不同模式扰动方案在风暴尺度集合预报中的对比试验研究

Comparison of different model perturbation schemes on storm-scale ensemble forecast

  • 摘要: 由于适用于中长期集合预报的模式扰动技术在风暴尺度集合预报系统中的影响并不明确,为探究不同模式扰动方案在风暴尺度集合预报中的效果,基于WRF模式设计了3组模式扰动方案:多物理扰动(MP)方案、随机物理倾向扰动(Stochastically Perturbed Parameterization Tendencies,SPPT)方案以及由MP方案与SPPT方案组合构建的一种新混合扰动(SPMP)方案。对2013年7月5—6日发生在江淮流域的一次强对流天气过程进行了数值模拟。结果表明:MP方案在积分前期的降水概率评分较高,对高层大气的扰动效果更为合理;SPPT方案主要作用于积分中后期,对大气低层及近地面的扰动效果最为理想,尤其是对于地面水汽场的模拟;SPMP方案能显著提高大气中高层各预报变量的离散度,降低均方根误差,提升集合成员的可信度,有效弥补降水预报评分在单独使用MP方案和SPPT方案不同积分时段的不足。在扰动水平传播方向上,SPMP方案的扰动形态主要受MP方案主导;垂直方向上,SPMP方案在低层的扰动形态与SPPT方案一致,在高层受MP方案控制。波谱能量分析表明3组方案的扰动能量随积分时间均有向大尺度传播的趋势,SPMP方案能有效补偿两种方案能量在各尺度的耗散。

     

    Abstract: The impact of model perturbation technique that is applied to medium and long-term ensemble forecast is not clear when applied to the storm-scale ensemble forecasting system. In order to explore the possible impacts of this technique on storm-scale ensemble forecasting, three perturbation schemes are designed to study a severe convection weather process in Changjiang-Huaihe River basin from 5-6 July 2013 using the Weather Research and Forecasting (WRF) model. These perturbation schemes include the multi-physics (MP) scheme, the Stochastically Perturbed Parameterization Tendencies (SPPT) scheme and the SPMP scheme. The SPMP scheme is a mixing of MP and SPPT. Results show the precipitation probability score of the MP scheme is better than that of the SPPT in the early period of integration and the effect of MP scheme in the upper atmosphere disturbance is more reasonable. The SPPT scheme mainly affects simulation in the middle and later periods of integration and performs well in the lower atmosphere and over the land, especially for the simulation of surface water vapor field. The SPMP can significantly improve the spread of forecast variables and reduce the root mean square error in the upper troposphere, and thus enhances the credibility of the ensemble members. The use of SPMP scheme can effectively compensate for the shortcomings that occur when only using the MP or SPPT scheme in different integration periods. The propagation of perturbation stream function in the SPMP is mainly dominated by MP in the horizontal direction. In the vertical direction, the pattern of SPMP in the lower layer is consistent with that of SPPT, but it is controlled by MP in the upper layer. The analysis of spectral energy shows the energy has a tendency to propagate from small scale to large scale with increasing integration time. And SPMP can effectively compensate for the energy dissipation shown in the other two schemes in different scales.

     

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