WRF模式边界层参数化方案对西南低涡模拟的影响

Effects of planetary boundary layer parameterization schemes in WRF model on southwest vortex simulation

应用中尺度数值模式WRF(V3.3版本)选用4种行星边界层参数化方案(YSU、ACM2、MYJ和NOPBL)对2011年6月16—18日造成强降水的西南低涡过程进行敏感性试验,对比分析不同边界层参数化方案对西南低涡过程模拟的影响。模拟结果表明:4种边界层参数化方案均能较好地模拟出西南低涡以及暴雨带的东移,其中YSU方案对低涡路径、强度及降水的总体模拟效果最好。YSU和ACM2方案,与MYJ和NOPBL方案相比,模拟的低涡中心区域正涡度柱和垂直上升运动较强,达到的垂直高度更高。造成这种差异的主要原因是对边界层上的夹卷效应以及垂直混合作用考虑的不同。不考虑边界层作用的NOPBL方案模拟的地表风速异常偏大,造成地表热通量明显偏强、边界层高度偏高。YSU、ACM2和MYJ 3种方案模拟的边界层高度和热通量的日变化比较一致,夜间基本维持少变,白天变化大,其中MYJ模拟的边界层高度和热通量较大,ACM2模拟的较小。地表风速是造成热量输送以及边界层高度模拟差异的主要因子。

With four different planetary boundary layer （PBL） parameterization schemes （YSU, ACM2, MYJ and NOPBL）, a southwest vortex on June 16-18, 2011 is tested using the Weather Re- search and Forecast （WRF V3.3 version） model and the effect of different schemes on its simulation is preliminarily analyzed. The simulation results show that all the four PBL parameterization schemes can better simulate the eastward shift of rainstorm along with southwest vortex, where the YSU performs best in precipitation, track and intensity of southwest vortex. Compared with the MYJ and NOPBL, the YSU and ACM2 simulate the stronger positive vorticity and higher vertical upward motion in the center of southwest vortex, which are mainly caused by the differences in vertical mixing and entrainment of air a- bove PBL＇s. Taking no PBL effect into account, NOPBL simulates a greater abnormal surface wind speedand leads to heading on the significant larger surface heat flux and PBL height. The YSU, ACM2 and MYJ simulate comparatively consistent diurnal change of the PBL height and heat flux with less variation at night and greater variation in the day. Among these three schemes, the MYJ simulates larger surface heat flux and PBL height, while ACM2 simulates smaller ones. The surface wind speed is the primary fac- tor for the difference of simulated heat transportation and PBL height.