Changes in ENSO-driven Hadley circulation variability under global warming

The Hadley circulation (HC) variability induced by ENSO (ENSO-driven HC) plays an important role in the changes of the tropical and even global climate. In the present study, we investigated the changes in ENSO-driven HC using the historical and RCP8.5 (SSP585 in CMIP6) runs from 34 models in CMIP5 and 24 models in CMIP6, and separated the roles of the changes in the ENSO SST and background SST using three atmospheric model experiments (amip, amip-p4K, and amip-future4K) in 8 CMIP5 and 7 CMIP6 models. The results showed that although the zonal-mean ENSO-driven HC strengthens slightly, the ENSO-driven HC is significantly intensified in a warmer climate from a regional perspective, especially over the eastern Pacific. The intensified ENSO-driven HC over the eastern Pacific dominates the zonal-mean changes after the counteraction of the changes in different longitudes. When the state-of-the-art CMIP5 and CMIP6 models project a robust El Nin similar to o-like warming pattern for the background SST changes in the eastern Pacific, the background SST changes enhance the changes in ENSO-driven HC over the eastern Pacific. In contrast, the changes of ENSO SST show large intermodel spread, resultantly playing a weak role in ENSO-driven HC in the multi-model ensemble, although an intensified ENSO SST can strengthen ENSO-driven HC over the eastern Pacific and vice versa. The contributions of the ENSO SST are stronger than that of the background SST, and dominate the zonal-mean changes in ENSO-driven HC.

Automated summary

The study investigates the changes in ENSO-driven Hadley circulation (HC) and the role of ENSO SST and background SST changes using multiple models. The results show that ENSO-driven HC intensifies in a warmer climate, especially over the eastern Pacific, and the changes in background SST enhance this intensification.