Mean Vertical Gradient of Potential Refractive Index in Turbulent Mixing and Radar Detection of CAT

Óttersten, Hans

doi:10.1029/rs004i012p01247

Cited by 83 publications

(28 citation statements)

References 4 publications

(8 reference statements)

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“…Such a condition has been cited as an indication of radar returns by Fresnel re¯ection, whereas a correlation between signal strength and spectral width was expected for radar returns by backscatter (Thomas et al, 1992;Miller et al, 1993). Backscattered signal strength, however, depends on both the degree of turbulence and on the vertical gradient of potential refractive index (Ottersten, 1969). At mesospheric altitudes, variations in refractive index are dominated by changes in the electron density (Woodman and Guillen, 1974).…”

Section: Discussionmentioning

confidence: 99%

The small-scale structure of VHF mesospheric summer echo layers observed at mid-latitudes

Hooper

Thomas

1997

Ann. Geophys.

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Abstract. The VHF radar system at Aberystwyth (52X4 N, 4X1 E) has been used to make high-timeresolution, multi-beam observations of mesospheric summer echo layers. These show that the altitude and the sense of vertical movement of the layers can vary over time-scales of minutes and horizontal scales of kilometres. In general, the altitude pro®les of signal-tonoise ratio provide evidence of a bifurcated structure with sharp changes in the horizontal wind vector and vertical velocity, and enhanced spectral width occurring at the bifurcation level. The implications of the smallscale structure for studies of the aspect sensitivity of radar returns are discussed, and the changes in wind®eld at the bifurcation level are compared with`wind corners' observed in rocket studies of the mesosphere at polar latitudes.

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Section: Discussionmentioning

confidence: 99%

The small-scale structure of VHF mesospheric summer echo layers observed at mid-latitudes

Hooper

Thomas

1997

Ann. Geophys.

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“…6. Ottersten (1969) defined the vertical gradient of the generalized potential refractive index M as follows:…”

Section: Introductionmentioning

confidence: 99%

Comparisons of refractive index gradient and stability profiles measured by balloons and the MU radar at a high vertical resolution in the lower stratosphere

et al. 2007

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Abstract.Many experimental studies have demonstrated that VHF Stratosphere-Troposphere (ST) radar echo power is proportional to the generalized refractive index gradient squared M 2 when using a vertically oriented beam. Because humidity is generally negligible above the tropopause, VHF ST radars can thus provide information on the static stability (quantified by the squared Brunt-Väisälä frequency N 2 ) at stratospheric heights and this capability is useful for many scientific applications. Most studies have been performed until now at a vertical resolution of 150 m or more. In the present paper, results of comparisons between radar-and (balloon borne) radiosonde-derived M 2 and N 2 are shown at a better vertical resolution of 50 m with the MU radar (34.85 • N, 136.15 • E; Japan) by benefiting from the range resolution improvement provided by the multifrequency range imaging technique, using the Capon processing method. Owing to favorable winds in the troposphere, the radiosondes did not drift horizontally more than about 30 km from the MU radar site by the time they reached an altitude of 20 km. The measurements were thus simultaneous and almost collocated. Very good agreements have been obtained between both high resolution profiles of M 2 , as well as profiles of N 2 . It is also shown that this agreement can still be improved by taking into account a frozenin advection of the air parcels by a horizontally uniform wind. Therefore, it can be concluded that 1) the range imaging technique with the Capon method really provides substantial range resolution improvement, despite the relatively weak Signal-to-Noise Ratios (SNR) over the analyzed region of the lower stratosphere, 2) the proportionality of the radar echo power to M 2 at a vertical scale down to 50 m in the lower stratosphere is experimentally demonstrated, 3) the MU radar can provide stability profiles with a vertical resolution of 50 m at heights where humidity is negligible, 4) stable Correspondence to: H. Luce (hubert.luce@lseet.univ-tln.fr) stratospheric layers as thin as 50 m or less have at least a horizontal extent of a few km to several tens of kilometers and can be considered as frozenly advected over scales of a few tens of minutes.

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“…According to Ottersten (1969), in the troposphere the generalized refractive index gradient M is defined as…”

Section: Observationsmentioning

confidence: 99%

Derivation of turbulent energy dissipation rate with the Middle Atmosphere Alomar Radar System (MAARSY) and radiosondes at Andøya, Norway

Rapp

Schrön

et al. 2016

Ann. Geophys.

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Abstract. We present the derivation of turbulent energy dissipation rate ε from a total of 522 days of observations with the Middle Atmosphere Alomar Radar SYstem (MAARSY) mesosphere-stratosphere-troposphere (MST) radar running tropospheric experiments during the period of 2010-2013 as well as with balloon-borne radiosondes based on a campaign in the summer 2013. Spectral widths are converted to ε after the removal of the broadening effects due to the finite beam width of the radar. With the simultaneous in situ measurements of ε with balloon-borne radiosondes at the MAARSY radar site, we compare the ε values derived from both techniques and reach an encouraging agreement between them. Using all the radar data available, we present a preliminary climatology of atmospheric turbulence in the UTLS (upper troposphere and lower stratosphere) region above the MAARSY site showing a variability of more than 5 orders of magnitude inherent in turbulent energy dissipation rates. The derived ε values reveal a log-normal distribution with a negative skewness, and the ε profiles show an increase with height which is also the case for each individual month. Atmospheric turbulence based on our radar measurements reveals a seasonal variation but no clear diurnal variation in the UTLS region. Comparison of ε with the gradient Richardson number Ri shows that only 1.7 % of all the data with turbulence occur under the condition of Ri < 1 and that the values of ε under the condition of Ri < 1 are significantly larger than those under Ri > 1. Further, there is a roughly negative correlation between ε and Ri that is independent of the scale dependence of Ri. Turbulence under active dynamical conditions (velocity of horizontal wind U > 10 m s −1 ) is significantly stronger than under quiet conditions (U < 10 m s −1 ). Last but not least, the derived ε values are compared with the corresponding vertical shears of background wind velocity showing a linear relation with a corresponding correlation coefficient r = 58 % well above the 99.9 % significance level. This implies that wind shears play an important role in the turbulence generation in the troposphere and lower stratosphere (through the Kelvin-Helmholtz instability).

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Mean Vertical Gradient of Potential Refractive Index in Turbulent Mixing and Radar Detection of CAT

Cited by 83 publications

References 4 publications

The small-scale structure of VHF mesospheric summer echo layers observed at mid-latitudes

The small-scale structure of VHF mesospheric summer echo layers observed at mid-latitudes

Comparisons of refractive index gradient and stability profiles measured by balloons and the MU radar at a high vertical resolution in the lower stratosphere

Derivation of turbulent energy dissipation rate with the Middle Atmosphere Alomar Radar System (MAARSY) and radiosondes at Andøya, Norway

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