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The relations of the low-level extratropical cyclones in the southeastern Pacific and South Atlantic with the sea surface temperature (SST) anomalies associated with the Atlantic multidecadal oscillation (AMO) during the summer and winter of the 1979–93 cold AMO (CAMO) and 2003–17 warm AMO (WAMO) are analyzed. During both seasons and in both AMO phases, the cyclone trajectories defined by cyclone local counts exceeding 10 events per grid box occur approximately in the areas with the AMO-related positive SST anomalies. The cyclone densities in most latitudes during both seasons are higher in the CAMO than in the WAMO. Thus, the cyclone density in the study domain presents a reduction trend during the 1979–2017 period. The large-scale northward SST anomalous gradients between the bands north and south of 40°S increase the long-wave baroclinicity in the midlatitudes in the WAMO, and the southward SST anomalous gradients decrease it in the CAMO. Consequently, the short-wave baroclinicity is higher in the WAMO than in the CAMO in the southeastern Pacific midlatitudes. Thus, the cyclones are more energetic in the WAMO than in the CAMO. In the South Atlantic region off the Argentinean coast, both the barotropic and baroclinic conversion terms are positive, indicating an increase of the kinetic energy of the short waves. The low-level cyclones in the southeastern Pacific and South Atlantic are modulated by the AMO. As far as we know, the relation of the SH low-level extratropical cyclones to the AMO documented here was not studied before.

Convective cells are cloud formations whose growth, maturation and dissipation are of great interest among meteorologists since they are associated with severe storms with large precipitation structures. Some works suggest a strong correlation between lightning occurrence and convective cells. The current work proposes a new approach to analyze the correlation between precipitation and lightning, and to identify electrically active cells. Such cells may be employed for tracking convective events in the absence of weather radar coverage. This approach employs a new spatio-temporal clustering technique based on a temporal sliding-window and a standard kernel density estimation to process lightning data. Clustering allows the identification of the cells from lightning data and density estimation bounds the contours of the cells. The proposed approach was evaluated for two convective events in Southeast Brazil. Image segmentation of radar data was performed to identify convective precipitation structures using the Steiner criteria. These structures were then compared and correlated to the electrically active cells in particular instants of time for both events. It was observed that most precipitation structures have associated cells, by comparing the ground tracks of their centroids. In addition, for one particular cell of each event, its temporal evolution was compared to that of the associated precipitation structure. Results show that the proposed approach may improve the use of lightning data for tracking convective events in countries that lack weather radar coverage.

An analysis of 58 cyclogenesis cases occurred from 2003 to 2011 over the southern Brazilian coast is presented focusing on the energy cycle proposed. For this analysis the National Centers for Environmental Prediction (NCEP) data was utilized to create the composite fields of all selected days as also to that of transitional seasons (austral spring and autumn), when it was verified a high number of cyclones. In the analysis, a deepening of a pre-existing surface trough over Paraguay was observed two days (D-2) before the surface pressure had reached its minimum over the southern Brazilian coast. Typically, the cyclogenetic process begins on the southern Brazil coast and spreads in a NW-SE direction, strengthening along its path. On D-2 the jet stream is almost zonally oriented and then when the cyclone is completely formed (D0), this acquire a cyclonic curvature, with two cores: one strongest in the SE and the other one in the NW direction. As soon as the geopotential anomaly for short waves (Gh) is in phase with anomaly for long waves (Gl) on D-1, the PhKh term increases in magnitude, becoming the dominant one. During all evolution stages, the dominant terms were the baroclinic (PlPh and PhKh), followed by the barotropic (KlKh) term. The friction term (RKh) had a secondary role and the source/sink of non conservative energy and flux of the available potential energy (RPh) did not contributed to the deepening of the surface low, which is not depending of the convective activity inside it. Significant differences were not observed in the mechanisms of cyclogenesis development and maintenance during the transition months, except for a greater availability of kinetic (Kh) and potential (Ph) energy and baroclinic and barotropic conversion terms during the austral autumn. Neste estudo é feita uma análise de 58 casos de ciclogênese ocorridos entre 2003-2011 sobre a costa do sul do Brasil, focando o ciclo de energia. Nesta análise foram utilizados dados do National Centers for Environmental Prediction (NCEP) para criar os campos compostos dos dias selecionados e das estações de transição (primavera e outono austral), quando foi verificado um elevado número de ciclones. Observou-se um aprofundamento de um cavado pré-existente em superfície sobre o Paraguai, dois dias antes (D-2) da pressão na superfície atingir o seu mínimo sobre a costa da região sul do Brasil. Tipicamente, o processo de ciclogênese começa sobre esta região e se propaga para sudeste, intensificando ao longo de sua trajetória. Em D-2 a corrente de jato está quase zonalmente orientada, mas adquire uma curvatura ciclônica, com um núcleo no setor SE e o outro à NW quando o ciclone está completamente formado (D0). Quando a anomalia de geopotencial para ondas curtas (Gh) entra em fase com a anomalia para ondas longas (Gl), em D-1, ocorre o aumento de PhKh, que se torna dominante. Durante todas as fases de evolução, os termos mais importantes foram o baroclínico (PlPh e PhKh), seguido pelo barotrópico (KlKh). O termo de atrito (RKh) teve um papel secundário, e o termo de fonte/sumidouro de energia e fluxo de energia potencial disponível (RPh) não contribuiu para o aprofundamento de baixa superfície, mostrando que este último não depende da atividade convectiva local. Durante os meses de transição, não foram observadas diferenças significativas nos mecanismos de desenvolvimento ciclogenético e manutenção, exceto por haver uma maior disponibilidade de energia cinética (Kh) e potencial (Ph), e também por haver uma maior troca de energia por conversão baroclínica e barotrópica durante o outono austral.

