Pacific Walker Circulation strengthened by tropospheric aerosol forcing

The recent strengthening of the Pacific Walker Circulation (PWC) has attracted extensive attention due to its broad impact on global climate, but its cause remains under intense debate. Here by analyzing the Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations, we show that aerosol forcing since the early 1980s has induced an increase of sea level pressure and an anticyclonic wind anomaly in the North Pacific accompanied with a Pacific Decadal Oscillation (PDO) like sea surface temperature anomaly and thus strengthened the PWC. The large inter-model spread is likely induced by the discrepancies of cloud radiative effect in response to aerosol forcing in the Northern Hemisphere mid-to-high latitudes. A set of steady-state climate simulations forced with reanalysis aerosol fields further confirm the positive contribution of aerosol forcing to the strengthening of PWC.