores de conteúdo e distribuidores poderiam adotar o P2P como mecanismo de distribuição. Houve um caso forte para o P2P como um sistema de entrega de conteúdo de baixo custo (CDS) por muitos anos, mas a maioria dos provedores de conteúdo e distribuidores optaram pela distribuição direta, com exceção de aplicativos como o PPStream e o PPLive na China, que Oferecer transmissão de vídeo ao vivo através do P2P e teve um grande sucesso. Se os provedores de conteúdo em outras regiões seguem o exemplo, o tráfego pode rapidamente se tornar altamente simétrico. Comunicações de vídeo high-end podem acelerar, exigindo largura de banda simétrica. A chamada de vídeo de PC para PC está ganhando impulso, e o mercado de chamada de vídeo móvel nascente parece ser promissor. Se a chamada de vídeo de ponta se tornar popular, o tráfego pode avançar para uma maior simetria. Geralmente, se os provedores de serviços fornecem ampla largura de banda a montante, as aplicações que usam a capacidade a montante irão começar a aparecer. Tendência 6: Análise de Corte de Cordas No contexto da Previsão de VNI, Cord-cutting refere-se à tendência em que a visualização de televisão tradicional e por assinatura é cada vez mais suplantada por outros meios de visualização de vídeo, como vídeos online e móveis, que estão disponíveis Para espectadores através de conexões de internet fixas e móveis. Estamos vendo uma tendência em que o crescimento no serviço de televisão digital que denota visualização de televisão em todas as plataformas digitais (cabo, IPTV, satélite, etc.) está crescendo muito mais lentamente em relação ao vídeo móvel (Figura 16). Essa tendência é mais pronunciada em regiões como América do Norte e Europa Ocidental, onde a penetração da TV digital já é alta. O vídeo on-line, que encontramos foi crescendo mais rápido até o ano passado, agora está crescendo quase a par com a televisão digital. Além disso, nas regiões emergentes as taxas de crescimento de vídeo móvel são ainda maiores, porque essas regiões estão ignorando a conectividade fixa. Figura 16. Vídeo móvel aumentando o vídeo e a TV digital em linha mais rápidos crescem de forma similar Fonte: Previsão de tráfego IP global da Cisco VNI, 20152020 Outro fator que apóia essa tendência é que os mercados endereçáveis ​​totais para esses usuários residenciais da Internet, consumidores e usuários domésticos totais. Para famílias de TV digital) mostram padrões de crescimento significativamente diferentes (Figura 17). Espera-se que os usuários de Internet residencial aumentem um CAGR de quase 3,2 por cento e os usuários móveis do consumidor em 2,8%, ao mesmo tempo em que o número de casas de TV é achatado, com um CAGR previsto de 1,8%. Figura 17. Crescimento em usuários globais de Internet residencial comparados ao crescimento em casas de TV globais Fonte: Cisco VNI Global IP Traffic Forecast, 20152020 Além disso, se olharmos para dispositivos de Internet, como adaptadores de mídia digital (DMAs), achamos que, embora representem apenas 9 por cento de todos os set-top boxes conectados à Internet (STBs) incluindo, STBs de provedores de serviços, consoles de jogos e sets de TV de Internet diretamente conectados em 2020, representarão 32% do tráfego global de Internet STB. Esta tendência mostra novamente que há cada vez menos confiança nos STBs gerenciados pelos provedores de serviços para o acesso à Internet em geral e para o vídeo especificamente (Figura 18). Figura 18. Crescimento em adaptadores globais de mídia digital Os DMAs incluem dispositivos como Roku, Apple TV, Chromecast, etc. Fonte: Cisco VNI Global IP Traffic Forecast, 20152020 Do ponto de vista do tráfego, esperamos que, em média, uma família que ainda esteja linear A TV gerará muito menos tráfego do que uma casa que cortou o cabo e está confiando no vídeo na Internet (Figura 19). Uma família de corte de cordas gerará 102 GB por mês em 2016, em comparação com 49 GB por mês para uma família média. Essa diferença ocorre porque a televisão linear gera muito menos tráfego (um fluxo de vídeo compartilhado em várias famílias de TV linear) do que o vídeo na Internet, que é unicast para cada dispositivo de vídeo da Internet. Figure 19. Global Cord Cutting Generates Double the Traffic Source: Cisco VNI Global IP Traffic Forecast, 20152020 Trend 7: Security Analysis Users expect their online experience to be always available and always secureand for their personal and business assets to be safe. Annual security reports for 2016 from industry giants in the security space highlight the need for increased focus on cybercrimes, data breaches and espionage, and mitigation strategies (Figure 20). Figure 20. SecurityIndustry Top of Mind The last several years have been easily the most eventful period from a security threat perspective, with many serious data breaches that have been discussed widely in the media. There were a total of 780 breaches with a total of nearly 178 million records stolen in 2015. The number of records stolen per data breach averaged 228 thousand in 2015, according to 2015 data breach statistics from IDT911. The average cost paid for each sensitive lost or stolen record increased 6 percent from 2015 to 2016, according to a joint study by IBM and Ponemon Institute. More secure Internet servers leads to a large footprint of security and authentication, better serving end users with secure transactions and communication. The percentage of secure Internet servers that conduct encrypted transactions over the Internet using Secure Sockets Layer (SSL) compared to the total number of web-facing servers depicts the nature of the secure footprint. Western Europe led with the number of secure Internet servers per 1 million people with 50 percent, followed by Central and Eastern Europe with 29 percent, North America with 27 percent, and Asia Pacific with around 23 percent. The average number of breaches was highest in Asia Pacific organizations and lowest in U. K. and U. S. enterprises in 2015, according to a recent study published by McAfee. Sixty percent of data stolen was through web protocols, file transfer and tunneling protocols, or email. Two-thirds of breaches involved traditional corporate networks, and cloud break-ins accounted for the remaining one-third, according to McAfee and LemonFish (Figure 21). Figure 21. How Is Data being Breached Source: McAfee, Lemonfish, Cisco VNI 2016 Frequency of distributed denial-of-service (DDoS) attacks has increased more than 2.5 times over the last 3 years, according to Arbor Networks. DDoS attacks are increasing at roughly the same rate as traffic. Peak DDoS attack size (Gbps) is increasing in a linear trajectory, with peak attacks reaching 300, 400, and 500 Gbps respectively, in 2013, 2014, and 2015, at about 10 to 15 percent per year. DDoS attacks can represent up to 10 percent of a countrys total Internet traffic while they are occurring. The average size of DDoS attacks is increasing steadily and approaching 1 Gbps, enough to take most organizations completely off line. In 2015 the top motivation behind DDoS attacks was criminals demonstrating attack capabilities, with gaming and criminal extortion attempts in second and third place, respectively. DDoS attacks account for more than 5 percent of all monthly gaming-related traffic and more than 30 percent of gaming traffic while they are occurring. The events from 2015 and the first quarter of 2016 once again demonstrated that the attackers are increasing their computing resources to perform DDoS attacks. Amplification attackers, who have tools for carrying out a DDoS attack, exploit vulnerabilities in the network and compute resources. With the growth of the IoE and spread of vulnerable devices and traditional PCs, the abundance of configuration drawbacks with applications can be targeted. Security vendors continue to ensure these attacks are financially unviable for the cybercriminals. Globally the number of DDoS attacks grew 25 percent in 2015 and will increase 2.6-fold to 17 million by 2020 (Figure 22). Figure 22. Global DDoS Attacks Forecast, 2015-2020 Figures (n) refer to 2015, 2020 traffic shares. Source: Cisco VNI Global IP Traffic Forecast, 2015-2020 Trend 8: Impact of Accelerating Speeds on Traffic Growth Broadband speed is a crucial enabler of IP traffic. Broadband-speed improvements result in increased consumption and use of high-bandwidth content and applications. The global average broadband speed continues to grow and will nearly double from 2015 to 2020, from 24.7 Mbps to 47.7 Mbps. Table 4 shows the projected broadband speeds from 2015 to 2020. Several factors influence the fixed broadband-speed forecast, including the deployment and adoption of fiber to the home (FTTH), high-speed DSL, and cable broadband adoption, as well as overall broadband penetration. Among the countries covered by this study, Japan, South Korea, and Sweden lead within the VNI countries in terms of broadband speed largely because of their wide deployment of FTTH. Table 4. Fixed Broadband Speeds (in Mbps), 20152020 Source: Cisco VNI, 2016 Consider how long it takes to download an HD movie at these speeds: at 10 Mbps, it takes 20 minutes at 25 Mbps, it takes 9 minutes but at 100 Mbps, it takes only 2 minutes. High-bandwidth speeds will be essential to support consumer cloud storage, making the download of large multimedia files as fast as a transfer from a hard drive. Table 5 shows the percentage of broadband connections that will be faster than 10 Mbps, 25 Mbps, and 100 Mbps by region. Table 5. Broadband Speed Greater Than 10 Mbps, 20152020 Greater Than 10 Mbps Greater Than 25 Mbps Greater Than 100 Mbps Central and Eastern Europe Middle East and Africa Source: Cisco VNI, 2016 There is a strong correlation between experienced speeds and number of video minutes viewed per viewer (Figure 23). As speeds increase in each country covered in the study, the number of video minutes per viewer also increases. Figure 23. Increase in Experienced Speeds (Mbps) Increases Internet Video Viewership (Minutes)2016 Source: Cisco VNI Global IP Traffic Forecast, 20152020 Globally, the average mobile network connection speed in 2015 was 2.0 Mbps. The average speed will more than double and will be 6.5 Mbps by 2020. Smartphone speeds, generally third-generation (3G) and later, are currently nearly three times higher than the overall average. Smartphone speeds will nearly double by 2020, reaching 12.5 Mbps. Anecdotal evidence supports the idea that overall use increases when speed increases, although there is often a delay between the increase in speed and the increased use, which can range from a few months to several years. The reverse can also be true with the burstiness associated with the adoption of tablets and smartphones, where there is a delay in experiencing the speeds that the devices can support. The Cisco VNI Forecast relates application bit rates to the average speeds in each country. Many of the trends in the resulting traffic forecast can be seen in the speed forecast, such as the high growth rates for developing countries and regions relative to more developed areas (Table 6). Table 6. Projected Average Mobile Network Connection Speeds (in Mbps) by Region and Country Source: Cisco VNI Mobile, 2016 Current and historical speeds are based on data from Ooklas Speedtest. Forward projections for mobile data speeds are based on third-party forecasts for the relative proportions of 2G, 3G, 3.5G, and 4G among mobile connections through 2020. A crucial factor promoting the increase in mobile speeds over the forecast period is the increasing proportion of fourth-generation (4G) mobile connections. The impact of 4G connections on traffic is significant, because 4G connections, which include mobile WiMAX and Long-Term Evolution (LTE), generate a disproportionate amount of mobile data traffic. Wi-Fi Speeds from Mobile Devices Globally, Wi-Fi connection speeds originated from dual-mode mobile devices will nearly double by 2020. The average Wi-Fi network connection speed (10.6 Mbps in 2015) will exceed 18.5 Mbps in 2020. North America will experience the highest Wi-Fi speeds, 29 Mbps, by 2020 (Table 7). Wi-Fi speeds inherently depend on the quality of the broadband connection to the premises. The speed also depends on the Wi-Fi standard in the CPE device. The latest standard, IEEE 802.11ac, is considered a true wired complement and can enable higher-definition video streaming and services that require higher data rates. Also an important factor in the use of Wi-Fi technology is the number and availability of hotspots. Table 7. Projected Average Wi-Fi Network Connection Speeds (in Mbps) by Region and Country Source: Cisco VNI, 2016 Trend 9: Mobility (Wi-Fi) Continues to Gain Momentum Globally, there will be nearly 433 million public Wi-Fi hotspots by 2020, up from 64 million hotspots in 2015, a sevenfold increase. By 2020, China will lead in total number of hotspots, followed by the United States and France. Western Europe had 45 percent of the worlds Wi-Fi hotspots share in 2015. By 2020, public Wi-Fi along with community hotspots are accounted for as well. Community hotspots or homespots are just emerging as a potentially significant element of the public Wi-Fi landscape. In this model, subscribers allow part of the capacity of their residential gateway to be open to casual use. The homespot may be provided by a broadband or other provider directly or through a partner. Asia Pacific will lead in adoption of homespots. By 2020, China will lead in total number of homespots, followed by France and Japan. Adoption of homespots has been led by Western Europe and then North America in 2015, but Asia Pacific will lead by 2020. Critical enablers of Hotspot 2.0 adoption are higher-speed Wi-Fi gateways and the adoption of the IEEE 802.11ac and 802.11n standards. Globally, the prevalence of IEEE 802.11ac, the latest Wi-Fi standard, will gain