Abstract
Interannual sea surface temperature (SST) variations in the tropical Atlantic Ocean lead to anomalous atmospheric circulation and precipitation patterns with important ecological and socioeconomic consequences for the semiarid regions of sub-Saharan Africa and northeast Brazil. This interannual SST variability is characterized by three modes: an Atlantic meridional mode featuring an anomalous cross-equatorial SST gradient that peaks in boreal spring; an Atlantic zonal mode (Atlantic Niño mode) with SST anomalies in the eastern equatorial Atlantic cold tongue region that peaks in boreal summer; and a second zonal mode of variability with eastern equatorial SST anomalies peaking in boreal winter. Here we investigate the extent to which there is any seasonality in the relationship between equatorial warm water recharge and the development of eastern equatorial Atlantic SST anomalies. Seasonally stratified cross-correlation analysis between eastern equatorial Atlantic SST anomalies and equatorial heat content anomalies (evaluated using warm water volume and sea surface height) indicate that while equatorial heat content changes do occasionally play a role in the development of boreal summer Atlantic zonal mode events, they contribute more consistently to Atlantic Niño II, boreal winter events. Event and composite analysis of ocean adjustment with a shallow water model suggest that the warm water volume anomalies originate mainly from the off-equatorial northwestern Atlantic, in agreement with previous studies linking them to anomalous wind stress curl associated with the Atlantic meridional mode.
Highlights
Sea surface temperature (SST) variations in the tropical Atlantic Ocean influence local atmospheric circulation patterns and precipitation in neighboring African and South American countries (Xie and Carton 2004)
Hu et al (2013) show that the warm water volume (WWV) and tilt modes are to some extent connected, with WWV changes leading tilt changes. Their findings are consistent with other studies linking changes in tropical Atlantic oceanic and atmospheric conditions associated with the AMM to the development of the zonal mode in the equatorial Atlantic (Servain et al 1999; Murtugudde et al 2001; Foltz and McPhaden 2010; Zhu et al 2012a, b; Burmeister et al 2016; Martín-Rey and Lazar 2019)
heat content (HC) is defined as the volume average of temperature from the surface to 400 m depth
Summary
Sea surface temperature (SST) variations in the tropical Atlantic Ocean influence local atmospheric circulation patterns and precipitation in neighboring African and South American countries (Xie and Carton 2004). Their findings are consistent with other studies linking changes in tropical Atlantic oceanic and atmospheric conditions associated with the AMM to the development of the zonal mode in the equatorial Atlantic (Servain et al 1999; Murtugudde et al 2001; Foltz and McPhaden 2010; Zhu et al 2012a, b; Burmeister et al 2016; Martín-Rey and Lazar 2019) While these previous studies have shown an influence of equatorial recharge on the development of EEA SST anomalies in boreal summer, the seasonality in the strength of this relationship has not been fully investigated.
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