Frontal Rain and Summer Monsoon Rain During Pre-rainy Season in South China.Part I: Determination of the Division Dates
Frontal Rain and Summer Monsoon Rain During Pre-rainy Season in South China.Part I: Determination of the Division Dates
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发表时间：
2006
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通讯作者：
Liang Jian
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作者：
Liang Jian
前汛期暴雨是造成华南地区洪涝灾害的主要原因，但前汛期暴雨的预报一直是气象工作者面临的一个挑战，对前汛期暴雨的预报在很大程度上取决于对前汛期暴雨特征的认识，一般认为前汛期暴雨是锋面暴雨，但南海夏季风可以入侵华南地区，并在6月左右主导华南地区的降水，由于前汛期降水特征差异很大，因此区分前汛期降水和前汛期锋面降水是很重要的，为了区分前汛期降水和前汛期锋面降水，利用NCEP/NCAR再分析资料，利用中国气候预报中心降水合并分析（CMAP）资料和全国730个地面站资料，分析了2000 - 2010年前汛期锋面降水和季风降水的差异。平均气候条件下的雨季（1971-2000），并提出华南夏季风降水开始的基本判据：100 hPa纬向风由西风向东风转变，东风持续时间长达5天，对流层上部纬向风由西风向东风转变是南海夏季风爆发的一个重要特征，与南亚高压的北移相对应。为了确保华南地区对流层上层稳定以偏东风为主，偏东风必须持续五天以上。随着纬向风场的移动，对流层低层温度和湿度也发生突变，因此，100 hPa纬向风场的移动可以用来判断华南夏季风降水的开始，而对流层低层温度和湿度的变化可以用来验证和修正100 hPa纬向风场移动所确定的华南夏季风降水的开始日期。在平均气候条件下，得出华南夏季风降水开始日为5月24日，通过分析，合成分析的结果表明，所提取的年代能够区分1951 - 2004年期间的对流层特征锋面雨与季风雨的区别。
Heavy rain during pre-rainy season usually causes a flood in South China,but the prediction for the rain during pre-rainy season is still a challenge for meteorologists.To a large degree,the rain prediction depends on understanding of its characteristics.Generally,the rain during pre-rainy season is considered as frontal rain.But,the South China Sea summer monsoon(SCSSM) can invade South China and dominate rain there in June,even early May.Since the characteristics of rain during pre-rainy season are so different,it is important to distinguish SCSSM rain from frontal rain.In order to distinguish them,NCEP/NCAR reanalysis data,the Climate Prediction Center(CPC) Merged Analysis of Precipitation(CMAP) and data of 730 surface stations of China are used to analyze the differences of frontal rain and monsoon rain during pre-rainy season under the mean climatological condition(1971-2000),and the basic criterion of beginning of summer monsoon rain in South China is made as follows: zonal wind at 100 hPa shifts from westerly to easterly and easterly persists for exceedingly five days.An important feature of SSCSM onset is upper tropospheric zonal wind shift from westerly to easterly,corresponding the northward move of South Asia High.To make sure that the upper troposphere over South China is dominated steadily by easterly,easterly wind must persist for over five days. Accompanying the zonal wind shift,lower tropospheric temperature and moisture change abruptly.Therefore,zonal wind shift at 100 hPa can be used to determine the start of summer monsoon rain in South China,and the changes of lower tropospheric temperature and moisture are used to validate and revise the start date determined by zonal wind shift at 100 hPa.By the criterion,beginning date of summer monsoon rain in South China has been derived as 24 May under the mean climatological condition.Through the analyses,the beginning dates of that from 1951 to 2004 are obtained too.The results of composite analysis indicate that the derived dates distinguish tropospheric characters during frontal rain from that during monsoon rain.