momentum from 2015 through 2020. In 2015, 59.5 percent of all home Wi-Fi routers shipped globally were 802.11ac-enabled. By 2020, 96.6 percent of all home Wi-Fi routers will be equipped with 802.11ac. IEEE 802.11n, which was ratified in 2007, provides a range of speeds that allow users to view medium-resolution video streaming because of the higher throughput. The latest standard, IEEE 802.11ac, with very high theoretical speeds, is considered a true wired complement and can enable higher-definition video streaming and services with use cases that require higher data rates (Figure 24). Figure 24. Future of Wi-Fi as Wired Complement The rapid growth of mobile data traffic has been widely recognized and reported. The trend toward mobility carries over into the realm of fixed networks as well, in that an increasing portion of traffic will originate from portable or mobile devices. Figure 25 shows the growth in Wi-Fi and mobile traffic in relation to traffic from wired devices. By 2020, wired networks will account for 34 percent of IP traffic, and Wi-Fi and mobile networks will account for 66 percent of IP traffic. In 2015, wired networks accounted for the majority of IP traffic, at 52 percent Wi-Fi accounted for 43 percent and mobile or cellular networks accounted for 5 percent of total global IP traffic. Figure 25. Global IP Traffic, Wired and Wireless Wireless traffic includes Wi-Fi and mobile. Source: Cisco VNI Global IP Traffic Forecast, 20152020 Narrowing the focus to Internet traffic and excluding managed IP traffic yields a more pronounced trend. By 2020, wired devices will account for 22 percent of Internet traffic, and Wi-Fi and mobile devices will account for 78 percent of Internet traffic (Figure 26). In 2015, wired devices accounted for less than half of Internet traffic, at 38 percent. Figure 26. Global Internet Traffic, Wired and Wireless Source: Cisco VNI Global IP Traffic Forecast, 20152020 Trend 10: Traffic-Pattern Analysis (Peak Compared to Average and CDN Uptake) Although average Internet traffic has settled into a steady growth pattern, busy-hour traffic (or traffic in the busiest 60minute period of the day) continues to grow more rapidly. Service providers plan network capacity according to peak rates rather than average rates. In 2015, busy-hour Internet traffic grew 51 percent, and average traffic grew at 29 percent. Between 2015 and 2020, global busy-hour Internet use will grow at a CAGR of 36 percent, compared with 25 percent for average Internet traffic (Figure 27). Video is the underlying reason for accelerated busy-hour traffic growth. Unlike other forms of traffic, which are spread evenly throughout the day (such as web browsing and file sharing), video tends to have a prime time. Because of video consumption patterns, the Internet now has a much busier busy hour. Because video has a higher peak-to-average ratio than data or file sharing, and because video is gaining traffic share, peak Internet traffic will grow faster than average traffic. The growing gap between peak and average traffic is amplified further by the changing composition of Internet video. Real-time video such as live video, ambient video, and video calling has a peak-to-average ratio that is higher than on-demand video. Figure 27. Busy-Hour Compared with Average Internet Traffic Growth Source: Cisco VNI Global IP Traffic Forecast, 20152020 Changes in traffic topology are being brought about by the increasing role of content delivery networks (CDNs) in data delivery. CDNs will carry 64.5 percent of total Internet traffic by 2020 (Figure 28). Although network performance is usually attributed to the speeds and latencies offered by the service provider, the delivery algorithms used by CDNs have an equal if not more significant bearing on video quality. Figure 28. Global Content Delivery Network Internet Traffic, 2015 and 2020 Source: Cisco VNI Global IP Traffic Forecast, 20152020 Speed is a critical factor in Internet traffic. When speed increases, users stream and download greater volumes of content, and adaptive bit-rate streaming increases bit rates automatically according to available bandwidth. Service providers find that users with greater bandwidth generate more traffic. In 2015, households with high-speed fiber connectivity generated 58 percent more traffic than households connected by DSL or cable broadband, globally (Figure 29). The average FTTH household generated 68 GB per month in 2015 and will generate 138 GB per month in 2020. Figure 29. Fiber-Connected Households Generate More Traffic Than Households with Other Sources of Broadband Source: Cisco VNI Global IP Traffic Forecast, 20152020 To limit the volume of traffic, service providers can institute use-based tiered pricing and data caps. On mobile networks, by looking at the use of more than 33,000 lines from Tier-1 mobile operators from 2010 to 2015, we found that monthly traffic from the top 1 percent of users is down to 18 percent of overall use compared to 52 percent in 2010, showing the effects of tiered pricing. With mobile penetration reaching a saturation point in many countries across all regions, the trend has been toward tiered plans as a way to monetize data and effectively manage or throttle the top users of traffic. On the fixed networks, data caps continue to increase to match subscribers growing appetite for video. In the United States, Tier-1 carriers are offering a variety of fair usage limits today, as high as 1 TB per month. A large provider in Japan has a 30-GB-per-day upload cap. In several countries, Netflix has a sizable percentage of the Internet video minutes and traffic. Wildcard traffic generators such as Twitch. TV, a live streaming service in which video gamers watch each other play, has established itself on many fixed networks around the world. Data caps affect a larger percentage of mobile users than fixed users. With Tier-1 carriers, approximately 12 percent of mobile users consume more than 2 GB per month (a common mobile data cap), whereas only 1.4 percent of fixed users consume more than 500 GB per month (a common fixed data cap). Other Trends to Watch Ciscos approach to forecasting IP traffic is conservative, and certain emerging trends have the potential to increase the traffic outlook significantly. Growth of smartphones as the communications hub for social media, video consumption, tracking IoEdigitization applications (et al.), as well as traditional voice. This trend demonstrates the impact that smartphones have on how consumers and businesses users access and use the Internet and IP networks. Internet gaming is seeing a resurgencethe traffic nearly doubled in 2015 and will grow seven-fold by 2020. Gaming on demand and streaming gaming platforms have been in development for several years, with many newly released in 2014 and 2015. With traditional gaming, graphical processing is performed locally on the gamers computer or console. With cloud gaming, game graphics are produced on a remote server and transmitted over the network to the gamer. If cloud gaming becomes popular, gaming could quickly become one of the largest Internet traffic categories. Virtual reality . With new hardware available to individuals, and a growing body of content to consume, virtual reality has experienced high growth in recent years. Traffic associated with virtual and augmented reality applications quadrupled in 2015 and is poised to grow 61-fold by 2020. This growth stems mainly from the download of large virtual reality content files and applications, but a significant wild card is the potential adoption of virtual reality streaming, which could raise our prediction of high-growth even higher. Immersive video . This emerging traffic type can cause significant new network design implications as it is a high-bandwidth consuming application. Social media platforms such as Facebook have launched support for spherical, or immersive video that integrates multiple camera angles to form a single video stream and can be watched from the viewers preferred perspective. It can generate bit rates 3 to 10 times greater than non-immersive HD bit rates. Video surveillance . New Internet-connected video surveillance cameras upload a constant video stream to the cloud for remote viewing. With a steady flow of video traffic from each camera, video surveillance is already having an impact on overall Internet traffic and accounts for 1.5 percent of total Internet traffic today, growing to nearly 4 percent by 2020. If such devices become mass market in the next five years, we could see video cameras generating a significantly higher volume of traffic, since Internet-enable cameras can produce up to 300 GB per camera per month for full HD-resolution monitoring of high-activity areas. For More Information For more information about the Cisco IP traffic forecast, refer to Cisco VNI: Forecast and Methodology, 20152020 and visit the other resources and updates at ciscogovni. Several interactive tools allow you to create custom highlights and forecast charts by region, country, application, and end-user segment. Refer to the Cisco VNI Highlights tool and the Cisco VNI Forecast Widget tool. For regional details about the VNI service adoption forecast, please visit the Cisco VNI SA highlights tool and Cisco VNI SA Graphing tool. Inquiries can be directed to trafficinquiriescisco . Appendix A: Cisco Global IP Traffic Forecast Table 8 shows a summary of the Cisco global IP traffic forecast. For more information and additional tables, refer to Cisco VNI: Forecast and Methodology, 20152020. Table 8. Global IP Traffic, 20152020There now follows an alphabetical list of some commonly used wordsphrasesabbreviations that you might see in the newsgroup (or via other weather-related sites on the WWW), but which may not be readily understood. The list has been prepared in association with Paul Bartlett, David Reynolds and many others: I would welcome suggestions for inclusion, but I will also scan the posts in the newsgroup and if I see a wordphraseabbreviation that is causing problems, I will include same. Where a longer explanation is required, a QA in the FAQ will be worked up, and referred to hereunder. For the professionalacademic community, these terms etc. will not be rigorous enough, but I ask for some understanding in this respect, as the list is intended to convey the idea of a concept, process etc. so that casual readers in the newsgroup can keep up with discussions without having to delve too deeply into a meteorological textbook. However, if Ive made a fundamental mistake, then by all means let me have a corrected entry for consideration. Glossary terms A-F Absolute drought A period of at least 15 consecutive days, to none of which is credited 0.01 inches 0.2 mm or more of precipitation. (See also drought partial drought dry spell ) Absolute vorticity (or total vorticity) of air particles at any particular point is comprised of two elements: (i) on the rotating earth, air adopts the local vorticity due to the earths solid-body rotation about its pole-to-pole axis, which is latitude dependent, and is known as the Coriolis parameter. This increases to a maximum over the poles and decreases to zero at the equator. The Coriolis rotation sense is always positive (or zero). (ii) the other element is known as the relative vorticity, the spin tendency of air particles due to their motion relative to the earth - driven by atmospheric forces. Relative vorticity can be either positive (cyclonic sense) or negative (anticyclonic). (See also: Vorticity Relative vorticity .) (abbr) Altocumulus (AC for METARSIGWX charts etc. Ac otherwise) a medium level, layer cloud type, but with varying levels of instability associated - the extreme event being ACCAST . (quot Alto-Q-Cast quot)(Altocumulus castellanus or castellatus the proper abbreviation for the Daily Register is Ac cas) These are medium level clouds (between circa 8000 and 18000 ft 2.5 to 5.5 km) which exhibit, at least in their upper parts, marked cumuliform turreted appearance - the convective towers are often taller than the width of the individual base the bases are connected and often appear to be arranged in lines or streets. These clouds are a good indicator of medium level instability and high moisture content - and often the precursor for widespread thundery activity within the following 24 to 48 hours. Observers used to SYNOP coding may also refer to these (along with Altocumulus floccusAc flo), as CM8 clouds. A process where temperature changes occur in a system, without heat being supplied to, or lost from that system. In meteorology, used in connection with changes involving air parcels moving vertically in the atmosphere. If heat exchange is involved, the process is non-adiabatic (or diabatic). Adiabatic lapse rate The change of temperature of an air parcel rising (cooling) or descending (warming) adiabatically. For dry (i. e. unsaturated) ascent or descent, the rate is 10degC km for moist or saturated processes, it varies but a useful average is 5 or 6degC km. The transfer by horizontal air movement of heat, moisture (or humidity), momentum etc. The atmosphere at all levels is usually in some form of motion at most times, thus it is necessary to identify areas of significant advection. For the lowmiddle troposphere thickness products (e. g. 500-1000 hPa) are often used. Solid particles suspended in the air. They include dust, salt particles, products of combustion etc. These are very important to the formation of water droplets or ice particles in the atmosphere, acting as nuclei for condensation sublimation. Ageostrophic effects An extensive volume of air possessing uniform physical characteristics at similar heights in terms of humidity and temperature structure. The proportion of solar incoming visible light (after passage through the atmosphere) reflected by a surface (e. g. sea, cloud-tops, ice etc.), expressed as a fraction or percentage of the incident light falling on that surface. Clouds have highly varying albedo, dependent upon thickness and composition. Old snow is about 55 (or 0.55), new snow around 80 (or 0.8). Water surfaces vary from very low (about 5 or so) at high sun elevation, to at least 70 (0.7) at low sun-angles: very smooth water surfaces with a low sun-angle can give rise to the phenomenon known as sun glint sometimes seen in visible satellite imagery where the albedo value is very high. (abbr) Above mean sea level. Anabatic wind A local-scale wind which blows up-slope, after strong heating of the hillmountain-side by the sun. Such upslope winds can sometimes drag fogstratus in the valley bottom (formed after a cold night) to upland areas that were previously clear of these phenomena. Airfields that were previously clear can suddenly fog-out well after sunrise due to this effect. When warm air ascends relative to the cold air at a frontal surface, the front is said to be an ana-front. Such fronts are normally active, in that thickprecipitation producing clouds (possibly with embedded instability), are usually located in the warm air associated with both a warm and cold front. Anticyclones A pressure feature where a maximum of pressure is surrounded by relatively lower values. On a synoptic chart, a system of closed isobars will be found, enclosing the central High. The circulation (of wind) is clockwise in the northern hemisphere (anticlockwise in the southern hemisphere). The structure of such features in the vertical is that high-level convergence coupled to gentle divergent-outflow at the surface leads to descent (or subsidence) of air within the anticyclone: this in turn leads to a decrease in humidity and an increase in the stability of the air, often producing an inversion close to the surface. Two types are defined: cold and warm see Cold anticyclone Warm anticyclone . Anticyclonic trough disruption If the northern (southern in the southern hemisphere) portion of an upper trough moves forward and warms out, leaving a quasi-stationary cut-off low in the base of the trough, the process is described as anticyclonic trough disruption - because the net result is a strong build of pressurenew high cell formation behind the retreating trough. (See also cyclonic trough disruption ) Arctic Oscillation The Northern Hemispheric broad-scale oscillation of long-wave type, of which the North Atlantic Oscillation (NAO) is our regional-scale component. (q. v. here ) (abbr) Altostratus (AS for METARSIGWX charts etc. As otherwise) a medium level, layer cloud type, formed by wide-scale rising motion in the troposphere, varying from thin, non-precipitating type through which the sunmoon can be seen, to thick layer(s) associated with frontal development giving persistent, significant precipitation, amp moderate in-flight turbulence amp icing. Over the many years that operational meteorology has developed, certain hours have been designated synoptic hours, and observation times standardised around these points the MAIN synoptic hours currently being 00, 06, 12 and 18 UTC(formerly GMT), with intermediate hours at 03, 09, 15 and 21 UTC. Increasingly however, observing systems (e. g. satellite, radar-networks, drifting buoys etc.) provide data at times other than these fixed hours - these are designated non, or asynoptic observations. NWP models can assimilate these observations during the initialisation process. Abbreviation used to stand for aviation. A term applied when a forecast wind direction changes in an anti-clockwise sense, i. e. from south back to northeast, via east. The opposite term is veering, thus quot southwest 4 veering north 5 or 6 quot, would imply a wind originally force 4 from the southwest, becoming a northerly force 5 or 6 by the end of the forecast period, passing via west. Baroclinic The temperature along a constant pressure surface (say 500 mbar) varies a thickness gradient exists. The degree of baroclinicity is given by the product of the layer thermal wind (q. v.) and the Coriolis parameter. For practical purposes, the strength of the thermal wind alone is a good guide. Baroclinic leaf An elongated cloud pattern formed within the jet stream zone associated with marked baroclinicity (i. e. strong thermal contrast). The boundary (in satellite imagery) on the polar air-mass side of the development is well defined, and has the look of a stretched-out quotSquot shape. The downstreamwarm air-mass edge is less distinct. This feature represents the initial (or frontogenetic) stage of a system development, certainly in the mid-troposphere, and often (but not always) at the surface. Not all baroclinic leaves lead to marked cyclogenesis although they will be the first stage of such. (See also Dry Intrusion ). Baroclinic zone Area where there is a marked contrast between cold and warm air masses. Can be determined on a thickness chart by a quotpacking togetherquot of thickness (q. v.) contours. Usually associated on a msl chart with classical fronts, and therefore an area for potential cyclonic development. Barotropic A (theoretical) state in which surfaces of constant pressure and constant temperature coincide at all levels. The atmosphere cannot sustain development, and thickness (q. v.) gradients are zero. If thickness contours are widely spaced (the realistic state), the atmosphere is said to be quasi-barotropic. (abbr) Patches (as in BCFG in METAR coding, meaning patches of fog). Beaufort wind scale This scale was originally devised by Francis Beaufort (later Admiral Sir Francis, Hydrographer of the Royal Navy), who lived from 1774 to 1857. He had a very active naval career and was also interested from an early stage in meteorological observations afloat. In 1805 amp 1806, he devised a scale for his own use, which was based upon the amount of canvas a sailing vessel could carry in the given conditions. The scale underwent various modifications and was not introduced into general RN use until the middle part of the 19th century but thereafter, it quickly gained world-wide acceptance. However, various versions developed. and in 1906, the UK Meteorological Office attempted to co-ordinate the usage, and at the same time provided the first definitive wind speed equivalents for each level of force, and since 1920, the scale has been used to define forecast wind conditions in the Shipping Forecasts for waters in the NE AtlanticNW Europe continental shelf. For a description of the current scale in use, see zetnet. co. uksigsweatherMetCodescodes. htm (abbr) quotBecomingquot, used in aerodrome (TAF) issues and others. A permanent change in conditions. (abbr) quotBrokenquot, 5 to 7 oktas (eighths) of cloud cover. (abbr) quotBlowingquot, used in connection with snow, sand etc. for the U. K. Met Office only - other services will have different criteria and the definition has changed over time it has not always been so strictly defined quotThe simultaneous occurrence of moderate or heavy snowfall with winds of at least force 7, causing drifting snow and reduction of visibility to 200 m or lessquot. (Moderate snow is said to occur when the visibility is substantially impaired, and the snow cover increases in depth at a rate up to about 4 cm per hour. Heavy snow should reduce the visibility to a low value (in the low hundreds of metres), and the snow cover increases at a rate exceeding 4 cm per hour. ) Blocked pattern Large scale obstruction of the normal west to east progression of surface cyclones in the mid-latitudes. The upper flow changes from predominantly zonal (q. v.) to meridional (q. v.). In a meridional block, the upper flow divides upwind of the block and flows around quasi-stationary vortices - one anticyclonic and the other cyclonic. In the omega block case the strongest flow is diverted to lower latitudes, leaving a slow-moving anticyclonic vortex on the poleward flank of the displaced zonal flow. Blocking anticyclone Acellular pattern of high pressure in the mid-latitudes, which diverts or prevents the normal west-to-east motion of depressions (areas of low pressure). A name applied to mid-latitude depressions which deepen violently. The term was coined by Sanders amp Gyakum (US Monthly Weather Review), in a 1980 paper dealing with such events, and requires a pressure fall in the depression centre of 24 hPa (or mbar) or more in 24 hours at latitude 60degN for the name to be applied. At latitude 45degN, the required value is 19hPa, and at 55degN, 23hPa. (see Explosive cyclogenesis .) Boundary layer In operationalsynoptic meteorology this is usually taken to be the layer at the bottom of the atmosphere wherein surface friction is important. It can vary in depth from as little as 100 m or less on a still, cold night to upwards of 1 km or more in a windy, well-mixed situation. Also known variously as the mixed layer or friction layer and is a function of wind speed, vertical temperature profile (i. e. stability) and surface roughness. (N. B: micrometeorologists regard the boundary layer as the first few cm of the lower atmosphere and this can lead to confusion when reading some texts. ) Mist (abbr. from French): vis gt1000m and not more than 5000m, where obscuration is caused by water droplets in suspension. Used in aviation reports, forecasts etc. Bright band effect As snow descends through the melting (or freezing) level, the melting snowflakes look like huge raindrops causing radar reflectance to increase sharply, implying heavier precipitation than is actually occurring. Corrections can be applied, provided the calibration system has some knowledge of the vertical temperature profile. The effect is usually confined to a layer about 1000 ft (300 m) thick. Buys Ballots Law As originally formulated, quot if you stand with your back to the wind (in the northern hemisphere), then low pressure lies on your left-hand side quot. For the southern hemisphere, then the low pressure is on the right-hand side. (Personally, I feel we should face the wind to see what is coming, so I would reverse these, i. e. face the wind, low pressure on right etc.) Prof. C. H.D. Buys Ballot (1817-1890) was a famous Dutch Meteorologist who founded the Royal Netherlands Meteorological Institute (KNMI) in 1854 and played an important role in establishing the first international organisation for meteorology - after the inaugural meeting of the International Meteorological Congress in Vienna in 1873. However, he is now best known for the Law as above it is possible that the credit for a rigorous treatment of the physics might be credited to Alexander Buchan, long-serving (1860-1907) Secretary of the Scottish Meteorological Society. cloud-to-air lightning flash Used when describing lightning which branches from a cumulonimbus cloud and terminates in clear air. This is an uncommon type of lightning.(See also CC. CG amp GC ) Calibration (radar) As well as de-cluttering for permanent echoes, and other adjustments, rainfall radar returns are calibrated (in real-time) against a network of telemetering rain gauges. This means of course that if the return is over areas without rain gauges (e. g. the sea), over-reading can occur, and caution is needed in blindly following radar imagery to assess rainfall ratesaccumulations for this reason. Convectively Available Potential Energy A measure of the energy released once convection is initiated, often from the surface (for high values), but mid-level convective initiation is also very important. Assessed on a thermodynamic diagram (e. g. a tephigram) by noting the area enclosed by the environment curve (i. e. actual temperature found by a radio-sonde), and the parcel-path curve where it intersects the environment curve at height. Used extensively in severe convective storm studies, although worth noting that just because high values of CAPE are observed, other factors need to be right for a severe storm to develop. (see also HERE ) Clear Air Turbulence Bumpy conditions in the upper atmosphere when no clouds are present to betray the possibility of such. Caused by sharp vertical and horizontal shear of wind, often (but not exclusively) in association with upper-level jet streams (see quotWhat are jetstreams quot). Can occur in, or be enhanced by mountain wave activity. Conservation of Absolute Vorticity -- The principle first outlined by Carl-Gustav Rossby in the 1930s which accounts for the tendency for upper atmospheric flow to take up a wave-like pattern. The theory can be used to predict the wavelength and speed of translation of the long-waves found in the atmosphere, which in turn govern the broad weather type at any one point. quot C eiling A nd V isibility OK quot: No CB, no cloud with base lt 1500m5000ft or below the highest minimum sector altitude, whichever is greater amp visibility 10km or more amp no weather of significance i. e. DZ, RA, SN, SG, PL, IC, GR, GS, FG, BR, SA, DU, HZ, FU, VA, PO, SQ, FC, DS, SS. and variants (see this glossary for decodes). CB (strictly Cb) Abbreviation for cumulonimbus, the cloud type associated with a thunderstorm, when the upper portion of the cloud exhibits glaciation (supercooled water droplets converting to ice crystals). Broadly, there are two species: Cumulonimbus calvus (Cb cal) and Cumulonimbus capillatus (Cb cap). The former is used when glaciation has only just begun, and is often taken to be the start of the most active phase of development - transition from Cumulus congestus (Towering CU) the latter type exhibits the traditional anvil shape, when major activity may be (but not necessarily) beginning to wane. (See also TCU ) (abbr)cloud-to-cloud lightning flash Used when describing lightning that originates in cloud and terminates in cloud. Thus it describes lightning with passes from one cumulonimbus cloud to another and lightning which is contained within a