Proximity soundings of thundersnow in the central United States
Proximity soundings of thundersnow in the central United States
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美国中部雷雪近距离探测
DOI：
10.1029/2006jd007061
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发表时间：
2006
期刊：
影响因子：
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通讯作者：
A. E. Becker
中科院分区：
文献类型：
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作者：
P. Market;Angela M. Oravetz;David Gaede;Evan Bookbinder;A. Lupo;C. Melick;Larry L. Smith;R. Thomas;Rachel Redburn;B. Pettegrew;A. E. Becker
1961年至1990年期间有闪电和雷声的雪事件的近距离气球探测显示，与类似的无雷声雪事件相比，雪事件的静态稳定环境更差。当雷雪存在时，在这里所检查的所有雷暴情况中，高空会发现一个不太稳定的环境（在某些情况下会出现垂直对流）；所有这些事件的特征都是它们最不稳定的包裹起源于锋面逆温上方。事实上，本研究只包括温带气旋以北的冷空气事件。具有湖泊效应或地形增强的事件从样品中消除。根据确定间隔的平均温度得出的基本复合数据显示，低层大气接近饱和，整个深度低于0°C，存在锋面逆温，其最不稳定的包裹恰好出现在逆温顶部上方。R. A. Brown（1993）保留特征的复合方法较好地定义了锋面逆温底部和顶部以及最不稳定包裹的高度和温度；这些都是需要保护的特征，这样做会产生一个不太稳定的环境。其他显著特征包括最不稳定的包裹起源于锋面逆温顶部上方约30-50毫巴，以及最不稳定包裹上方约100毫巴的明显干燥。整体探测特征也有利于闪电的存在。最不稳定包裹层的复合温度为- 8.7°C，这允许大量的过冷水进入任何可能形成的上升气流。最不稳定包裹在其起源处的温度也高于电荷反转温度；因此，任何相当深度的对流都会跨越那个高度。此外，−10°C复合层的高度在地面以上2959米，这已经足够高，有利于闪电的产生。然而，两种复合方法均未得到对流有效势能（CAPE），这与以往的研究结果一致。虽然有几个复合构件具有高架层的CAPE特征，但大多数没有，这表明其他过程（例如，对称不稳定性的释放）难以从一次探测中评估，往往在起作用。
[1] Proximity balloon soundings for snow events with lightning and thunder during the period 1961 through 1990 reveal a less statically stable environment than similar nonthundering snow events. When thundersnow is present, a less stable environment (and in some cases subsequent upright convection) is found aloft in all of the thundering cases examined here; all of the events feature their most unstable parcel originating above a frontal inversion. In fact, only events in the cold air north of an extratropical cyclone are included in this study. Events with a lake effect or orographic enhancement are eliminated from the sample. The basic composite derived by averaging temperatures at an established interval reveals a nearly saturated lower atmosphere, below 0°C throughout its depth, with the frontal inversion present and its most unstable parcel occurring just above the top of the inversion. The feature-preserving composite approach of R. A. Brown (1993) better defines the frontal inversion bottom and top as well as the level and temperature of the most unstable parcel; these are the features in need of preservation, and a less statically stable environment emerges by doing so. Other salient features include the most unstable parcel originating some 30–50 mbar above the top of the frontal inversion and significant drying ∼100 mbar above the level of the most unstable parcel. The bulk sounding characteristics also favor the existence of lightning. The composite temperature at the level of the most unstable parcel is −8.7°C, which allows for enhanced amounts of supercooled water to enter any updraft that may form. The temperature of the most unstable parcel at its origin is also warmer than the charge reversal temperature; therefore convection of any appreciable depth will span that level. Moreover, the height of the composited −10°C level is 2959 m above ground level, which previous investigators have shown is sufficiently high to favor lightning production. Yet no convective available potential energy (CAPE) appears with either composite approach, which concurs with previous studies. While several of the composite members feature CAPE for elevated layers, the majority do not, suggesting that other processes (e.g., the release of symmetric instability), which are difficult to assess from a single sounding, tend to be at work.