The South Atlantic Subtropical Anticyclone: Present and Future Climate

Abstract

The South Atlantic Subtropical Anticyclone (SASA) is the main feature of the atmospheric circulation over the South Atlantic Ocean, and its study is of great importance to explain many characteristics of the Brazilian weather and climate. Therefore, this study aims to present (1) a review of the literature on SASA including the drivers of the semi-permanent anticyclones and (2) the main features of the SASA in the future climate obtained through the projections of three global climate models (HadGEM2-ES, GFDL-ESM2M, and MPI-ESM-MR), from the Coupled Model Intercomparison Project (CMIP5), using the Representative Concentration Pathway 8.5 (RCP8.5) scenario. SASA is zonally wider in winter and retracted to the east in summer, when it presents a more circular format. These features of the SASA in the present climate (1979-2005) are well represented by the three global climate models, which also project this same SASA seasonal pattern for the future climate (2065-2095). Considering the projections, they indicate a slightly poleward expansion of the SASA, which is associated with the widening of the Hadley cell. At the SASA core, the pressure can be similar or slightly more intense than the present climate.

What is the return period of intense rainfall events in the capital cities of the northeast region of Brazil?

“…At the beginning of the year, the NASA is stronger than the SASA, which results in warmer sea surface temperatures (SST) south of the equator. This configuration leads to the convergence of northeastern and southeastern tradewinds, transporting moisture originated from high evaporation rates over the Atlantic to the NEB (Seager et al ., ; Reboita et al ., ). On the other hand, in the second half of the year, the opposite process is observed.…”

Relação entre o Vapor D’Água Atmosférico e a Temperatura da Superfície do Mar Sobre a Região da Confluência Brasil-Malvinas, com Base em Dados Coletados In Situ (Relationship between Atmospheric Water Vapor Content and the Sea Surface Temperature in the Brazil-Malvinas Confluence considering Data Collected In Situ)

“…No mês de outubro, mês de realização de maior parte dos cruzeiros analisados neste estudo, a ASAS normalmente se encontra em torno de 2°W. Degola (2013) e Reboita et al, (2019) demonstraram que a ASAS apresenta um deslocamento zonal, e durante o período de inverno-primavera austral a ASAS adentra o continente sul-americano, tendo maior influência no clima das regiões Sudeste e Nordeste do Brasil e, consequentemente, influencia também a região da CBM, como demonstrado nos resultados do presente estudo.…”

A potential vorticity perspective on cyclones over South America

“…To this aim, SLP fields and winds and specific humidity at 850 hPa are shown in Figures 5.2c-f. Over the year, the main circulation systems are the two subtropical anticyclones, one over the South Pacific and another over the South Atlantic. The anticyclone over the South Atlantic reaches the eastern part of SA, where it prevents convection in winter (Figures 5.2d,f)(Reboita et al, , 2019. In summer, however, the subtropical anticyclone is located far from the coast(Figures 5.2c,e), contributing to organize the moisture transport from the South Atlantic to subtropical latitudes over the continent, hence, favoring precipitation(Sun et al, 2017;Reboita et al, 2019).…”

“…The anticyclone over the South Atlantic reaches the eastern part of SA, where it prevents convection in winter (Figures 5.2d,f)(Reboita et al, , 2019. In summer, however, the subtropical anticyclone is located far from the coast(Figures 5.2c,e), contributing to organize the moisture transport from the South Atlantic to subtropical latitudes over the continent, hence, favoring precipitation(Sun et al, 2017;Reboita et al, 2019). During summer (Figure 5.2c), a semi-permanent thermal low-pressure system occurs in the lee of the Andes (around 20°S), coinciding with the location of the aforementioned cyclogenetic region lee of the Andes.…”