single cumulonimbus cloud. This includes the diffuse lit from within (sheet) type lightning, as well as that whose channel is directly visible as it loops out of the cloud before returning back into it. (see also CA. CG amp GC ) (abbr) Cirrocumulus (CC in aviation reports etc. Cc otherwise) a high level, layer cloud type, with elements of instability, but rarely of significance for aviation or general meteorology. (abbr)convective condensation level Provided the dew-point of an air parcel is high enough, then during convective ascent the resultant cooling will lead to condensation at some altitude as the air temperaturedew point. The precise height this is achieved will depend upon the difference between the initial air temperature and dew-point of the parcel, and also the amount of mixing with the environment of the air through which the parcel is rising. The level where condensation is achieved (and thus the theoretical cloud base for cumulus clouds), is known as the Convective Condensation Level (CCL). to a rough approximation, the CCL is given by (T-D)400, where Tair temperature at the surface, Ddew point temperature (as the surface): the answer will be in feet. DONT use slavishly - regard as good to the nearest couple-of-hundred of feet at best. (abbr)Central England Temperature -- A series used to track temporal changes in the average temperatures over a large area of central England. see quotWhat is the Central England Temperature Series quot. CLICK HERE FOR LATEST DATA FROM THE HADLEY CENTRE. Abbreviation for cold front. (abbr)cloud-to-ground lightning flash Used when describing lightning which branches from the cumulonimbus cloud to the ground. It is sometimes referred to as fork lightning from its appearance. (see also CA. CC amp GC ) The lightning discharge process is complex it involves two discharges per stroke and there may be several strokes in one flash (which result in the flickering which is often observed). The initial and very weakly luminous discharge establishes a conductive (ionised) and usually highly-branched path through the air. The second and intensely luminous discharge moves in the opposite direction and drains the charge from the groundcloudair to the cloudground. For instance, a CG refers to a strokeflash where the initial discharge is from cloud to ground, although the intensely luminous discharge that we see is from ground to cloud. Channel Rat (Dutch Kanaalrat )An intense (small scale) developing depression that scuttles along the English Channel. It comes (and goes) in a matter of a couple of hours to half a day. Because of its speed of movement, coupled with its often rapid development (increase in wind speed), it can cause severe problems for areas adjacent to the Channel and southern North Sea. The term probably in use (in the Netherlands) since at least the early 1980s. Examples 12th May, 1983 amp 28th May, 2000. Average weather over fairly long intervals of time, usually greater than one year and often 30 years. Care should be taken to state (or ascertain) the period for which particular climate normals are applicable. Cloud head (strictly Baroclinic cloud head) During the early stages of explosive cyclogenesis (q. v.), a very marked area of dense layered cloud - convex away from the developing depression - can be observed in IR, VIS and WV imagery, detached from the cloud area associated with the development. This feature is the result of air rapidly ascending as the intense development gets underway. Studies have shown that all mid-latitude cyclogenetic events over oceanic areas giving rise to winds of hurricane force were preceded by such features. However, care is needed to correctly identify such and true detection is only possible with animated imagery. (See also Baroclinic leaf Dry intrusion .) In ensemble forecasting (q. v.), individual members often show strong grouping around a few results. Each grouping is referred to as a cluster. The more members making up a particular cluster, the higher is the confidence in that particular solution. (See also Ensemble Ensemble mean ) Cold advection The replacement (usually quasi-horizontally) of a warm air mass by a colder one. The process can be gradual or abrupt: the latter often occurring at well-marked cold-frontal boundaries. Cold anticyclone Area of high pressure with a cold core (relative to surrounding air), with the cold dense air dominant in the lower part of the troposphere contributing to the surface high pressure. Has a shallow circulation (i. e. high characteristics confined to lower layers), with a low warm tropopause etc. It often forms in the polar air behind a depression, moving with the synoptic-scale features with which it is associated. However, if a major change of type (from mobile to blocked) is underway, then the High may transform to a warm type. Persistent cooling of continental areas in winter at high latitudes (e. g. over Scandinavia, Russia, Siberia) produces semi-permanent cold anticyclones, with mean sea-level pressure often above 1050 hPa. (See Anticyclones Warm anticyclone ) Cold Occlusion If air (at the surface) behind an occluded front is colder than the air it is displacing (the usual case in the NE Atlanticmaritime NW Europe), then the front is known as a cold occlusion. The occlusion may be shown on synoptic charts as a linear extension of the cold front. (see also Warm occlusion ). An area where the atmosphere (in depth) is colder than its surroundings. The temperature is not measured by means of surface-based sensors (such as screen temperatures), but often (though not necessarily) by using thickness values (q. v.), with the 500-1000 hPa measure (roughly sampling the lower half of the troposphere) the most commonly used for this purpose. Closed centres with low thickness value (relative to adjacent regions) will define a cold pool. The opposite term (for a closed centre of high relative values), is quotwarm domequot, although this term will not be heard much nowadays. Cold-Front wave A secondary low pressure system forming on an extended cold front, where the thermal contrast across the front (in the troposphere) is large, and the upper pattern is conducive to falling pressure at the surface. The wave can move quite rapidly (in the direction of the general upper driving flow), and will lead to a hesitation in the clearance of the main cold front at the surface, or its return to areas that previously experienced a clearance. Not all such waves develop closed-low characteristics some will just run quickly along the length of the trailing cold front with little development, other than enhancing rainfall. Because of the small-scale of the initial development, NWP models dont always place and forecast these correctly. (See also warm-front wave .) Cold undercut A term often used in situations where advection of relatively milder air as traced by 850hPa variables (e. g. actual 850 temperature, ThetaE, ThetaW. partial thickness etc.) does not fully reflect events in the lowest 50 to 100hPa (i. e. within the planetary boundary layer). In winter amp spring especially, warm-air advection may be indicated by levels at above 850hPa, but the surface wind is well backed amp coming from a colder direction - the cold (relatively denser) air undercuts the overlying milder airstream: a decoupling occurs, depressing temperatures and creating a marked inversion potential cloudy mixing layer. The cold air may be either an airmass feed, or from a local source, e. g. cold air off the North Sea at the end of winter or early spring. Colour states METAR reports from military airfields operated by the RAF, some USAF and others may have a colour-code appended (usually only when ATC is open), which describes the airfield fitness: these run from BLU best, through WHT GRN YLO (1 and 2), AMB and RED . The colour is based on the lowest cloud base (usually 3 oktas or more cover, but some use 5 oktas) and the horizontal MET visibility. BLACK is also used, for airfield closed for non-weather reasons. Condensation The transformation of water vapour to liquid water in the process, latent heat (of vaporisation) is either released or absorbed. also see Evaporation Condensation nuclei Microscopic particles in the atmosphere that act as a focus or stimulant for cloud-drop growth. Conduction Heat transfer through a substance from point-to-point by means of the movement (or excitement) of adjacent molecular motions. When streamlines (q. v.) approach one another, the pattern is a confluent one. However, note that because streamlines only define the wind direction . and not the wind speed . a confluent pattern is not necessarily a con vergent pattern. The opposite of confluent is diffluent (often spelt difluent in North American texts.). This case denotes the spreading apart of streamlines. Again, such diffluent patterns are not necessarily divergent. (see also convergence. divergence .) Conservative property Meteorologists are always keen to label an air mass using a value that can be calculated from variables measured within that air mass (at various levels), but which remain constant, or nearly so in vertical (adiabatic q. v.) motion. Many properties are defined, such as potential temperature (Theta), equivalent potential temperature (Theta-e) and wet-bulb potential temperature (Theta-w). This latter measure is often used in operational meteorology in NW Europe: At the 850hPa level, it is used as a tracer for air masses, and is much used for defining frontal boundaries, and for defining the axes of warm plumes of air. (See also the entry under Wet Bulb Potential Temperature ) Lines on an upper air (constant pressure) chart (actual or forecast) joining places of equal height, 700 mbar 500 mbar etc. or of equal thickness. CONdensation TRAIL. Also abbreviated (from old coding practice) to COTRA. See quotWhy do some high flying aircraft leave white trails in their wake quot and MINTRA (this Glossary) Control run The principle of ensemble forecasting is to slightly perturb an analysis by small amounts and see what the outcome is for each change. Rather than use a centres operational model analysis and forecast output (which needs much computing time and maximum data ingress), an early look analysis and forecast run, using the same physics as the operational (OPOPER ) run, but performed at lower resolution (typically half-scale) is employed. This is known as the control run. Given the increase in computing power in recent years, the control can have higher specifications than some operational models of less than a decade ago Convection The transfer of heat by the actual movement of the heated substance, such as air or water. In meteorology, convection also means vertical transport through density imbalance, transporting mass, water vapour, and aerosols as well as heat. Convective condensation level Convective precipitation For precipitation production (rain, snow etc.), other conditions being satisfied, there must be a supply of upward motion through the cloud producing the rain, snow, hail or whatever. In convective precipitation, upward motion is provided by the release of convection in an unstable environment. (See quotStable and unstable air masses quot). Computer models in operational use cope with instability features via parametrisation schemes (q. v.), which model ideal convective towers within each model grid square, taking into account entrainment of dry air, moist convective vigour amp depth, temperature structure etc. Algorithms will assign model rainfall to either dynamic or convective: the type giving the greatest rate of rainfall is (usually) that which appears on the output chart.(See also Dynamic and Orographic precipitation) Convergence When air flows in such a way that the area occupied by a particular group of air particles lessens (drawing together), the pattern is said to be convergent. Convergence in the atmosphere is associated with vertical motion, and hence development (or weakening) of weather systems. For example, convergent flow near the surface is coupled to, and may be the primary cause of, upward motion, leading to cloud formationshower initiation etc. (See also divergence. confluent .) Convergence zone Usually referring to a low-level feature, this is a narrow elongated area where two different airstreams are converging such that air within the zone must ascend, leading to enhanced cloud precipitation formation, particularly if the airmass is potentially unstable. The zone may propagate downstream with time, and its activity, location and extent will be governed by the synoptic patterns giving rise to the zone in the first place. Marked on a synoptic chart by a solid line along the axis of the zone, with angled branches indicating the convergence. In synoptic systems (e. g. a developing depression) airflow is not uniformly horizontal, and the system velocity (i. e. the speed of translation of the Low) must also be allowed for. High-velocity air aloft overtakes the synoptic feature, whilst lower down, the system often moves faster in a given direction than the low level airflow. To cope with all this, the concept of conveyor belts was adapted for use in synoptic and mesoscale meteorology as a means of explaining the movement of heat, moisture and momentum around such systems. For example, in a developingmobile depression, a warm conveyor belt (WCB) is assumed to rise from low levels in the warm sector just ahead of the surface cold front, to middle and upper altitudes over and well forward of the surface warm front. A compensating cold conveyor belt (CCB), descends from mediumupper levels well ahead of the surface warm front underneath the WCB then tucks around the backside of the low merging with the boundary layer flow. Coriolis effect As a consequence of earths rotation, air moving across its surface appears to be deflected relative to an observer standing on