Ocean–Atmosphere–Land Feedbacks on the Western North Pacific–East Asian Summer Climate

Abstract

In this review paper, we summarize mechanisms limiting poleward extent of the summer monsoon rain zones, the Asian summer monsoon in particular. They include local processes associated with net heat flux into the atmosphere and soil moisture, ventilation by cross-continental flow, and the interactive Hodwell-Hoskins (IRH) mechanism which is defined as interaction between monsoon convective heating and baroclinic Rossby wave dynamics. The latter two mechanisms, ventilation and the IRH mechanism, also induce an east-west asymmetry of the summer monsoon rain zones. Processes that change land-ocean heating contrast, differences in net heat flux into the atmosphere rather than in surface temperature, are also discussed. Convection associated with the Asian summer monsoon is initiated by net heat flux into the atmosphere and modified by soil moisture via an evaporation process. In Asia, ventilation by moisture advection is particularly important and the IRH mechanism tends to favor interior arid regions and east coast precipitation. Land surface condition, such as surface albedo and topography, and ocean heat transport tend to modify land-ocean heating contrast, in term of a tropospheric temperature gradient, and then change the Asian summer monsoon circulation and its associated rain zone. The stronger meridional gradient of tropospheric temperature tends to enhance the summer monsoon rainfall and extend the rain zone farther northward. Local SST, such as the warm SST anomalies in the western North Pacific during El Niño, is also important in the summer monsoon rainfall and its position. RECENT PROGRESS IN ATMOSPHERIC SCIENCES WITH APPLICATION TO THE ASIA-PACIFIC REGION1