Investigating the impact of atmospheric stability on thunderstorm outflow winds and turbulence
Investigating the impact of atmospheric stability on thunderstorm outflow winds and turbulence
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DOI：
10.5194/wes-3-203-2018
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发表时间：
2017-10
期刊：
影响因子：
1.5
通讯作者：
P. Hawbecker;S. Basu;L. Manuel
中科院分区：
文献类型：
--
作者：
P. Hawbecker;S. Basu;L. Manuel
摘要。本文模拟了在夜间过渡（ET）期间不同时间初始化的下暴事件，以确定环境稳定性对下暴风流出的影响。采用高分辨率的伪谱大涡模拟模式进行了模拟，以捕捉降暴风的大尺度流动和湍流特征。首先，对ET进行模拟，为后续的降暴模拟生成真实的初始条件和边界条件。在ET的每小时，从ET的模拟中单独初始化一个下暴模拟集合，其中模式域中的一个升高的冷却源产生负浮力空气来模拟下暴的形成。模拟结果表明，虽然稳定状态发生变化，但峰值风速的集合平均值保持相当稳定（在35 ~ 38 m s−1之间），并且在每次模拟的最低模式水平上发生。然而，随着稳定性的增加以及这些最强风持续时间的增加，最大流出风的强度略有增加，传播范围略有减少。这似乎是由于低层逆温增强了环涡的维持，增加了环境切变，以及在稳定情况下缺乏湍流。相干湍流动能和小波谱分析通常显示对流情况下能量增加，并且随着下暴经过，能量在所有尺度上都增加。
Abstract. Downburst events initialized at various hours during the evening transition (ET) period are simulated to determine the effects of ambient stability on the outflow of downburst winds. The simulations are performed using a pseudo-spectral large eddy simulation model at high resolution to capture both the large-scale flow and turbulence characteristics of downburst winds. First, a simulation of the ET is performed to generate realistic initial and boundary conditions for the subsequent downburst simulations. At each hour in the ET, an ensemble of downburst simulations is initialized separately from the ET simulation in which an elevated cooling source within the model domain generates negatively buoyant air to mimic downburst formation. The simulations show that while the stability regime changes, the ensemble mean of the peak wind speed remains fairly constant (between 35 and 38 m s −1 ) and occurs at the lowest model level for each simulation. However, there is a slight increase in intensity and decrease in the spread of the maximum outflow winds as stability increases as well as an increase in the duration over which these strongest winds persist. This appears to be due to the enhanced maintenance of the ring vortex that results from the low-level temperature inversion, increased ambient shear, and a lack of turbulence within the stable cases. Coherent turbulent kinetic energy and wavelet spectral analysis generally show increased energy in the convective cases and that energy increases across all scales as the downburst passes.