Diagnostic Analysis on Potential Vorticity Budget of One Severe Torrential Rain Process in Southern Henan in 2009

Using mesoscale WRF model,conventional meteorological data and NCEP/NCAR reanalysis data,the severe rainstorm process from 28 to 30 August in Henan Province is simulated and diagnosed with the equation of potential vorticity budget.Using the simulation results,this paper diagnoses the rainstorm by the potential vorticity and potential vorticity budget.The results show that WRF model has good simulation results to severe rainstorm.The simulated intensity and location of the rainstorm is well consistent with the observation.Potential vorticity can reflect the main dynamic and thermodynamic characteristics of the rainstorm.High potential vorticity value area has a better correlation with the rainstorm center,which is located in the southeast of the high potential vorticity area.The various items of potential vorticity budget can well show the main dynamic and thermodynamic characteristics of the rainstorm.The potential vorticity in the low-middle atmosphere increases locally with the large value area corresponding to the rainstorm center in the process of rainstorm developing.Among the items of the potential vorticity budget,the latent heat and the horizontal advection and vertical transportation and friction are the main contribution items,of which the horizontal advection and the latent heat contribute positively to the local changes of potential vorticity.The latent heat makes the potential vorticity gradually increase.The horizontal advection is helpful for the potential vorticity to gather to the convergence zone of the flow field.The vertical transportation and friction make the negative contribution to the local changes of potential vorticity.The vertical transportation can transfer the potential vorticity from the lower to the high-level and reduce the lowlevel potential vorticity.Under the influence of the friction,the potential vorticity in low-level is dissipatived and reduced.