边界层方案对一次西南涡背景下局地暴雨过程影响分析北大核心

利用WRF模式对2017年6月9日重庆合川区一次局地暴雨过程开展对流可分辨尺度的模拟试验,比较三种边界层参数化方案对降水模拟的影响。结果表明,不同试验均能模拟出此次降水的主要分布特征,而不同边界层参数化方案能够显著影响降水落区和强度的模拟。MYJ方案对强降水的模拟最好,能较好地模拟出降水触发的时间和位置;其次为BouLac方案,触发时间偏晚约2 h,降水落区与MYJ方案相近;YSU方案模拟的降水分布偏差较大,降水触发的位置和落区偏北。湍流混合强度是造成落区模拟差异的主要原因,通过影响1.5 km高度以下风场分布改变造成此次局地强降水过程的西南涡位置,进而影响到降水的落区。基于YSU方案的湍流混合减弱试验证明了湍流混合强度与降水落区的关系。

Analysis of the influence of planetary boundary layer parameterization schemes on a local heavy rainfall event along southwest vortex

This study examines the performance of the convection-permitting simulations of a local heavy rainfall occurred in Chongqing Hechuan district on June 9, 2017 which use three different PBL schemes. Compare of the gauge-satellite merged precipitation analysis and WRF simulations with different schemes shows that the MYJ and BouLac schemes give better performance than the YSU scheme. The YSU scheme produced the northernmost location bias. The simulation with MYJ scheme produced not only a better rain band location, but also better position and time of the convective initiation. The differences among the schemes are due to differences in vertical turbulent mixing strength. The winds below 1.5 km above ground level that affected by turbulent mixing strength could change the position of the southwest vortex system which is a critical meso-scale system to this heavy rainfall. Sensitivity studies based on the YSU scheme confirm the connection between the strength of turbulent mixing effect and the location of precipitation.