边界层参数化方案对一次西北地区沙尘天气过程影响的数值模拟研究

Impact of boundary layer parameterization schemes on the simulation of a dust event over Northwest China

使用耦合化学模块的高分辨率中尺度数值模式WRF-Chem3.4,结合近地层观测资料评估YSU、MYJ、QNSE、MYNN2.5和BouLac共5种边界层参数化方案对2007年3月27日西北地区一次沙尘天气过程模拟效果的影响,结果显示5种边界层参数化方案均可模拟出此次沙尘天气的发展演变过程,其中YSU和BouLac方案模拟出相对较高的地表摩擦速度、10 m风速、2 m温度和地面PM10浓度以及相对较低的2 m相对湿度,从而模拟的地表沙尘天气过程较强,MYJ、QNSE和MYNN2.5方案模拟的地表沙尘天气则相对较弱,这表明不同边界层参数化方案通过摩擦速度的不同模拟效果对沙尘排放通量和PM10浓度的模拟有重要影响,较大的摩擦速度会使起沙参数化方案计算的沙尘排放通量和PM10浓度更高,加之午后近地层的强风、高温和低湿特征对沙尘天气的增强作用,使得BouLac方案模拟的沙尘天气最强,而QNSE方案的模拟结果最弱;利用民勤站观测资料对5种边界层参数化方案模拟结果的统计分析表明,不同方案对民勤站沙尘暴前后有关气象要素的模拟效果存在一定的差异,其中QNSE方案对PM10浓度的模拟效果最好,BouLac方案对10 m风速的模拟效果最好,YSU方案对2 m温度和2 m相对湿度的模拟效果最好,整体而言,YSU方案对民勤站近地层气象要素的模拟有一定的优势,QNSE方案的模拟结果相对最差。

In this study,WRF-Chem(version 3.4)model was used to compare the performance of different Planetary Boundary Layer(PBL)parameterization namely,the YSU(Yonsei University),MYJ(Mellor-Yamada-Janjic),QNSE(Quasi-Normal Scale Elimination),MYNN2.5(Mellor-Yamada-Nakanisfii and Niino 2.5)and BouLac PBL schemes,over the dust event in northwest china on 27 March 2007.Surface observations were used for comparisons and evaluating model performance for meteorological variables.It is shown that simulations with the five PBL schemes can successfully reproduce the evolution of the dust event.The YSU and BouLac schemes produced higher surface friction velocity,10 m wind speed,2 m air temperature and surface PM10 concentration and lower 2-mrelative humidity,thus simulating stronger weather processes than those of the MYJ,QNSE and MYNN2.5 schemes.These results indicate that different boundary layer schemes affect the dust emission flux and PM10 concentration through different simulation effects of friction velocity.The dust emission flux and PM10 concentration tend to increase with higher friction velocity.Therefore,the dust event was enhanced due to the high friction velocity and the characteristics of high temperature as well as lower humidity in nearsurface layer in the afternoon.As a result,the simulated dust event with the BouLac scheme was the strongest while the weakest by the QNSE scheme.Observations from Minqin meteorological station are used to validate the simulated results over Minqin region.Statistical analysis of the five simulations shows that the QNSE scheme simulated better PM10 concentration,the BouLac scheme performs well for 10 m wind speed and the YSU scheme resulted in the best model performance for simulating air temperature and relative humidity at 2 m.Overall,the YSU scheme was concluded as the best PBL scheme for the dust storm and the QNSE scheme was the worst one.