A Retrieval Study Of Two-Dimensional Wind Field From Single-Doppler Radar Data

The new era Doppler Radar network of China is building, and 5 sets of Doppler Radar are installed in Shandong province. So, the study is very necessary to exploit and apply radar productions.In the paper, the EVAP (extended VAP method) method is developed, the procedure is firstly to calculate the radial velocity at attitude with the ascend velocity ignored and descent velocity of particle considered, secondly to retrieve Two-Dimensional Wind Field by VAP method. The error analysis shows: when ascent velocity is 2.0 m-s-1 and elevation is 20 degree, the error doesn't exceed 10 percent It indicates the error of ignoring descent velocity is very little when convection is not very strong.A"K- Neighborhood Frequency" method is used to preprocess original data of Doppler weather radar, and the effect of parameter to the preprocessing result is analysed. The method is modified according to practical need, the main results are: when eliminating isolated point, the result is influenced by the statistical size of area and value of k1. When filling up absence point, there is a maximum number of points filled up by "K- Neighborhood Frequency" method. For the parameter k2, a small value is selected in order to fill up more absence points. However, it is not enough to fill up the absence point only using mid-value of maximum Frequency area, it is better to fill up the absence point also using mid-value of second maximum Frequency area.The test by using model MM5 simulated results shows that, two-dimensional interpolation will produce smaller impact, but three-dimensional interpolation will produce notable effect. The wind error retrieved with VAP method mainly focus on tangential velocity, sometimes the error is very big. In addition, filting the radial velocity can improve the accuracy of tangential velocity retrieved with VAP method.Comparing the wind field retrieved with EVAP and VAP method shows that the VAP method just can use the PPI data of the lowest elevation to retrieve the lower wind field, because the wind is not in the same altitude, it often produce phonily structure, that is the main shortcoming of VAP method. For the EVAP method, the main shortcoming is the range in the low high too small, it is not benefit to realize the whole wind field structure for lower high layer. The advantage is that it can retrieve the two-dimensional wind field in different high layer benefiting to realize the three-dimensional wind field structure of weather system.The rainstorm example of April 17th, 2003 is analysed and the result indicates that comaring to the wind field retrieved by EVAP method and simulated by MM5 model, the first phase the result is very consistent, above 2km there is a meso-scale divergence line ,in the same site the radar echo is higher than 40dbz. Below 2km the meso-scale divergence line is not clear. In the second precipitation phase it is difference between the wind field retrieved by EVAP and simulated by MM5 model.