THE RADAR DATA ASSIMILATION AND ANALYSIS OF A SQUALL LINE UNDER ULTRASTRONG INSTABILITY AND WEAK VERTICAL WIND SHEAR

CAO Qian; ZHANG Shu-wen; CAO Bang-jun; YE Dan; QIU Xue-xing

doi:10.16032/j.issn.1004-4965.2016.05.007

Abstract：With the mesoscale model WRF(Weather and Research Forecasting)and a corresponding 3DVar as-similation system,Doppler radar data in Wuhan are assimilated.Then,a squall line that formed in Hubei on July 26,201 1 is investigated by using the data assimilation results,NCEP FNL data,observed precipitation da-ta,radiosonde observations as well as observations of Doppler radars.The radiosonde observations show that the squall line is formed under the environment condition of weak low-level vertical wind shear and strong convective instability.The Doppler radar observations show two strong convective lines respectively in the directions of Northeast-Southwest and Northwest-Southeast;the first one moves slowly during its organization period,,the northwest side of the second one disappears rapidly and the southeast side merges into the first one.Diagnostic analysis by using the forecasts with assimilated radar data indicates that during the initial period,the dynamical condition is not beneficial to the formation and development of new convective cells,but the strong convective instability energy provides strong thermal lifting condition.Later on,low-level ambient vertical wind shear and a cold pool become in favor of development of the squall line,but dynamical lifting condition is weak and the con-vective instability energy still plays the vital role.With the increase of dynamical lifting and strong thermal lift-ing,the system gradually becomes mature.Finally,the convective instability energy releases,the strength of the cold pool becomes much stronger than the low-level vertical wind shear,and the squall line disappears.