Reassessing the ENSO-related Hadley circulation contraction from a regional perspective

Abstract

El Niño event usually intensifies Hadley Circulation (HC), meanwhile reducing its meridional extension. From a global perspective, the width change of HC is associated with the meridional movement of baroclinic instability and eddy activities over the subtropics. However, these hypotheses may not work for regional HC. In this study, we construct the three-dimensional structure of HC and investigate the El Niño-related regional HC variability, focusing on the meridional extension. El Niño is associated with an expansion of HC over the central-eastern Pacific but a contraction over the west. Unlike the global HC, the strengthening (weakening) of regional HC usually coincides with an expansion (contraction). Nevertheless, the “narrow” equatorial intensification over the eastern Pacific and the “widespread” subtropical weakening over the Indo-Western Pacific of regional HC collectively form a strengthening and contraction of global HC. This spatial pattern of regional HC intensity changes is tightly associated with the ENSO-related precipitation and sea surface temperature (SST) gradient anomalies. Our result has broad implications for global climate predictability, highlighting the importance of a better understanding of the interactions between the regional HC and tropical/subtropical climate variabilities.