湖北一次飑线过程的观测分析及数值模拟

Observation Study and Numerical Simulation of the Structure for a Squall Line Case in Hubei

用武汉新一代多普勒天气雷达(CINRAD)9层体扫模式观测资料、常规和地面加密观测资料、以及NCEP一日4次的1°×1°再分析资料,采用中尺度非静力模式(WRF)对2007年5月31日湖北飑线过程进行观测分析及数值模拟研究。结果表明,雷达回波显示出飑线前方强而窄的回波带、过渡带、后方宽广的次强层状回波区特征;新单体在对流区前沿周期性地产生,成熟单体减弱为后面的弱回波区,在不断的生消交替过程中系统向前传播。数值模拟表明,在飑线前方上空是强而窄的上升气流,后方中层偏上是一支宽广的从前向后(由南向北)斜上升气流,下方是从后向前(由北向南)的斜下沉气流;飑线低空有两支入流:前方偏南气流和后方下沉入流,高空出流一部分向北倾斜上升,另一部分翻转向南。飑线系统内气流沿着湿而高θse值带进入和上升,在干而低θse值区下沉。低层风切变和飑线后部冷丘的作用是造成飑线垂直结构的可能原因。飑线结构的数值模拟与雷达观测结构基本一致,其特征与美国经典飑线概念模型(TS型:拖曳层状)类似。

A squall line attacks the mid-north areas of Hubei Province on May 31,2007.The severe convective system results in heavy rainstorm as strong as 50~70 mm/1h,combined with thunder and lightning.This process is observed by the CINRAD in Wuhan.The interior structure of the convective system are analyzed using the radar observation data,intensive observational data and NCEP reanalysis data（1°×1°） are used,and mesoscale numerical model（WRF2.2） is also used to simulate this process.The results are as follows： A strong and narrow echo band is in the front of convective line,and a sub-strong and broad echo area is behind of this convective line,there is a weak echo gouge between them.The new cell is periodically producing along convective line front,and the old cell is weakening into rear weak echo area,thus the convective system spreads forward. The mature cell contains an intense narrow updraft that can penetrate above the tropopause.This updraft is often followed by a convective scale downdraft at mid-upper levels.The broad ascending front-to-rear flow is at middle level of trailing stratiform area,and the descending rear-to-front flow is under of ascending flow.There are two inflows in lower level of squall line： Front south air and rear descending air.In upper level,one outflow overturns to south,and another to north.The stream ascend along the moisture and high θ se band,then subside in dry and low θ se area.The effect of lower-level shear and rear cold pool is likely the reason to result in the vertical structure of squall line.The numerical simulative structure is basically consistent with the radar observationa analysis,and the major structure characteristic of this squall line resembles the typical conceptual model（trailing stratiform） of the midlatitude squall line in America.