The Application Of Spectral Nudging Method In Simulating Heavy Rainfall Process And The Analysis Of Period Characteristics

Spectral nudging method was used in the rolling test to analysis the feasibility in simulating weather process within two weeks firstly, which implied that there is some improvement to some extent. The sensitive experiment of spectral nudging coefficient indicated that even though the modeling result was improved, the degree of improvement lacked significant sensitivity in it. Combined with previous research, the parameter setting of this method suitable for weather process within two weeks was obtained. No other than zonal and meridional wind were processed, with the cut-off wavelength more than 1000 km and one-hour intervals for nudging coefficient(frequency).As a sample, the continuous precipitation processes in south China from 25 January to 5 February in 2008 was simulated. In order to find out the importance of exogenous cycle information introduced by this method, the circulation characteristic on lower level and the column water vapor feature were analyzed from spectrum period perspective, as well as the water vapor channel and its critical area period character. The results showed the distribution and intensity of simulated precipitation in the experiment using spectral nudging method was obviously better than that without this method. In term of region affected frequently by trough and wind shear lines on lower layer, a 2-4 days significant period characteristic of meridional wind was simulated successfully in the spectral nudging experiment, which enhanced the simulating ability of meridional wind field. After analyzing the period features of 24-hours earlier high-related areas of water vapor channel and the simulating domain, it could be noticed that the spectral nudging method may introduce the meridional vapor transporting information east of Indo-China Peninsula into the model, which may improve the simulation of the cycle of the water vapor budget in the precipitation area. It could be an important reason why spectrum nudging method can improve rainfall simulation result in the simulation experiment using spectral nudging method. As to those model variables indirectly affected in the spectrum nudging method, they also had been improved in statistical results during the process of interaction among model variables.All the above results indicated, the model simulation within two weeks could be improved due to adding the exogenous cycle characteristic factors into models integration progress with the spectrum nudging method, which adjust the coordination between model and large scale driving field. This method maybe has a certain practical use value in the numerical forecast model.