Imaging Doppler interferometry and the measurement of atmospheric turbulence

Roper, R. G.; Brosnahan, J. W.

doi:10.1029/97rs00089

Cited by 22 publications

(27 citation statements)

References 27 publications

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“…The wind velocity variance relates to the TKE, provided that the non-turbulent contributions to that variance can be removed. A variety of radar techniques exist for estimating the wind velocity: from the line-of-sight velocity differences from meteors (Roper, 1966); from the imaging Doppler interferometry scattering positions (Roper and Brosnahan, 1997), from spaced antenna full correlation analysis (Briggs, 1980;Manson et al, 1981), and from the spectral broadening observed by MST Doppler radars. (Hocking, 1983).…”

Section: Radar Measurements Of the Turbulence Energeticsmentioning

confidence: 99%

Turbulent diffusivity in the free atmosphere inferred from MST radar measurements: a review

Wilson¹

2004

Ann. Geophys.

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Abstract. The actual impact on vertical transport of smallscale turbulence in the free atmosphere is still a debated issue. Numerous estimates of an eddy diffusivity exist, clearly showing a lack of consensus. MST radars were, and continue to be, very useful for studying atmospheric turbulence, as radar measurements allow one to estimate the dissipation rates of energy (kinetic and potential) associated with turbulent events. The two commonly used methods for estimating the dissipation rates, from the backscattered power and from the Doppler width, are discussed. The inference methods of a local diffusivity (local meaning here "within" the turbulent patch) by using the dissipation rates are reviewed, with some of the uncertainty causes being stressed. Climatological results of turbulence diffusivity inferred from radar measurements are reviewed and compared.As revealed by high resolution MST radar measurements, atmospheric turbulence is intermittent in space and time. Recent theoretical works suggest that the effective diffusivity of such a patchy turbulence is related to statistical parameters describing the morphology of turbulent events: filling factor, lifetime and height of the patches. It thus appears that a statistical description of the turbulent patches' characteristics is required in order to evaluate and parameterize the actual impact of small-scale turbulence on transport of energy and materials. Clearly, MST radars could be an essential tool in that matter.

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Section: Radar Measurements Of the Turbulence Energeticsmentioning

confidence: 99%

Turbulent diffusivity in the free atmosphere inferred from MST radar measurements: a review

Wilson¹

2004

Ann. Geophys.

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“…Despite this agreement Holdsworth and Reid (1995b) were careful not to suggest that the volume scatter was applicable experimentally, or that the interferometric techniques would fail experimentally. However, Roper and Brosnahan (1997) and Turek et al (1998) appear to have interpreted the results as implying otherwise. Quoting verbatim from both: " Holdsworth and Reid (1995b) were unable to recover the actual scatterer positions and concluded that the scatterers identified by the IDI technique were fictitious."…”

Section: Imaging Doppler Interferometry and The Volume Scatter Situationmentioning

confidence: 94%

“…We therefore attribute the larger hourly estimated turbulent velocities to the effects of gravity waves, and suggest hourly (or larger) turbulent velocity estimates (e.g. Roper and Brosnahan, 1997) will be significantly overestimated.…”

Section: Long-term Velocity Comparisonsmentioning

confidence: 99%

“…Such hourly wind estimated are hereafter referred to as "hourly averaged", while those made using 30 two-minute data acquisitions are referred to as "hourly estimated". Turbulent velocities are estimated as described by Roper and Brosnahan (1997), using a 5 • threshold, rather than 2 • . The larger threshold used in this study is necessary since the analysis is applied using two-minute AOA skymaps, when there are occasionally few AOAs within 2 • of zenith.…”

Section: Idi Implementation Using the Buckland Park Mf Radarmentioning

confidence: 99%

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Comparisons of full correlation analysis (FCA) and imaging Doppler interferometry (IDI) winds using the Buckland Park MF radar

Holdsworth

2004

Ann. Geophys.

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Abstract. We present results from three years of mesospheric and thermospheric wind measurements obtained using full correlation analysis (FCA) and imaging Doppler interferometry (IDI) for the Buckland Park MF radar. The IDI winds show excellent agreement with the FCA winds, both for short (2-min) and longer term (hourly, fortnightly) comparisons. An extension to a commonly used statistical analysis technique is introduced to show that the IDI winds are approximately 10% larger than the FCA winds, which we attribute to an underestimation of the FCA winds rather than an indication that IDI overestimates the wind velocity. Although the distribution of IDI effective scattering positions are shown to be consistent with volume scatter predictions, the velocity comparisons contradict volume scatter predictions that the IDI velocity will be overestimated. However, reanalysis of a 14-day data set suggests the lack of overestimation is due to the radial velocity threshold used in the analysis, and that removal of this threshold produces the volume scatter predicted overestimation of the IDI velocities. The merits of using hourly IDI estimates versus hourly averaged 2-min IDI estimates are presented, suggesting that hourly estimated turbulent velocities are overestimated.

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“…Roper and Brosnahan [1997] (hereafter referred to as RB), in a development of the concept of the structure function representation of turbulence, with emphasis on e, the rate of dissipation of turbulent energy, assumed that the characteristic length Lo of the energy-bearing eddies was defined by the correlation coefficient of the characteristic velocity Uo falling to l/e, and arrived at the formula (their equation (2) The fact that the shears are larger at the smaller scales results in the disappearance of the smaller scales first, if the turbulence spectrum is decaying [Frisch, 1995]. This is pertinent to our later discussion of the intermittent, decaying turbulence responsible for the scatter which produces identifiable imaging Doppler interferometry (IDI) echoes.…”

Section: Turbulencementioning

confidence: 99%

On the reality of upper mesospheric/lower thermospheric turbulent “eddies”

Roper¹

1998

Radio Science

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Abstract. The structure of atmospheric turbulence and its relationship to the refractive index discontinuities responsible for the scattering of radio waves are discussed. Emphasis is placed more on the nature of the intermittent scatterers observed at upper mesospheric/lower thermospheric altitudes than on volume scattering. The preferred model is of transient patches composed of vortex strings. An overview of the methods used to estimate the rate of dissipation of turbulent energy using MF radar data which emphasizes the advantages of imaging Doppler interferometry is presented, together with a review of pertinent laboratory investigations of coherent structures. An attempt is made to remove the contamination by gravity waves from imaging Doppler interferometry fluctuating velocity data. Emphasis is given to the fact that all radar measurements of turbulent intensity to date are upper estimates, not only because of the presence of gravity wave fluctuations contaminating the data, but also because the turbulence itself is not stationary and homogeneous but intermittent in both space and time. The intermittent nature of the turbulence, in which the refractive index discontinuities responsible for the radar backscatter are associated with decaying, homogeneous turbulent coherent structures, is in contrast to the theory of volume scattering, which assumes the radar pulse volume to be partially filled with stationary, homogeneous turbulence.

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Imaging Doppler interferometry and the measurement of atmospheric turbulence

Abstract: Abstract. Data taken by an imaging Doppler interferometer (IDI) 3.175-MHz radar during the

Cited by 22 publications

References 27 publications

Turbulent diffusivity in the free atmosphere inferred from MST radar measurements: a review

Turbulent diffusivity in the free atmosphere inferred from MST radar measurements: a review

Comparisons of full correlation analysis (FCA) and imaging Doppler interferometry (IDI) winds using the Buckland Park MF radar

On the reality of upper mesospheric/lower thermospheric turbulent “eddies”

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