the surface. The deflection is to the right of movement in the northern hemisphere, to the left in the southern hemisphere. (also known as the Coriolis acceleration, or deflection) Coriolis parameter A important quantity in theoretical meteorology because it plays a major part in describing (mathematically) how air moves on our spinning planet under the influence of a pressure gradient. It is usually denoted as f . and defined as twice the product of the angular velocity of the earth and the sine of a particular latitude. The angular velocity of our spinning earth is (for practical purposes) constant, therefore the important variable is latitude: from the definition, f varies from a maximum at the poles (sine 90deg1) to zero at the equator (sine 0deg0). see also Absolute Vorticity Cross-contour flow (abbr) Cirrostratus (CS in aviation reports etc. Cs otherwise) a high level, layer cloud type, due to wide-scale ascent in the upper troposphere: of no significance for aviation but is a pre-cursor to frontal activity to come. (abbr) Cumulus (CU in METARSIGWX reports etc. Cu otherwise) a convective cloud type, with a base in the lower part of the troposphere, and varying from weak to vigorous vertical penetration, possibly into medium or upper levels. (see also TCU ) Cut-off time NWP models that are used in operational meteorology must have a nominal time at which the gates are closed to new data, and the forecast computation cycle is started. For models used for primary forecast guidance at short lead times, only a couple of hours at most is allowed after the nominal data time. So for example, the cut-off for 12UTC data might be around 1345UTC. For global models, i. e. those used for international aviation, a slightly longer time is allowed, but usually no more than 3.5hrs after data time. However, some centres (e. g. ECMWF ) with less demand for immediate products allow over 9 hours or more of data to be assimilated. Cyclogenesis The formation of a major low pressure system along a baroclinic zone (q. v.) (or frontal boundary), with primary forcing due to imbalances along the upper jet. (depressions) Weather systems characterised by low pressure and rising air flows. Wind circulation is anticlockwise in the northern hemisphere and clockwise in the southern hemisphere. Cyclonic trough disruption The southern (northern in the southern hemisphere) portion of a trough advances, perhaps developing a cut-off circulation, and slowly warming out, whilst the opposite (residual) portion of the trough becomes quasi-stationary, maintaining a cyclonic pattern at the surface. (also see: anticyclonic trough disruption ) (abbr) Dry Adiabatic Lapse Rate. The rate of cooling (for ascending air), or warming (for descending air) when air parcels are displaced by whatever mechanism. Usually taken to be 10degC1km (or 3degC1000ft). Dekametres (i. e. 10s of metres) - often used on upper air charts: thus a 500 hPa height quoted as 540 dam is equivalent to 5400 metres. (NB: although DM may still be seen on some model output, this is regarded as a non-standard abbreviation. dm should definitely not be used, as it is the abbreviation for decimetres, i. e. tenths of a metre) Daughter cell As the precipitation downdraught associated with a marked Cumulonimbus event meets the ground, it will spread out in all directions. Where this cold outflow current meets the low level inflow (relative to the cloud motion) head-on, then this is a point of maximum convergence, leading to forced lifting of the air at that point, and provided the air is unstable enough, and convection is not otherwise inhibited (e. g. widescale descent), then a new convective cloud event will be initiated - a daughter cell. Decoupling Even given the strongest pressure gradients, surface-based friction will slow airflow in the lowest 800 m or so of the atmosphere, leading to the familiar cross-isobaric flow (from high to low pressure). With strong free-air gradients (Vgr) (roughly above 25 knots or 12 ms), surface winds will bear some relationship to Vgr however, below these (approximate) levels, come nightfall under clear skies, surface cooling will lead to stabilisation of the lowest layers and the atmosphere finds it increasingly difficult to transfer momentum from the free-air levels to the near-surface. The surface wind may drop away completely as the surface-based inversion develops (often within the course of half-an-hour), allowing mist, fog or surface frost to form (other factors being in place): this process has come to be known as decoupling of the boundary-layer air from the flow inferred by the isobaric flow. Once the flow is decoupled, then the surface cools even more efficiently, thus reinforcing the nocturnal inversion. (See quotStable and unstable air masses quot for discussion of stability etc. and quotWhy does the wind blow quot for matters concerning surface wind-flow.) (used in METAR reports) - fog dispersal operations are in progress (probably obsolete now so included for historical purposes). Deterministic forecast A forecast that says rain will occur at such-and-such a place within a given time band, i. e. a yesno forecast, is an example of deterministic forecasting. (See also probability forecasting .) (strictly dew-point temperature) The temperature (of an air sample that contains water vapour), to which that sample must be cooled (Pressure and humidity content being held constant) to achieve saturation with respect to a water surface. It can be measured indirectly using a wet amp dry hygrometer (ordinary dry bulb thermometer, and anotheradjacent thermometer with its bulb covered in a damp muslin - hygrometric tables or calculator then being used to calculate the dew point, relative humidity, vapour pressure) also by a dew-cell type of instrument that measures relative humidity, from which the dew point can be calculated, or it can be measured directly by a dew-point hygrometer. The screensurface dew-point temperature is used in air mass analysis, and also in the calculation of night-minimum and fog-point temperatures, as well as being used in the estimation of convective condensation levels, human-comfort indices, probability of snow at the surface etc. Dew point values above the surface (from radio-sonde ascents) are used to define cloudy or potentially cloudy layers etc. in the upper air (see also Frost point ). Dew-point depression (DPD) The numerical difference between the temperature of a sample and its dew-point. The greater the difference, the lower the relative humidity. Values (deg. C) of less than 3 would be considered to indicate high relative humidity those of 7 or greater would indicate low relative humidity. (See quotWhat is the dew point depression quot) Discontinuity Where a steep gradient (i. e. sharp change over a small horizontal distance) occurs in a meteorological variable (i. e. temperature, humidity, wind direction etc.), there is said to exist a discontinuity in that variable. Diurnal cycle Changes which take place over the course of a 24hr period. The most obvious cycle is the rise and fall of surface temperature. Divergence When air flows in such a way that the area occupied by a particular group of air particles grows (spreads apart), the pattern is said to be divergent. Divergence in the atmosphere is also (along with convergenceq. v.) associated with vertical motion, and hence development (or weakening) of weather systems, depending upon the level where the divergence is dominant in a particular atmospheric column. For example, divergent flow aloft is coupled to, and may be the primary cause of, upward motion, leading to widespread cloud formationcyclogenesis etc. ( see also diffluent.) (obsolete abbreviation for dekametre - see entry for dam ) Downward penetration of Snow Falling snow modifies the temperature structure of the atmospheric boundary layer as both melting amp evaporation takes place. (See this question in the FAQ). Even if snow does not initially penetrate to the surface (after having fallen out of the parent cloud), if the Wet Bulb Freezing Level (q. v.) is low enough, the intensity of the precipitation is more than just light and the mean wind strength in the melting layer is not too strong, then the snow level can descend considerably below initial conditions. The depth of this downward penetration of snow as it is called, increases as the intensity of rain increases, andor the wind speed decreases. It will be immediately apparent that the prospect for error in snow forecasting due to these variables in marginal situations will be large Used in METAR reports - low drifting (snow, sand etc.), not appreciably affecting the visibility, e. g. DRSN. Partial amp absolute droughts are terms that are no longer used in official summaries they were introduced in 1887 by G. J. Symons in British Rainfall, (with the term dry spell added in 1919) but ceased to be used circa 1960. Drought hydrology is a complex field of study and as statistical amp data-processing techniques have become sophisticated, there was no longer an official requirement for the use of these rather crude definitions. It is however useful to know what the definitions were, and even today, for hobby-use, defining periods of drought using these standards can be an interesting exercise. They are detailed elsewhere in this Glossary. (See Absolute drought partial drought dry spell). Droughts - types of Droughts as defined above are essentially meteorological in other words, they are defined in terms of the amount of rain (or rather lack of rain) that occurs. Hydrological drought episodes by contrast take account of the wider cycle of water use, with focus on the imbalance between precipitation input (rain, snow etc.) against water availability via aquifer storage, reservoir levels, land-surface run-off riverflow etc. Finally, agricultural droughts are usually defined in terms of the soil moisture deficit (SMD) across a growing season - the degree of irrigation (natural or artificial) needed to bring a particular soil type back to optimal production - balancing the outgoing moisture due to evaporation amp transpiration. Dry Intrusion (or dry slot) -- A narrow region, virtually cloud-free which separates a baroclinic leaf (q. v.). and the adjacent frontal cloud. This region is the result of abruptly descending upper troposphericlower stratospheric air into a rapidly developing and potentially damaging low pressure system -- hence the low humidity contentabsence of cloud. Water vapour imagery (see quotWhat are the various types of Satellite imagery available quot) in particular is used to diagnose this feature, and the rate of darkening of the dry slot gives a clue to the rate of development of the whole storm complex. A period of at least 15 consecutive days, to none of which is credited 0.04 inches 1.0 mm of precipitation. (See also drought. absolute drought. partial drought ). Duststorm (used in METARTAF reports etc.) visibility generally lt 1km due to dust raised by strong winds over a large area. Dust (widespread, in suspension) (used in METARTAF reports etc.) Visibility is 5000 m or less. Deutscher Wetterdienst (German Weather Service), based at Offenbach. Visit their web site at: dwd. de Dynamic precipitation For precipitation production, other conditions being satisfied (i. e. enough humidity, required temperature structure, sufficient depth of cloud), there must be a supply of upward motion through the cloud producing the rain, snow or whatever. In the case of dynamic precipitation, the primary agent for providing upward motion is broad-scale ascent due to, for example, short-wave troughs in the prevailing upper flow, jetstream developmental areas, mass convergence or strong warm advection. Computer models in operational use deduce dynamic precipitation by testing for super-saturation of a layer taking into account the total water content (all phases) in a layer: the excess found is precipitated out. The type (dynamic or convective) giving the greatest amount is (usually) that seen on output charts. (See also Convective and Orographic precipitation). Drizzle (as in METARTAF reports). Eclipse (of a geostationary satellite) The earths equator (and therefore a geostationary satellites orbit) is inclined to the orbit of the earth around the sun. This inclination allows sunlight to power the satellite on-board systems for most of the year. However, there is a period of about 3 weeks either side of the vernal and autumnal equinoxes when a satellite will be in the earths shadow for about 70 minutes each day (around local midnight). Because most of these platforms do not carry sufficient battery power to tide them over this gap, no imagery is generated and thus a local-midnight image is missing. European Centre for Medium Range Weather Forecasts, located on the southern outskirts of Reading, Berkshire, UK. Visit their web site at ecmwf. int Eden Winter Snow Index Embedded (in cloud, as in CB embedded in LYR cloud). A collection of NWP runs (typically in excess of 15, many having 50 or more) from the same start time (t0) and using the same model physics, but each run (or member) having a slightly perturbed (altered) set of initial conditions from the control run (q. v). The alterations are constrained within limits which are calculated in various ways - one example being that of performing a separate short-range model run and identifying the errors that would grow most over a 48 hr period. These errors are then applied in varying amounts to the initial conditions before performing the operational ensemble run. Another technique is to use (known) errors from a previous run and apply these in small amounts to the initial conditions of the new run. NB: these output are in addition to (and run some time after) the operational model output, i. e. the deterministic run which is the set of charts most often seen on web sites: it