第八届青年地学论坛

Based on radar observation and convection-permitting numerical simulation, this work investigates the storm-scale dynamics governing the generation of two episodes of high winds by an unusually long-lived quasi-linear convective system (QLCS) in South China on 21 April 2017. The first episode of high winds occurred at the apex of a bow segment embedded in the southern QLCS, due to the downward transport of high momentum by the descending rear-inflow jet (RIJ) behind the apex. The jet was initially elevated, forming as the thermal contrast between the cold pool and tilted front-to-rear flow induced a midlevel pressure minimum. The descent of the RIJ was initiated by the negative buoyancy of cold pool but was mainly strengthened by hydrometeor loading. The second episode of high winds occurred as the QLCS evolved into a large bow echo and merged with another mesoscale convective system (MCS) at its northern end where a meso-β-scale cyclonic vortex was present in the middle level. During the merger, the line-end vortex experienced a downward development, because of the enhancement of low-level convergence which increased the vertical vorticity through vertical stretching. The high winds were generated by the superposition of ambient flow with the low-level rotational flow of line-end vortex which contributed up to 30%. The findings suggest the complexity in the generation of high winds by QLCSs and highlight the importance of merger which can produce more damaging winds than the well-recognized RIJ at the bow apex.
 

• Two episodes of high winds within a long-lived QLCS in South China were caused by descending RIJ and merger with another MCS respectively.,• The RIJ resulted from the thermal contrast between cold pool and front-to-rear flow and descended due in large p