摘要
利用非静力中尺度数值模式WRF并结合NCEP-FNL分析资料、常规气象观测资料、FY-2F卫星TBB数据以及CM ORPH降水资料,对2014年6月29日至7月1日的一次高原横切变线过程进行了数值模拟并分析了其演变过程中降水、热力、水汽和动力的结构特征。结果表明,WRF模式较成功地模拟了此次高原切变线过程的降水量和落区。在高原切变线活动期间,不同阶段结构特征存在明显差异。切变线附近通常对应TBB<-20℃的云区;随着切变线的发展,TBB值降低,在云区内有多个TBB<-60℃的对流活动中心,对应主要降水期;在切变线减弱阶段,TBB值升高,降水趋于结束。高原切变线存在"南暖北冷"的热力结构,在切变线发展维持阶段呈现高层稳定、低层不稳定的垂直分布特征;高原切变线也是水汽的聚集带,水汽通量散度的转变对高原切变线的发展具有一定指示作用。在切变线初生阶段和维持、发展阶段,垂直方向上存在正涡度中心和辐合中心,呈现对流层低层正涡度和高位涡中心相耦合的动力结构;气旋式切变有利于高原切变线上正涡度的维持;散度场上的低层辐合、高层辐散的结构特征有利于切变线上垂直上升运动的发展;高原切变线上的辐合带先于正涡度带开始减弱、消失是高原切变线减弱的一种特征信号。
Using the non-hydrostatic mesoscale WRF( Weather Reaserch Forecast) model,and combining with the National Centers for Environment Prediction Final Analysis( NCEP-FNL) data,the conventional observation data,the temperature of black body( TBB) data from the Fengyun-2 F( FY-2 F) satellite and the Climate Prediction Center Morphing Technique( CMORPH) precipitation data,the plateau transverse shear line process occurring from 29 June 2014 to 1 st July was simulated,and the structural characteristics of precipitation,thermodynamic,water vapor and dynamic in the course of evolution were analyzed. The results show that the WRF model successfully simulated the precipition and precipition area caused by the Plateau shear line. During the shear line process,there are significant differences in the structural characteristics of different stages. It usually corresponds to the cloud sector of TBB<-20 ℃ nearby the shear line; with the developing of the shear line,the TBB decreases,and there are many convective activities centers of TBB<-60 ℃,corresponding to the main period of precipitation;TBB increases again during the weakening stage of the shear line and the precipitation goes to end. The plateau shear line has a thermodynamic structure of"warm south but cold north",the vertical distribution characteristic of high level stability and low layer instability appears during the development and maintenance stage of the shear line; the plateau shear line is the water vapor congregated zone,the change of water vapor flux divergence has a certain effect on the development of plateau shear line. Above the vertical direction of the nascent,developing and maintenance stage,there are positive vorticity and converge centers which both present a dynamic system of lower troposphere positive vorticity coupled with the high potential vorticity. The cyclonic shear is favorable for maintaining the positive vorticity of plateau shear line; lower level convergence and upper level divergence structure on divergence field is conducive to the development of vertical ascending motion of the shear line; and it is a characterstic signal of plateau shear line weakened that the converge zone begins to subside then disappear in advance of the positive vorticity does.
引文
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