THE EFFECTS OF ANOMALOUS HEATING ON SUMMER MONSOON OVER ASIA

Based on a zonally non-uniform mean circulation in summer simulated by numerical modelling,perturbation heatings over South Asia and a perturbation cooling over Northwest Australia were incorporated in a numerical model to discuss their effects on summer monsoon over Asia and the structure of flow disturbance in this paper.It is shown that the perturbation heatings over the Southern Asia may make the upper easterlies to the south of the Tibetan High and the lower southwest flows strengthen,whereas the perturbation cooling over Australia can force a baroclinic disturbance and make the southeasterlies in the lower levels increase on its north side.However,so far as the scope of the anomalous heating/cooling introduced in the model and the time scale of model integration are concerned,the flow changes due to these perturbations may be mainly local and in the hemisphere where the perturbation heating/cooling is located.These changes are not strong enough to change the major features of the summer monsoon which is maintained by the global mean heating forcings and to explain the apparent strengthening of the cross-equatorial flows.The changes in divergence and vertical velocity fields are consistent with the distribution of the perturbation heating,indicating the direct contribution of anomalous heating to these changes.But the flow disturbances deviate from the perturbation heating,suggesting that the flow changes are related not only to the perturbation heating,but to the mean monsoonal circulation.