Analysis on Water Vapor Condition of a Short-Time Heavy Rainstorm Process in Guanzhong,Shaanxi in August 2007

The water vapor condition of a stort-time heavy rainstorm in the Guanzhong,Shaanxi on 8-9 August 2007 was carefully analyzed using the T213 data and automatic meteorological observing data.The results indicate that the water vapor of heavy rainstorm is from a high humidity around the Guanzhong Shaanxi.Water vapor over the rainstorm area is shallow during the heavy rainstorm.Humidity change in rainstorm area has the process of 'reduced-increases suddenly-reduces fast',because of wind direction fast change at the low level,and the vapor accumulation is obtained through the easterly current.The moisture convergence in the east-west direction is main contribution of convergence of vapor in the heavy rainstorm area.Occurring,intensification and weaken of heavy rainstorm had a close relationship with inflow and outflow of moisture flux on the north boundary and sudden increase and decrease of vapor flux inflow on the east boundary.The heavy rainstorm center locates in region between the maximum of water vapor flux and convergence center of vapor flux.The precipitable water in heavy rainstorm area primarily depends on the vapor flux convergence in horizontal direction,and vapor flux convergence largely is decided in convergence of horizontal wind.The occurrence and weakening of severe precipitation have more closer relationship with the local change of water vapor and water vapor advection change.Anti-circulation circle owing to the sufficient vapor supply at the surface layer and the water vapor vertical transportation causes rapid enhancement and lifting in the water vapor and energy,establishing the atmosphere of instability and triggering the energy release,which lead to formation of heavy rainstorm.On the contrary,vapor condition of formation rainstorm disappeared,severe precipitation end.