区域集合预报基于SKEB和多物理过程的混合模式扰动方法研究

Study on a Synthetic Model Perturbation Method Based on SKEB and Multi-Physics for Regional Ensemble Forecast

为了研究随机动能后向散射(stochastic kinetic energy backscatter,SKEB)模式扰动方法在区域集合预报中的应用效果,基于WRF模式构建了集合预报系统,针对SKEB的扰动振幅进行了敏感性试验,以了解SKEB扰动的作用特征;发展了一种多物理过程组合(multi-physics,MPHY)与SKEB相结合的混合模式扰动方法(SKEB-MPHY),并对比了SKEB、MPHY以及SKEB-MPHY的预报效果,以探索区域集合预报的最优模式扰动实现方案。试验结果表明:SKEB方法通过固定的动能耗散率计算出流函数及温度扰动,从而对模式积分产生影响,且耗散率大小与预报离差正相关,垂直结构扰动不利于预报离差的发展。SKEB、MPHY以及SKEB-MPHY方法的对比试验表明,对于高空动力场预报离散度的增长,SKEB方法比MPHY方法占优,而低层温度预报离散度增长,MPHY比SKEB扰动方法占优,混合模式扰动方法的扰动增长能力在三种方案中表现最好。集合预报检验结果表明SKEB-MPHY方法评分优于单独的SKEB和MPHY方法。降水个例分析及降水评分结果表明与单独采用MPHY方法相比,引入SKEB方法可以对大雨预报有所改进。本文研究结果表明SKEB方法及在其基础上建立的混合模式扰动方法具有较好的应用前景。

To investigate the application effect of stochastic kinetic energy backscatter(SKEB) perturbation scheme, a regional ensemble forecast system(REFS) is constructed based on the WRF model. Sensitivity experiments on perturbation amplitude are conducted to find the functional characteristic of SKEB. Additionally, a synthetic model perturbation scheme which combines multi-physics(namely MPHY) and SKEB, called SKEB-MPHY, is developed, and the forecast effects of the three schemes of SKEB, MPHY and SKEB-MPHY are compared and evaluated. The results show that the SKEB scheme can estimate the stream function and temperature perturbation through a constant kinetic dissipation rate, and the exhibited difference of model integration is correlated to the amplitude of the kinetic dissipation rate. Perturbing the vertical structure is not helpful to the difference growth. The comparison results of SKEB, MPHY and SKEB-MPHY schemes indicate that the SKEB has advantage on upper-air wind spread growth compared to MPHY while MPHY has larger spread for low-level temperature than SKEB. The SKEB-MPHY scheme exhibits the best perturbation growth characteristic of the three schemes not only for upper-air variables but also for low-level variables. In addition, the SKEB-MPHY scheme has the most skillful performance of the three schemes in terms of ensemble verifications. Furthermore, compared with single MPHY scheme,applying the SKEB scheme will improve precipitation forecast skill of heavy rain. All the results from this study indicate that the SKEB scheme and the SKEB-based synthetic scheme are promising.