两次江淮气旋的云雨特征及其人工播云效果的综合分析

TWO CASE STUDIES OF CHARACTERISTICS OF RAINS AND CLOUDS OVER JIANGHAI CYCLONE AND THE COMPOSITE ANALYSIS OF ARTIFICIAL SEEDING EFFECTIVENESS

用天气学、云物理学、统计计算和数值模拟等方法 ,对 1 997年 5月份影响我省的两次江淮气旋降水系统进行了综合分析研究 ,发现 :( 1 )中低空水汽输送条件较好 ,都形成了大范围较稳定的降水性层状云系 ,出现了连续性降水。两次过程的深厚程度、动力条件有差别 ,云雨的宏微观特征也有所不同 ;( 2 )云中过冷层较厚 ,过冷水含量较高 ,大滴浓度较高 ,众数直径较大 ,有利于人工催化 ;( 3)云层降水粒子的形成 ,在冷层以凝华和淞附增长为主 ,核化和繁生相对较小 ,进入暖层后 ,主要是云滴与雨滴以及雨滴间碰并为主 ;( 4 )用干冰进行了 6架次人工增雨催化作业 ,经综合检验 ,约增雨 1 0 %～ 40 % ;( 5)使用层状云数值模式进行人工催化模拟 ,当加入 50个 /L人工冰核 ,可使地面降水增加 30 %左右。如果过量播撒 (加入50 0个 /L)人工冰核 ,降水反而减少。

The composite analysis on two precipitation processes caused by the Jianghai Cyclone in May 1995 is made by means of synoptic, cloud physical and statistical methods. The results indicate: (1) There were favorable conditions for vapor transportation and extended stable precipitable stratiform clouds and a persistent precipitation occurred. (2) The supercooled layer is thicker; supercooled water and large drop concentrations and the mode diameter are higher, favorable to the artificial seeding. (3) The precipitation particles in the cloud layer are mainly formed in a manner of sublimation and riming in cool layers with less obvious nucleation and reproduce while mainly in a manner of collision and collection of cloud and rain drops in the warm layer. (4) Six artificial seeding operations using dry ice are conducted and the composite appraisal indicates that there is about 10%-40% rain increment. (5) The numerical simulation of artificial seeding indicates that when introducing artificial ice nuclei by 50/L, surface precipitation increases by 30% but the over-seeding of ice nuclei would result in less precipitation.