WSM6云微物理方案对华北地区一次降雪预报偏强的原因分析  

Study on the Reason for Overestimation of a Snowfall Case by WSM6 Cloud Microphysical Scheme over North China

作　　者：马占山 刘奇俊[1,2] 孙健 孔期[1] 李喆 沈学顺[1,2] 赵传峰 代刊 陶法[4] MA Zhanshan;LIU Qijun;SUN Jian;KONG Qi;LI Zhe;SHEN Xueshun;ZHAO Chuanfeng;DAI Kan;TAO Fa(National Meteorological Centre,Beijing 100081;Numerical Weather Prediction Centre of CMA,Beijing 100081;College of Global Change and Earth System Science,Beijing Normal University,Beijing 100875;CMA Meteorological Observation Centre,Beijing 100081)

机构地区：[1]国家气象中心,北京100081 [2]中国气象局数值预报中心,北京100081 [3]北京师范大学全球变化与地球系统科学研究院,北京100875 [4]中国气象局气象探测中心,北京100081

出　　处：《气象》2021年第9期1029-1046,共18页Meteorological Monthly

基　　金：国家重点研发计划(2017YFC1501406、2017YFC1502001、2017YFC1501902和2018YFC1505702);国家自然科学基金重大项目(42090032)共同资助。

摘　　要：国家气象中心GRAPES区域业务模式对2019年11月29—30日在华北地区降雪过程的预报出现显著高估现象,针对该模式中采用的WSM6云微物理方案进行了深入分析,并与Liu-Ma云微物理方案以及ERA5再分析数据进行比较,探究其可能存在的原因。主要结论如下:冰晶和雪的沉降是WSM6方案在本次地面降雪形成的最主要贡献,Liu-Ma方案则是以大粒子雪和霰的沉降为主,冰晶产生的贡献较少。WSM6方案严重低估了大气中的液态水含量,冰相粒子构成中以冰晶含量为最多,雪含量次之,这些特征都与ERA5资料和Liu-Ma方案有显著的不同,后两者具有较好的一致性。与Liu-Ma方案相比,WSM6方案在模式低层冰晶含量更高、冰晶平均落速更大,二者共同作用使冰晶沉降在本次降水形成中具有重要贡献;WSM6方案中雪的平均落速大于Liu-Ma方案,这是其雪的柱积分总量小而雪的沉降降水多于Liu-Ma方案的直接原因。在WSM6方案中冰晶的凝华/升华过程在冰相微物理过程中占据主导地位,致使雪和霰的凝华过程以及云水凝结过程都明显不足,这是该方案冰晶偏多、雪偏少、液水明显偏少的主要原因。针对冰晶凝华/升华过程(SVI)的敏感性试验发现,SVI转化率与地面降水呈正相关关系、与液水柱积分总量呈“跷跷板”关系,当降低SVI的转化率,地面降雪将显著减少,而柱积分液水总量则会明显增多。The GRAPES regional operational model in the National Meteorological Centre significantly overestimated the snowfall amount over North China that occurred in 29-30 November 2019.In this paper,the simulated results from the operational WSM6 cloud microphysics scheme are compared with those from Liu-Ma scheme and the ERA5 reanalysis data to investigate the possible reasons.The results show that during this snowfall,the sedimentations of ice crystals and snow were the main contribution in WSM6 scheme,while the precipitation of Liu-Ma scheme was mainly through the sedimentations of snow and graupel,and ice crystals produced less precipitation.The WSM6 scheme evidently underestimated the liquid water content in the atmosphere and the ice crystal content was the largest composition of the ice-phase particles,followed by the snow content.These features were significantly different from the ERA5 data and the Liu-Ma scheme,and the latter two were in good agreement.Compared with the Liu-Ma scheme,the WSM6 scheme had a higher ice crystal content in the lower layer of the model and a larger average ice crystal falling speed,and their combination made ice crystal precipitation become an important contribution to the formation of this snowfall case.The average snow falling speed in the WSM6 scheme was greater than that of Liu-Ma scheme,which was the main reason why the column snow content was small and the precipitation of snow was more than that of the Liu-Ma scheme.In the WSM6 scheme,the deposition/sublimation process of ice crystals dominated the ice-phase microphysical processes so that the sublimation processes of snow and graupel and the condensation process of cloud water were obviously insufficient.This was the main reason for more ice crystals,less snow and cloud water in WSM6 scheme.The sensitivity test for the ice crystal deposition/sublimation process(SVI)revealed that the SVI conversion rate was positively correlated to surface precipitation,and took on a“seesaw”relationship with the column cloud water content

关 键 词：WSM6云微物理方案 Liu-Ma云微物理方案 降雪预报 高估 原因分析 

分 类 号：P456[天文地球—大气科学及气象学] P458