2012年7月下旬河套地区4次切变暴雨的对比分析

Comparative Analysis of Four Shear Rainstorm Processes in July of 2012 in Hetao Area of Inner Mongalia,China

应用日常预报业务中可以方便使用的常规观测资料、数值预报产品、卫星云图、加密自动站观测资料以及雷达资料等,从环流背景、流型配置、物理机制等方面对比分析了河套地区4次暴雨过程,旨在提高对暴雨的短期预报预测能力及短时强降水的临近预警能力。分析发现:(1)副热带高压西侧的偏南气流以及来自孟加拉湾的暖湿偏南气流在35°—40°N与来自高纬度的干冷的偏北气流多次交汇,水汽在该带中明显辐合,为河套地区持续性暴雨发生发展提供源源不断的水汽,提供水汽辐合上升动力条件;(2)暴雨落区与低层的显著流线出口区或急流出口区的位置、切变线的位置密切相关,暴雨一般落在高空急流的右侧、低空急流的左侧;(3)暴雨天气出现前一般会出现500hPa以下θ随高度的增加而减少的特征;(4)暴雨天气出现前一般都会出现风随高度顺转的特征;(5)暴雨过程中地面辐合线起到动力抬升作用,触发中小尺度系统的生成和发展;(6)抬升凝结高度和自由对流高度都比较低,利于水汽凝结,而平衡高度较高,利于能量的积累,对于对流天气的预报有较好的指示意义。

The atmospheric circulation pattern, the physical mechanism of four rainstorm events are analyzed over Hetao area of Inner Mongolia by routine observational data, numerical forecast product, satellite cloud images, automatic weather station＇s data and radar data. These data mentioned above is easy and convenient access in daily forecast business. The purpose of the comparative analysis of the four rainstorm events is to discuss the predictability of the four rainstorm events and improve short-term forecast ability of the rain- storm and early warning capability of short-term strong precipitation. （1） The warm and wet southerly wind from the Bay of Bengal and west side of West Pacific Subtropical High meets with the dry and cold air from higher latitude over 35°--40° N, and the water vapor in the zone has obvious convergence, the premise con- dition provide a steady stream of water vapor sources and water vapor flux convergence, which is favorable for persistent rainstorm over Hetao area. （2） The exit region of significant streamline and jet stream and shear line of low level is closely related to rainstorm area; Rainstorm always happens to the right of high level jet and to the left of low level jet. （3） The pseudo-equivalent potential temperature usually decreases with the increasing height under 500 hPa before rainstorm; （4） The rainstorm usually appears after warm advection. （5） Ground convergence line is favorable for the upward momentum and triggers the meso-mi- croscale system appearance and development during rainstorm process. （6）The lifting condensation level and the level of the free convection are relatively low, which is favorable for vapor condensation, and equi- librium level is relatively high, which is helpful to the accumulation of energy for convection weather, and these are good denotative signals for convective weather.