The South Atlantic Subtropical Anticyclone: Present and Future Climate

Michelle Simões Reboita,Raniele Fátima Pinheiro,Rosmeri Porfírio Da Rocha,Bruna Andrelina Silva,Tércio Ambrizzi

doi:10.3389/feart.2019.00008

Michelle Simões Reboita, Raniele Fátima Pinheiro + Show 3 more

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https://doi.org/10.3389/feart.2019.00008

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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.

Highlights

Mean sea level pressure (MSLP) charts show closed isobars, some with values that increase from the center to the periphery, characterizing cyclones, and others in which the pressure decreases from the center to the periphery, characterizing anticyclones
There is no unique mechanism that explains the genesis and maintenance of the subtropical anticyclones; here we summarize the findings of the literature: (a) subsidence of the polar branch of the Hadley cell (Namias, 1972; Rodwell and Hoskins, 2001; Dima and Wallace, 2003; Seager et al, 2003) located at about 30 degrees latitude in both hemispheres (Guo et al, 2016); (b) seaair interactions (Seager et al, 2003); and (c) subsidence over the ocean caused by monsoons over adjacent continents during the summer season (Rodwell and Hoskins, 1996, 2001; Chen et al, 2001; Liu et al, 2004), as well as by teleconnection effects from the Northern Hemisphere monsoon (Kosaka and Nakamura, 2010; Lee et al, 2013; Ji et al, 2014)
As there is little literature that addresses South Atlantic Subtropical Anticyclone (SASA), and even less in terms of climate projections of this system, this study aims to contribute with: (1) a review of the literature on the genesis and maintenance mechanisms of subtropical anticyclones focusing on the SASA as well as the main features of this anticyclone; and (2) an analysis of the SASA seasonal features in the present climate and in projections of three global climate models from the Coupled Model Intercomparison Project – Phase 5 (CMIP5) using the Representative Concentration Pathway 8.5 (RCP8.5) scenario from the Intergovernmental Panel on Climate Change (IPCC)

Summary

Introduction

Mean sea level pressure (MSLP) charts show closed isobars, some with values that increase from the center to the periphery, characterizing cyclones, and others in which the pressure decreases from the center to the periphery, characterizing anticyclones. There are two types of anticyclones: migratory (or transient) and semi-permanent The former, which occurs eventually, is associated with baroclinic waves and has a reduced lifetime (2–6 days; Sinclair, 1996; Ioannidou and Yau, 2008; Pepler et al, 2018). The latter persists for most of the year over subtropical latitudes and is usually called subtropical anticyclone or subtropical high (Chen et al, 2001; Ynoue et al, 2017). The center of these systems is a region of calm while their borders have more intense winds

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