高分辨率WRF模式中土壤湿度扰动对短期高温天气模拟影响的个例研究

本文利用WRFV3.6中尺度预报模式就土壤湿度扰动对2003年7月22~23日和29~30日短期高温天气过程的影响进行了高分辨率模拟研究。结果表明:(1)WRF模式地表气温对土壤湿度扰动有较强的敏感性,且随着土壤湿度的增加(减小)而降低(升高)。同时,模式中土壤湿度对地面气温影响的强度对模式分辨率具有较高的依赖性。(2)不同模式分辨率下气温随土壤湿度变化的规律一致;由于更高分辨率的地形资料的应用,提高分辨率可在较大程度上改善模拟效果。(3)不同土壤湿度试验模拟的地表感热、潜热通量可直接影响气温变化;(4)土壤湿度扰动通过间接影响高温发展的近地层各物理过程使得地表气温发生变化。这些过程中,对流(平流)过程在全天表现为增温(冷却)的作用,强度在白天均随土壤湿度的减小而增加。在较干的土壤条件下,非绝热增温在白天的主导地位加强;在夜间,非绝热冷却的强度减弱,且小于占据主导的对流绝热增温的强度。以上结果表明,在模拟和预报高温天气时土壤湿度非常重要,也意味着通过土壤湿度扰动的集合预报方法来改进模式高温模拟预报具有较大的潜力。

Impact of Soil Moisture Perturbation on High Resolution Simulation of Short-Range High Temperature Weather:A WRF Case Study

The Weather Research and Forecasting model version 3. 6(WRFV3. 6) is used to investigate the impact of soil moisture on high-resolution simulation of the short-range high temperature weather occurred during 22-23 and 29-30 July 2003. Experimental results indicate that:(1) the simulated surface air temperature (SAT) SAT is highly sensitive to soil moisture perturbation. SAT increases (decreases) significantly in response to soil moisture decrease (increase). Meanwhile, the influence of soil moisture on SAT strongly depends on model resolution;(2) characteristic changes in SAT in response to soil moisture perturbations are similar in results of experiments at different model resolutions, and the model performance for SAT simulation improves with increased resolution;(3) changes in SAT are directly influenced by simulated sensible and latent heat fluxes in the sensitivity experiments;(4) soil moisture perturbation affects SAT simulation through altering the physical processes important for the development of high temperature weather. Among these processes, the convection (advection) exerts a warming (cooling) effect during the entire day, and the effect becomes weak with increases in soil moisture during the daytime. Under dry soil conditions, the diabatic heating plays a dominant role and its effect intensifies during the daytime;the effect of diabatic cooling weakens and weaker than the adiabatic heating of the convection process during the night-time. The above results show that soil moisture is important in the simulation and prediction of high temperature weather. Thereby it is feasible to improve the model ability of simulating and predicting high temperature using ensemble forecast with soil moisture perturbations.