Model Perturbation Scheme Research For Storm-scale Ensemble Forecast System

Ensemble forecasting is an effective way to provide probabilistic weather prediction and estimate the forecasting uncertainties. Developing reasonable storm-scale ensemble forecasting system has become the current international research hotspot. Based on WRF, firstly, the stochastic physical tendency perturbation scheme (SPPT) is introduced into the storm-scale ensemble forecasting system. The optimal SPPT scheme parameters suitable for this experimental study are obtained. Precipitation characteristics are simulated through. Secondly, a new combined perturbation scheme (SPMP) is proposed. The simulation performance and perturbation propagation of the three model perturbation schemes, respectively MP,SPPT and SPMP,are analyzed. The main conclusions are as follows:(1) The choice of SPPT space-time parameters is related to the large-scale information, the activeness of small and medium-scale system and the space-time resolution of the model. The selection of SPPT amplitude can be as big as possible in a certain range. Space-time scales are 6h and 100km, and amplitude is 0.525 in the study of this case. SPPT can improve the simulation performance of rainfall significantly in the local area, though there are some limitations to the accurate simulation of the precipitation area.(2) SPPT scheme does well on the lower layer and the ground, especially the surface water vapor field. It is mainly related to the middle and late integral time.The SPMP scheme is more significant in the middle and high layers, and more reliable to the wind and temperature field of the whole integration period at all levels.The SPMP scheme can effectively compensate for the shortcomings in the MP and SPPT schemes, and perform best in the short-term heavy rainfall forecast.(3) SPMP are controlled by MP in the horizontal; while in the vertical direction,SPMP is affected by SPPT in the lower level and at high levels is dominated by MP during the late integration time. From the perturbation energy analysis, the energy of the small scale energy of the scheme is saturated first, and tends to spread to the large scale as time goes by. The perturbation energy of SPPT propagates faster than that of multi-physics and mixed disturbance. The SPMP can effectively compensate the energy dissipation of the other two schemes on different scales.