The structure of turbulence in the middle and lower atmosphere seen by and deduced from MF, HF and VHF radar, with special emphasis on small-scale features and anisotropy

Hocking, W. K.; Röttger, J.

doi:10.5194/angeo-19-933-2001

Cited by 21 publications

(16 citation statements)

References 58 publications

(72 reference statements)

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“…The former is thought to be mostly responsible for MST radar echoes and the latter for wide-beam MF radar echoes. However, the mechanisms are still not fully understood, and both scatters are thought to coexist in reality (Hocking and Röttger 2001;Reid 2015). We found that the AOAs of the MF echoes were more widely distributed in winter than in summer, implying more isotropic (less specular) echoes in winter.…”

Section: Discussionmentioning

confidence: 71%

Characteristics of Mesosphere Echoes over Antarctica Obtained Using PANSY and MF Radars

Tsutsumi

Sato

et al. 2017

SOLA

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We investigated characteristics of mesosphere echoes over Syowa Station (69S) in the Antarctic, which were detected by the Program of the Antarctic Syowa Mesosphere, Stratosphere and Troposphere/Incoherent Scatter (PANSY) radar (47 MHz) and Medium Frequency (MF) radar (2.4 MHz). Winter echoes from the PANSY radar and low altitude MF echoes below approximately 70−75 km mostly coexisted, appearing during the daytime as well as for a few hours post sunset. Summer echoes in the lower height region were absent in both radar observations, suggesting a close relationship in the generation mechanisms of these two radar echoes. High correlation between local K-index and the occurrence of winter echoes suggested that electron density enhancement due to ionized particle precipitation was one of the triggers of echo generation. Angles of arrival of the MF echoes were more isotropic in winter. Because gravity wave activity is much higher in winter over Syowa, higher turbulence energy caused by gravity wave breaking may also be responsible for the generation of the winter echoes and their isotropic behavior. The horizontal wind velocities of the two systems were further compared and agreed well throughout the height region of 60−90 km.

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Section: Discussionmentioning

confidence: 71%

Characteristics of Mesosphere Echoes over Antarctica Obtained Using PANSY and MF Radars

Tsutsumi

Sato

et al. 2017

SOLA

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“…On the other hand, as will be further discussed in Sect. 6, a statistical description of turbulent events (layers depths, lifetime, filling factor, intensity) is required for estimating the effective diffusivity of a patchy turbulence (Hocking and Röttger, 2001). …”

Section: The Turbulent Fractionmentioning

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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“…It has been argued by Bolgiano (1968) and later by Woodman and Chu (1989) and Hocking and Röttger (2001) that the boundaries or edges of turbulent layers in the atmosphere should exhibit anisotropic flows -i.e., eddies elongated along the edges -and contain elongated density structures with a spectrum |δN (ω, k)| 2 which is sensitive to the direction of wavevector k. Radar echoes from turbulent layer edges should then exhibit random statistics as well as aspect sensitivity. The early MST experiments of Fukao et al (1980) and Røyrvik (1983) lacked the height resolution required to observe the peculiar characteristics of layer boundaries predicted by Bolgiano (1968) and, in general, to distinguish between specular reflections and anisotropic turbulence; the radar volumes often contained a multitude of density structures, potentially associated with different echoing mechanisms.…”

Section: Introductionmentioning

confidence: 99%

“…(1) -have been debated since the early days of the MST radar technique (e.g., Woodman and Chu, 1989;Hocking and Röttger, 2001). Since partial reflections are caused by time-invariant density structures their "correlation times" should be long and their Doppler frequency spectra narrow.…”

Section: Introductionmentioning

confidence: 99%

A high-resolution study of mesospheric fine structure with the Jicamarca MST radar

et al. 2006

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Abstract. Correlation studies performed on data from recent mesospheric experiments conducted with the 50-MHz Jicamarca radar in May 2003 and July 2004 are reported. The study is based on signals detected from a combination of vertical and off-vertical beams. The nominal height resolution was 150 m and spectral estimates were obtained after ∼1 min integration. Spectral widths and backscattered power generally show positive correlations at upper mesospheric heights in agreement with earlier findings (e.g., Fukao et al., 1980) that upper mesospheric echoes are dominated by isotropic Bragg scatter. In many instances in the upper mesosphere, a weakening of positive correlation away from layer centers (towards top and bottom boundaries) was observed with the aid of improved height resolution. This finding supports the idea that layer edges are dominated by anisotropic turbulence. The data also suggests that negative correlations observed at lower mesospheric heights are caused by scattering from anisotropic structures rather than reflections from sharp vertical gradients in electron density.

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The structure of turbulence in the middle and lower atmosphere seen by and deduced from MF, HF and VHF radar, with special emphasis on small-scale features and anisotropy

Cited by 21 publications

References 58 publications

Characteristics of Mesosphere Echoes over Antarctica Obtained Using PANSY and MF Radars

Characteristics of Mesosphere Echoes over Antarctica Obtained Using PANSY and MF Radars

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

A high-resolution study of mesospheric fine structure with the Jicamarca MST radar

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