摘要
提出一种针对对流不稳定构造具有中尺度运动特征的集合预报扰动初值的新方法———异物理模态法,介绍了异物理模态法产生初值扰动区域和扰动振幅的数学处理方案,即由不同对流参数化方案预报离差获得集合预报初值扰动区域、扰动结构和扰动振幅的数学处理过程。利用美国PSU/NCAR的MM5中尺度模式,对一次典型暴雨进行异物理模态法初值扰动集合预报试验,详细分析了扰动初值的结构和集合预报结果。结果表明,该方法产生的初值扰动场具有合理的中尺度环流结构,可以反映对流敏感区域的对流不稳定的预报不确定性,集合预报结果可以明显改善控制预报。
With the focus on the convective instability in the atmosphere, a new initial perturbation method of ensemble mesoscale heavy rain prediction, namely Different Physical Mode Method （DPMM）, is designed. The approach of DPMM is attempted to generate initial perturbation structure and amplitude and reflects the uncertainty of convection instability by the prediction difference of the different Cumulus Convective Parameterization （CCP） schemes which primarily are associated with the regions. The methodology and mathematic scheme of DPMM to generate initial perturbation structure and amplitude of mesoscale ensemble prediction initial conditions are as follows： Firstly, the prediction differences of moisture flux divergence at 500 hPa at 12-h prediction are employed to generate the normalization initial perturbation mode;secondly, the observation errors of the actual atmosphere are employed to determine the maximum perturbation amplitude of zonal wind u, meridional wind v and temperature T, thirdly, the perturbation of specific humidity q is calculated with temperature T and relative humidity r; finally, by adding the perturbation value and deducting it from the control initial condition to generate the initial perturbation conditions. In the context of non-hydrostatic MM5 version, an ensemble simulation experiment is made on a heavy rain case occurring in Guangdong and Fujian Provinces on 8 June 1998 by using DPMM initial perturbation methods. The resuits show that the DPMM normalized initial perturbation mode is not evenly distributed with reasonable mesoscale circulation structure. The horizontal structure and scale are similar to those of the atmosphere gravity wave mode. The area of maximum perturbation amplitude appears in the warm and humid air belt associated with the southwest low-level jet on the west side of the western Pacific subtropical high, where the heavy rain mainly occurs according to the previous studies. Different initial perturbations can trigger different convective activities with apparent differences of location and strength of precipitation among ensemble members. The ensemble outputs of 24-h accumulated precipitation, inclu- ding the ensemble mean, probability exceeding 50 mm and spread, show that ensemble predictions can obviously improve the controlling prediction by DPMM initial perturbation methods. Both the structures of normalized initial perturbations and ensemble outputs show that DPMM can find the convection-sensitive area and reflect the prediction uncertainty in the sensitive regions of convection instability. In the design of DPMM initial perturbation scheme two problems are worthy to be further studied and discussed. The first problem is that the structure of normalization perturbation mode is related to the selected physical element. What are the effects of different physical elements on it and ensemble prediction？ The second problem is that initial error features have a great impact on the perturbation amplitude of ensemble prediction and they also determine the amplitude of initial error. Observation error is employed in this study to determine the maximum pertur- bation amplitude, but it is still different from initial errors. How to construct a more accurate initial error distribution？ What are the influences of initial error distribution on heavy rain ensemble prediction？ More efforts should be made to study these problems.
出处
《大气科学》
CSCD
北大核心
2005年第5期717-726,共10页
Chinese Journal of Atmospheric Sciences
基金
国家自然科学基金资助项目40475045
科技部社会公益研究专项项目2004DIB3J119
四川省气象局重大项目"数值集合预报技术与业务应用开发
国家十五重点科技攻关项目"中国气象数值预报系统技术创新研究
科技部重点项目"奥运气象保障技术研究"共同资助
关键词
中尺度暴雨
集合预报
初值扰动方法
mesoseale heavy rain, ensemble prediction, initial condition perturbation method
