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Chuvas intensas sao eventos de baixa previsibilidade, mas com grande impacto social, causando prejuizos tanto financeiros quanto humanos. Neste interim, os indices de instabilidade sao uma boa ferramenta para auxiliar os previsores, pois podem indicar se o ambiente atmosferico e ou nao propicio para a formacao de nuvens profundas. Neste trabalho, foi analisado o comportamento de alguns indices de instabilidade para diferentes taxas de precipitacao. Foram utilizados os dados SYNOP (1996 a 2014), provenientes de estacoes meteorologicas das Regioes Sul e Sudeste do Brasil, para as quais tambem estavam disponiveis os dados das sondagens atmosfericas. Os dados coletados foram categorizados em tres intervalos de classe de interesse de acordo com os registros dos acumulados pluviometricos: acima de 60 mm/dia (classe 1 – chuva intensa), entre 60 mm/dia e 5 mm/dia (classe 2 – chuva moderada) e abaixo de 5 mm/dia (classe 3 – chuva fraca/nao chuva). Os eventos de chuvas intensas (classe 1) mais frequentes ocorreram associados a atuacao de Sistemas Frontais, desta forma optou-se por selecionar, para as tres classes, eventos de chuva que estivessem associados a esse sistema. Ao final, 12 eventos de chuvas intensas foram identificados. De forma a uniformizar as classes, foram selecionadas tambem 12 eventos das classes 2 e 3, onde todos os casos com chuva (fraca e moderada) tambem estavam associados a Sistemas Frontais. Os casos sem chuva (precipitacao igual a zero) da classe 3 nao tinham nenhum sistema associado. Foram calculados cinco indices de instabilidade para as tres classes de precipitacao (12 eventos em cada). Os indices K, Total Totals (TT) e Severe Weather Threat (SWEAT) se destacaram como bons indicadores nos casos de chuvas moderadas a intensas (classes 1 e 2). Os indices Lifted Index (LI), Indice Showalter (IS) e Convective Potential Available Energy (CAPEv), entretanto, nao caracterizam bons resultados para os eventos de chuva analisados (associados com sistemas frontais). A analise combinada entre os indices K, TT e SWEAT tambem se mostrou eficiente como um indicador atmosferico para a ocorrencia de chuvas moderadas a intensas.

Padroes de teleconexoes, tais como El Nino-Oscilacao Sul (ENOS) e o Modo Anular Sul (SAM) afetam a circulacao e, consequentemente, o clima da America do Sul. Alguns trabalhos mostram que esses padroes podem estar relacionados a variacoes na ocorrencia de sistemas transientes, tais como, as frentes frias. A extensao de gelo marinho antartico tambem afeta a circulacao em todo o Hemisferio Sul. Porem, nao ha um estudo analisando os impactos em conjunto do ENOS, do SAM e do gelo marinho antartico na atuacao das frentes frias na America do Sul. Desta forma, o objetivo deste trabalho foi avaliar a frequencia de frentes frias na America do Sul nos anos com anomalias do gelo marinho antartico nos mares de Bellingshausen-Amundsen (MBA) e Weddel (MWD) em conjunto com a atuacao das fases do SAM e do ENOS. Os resultados apresentam diferenca nas atuacoes das frentes entre o continente e o Oceano Atlântico adjacente. Em geral, para ambos os mares analisados, e possivel notar a atuacao da La Nina e SAM positivo em todas as analises de frequencias maximas de frentes frias sobre o oceano, variando somente a extensao do gelo marinho. No continente, o El Nino junto com a fase negativa do SAM domina as maximas frequencias de frentes em ambas as extensoes de gelo marinho no MBA e combinado com maxima extensao de gelo marinho no MWD. As diferencas entre o oceano e continente indicam que os tres fatores (SAM, ENOS e gelo marinho) influenciam na trajetoria das frentes, mais meridional e continental ou entao mais maritima.

