华南中尺度暴雨数值预报的不确定性与集合预报试验
THE UNCERTAINTY OF MESOSCALE NUMERICAL PREDICTION OF SOUTH CHINA HEAVY RAIN AND THE ENSEMBLE SIMULATIONS
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摘要: 利用非静力MM5模式,分析了不同积云对流参数化方案对华南暖区暴雨数值预报的不确定性影响,进行了中尺度暴雨模式扰动集合预报试验.不同对流参数化方案的对流凝结加热引起不同的局地温度扰动,通过大气内部的热力动力过程,导致垂直速度的差异,进而影响网格尺度和次网格尺度降水时间、地点和强度.后续降水再通过凝结潜热释放形成新的扰动源.不同积云对流参数化方案还可引起扰动源能量传播方式不同,最终使模拟大气的动力和热力结构有差异.针对物理过程的不确定性,使用两种模式扰动方法构造集合预报扰动模式,第一种方法是随机组合不同积云对流参数化方案和边界层方案,第二种方法是扰动Grell积云对流参数化方案中主要参数振幅.集合预报结果表明,第一种方法的集合预报效果优于第二种方法,仅扰动参数振幅值似乎还不足以反映华南暴雨预报的不确定性.单一的确定性预报在暴雨落区和强度方面的可信度不稳定,集合产品能给华南暴雨过程提供更有用价值的指导预报,具有较高的应用价值.Abstract: In the context of non-hydrostatic MMS version we explore the impact of convective parameterization schemes on the uncertainty in mesoscale numerical prediction of South China heavy rain and mesoscale heavy rainfall short-range ensemble simulation by using two kinds of physics perturbation methods through a heavy rain case occurring in 8 June 1998 in Guangdong and Fujian Provinces.The results show the physical process of impacts of convective shcemes on heavy rainfall is that different latent heat of convective condensation produced by different convective schemes can make local temperature perturbation,leading to the differences of local vertical speed by the intrinsic dynamic and thermodynamic processes of atmosphere,and therefore,making difference of the timing,locations and strength of mesh scale and subgrid scale precipitation later.New precipitations become the new source of latent heat and temperature perturbation,which finally makes the dynamic and thermodynamis structures different in the simulations.Two kinds of methods were used to construct different model version stochastically, the first one is by using different convective parameterization and planetary boundary layer schemes,the second is by adjusting different parameters of convective trigger function in Grell scheme.The results indicate that the first ensemble simulations can provide more uncertainty information of location and strength of heavy rainfall and than the second.The single determinate predictions of heavy rain are unstable,physics ensemble predictions can reflect the uncertainty of heavy rain,providing more useful guidance and have higher application value.Physics ensembles suggest that model error should be under consideration in the heavy rainfall ensembles.Although the method of using different parameters in Grell scheme could not produce good results and how to construct the perturbation model or adjust the parameter in one scheme according to the physical meaning of the parameter needs further investigation.A limitation of the current study is the restriction to a single case and more cases will be addressed in the future researches.