城市阻碍效应对上海局地台风降水落区及强度影响的可能机理研究

Urbanization of Shanghai is most obvious in China, and typhoon is one of important high impact weather systems which affect Shangahi city safty. Till now, fallout region and intensity of local precipitation from typhoon in Shanghai is difficult to provide a precise operational forecasting, whose cause is that its genesis mechanism can not be understood completely. Pointing to the scientific problems to be solved in Shanghai’s operational precdiction for precipitation from typhoon, the study on possbile mechanism of urban barrier effect affacting fallout region and intensity of local precipitation from typhoon in Shanghai has important scientific meanings and actual application values. Based on historical typhoon sample data affecting Shanghai, ERA-Interim reanalysis data, and routine and unconventional dense observational data in Shanghai and surrounding since 2000, along with using research method including census, diagnosis, numerical simulation and sensitive experiment and so on, this project will mainly focus on four contents as follows: 1) The characteristics of fallout region and intensity of local precipitation from typhoon affecting Shanghai are analyzed statistically. 2) The corrresponding relationships of wind direction, wind speed and moistute transport to fallout region and intensity of local precipitation from typhoon affecting Shanghai are revealed. 3) Assemble diagnosis on the basis of multi phyiscal quantities is used to disclose the key dynamic and thermodynamci factors affecting fallout region and intensity of local precipitation from typhoon in Shanghai. 4) Numercial simulation of urban canopy model coupling with WRF model is carried on the basis of typical case, along with sensitive experiments which can disclose urban barrier effect. Above results will be constructive to understand the possbile mechanism of Shanghai urban barrier effect affecting fallout region and intensity of local precipitation from typhoon further in-depth, which are also contributed to support operational forecasting of precipitation from typhoon effcetively.

上海城市化特征显著。台风是影响上海城市安全高影响天气之一。当前上海局地台风降水落区及强度仍难以准确预报，原因在于对其形成机理认识尚未完全清楚。针对上海台风降水业务预报中有待解决的科学问题，开展城市阻碍效应对上海局地台风降水落区及强度影响的可能机理研究具有重要科学意义和实际应用价值。本项目将基于影响上海台风样本、再分析资料、上海多种常规及非常规观测资料，采用统计合成、诊断分析以及数值模拟、敏感性试验研究方法，拟开展四方面研究：1）统计分析上海局地台风降水落区及强度特征，2）揭示风向、风速及湿度传输与上海局地台风降水落区及强度对应关系，3）开展多物理量组合诊断分析揭示影响上海局地台风降水落区及强度关键动、热力因子，4）选取典型个例开展数值模拟及能揭示城市阻碍效应的敏感性试验。以期进一步深入理解和全面认识城市阻碍效应对上海局地台风降水落区及强度影响的可能机理，为实际台风降水业务预报提供有效支撑。

上海城市化特征显著。台风是影响上海城市安全高影响天气之一。当前上海局地台风降水落区及强度仍难以准确预报，原因在于对其形成机理认识尚未完全清楚。针对上海台风降水业务预报中有待解决的科学问题，开展城市阻碍效应对上海局地台风降水落区及强度影响的可能机理研究具有重要科学意义和实际应用价值。项目组4年来基于2000年以来影响上海台风样本、再分析资料、上海多种常规及非常规观测资料，采用统计合成、诊断分析以及典型个例数值模拟、敏感性试验研究方法，开展了四方面研究：（1）统计分析上海局地台风降水落区及强度特征发现，上海城区台风过程雨量强度大于郊区，平均而言，城区较郊区约高20 %。（2）分析台风“菲特”（1323）减弱后的残留云团造成上海强降水发现，地面风向与降水落区有很好对应，地面风速辐合与强降水中心也有较好对应。中心城区及其下风向水汽辐合中心与强降水中心有很好对应。（3）基于“菲特”台风（1323）和“利奇马”台风（1909）开展风场散度、Q 矢量及其分解、水汽通量及其散度等多物理量组合诊断分析发现，风场辐合、Q矢量散度辐合、水汽通量散度辐合及不同天气尺度强迫作用与台风降水落区及强度有很好对应关系，而城市热岛效应较弱且与台风降水落区及强度无对应关系。（4）选取“利奇马”台风（1909）开展数值模拟及能揭示城市阻碍效应的敏感性试验发现，城市化效应改变了上海累计降水的水平分布特征，对降水强度略有增强。抬升城市建筑高度使得地表摩擦动力作用显著增强，有利于增强降水。进一步通过改变建筑物的形态（高度、密度）、规模（水平范围）等进行敏感性试验发现，建筑物产生了动力阻碍作用，导致低层风速削弱，进一步导致垂直风切变增强，使得城市局地降水增加。上述研究成果有助于进一步深入理解和全面认识城市阻碍效应对上海局地台风降水落区及强度影响机理，并可为汛期影响上海台风降水短期气候预测和日常业务预报提供参考。