边界层参数化方案对不同性质降水模拟的影响

Impact of Boundary Layer Parameterization Schemes on Numerical Simulation of Different Property Precipitation

利用MM5模式的4种边界层方案(ETA方案、MRF方案、Blackadar方案、Gayno-Seman方案),对2008年9月22～27日发生在四川盆地先是对流性,后来是稳定性的暴雨过程进行了该4种不同边界层方案的数值模拟比较试验。整体而言,ETA方案对雨带的预报能力较差,但对对流性降水有一定的预报能力;MRF方案对雨带(特别是稳定性降水)的预报能力相对最强;Blackadar方案对后24h强降水最具能力,且对对流性和稳定性降水的预报能力没有太大差别;Gayno-Seman方案对后24 h强降水预报能力较差。边界层对物理量场的影响随时间增大。在预报积分的前10 h以内,各方案的涡度、相对湿度、垂直速度等物理量预报几乎无异;积分10～24 h,它们的量值间出现差异;24 h后,不同方案的预报不仅量值上有差异,甚至变化趋势都不尽相同。高度场受边界层的影响最小,受边界层方案影响最大的是U场,V场受边界层的影响呈高度和时间的分段函数,湿度场受到的影响有明显的时间滞后性特征。对于温度场而言,600 hPa似乎是温度场受边界层影响的一个拐点,边界层影响在通过600 hPa后改变了影响规律。

Using the four boundary layer schemes accompanied with mesoscale model MM5,the comparative experiments are run on a rainstorm process in Sichuan Basin during 22~27 September 2008.As for rainfall prediction,on the whole,each of the four schemes has its own prediction dominance,no one is superior to others on all grades.ETA is inferior in rainbelt prediction,but somewhat superior in location prediction of convective rain;in addition to the best rainbelt prediction,MRF predicts steady rain better than convective one;Blackadar performs better in the later 24 h rainfall prediction,with a equal ability of convective and steady rain prediction;contrarily,Gayno-Seman outstands a little bit in earlier 24 h heavy rain prediction. The impact of PBL on physical field increases with time.Before 10 h,there is little difference among vorticity predictions from the four PBL schemes,and the same to relative humidity,vertical velocity,etc;for 10~24 h,the physics fields from the four schemes have the same variation trend;after 24 h,the differences are not only in the value,but also in the trend.U is the most sensible to PBL scheme among the elements,H,the least;the influence of PBL scheme on V presents a subsection function of height;RH is affected in delayed feature.As for temperature,600 hPa seems to be the inflexion of influence.