should not be assumed that the operational run (OPOPER: q. v .) is close to the ensemble mean (q. v.) or mode - significant deviations can and do occur at longer lead times. Also note that a particular centres operational model is often run at a higher spatial resolution than that used for the ensemble generation - the control . Ensemble mean An average of the ensemble output from a particular computer run - this is usually more accurate than just following one of the individual forecasts that make up the average. Further, by comparing the individual members spread about the mean, some estimate can be made of the reliability of the forecast: if there is strong agreement and therefore small divergence from the mean solution, then high confidence can be assigned to the average solution. Wide divergence, or clustering of groups of individual members well away from the mean will lead to considerable caution regarding using the output too slavishly and lower confidence in issued forecasts. Environmental Lapse Rate The actual plot of temperature against height (or equivalent) on a thermodynamic diagram. Evaporation The transformation of liquid water to water vapour - in the process absorbing latent heat (of vapourisation). (abbr)(also EWR) England and Wales Precipitation (or Rainfall). A data series combining the rainfall (and melted snowfall) amounts from a matrix of recording stations (well over 30) averaged to produce a single figure for an area taken to represent England and Wales. The series runs from 1766 - maintained (separately) by the Hadley Centre (EWR) and the University of East Anglia (EWP), though I understand that a unified data-set is to be (has been) produced. CLICK HERE FOR LATEST DATA FROM THE HADLEY CENTRE. Explosive cyclogenesis Sometimes, in an otherwise normal cyclogenetic situation, factors are conducive to rapid falls of pressure leading to very tight isobaric gradients extreme low pressure. These situations often give rise to damaging or stormy hurricane force winds: watch for 3-hourly pressure falls in excess of 10.0 mbar. (sometimes referred to as bombs , particularly in North American meteorological circles.) (abbr.) Funnel Cloud - (in METARTAF, this includes tornadowaterspout, so differs from the classical distinction between a funnel cloud not touching down, and one that does. See entry for Funnel cloud ). 1 or 2 oktas cloud amount, used in AviationMETAR reports etc. (see also SCT ) (abbr) Fog (vis lt 1000m, except when qualified by MI, BC, PR, VC) used in METARTAF reports etc. (abbr) Flight level (e. g. FL240. 24000ft amslstandard atmosphere) used in aviation reports, forecasts etc. Foehn (or Foumlhn) effect Mechanisms which give rise to a warm, dry wind on the leeward side of mountains or significant hills. Broadly, there are two: (i) the subsidence type where air at amp just above the hillmountain crest descends by lee-wave action, becoming even drier amp warmer than when it started out (ii) all air in a moist airstream on the upstream side of the hillmountain rises, leading to cloudprecipitation formation, thence lowering the humidity content, this air then descendingwarming adiabatically on the leeside. Reduction in visibility to under 1 km caused by suspension of minute water droplets (water fog) or ice crystals (Ice fog - q. v.). Water fogs are further sub-divided according to the process by which the fog forms, e. g. Radiation fog (caused mainly due to loss of surface heat from the ground at night in conditions of near-calm wind and high relative humidity) Advection fog (caused by movement of humid air over a relatively colder surface) Upslope fog (adiabatic cooling of air having high relative humidity as it climbs over high ground) and Evaporation fog (caused by evaporation into cold air which lies over a relatively warm water surface). ( If the visibility is below 200M but greater than 50M then it is usually referred to as Thick Fog (amp colloquially in the UK as motoring fog ) amp if below 50M then Dense Fog . However, there are different criteria for climatological stations, and other services will have different rules - treat this note as a guide only. ) (strictly fog-point temperature) The air temperature (as measured in a standard thermometer screen) at which fog is expecteddoes form. Its calculation (before an event) is usually based on empirical work which employs either the surface air temperaturedew point at some time earlier in the day, or by construction on a thermodynamic diagram. The fog point is lower than the air-mass dew point. because as air cools through the evening and night, moisture is condensed out on contact with the chilled land surface, and this lowers the dew point from afternoon values. Freezing fog As for the definition of fog (above), but the droplets are super-cooled (i. e. temperature below zero), and strictly, the fog should be depositing rime-ice. However, in METAR TAF coding, as long as the air temperature is below zero degC, then fog is coded as freezing irrespective of whether rime is observed. Freezing level Taken as the altitude where the air temperature is 0 deg. C. However, it should be carefully noted that in the free atmosphere, liquid water does not necessarily freeze at this level, or indeed at altitudes some way above this value -- it should more correctly be called the melting level, or as in operational aviation meteorology, the level (or altitude) of the zero degree isotherm. (see ZDL and Wet Bulb Freezing Level) . A boundary separating two air masses such as warm, moist air and cold, dry air. If the cold air pushes into a region of warm air, a cold front occurs and if the warm air advances relative to the cold, a warm front occurs. Frontal fracture During rapid cyclogenesis events, a weakness appears along the portion of the cold-front nearest to the depression centre, thought to be due to a combination of subsidence in this region, plus differential thermal advection, as, unlike in the Norwegian model. cold air is not advected so quickly eastwards to maintain the baroclinicity in this region. (See quotWhat is the Shapiro-Keyser cyclone model quot) Frontogenetic Any atmospheric process which leads to frontal formation, or an existing weak frontal zone to become enhanced, is termed frontogenetic. On charts issued by some national meteorological services, such fronts are shown with the normally solid line defining the front broken by spaces and large dots. Frontolysis When fronts weaken markedly due to, for example, marked anticyclonic subsidence across the front, then the feature is undergoing frontolysis. On charts issued by some national meteorological services, such fronts are shown with the line defining the front struck-through by short inclined strokes. Frost point (strictly frost-point temperature) The temperature (of an air sample that contains water vapour), to which that sample must be cooled (Pressure and humidity content being held constant) to achieve saturation with respect to an ice surface. (see also dew point ). (abbr) Frequent (hardly or not separated, as in FRQ CB in aviation forecasts). (abbr) Smoke (as used in METARTAF reports etc.) Funnel cloud (FC) A visible rotating tube of condensation particles, formed as the pressure falls in an intensifying vortex (extending below a cumulonimbus cloud) - perhaps reaching the groundsea. It should be noted that the funnel cloud simply betrays the zone where the pressure is low enough and humidity high enough for cloud to form - the vortical circulation may well be in contact with the ground, but of such relatively weak intensity that it either causes little or no damage, or is detected only by surface dust soil disturbance. There are well documented cases where tornadoes (as defined elsewhere) do not have cloudy funnels all the way to the surface. (based on Doswell, C. A. III, 2001) (abbr) Freezing (used in connection with rain, drizzle, fog, all giving rise to ice deposition due to supercooled water droplets impacting upon surfaces with temperatures below 0.0degC, OR when temperature lt 0.0degC anyway, whether or not ice deposits are observed.) Glossary terms G-L The word gale is used in everyday speech in a rather loose way to describe any strong wind, for example. quot its blowing a gale outsidequot, when it may be just a strong blow in inland areas of the southern Britain. Meteorologists must work to a strict definition of a gale. For operational forecasting (UK Met Office practice) both for land and sea use, a gale Force 8 on the Beaufort scale is defined as a mean wind (over 10 minutes) of 34 knots (39mph, 63 kmhr, 17 ms ) or more, or gusts of 43 knots (49 mph, 79 kmhr, 22 ms) or more. This definition is also used for verifying Shipping Forecasts and Gale Warnings. Isolated gusts accompanying squalls or thunderstorms are not counted. However, for climatological purposes (i. e. post-event analysis), only the mean wind is considered, i. e. a mean wind of 34 knots or more, as specified in the Beaufort wind scale (q. v.). see also definitions for Severe Gale. Storm. Violent Storm and Hurricane Force. (abbr)ground-to-cloud lightning flash Used when describing lightning which branches from the ground to the cloud. The upward branching often results in an appearance like a trident, etc. This is an uncommon type of lightning. (See also CA. CC amp CG ) (abbr) Global Ensemble Forecast System (of NCEP q. v.) Geopotential quotPotential energy per unit mass of a body due to the earths gravitational field, referred to an arbitrary zeroquot (The Meteorological GlossaryUK in meteorology, mean sea level is the reference level). A geopotential metre (by this definition) is related to the dynamic metre (straightforward unit of length) by the expression: 1 gpm0.98 dynamic m. Geopotential height differs from geometric height where the value of the gravitational constant (g) departs from 9.8 ms2. Gravity does vary, both by altitude and latitude, but for practical purposes, when looking at NWP output on the web, you can ignore these slight differences. Geopotential heights are used in meteorology because flow along a geopotential surface involves no loss or gain of energy, whereas flow along a geometric surface may do so - so for strict physical mathematical calculations within computer models, the distinction between the two must be maintained. Geostrophic wind Defined as the (theoretical) wind that would blow on a rotating planet which results from a balance between the pressure gradient causing the initial displacement of the air, and the apparent (to us on the earth) deflecting force due to the planetary rotation. Many corrections are needed to find the true wind vector amongst which are the effects of friction and the several forces involved when the pressure pattern changes - which is the usual case. However, by this definition we get the general statement that the speed of the geostrophic wind is proportional to the pressure gradient, or inversely proportional to the distance between isobarscontours. Curvature of the flow must also be taken into account. see Gradient wind . Global Forecast System The primary forecast model (NWP ) from the US NCEP service (q. v.). The model suite is run to T 384 hr, in two bursts one to T 120 (5 days) then a further run to the 16 days (384hr). The model is run four times daily, though not all WWW sites hold all runs (or full output for each run). Hail (abbr. from French) dia: gt 0.5 cm used in METAR aviation reports etc. Gradient wind When the path that an air parcel takes is curved (relative to the earths surface), as so often in meteorology, that airflow is subject to an additional force necessary to maintain a curved path. For cyclonic flow, the true wind that blows will be less than the theoreticalgeostrophic wind for anticyclonic flow the true wind is greater, subject to a limiting maximum. This is why, for example, around what initially looks like a dramatically intense depression, the wind may not be quite so excessive: cyclonic curvature will account for substantial negative correction to the theoretical value. Around a surface ridge, the wind is often surprisingly stronger than might be implied by isobaric spacing. Small hail dia: lt0.5cm used in METARaviation reports etc. Given that the wind in the surface boundary level varies markedly about the mean wind (q. v.), it is often necessary to report the accompanying instantaneous maximum (or gust speed) in a defined period. For METAR reports, then the period over which this peak wind is reported is between 2 and 10 minutes (depending upon the country). For SYNOP reports, the period is either the last hour (most likely in NW Europe), or the period covered by the past weather group in the report - reference to the accompanying amplifying groups will usually sort this out. Hectopascal Horizontal vorticity Even the classical vertical vorticity term (q. v.) has some upward downward component, but this is usually ignored for practical synoptic-scale meteorology. However, when coming down a scale or two, to local mesoscale development, ( e. g. severe convective storms ), then vorticity about a horizontal axis is most important. It is often assessed in the lowest 3 km of atmosphere, and is driven by two terms: vertical speed shear (increase decrease of wind with increasing altitude) and directional (twisting) shear, the change of direction with increasing altitude. If, in the lowest 3 km of atmosphere (up to 700 hPa), there is both a sharp increase of wind speed and a directional veer of wind with height, then horizontal vorticity will be potentially significant, provided it is coupled to the vigour of a developing cumulonimbus complex. (See also Vorticity Vertical vorticity and quotWhat is Helicity quot (abbr) Hectopascal - equivalent to a millibar (q. v.). An attempt to use SI units without doing away with the idea of millibars (from the c. g.s. system). 