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1. Introduction
Located over the South Atlantic basin, the South Atlantic subtropical high (SASH) plays a significant role in the regional climate. For instance, this high pressure system is closely related to the South Atlantic subtropical dipole (SASD) mode, characterized by sea surface temperature (SST) anomalies oriented from the southwest to the northeast (Venegas et al. 1997; Sterl and Hazeleger 2003; Haarsma et al. 2005; Morioka et al. 2011). Recent studies (e.g., Richter et al. 2010; Lübbecke et al. 2010, 2014) also suggest that the strength of this anticyclone is influential in the development of the cold tongue in the eastern equatorial Atlantic, including its onset and peak amplitude during the boreal summer. Although the Indian Ocean functions as the primary moisture source for southern Africa, rainfall variability over southern Africa is found to be associated with the intensity and position of the SASH (Hermes and Reason 2009; Vigaud et al. 2009). On the western side of the South Atlantic basin, this anticyclone also affects precipitation over southeastern South America through its impact on SSTs and the South Atlantic convergence zone (Bombardi and Carvalho 2011; Bombardi et al. 2014). Understanding variations in this high pressure system is essential for understanding regional climate variations. In the past several decades, some progress has been made on the formation of subtropical highs, but investigations of the SASH are limited, and to our knowledge there have been no previous studies dedicated to directly addressing its interannual variability.
The purpose of this study is to improve our understanding of the annual cycle and interannual variability of the SASH, and how its variability is connected to the regional and large-scale circulation and coupled with the ocean. Background about subtropical anticyclones and the SASH is summarized in section 2. Section 3 provides a description of the datasets analyzed and methodologies applied. Results regarding the annual cycle and interannual variability of the SASH are reported in section 4, while the role of large-scale circulations and the underlying ocean are discussed in section 5. Conclusions are drawn in section 6.
2. Background
The historical view on the formation of subtropical anticyclones relies on the descending arm of the Hadley cell. This notion, however, is contradictory to the observation that Northern Hemisphere subtropical anticyclones are...