Study on Three-dimensional Wind Fields of Mesoscale Convective Systems in Xinjiang

The dual Doppler radar system constructed by two C-band Doppler radars in Urumqi and Wujiaqu is used to detect convective systems in Xinjiang Uighur Autonomous Region in 2004, it is supported by the project of National Natural Science Foundation of China (NSFC) "Study on Meso-scale Kinetic and Thermodynamic Feature of Precipitation System with Dual Doppler Radar in Xinjiang". It focuses on the three-dimensional wind field retrieved with dual Doppler radar technique in the strong mesoscale convective systems that produces relatively heavy rainfall within the observational network from 22:30 (BT) 7 August to 02:30 8 August 2004, and the three-dimensional wind structure of these systems as well as their evolution processes are analyzed. Moreover, the radar data quality and reliability of the wind retrieval algorithm with dual Doppler radar are also examined.The positions and structures of radar echoes captured by the two radars are well matched, the radial velocities observed by the radars above the radar baseline are mostly the same, the dual Doppler radar technique is reliable and suitable for the observations of mesoscale convective systems. The sensitivity analysis of the interpolation algorithm on wind retrieval framework demonstrates that the influence radius of Cressman interpolation does not play a significant role in determining the wind structures of mesoscale convections. Even though the wind retrieval errors resulted from the radial velocity measurement errors are associated with their relative positions to the radars, however, such type of errors within 1 m/s on redial velocity would not change the major shapes of the mesoscale wind structures.According to the evolutions of these mesoscale systems, the several convective cells develop into convective precipitation band. Some new cells are generated along the left side of the old ones, whose reflectivity vary from 50 to 55 dBz with the maximum 8 km top height, and finally develop as a band-shaped convective cluster (with 90 km length) after 4 hours. The convective band is corresponding with a strong convergence produced by a branch of strong northeasterly wind and a weak westerly wind, and the updraft is just located at the maximum reflectivity center. The different convective cells actually have their independent wind structures respectively, but they would subsequently interact with each other to engender heavy rainfall weathers. Besides, there are limits to the measurements on this type of mesoscale convective systems in the conventional observations, such as radio sounding, whose spatial and temporal resolutions are limited at hundreds kilometers and 12 hours respectively. Consequently, it is not sufficient to determine their dynamic structures, which develop quickly and have relatively short lifecycle. Fortunately, due to the retrieved wind fields of these mesoscale convections with dual Doppler radar observations, it would be easier to analyze their kinetic features and therefore study the initiation and development mechanism of the mesoscale rainfall systems.