Responses and mechanisms of East Asian winter and summer monsoons to weakened Atlantic meridional overturning circulation using the FGOALS-g2 model

ABSTRACT

This study investigates the responses and mechanisms of East Asian winter monsoon (EAWM) and East Asian summer monsoon (EASM) to weakened Atlantic meridional overturning circulation (AMOC) through three perturbation experiments with different intensities of freshwater hosing in the North Atlantic, using the Flexible Global Ocean – Atmosphere – Land System Model, Grid-point Version 2. These experiments show that a subtle weakening of AMOC does not significantly influence either the EAWM or the EASM. When AMOC weakens more substantially, northerly wind anomalies emerge in East Asia throughout the year, strengthening the EAWM and weakening the EASM. The northerly wind anomalies result from an anomalous westward sea level pressure (SLP) gradient, namely positive SLP anomalies across Eurasia and negative anomalies in the western North Pacific (WNP). In winter, negative WNP SLP anomalies are found in mid-high latitudes. They are caused by anomalous stationary wave activity, which is associated with the Aleutian Iceland seesaw teleconnection. In summer, negative WNP SLP anomalies are present in the subtropics, and are linked with an anomalous cyclonic circulation over the north of the Philippian Sea. This cyclonic circulation anomaly is induced by the anomalous warm water in the subsurface of the South China Sea and Philippian Sea through the Gill mechanism.