A Heavy Rain Ensemble Forecasing Research Based On Model Resolution And Physics Perturbations

The constantly optimized of the numerical model for the improvement of ensemble forecast utility is very important. Heavy rain is the result of the weather system interaction on all scales, so it’s feasible to examine the uncertainty of the weather system at finer or coarser detail through model multresolution. In consideration of model resolution and constantly optimized the physical process, as well as adding the initial perturbation to the ensemble forecast system, so as to improve the mesoscale numerical prediction skills, is of great significance to the research.This paper, by using WRF mesosacle numerical prediction model and setting model error as the research object including model resolution and physical process scheme to structure mode disturbance scheme comparing with the foecast effect of initial disturbance scheme and finally achieve the comprehensive disturbance scheme through combining both, is to simulate the process of Jianghuai Valley on July7th-9th of2007, a typical Meiyu Front heavy rain. The following are the main conclusions and results:(1) The ensemble forecast with appropriate model resolutions and physical parameters, to a certain extent, can abate model uncertainty and reflect the multi-scale characteristics of atmosphere. With coarser resolution, the forecasts can response characteristics of large scale of the process of precipitation and provide reliable information for the evolution and forecast of weather process. The overall simulate trend gets close to the control forecast, but rainfall is underweight. While with finer resolution, they more reflect medium and small scale of weather information because the precipitation influenced by the force factors more apparently so as to improve the forecast accuracy of strong rainfall. The most value center is more closed to the truth but there are also increased rainfall center, spread and rainfall is overweight.(2) By circulation field and physical analysis, we can see that the difference of model resolution less influence the distribution of wind and height field but to the range and intensity of rapids center is more. At the same time, it can lead to the pros and cons of rainfall process simulation performance by the vertical structure and thermal differences. With finer resolution, terrain, land surface and other local force factors effect more apparently and lead to the differences between vertical contour lines increased. It is helpful for the improvement of the ensemble forecast effect.(3) Considering the change of sensitive factors in each parameterization scheme and the different resolution, the precipitation forecast effect is obviously improved relative to the control forecast. Grading the forecast results offers advantages of the ensemble forecast compared with single deterministic prediction. With the decrease of volume rate in cumulus parameterization scheme, the cumulus structure diluted.5times is advisable for the adjustments of cumulus radius. The increased of resolution in the WSM6microphysics scheme can improved the scope and center simulation significantly, but the precipitation grades will be too large.(4) To improve ensemble forecast spread for research motivation, in different model resolutions with the BGM method making up the initial perturbed field, the application for Meiyu front heavy rain is a reasonable and meaningful attempt. Comparing the model with the initial perturbation scheme, the latter because of its explicit dynamics can further improve the ensemble spread, so using the integrated scheme has an obviously contribution to the forecast skills improved. The ensemble forecasting system simulated out the Meiyu front heavy rain process properly, providing valuable reference to configuration parameters of heavy rains forecast on Jianghuai region in China.