Atlantic Meridional Overturning Circulation Weakening Warmed the Southern Tibetan Plateau in Spring During the 8.2 ka Cold Event

Abstract

Past North Atlantic abrupt cold events have the potential to provide insights into the future climatic response to the slowdown of the Atlantic meridional overturning circulation (AMOC). This study explores spring temperature changes on the southern Tibetan Plateau during the 8.2 ka cold event through simulations forced by North Atlantic freshwater hosing. Simulation results reveal anomalous warming on the southern Tibetan Plateau due to hosing-induced AMOC slowdown. This warming was primary caused by the increase of net solar flux and the presence of an anomalous warm anticyclone over the Tibetan Plateau. The enhanced net solar flux resulted from the decrease in snowfall, which led to a reduction in albedo. The snowfall was mainly reduced by the decrease in westerly moisture transport, resulting from weakened lower-level westerlies induced by AMOC-driven climate variabilities over the North Atlantic and tropical Indian Ocean. The warm anticyclone was induced by the anomalous vertical northerly shear over the southeastern Tibetan Plateau, which resulted from enhanced diabatic heating released by Asian monsoon rainfall. Asian monsoon rainfall increased due to anomalous lower-level cyclone over the tropical Indian Ocean. This anomalous cyclone was induced by the Mastuno-Gill response over the tropical Indian Ocean and amplified by a wave train propagating from the North Atlantic, both of which were resulted from the AMOC slowdown. The AMOC weakening is likely to play an important role in the recent and ongoing amplification of spring warming on the southern Tibetan Plateau.