Analysis of environmental condition and mesoscale characteristics for a heavy rainstorm event in Spring in northeast Henan

Using conventional observations, satellite images, radar data, precipitation data from regional automatic weather stations and the NCEP/NCAR reanalysis with 1°×1° resolution, we have conducted analysis on the precipitation characteristics, environmental conditions and mesoscale features of a rare heavy rainstorm event in northeast Henan on 15 May 2018. The results indicate that (1) the event occurred due to the transport of moisture by large scale southwest jet in west part of the subtropical high, the effect of short-wave trough in the middle troposphere, the strengthening and extending northward of the low-level jet and strong divergence in the upper levels. Such environmental conditions are favorable to the occurrence of heavy rainstorm. The powerful low-level jet provides the abundant water vapor and the potential instability for the formation of heavy rainstorm. The triggering of low-level shear line, the diffusion of weak cold air and the lifting of surface mesoscale convergence line are the dynamic mechanism for this heavy rainstorm event. (2) The occurrence of this heavy rainstorm event is mainly characterized in the environment field by sufficient transport and strong convergence of water vapor in the ultra-low level, abnormally high convective unstable energy and extremely unstable atmospheric stratification. (3) The heavy precipitation of this event is mainly caused by the two β-mesoscale convection systems, while the newborn and continuance or the migration of convective cloud clusters over the rainstorm area is an important reason for the long-term maintenance of severe precipitation. (4) Radar observations show that the γ-mesoscale echo cells are continuously generated in the large temperature gradient area in front of the convective cloud clusters in Northern Henan under the extremely strong convective instability, which strengthens when moving eastward and develop strongly to form line-or belt-type convective multi-cell storms over Northeast Henan. The local heavy rainstorm in northeast Henan is due to the direct effect of the"train effect" formed by the obvious local strong echoes