The Effect of Qinghai-Tibet Plateau Forcing on the Meso-Scale Rain-bearing Circulation Systems over Eastern China during Presummer Rainy Season

Abstract

The low level jet and the associated low level south-west vortex are the main mesoscale systems which bring heavy rains over East Asia. In order to examine the influence of Qinghai-Tibet Plateau (QTP) on these circulation systems, a control and two experiments were performed with the ECMWF grid point limited area model for a typical heavy rainfall case during the presummer rainy (Mei-yu) season.The control experiment, in which the orography represents the mean value over a grid box, reproduces the variation of the low level jet, the formation of the south-west vortex and the heavy rainfall area. When the height of QTP is halved, the south-west monsoon south of the Plateau interacts with the middle latitude westerlies.A baroclinic disturbance then develops instead of the meso-scale systems, and the heavy rainfall zone is shifted to the east. Increasing the QTP height causes the meso-scale systems to be enhanced and restricted to the vicinity of the Plateau, and the rainfall zone is shifted to the west.The results show that the forcing effect of the QTP on the three low level branches of the flow (the northerlies from middle latitude, the south-west monsoon from the Bay of Bengal and the easterlies from the West Pacific) develops and maintains the meso-scale rain-bearing systems.