基于西南区域中尺度模式系统预报的陡峭地形过渡带降水订正方法

Correction method of precipitation in steep terrain transition zone forecasted based on southwest center WRF ADAS real-time modeling system

基于地形和西南区域中尺度模式系统(southwest center WRF ADAS real-time modeling system,SWCWARMS)20:00(北京时,下同)和08:00起报的逐3 h风场、相对湿度场,计算地形降水估算量并结合SWCWARMS预报降水场构建降水订正方程,进而对2018—2020年汛期6—8月日降水、四川盆地降水过程及四川盆地西部降水过程3类降水进行订正,并仅对川西高原东坡到四川盆地西部的陡峭地形过渡带进行检验评估。结果表明:(1)各量级降水量订正值TS相对于SWCWARMS预报降水量的TS均有不同程度提高,20:00起报的订正效果优于08:00。对于大雨及以上量级均以四川盆地西部降水过程订正效果最佳,20:00起报的12~36 h大雨、暴雨和大暴雨的降水量订正值TS相对提高率分别为19%、25%和37%,且命中率高,空、漏报率明显减小,订正效果较好。(2)降水订正方程对四川盆地西部降水过程类型中的区域性暴雨个例和一般性降水个例均有较好的订正效果,即使是SWCWARMS模式预报的大雨、暴雨和大暴雨预报降水落区与实况差异甚远的个例也有一定订正效果。

Based on topography and forecasted 3-hour wind fields,relative humidity fields initialed from 20:00 BST and 08:00 BST by using the SWCWARMS(southwest center WRF ADAS real-time modeling system),the precipitation correction equation was constructed by calculating the terrain precipitation estimates combined with precipitation fields forecasted by SWCWARMS.The daily precipitation,precipitation processes in Sichuan Basin and in western Sichuan Basin during flood season from June to August during 2018-2020 are corrected,and the precipitation in the steep terrain transition zone from the eastern slope of western Sichuan Plateau to the western Sichuan Basin was tested and evalcated only.The results are as follows:(1) The TS of the precipitation correction value with each magnitude was improved compared with TS of forecasted precipitation by the SWCWARMS.The correction effect of precipitation forecasted initialed from 20:00 BST was better than that initialed from 08:00,and the correction effect of the precipitation processes in western Sichuan Province was the best for heavy rain and above.Compared with the SWCWARMS,the relative improvement rates of TS of corrected value of precipitation with heavy rain,torrential rain and heavy downpour were 19%,25% and 37%,respectively,the hit ratio was higher,the false alarm rate and miss rate were decreased significantly.(2) The correction equations of precipitation had a good correction effect on both torrential rain and general precipitation cases of precipitation processes in western Sichuan Province occurring in the steep terrain transition zone,even for cases of precipitation area predicted by the SWCWARMS was far from the actual situation.