Analysis Of Environmental Conditions And Numerical Simulation Of Continuous Severe Convective Weather Events Caused By Long-Life Cold Vortex

Strong convective precipitation is one of disaster in Tianjin area. In order to study the the dynamical, thermodynamical mechanism of the occurrence and development of the strong precipitation, at first, Using NCEP reanalysis data and the observational data of Micaps, the Environmental Conditions of Continuous Severe Convective Weather Events Caused by Long-Life Cold Vortex occurred in Tianjin area on 23th June-1st July 2008 is preliminary analyzed. Main conclusions are as follow:(1) Mongolia cold vortex subsisting and continue to split the cold air southward, so the air temperature in mid-high level was anomal colder,which triggered the occurrence of severe convective weather in Tianjin.(2)The coupling upper and lower level jet stream provide favorable moisture and upward movement.At the same time, the strong vertical wind shear also promote the development of strong precipitation.(3)The heavy rainfall in Tianjin area was generally accompanied by the development of vertical upward movement,Upward motion occurred in the situation which vertical vorticity field turned to positive from negative and the characteristics of divergence field was high-level divergence, low-level convergence.(4)In this 9 days, water vapor was transported to Tianjin area introduced by southwest airflow which in the northwest of anticyclone center occurred in the Shandong Peninsula.(5)In this 9 days,the average pseudo-equivalent temperature in Tianjin was anomal high,which means Tianjin had enough convective energy before the severe precipitation happened. With the cold vortex split the cold air southward, triggering the occurrence of severe convective precipition many times. (6) Temperature advection and V components (ie north-south wind component) can reflect the situation of the cold air in the mid-high level. Through the analysis,9 days convective precipitation is directly related to the cold air splitted by the cold vortex. On the basis of background analysis, the paper also use WRF mesoscale numerical model to simulate the strong precipitation process on June 25. Based on the meteorological fields of the simulation results being consistent with the real field,using the higher spatial and temporal resolution data output by WRF model, the characteristics of strong convective precipitation process were analyzed,and the conditions for the occurrence and development,the rule of evolution, dynamic mechanism were explained. Simulation results show that:(1)When heavy rainfall happened,dry and warm air transported by southwest jet stream to the north and meet the cold wet air,forming dew point front.The dew point front is a very favorable mechanism to trigger the convective motion,whose spatial distribution played a vital role in the spatial distribution of convective clouds and heavy rain. (2)Instability energy accumulation and release played a very important role in the occurrence and development process of precipitation; (3) It was found that the heavy rainstorm area had a better corresponding to higher rotational helicity. Analysis also shows rotational helicity have certain instructions to 1 hour precipitation forecast; (4)The analysis of the wet Q vector shows that the convergence zone of wet Q vector had a better corresponding to the generation and development of convective precipitation, vertical distribution of wet Q vector component reveals the direction and strength of secondary circulation, convective precipitation was not far from ascending branch of secondary circulation; (5)The movement and development of the heavy rainfall point closely related to potential vorticity on isentropic surface. In the vertical direction, the high value area of potential vorticity center, which represent cold air in the upper level,invaded to the mid-low level over Tianjin region,and then stretched in the vertical direction,thus,the positive feedback between positive anomalies of potential vorticity and ascending motion,promoted the development of heavy rainfall.(6)MPV is a good physical quantity to signify the atmospheric stability. When the times corresponding to heavy rain, MPV has remained a low negative value, corresponding to unstable region; high-level is positive, corresponding to a stable area distribution.Though the analysis of MPVl and MPV2, we found not only the role of barotropic instability, but also the role of baroclinic instability in this process. Finally, the relevant terrain sensitivity experiment about this convective precipitation process showed that the convergence of air flow, vertical ascending motion and the pseudo-equivalent temperature distribution were affected by topography,which affecting the intensity and location of severe convective precipitation.