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

Green, J. L.; Gage, K. S.

doi:10.1029/rs015i002p00395

Cited by 42 publications

(17 citation statements)

References 14 publications

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“…This mechanism involves a statistical approach since it assumes that many thin turbulent layers or sheets, highly coherent along the horizontal, are randomly distributed within the range gate. It was shown that this model provides an expression of the received power proportional to the mean squared gradient of the potential refractive index M 2 , which is a measure of the atmospheric stability (Hocking and Röttger, 1983;Gage et al, 1985) or N 4 if humidity effects are negligible (Green and Gage, 1980). Experimental studies confirmed the clear relationship between M 2 deduced from in-situ measurements with the echo power received at vertical incidence (e.g.…”

Section: Various Interpretations Of Aspect Sensitive Echoing Layerssupporting

confidence: 52%

“…The isotropic level is thought to be detected for a zenith angle larger than ∼10-15 • (e.g. Green and Gage, 1980;Röttger et al, 1981;Tsuda et al, 1986;Hocking et al, 1990). However, some recent results obtained with a Beam-Scanning analysis (see appendix) emphasized that residual aspect sensitivity can occur at larger zenith angles with an azimuthal dependence up to 20 • (Tsuda et al, 1997a), or even 30 • in extreme cases (Worthington et al, 1999a,b).…”

Section: Errors In Isotropic Turbulence Parameter Measurementsmentioning

confidence: 99%

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Temperature sheets and aspect sensitive radar echoes

Luce

Crochet

Dalaudier³

2001

Ann. Geophys.

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Abstract. There have been years of discussion and controversy about the existence of very thin and stable temperature sheets and their relationship to the VHF radar aspect sensitivity. It is only recently that very high-resolution insitu temperature observations have brought credence to the reality and ubiquity of these structures in the free atmosphere and to their contribution to radar echo enhancements along the vertical. Indeed, measurements with very highresolution sensors are still extremely rare and rather difficult to obtain outside of the planetary boundary layer. They have only been carried out up to the lower stratosphere by Service d'Aéronomie (CNRS, France) for about 10 years. The controversy also persisted due to the volume resolution of the (Mesosphere)-Stratosphere-Troposphere VHF radars which is coarse with respect to sheet thickness, although widely sufficient for meteorological or meso-scale investigations. The contribution within the range gate of many of these structures, which are advected by the wind, and decay and grow at different instants and could be distorted either by internal gravity waves or turbulence fields, could lead to radar echoes with statistical properties similar to those produced by anisotropic turbulence. Some questions thus remain regarding the manner in which temperature sheets contribute to VHF radar echoes. In particular, the zenithal and azimuthal angular dependence of the echo power may not only be produced by diffuse reflection on stable distorted or corrugated sheets, but also by extra contributions from anisotropic turbulence occurring in the stratified atmosphere. Thus, for several years, efforts have been put forth to improve the radar height resolution in order to better describe thin structures. Frequency interferometric techniques are widely used and have been recently further developed with the implementation of high-resolution data processings. We begin by reviewing briefly some characteristics of the ST radar echoes with a particular emphasis on recent works. Their possible coupling with stable sheets is then presented and their known characteristics are described with some hypotheses concernCorrespondence to: H. Luce (luce@kurasc.kyoto-u.ac.jp) ing their generation mechanisms. Finally, measurement campaigns that took recently place or will be carried out in the near future for improving our knowledge of these small-scale structures are presented briefly.

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Section: Various Interpretations Of Aspect Sensitive Echoing Layerssupporting

confidence: 52%

Section: Errors In Isotropic Turbulence Parameter Measurementsmentioning

confidence: 99%

Temperature sheets and aspect sensitive radar echoes

Luce

Crochet

Dalaudier³

2001

Ann. Geophys.

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“…This good correlation between high atmospheric stability and vertical echo power could be considered as possibly resulting from partial reflection mechanism, as remarked by many authors (e.g. Green and Gage, 1980;Gage et al, 1985;Tsuda et al, 1988;Dalaudier et al, 1989, Chu et al, 1990Luce et al, 1995). However, it must be noted that the same region is also observed by the OHP and Toulon radar as a zone of enhanced radar echo power in the oblique direction.…”

Section: Detection By the Ohp Vhf St Radar And Raman Lidarmentioning

confidence: 75%

Mixing processes in a tropopause folding observed by a network of ST radar and lidar

Bertin¹,

Campistron²,

Caccia³

et al. 2001

Ann. Geophys.

