Abstract: By using conventional detection data,Doppler weather radar data,FY2E geostationary satellite and the 0.5°×0.5° reanalysis data provided by NCEP/NCAR,the comparison between two hail weather courses occurred in Korla City,Xinjiang,China in 2015 were analyzed in this paper.The results showed that it was a shallow system with shortwave trough on 17^th April 2015 while it was a deep system with vortex circulation on 1^st June 2015.Before the occurrence of the hail,there was strong vertical wind shear and the height from the 0 ℃ layer to the -20 ℃ layer was suitable to have a shallow saturated wet layer between them.Due to the humidifying by the rainfall in the southeastern part of the Tarim Basin,water vapor was transported to the area with the cyclonic flow field and raised in front of mountain.The strong convection was triggered by the shear line between the southeast wind and northeast wind over Korla City and Luntai County.From the satellite image,the rapid development of hail clouds near the shear line was also reflected.The hail appeared near the southeast edge of the cold cloud cover with a cloud top temperature less than -50 ℃,where the cloud clusters merged.The hail system mainly moved along the average wind direction in the middle and lower layers.Both the two hail processes,the echo intensity of the center exceeded 55 dBz and the upwind zone occurred along with the development of the hail.The strong echo broke through the -20 ℃ layer and there was a strong echo with the intensity more than 50 dBz between 0 and -20 ℃ layer.The intensity and the time of duration of the hail on 1^st June were much more than those on 17^th April,especially for the echo overhang and weak echo regions,which was directly related to the strong upwind with long duration.When the center of the strong echo dropped to the lower level and the flow field of the lower layer was divergent,the hail weather tended to end.Under favorable environmental conditions,it was the most prominent feature of the two hails that the water vapor was transported at the edge of the Tarim Basin and cloud clusters combination resulted in hail near the shear line.It could provide useful support for hail warning by comprehensive utilization of the highresolution satellites,weather radar and automatic station data to monitor and judge the development,retainment,movement and extinction of the hail cloud.

Key words: hailstorm, trigger mechanism, Doppler radar characteristics, VWP