In this review article, we summarize mechanisms limiting the poleward extent of the summer monsoon rain zones, particularly for the Asian summer monsoon. 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, defined as the interaction between monsoon convective heating and baroclinic Rossby wave dynamics. The last 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, and 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 conditions, such as surface albedo and topography, and ocean heat transport tend to modify land–ocean heating contrast, in terms 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 Ni~no, is also important in the summer monsoon rainfall and its position.
All Science Journal Classification (ASJC) codes
- Earth and Planetary Sciences(all)