On the Tornadic and Nontornadic Mesovortices within a Quasi-Linear Convective System Observed by Dual-Polarization Radar in Northeast China

Limited observations have resulted in few studies examining mesovortices within quasi-linear convective systems (QLCSs) in China, especially in Northeast China, where the polarimetric signatures of tornadic versus nontornadic vortices remain unclear. This study examined 12 mesovortices (including one that produced a tornado) within a QLCS that occurred on 18 August 2020 over the Liaohe Plain, Northeast China, using conventional observations, reanalysis data, and Doppler weather radar observations. The QLCS was associated with notable conditional instability and moderate-to-strong low-level shear under the influence of a cold vortex. Observed extreme winds, reaching up to 41.5 m s⁻¹, were located north of the rear-inflow jet (RIJ) core, aligning with mesovortices along the gust front rather than those at the bow echo apex. Tornadic mesovortices exhibited faster propagation speeds and stronger low-level rotation compared to their nontornadic counterparts. Notably, dual-polarization radar parameters indicated a marked increase in mid-level specific differential phase (K_DP) and lower average differential reflectivity (Z_DR) for tornadic mesovortices. Hydrometeor identification (HID) analysis further revealed that above the wet-bulb zero (WBZ) level, tornadic mesovortices contained a higher proportion of hail, whereas below the WBZ, they exhibited a greater concentration of smaller raindrop particles. The Eulerian vorticity budget analysis identified the stretching term as the largest contributor to the vortex intensification, especially in its initial stage. The tornadic mesovortex originated as a bookend vortex at the intersection of two QLCS segments, with a transient northern anticyclonic vortex observed in its immediate vicinity during the convective merger process. These findings provide valuable observational context and conceptual models on the structure and evolution of mesovortices within QLCSs, offering guidance on improved forecasting of tornadic and nontornadic mesovortices in QLCSs over Northeast China.