How will the South Atlantic Subtropical High Respond to Climate Change? - Evaluating CMIP5 Model Predictions

High-pressure systems over the subtropical oceans have a significant influence on local climate. The South Atlantic Subtropical High (SASH), upon which this study is focused, influences South Atlantic wind stress and sea surface temperatures, as well as precipitation over southern Africa and southeastern South America. Several studies have investigated how circulation over the land and ocean that is closely related to summer subtropical highs will change in climate model projections (e.g. Li et al. 2013; He et al. 2017). However, the other seasons remain largely uninvestigated, as well as the extent to which results hold across various methods of characterizing subtropical highs. This study aims to address these gaps focusing on projected changes in the intensity and area of the SASH under global warming across all seasons. Using the Coupled Model Intercomparison Project Phase 5 (CMIP5) archive and reanalysis data (ERA-interim), our analysis shows that the area and strength of the SASH increases during all seasons in both RCP 8.5 and abrupt 4xCO₂ simulations. Analyzing sea level pressure (SLP), wind divergence at 925 hPa, and vertical velocity at 925 hPa, we find decreased SLP and weakened anticyclonic circulation near the equatorial flank of the SASH. However, coherent agreement exists across all variables that the center and poleward flank of SASH intensifies with its area increasing and extending poleward. This indicates a poleward shift in the SASH circulation, consistent with a poleward shift of the Hadley cell edge. In this study, we also analyze the extent to which the CMIP5 models capture 20th century SASH area and intensity trends.