陆面过程参数化对太湖地区雷暴过程模拟的影响

以2010年8月发生在太湖地区的一次雷暴过程为例,利用WRF模式进行48 h的短期天气模拟,分析两个陆面参数化方案(Noah方案和RUC方案)对雷暴过程模拟的影响。对比模式结果与实况降水以及太湖地区两个站点的近地面要素表明:雷暴过程对陆面参数化方案的选取较为敏感,不同陆面参数化方案可影响雷暴发生的时间、地点及强度,两种方案的降水中心值差达40 mm以上,其中Noah方案所模拟的降水与实况更为接近。通过对两个方案模拟的物理量场的对比分析发现,RUC方案中对流发展滞后于Noah方案2 h;这表明陆面过程对雷暴等中尺度对流过程有显著的反馈作用,不同陆面参数化方案的使用影响雷暴发生的动力和热力作用,并改变雷暴的时空分布特征。陆面过程通过改变地面热通量输送影响边界层结构,使得水平和垂直方向上的风和温度等发生变化并产生辐合辐散,进而影响对流的启动时间和对流发展强度。由于对不同植被的参数化处理的差异,Noah方案对下垫面特征的描述能力优于RUC方案,尤其是对城市下垫面的处理,这也使得之后该方案模拟的雷暴发生时间更加接近于实况且雷暴过程更加强烈。

Impact of land surface parameterizations on simulation of a thunderstorm over Tai Lake region

A thunderstorm happened in Tai Lake region in August 2010, which is used to test the impact of two different land surface models(Noah and RUC schemes) coupled with the weather research forecasting(WRF) model on simulation of the thunderstorm.The short-range weather simulation is performed for 48 h.The simulated results are compared with the observed rainfall, surface temperature and wind speed at Yixing and Wuxian stations.Results show that Noah scheme has a fairly better performance than RUC scheme, and the simulated thunderstorm is sensitive to the chosen land surface model(LSM).The different LSMs can lead to the differences of location, time and intensity of thunderstorm, and the maximum of daily precipitation difference between the two schemes can be above 40 mm.Comparison of the simulated results shows that the convection development delays for 2 h in RUC experiment relative to Noah experiment, which indicates that the land surface representation has a prominent feedback on the mesoscale convection of thunderstorm.Different land surface models can lead to different thermal and dynamic effects, which influence the development of thunderstorm and result in differences of convection initialization, development and maintenance between the two WRF runs with different LSMs.Due to parameterization difference of vegetation properties for different land use categories in the two land surface models, Noah scheme describes the characteristics of underlying surface reasonably better than RUC scheme, especially the urban land use category, which can improve the ability of WRF run with Noah LSM to simulate the thunderstorm.