Abstract:

Using the data from conventional and automatic weather stations, Doppler radar, satellite and wind-profiler radar as well as the associated NCEP (National Centers for Environmental Prediction) reanalysis , we analyzed the convectie conditions and mesoscale characteristics of a short-time heavy rainfall in the middle Tianshan of Xinjiang province on June 27-28, 2015. The mesoscale diagnostic analysis under the background of the central Asian vortex was carried out to provide a reference for the forecasters. The results indicate that this strong convective weather process is caused by the interaction of the northeast to southwest anticyclonic shear in front of the central Asian vortex and the deep warm-wet flow coming from southwest. The direct impact systems to this process are convective instability, including the dynamic lifting condition, shear line in the lower troposphere, surface mesoscale convergence line and the cyclone type convergence center. The convergence of water vapor at the bottom of the central Asian vortex along west and that in front of the central Asian vortex along southwest attributes a favorable vapor condition to this process. Analysis shows that the abrupt variation of GPS-PWV (Global Position System, Precipitable water vapor) and vertical variation of  wind from wind-profiler radar have a good correspondence to the beginning, strengthening and ending of the precipitation. Satellite IR imagery shows that the short-time strong rainfall occurs at the maximum gradient area of the  brightness temperature of convective clouds and is identified by the low centroid and the high-efficiency precipitation echoes. The precipitation intensity is positively correlated with the height of echo top. This study provides a quantitative index for improving the forecast accuracy of short-time strong rainfall.

Key words: Middle Tianshan, Central Asian vortex, Short-time heavy rainfall, Mesoscale characteristics, Precipitable water vapor, Wind profile, TBB