1 hPa100 Pa (or Nm 2 ) Hurricane Force This term (in UK Met Office use) is only used in shipping bulletins and associated GaleStorm warnings in the form quotHurricane Force 12quot, from the modified Beaufort scale. It is strictly defined as a mean (10 minute) wind of 64 knots or more. (Gusts not defined) (See also comments at Severe Gale ). Please note carefully that just because an area of low pressure produces winds to hurricane force as defined here, it does NOT make that feature a Hurricane For more on this, see this question on the October 1987 storm Haze: used in METARTAF reports etc. when visibility is reduced in a dry atmosphere. (visibility gt 1km, relative humidity roughly lt 90). (abbr) Ice crystals (also known as diamond dust) used in METARaviation re ports. When used in aviation weather reportsforecasts, implies aircraft superstructure icing. A period of 24hr (conventionally beginning 0900UTC), during which the air temperature is less than 0 degC. Visibility reduced to less than 1000 m by suspension of minute collection of ice crystals in high concentration. The crystals will glitter and may give rise to optical phenomena. (NB: this is NOT the same as freezing fog, which is composed of water droplets - see definition elsewhere.) Initialisation The process whereby a model analysis is produced by utilising model fields from an earlier run, and integrating synoptic, and asynoptic observations to produce the initial state at t0. The model analysis may not be the same (in detail), as a hand-drawn analysis, and intervention (q. v.) is sometimes needed as a result to preserve some small scale features which can influence the forecast run. Insolation Radiant energy received from the sun on any particular surface. Often used when discussing receipt of infra-red radiation on the surface of the earth. Instant Occlusion or pseudo-occlusion The name that has been coined to label the cloud mass associated with an active trough in the cold air, that comes close to, and interacts with a pre-existing baroclinic zone, forming a pattern that looks superficially as if it was part of a traditional occlusion process. Intertropical Convergence Zone (usually abbr. ITCZ) A zone (often rather broad, but sometimes quite narrow), which separates the air-masses brought together by the low-level outflow from the sub-tropical high pressure belts north and south of the equator. Over the oceans, the zone can be well marked over land, sensible heating usually leads to breaks or other anomalies, and the regional-scale monsoon circulations also distort, or swamp the idealised structure of the ITCZ. Cloudiness (and hence precipitation activity) can vary sharply over a period of 24hr. Day-to-day change of position is often small, but the zone migrates north amp south through the course of a year, roughly in sympathy with the changing position of the sun. Intervention A process where forecasters force acceptance of a report rejected in the model initialisation routine (supporting), or use bogus observations to input a conceptual model observed in imagery. (abbr) Intensifying (as used in SIGMETs for a phenomenon becoming more intense or extensive). Inversion (of temperature) A layer in the atmosphere (usually very shallow lt 0.4 km), where temperature rises with increasing height. Two of the best-known in operational meteorology are the nocturnal inversion (formed due to strong cooling of land surfaces after sunset), and the subsidence inversion (due to descent amp adiabatic warming of air associated with anticyclones). Another near-surface type is that formed when warm air travels over a cold surface (e. g. cold seas or icesnow). (abbr) Isentropic Potential Vorticity - the product of the absolute vorticity of an air parcel, and its static stability, calculated along a constant surface of theta (potential temperature), hence the isentropic. Anomalies in IPV around the level of the tropopause (and hence in the region of the driving jet stream) can be related to developments through the troposphere, leading to cyclogenesis. Because IPV is a highly conservative property for any sample of air, it is found to be particularly useful for tracking the path that stratospheric air (high IPV values) will take as it enters the upper troposphere during rapid cyclogenesis events. NWP models can be programmed to output the height of a particular IPV value - defined such that it samples air in the model stratosphere. These patterns are then overlaid on water vapour imagery, and any mis-match between model and reality are quickly seen and allowed for. (See also Potential Vorticity ) and also this article on Water Vapour Imagery. (abbr) International Standard Atmosphere. A standard reference for temperature, pressure, and relative density structure in the troposphere and lower stratosphere, used for the calibration of (pressure) altimeters. A line on a synoptic chart joining points of equal atmospheric pressure. Isolated (as in ISOL CB etc.) Abbreviation used in aviation work to stand for quotover-landquot. Lapse rate (of temperature) The decrease of temperature with height in the atmosphere. Confusingly, the opposite case, an increase in temperature with height, is known as a negative lapse rate. Latent heat The amount of energy needed to accomplish a phase change. Latent heat of fusion is the amount of energy required to melt ice, and at 0degC is 3.34 10 5 J kg -1 (or about 80 calg). The latent heat of vaporisation is the amount of energy needed to evaporate liquid water. It is equivalent to 2.50 10 6 J kg -1 (or about 600 calg) at 0degC. The latent heat of sublimation is the energy needed to carry out a change from solid (ice) to gas (vapour). It is the sum of the latent heats of fusion and vaporisation, i. e. 2.83 10 6 J kg -1 (or about 680 calg) at 0degC. When water freezes, condenses or changes from a gas to a solid, 80 calg, 600 calg and 680 calg are released to the environment respectively. The processes are all reversible. Lies on the cold side of the jet axis, in the region of marked deceleration of flow. A preferred region for cyclonic development. Lenticular clouds These form within the crest(s) of orographic (or lee) wave-trains, over and downwind of hills mountains islands, provided of course that the air is humid enough. The clouds are formed because air cools as it is forced to rise and if condensation takes place, lens-shaped clouds are observed with clear space in between the elements. The cloud forms within the upwind leg of each wave-crest and dissipates (evaporates) on the downwind leg: the air is therefore flowing through the cloud, with the cloud itself staying quasi-stationary change in the cloud requires an alteration in the windflow or temperature humidity environment. Sometimes, under very special circumstances, a pile of plates is observed, where lenticular clouds are stacked vertically. The most common form of wave-forced cloud is perhaps Altocumulus lenticularis (Ac len), but lenticular cloud forms are found at all levels. Standing wave motion can also lead to a previously uniform sheet of cloud developing a lenticular appearance, and on occasion, complete dispersal. (See also MTW ). Loaded gun scenario On a day of instability through a great depth of the troposphere, and high values of CAPE (q. v.), rising surface temperatures will at some point ensure that convection parcels leave the surface, the condensation level will be reached, cloud will grow (given sufficient moisture), and a heavy shower, or even a thunderstorm will result. It sometimes happens though that although the atmosphere is markedly unstable above, say, 2 km a lid opposing surface-based convection exists at or below this level, due often to a layer of warmdry air that has become entrained in the airflow from some source. This means that surface temperatures must become very high to overcome this lid, often requiring additional triggers, such as low-level convergence or release of medium level potential instability by a mid-level trough, thus lifting the whole column and releasing the pent-up energy in a sudden burst. and the loaded gun will be fired, perhaps leading to a severe stormsupercell event. (see Spanish plume ). Layer(s) (as used in cloud forecasting in aviation products). Glossary terms M-R Operational model A term used to differentiate the primary NWP output from a particular centre from any ensemble products from the same source. The operational model will almost always be run at a higher resolution than that used for ensemble output. It must not, however be assumed that the OpOPER is necessarily the best outcome, particularly beyond 3 days or so. (see Ensemble ) Orographic forcing An airstream encountering a barrier to its passage is forced to go around or over the obstacle. The upward deflection of the airflow is sufficient to give rise to adiabatic cooling, and if the air is moist enough, the formation of clouds, precipitation etc. In addition, convergence of the flow on the windward side (due to a rapid decrease in velocity) when the air encounters a sharply graded barrier not only enhances the vertical motion, but also leads to a deformation of the flow which in turn alters the vorticity of the air particles. Thus, hill and mountain ranges are most important in a study of meteorology. Orographic rainfallsnowfall For precipitation to occur, other conditions being satisfied (i. e. enough humidity, required temperature structure, sufficient depth of cloud etc.), there must be a supply of upward motion through the cloud producing the rain, snow or whatever. In orographic precipitation, the forcing agent is provided by large ranges of hillsmountains blocking the flow of humid air in such a way that vertical (upward) currents of air are produced, leading to adiabatic cooling gtgt condensation gtgt cloud formationenhancement gtgt precipitation element growth. Orographic forcing OF ITSELF usually only produces small amounts of precipitation, but can be the means of enhancing or triggering other mechanisms (e. g. convective activity), and is one of the important elements in the seeder-feeder model (q. v.). Computer models in operational use do now have sufficiently realistic orography and vertical resolution to model such, but the output (usually) does not explicitly define orographic precipitation. Orographic waves (in an NWP ensemble suite) When considering a collection of solutions at a particular lead time (from a single-centre, or as part of a Poor Mans ensemble ), some clustering is usually observed - i. e. a large number of members pointing to a similar outcome. However, as lead times get longer (especially beyond 72 hours), one or two members may depart significantly from the ensemble mean, (andor mode of larger clusters) - these are termed outliers such indications carry small weight, but cannot be totally ignored. In particular, at extended range (beyond about 7 days), there may be no clear clustering signal, and an outlier is just as likely to be right as a solution nearer the meanmedian of the output. (See also ensemble. clusters. ensemble mean etc.) (abbr) Overcast 8 oktas (cloud amount, as used in aviation reports, forecasts etc.) Overconvection The promise of a fine, sunny day is sometimes spoiled because cumulus cloud builds and spread out into an almost unbroken sheet of stratocumulus by late morning - which then refuses to break up for the rest of the day. For this to occur, there must be a marked inversion (see quotWhat is an inversionquot ) within 100 to 300 hPa of the surface, which must be intense enough to stop convective currents breaking - through the inversion even at maximum temperature the convective condensation level (CCL ) must be at least 60 hPa below the inversion level, and the layer between CCL and inversion must have a reasonably high relative humidity. For some rather obscure reason, this phenomenon has come to be called overconvection (at least in the UK, probably originating within the gliding community) - possibly because convective cumulus spills-over to cover the sky ( though, other conditions being right, the cloud may disperse around or just after dusk.) Over-running trough An active, mid-latitude frontal system is associated with a marked short-wave trough. The active weather associated with the front lies forward of the trough, driven by the dynamics associated with it. At some stage in its life though, the trough (or a portion of it) will relax (and effectively weaken), allowing the trough to run well ahead of the lower-tropospheric portion of the frontal system - it over-runs the (surface) location of the front, and the activity at that position will decay. Note however that the upper trough will still have weather associated with it - and may be the means of driving an uppersplit frontal structure well away from the classical surface front as drawn on conventional analyses. See also quotWhy fronts die quot. Pascal - allocated in honour of Blaise Pascal, to a unit of one Nm 2. the basic unit of pressure in the SI system. Parametrisation Some atmospheric processes are below the grid-scalewavelength of operational meteorological computer models and cannot be handled explicitly by such schemes - for example individual showers, which are not only important for local weather, but have a feedback effect within the atmosphere that needs to be included in the NWP routines to maintain a realistic model of the real atmosphere. Larger scale model parameters (e. g. wind vector, temperature, humidity) are used to diagnose and represent the effects of such sub-gridscale processes: this is know as parametrisation. See HERE Partial drought A period of at least 29 consecutive days, whose mean daily precipitation does not exceed 0.01 inches 0.2 mm. (See also drought absolute drought dry spell ). Is the study of times of naturally occurring events, such as the first blossom appearance in a long