旋转风螺旋度及其在暴雨演变过程中的作用

ROTATIONAL WIND HELICITY AND ITS EFFECTS ON TORRENTIAL RAIN PROCESSES

摘要:

利用中尺度有限区域模式MM4对1991年7月5～6日的江淮梅雨锋暴雨过程进行了数值模拟,在模拟结果可靠的基础上,用模式输出的细网格动力协调资料,根据螺旋度(Helicity)理论分析了这次过程中的暴雨演变以及对流层低层的中尺度低涡及地面气旋发生发展的原因。结果表明,正的旋转风螺旋度大值中心及其演变较好地对应和反映了暴雨中心及造成暴雨的中尺度涡旋的发生位置及演变,较大的螺旋度值是暴雨及低层中尺度低涡和地面气旋系统发生发展的机制之一;螺旋度的强度变化对暴雨发生有一定的指示意义。

关键词:MM4模式;旋转风螺旋度;暴雨

Abstract:

The MM4 model is used to simulate the torrential rain associated with Mei-Yu front on 5~6 July 1991 in the Changjiang-Huaihe Basin, and the simulation is satisfactory. Based on the dynamical trade-off reliable outputs with high space-time resolution, the cause of mesoscale cyclogenesis in the lower troposphere and the ground surface is investigated in terms of helicity principle. The result shows that there exists close relationship between rotational wind helicity and the torrential rain process. The higher rotational helicity might be one of the mechanisms for rain storm development. The variation of helicity intensity may give a clue to torrential rain occurence.

Key words:MM4 model;rotational wind helicity;torrential rain