不同边界层参数化方案对一次梅雨锋暴雨过程湍流交换特征模拟的影响

利用WRF模式结合不同的边界层参数化方案，对2007年7月3—5日发生在江淮流域的一次梅雨锋暴雨过程进行多组数值模拟试验。结果发现，边界层方案的选取对于降水的落区和强度模拟会产生较显著的影响；在降水率及地面要素的模拟上，各方案在降水中后期的模拟差异明显大于降水发生阶段；不同边界层方案的选取对于降水时段内的水平风场、垂直运动和假相当位温的垂直分布都产生影响，直接影响降水时空分布的模拟；不同方案都模拟出了在降水发生之后不同于晴空日变化的湍流动能垂直分布，经分析发现与局地较强的垂直风切变和近地面强湍流气团被抬升有关，而浮力项起着耗散作用；各方案的湍流交换特征与湍流动能特征基本吻合，相比于其他方案，MYJ方案在降水区域的湍流动能及湍流交换强度明显偏弱，对热通量的输送也偏弱；GBM方案在边界层内的湍流混合偏弱而在边界层以上湍流混合显著偏强，热通量输送在边界层以上的高度上误差明显，影响了对降水区域气象要素的模拟能力，仍需要进一步改进。 

THE EFFECT OF BOUNDARY LAYER PARAMETERIZATION SCHEMES ON THE SIMULATION OF TURBULENT EXCHANGE PROPERTIES OF A MEI-YU RAINSTORM

Different planetary boundary layer parameterizations in the WRF model are used to simulate a heavy rainfall in Yangtze-Huaihe basin during July 3—5, 2007. The results indicate that the use of different parameterization schemes has impact on the distribution and intensity of the rainstorm. The differences in precipitation rate and surface factors become larger as the rainstorm goes on. The differences in the vertical distribution of horizontal wind fields, vertical velocity and potential pseudo-equivalent temperature caused by the use of different schemes, have direct effect on the simulation of the rainstorm. The vertical distribution of turbulent kinetic energy (TKE) different from the clear state is simulated well by all schemes, with positive effect from wind shear and TKE transport and negative from buoyancy. The characteristics of turbulent exchange simulated by different schemes correspond well to those of TKE. Compared with other schemes, MYJ simulated weaker TKE development and turbulent exchange, and weaker vertical transport of heat fluxes. GBM predicted weaker exchange within the boundary layer, and much larger exchange coefficients above PBL. The vertical transport of heat flux at higher levels simulated by GBM showed obvious errors and influenced the simulation of meteorological elements in the precipitation area. Thus, further improvement is still needed. As to this case, the MYNN Level-3 scheme performs the best simulation.