Comparative analysis on β-mesoscale convective systems in "7.14" extreme precipitation and "8.02" thunderstorm gale events in Henan

Using conventional meteorological observation data, observations from mesoscale automatic weather stations over Henan, Doppler weather radar data, FY-C/D satellite cloud images and NCEP/NCAR reanalysis data with 1°×1° resolution, we have conducted a comparative analysis of the structures and the causes of β-mesoscale convective systems (M_βCS) during "7.14" extreme precipitation event and " 8.02" thunderstorm gale event in Henan. The results show that the M_βCSs with similar morphological features as detected by satellite in the two events show different severe convective weather characters due to the differences in dynamic, water vapor and thermodynamic instability. M_βCS characterized by extreme precipitation is shown a north-south belt convection system formed in the mixed precipitation region, while M_βCS by thunderstorm gale is shown a west-east bow echo developed in cloud-free region in the radar chart. The former results in heavy rainfall due to the merging of convective clouds, but the latter results in thunderstorm gale due to the γ-mesoscale wind disturbance. Both M_βCSs form in the low-level high energy areas and the mid- and low-level convergence areas (about 100 km wide) where vertical relative vorticity (divergence) presents a "positive-negative (negative-positive)" alternate distribution from bottom to top, and, where secondary circulation develops when the descending motions are on both sides of narrow vertical ascending motion area. "7.14" extreme precipitation event is characterized by a deeper convergence zone, quasi-saturated wet area and vertical ascending motion in the mid- and low-level, and larger precipitable water vapor, stronger warm advection in low-level during the initial convection period and weak cold inflow in boundary layer triggering convection, while "8.02" thunderstorm gale event has stronger condition instability, greater vertical wind shear of 0-2 km height and convergence line in boundary layer which plays an important role of triggering convection.