Complementary criteria for identifying regions of intense atmospheric turbulence using lower VHF radar
Complementary criteria for identifying regions of intense atmospheric turbulence using lower VHF radar
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DOI：
10.1016/s1364-6826(97)00054-0
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发表时间：
1998-01-01
影响因子：
1.9
通讯作者：
Thomas, L
中科院分区：
文献类型：
--
作者：
Hooper, DA;Thomas, L
使用了对阿伯里斯特威斯(北纬52.4度，西经4.1度)对流层和平流层下部的多波束甚高频雷达和无线电探空仪联合观测的三次活动的数据。它们除了提供Brunt-Vaisala频率omega(B)和梯度理查森数Ri之外，还提供了通常雷达信号参数的高度分布。结果表明，在Ri所确定的包含强烈湍流的区域内，由偏离垂直12度方向的雷达波束所观测到的信号强度并不一定增强，这将仅代表后向散射。此外，信号强度高度分布的扰动与omega(B)(2)分布的扰动有关。在天顶角如此大的情况下，菲涅耳散射对雷达回波的贡献是不可忽视的。结果表明，强湍流区可以通过雷达回波的方向性不敏感、垂直波束谱宽的增大(已对波束展宽效应进行了修正)和Ri值接近或小于？的组合来识别。这种方法突出了强烈湍流层的存在，这些湍流层跟随着平流层下部长周期重力波的下降相锋。(C)1998爱思唯尔科学有限公司。保留所有权利。
Use is made of data from three campaigns of combined multi-beam lower VHF radar and radiosonde observations of the troposphere and lower stratosphere at Aberystwyth (52.4 degrees N, 4.1 degrees W). These provide altitude profiles of the usual radar signal parameters in addition to those of the Brunt-Vaisala frequency, omega(B),, and the gradient Richardson number, Ri. It is shown that the signal strength observed by a radar beam directed 12 degrees off-vertical, which is expected to represent backscatter alone, is not necessarily enhanced within regions identified by Ri as containing intense turbulence. Furthermore, perturbations of the signal strength altitude profiles are associated with those of the omega(B)(2) profile. The possibility that Fresnel scatter contributes to radar returns at such a large zenith angle cannot be discounted. It is shown that regions of intense turbulence can, however, be identified by a combination of an absence of aspect sensitivity of radar returns, an enhancement of vertical beam spectral width, which has been corrected for the effect of beam broadening, and values of Ri close to or less than ?. This method has highlighted the presence of layers of intense turbulence which follow descending phase fronts of long-period gravity waves in the lower stratosphere. (C) 1998 Elsevier Science Ltd. All rights reserved.