Abstract This paper documents an increase in the number of observed explosive cyclones (EC) at King George Island, South Shetland Islands, Antarctica, over the 1989‒2020 period. In ECs at 60o latitudes the surface atmospheric pressure drops ≥24 hPA in 24 hours. The annual EC frequency time series shows a significant positive trend of ~2.7 cyclones/decade, with a break in 2003 and average numbers of 7.3 and 11.8 events before and after that break, respectively. The increase follows closely earlier documented global sea surface temperature (SST) anomaly trends for the 1981‒2018 period, partially attributed to global warming and to the Pacific Decadal Oscillation (PDO). Connections between EC frequency and SST might occur through variations in SST in the southeastern Pacific and southwestern Atlantic, with anomalous cold conditions favoring an increase in ECs. We also found close relations between the number of ECs with simultaneous occurrences of PDO and Atlantic multidecadal oscillation in opposite phases, so that after 2003 they were in the cold and warm phases, respectively, and vice-versa before 2003. Both low-frequency modes seem to modulate the number of ECs. As per the authors knowledge these results have not been discussed before and may help climate modeling studies and weather forecasts.

Abstract The Colombian Biogeographic Choco (CBC) and the La Plata Basin (LPB) are regions with high biodiversity. However, these areas are characterized by scarce climatological information, complex orography, and rain-gauge network unevenly distributed. Interpolated data from the ground station might overcome these aspects. For this reason, is necessary to identify the best technique for the spatial interpolation of rainfall. Hence, the spatial interpolation techniques were applied to annual and seasonal rainfall in the CBC and LPB. Geostatistical results and deterministic approaches were compared by cross-validation. Cokriging with spherical (gaussian) model is the best interpolator in the CBC (LPB), as indicated by the lowest root mean square error (RMSE) and a standardized RMSE close to one. The CBC shows three rainfall cores: the northern, 9,000 mm/year; the central-southern, 10,000 mm/year; and the southern, 7,000 mm/year. The LPB shows a west-east rainfall gradient, with a minimum to the west (450 mm/year) and a maximum in the mid-west (2,000 mm/year). To the north of the LPB, rainfall reaches 1,500 mm/year, while in the south it reaches only 900 mm/year. The results in our study may be useful for scientists and decision-makers for use in environmental and hydrological models for the CBC and the LPB.

Uma técnica de pós-processamento é aplicada para corrigir estatisticamente, as previsões de precipitação geradas pelos modelos climáticos numéricos disponíveis no CPTEC. O método chamado de Esquema Estatístico de Combinação e Correção de Previsões Climáticas (ECCOCLIM) é determinístico e baseia-se no método de Regressão Linear Múltipla (RLM). A verificação do desempenho é feita com a técnica de validação cruzada. Apesar dos ganhos observados nas previsões com o novo método serem localizados e variados ao longo dos anos, estes são destacados em áreas da América do Sul, as quais usualmente apresentam baixa previsibilidade climática, como no caso das regiões Sudeste e Centro-Oeste. Em geral, sobre a América do Sul o ECCOCLIM mostra resultados melhores, reduzindo os erros, comparados à tradicional média aritmética das previsões de diferentes modelos.

A post-processing technique is applied to statistically correct the rainfall forecasts done by numerical climate models available at CPTEC. The statistical algorithm, called Climate Forecast Combining and Correcting Statistical Scheme (ECCOCLIM), is deterministic and based on the Linear Multiple Regression (LMR) method. The skill of the ECCOCLIM is verified with the cross-validation method. Although the forecast improvements using the new method are localized in certain regions and vary throughout the year, they are remarkable over South America, mainly in those areas where climatic previsibility is commonly low as the case of Southeast and Central-West regions. ECCOCLIM shows encouraging results over South America reducing the errors when compared to the traditional arithmetic mean of forecasts of different models.

A influência dos modos dc variabilidade climática dc grande escala dominantes no Pacifico e Atlântico nas chuvas da Amazônia é investigada. A técnica de compósitos das anomalias dc precipitação na Amazônia é usada neste trabalho. Os anos base destes compósitos são aqueles do período 1960-1998 com ocorrências de extremos na Oscilação Sul (El Niño ou La Niña) e de padrão de dipolo norte/sul quente (ou frio) nas anomalias de TSM no Atlântico tropical. Dipolo quente (frio) significa anomalias positivas (negativas) no Atlântico tropical Norte e negativas (positivas) no Atlântico tropical Sul. Compósitos dc verão e outono austrais para extremos na Oscilação Sul (El Niño ou La Niña) e independente para padrão de dipolo norte/sul (quente ou frio) de anomalias de TSM no Atlântico tropical, apresentam valores (magnitude e signal) consistentes com aqueles encontrados cm trabalhos anteriores sobre a relação entre as variações de precipitação na Amazônia c anomalias de TSM no Pacífico e Atlântico tropicais. No entanto, compósitos dos verões e outonos austrais para os anos com ocorrências simultâneas de El Niño e dipolo quente norte/sul dc anomalias de TSM no Atlântico tropical mostram anomalias negativas de precipitação estendendo-se para leste sobre a Amazônia ccntro-leste. Este resultado indica o importante papel desempenhado pelo Atlântico tropical na distribuição anômala de precipitação na Amazônia.

The influence of the large-scale climatic variability dominant modes in the Pacific and in the Atlantic on Amazonian rainfall is investigated. The composite technique of the Amazon precipitation anomalies is used in this work. The basis years for these composites arc those in the period 1960-1998 with occurrences of extremes in the Southern Oscillation (El Niño or La Niña) and the north/south warm (or cold) sea surface temperature (SST) anomalies dipole pattern in the tropical Atlantic. Warm (cold) dipole means positive (negative) anomalies in the tropical North Atlantic and negative (positive) anomalies in the tropical South Atlantic. Austral summer and autumn composites for extremes in the Southern Oscillation (El Niño or La Niña) and independently for north/south dipole pattern (warm or cold) of the SST anomalies in the tropical Atlantic present values (magnitude and sign) consistent with those found in previous works on the relationship between Amazon rainfall variations and the SST anomalies in the tropical Pacific and Atlantic. However, austral summer and autumn composites for the years with simultaneous occurrences of El Niño and warm north/south dipole of the SST anomalies in the tropical Atlantic show negative precipitation anomalies extending eastward over the center-eastern Amazon. This result indicates the important role played by the tropical Atlantic in the Amazon anomalous rainfall distribution.