Este artigo tem como objetivo analisar relacoes entre as fases de padroes de teleconexoes tropicais, subtropicais e extratropicais e as extensoes de gelo marinho antartico no Mar de Weddell (MW). Busca-se melhor compreensao acerca da variabilidade do gelo marinho e das interacoes entre a criosfera e a atmosfera, alem de prover dados para estudos sobre previsoes e variabilidade climaticas. Este artigo analisa setembro, o mes com a maior cobertura de gelo marinho no Mar de Weddell. Utilizou-se os indices mensais dos padroes Modo Anular do Sul ( Southern Annular Mode – SAM), Modo Meridional do Atlântico ( Atlantic Meridional Mode – AMM) e Gradiente Subtropical do Atlântico Sul (GSA). O indice SAM foi calculado atraves da Funcao Ortogonal Empirica nas anomalias de altura geopotencial em 700 hPa na regiao ao sul de 30oS, o indice AMM foi extraido do National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) e o indice GSA foi criado a partir dos dados de temperatura da superficie do mar (TSM) do ERSSTv5 do National Oceanic and Atmospheric Administration (NOAA). Nas avaliacoes conjuntas, as combinacoes de fases que se relacionaram as maiores extensoes de gelo foram SAM negativo/AMM positivo e SAM negativo/GSA positivo enquanto as que se associaram as menores extensoes foram as de sinais opostos. As correlacoes do SAM com o gelo marinho sao negativas e dos indices AMM e GSA com o gelo marinho sao positivas, mostrando coerencia com os resultados apresentados nos compostos e nos graficos boxplots. Extreme Antarctic Sea Ice In The Weddell Sea And Links With Teleconnection Patterns Of Climate Variability ABSTRACT This article examines the links between the phases of teleconnection patterns of climate variability and the Weddell’s Sea ice extent. The goal is to understand better the sea ice variability and connections between the cryosphere and the atmosphere. This paper focuses on September, the month with the largest sea ice cover in the Weddell Sea. The Southern Annular Mode (SAM), the Atlantic Meridional Mode (AMM) and the Atlantic Subtropical Gradient (ASG) monthly indices were used. The SAM index was calculated through Empirical Orthogonal Function in the geopotential height anomalies of 700 hPa. The AMM index was obtained by the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR). The ASG index was created using sea surface temperature (SST) data obtained by the National Oceanic and Atmospheric Administration (ERSSTv5/NOAA) through the difference of SST anomalies averaged at two distinct areas situated in the Subtropical Atlantic Ocean. Considering the effect of these indices combined, the negative SAM/positive AMM phase and the negative SAM/positive ASG phase were associated with maximum Antarctic sea ice extents. The opposite combinations of indices were related with minimum Antarctic sea ice extents. The correlations between the SAM and the sea ice extent are negative and between AMM and ASG with the sea ice extent are positive. These results are coherent with the results presented in the composite maps and the boxplots charts. Keywords: Teleconnection patterns, climate variability, antarctic sea ice, Weddell Sea.

The goal of this paper is to study month-to-month impacts of Southern Hemisphere Annular Mode (SAM) phases over South America (SA). Composite analyses were performed excluding ENSO years. Southeastern SA (SESA), part of Southeastern and Central-West of Brazil seem to be more affected by SAM. However, SAM influences are different for each month, and there are also differences of the influences between SAM phases (not always opposite). For air temperature, March, May, July, August, September, and November show positive (negative) anomalies affecting regions cited above during the negative (positive) SAM phase. Although, the coverage of these anomalies is different among these months. February and December present a temperature anomaly dipole, with positive (negative) anomaly at SESA and negative (positive) northward, in the negative (positive) SAM phase. January has a different behavior compared with other months but also presents a nearly opposite signal between SAM phases. Precipitation anomalies composites indicate a weakening (strengthening) of South Atlantic Convergence Zone configuration at negative (positive) SAM phase (November-January and March). SESA region shows positive (negative) precipitation anomalies at negative (positive) SAM phases, during March-June and December. Nevertheless, in October, SAM oppositely influences this region. A case study (January 2017 - negative SAM - neutral ENSO) shows great similarity with the precipitation composites, ratifying the results. However, for temperature, the coastal region is the only which presents similarity with the composites. The goal of this paper is to study month-to-month impacts of Southern Hemisphere Annular Mode (SAM) phases over South America (SA). Composite analyses were performed excluding ENSO years. Southeastern SA (SESA), part of Southeastern and Central-West of Brazil seem to be more affected by SAM. However, SAM influences are different for each month, and there are also differences of the influences between SAM phases (not always opposite). For air temperature, March, May, July, August, September, and November show positive (negative) anomalies affecting regions cited above during the negative (positive) SAM phase. Although, the coverage of these anomalies is different among these months. February and December present a temperature anomaly dipole, with positive (negative) anomaly at SESA and negative (positive) northward, in the negative (positive) SAM phase. January has a different behavior compared with other months but also presents a nearly opposite signal between SAM phases. Precipitation anomalies composites indicate a weakening (strengthening) of South Atlantic Convergence Zone configuration at negative (positive) SAM phase (November-January and March). SESA region shows positive (negative) precipitation anomalies at negative (positive) SAM phases, during March-June and December. Nevertheless, in October, SAM oppositely influences this region. A case study (January 2017 - negative SAM - neutral ENSO) shows great similarity with the precipitation composites, ratifying the results. However, for temperature, the coastal region is the only which presents similarity with the composites.