微物理过程参数化方案对辽宁一次暴雪的数值模拟差异分析

Comparative analysis of simulations on a heavy snow event in Liaoning province using different cloud microphysical parameterization schemes

  • 摘要: 利用WRFv3.9.1中尺度数值模式,采用Lin、WSM6、Thompson、WDM6四种微物理过程参数化方案对2007年3月4日辽宁特大暴雪过程进行了数值模拟研究。使用61个国家级气象站降水观测资料,评估了模式对此次降水过程的模拟能力,对比分析了不同微物理过程参数化方案模拟降雪过程中相态变化和水成物空间分布的差异。结果表明:4种微物理过程参数化方案均能模拟出与CloudSat卫星反演反射率分布相接近的结果,其中Thompson方案模拟的回波顶更高,向北伸展的范围也更大,其他3种方案回波顶高均在8 km附近。4种方案对降水落区的模拟略有差异,整体来看WSM6方案对本次降水的极值中心位置,以及不同降水量级的TS评分整体都优于其他3种参数化方案。降水相态模拟与观测的对比分析发现,WSM6、Lin和WDM6三种方案均能够模拟出雨雪分界线不断南压的过程且雨雪分界线位置准确,而Thompson方案对辽宁南部地区雨转雪时间模拟偏晚。从云微物理特征上看,4种方案均能模拟出大气低层存在的雨水粒子,其中WDM6方案模拟的雨水含量明显较其他3种方案更多,Thompson方案模拟出更多的雪粒子和最少的霰粒子,Lin方案霰粒子南北范围广、伸展高度高,WSM6和WDM6两种方案模拟出较少的霰粒子,这两种方案模拟的云冰高度也更低,正是各种水成物空间分布的差异决定了不同微物理过程参数化方案对降水量和降水相态模拟的差异。

     

    Abstract: A heavy snow event that occurred in Liaoning province on 4 March 2007 was simulated using four different microphysical parameterization schemes included in the WRFv3.9.1 model (Lin, WSM6, Thompson, WDM6). The capability of the model for precipitation simulation was evaluated based on observations collected at 61 national weather stations. The precipitation phase and spatial distribution of hydrometeors were compared between simulations using different cloud microphysical parameterization schemes. The result shows that the reflectivity simulated by the four schemes is consistent with the CloudSat satellite observations, the echoes simulated by the Thompson scheme are higher and extend further north than the simulations by the other three schemes, which are all located at around 8 km altitude. The precipitation area is slightly different between simulations by the four schemes, and the simulated rainfall area by all these schemes is located further north than the observations. From the perspective of subjective evaluation and objective skill scores, the WSM6 scheme performs best according to the TS score and the precipitation cell location. The boundary between rain and snow areas and its southward moving are well simulated by the WSM6, Lin and WDM6 schemes, but the transition time from rain to snow simulated by the Thompson scheme is later than observation. All of these schemes can simulate rain drops at lower levels, but the rain water content simulated by the WDM6 is more than that simulated by the other three schemes. More snow and less graupel are found in the result of the Thompson scheme, while the graupels are distributed at higher levels and extend widely in the simulation by the Lin scheme. Both the WSM6 and WDM6 schemes simulate less graupels and simulated cloud ice particles are located in lower levels. Different distributions of hydrometeors simulated by different microphysics schemes lead to different simulations of precipitation and precipitation phase.

     

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