台风云娜与桑美对鄂东南降雨影响的对比分析

Contrast Analyses of Influence of Tropical Depressions Rananim and Saomai on Precipitation in Southeast Hubei Province

2004年第8号强台风云娜、2006年第8号超强台风桑美均在8月份登陆浙江并偏西行,但它们造成鄂东南降雨却有较大区别。鄂东南出现大雨以上降水的站数和持续时间,云娜台风低压影响期间明显多于桑美台风低压影响期间,桑美影响期间降雨强度大但持续时间短。对比分析发现:云娜活动期间,低压环流和对流云系影响鄂东南时间长、偏东风低空急流强大、地面冷空气活跃;鄂东南区域平均水汽辐合量大、中低层等相当位温线陡立、有利于降雨的动力条件好,且这三者持续时间长;鄂东南区域平均湿螺旋散度低层正的数值大且持续时间长。桑美影响期间鄂东南对流云发展十分旺盛但快速移走,低层正的湿螺旋散度数值不大但发展层次却比较高。

Although STY Rananim and Super TY Saomai all landed in Zhejiang Province and moved westward, the area and duration of heavy rain influenced by tropical depression Rananim at Southeast Hubei Province were larger and longer than those influenced by tropical depression Saomai. When influenced by Saomai, it rained hard but lasted short there. Conventional analyses show that during Rananim period the duration of tropical depression and convective clouds influencing the Southeast Hubei Province was longer, the low level jet stream was stronger, and the cold air at ground surface was active. At the Southeast Hubei Province during Rananim period the averaged water vapor convergence was larger, the iso-equivalent potential temperature lines at low and middle levels were steeper, the dynamic factors were more favorable to rainfall, and the above three factors lasted longer. The averaged positive moisture helix divergence was larger and lasted longer after Rananim depression landed. Influenced by Saomai, convective clouds were strong but moved quickly, and positive moisture helix divergence at low levels was not large but rose to a higher level.