established species, or the departure of migratory birds. From 1875 to 1948, a register of such events was maintained by the Royal Met. Society, but after a period when the science was in the doldrums, the Woodland Trust and Centre for Ecology amp Hydrology combined in the late 1990s to kick-start the observing network, recognising that such data can complement studies into long-term climate change. For more detail, see:- phenology. org. uk (abbr) Ice Pellets (was PE) used in aviation weather reports. (abbr) Polar mesospheric clouds (or Noctilucent clouds ). (abbr) Pressure at mean sea level: often seen in connection with NWP model products. (abbr) Well developed sanddust swirls as used in aviation weather reports. Polar front A boundary that separates polar air masses from tropical air masses . Polar mesocyclones A term now used to encompass the whole family of disturbances resulting from arctic air flowing equatorward over progressively warmer seas the term Polar Low (q. vabove) is now often used only for extreme systems where gale or near gale-force winds are observed. Polar mesospheric clouds quot Poor Mansquot Ensemble Technique A true NWP ensemble (q. v.) is the product of multiple iterations of a single atmospheric model on a single centres computer: the individual members of the ensemble run are obtained by perturbing the initial conditions very slightly to simulate the uncertainty that is always present at analysis time. However, long before these techniques were perfected, operational forecasters would (and still do) absorb the differing output from various international centres (e. g. EC, NCEP, DWD etc.) and or different runs from the same centre - treating all the various outputs as members of what has been dubbed a Poor Mans Ensemble. As with true ensembles, the more model runs that agree at a certain lead time, the higher is the confidence in that particular solution. Potential Instability (also known as Convective Instability) Said to exist when forced lifting (e. g. ascent over mountains or broad - scaledynamic ascent) causes a layer, initially (just) stable to such forced ascent to become unstable. Decreasing humidity aloft is required within the layer, and heavy rainthunder can be the result. Theta-W or Theta-E (q. v.) difference charts are often used to find such areas of potential instability: the usual levels used are at 850hPa and 500hPa. The value at 850hPa is subtracted from that found for 500hPa, and negative values so found indicate potential instability. Only slightly negative differences can lead to some significant convective activity. all other factors being favourable of course. Such layers can also be inferred using a thermodynamic diagram (or tabular listing of Theta E or Theta W), noting where values decrease with increasing altitude within the low-to-middle troposphere (roughly up to 400hPa). Potential Vorticity The ratio of the absolute vorticity (q. v.) of an atmospheric column to the (defined) pressure difference across the column. This quantity is used to label air in much the same way as we use other conservative properties. As a column of air moves along, it shrinks vertically (due to mass divergence) in just the right amount to decrease its absolute vorticity as it expands vertically (due to mass convergence), its absolute vorticity increases. Therefore, Potential Vorticity tends to remain constant following the motion of the flow, for adiabatic motion. Precipitation Anything precipitated by clouds (rain, snow, hail, drizzle etc.) is covered by this noun. Often abbreviated to ppn or pptn. (for definitions of various types of precipitation, see:- quotBeaufort Lettersquot ) Pressure Gradient The difference in atmospheric pressure over a defined (usually horizontal) distance. (See quotWhy does the wind blowquot ) Pressure Gradient Force (abbr. PGF)The force exerted on the air due to a pressure gradient, causing a tendency for movement (i. e. wind) from areas of high pressure to areas of low pressure.(See quotWhy does the wind blowquot ) Prevailing visibility Prevailing wind The most frequent wind direction for any particular location in a given period, e. g. a day, month, year or climatological period. Partial fog (i. e. fog quotbanksquot substantial portion of airfield covered by fog - but not completely visibility lt 1000m.) Probability (as used in aviation forecasts, e. g. TAFs in the latter, under current 2002 rules, only PROB30 or PROB40 are allowed, e. g. moderate probability of an event occurring. Probability forecasting Given that there is always a measure of uncertainty in forecasting the weather, the likelihood of an event happening can be expressed as a probability: thus a 70 chance of rain, 20 chance of thunderstorms etc. Often useful in finely balanced situations i. e. rain vs. snow severe storms vs. no storm etc. (see also Deterministic forecasts). Progression When large scale features in the upper air, such as a 500 or 300 hPa troughvortex drift west-to-east this is said to be a normal progression of the pattern. (See also retrogression). (abbr: Polar Stratospheric Clouds) During the polar night (i. e. the period in the middle of the winter when insolation does not penetrat e to ultra-high latitudes), the stratosphere cools significantly leading to closed-loop circulations (both vertical and horizontal) which virtually isolate these polar stratospheric regions - the quotPolar night vortexquot is found, within which temperatures can be found well below (minus)75degC. In these extremely cold conditions, clouds are observed to form in the stratosphere, which appear to be composed of a combination of nitric acid and water. Stratospheric clouds can also form from ordinary water ice (i. e. as in the troposphere) but these are much less common at these high altitudes as the stratosphere is normally very dry and water-ice clouds only form at the lowest temperatures. The presence of PSCs and the part they play in the chemical interactions at these levels have been a subject of much debate in recent years. (See main FAQ here for the Stratospheric Night Jet and here for Stratosphere amp various web-sites dealing with upper atmosphere ozone depletion.) Pulse storms (a term often used in North America) Random air-mass thunderstorms forming in an environment of little or no vertical wind shear, which appear as individual returns (without any obvious organisation) on radarhigh-resolution satellite imagery systems. They usually last 20 to 30 minutes, perhaps up to 60 minutes, and give rise to small hail, sometimes heavy rain and perhaps weak tornadoes. They can be regarded as a more intense version of the single-cell convective type discussed in the main FAQ here. i. e. higher CAPE values are involved than for an ordinary shower. PVA region An area where marked advection (movement) of positive, or cyclonic vorticity (q. v.) is occurring - hence P ositive V orticity A dvection often associated with a small upper trough running through the broadscale upper pattern. Cyclonic development will occur - other factors being favourable. Pressure at airfield level set on an aircraft (pressure) altimeter when height above local aerodrome level (strictly the official threshold elevation) is required. Pressure at mean sea level (reduced according to actualmean temperature). Pressure at mean sea level (reduced according to ISA profile) set on an aircraft (pressure) altimeter when height above local mean sea level is required. (abbr) Rain as used in aviation (e. g. METARTAF) reports. This is the transmission of energy by electromagnetic waves, which may be propagated through a substance or through a vacuum at the speed of light. Electromagnetic radiation is divided into various classes on the basis of wavelengths these are, in order of increasing wavelength: gamma radiation, X-rays, ultra-violet (UV) radiation, visible (VIS) light, infra-red (IR) radiation and radio waves. Radiosonde ( sometimes abbreviated to RS ) An instrument that measures temperature, pressure and humidity of the atmosphere as it is carried aloft on a balloon. The quotsondequot transmits its measurements to a ground-based radio receiver via radio signals, and by accurate tracking (radar or satellite) of the sonde unit, upper winds can be deduced. A period of 24hr, conventionally beginning at 09UTC, during which precipitation of 0.2mm or more has been recorded. (See also Wet day ). Relative humidity (RH) See the main FAQ here . Relative Vorticity The vorticity (or tendency for air particles to spin) relative to the earth. It can be considered for practical purposes (and crudely assessed on meteorological charts) as the combination of two factors: (i): the spin imparted due to the curved path that air takes in its passage through the atmosphere (cyclonically curved contourspositive, anticyclonically curved contoursnegative). (ii) the other factor is due to the shear developed along the flow due to the differing velocities of the moving particles. Swiftly moving air will generate a twist element relative to the lower-velocity flow on either side shear vorticity : where the twisting generated is in a cyclonic sense, that is counted as positive where in the anticyclonic sense then it is negative. ( See also Vorticity Absolute Vorticity .) Relaxation When the amplitude of a trough decreases with time, the trough is said to have undergone relaxation. The change is usually measured in terms of a latitude change of a chosen contour or thickness line. Retrogression When an upper trough (or ridge) moves against the normal west-to-east flow in mid-latitudes, the feature is retrogressing, or undergoing retrogression. (abbr)Relative Humidity (expressed as a value). See Upper ridge Ridge amplification When contour heights along the axis of an upper ridge increase, the ridge is amplifying. Right entrance On the warm side of the jet core, in the region of maximum acceleration of flow. Often associated with marked cyclogenesis. (abbr) Saturated adiabatic lapse rate. The rate of cooling (variable) of a saturated air sample rising in the atmosphere. (see quotStable and unstable air massesquot ) Saturation The condition air reaches when it contains the most water in the vapour state that it is capable of holding at any particular temperature. If any more vapour is injected into the sample (or if the sample is cooled), then condensation will occur. (abbr) Stratocumulus (SC in METARSIGWX charts etc. Sc otherwise) a low-level cloud type, varying from thin, well broken layers with little impact for aviationgeneral weather, to deep, sometimes unstable character giving rise to persistent PPN, and a risk of moderate turbulence amp moderate (some situations severe) icing. (abbr) Scattered (3 or 4 oktas) cloud amounts used in aviation reports, forecasts etc. (of historical note, SCT used to mean 1 to 4 oktas, until the introduction of FEW on revamp of the METAR code in the 1990s). In mid-latitudes, we are used to the idea of the four seasons: spring, summer, autumn and winter. For climatological accounting purposes, these are defined using three calendar month blocks thus:- March, April amp May spring June, July amp August summer September, October amp November autumn and December, January amp February winter. (For more, see quotHow are the seasons definedquot ) Seclusion process During the process of rapid cyclogenesis (q. v.), the standard Norwegian theory of development leading to an occluded front is not appropriate. What appears to happen is that the original cold front becomes weakill-defined (close to the low centre), and a new cold front appears further to the west. (This is effectively what has been drawn in the past as a back-bent occlusion). So, what happens to the warm air associated with the warm frontal zone near the low centre Around and immediately to the equatorward side of the low, it becomes trapped or secluded from the rest of the development in a discrete region enclosed by relatively colder air encircling the development - a so-called seclusion. (This is therefore a different process from that producing the classical occlusion whereby warm-sector air is lifted by the advancing cold air.) (see quotWhat is the Shapiro-Keyser clyclone modelquot ) Seederfeeder mechanism When very moist (e. g. tropical maritime) air flow is forced to rise over upland areas, thick layers of stratus or stratocumulus cloud form. As noted elsewhere, these orographic clouds of themselves produce relatively little rainfall (in a thermally stable environment). If however rain is already occurring from medium layer cloud (thick altostratus, nimbostratus) seeder clouds, it will have to fall through the low-level feeder cloud, with collisioncollection processes markedly enhancing the net rainfall rate at the surface. This effect often produces prolonged heavy rainfall in the warm conveyor regime within a warm sector, particularly if the system is slow-moving. Sensible heat transfer The transfer of heat by conduction and convection (i. e. it can be sensed or detected directly). (abbr) Severe (as in SEV ICE, for severe icing). Severe Gale The definition of a Severe GaleForce 9 is strict for operational (UK) forecasting for maritime purposes. Either the mean (10 minute) wind must be 41 knots or more, up to 47 knots or the gusts must be 52 knots or more, up to 60 knots. The term will also be heard on broadcast weather forecasts, although its arguable that the general population cannot be expected to know what this definition is, and the practice now is to explicitly forecast gust values rather than just relying on the adjective severe to imply possible problems. (See also Gale. Storm and notes at the Beaufort wind scale .) Part of the WMO header code used in bulletins that carry atmospheric reports, more commonly known as sferics, or SFLOCS. (See quotWhat are sfericsquot ) (abbr) Snow grains as used in aviation weather reports.