First observations of Kelvin‐Helmholtz billows in an upper level jet stream using VHF frequency domain interferometry
First observations of Kelvin‐Helmholtz billows in an upper level jet stream using VHF frequency domain interferometry
复制标题
使用 VHF 频域干涉仪首次观测上层急流中的开尔文-亥姆霍兹波涛
DOI：
10.1029/97rs00088
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发表时间：
1997
期刊：
影响因子：
1.6
通讯作者：
G. Schmidt
中科院分区：
文献类型：
--
作者：
P. Chilson;A. Muschinski;G. Schmidt
在本文中，我们报告了使用VHF频域干涉测量法（FDI）对对流层上部Kelvin-Helmholtz浪的第一次高分辨率观测。这些测量是使用位于德国哈尔茨山脉的探测系统甚高频雷达进行的，雷达工作频率为53.25和53.75兆赫。通过FDI技术的应用，已经可以跟踪薄散射层的高度，精度为几十米，时间分辨率为13秒。利用FDI技术，我们发现了几个与风切变大值相一致的区域的开尔文-亥姆霍兹不稳定性（KHI）的例子。一个特别好的例子是详细介绍。KHI发生在9.1公里高度的喷流轴线下方。它在8-10公里高度范围内的垂直速度场产生振荡。振荡有一个90秒的本地周期，并持续超过10分钟的时间间隔。在KHI的时间和高度的水平风的大小的基础上，巨浪列车的水平范围约为27公里，而个人巨浪的水平长度约为4.0公里。在雷达信号功率、FDI导出的层高度以及两个频率下接收到的雷达信号之间的相干性方面也观察到了90 s振荡。使用FDI数据，我们能够识别位于列车内的单个巨浪，并观察到它们的最大波峰到波谷幅度在220到230米之间。这低于实验期间使用的300米的传统雷达分辨率。
In this paper we report the first high‐resolution observations of upper tropospheric Kelvin‐Helmholtz billows using VHF frequency domain interferometry (FDI). The measurements were made using the sounding system VHF radar located in the German Harz Mountains operating at the frequencies of 53.25 and 53.75 MHz. Through an application of the FDI technique it has been possible to track the altitude of thin scattering layers with an accuracy of a few tens of meters and a temporal resolution of 13 s. Taking advantage of the FDI technique, we found several examples of Kelvin‐Helmholtz instability (KHI) in regions coinciding with large values of wind shear. One particularly good example is presented in detail. The KHI occurred just below the axis of the jet at an altitude of 9.1 km. It produced oscillations in the vertical velocity field in the altitude range of 8–10 km. The oscillations had a local period of 90 s and persisted over a time interval of 10 min. On the basis of the magnitude of the horizontal wind at the time and height of the KHI, the billow train had a horizontal extent of about 27 km, while the horizontal length of the individual billow amounted to about 4.0 km. The 90‐s oscillations were also observed in the radar signal power, the FDI‐derived layer height, and the coherence between the received radar signals for the two frequencies. Using the FDI data, we were able to identify the individual billows located within the train and observe their maximum crest‐to‐trough amplitudes to be between 220 and 230 m. This was less than the conventional radar resolution of 300 m used during the experiment.