Environmental Characteristics Associated with Nighttime Tornadoes
Environmental Characteristics Associated with Nighttime Tornadoes
复制标题
与夜间龙卷风相关的环境特征
DOI：
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
A. Fischer
中科院分区：
文献类型：
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作者：
J. Davies;A. Fischer
夜间龙卷风比白天的龙卷风不太常见，但造成的风险不成比例。虽然已经有一些关于超级单体和龙卷风环境参数的研究，但没有一个专注于与天黑后的龙卷风环境相关的特征。本研究探讨了一个大型数据库的快速更新周期（RUC）分析与龙卷风和nontornadic超级单体风暴探测，比较夜间和白天的环境参数。结果表明，夜间龙卷风的不稳定性较小，但风暴相对螺旋度（SRH）比白天大得多，这主要是由于天气尺度风暴系统前的低空急流在夜间增强所致。在夜间，大的对流抑制（CIN）可能是龙卷风的限制因素，尽管有时会出现非常大的温暖扇形SRH和深切变的例外情况。在地理上，高架混合层（EML），往往蔓延到平原从沙漠地形到西南部通常会导致更大的CIN与夜间龙卷风比在墨西哥湾沿岸国家。这可能是平原地区夜间显著龙卷风发生频率较低的原因之一，通常与更远东部的相应龙卷风相比，CAPE更大。由此产生的更强的CAPE切变组合可能有助于风暴上升气流克服较大的低层稳定性的存在下，EML时，重大龙卷风发生在夜间在平原。由于平原州以东和墨西哥湾沿岸地区普遍缺乏地形驱动的EML，夜间龙卷风更常见，并且往往发生在较小的CAPE和CIN，特别是在强劲的风场和动态早期季节系统产生的切变。
Nighttime tornadoes are less common than tornadoes during daylight, but pose a disproportionate risk. Although there have been a number of studies about supercell and tornado environmental parameters, none have focused on characteristics specifically associated with tornado environments after dark. This study examines a large database of Rapid Update Cycle (RUC) analysis soundings associated with tornadic and nontornadic supercell storms, comparing nighttime and daytime environmental parameters. Results show that significant nighttime tornadoes generally occur with smaller instability but much larger storm-relative helicity (SRH) than during the day, mainly due to nocturnal intensification of the low-level jet ahead of synoptic-scale storm systems. At night, large convective inhibition (CIN) can be a limiting factor for tornadoes, although exceptions sometimes occur with very large warm sector SRH and deep shear. Geographically, the elevated mixed layer (EML) that often spreads into the Plains from desert terrain to the southwest usually results in larger CIN associated with nighttime tornadoes than in the Gulf Coast states. This may be one reason that nighttime significant tornadoes in the Plains are less frequent and typically associated with larger CAPE than corresponding tornadoes farther east. Resulting stronger CAPE-shear combinations may help storm updrafts overcome larger low-level stability from the presence of the EML when significant tornadoes occur at night in the Plains. With the general absence of a topographically driven EML east of the Plains states and near the Gulf Coast, nighttime tornadoes are more common and tend to occur with smaller CAPE and CIN, particularly with strong wind fields and shear generated by dynamic early season systems.