Synoptic Climatology of Subtropical Cyclone Impacts on Near‐Surface Winds Over the South Atlantic Basin

Abstract

AbstractWinds and precipitation are two meteorological variables of great impact on the economy and society, especially when extreme events occur. The objective of this study is to investigate the subtropical cyclone (SC) impacts on near‐surface wind extremes (defined by 95th percentile) and precipitation in the South Atlantic basin. For the period 1979–2015, the analysis used two reanalysis data (ERA5 and Climate Forecast System Reanalysis [CFSR]) and estimated precipitation from the Tropical Rainfall Measuring Mission (TRMM) considering the extended warm (from September to February) and cold (from March to August) seasons. A total of 169 SCs occurred in the warm season against 87 in the cold one. Two approaches are used to quantify SC impacts: Lagrangian, where the composites follow the cyclone center, and Eulerian, which considers the averaged environment during the cyclone lifecycle. In general, both approaches indicate SC contribution to the positive anomalies of mean and extreme near‐surface wind speeds to the east and northeast of a cyclogenetic region in southeastern Brazil (RG1). For all analyses conducted, wind speeds from CFSR are higher than in ERA5. The SC activity contributes to the enhancement of precipitation to the east and inside RG1 in an organized northwest‐southeast positive anomaly band from the continent to the ocean, while favoring drier conditions to the south. These positive precipitation anomalies are associated with an anomalous low pressure, low‐level moisture flux convergence and warm advection occurring at the same time with an upper‐level divergent flow near RG1. All these features are intensified in the cold season.