Abstract:

 Based on conventional meteorological data from automatic weather stations and intensive stations, FY2C TBB data, Doppler radar data, wind profiler radar data, and the NCEP reanalysis data with 1°×1° resolution, the cause of heavy rain by shear line in the Haihe river basin was analyzed. The result shows that the heavy rain occurs under the favorable configuration condition of the low-level shear line and the upper and lower level jets. The differences of the cold air path and the vertical structure lead to the heavy rain falling in the different areas with different intensity. The banded α-mesoscale convective cloud generates and develops along the shear line, and the β-mesoscale MCS (Mesoscale Convective System) develops, moves, combines, strengthens along the band. The MCC (Mesoscale Convective Complex) will generate within the banded convective cloud system if the vortex is formed along the lower shear line. The position of heavy rainfall is located in the front side of the MCS or MCC moving direction and in the area of the maximum gradient of the TBB contour. The water vapor convergence stretches from the ground to high level before the heavy rainfall. The higher the stretching height of water vapor layer is, the stronger the rainfall is. The center of the heavy rain is corresponding to the two large values of water vapor flux convergence zones in the southwest and east areas where the contours are intensive. The VAD (Velocity Azimuth Display) wind profiles and wind profile radar data show that the low-level jet and ultra low-level jet successively appear which makes the rain intensity strengthened again.

Key words:  Low-level shear line, Mesoscale convective system, Temperature brightness (TBB) , Wind profiler radar