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, a pattern consistent with mesovortices along the gust front rather than those at the bow echo apex. The tornadic mesovortex exhibited faster propagation speeds and stronger low-level rotation compared to its 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 the tornadic mesovortex. Hydrometeor identification (HID) analysis further revealed that above the wet-bulb zero (WBZ) level, the tornadic mesovortex contained a higher proportion of hail, whereas below the WBZ, it exhibited a greater concentration of smaller raindrop particles. The Eulerian vorticity budget analysis identified the stretching term as the largest contributor to 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 for improving the forecasting of tornadic and nontornadic mesovortices in QLCSs over Northeast China.

During the winter of 2020–2021, extremely cold air activities broke out over the Arctic, leading to occurrences of multiple Polar Low (PL) events over the Norwegian Sea, which significantly affected the weather in East Asia and North America. In this study, the Polar Weather Research and Forecasting Model (WRF) and the associated three-dimensional variational (3D-Var) data assimilation system are employed to investigate the effects of assimilating clear-sky radiance data from the Microwave Humidity Sounder-II (MWHS-II) onboard the Fengyun-3C (FY-3C) and Fengyun-3D (FY-3D) satellites on two PL cases. Simulation experiments at 9-km resolution with one-way nesting for dynamical downscaling to 3-km resolution over the Norwegian Sea during the forecast period are conducted. The results reveal that assimilating the FY-3D MWHS-II data produces smaller observation minus background (OmB) results in one-month statistical averages, achieving accurate thermal and dynamic analysis variations with lower biases in variational bias correction (VarBC). Direct assimilation of the FY-3D MWHS-II radiance data enhances forecasts of ocean surface winds, pressure, PL tracks, and coastal precipitation along western Norway. Furthermore, it provides stronger 850-hPa relative vorticity, larger differences between the sea surface temperature and 500-hPa temperature (SST – T₅₀₀), and more accurate vertical potential vorticity and static instability, consistent with the observed development of the PL in Case 1. For Case 2, benefits are also observed from assimilating the FY-3D data. However, simultaneous assimilation of both FY-3C and FY-3D data does not demonstrate a superior performance. This investigation highlights the importance of satellite radiance data assimilation in analyzing and forecasting of PL events.

An EF1 tornado occurred in the northern coast of the Bohai under the background of cold vortex on 16 August 2019. Using the Yingkou S-band dual-polarization Doppler weather radar data, surface automatic weather station (AWS) observations at 5 min interval, the Panjin wind profile radar data and ERA5 reanalysis data, the environmental background, the structure and formation of the tornadic storm and the tornadogenesis are studied. The results show that the tornado occurred under the background of a cold vortex at 500 hPa, and it was located in the water vapor conveyor belt on the west side of the residual vortex of typhoon "Lekima". The environmental condition is characterized by weak vertical wind shear and strong low-level thermal instability. The Yingkou dual-polarization radar is located 15 km away from where the tornado originated. The hook echo, the descending reflectivity core (DRC), the weak echo hole (WEH), and the tornadic debris signature (TDS) in mini supercell are detected by the radar. The outflow of the decaying thunderstorm gust front moved westward, while the sea breeze front near Yingkou slowly moved eastward. The two boundary layer convergence lines merged, leading to the forming of γ-mesoscale vortex under the influence of horizontal shear instability. The intersection of outflow boundaries, the large positive ambient buoyancy and the vertical perturbation pressure gradient associated with the low pressure induced by the middle level mesocyclone jointly produced strong updrafts. The collocation of the updrafts and the γ-mesoscale vortex played a critical role for the genesis of misocyclone by strong stretching. The combination of the maximum rotation velocity and the minimum diameter of the misocyclone corresponded to the tornadogenesis, and the separation of the misocyclone and the mesocyclone in the middle level led to the dissipation of the tornado.