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.

Migration of the Northern Boundary of the East Asian Summer Monsoon Over the Last 21,000 years

“…In general, the physical mechanisms for boundary migration driven by meltwater fluxes are generally similar to those in the orbital experiment, but the responses of the circulation to the former forcing are weaker than those to the latter forcing (Figures 7 and 8). The mild responses may be associated with the freshwater hosing intensity, and the weak meltwater discharge does not significantly influence the AMOC and thus the EASM (Yu et al., 2018). Additional sensitivity experiments are needed to assess the responses of circulation and the EASM northern edge to meltwater discharges with various intensities.…”

Decadal‐ to Centennial‐Scale East Asian Summer Monsoon Variability Over the Past Millennium: An Oceanic Perspective

“…The EASM record presented in this study is stronger during the AMOC reduction periods (Figure 3). Climatic simulations indicated that weakened AMOC enhances Walker circulation in the North Pacific (Sun et al, 2011;Yu et al, 2009Yu et al, , 2018Zhang & Delworth, 2005). Enhanced Walker circulation can result in more moisture transportation to the Asian summer monsoon region and thus more precipitation there (Ning et al, 2017;Wang et al, 2013).…”