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首页> 外文期刊>Weather and forecasting >Midlevel dry intrusions as a factor in tornado outbreaks associated with landfalling tropical cyclones from the Atlantic and Gulf of Mexico
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Midlevel dry intrusions as a factor in tornado outbreaks associated with landfalling tropical cyclones from the Atlantic and Gulf of Mexico

机译：中层干旱入侵是龙卷风爆发的一个因素，与来自大西洋和墨西哥湾的热带气旋登陆有关

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Midlevel dry intrusions have been mentioned as a factor in tornado outbreaks associated with landfalling tropical cyclones for more than three decades, but a systematic analysis of historical outbreak cases with respect to this pattern has been missing. Herein, following an examination of all named tropical cyclone landfalls from the Atlantic and Gulf of Mexico for the period 1960-99, 13 "outbreak'' cases (defined as storms producing 20 or more tornadoes) have been identified with 11 of the cases offering clear evidence of a dry intrusion at midlevels over the outbreak area. The outbreaks all occurred when the favored area for tornadogenesis (the right-front or northeast quadrant of the storm) coincided with a pronounced gradient of relative humidity, with the gradient best reflected at the 700- and/or 500-hPa level(s). Two distinct patterns were identified with respect to the origin of the midlevel dry air involved in these cases: in one, a mass of dry air that impinged on much of the northern or northwestern semicircle of the storm's outer circulation gradually divided into two separate areas (one to the northwest and the other to the northeast of the storm center) as the storm advanced; the other involved ingestion of a lobe of dry air from a reservoir most often located in the eastern semicircle of the storm. The outbreak cases were determined to have a strong diurnal signal detected in the temporal distribution of the tornadoes, as almost two-thirds (65%) of the tornadoes in the 11 "positive'' cases occurred between 1500 and 2400 UTC (daylight hours in the region examined). A review of all tropical cyclone landfall events since 1960 revealed that there are only three cases with clear evidence of a midlevel dry intrusion that were not accompanied by an outbreak as defined herein.
机译：在过去的三十多年中，已经提到中层干侵入是与登陆热带气旋有关的龙卷风暴发的一个因素，但是关于这种模式的历史性暴发病例的系统分析已经缺失。在此，在检查了1960-99年期间从大西洋和墨西哥湾所有命名的热带气旋登陆之后，确定了13个“暴发”案例（定义为产生20个或更多龙卷风的暴风雨），其中提供了11个案例暴发发生的最明显的证据是爆发区域中部的干侵入，所有爆发都发生在龙卷风形成的有利区域（风暴的右前或东北象限）与相对湿度的明显梯度相吻合时，该梯度最好地反映在700和/或500-hPa的水平，在这些情况下，关于中层干燥空气的起源，确定了两种不同的模式：一种是撞击到北部大部分地区的干燥空气，另一部分是随着风暴的进行，风暴的西北半圆的外部循环逐渐分为两个独立的区域（一个区域位于西北部，另一个区域位于风暴中心的东北部）;另一个区域涉及摄入干叶来自最常位于风暴东部半圆的水库的空气。确定暴发病例在龙卷风的时间分布中检测到强烈的昼夜信号，因为11例“阳性”病例中几乎三分之二（65％）的龙卷风发生在1500和2400 UTC（夏令时）之间。对自1960年以来所有热带气旋登陆事件的回顾表明，只有三起明显证据表明中级干地侵入没有伴有本文定义的暴发。

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