Comparative analysis on two severe convective weather events associated with northeast cold vortex in Henan in 2015

Based on the conventionally observed data, NCEP 1°×1° 6 hourly reanalyzed data, intensive weather station data, satellite cloud images and radar data, the weather systems, their environmental conditions and mesoscale characteristics of two severe convective weather events associated with northeast cold vortex in Henan on 6 May ("05.06"called for short) and 30 August ("08.30"called for short) in 2015 were analyzed in detail. The results show that (1) two events occurred in the circulation background of northeast cold vortex. The "05.06"was a mixed convection event that has strong wind and hail with short heavy rainfall caused by dry and cold advections in the high-level. The "08.30"was a moist convection event that was mainly heavy rainfall with local wind caused by the warm and humid air mass and horizontal groove. (2) For the "05.06"event, the abundant moisture in the low-level with certain dynamic lifting and vertical wind shear conditions were conducive to the formation and development of severe weather. Strong cold advection appears in the middle-high levels stacking on the warm advection in the low-level, forming a strong unstable stratification. Strong vertical wind shear located in the middle and low levels, together with a certain power uplift conditions, was conducive to the occurrence and development of hail. The "08.30"event is similar to the convection of the quasi-positive pressure. Weak warm advection uplift together with the upper cold advection formed instability. The weak vertical wind shear and thick wet layer were conducive to short-term heavy rainfall. (3) The two events occurred in an area of high gradient region of temperature and dew point. High temperature and humidity provided unstable energy and high moisture conditions. Surface convergence line was not only the trigger of convective systems, but also the organizer of strong convective weather. Both were interdependent and mutually reinforcing. In "05.06"event, the intersection of cold and warm was clear and the contrast of dry and wet was significant. The instability of cold and warm and the instability of dry and wet together caused the severe convective weather. In the "08.30"event, the convective instability was produced by the vigorous intersection of cold and warm in the high humidity area, and it was mainly heavy rainfall. (4) Two events were generated by the strong developing convective clouds moving from north to south. The correlations between mesoscale rain clusters and TBB high gradient region were significant. From the radar signature point of view, the convective cells had obvious hanging echo, weak echo area and bounded weak echo and so on. There were low-level convergence and high level divergence, middle radial convergence, wind zone, cyclone and other features in the speed field.