吕梁山两次夜间暴雨的边界层特征及能量来源与转换

Boundary Layer Characteristics,Energy Sources and Conversion of Two Night Rainstorms in Lyuliang Mountains.

利用常规观测、NCEP/NCAR 1°×1°再分析、FY-2E卫星数据等资料,对分别由β-中尺度持续拉长状对流系统(MβECS)和中尺度对流复合体(MCC)造成的两次吕梁山夜间暴雨过程进行数值模拟和粒子后向轨迹追踪,结果表明:过程1受边界层南风急流和西南气流影响,山西西部低空急流偏西分量和晋中盆地边界层西南气流的增强是对流不稳定能量重建的重要因子。过程2则受边界层南风和东风急流作用,南风急流被显著抬升到对流层中高层,形成含有冰晶层的中高层云系,东风急流则供应低空水汽。两次过程边界层(0.8-1.2 km)粒子携带的水汽均明显超过低层(1.5-3 km),是夜间短时强降水所需水汽的最大贡献者。700 hPa及以上非绝热作用产生扰动有效位能,之后向扰动动能的转化是两次过程中短时强降水发生所需能量的主要来源。

Using the conventional observations,NCEP/NCAR 1°×1°reanalysis and FY-2E satellite data,two night torrential rain processes,triggered respectively by meso-βelongated convective system(MβECS)and mesoscale convective complex(MCC)in Lyuliang Mountains,were simulated,and the backward trajectorys of the particles were traced.The conclusions were as follows:In the first process,the southerly jet and southwest airflow in the boundary layer had a significant impact.The westerly component of the low-level jet in western Shanxi and the strengthening of southwest airflow in the Jinzhong Basin emerged as crucial factors contributing to the resurgence of convective instability energy.In the second process,the southerly jet in the boundary layer was notably elevated,leading to the formation of clouds containing ice crystals in the middle and upper layers.Concurrently,the easterly jet supplied essential water vapor at lower altitudes.Notably,in both processes,the water vapor transported by particles in the boundary layer(0.8-1.2 km)significantly exceeded that in the low-level layer(1.5-3 km).Furthermore,the diabatic processes occurring above 700 hPa generated perturbative available potential energy,which was converted into perturbative kinetic energy,serving as the primary energy source for the short-term heavy precipitation observed in both processes.