Resumo A rede de estações meteorológicas no Brasil é muito recente, com poucas estações no país com mais de 100 anos de dados. Além disso, muitas das séries oriundas destas estações apresentam falhas, seja por falta de medição (no caso das estações convencionais), seja por falha nos equipamentos (no caso das estações automáticas). Encontram-se diferentes métodos na literatura para o preenchimento destas falhas. Neste trabalho são comparados seis métodos, os quais foram aplicados a séries de dados mensais conhecidas de temperatura média compensada e precipitação para estações meteorológicas localizadas no estado do Rio Grande do Sul, região sul do Brasil. Os resultados para temperatura média compensada indicaram os métodos de regressão linear múltipla e ponderação regional como os mais adequados para estimativas de dados faltantes enquanto que para precipitação não houve um método a se sobressair.

Dry conditions occurred over São Paulo state (southeastern Brazil) from February to July 2018, causing the driest semester in 35 years. Socioeconomic impacts included a record number of fire spots, most adverse conditions to pollutant dispersion in 3 years and the winter's lowest water reservoirs stored volume in 17 years. This paper discusses climate drivers to the onset and persistence of the dry conditions, with special attention to the intraseasonal forcing. Barotropic atmospheric circulations forced by the intraseasonal Pacific-South America teleconnection pattern, embedded in the lower frequency setup of the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation, were identified as main large-scale forcings to reduce precipitation. Drought evolution was modulated by other intraseasonal drivers such as the Madden Julian, Antarctic and 10–30 days Oscillations. A break in the 6-month dry condition, in March 2018, highlighted the important role of such oscillations in determining precipitation anomalies over SP. Results show that intraseasonal phenomena and their interactions control drought characteristics such as magnitude, persistence and spatial distribution within a setup determined by lower-frequency oscillations. The intraseasonal timescale seems to be key and must be considered for a complete description and understanding of the complex drought evolution process in São Paulo.

Changes in physical features of the South Atlantic Ocean (SAO) have been observed over the last few decades as a result of anthropogenic climate change. As an example, the increase in Agulhas Leakage, the continental melting of Greenland and changes in wind-forced ocean circulation are factors associated with changes in the Atlantic Meridional Overturning Circulation (AMOC). Within this context, important means of ocean-atmosphere interaction on a climate scale, such as the main mode of coupled variability of the SAO, known as the South Atlantic Dipole (SAD), may also be subject to variations. This work aimed to investigate changes in the SAD over different phases of the Interdecadal Pacific Oscillation (IPO) since the 1950s and assess their impacts on the climate of South America during the austral summer. The main finding is a southward shift of the entire SAD pattern over the analyzed period, consistent with other observed oceanic and atmospheric changes attributed to global warming. Associated with that, a change from a tripole to a dipole pattern of precipitation anomalies was observed over the South American continent during summer. Besides, the SAD displayed an alternate relationship with IPO phases, with a positive (negative) correlation with Pacific Niño SST anomalies during the IPO negative (positive) phase.

Dry events occurring in the Southeast Region of Brazil (SEB) during the summer (rainfall season) have been in evidence in the last years, mainly due to previous extreme events in the 2013/14 and 2014/15 seasons. Drought analyses are usually carried out with monthly data. Here our methodology addresses the issue with daily data in order to generate a thorough analysis. Dry events were evaluated for different homogeneous precipitation sub-regions within the SEB, over 37 December-February (DJF) seasons and with two different timescales of duration: synoptic (5-9 days) and intraseasonal (≥10 days). Two main distinct dynamic patterns were found for dry events in southern and central-northern parts of SEB, respectively, but no major differences were identified for the different timescales of occurrence. Southern events were characterized by a stationary ridge acting over the whole southern South America, making the transient systems approximation to southern SEB difficult. At the same time, this pattern showed a northern-shifted South Atlantic Convergence Zone (SACZ) configuration. In the central-northern events, a high pressure centered between the South and Southeast regions of Brazil was associated with the dryness conditions. An anomalous southward shift of meteorological systems characteristic of the South American summer was also verified for these events. Over the South Atlantic, an opposite SST anomaly configuration was identified between southern and central-northern events.

those obtained previously by other authors, indicating a higher activity of frontal systems during the winter and early spring. From these findings, the same methodology can be used with series of future climate generated by the model. 1.INTRODUÇÃO As frentes são sistemas que atuam em escala sinótica, especialmente em latitudes médias, e são os principais agentes modificadores nas condições do tempo. Eles ocorrem ao longo de todo o ano, com maior intensidade no inverno, acompanhados de massas de ar polar que, muitas vezes, causam geadas sobre o Sul e Sudeste do Brasil. Algumas vezes, elas atingem latitudes mais baixas, chegando até a região Nordeste e sul da Amazônia causando o fenômeno conhecido como friagem (Cavalcanti, 2009). Petterssen (1956) propôs um método objetivo para determinar locais preferenciais para formação (dissipação) de sistemas frontais utilizando agentes indicadores como gradiente de temperatura, orientação do eixo de dilatação, deformação total e divergência. Além disso, o principal agente causador da intensificação do gradiente horizontal de temperatura está associado à deformação no escoamento de baixos níveis.Portanto, o objetivo principal desta pesquisa está concentrado em determinar uma climatologia da passagem de sistemas frontais sobre a América do Sul para uma série histórica e baseada nestes resultados, analisar as possíveis alterações neste regime sob um cenário de clima futuro.