基于单站探空资料的不同强度短时强降水预报指标研究

Study of the forecasting index for short-duration heavy rainfall with different intensities based on sounding data at Hangzhou

使用浙江省69个基准站2006—2015年5—9月以及同期杭州城区58个区域自动站小时降水资料,利用Gamma分布计算浙江省短时强降水的累积概率,同时综合其频率分布,揭示杭州市小时降水强度的分布特征。此外,以杭州市区为例,利用探空资料分析不同量级(≥50 mm·h-1、30~<50 mm·h-1、20~<30 mm·h-1、<20 mm·h-1)小时雨强出现的环境指标,并基于核密度估计方法提取预报指标。结果表明:杭州城区出现小于等于10 mm·h-1的降水概率高达98.4%,≥20 mm·h-1的概率仅0.05%;受杭州湾偏东气流影响,杭州市区发生短时强降水频率相对较高,尤其是余杭区的东部和西北山区;自2008年以来杭州市区每年短时强降水日数为18~28 d,其中大于等于50 mm·h-1的短时强降水日所占比例高达10%~20%(除2009年和2012年低于10%外);可用于预报杭州市区短时强降水的最佳环境因子依次为整层可降水量、K指数、最佳抬升指数、沙氏指数、925 h Pa露点温度和强天气威胁指数;在判断杭州市区短时强降水强度上表现最好的环境因子为整层可降水量,其次是850 h Pa垂直速度和925 h Pa散度。

Using hourly rainfall data from69national automatic benchmark stations over Zhejiang Province and58regional automatic weatherstations over the urban area in Hangzhou between May and September from2006to2015,we have calculated the cumulative probability ofshort-duration heavy rainfall in Zhejiang by Gamma distribution function,and integrated their frequency distributions to investigate the characteristicsof hourly rainfall intensity in Hangzhou.In addition,taking Hangzhou urban area as an example,the radiosonde dataset is used toanalyze the environmental indices when hourly rain intensity occurred with different levels(≥50mm·h-1,30-50mm·h-1,20-30mm·h-1andbelow20mm·h-1),from which we extract the forecasting indices based on the kernel density estimation method.The results show that theprobability of less than10mm·h-1precipitation at Hangzhou station is as high as98.4%,and the probability that is equal to or greater than20mm·h-1is only0.05%.Due to the effect of easterly airstream from Hangzhou Bay,the frequency of more than20mm·h-1heavy rainfall is relativelyhigh in Hangzhou urban area,especially in the east part and northwest mountain region of Yuhang district in Hangzhou.The number ofdays of annual short-duration heavy rainfall ranges from18to28d in Hangzhou urban area since2008,of which the percentage of days ofshort-duration heavy rainfall that is equal to or greater than50mm·h-1accounts for10%-20%of the total ones,except being less than10%in2009and2012.The most significant factor that can be used to predict the local short-duration heavy rainfall is atmospheric precipitablewater,followed by K index,best uplift index,showalter index,dew point temperature at925hPa and sweat index in descending order of significance.The best factor in determining of the rainfall intensity in Hangzhou is again atmospheric precipitable water,followed by vertical velocityat850hPa and divergence at925hPa.