found to be part of a large-scale teleconnection wave train linked with the subsidence branch of the Walker circulation in the tropical east Pacific, which in turn was generated by an anomalous tropical heat source in north/northeastern Australia. A regional Hadley circulation with an ascending branch to the south of the subsidence branch of the Walker circulation in the tropical east Pacific was identified as an important component connecting the tropical and extratropical circulation. The ascending branch of this Hadley circulation in the south Pacific coincided with an identified Rossby wave source region, which contributed to establishing the extratropical component of the large-scale wave train connecting the south Pacific and the Atlantic region surrounding southeast Brazil. This connection between the Pacific and the Atlantic was confirmed with Rossby ray tracing analyses. The local circulation response was associated to downward air motion (subsidence) over Southeast Brazil, contributing to the expressive negative precipitation anomalies observed during summer 2014, and leading to a major drought event in the historical context. The analysis of atmospheric and oceanic patterns of this event helped defining a schematic framework leading to the observed drought conditions in southeast Brazil, including the involved teleconnections, blocking high pressure, radiative and humidity transport effects.

Southeastern Brazil is the most populated and economically developed region of this country. Its climate consists of two distinct seasons: the dry season, extending from April to September, the precipitation is significantly reduced in comparison to that of the wet season, which extends from October to March. However, during nine days of the 2016 dry season, successive convective systems were associated with atypical precipitation events, tornadoes and at least one microburst over the southern part of this region. These events led to flooding, damages to buildings, shortages of electricity and water in several places, many injuries, and two documented deaths. The present study investigates the synoptic and dynamical features related to these anomalous events. The convective systems were embedded in an unstable environment with intense low-level jet flow and strong wind shear and were supported by a sequence of extratropical cyclones occurring over the Southwest Atlantic Ocean. These features were intensified by the Madden–Julian oscillation (MJO) in its phase 8 and by intense negative values of the Pacific South America (PSA) 2 mode.

The variability of Antarctic sea ice (ASI) has great potential to affect atmospheric circulation, with impacts that can extend from the surface to the middle and high levels of troposphere. The present study has evaluated the response of South Atlantic tropospheric circulation to increased coverage in area and volume of ASI. Monthly data of air temperature, zonal and meridional wind and mean sea level pressure were obtained from two ensemble simulations performed with the GDFL/CM2.1 model, covering the period from July 2020 to June 2030. In general, the response of South Atlantic tropospheric circulation to increased ASI showed that the climatic signal extended up from the surface to the high levels, propagating as a South Pole-Tropics teleconnection. The results show a general cooling of the southern troposphere, which for instance lead to the strengthening and northward shift of the polar jet and the southward shift of the subtropical jet and to an inversion f rom the positive to negative phase of the Southern Annular Mode. This study has great relevance for understanding the global climate changes in short term, by assessing the sensitivity of South Atlantic tropospheric circulation to extreme variations in ASI.

ResumoComo a borda do gelo marinho antártico está localizada em uma região muito sensível, sob a Frente Polar Antártica, existe um grande potencial da variabilidade do gelo marinho afetar a circulação atmosférica. Assim, o objetivo deste estudo foi investigar as possíveis relações entre os eventos extremos de gelo marinho antártico e as células de circulação meridional no Pacífico Sudeste, região onde há intensa variabilidade em várias escalas de tempo. Os resultados mostram que quando há eventos extremos de expansão de gelo marinho no setor do mar de Ross, existe um resfriamento da TSM, que resulta em uma atmosfera adjacente fria, aumentando os gradientes térmicos entre a borda do gelo marinho e a região de mar aberto. Os gradientes de pressão são fortalecidos, fortalecendo o cinturão circumpolar de baixas pressões e o jato polar. Assim, existe um fortalecimento do ramo ascendente da célula de Ferrel sobre o Oceano Austral, enquanto há enfraquecimento nas latitudes médias, por conservação de massa. Observamos o padrão oposto em eventos extremos de retração de gelo marinho no setor do mar de Ross e expansão no setor do mar de Weddell. Palavras-chave: células de circulação meridional, gelo marinho, variabilidade interanual. Cells of Meridional Circulation During the Extreme Events of Antarctic Sea Ice AbstractBecause the Antarctic sea ice edge is located in a region quite sensible, under the Antarctic Polar Front, there is a great potential of sea ice variability to affect the atmospheric circulation. The objective of this study was to investigate possible relationships between the extreme events of Antarctic sea ice and the cells of meridional circulation over the Southeastern Pacific, where there is intense climate variability on various time scales. The results show that when there are extreme events of sea ice expansion in the Ross Sea sector there is cooling of the SST, which results in the surrounding atmosphere cools, increasing the thermal gradient between the edge of sea ice and the open water region. The southern pressure gradients are strengthened, which strengthens the circumpolar low pressure belt and the polar jet. So there is a strengthening of the ascending branch of the Ferrel cell over the Southern Ocean while there is a weakening in midlatitudes via conservation of mass. We observe the opposite pattern in extreme events of sea ice decrease in the Ross Sea sector and expansion in the Weddell Sea sector.