海风与热岛耦合对上海强对流天气影响的数值模拟

Numerical Simulation of the Impacts of the Sea-Breeze and the Urban Heat Island on the Severe Convective Event in Shanghai

使用新一代区域中尺度数值天气模式WRF并耦合多层次城市冠层模式(BEP+BEM),采用NCEP GFS 0.25°×0.25°全球模式3 h预报为初始场和边界条件,对2013年9月13日发生在上海地区的午后强对流天气过程进行数值模拟。通过对比耦合了城市冠层模块的试验(Ctrl)和替换城市为农田的试验(Crop),探究城市效应对本次降水过程造成影响的机理。通过分析发现:(1)此次降水主要受天气系统支配,但城市的存在对局地的降水过程有重要的调节作用;(2)城市热岛使得城市地区温度升高,气压降低,有力地增强了海风以及城市地区的上升气流,最终影响局地的降水分布和降水强度;(3)城市热岛效应能够使降水较早的发生,并且降水落区更为集中。

A new-generation Weather research and Forecasting（WRF） model,which coupled with a multi-layer urban canopy model（BEP＋BEM）,was used to simulate an early-afternoon severe convection that occurred in Shanghai on 13 September 2013. Using the daily global forecasting dataset with 0. 25°×0. 25° resolution from the National Centers for Environment Predication Global Forecast System（ NCEP GFS） as the initial field and boundary conditions,two numerical experiments were conducted. The impact of urbanization on this precipitation process was explored by comparing the results from the case（Ctrl） of coupling with the urban canopy module with those from the case（Crop） of replacing city as farmland. The results showed that：（1） The occurrence of precipitation was mainly affected by the large-scale weather system,but the urbanization also played an important role in modulating the local-scale precipitation;（2） With the effect of the urban heat island,the temperature increased and the pressure decreased in urban region,which enhanced the sea breeze and the updraft in urban area.And as a result,it finally influenced the distribution and intensity of the local-scale precipitation;（3） The effect of urban heat island made the precipitation occur earlier and made the distribution of precipitation more concentrating.