Sensitivity Analysis Of Initial Error Of Rainstorm Forecast In Warm Regions Of South China

Through high-resolution Weather Research and Forecasting model(WRF),this paper conducts research and analysis on the warm sector rainstorm and frontal rainstorm in South China.Through the use of different initial field data,the impact of different scale systems on the results of rainstorm and the sensitivity of different initial weather fields to the results of rainstorm forecasts in warm areas are analyzed,revealing the reasons for the triggering of this warm sector rainstorm.Based on the good simulation results and using ensemble forecasts,the temporal and spatial evolution characteristics of frontal rainstorms and warm sector rainstorms are analyzed,and the predictable behaviors of frontal rainstorms and warm sector rainstorms are compared,revealing that it is difficult to accurately predict warm sector rainstorms.The reason for the forecast.The main conclusions of the study are as follows:Compared with the FNL reanalysis data,the lower layer of ECMWF reanalysis data is warmer and wetter,and the radiosonde data is used as the true value ratio,and it is found that the error of the ECMWF data is smaller than the FNL data.Therefore,after using the ECMWF data as the initial field,a result of FNL data is obtained.The comparison of the two pros and cons found that the small differences in the large-scale circulation patterns caused changes in the medium-and small-scale systems and ultimately affectted the forecast results.The medium-scale and small-scale systems had a greater impact on the warm rainstorm.Small differences in the initial field will have a significant impact on the forecast results.For different initial element fields,the forecast result is the most sensitive to the initial water vapor field,and other elements have little influence on the test results.The increase of water vapor advances the trigger time of convection,which is beneficial to the generation of convective monomer.The ground convergence line is the triggering mechanism of the heavy rain in the warm zone.With the strengthening of the ground convergence,the upward movement continues to strengthen,transporting the unstable warm and humid air from the lower layer to the upper layer,which eventually leads to the triggering of convection.The warm sector rainstorm in South China is more sensitive to small initial errors than the frontal rainstorm.In the process of forecasting heavy rain in warm sector,the initial error increases rapidly,while the initial error increases slowly in the process of frontal heavy rain.Frontal rainstorms and warm sector rainstorms are the result of various systems at different scales.The major impact on frontal rainstorms is the smaller-scale or larger-scale convective systems.Heavy rainfall in warm sector are mainly small-scale scales or scale-convective systems.Both warm sector rainstorm and frontal rainstorm have inherent predictability limits.The non-linear characteristics of error growth in the process of warm sector rainstorm forecasting are more obvious,and its inherent predictability is lower than that of frontal rainstorm.By increasing the forecast rate of the large-scale system,the forecast effect of frontal rainstorm can be improved;the rainstorm in the warm sector is mainly affected by the medium and small-scale systems,and it is difficult to improve its forecast accuracy.