一次低温天气过程的数值模拟与诊断

Numerical Simulation and Diagnosis of a Low Temperature Weather Process

利用WRF模式对2009年1月23～25日出现的覆盖沪宁高速公路的一次低温天气过程进行了数值模拟。结果表明,江苏处于西北气流的风场中,北方冷空气源源不断地输送至此,使江苏大幅度降温;苏南大部分地区存在较强的冷平流,沪宁高速公路沿线均被冷平流控制,温度平流为低温的形成、发展及维持提供了一个相对稳定的热力背景;对流层低层几乎没有垂直运动,绝热冷却项不是造成此次低温天气的主要原因;模拟区域内高低层水汽含量较低,且近地层风速较小,上下层空气热量交换不显著,此形势有利于夜间辐射降温;研究地段内的向下长波辐射较弱,地面吸收的热量少,使江苏维持低温天气。

By using WRF model,a low temperature weather process covering Shanghai-Nanjing expressway from Jan.23th to 25th in 2009 was simulated and diagnostic analysis was made based on the output data from the model.The results showed that： Jiangsu Province was in the wind field of northwest airflow and the northern cold air was continuously transmitted to Jiangsu.As a result,the temperature dropped significantly.There was strong cold advection in the southern part of Jiangsu and the regions along the Shanghai-Nanjing Expressway were controlled by the cold advection.The relatively stable thermal background was provided for the formation,development and maintenance of the low temperature weather by the temperature advection.There was hardly vertical movement in the lower troposphere,so the adiabatic cooling was not the main reason which caused the low temperature weather.The relative humidity was low in the high and low level of the atmosphere in the simulated area.The wind speed at ground surface was small,so the heat exchange between the upper and lower layers of the atmosphere was not significant,which was favorable to radiation cooling at night.The downward long-wave radiation was weak in the simulated area and the ground absorbed less heat,which contributed to the maintenance of the low temperature weather in Jiangsu.