Asymmetric Impacts of El Niño Development and Decay Stages on the Hadley Circulation

Abstract

The impact of El Niño on the Hadley Circulation (HC) has been a topic of previous studies, but the results have been inconclusive. We study how El Niño affects the HC during different stages of its cycle. In development years, the HC anomaly shows an equatorial quasi-symmetric pattern, while in decay years, it shows an asymmetric pattern. This resolves previous discrepancies among studies about El Niño's impacts on the HC. The differences in tropical sea surface temperature (SST) during different stages of El Niño cause differences in SST meridional gradients, which determine the location of convergence. This explains why the HC anomalies have different spatial structures during El Niño development and decay years. Our results show that the meridional distribution of SST during different El Niño stages has significantly distinct impacts on meridional circulation and clarify the differences in El Niño's effects on climate.