Experimental Research On Doppler Radar Rdadial Velocity And Its Retrieved Wind Fields Assimilation

Doppler-Radar data with high temporal and spatial resolution could supply the resolution gap between models and observations, and many studies have been done on radar data assimilation. With the establishment of Doppler Radar Network in China, how to make a full use of the radar data in NWP to improve the rainstorm forecasting is an urgent task we are facing.A new single Doppler radial velocity retrieval method Extended VAP is described, and quality control method is developed and applied to the retrieved horizontal wind. Comparison with Dual Doppler retrieved wind field show that the quality control methods based on high spatial and temporal resolution could largely improve data quality.Tests with single observation are taken to check the validity of WRF 3DVAR system and the default background error file. Radial velocity simulated from an ideal storm case is assimilated to the system. Results show that WRF 3DVAR system could extract most of the wind information from radial velocity, but could hardly recover any information of mass fields;the system is able to reestablish the storm quite well after some assimilation circles;vertical velocity increments derived from Richardson Equation play an important role in radial velocity assimilation, they could accelerate convections.A JIANG-HUAI rainstorm case is studied in this paper, problems with preprocessing and error estimation of radar radial velocity are discussed. Several assimilation experiments with grided radial velocity data and E-VAP retrieved data are done. Results show that direct insertion of radial velocity could improve the initial wind fields with more small/meso scale information and rationalize the distribution of vertical velocity, and with the aid of wind the distribution of water vapor could be improved;while assimilation with the retrieved wind data is able to increase the small/meso scale information too, but not as good as direct assimilation. Precipitation fields analysis tells that both direct and retrieved data assimilation will improve the rainfall forecasting, but direct assimilation is better than retrieval assimilation, and experiment with 5-6 minutes assimilation window is better that 30minutes window.From the studies accomplished in this paper, the WRF 3DVAR system is verified, and the ability of assimilating radar data is evaluated. Also know that three dimensional variational method is easy to implement, and cheap in computation costs, and what's more experiments in this paper reveal that it has a good prospect in both research and operation. Work presented in this paper is primary, more studies should be done in future.