Though the Kelvin‐Helmholtz instability (KHI) has been extensively observed in the mesosphere, where breaking gravity waves produce the conditions required for instability, little has been done to describe quantitatively this phenomenon in detail in the mesopause and lower thermosphere, which are associated with the long‐lived shears at the base of this statically stable region. Using trimethylaluminum (TMA) released from two sounding rockets launched on 26 January 2018, from Poker Flat Research Range in Alaska, the KHI was observed in great detail above 100 km. Two sets of rocket measurements, made 30 min apart, show strong winds (predominantly meridional and up to 150 ms⁻¹) and large total shears (90 ms⁻¹ km⁻¹). The geomagnetic activity was low in the hours before the launches, confirming that the enhanced shears that triggered the KHI are not a result of the E‐region auroral jets. The four‐dimensional (three‐dimensional plus time) estimation of KHI billow features resulted in a wavelength, eddy diameter, and vertical length scale of 9.8, 5.2, and 3.8 km, respectively, centered at 102‐km altitude. The vertical and horizontal root‐mean‐square velocities measured 29.2 and 42.5 ms⁻¹, respectively. Although the wind structure persisted, the KHI structure changed significantly with time over the interval separating the two launches, being present only in the first launch. The rapid dispersal of the TMA cloud in the instability region was evidence of enhanced turbulent mixing. The analysis of the Reynolds and Froude numbers (R e  = 7.2 × 10³ and F r  = 0.29, respectively) illustrates the presence of turbulence and weak stratification of the flow.

中文翻译：

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静态地磁条件下静态稳定的高纬度中层和较低热层中性剪切不稳定性的原位观测

尽管在中层中已广泛观察到开尔文-亥姆霍兹不稳定性（KHI），在其中破裂的重力波产生了不稳定性所需的条件，但在中绝经期和低层热层中，很少有关于这种现象的定量描述，因此很少有人做在此静态稳定区域底部的长寿命剪切机。使用从2018年1月26日从阿拉斯加的扑克平地研究场发射的两枚探空火箭所释放的三甲基铝（TMA），在100公里以上的地方对KHI进行了详细观察。两套相距30分钟的火箭测量结果显示，强风（主要是子午线，最高150 ms ^-1）和大剪切力（90 ms ^-1  km ^-1）。在发射前的几个小时内，地磁活动很低，这证实触发KHI的增强剪切力不是E区极光射流的结果。对KHI涛动特征的四维（三维加时间）估计结果是，以102 km高度为中心的波长，涡流直径和垂直长度比例分别为9.8、5.2和3.8 km。垂直和水平均方根速度分别为29.2和42.5 ms ^-1， 分别。尽管风结构持续存在，但KHI结构在两次发射的间隔内随时间发生了显着变化，仅在第一次发射中才出现。TMA云在不稳定性区域的快速扩散是湍流混合增强的证据。雷诺数和弗洛德数（分别为R e  = 7.2  ×  10 ³和F r  = 0.29）的分析说明了湍流的存在和流动的弱分层。