Stronger Influence of the Tropical Atlantic on Interannual Variability of Northern Hemisphere Land Monsoon Rainfall since the Mid-1990s

Uncovering predictability sources of Northern Hemisphere land monsoon rainfall (NHLMR) is a vital importance for disaster prevention and mitigation as well as sustainable economic development. Using observations from 1971 to 2020, the present study reveals a regime shift of the tropical oceanic drivers of the interannual variation of NHLMR. We show that the interannual variation of NHLMR is dominated by a zonal sea surface temperature (SST) contrast in the tropical Pacific and a uniform SST pattern in tropical Atlantic, and accompanied by a dipole SST pattern in the tropical Indian Ocean. While the relationship of NHLMR with tropical Pacific remains stable over the past five decades, the relationship with tropical Atlantic is strengthened around the mid-1990s. Observations and numerical experiments demonstrate that decadal warming of the tropical Indian Ocean and Atlantic Ocean, associated with the phase transition of the Atlantic multidecadal oscillation, is the main contributor to the enhanced influence of the tropical Atlantic on NHLMR after mid-1990s by modulating the pantropical Walker circulation.