Mesoscale Characteristics of a Local Severe Convective Rainstorm Occurred at the Eastern Foot of Helan Mountains
The mesoscale characteristics of a local short-time severe convective rainstorm that occurred at the eastern foot of Helan Mountains in August Ningxia in 2019 were analyzed based on the data from H8 satellite, Doppler radar, ERA5 hourly reanalysis, automatic weather station and conventional observation data. The results showed that: (1) The southerly jet of 700 hPa that established 6 hours before the rainstorm and strengthened at night not only contributed to high temperature, high humidity, and the enhancement of atmospheric instability and dynamic and thermal uplift mechanisms in the lower layers of the rainstorm area, but also helped mesoscale ground convergence line to trigger the meso-β scale convective system in the eastern slope of Helan Mountains and strengthen it to meso-α scale convective system, leading to the generation and development of the severe convective rainstorm eventually. (2) The rainstorm occurred in the front-left of jet axis of 700 hPa, the high humidity area with water vapor flux ≥6 g?cm-1?s-1?hPa-1 of 700 hPa and specific humidity ≥12 g?kg-1 of 850 hPa, the high energy area with convective available potential energy ≥1500 J?kg-1, the high temperature area with θse ≥346 K of 850 hPa, the vertical upwarding area with centric intensity ≤-1.2 Pa?s-1 of 800 hPa, and the front of cold cloud where the large gradient (G) of cloud top brightness temperature (TBB) occurred. (3) During the strongest rainfall period, the jet axis was closest to the rainstorm area, the TBB ≤-66 ℃, the G ≥27 ℃?km-1, the radar composite reflectivity (Z) ≥65 dBZ, the echo tops (H ) ≥10 km, the vertical integrated liquid water (VIL) ≥11 kg?m-2, and the area of the cold cloud below -52 ℃ was about 1/5 of mesoscale convective complex. (4) The lower TBB was and the higher G and cooling rate (CR) were, the greater intensity of precipitation would be. The minimum TBB, the maximum G, the leap of Z and VIL, and the increase of echo height appeared 10~20 minutes earlier than the maximum rainfall, and the mesoscale ground convergence line appeared 30 minutes earlier than the rainfall.