Comparison Study Of The Retrieved Wind Fields From Single And Dual-Doppler Radar Data

A project is underway to set up the new generation Doppler weather radar network in China, and five sets of Doppler radar have been put into operation in Shandong province. Therefore, it is necessary to exploit and apply radar products. The retrieved wind fields from single and dual-Doppler radar data is provided with very precise temporal and spatial resolution, but they can not be directly compared with the real wind. The accuracy of retrieved wind fields can not be easily evaluated. So, the comparison analysis of the retrieved wind fields from single and dual-Doppler radar data may help to provide ways for application and improving the method of weather forecast.Wind field retrieval from single-Doppler radar data uses velocity azimuth processing(VAP) technique, and two-dimensional wind fields in different altitudes are retrieved. Wind field retrieval from dual-Doppler radar data uses synthesis technique, and the vertical velocity is obtained by using continuity equation, then the three-dimensional wind fields are retrieved. The retrieved wind fields from single and dual-Doppler radar are compared and analyzed by using the data of the rainstorm and squall line events. The advantage and weakness between two methods are compared, and the critical issues should be paid attention to in application are presented.The comparison of retrieved results between two methods for a rainstorm system in Jinan region on April 17, 2003 shows that: (1) The retrieved wind fields from dual-Doppler radar is more smooth. The retrieved wind fields with EVAP technique is very scattered in some fields. The retrieved wind speed from dual-Doppler radar is smaller than single-Doppler radar. The retrieved wind direction between with two methods is different. (2) The relation of the echo intensity fields corresponding with the wind fields is good. The shear region and middle-scale convergence line of retrieved wind fields corresponds with the high-value region of echo intensity fields.(3)The difference of wind direction and speed between with two methods ismainly around middle-scale convergence line. There the biggest difference of wind direction can extend 60° and the biggest difference of wind speed can extend 9. 0 m ■ s~l. In the other fields, the difference of wind direction is smaller than 30° and the difference of wind speed is -3. 0~3. 0m-s~l.The results of retrieved wind fields from single and dual-Doppler radar for a squall line event in West Shangdon on June 21-22, 2004 indicate that: (l)The retrieved wind fields from dual-Doppler radar is more smooth and the structure of the wind fields is more reasonable . The more wind fields is complex, for example the middle-scale convergence line, the bigger is the difference of the retrieved wind direction and speed between with two methods. The more wind fields is symmetrical, the smaller is the difference of the retrieved wind direction and speed between with two methods. (2) The reason of the difference between wind fields retrieved with two methods is mainly caused by the difference between two methods. The retrieved wind speed form single-Doppler radar is stronger than dual-Doppler radar, sometimes is double as well as dual-Doppler radar. (3) The two-dimensional horizontal wind fields in different altitudes which retrieved with two methods is different, sometimes the difference in different altitudes is very large, sometimes is very small.