Radar Measurements of Turbulent Eddy Dissipation Rate in the Troposphere: A Comparison of Techniques

Stephen A. Cohn National Center for Atmospheric Research Atmospheric Technology Division, Boulder. Colorado

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Abstract

Two independent radar methods for estimating the turbulent eddy dissipation rate ε are applied to a common dataset, and the results are compared. The first method estimates ε from backscattered power and relies on the effects of turbulent mixing of atmospheric refractive index gradients. It requires additional measurements of temperature and humidity from a balloon sounding. The second makes use of broadening of the backscattered Doppler spectrum by turbulent motions. The turbulent eddy dissipation rate ε is a measure of the energy cascade through scales of inertial subrange turbulence. Data were collected with the Millstone Hill UHF radar in Westford, Massachusetts, and with Cross-chain Loran Atmospheric Sounding System thermodynamic soundings launched from Hanscom Field about 25 km away. Encouraging similarities are found both in the magnitude and shape of the measured profiles, though differences are also found. Some differences may be explained by characteristics of the measurement techniques. The relative strengths and weaknesses of the methods, and limitations imposed by the radar, will be discussed.

Abstract

Two independent radar methods for estimating the turbulent eddy dissipation rate ε are applied to a common dataset, and the results are compared. The first method estimates ε from backscattered power and relies on the effects of turbulent mixing of atmospheric refractive index gradients. It requires additional measurements of temperature and humidity from a balloon sounding. The second makes use of broadening of the backscattered Doppler spectrum by turbulent motions. The turbulent eddy dissipation rate ε is a measure of the energy cascade through scales of inertial subrange turbulence. Data were collected with the Millstone Hill UHF radar in Westford, Massachusetts, and with Cross-chain Loran Atmospheric Sounding System thermodynamic soundings launched from Hanscom Field about 25 km away. Encouraging similarities are found both in the magnitude and shape of the measured profiles, though differences are also found. Some differences may be explained by characteristics of the measurement techniques. The relative strengths and weaknesses of the methods, and limitations imposed by the radar, will be discussed.

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