Analysis on dry intrusion of a remote typhoon rain

By using routine observation and NCEP reanalysis data,a typhoon remote heavy rainfall in Shandong province during 17- 19 July,2008 was diagnostically analyzed and simulated. The results show that the dry cold air intrusion process from mid-high level happened in this rainfall process can be classified into two forms: one is the dry intrusion from the top of troposphere while the other is from the lower layer of troposphere in the direction of northwest-north. The dry intrusion was located between 300- 600 hPa,and the upper levels are slightly behind the low ones,it was not good for the unstable development of convection. The unsaturated moist air turns to be saturated because of the dry intrusion,which led to the precipitation increasing,and the rain area was always located in the forefront of 500 hPa dry area. The disturbance of positive potential vorticity in the upper troposphere transporting downwards to the lower level along the intensive band of pseudo-equivalent potential temperature stimulated the development of the low-level mesoscale vortex. The in-phase relation between large-value potential vorticity at500 hPa and precipitation implies the development and movement of the precipitation.