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Abstract.A campaign devoted to stratosphere-troposphere exchange mechanisms studies has been held on 4-5 March 1995, during a tropopause folding passage over western Europe. The observational network included 1 UHF and 3 VHF radar, 1 temperature lidar, and 1 ozone lidar, deployed in the south of France. The fold is associated with a strong quasi meridional jet stream running along the west side of an upper level trough forming a potential vorticity (PV ) anomaly. During this campaign, the PV anomaly is advected eastwards without major deformations, with an average velocity of about 30 km per hour. Therefore, a frozen field hypothesis has been used in order to compare the results obtained in the different sites of the network. Under this hypothesis, the same structures associated with the anomaly are observed by each radar or lidar, at the same time relative to this anomaly. The fold is put into evidence by the ozone lidar of the network and by the VHF radars when computing the aspect ratio. The turbulent activity observed by the OHP VHF radar and by the high resolution UHF PROUST radar (30 m altitude resolution) is concentrated in the wind shear regions generated by the jet stream above and below its axis. In the lower level wind shear, turbulent layers are detected within the fold and across its anticyclonic boundary, thus allowing turbulent exchanges with the tropospheric air masses. A large area of aspect ratio greater than 3 is observed in the troposphere during more than ten hours after the passage of the fold by the VHF radars. This particular signature is tentatively analyzed as the progressive dilution of air masses of stratospheric origin extruded from the fold by the turbulent processes. In the upper level wind shears, turbulent layers parallel to the wind isotachs are observed, whose thickness is often smaller than 100 m and are separated by non turbulent regions. A good correlation is found between the spatiotemporal evolution of these turbulent structures observed by the PROUST radar, and the stability structures observed at the same relative time by the temperature lidar. In addition the same turbulent structures are observed to be parallel to Correspondence to: F. Bertin (francois.bertin2@wanadoo.fr) the iso-phase lines of the wind fluctuations, observed at the same relative time by the Lannemezan radar. These characteristics are compatible with the presence of unstable inertiagravity waves, generated by the jet stream while the turbulent layers could be the signature of their saturation processes.

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“…To our knowledge, all previous comparisons with balloon data have been made at relative levels, mainly due to the difficulty of power calibration (e.g., Röttger, 1979;Green and Gage, 1980;Larsen and Röttger, 1983;Tsuda et al, 1988;Vincent et al, 1998;Hooper et al, 2004). Balloonderived M 2 has been compared with radar echo power at zenith incidence without any assumption on the backscattering mechanism (which may be different at different altitudes, depending on turbulence and stability).…”

mentioning

confidence: 99%

Comparisons between high-resolution profiles of squared refractive index gradient <i>M</i><sup>2</sup> measured by the Middle and Upper Atmosphere Radar and unmanned aerial vehicles (UAVs) during the Shigaraki UAV-Radar Experiment 2015 campaign

et al. 2017

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Abstract. New comparisons between the square of the generalized potential refractive index gradient M 2 , estimated from the very high-frequency (VHF) Middle and Upper Atmosphere (MU) Radar, located at Shigaraki, Japan, and unmanned aerial vehicle (UAV) measurements are presented. These comparisons were performed at unprecedented temporal and range resolutions (1-4 min and ∼ 20 m, respectively) in the altitude range ∼ 1.27-4.5 km from simultaneous and nearly collocated measurements made during the ShUREX (Shigaraki UAV-Radar Experiment) 2015 campaign. Seven consecutive UAV flights made during daytime on 7 June 2015 were used for this purpose. The MU Radar was operated in range imaging mode for improving the range resolution at vertical incidence (typically a few tens of meters). The proportionality of the radar echo power to M 2 is reported for the first time at such high time and range resolutions for stratified conditions for which Fresnel scatter or a reflection mechanism is expected. In more complex features obtained for a range of turbulent layers generated by shear instabilities or associated with convective cloud cells, M 2 estimated from UAV data does not reproduce observed radar echo power profiles. Proposed interpretations of this discrepancy are presented.

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

Cited by 42 publications

References 14 publications

Temperature sheets and aspect sensitive radar echoes

Temperature sheets and aspect sensitive radar echoes

Mixing processes in a tropopause folding observed by a network of ST radar and lidar

Comparisons between high-resolution profiles of squared refractive index gradient <i>M</i><sup>2</sup> measured by the Middle and Upper Atmosphere Radar and unmanned aerial vehicles (UAVs) during the Shigaraki UAV-Radar Experiment 2015 campaign

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

Cited by 42 publications

References 14 publications

Temperature sheets and aspect sensitive radar echoes

Temperature sheets and aspect sensitive radar echoes

Mixing processes in a tropopause folding observed by a network of ST radar and lidar

Comparisons between high-resolution profiles of squared refractive index gradient &lt;i&gt;M&lt;/i&gt;&lt;sup&gt;2&lt;/sup&gt; measured by the Middle and Upper Atmosphere Radar and unmanned aerial vehicles (UAVs) during the Shigaraki UAV-Radar Experiment 2015 campaign

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Comparisons between high-resolution profiles of squared refractive index gradient <i>M</i><sup>2</sup> measured by the Middle and Upper Atmosphere Radar and unmanned aerial vehicles (UAVs) during the Shigaraki UAV-Radar Experiment 2015 campaign