Using Near-Ground Storm Relative Helicity in Supercell Tornado Forecasting
Using Near-Ground Storm Relative Helicity in Supercell Tornado Forecasting
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DOI：
10.1175/waf-d-19-0115.1
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发表时间：
2019-10-01
影响因子：
2.9
通讯作者：
Jewell, Ryan E.
中科院分区：
文献类型：
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作者：
Coffer, Brice E.;Parker, Matthew D.;Jewell, Ryan E.
本研究探讨了通过利用大气最低几百米（而非更深层）的风暴相对螺旋度（SRH）来改进超级单体龙卷风预报的可能性。这一假设源于越来越多的文献将近地面风廓线与低层中气旋的组织以及龙卷风生成的概率联系起来。本研究进一步探讨了近地面SRH对显著龙卷风参数（STP）技能的影响，STP可能是龙卷风雷暴最常用的环境指标。利用13年期间20194个强烈的、向右移动的超级单体样本，使用预报验证指标对探空导出的参数进行了比较，强调在对龙卷风超级单体有高探测概率的同时尽量减少误报。这种气候学研究表明，环境廓线的运动学成分在区分显著的龙卷风超级单体和强烈的非龙卷风超级单体方面比热力学成分更有效。就目前的定义而言，有效层SRH在STP的各个成分中具有迄今为止最大的预报技能。然而，使用越来越浅的层来计算SRH会提高预报技能。在STP公式中用0 - 500米高度（AGL）的SRH取代有效层SRH，可使正确预测的事件数量增加8%，漏报事件和误报数量减少18%。这些结果提供了有希望的证据，即通过进一步了解控制龙卷风形成过程的环境因素，预报参数仍可得到改进。
This study examines the possibility that supercell tornado forecasts could be improved by utilizing the storm-relative helicity (SRH) in the lowest few hundred meters of the atmosphere (instead of much deeper layers). This hypothesis emerges from a growing body of literature linking the near-ground wind profile to the organization of the low-level mesocyclone and thus the probability of tornadogenesis. This study further addresses the ramifications of near-ground SRH to the skill of the significant tornado parameter (STP), which is probably the most commonly used environmental indicator for tornadic thunderstorms. Using a sample of 20 194 severe, right-moving supercells spanning a 13-yr period, sounding-derived parameters were compared using forecast verification metrics, emphasizing a high probability of detection for tornadic supercells while minimizing false alarms. This climatology reveals that the kinematic components of environmental profiles are more skillful at discriminating significantly tornadic supercells from severe, nontornadic supercells than the thermodynamic components. The effective-layer SRH has by far the greatest forecast skill among the components of the STP, as it is currently defined. However, using progressively shallower layers for the SRH calculation leads to increasing forecast skill. Replacing the effective-layer SRH with the 0-500 m AGL SRH in the formulation of STP increases the number of correctly predicted events by 8% and decreases the number of missed events and false alarms by 18%. These results provide promising evidence that forecast parameters can still be improved through increased understanding of the environmental controls on the processes that govern tornado formation.