Microphysical and thermodynamical features of two tropical systems, namely Hurricane Ivan and Typhoon Conson, and one sub-tropical, Catarina, have been analyzed based on space-born radar PR measurements available on the TRMM satellite. The procedure to classify the reflectivity profiles followed the Heymsfield et al (2000) and Steiner et al (1995) methodologies. The water and ice content have been calculated using a relationship obtained with data of the surface SPOL radar and PR in Rondonia State in Brazil. The diabatic heating rate due to latent heat release has been estimated using the methodology developed by Tao et al (1990). A more detailed analysis has been performed for Hurricane Catarina, the first of its kind in South Atlantic. High water content mean value has been found in Conson and Ivan at low levels and close to their centers. Results indicate that hurricane Catarina was shallower than the other two systems, with less water and the water was concentrated closer to its center. The mean ice content in Catarina was about 0.05 g kg-1 while in Conson it was 0.06 g kg-1 and in Ivan 0.08 g kg-1. Conson and Ivan had water content up to 0.3 g kg-1 above the 0ºC layer, while Catarina had less than 0.15 g kg-1. The latent heat released by Catarina showed to be very similar to the other two systems, except in the regions closer to the center. No presente trabalho foram analisados as características microfísicas e termodinâmicas de dois sistemas tropicais, o Furacão Ivan e o Tufão Conson, e um sub-tropical, Catarina, a partir de medições feitas com o radar PR a bordo do satélite TRMM. Na análise, os perfis de refletividade foram classificados conforme as técnicas de Heymsfield et al (2000) e Steiner et al (1995) e em seguida foram calculados os conteúdos de água e gelo, a partir de uma relação obtida no Estado de Rondônia (Brasil). Com estes perfis calculou-se a taxa de aquecimento diabático devido a liberação de calor latente conforme Tao et al (1990). Após serem comparados os três furacões, fez-se uma análise mais detalhada do Catarina, que foi o primeiro furacão oficialmente registrado no Atlântico Sul. Os resultados mostraram que o Ivan e o Conson tiveram um alto teor médio de água, especialmente nos níveis mais baixos e perto de seus centros. Os resultados indicaram que o furacão Catarina foi mais raso, tinha menor teor de água líquida e mais concentrada próximo do centro. O teor médio de gelo no Catarina foi cerca de 0,05 g kg-1, enquanto no Conson foi de 0,06 g kg-1 e no Ivan 0,08 g kg-1. O Conson e o Ivan tiveram teor de água de até 0,3 g kg-1 acima da isolinha de 0ºC, enquanto que o Catarina teve menos de 0,15 g kg-1. A taxa de aquecimento, devido à liberação de calor latente, no Catarina, mostrou ter magnitudes similares aos outros dois sistemas, com maiores diferenças nas regiões próximas do núcleo.