“91.7”江淮暴雨低涡发展结构和演变的中尺度数值模拟

MESOSCALE NUMERICAL SIMULATION OF DEVELOPING STRUCTURE AND EVOLUTION FOR VORTEX WITH HEAVY RAIN IN JIANGHUAI AREAS DRUING 4—7 JULY 1991

本文对1991年7月4—7日发生在江淮流域的一次低涡切变线特大暴雨过程进行了高分辨行星边界层参数化的中尺度数值模拟。所用模式是通过系列检验和改进的MM4。控制模拟结果揭示:"91.7"江淮暴雨过程与中尺度暴雨低涡的生成和发展以及特有的动力和热力结构密切相关;垂直气旋性涡柱的形成和发展是这类暴雨低涡持续发展的一种重要而特有的中尺度结构;伴随暴雨低涡涡柱耦合发展的强上升运动是维持其低涡持续发展以及完成高、低空诸通量交换和输送所必须的次级垂直环流条件;深厚湿舌、强上升运动与涡柱三位一体的共存结构是暴雨低涡持续发展并产生对流云系和持续暴雨的典型结构;西南低空急流的发展和维持,不仅是暴雨低涡形成和持续发展的重要动力学条件,也是暴雨过程所需水汽的主要载体;对流层下部深厚不稳定层结的形成和维持是暴雨低涡能够产生持续对流活动以及对流性降水所必须的热力层结条件;与西南低空急流相伴的强暖湿带在850 hPaθ_e场上显示得最清楚,其暖湿带中轴北侧及其强湿斜压区与低涡切变线雨带基本一致;在暴雨低涡行星边界层内,感热通量有夜负昼正的日变化;而潜热通量却昼夜均为正值,且远大于相应时间的感热通量。这表明在低涡暴雨过程中,行星边界层内垂直向上输送的水汽通量和潜热通量远较感热通量重要。

Mesoscale numerical simulation of heavy rain event due to the vortex with shear line is conducted to use verified and improved MM4 with high resolution PBL parameterization. The control simulative results revealed the Jiang-Huai heavy rain event has close relation to the genesis and development of the mesoscale vortex and its special dynamic and thermodynamic structure. The intensive ascending motion of coupling development with the column of cyclonic vorticity is a necessary vertically secondary circulation condition for maintaining persistent development of the vortex and accomplishing the exchange and transport of the fluxes at upper and lower levels. The coexisting structure of three forming an organic whole, which consists of the deep moist tongue and the intensive ascending motion as well as the column of cyclonic vorticity, is a typical structure of persistent developing vortex with convective cloud system and continuous heavy rain. The development and maintenance of the SW lower levels jet are not only an important dynamic condition of the genesis and persistent development of the vortex, but also a main medium of moistureneeded for heavy rain event. The formation and maintenance of the deep unstable stratification in the lower troposphere are an necessary thermal stratification condition for the vortex with persistent convective activity and convective precipitation. The north side of the central axis of the strong warm-moist band at 850 hPa and adjacent moist baroclinic zone are basically consistent with the precipitation band of the vortex with shear line. Within the PBL of the vortex, the sensible heat flux is the positive flux at day-time and the negative flux at night-time. But the latent heat flux is always positive flux both day-and nigth-time, and larger than the sensible heat flux of corresponding time. This fact implies that the upward transferring moisture and latent fluxes are more important than that of the sensible heat flux during the heavy rain.