Common and Distinct Drivers of Convective Mass Flux and Walker Circulation Changes

Abstract

The weakening of convective mass flux and the Walker circulation is one of the most robust responses to global warming. However, recent decades have seen the Pacific Walker circulation strengthen despite a weakening convective mass flux. Here, we conduct a series of prescribed sea surface temperature (SST) experiments to separate the effects of global warming from changes in SST patterns. The tropical-mean convective mass flux weakens in proportion to the global warming amplitude, largely unaffected by SST pattern changes. Conversely, the Walker circulation response is sensitive to SST pattern changes, weakening with global warming if zonal SST contrast decreases or increases below a certain threshold and strengthening if the increase in SST contrast exceeds that threshold. Thus, the Walker circulation might continue to strengthen if the SST pattern effects dominate. Our results indicate that the weakening of convective mass flux alone is insufficient for projecting the Walker circulation response.