A Comparison of Right-Moving Supercell and Quasi-Linear Convective System Tornadoes in the contiguous United States 2003–2021 Weather and Forecasting

Tornadoes produced by right-moving supercells (RM) and quasi-linear convective systems (QLCS) are compared across the contiguous United States for the period 2003–2021, based on the maximum F/EF-scale rating per hour on a 40-km horizontal grid. The frequency of QLCS tornadoes has increased dramatically since 2003 while the frequency of RM tornadoes has decreased during that same period. Prior work noting that the most common damage rating for QLCS tornadoes at night is EF1 persists in this larger, independent sample. A comparison of WSR-88D radar attributes between RM and QLCS tornadoes shows no appreciable differences between EF0 tornadoes produced by either convective mode. Differences become apparent for EF1–2 tornadoes, where rotational velocity is larger and velocity couplet diameter is smaller for RM tornadoes compared to QLCS tornadoes. The frequency of tornadic debris signatures (TDS) in dual polarization data is also larger for EF1–2 RM tornadoes when controlling for tornadoes sampled relatively close to the radar sites, and during daylight versus overnight. The weaker rotational velocities, broader velocity couplet diameters, and lower frequencies of TDSs both close to the radar and at night for QLCS EF1 tornadoes suggest that a combination of inadequate radar sampling and occasional misclassification of wind damage may be responsible for the irregularities in the historical record of QLCS tornado reports.

本研究以2003-2021年美国本土范围内40千米水平网格上每小时的最大F/EF级龙卷评级为依据，对比了右移超级单体风暴（Right-Moving Supercells, RM）与准线性对流系统（Quasi-Linear Convective Systems, QLCS）所产生的龙卷。2003年以来，准线性对流系统龙卷的发生频率显著上升，而同期右移超级单体风暴龙卷的发生频率则呈下降趋势。此前研究指出，准线性对流系统龙卷在夜间的最常见破坏评级为EF1级，这一结论在本次更大规模的独立样本中依然成立。对两类龙卷的WSR-88D雷达属性进行对比后发现，两种对流类型产生的EF0级龙卷并无显著差异。当龙卷评级为EF1至EF2级时，差异开始显现：与准线性对流系统龙卷相比，右移超级单体风暴龙卷的旋转速度更高，且速度对直径更小。若控制雷达站点附近采样的龙卷数量以及日间/夜间采样时段变量，EF1至EF2级右移超级单体风暴龙卷在双偏振数据中的龙卷碎屑特征（Tornadic Debris Signatures, TDS）检出频率同样更高。准线性对流系统EF1级龙卷表现出更低的旋转速度、更宽的速度对直径，且在雷达站点附近及夜间的龙卷碎屑特征检出频率更低，这表明雷达采样不足与偶发的风灾破坏误分类，可能是准线性对流系统龙卷报告历史记录中存在异常的原因所在。