Zenith-angle dependence of VHF specular reflection echoes in the lower atmosphere

Details Zenith-angle dependence of VHF specular reflection echoes in the lower atmosphere Zenith-angle dependence of VHF specular reflection echoes in the lower atmosphere

May 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997jastp..59..761t&link_type=abstract

Journal of Atmospheric and Terrestrial Physics, v. 59, p. 761-775.

Physics

18

Scientific paper

We studied the characteristics of specular echoes reflected from stratified layers in the troposphere and lower stratosphere. In particular, we observed echoes at antenna-beam zenith angles, θ, from 0° to 28° in steps of 2°. When the radar measurements were averaged over about 30 min, the zenith angle dependence of the echo power normalized by the vertical power, <~(θ), was generally the same for sufficiently intense reflection echoes. That is, the echo power was largest in the vertical direction, decreased to about -10 dB at 6°, and then gradually decreased to a constant level between -15 and -25 dB at θ >= 20°. This constant level is interpreted as the isotropic turbulence scattering level <~i. The width of <~(θ) was significantly broader than expected for specular reflection from a perfectly horizontal layer. In order to explain this broadening, we developed two numerical models that describe statistically the slope of a reflection layer that has been distorted by vertical gravity-wave motions. With realistic gravity-wave spectra, the shape of <~(θ) for θ = 0-6° was successfully explained. However, from 8° to 18° the observed <~(θ) was enhanced by as much as 7 dB over the model. From the observations we showed that all of the reflection echoes, including the enhanced echoes at θ = 8-18°, are probably due to the same process. Then we showed that the discrepancy with the model may be the result of our neglect of the horizontal component of gravity-wave motions, which was done in order to constrain the number of calculations.

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