Atmospheric Stability Measurements at Tropopause Altitudes Using Forward-Scatter CW Radar

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Observations of the Sunset radar located near Boulder, Colorado, reveal order of magnitude enhancements of the signals received on the vertically directed antenna over the signals received nearly simultaneously on the antennas directed off the vertical. These enhancements are caused by Fresnel reflection and Fresnel scattering from thin stable layers. They are most pronounced from stable regions of the atmosphere in the troposphere and stratosphere and especially from the lower stratosphere just above the tropopause. The ability to detect stable layers from enhanced echoes on VHF radars is applied to the determination of the tropopause. It is concluded that the height of the tropopause can be determined within a few hundred meters.

mentioning

confidence: 57%

“…This is the same phenomenon Copyright ¸ 1980 by the American Geophysical Union. reported by Gage et al [ 1973] using bistatic radar. In this paper we present recent observations of the Sunset radar which further document its capability to observe stable layers in the troposphere and lower stratosphere and to detect the tropopause.…”

Section: Two Mechanismsmentioning

confidence: 99%

Observations of stable layers in the troposphere and stratosphere using VHF radar

Green¹,

Gage²

1980

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“…However, if the specular echoes are due to a volume scattering process such as Fresnel scattering, the magnitude of the received echoes would vary greatly with the pulse width. Presumably, the specular echoes reported by Gage et al [1973] arise from the same scattering process. Whereas recent experiments tend to favor the Fresnel scattering mechanisms in relation to Fresnel (partial) reflections to explain the specular echoes observed on VHF radars, further research will be required to determine whether it is possible to distinguish unambiguously between Fresnel scattering and anisotropic turbulence.…”

Section: Summary Discussionmentioning

confidence: 96%

On the scattering and reflection mechanisms contributing to clear air radar echoes from the troposphere, stratosphere, and mesophere

Gage¹,

Balsley²

1980

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146

With the advent of the MST (mesosphere‐stratosphere‐troposphere) radar technique the atmosphere from 0 to 100 km can be observed with a single radar system. Several different mechanisms have been identified as causing the echoes observed by MST radars. Two primary mechanisms are scattering from turbulent irregularities and Fresnel (or partial) reflection from horizontal strata. Two additional mechanisms that apply primarily to the upper mesosphere are meteor scatter and thermal (or incoherent or Thomson) scatter. Below the stratopause the refractive index structure responsible for the echoes arises solely from neutral atmosphere fluctuations; above the stratopause the radar cross section of such fluctuations is enhanced by the presence of free electrons (moreover, in the absence of small‐scale neutral fluctuations the electrons alone can provide the scattered signal). This paper is an attempt to unify the scattering and reflection theories in the light of observational studies.

“…More direct evidence that troposcatter is composed of a turbulent and specular component is contained in the work of Atlas et al [1969] and Gage et al [1973]. Using a bistatic radar, these authors were able to examine the intensity distribu- During the on-line data processing, the radar receiver output was sampled at those time delays from each transmitted pulse which were appropriate to the 16 pre-selected altitudes.…”

Section: Bistatic (Forward-scatter) Radio Propagation Experimentsmentioning

confidence: 99%

“…They concluded that turbulent scatter was primarily responsible for the observed echoes, but that specular reflection may be important at longer wavelengths. Until now the evidence for specular reflection in the neutral atmosphere has been limited almost entirely to bistatic radio observations [Beckmann and Spizzichino, 1963;du Castel, 1966;Atlas et al, 1969;Gage et al, 1973]. Radar backscatter from refractive index irregularities in the clear atmosphere has been studied rather extensively during the past decade [for a review, see Hardy, 1972, or Hardy andKatz, 1969].…”

Section: Introductionmentioning

confidence: 99%

Evidence for specular reflection from monostatic VHF radar observations of the stratosphere

Gage¹,

Green²

1978

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177

The received signal obtained on the vertical antenna of the 40 MHz Sunset radar often reveals an order‐of‐magnitude enhancement over the received signal obtained nearly simultaneously on an antenna pointed 30° from the zenith. The enhancement is most pronounced in regions of the atmosphere which are hydrostatically very stable. The enhanced vertical echoes are consistent with specular or partial reflection from thin stable laminae of radio index of refraction. An order‐of‐magnitude calculation is used to show that the expected reflectivity from a thin stable layer would easily be detected by the radar.