The Key Mesoscale Systems and Mesoscale Vortices of the Henan Extreme Precipitation in 2021

Based on the Doppler weather radar and surface observations, the key mesoscale systems and features of the rainstorm structure during the period of the extreme precipitation in Henan province on 20 July 2021 are investigated. The results show that a nearly meso-alpha-scale West Henan Low Vortex (WHLV) near the Songshan Mountain, a surface mesoscale front, a horizontal shear convergence line in the lower troposphere and two strong low-level jets (LLJs) were the main mesoscale systems that triggered the extreme precipitation process. Many mesoscale vortices including meso-beta-gamma-scale vortices (i.e., meso-vortices) were found within the WHLV. Hourly precipitation over 50 mm was mostly caused by the storms with meso-vortices. In the heaviest precipitation stage of the Zhengzhou Storm (ZZS), a clear meso-vortex above 2 km AGL was identified with the diameter of 15-20 km and the vorticity of 1.0-2.0 x 10(-3) s(-1), while its lifetime was about 2 h. The low-level ambient airflows converged into the storm from the north, east and south, forming a strong low-level convergence that promoted the development of the storm. Strong convergence and uplift occurred along the east edge of the storm, while the strong easterly LLJ converged with the shallow outflow of the storm. The strongest updraft under 2 km AGL occurred at the northeast end of the storm when a short-lived meso-gamma-scale vortex formed at that area. Both the strong low-level convergence and the merge of the convective cells from the east resulted in the eastward propagation of the ZZS.