Linking future tropical precipitation changes to zonally-asymmetric large-scale meridional circulation

Abstract

Tropical precipitation is projected to substantially change by the end of this century, including increased net precipitation over the Pacific Ocean and drying over the Indian Ocean. The underlying mechanisms responsible for these changes are still debated. Previous studies argued for the importance of the zonal circulation in the longitudinally-dependent tropical precipitation response, as the meridional circulation is often analyzed as the zonal mean. Here we show that the projected changes in the meridional circulation are highly longitudinally dependent, and explain the zonally dependent changes in net precipitation. Our analysis exposes a zonal shift in the meridional circulation's ascending branch, associated with a strengthened net precipitation over the central Pacific and weakened precipitation in the Indo-Pacific. Zonal circulation has minor influence on these projected tropical precipitation changes. These results point to the importance of monitoring the longitudinal changes in the meridional circulation for improving our preparedness for climate change impacts.