NUMERICAL EXPERIMENTS ON NH SUBTROPICAL UPPER TROPOSPHERIC QUASI-STATIONARY VORTICES IN SUMMER

To reveal the possible factors affecting the maintenance and interannual variations of the subtropical planetary-scale vortices such as the south Asian anticyclone and the mid-oceanic troughs, a series of nu-merical experiments are conducted with a quasi -geostrophic low-resolution spectral model. Firstly a simu-lation experiment is performed in which the realistic thermal and topographic forcing are incorporated. The results of simulation show a certain similarity to the actual subtropical flow field in July. On the basis of simulation experiment a series of contrast experiments are performed. It is found that the topog-raphic boundary forcing is less important than the thermal forcing in the dynamics of these systems, and that the anomaly of heating field may cause significant change in position and intensity of the south Asian high and the other systems. It is speculated that the response of the subtropical large-scale systems to heat-ing anomaly is an important cause for the interannual variations of circulation, especially the monsoon circulation.