Synoptic-scale and mesoscale controls for tornadogenesis on cold fronts: A generalised measure of tornado risk and identification of synoptic types
Synoptic-scale and mesoscale controls for tornadogenesis on cold fronts: A generalised measure of tornado risk and identification of synoptic types
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冷锋龙卷风发生的天气尺度和中尺度控制：龙卷风风险的通用测量和天气类型的识别
DOI：
10.1002/qj.3898
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发表时间：
2020
影响因子：
8.9
通讯作者：
Clark M
中科院分区：
文献类型：
--
作者：
Clark M
使用 ERA-中期再分析对英国和爱尔兰的 114 次事件（44 次龙卷）进行了样本调查，研究了龙卷风和非龙卷风窄冷锋雨带 (NCFR) 的环境。研究结果为预测这些潜在高影响事件中发生龙卷风的可能性提供了实用工具。在 22 个分析参数中，剪切涡度的大量测量以及锋面冷侧的锋面法向风分量在事件类别之间产生了最佳区分，在龙卷风事件中显示出明显更大的值。龙卷风概率的广义度量 p[TN] 是使用由这些参数定义的二维参数空间内的点分布获得的。识别了通常与龙卷风 NCFR 相关的天气情况，并开发了描述大规模演化的概念模型。大多数事件与沿尾随冷锋（≥54.5%）发展的次级气旋（即锋面波）有关，通常在西向西南的大规模气流内。另一类重要的事件对应于以下情况：强烈的中高层急流条纹在放大的大规模气流模式（上游山脊形成和下游槽延伸）内横穿锋面，通常在西北气流内（27.3％）。在锋面波中，龙卷风发生在波发展的相对早期，并且就在波中心的下方，随着波的放大，p[TN] 迅速增加。在西北气流的情况下，龙卷风沿着边界明确的 NCFR 隆起发生，靠近中高层急流条纹和相关的正位涡异常与锋面相交的地方。对龙卷风事件的高龙卷子集（产生 ≥7 个龙卷风的 NCFR）的分析显示，与额波的关联性更强（72.2% 的病例），这表明影响最大的事件通常与次级气旋发生有关。讨论了已确定的环境参数与 NCFR 和准线性对流系统中候选涡旋生成和龙卷风生成机制的可能相关性。
Environments of tornadic and non‐tornadic narrow cold‐frontal rain bands (NCFRs) are investigated using ERA‐Interim reanalyses for a sample of 114 events over the United Kingdom and Ireland (44 tornadic). The results offer a practical tool for prediction of the likelihood of tornadoes in these potentially high‐impact events. Of 22 analysed parameters, a bulk measure of shear vorticity, and the front‐normal wind component on the cold side of the front, yield the best discrimination between event classes, showing significantly larger values in tornadic events. A generalised measure of tornado probability,p[TN], is obtained using the distribution of points within the two‐dimensional parameter space defined by these parameters. Synoptic situations commonly associated with tornadic NCFRs are identified and conceptual models describing the large‐scale evolution are developed. Most events are associated with developing secondary cyclones (i.e., frontal waves) along trailing cold fronts (≥54.5%), generally within west to southwesterly large‐scale flow. Another significant class of event corresponds to situations where a strong mid‐ to upper‐level jet streak cuts across the front within an amplifying large‐scale flow pattern (upstream ridge building and downstream trough extension), generally within northwesterly flow (27.3%). In frontal waves, tornadoes occurred relatively early in the wave's development and just down‐front of the wave centre, where rapid increases inp[TN] occurred as the wave amplified. In northwesterly flow cases, tornadoes occurred along a well‐defined NCFR bulge close to where the mid‐ to upper‐level jet streak and an associated positive potential‐vorticity anomaly intersected the front. Analysis of a high‐tornadic subset of tornadic events (NCFRs producing ≥7 tornadoes) revealed an even stronger association with frontal waves (72.2% of cases), suggesting that the highest‐impact events are usually associated with secondary cyclogenesis. The possible relevance of identified environmental parameters to candidate vortex‐genesis and tornadogenesis mechanisms within NCFRs and quasi‐linear convective systems is discussed.