Quantifying the Separation of Enhanced ZDR and KDP Regions in Nonsupercell Tornadic Storms
Quantifying the Separation of Enhanced ZDR and KDP Regions in Nonsupercell Tornadic Storms
复制标题
量化非超单体龙卷风暴中增强型 ZDR 和 KDP 区域的分离
作者：
Scott D. Loeffler;M. Kumjian
与非超级单体风暴相关的龙卷风给预报员带来了独特的挑战。这些龙卷风虽然通常不像超级单体那样猛烈或致命，但在夜间和凉爽季节发生的比例过高，而此时公众更容易受到伤害。此外，与超级单元龙卷风相比，这些非超级单元龙卷风的预警能力明显较低。本研究利用双极化天气监视雷达 1988 多普勒 (WSR-88D) 数据来分析三年半期间重点关注大西洋中部和美国东南部的非超级单体龙卷风暴。在大量案例中发现的一个特征是低水平特定微分相位 KDP 和微分反射率 ZDR 增强区域的分离，这被认为是由于尺寸分类而产生的。本研究采用了一种新方法来定义“分离矢量”，其中包括增强区域之间的距离以及从 KDP 增强区域到 ZDR 增强区域的方向，相对于风暴运动进行测量。虽然不同情况之间存在一些差异，但初步结果表明，增强区域之间的间隔距离分布集中在 3-4 公里左右，并且在龙卷风发生时趋于最大化。分离方向的首选象限位于风暴运动右侧平行和 90° 之间，并且在龙卷风发生时最正交。此外，结果表明，对于给定的分离距离，分离方向从 0° 向 90° 增加与风暴相对螺旋度的增加相关。
Tornadoes associated with nonsupercell storms present unique challenges for forecasters. These tornadic storms, although often not as violent or deadly as supercells, occur disproportionately during the overnight hours and the cool season—times when the public is more vulnerable. Additionally, there is significantly lower warning skill for these nonsupercell tornadoes compared to supercell tornadoes. This study utilizes dual-polarization Weather Surveillance Radar-1988 Doppler (WSR-88D) data to analyze nonsupercell tornadic storms over a three-and-a-half-year period focused on the mid-Atlantic and southeastern United States. A signature found in a large number of cases is the separation of low-level specific differential phase KDP and differential reflectivity ZDR enhancement regions, thought to arise owing to size sorting. This study employs a new method to define the “separation vector,” which comprises the distance separating the enhancement regions and the direction from the KDP enhancement region to the ZDR enhancement region, measured relative to storm motion. While there is some variation between cases, preliminary results show that the distribution of separation distance between the enhancement regions is centered around 3–4 km and tends to maximize around the time of tornadogenesis. A preferred quadrant for separation direction is found between parallel and 90° to the right of storm motion and is most orthogonal near the time of tornadogenesis. Further, it is shown that, for a given separation distance, separation direction increasing from 0° toward 90° is associated with increased storm-relative helicity.