Simulation And Preliminary Assimilation Experiment Of A Severe Convective Weather Process On Northeast Side Of Tibetan Plateau

The topography of northern Shaanxi province area is very complicate.Most places have the small precipitation rain fall and few rainstorms.Because of particular geography circumstance and small rain fall in the northern of Shaanxi province,the establishments that are used to prevent the rain there is not good enough.The disaster,such as flood and sparry flow,are often caused by rainstorm.So it is very important to research the rainstorm of this area.In this paper,first of all,the t_bbdata of FY-2C satellite,routine data and the 6 hour NCEPl°×1°re-analyzed data are used to perform a diagnoses about a rainstorm of northern Shaanxi province at the night of 20^th.September,2006.The result shows that there exists a stronger southern airflow in 700 hPa whose position is associated with the rainstorm area.The low value of T_bbis corresponding to the center of rainstorm.The field of 850 hPaθ_seis presented as the type of"Ω".The airflow of 850 hPa and 700 hPa provides the rainstorm enough vapor.The release of unstable energy is caused by strong rising movement that is good at presenting the strong precipitation.When the rain occurred,the area of the rain is located in or approached the high area of helicity.A heavy rainstorm of 20^th.September,2006 is numerical simulated by meso-scale mode of WRF.Vorticity,divergence,vertical speed and relative humidity is analyzed with the basic physical element of mode output.Potential vorticity,humidity potential vorticity barotropic, baroclinic item and disturbance potential voriticity are calculated,It finds out the mechanism of the rainstorm.The diagnostic analysis shows that the coupling of humidity field and vertical rising movement is the dynamical mechanism that makes the rainstorm occur and last.The center of the rainstorm is located around the major area of 700hPa potential vorticity.The high of MPV1 is isolated with the convective stable cold air.The smaller positive or negative value area is isolated with the unstable or less convective stable warm air.The negative area of the lower MPV1 can signifies the character of the unstable warm air movement.The rainstorm happened around the zero line.The south warm air is transferred continuously to convergence area.This area is isolated with the MPV2 negative area.Because of the strong vertical movement caused by convergence,the intensity of the rain is raised,The heavy rainstorm is formed.The existence of middle-low positive potential voriticity disturbance is the important condition of the rainstorm development.The vector Q is analyzed by using mode output.The result posts the relationship of space-time configuration among the divergence of qusi-geostrophic vector Q,vector Q and rainstorm.It points out the effect of vector Q in the rainstorm forecast.The sensitive experiment shows that Qinlin mountains affect the rain fall of northern Shaanxi province.The initialization field of meso-scale numerical mode is improved by using the the cloud drift wind data calculated by the image data from the fenyun satellite.The using of cloud drift wind in the northern of Shaanxi rainstorm forecast experiment is elementarily discussed.It is useful for the fine forecast of northern Shaanxi province rainstorm.