2008年华南前汛期致洪暴雨特征及其对比分析

A preliminary study of the flood-causing rainstorm during the first rainy season in South China in 2008

着重对2008年华南前汛期持续性致洪暴雨的降水特征及成因进行了天气尺度的研究,并且对比分析了其与20世纪90年代以来华南前汛期洪灾较为严重的几年(1994、1998和2005年)的降水和环流场特征异同,主要得到以下结果:(1)根据影响系统和雨区分布的不同,将2008年华南前汛期降水过程分为4个阶段。第1阶段(5月26—30日)降水中心分布零星,降水局地性明显。第2阶段(6月7—11日)雨区以带状分布为主,带状雨区上还分布了多个强降水中心。第3阶段(6月12-14日)以片状分布为主,而第4阶段(6月15—19日)雨区既有带状分布,也有片状分布。(2)4个阶段中、低空平均环流场分析表明,环流形势的明显差异决定了雨区分布特点的差异。(3)南海季风涌的频繁活动有力地将水汽一次次地向中国南方地区输送,为暴雨提供了充沛的水汽条件。(4)2008年华南前汛期,500hPa上,中国西南部、华北、华南,华东以及低纬度的孟加拉湾地区均是负的位势高度场异常。华北、华东地区负的异常、青藏高原东部负的异常均有利于冷空气活动,而低纬孟加拉湾地区负的异常又有利于暖湿气流的输送,冷暖气流的活动均非常有利于中国南方地区持续性强降水的发生。(5)对比2008、2005、1998、1994年和气候态的5月15日6月30日总降水分布发现,2008年总降水中心主要位于两广地区及浙赣皖3省交界地区。而浙赣皖3省交界区域的强降水中心位置明显较气候态偏北,被称为"非典型梅雨",而这也是2008年明显不同于另外3年的一个降水分布特点,此外,分析发现,2008年华南前汛期降水强度明显强于另3年。(6)对比4年的500hPa环流及异常场表明,2008年的环流形势相对于另3年要更有利于冷暖空气在中国南方地区交汇,因此,有利于2008年的降水强度大于另外3年。(7)对比4年的850hPa风场异常场分布表明,2008年低层异常风场的偏南风的向北推进得明显偏北,使得总降水量中心原气候态上位于浙闽赣3省交界区域的降水中心向北推进到浙赣皖交界地区,从而出现了华南暴雨与"非典型梅雨"同时出现的特点。

The characteristics and causes of the flood-causing rainstorm occurred in south China during the first rainy season in 2008 were preliminarily studied in this paper.Additionally,the circulation field of the heavy rainfalls during the first rainy season in 2008 was compared with that of heavy rainfalls occurred in South China during the same period in recent years（such as 1994.1998,2005）. The conclusions were as follows：（1）According to the influencing systems and the distribution of rain area,the flood-causing rainstorm occurred in South China during the first rainy season in 2008 were divided into four stages.The distribution of precipitation centers in the first stage（May 26 to 30）was scattered.During the second stage（June 6 to 11）.the rainfall is in the form of band with several precipitation centers located seperately on the rainband.The rain area of the third stage（June 12 to 14）presented a sheet shape.During the fourth stage,the rain areas were either banded or sheet.（2）The analysis of the averaged circulation field in the middle and lower atmosphere for the four stages indicated that the difference characteristics of circulation field shaped the differences of rain area distribution.（3）The frequent action of the South China Sea monsoon was beneficial to the transportation of moisture vapor to South China,which supplied abundant moisture vapor for heavy rainfalls.（4）During the first rainy season in South China in 2008,there was negative anomaly of geopotential height at 500 hPa in North China.East China,South China and the Bay of Bengal.The negative anomaly in North China.East China and the eastern Tibetan Platean was favorable to cold air activities,but the negative anomaly in the Bay of Bengal was favorable to warm air activities.Both the clod air and the warm air were active during this rainy season,which contributed to the sustainable heavy rainfall in the south part of China.（5）The comparison of the total precipitation from May 15 to June 30 among 2008,2005,1998 and 1994 with the climate state indicated that the total precipitation center of 2008 was located at the junctional zone between the Province of Zhejiang.Jiangxi and Anhui.But this precipitation center was more northward than the climate stale.And the study showed that the total precipitation of 2008 was the highest.（6）The comparison of circulation field at 500 hPa presented that the circulation field of 2008 was more beneficial to the interaction between cold and warm air in the southern part of China than the other years,leading to the strongest heavy rainfalls among the four years.（7）The comparison of anomaly wind field presented that the anomaly south wind component of 2008 covered a more northward area than the other years,leading to the more northward location of the precipitation center.