Aircraft measurements of asymmetric temperature microstructure causing azimuth variations of VHF radar echo power |
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| Institution: | 1. Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Ho?a 69, 00-681 Warsaw, Poland;2. Institute of Geophysics, Faculty of Physics, University of Warsaw, ul. Pasteura 7, 02-093 Warsaw, Poland;3. Institute of Geophysics, Polish Academy of Sciences, ul. Ksi?cia Janusza 64, 01-452 Warsaw, Poland;4. Institute of Applied Optics, ul. Kamionkowska 18, 03-805 Warsaw, Poland;1. Laboratory of Cloud-Precipitation Physics and Severe Storms, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China;2. Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science & Technology, Nanjing, China;3. Weather Modification Office of Shanxi Province, Taiyuan, China;1. Department of Civil Engineering, University of Bristol, Bristol, UK;2. Institute of Industrial Science, The University of Tokyo, Tokyo, Japan;3. Department of Civil Engineering, Nagasaki University, Nagasaki, Japan |
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| Abstract: | VHF wind-profiling radars often measure a decrease of echo power with zenith angle, which can be explained from in situ measurements of horizontal layering or anisotropy of metre-scale temperature structure in the atmosphere. There can also be an azimuthal variation of echo power, which is increased in an azimuth opposite to the vertical shear vector of horizontal wind. This paper checks if the azimuth variation can also be linked to in situ observations of temperature structure, using aircraft flights in the tropopause region near a VHF radar. At heights where VHF radar measures wind shear and aspect sensitivity, there can be an asymmetry in the probability distribution of horizontal gradient of potential temperature, for horizontal scale of e.g. hundreds of metres. The asymmetry is often of opposite sign for up-shear and down-shear flights, and less when VHF echoes are isotropic instead of aspect sensitive. The range of horizontal scales with asymmetry can be used to distinguish e.g. sheared anisotropic turbulence and Kelvin–Helmholtz instability as causes of azimuthal VHF echo power variations. |
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