Northward propagation of Hadley Cell in the South Asian monsoon region driven by active convection over the Qinghai–Tibet Plateau triggered by sea surface temperature warming of the North Atlantic

Abstract

The sea surface temperature (SST) warming in the high-impact area of the North Atlantic prompts active convection over the Qinghai–Tibet Plateau (QTP), which consequently drives the Hadley Cell (HC) in the South Asian monsoon region to shift northward. This interaction mechanism stresses the “hub” effect of the QTP in the atmospheric energy and water cycle of the low- to mid–high latitude systems during the convergence of westerly and monsoon winds. The Rossby source, also famous as the “oscillation source,” formed in the upper troposphere by the SST variations in the high-impact area of the North Atlantic, is an essential “thermal driving source” for the interannual shifts in convection over the QTP. The meridional teleconnection wave train structure triggered by the warming (1991–2020)/cooling (1961–1990) of the SST in the high-impact area of the mid–high latitudes of the North Atlantic displays a reversed phase. The Rossby wave train, which spreads from the North Atlantic to the QTP during the high-impact sea surface warming phase in the North Atlantic, indicates a remarkable anticyclonic structure (strong divergence) in the high altitude (200 hPa) of the QTP, which favors the generation of active convective activity in the latter 30 years. By contrast, convective activity is blocked. During the two stages of 1961–1990 and 1991–2020, despite a significant interdecadal positive and negative phase reversal in the North Atlantic Multiyear Oscillation (AMO), the variance in the definition range between the AMO and the high-impact area of the North Atlantic led to substantial differences in the meridional teleconnection wave train structures and the corresponding effects. In addition, the latent heat emitted by the enhanced convective activity on the QTP during the sea surface warming phase in the high-impact area of the North Atlantic can strengthen the “heat pump” effect of the QTP, cause the northward shift of HC in the South Asian monsoon region, and spark the mutual feedback mechanism between the plateau convection and the HC in the South Asian monsoon region. According to these interdecadal response characteristics, this paper offers a comprehensive physical image that exhibits the mutual feedback between the convection over the QTP and the HC in the South Asian monsoon region, where the active convection is initiated by the SST warming in the high-impact area of the North Atlantic.