Evidence of tilted layers in angle of arrival and Doppler beam steering power measurements

Hobbs, Bridget G.; Holdsworth, David A.

doi:10.1029/1999rs002233

Cited by 6 publications

(9 citation statements)

References 21 publications

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“…This type of situation could arise either due to isolated intense turbulent patch advecting through the off-zenith beam or due to tilt of the echoing layers. Gage et al (1981a, b), Gage (1986) and Hobbs and Reid (2000) suggested that this type of situation could arise due to the passage of atmospheric waves over the radar site and associated fluctuation in vertical and oblique beam echo power. If the layers are horizontally stratified in both east-west (E-W) or north-south (N-S) directions, the power is expected to be equal between the two symmetric beams.…”

Section: Tilting Of Atmospheric Layers and Their Generation Mechanismsmentioning

confidence: 99%

“…There are only a few studies related to aspect sensitivity from tropical latitudes (Röttger et al, 1981;Worthington et al, 1999;Damle et al, 1994;Jain et al, 1997). Recently, there have been considerable efforts to understand radar backscatter and the aspect sensitivity of the radar echoes in terms of background atmospheric parameters (Tsuda et al, 1997a,b;Jain et al, 1997;Hooper and Thomas, 1998;Palmer et al, 1998;Worthington et al, 1999;Hobbs and Reid, 2000;Jain et al, , 2003.…”

Section: Introductionmentioning

confidence: 99%

“…Jain et al ( , 2003 have shown that, at some heights, echoes are from sharp gradients in radio refractivity structures associated with anisotropic turbulence. A number of attempts have also been made to understand the aspect sensitivity and its azimuthal anisotropy in terms of the background atmospheric parameters, such as winds and vertical shears of horizontal winds, using simultaneous radar measurements both in Doppler Beam Swinging (DBS) and Space Domain Interferometry (SDI) modes (Palmer et al, 1998;Hobbs and Reid, 2000;Kawano et al, 2001). Kawano et al (2001) observed backscatter layers to be tilted in zonal plane by 0.7 • and this tilt was used to correct the observed velocity.…”

Section: Introductionmentioning

confidence: 99%

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Aspect sensitivity in the VHF radar backscatters studied using simultaneous observations of Gadanki MST radar and GPS sonde

et al. 2004

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Abstract. Simultaneous observations made on four days using the MST radar and GPS-sonde at Gadanki (13.5 • N, 79.2 • E), a tropical station in India, are presented to address the aspect sensitivity of radar backscatters observed at different heights. The observations show that wherever stability parameter N 2 is high, vertical shear of horizontal wind is low and Richardson number (R i ) is high, the aspect sensitivity is high indicating that the aspect sensitive radar backscatters are due to thermal structures in the atmosphere. Such a case can be seen very clearly in the upper troposphere and lower stratosphere. At some heights, where N 2 is high, R i is high, but shears are relatively weak, the aspect sensitivity is found to almost disappear, indicating that some amount of shear provides favorable conditions for causing aspect sensitivity. Aspect sensitivity does not occur at all where N 2 is low or negative and R i is low in spite of wind shear being either high or low, indicating that the regions are well mixed and hence turbulent. The study also shows a power difference in the symmetric beams. A case study on this aspect suggests that this asymmetry is due to the tilting of layers by the action of atmospheric waves. There is indication that these waves are generated through Kelvin-Helmholtz-instability (KHI).

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Section: Tilting Of Atmospheric Layers and Their Generation Mechanismsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Aspect sensitivity in the VHF radar backscatters studied using simultaneous observations of Gadanki MST radar and GPS sonde

et al. 2004

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“…Tilt of the aspectsensitivity pattern can be measured using spatial domain interferometry (Hobbs et al 2000) (Fig. 2f) has been interpreted as tilted aspect-sensitive scatterers causing a vertical radar beam to point effectively offvertical, measuring a component of horizontal wind, whereas real W is near zero or opposite sign (Larsen and Röttger 1991;Palmer et al 1998;Kawano et al 2001).…”

Section: Observationsmentioning

confidence: 99%

VHF volume-imaging radar observation of aspect-sensitive scatterers tilted in mountain waves above a convective boundary layer

Worthington

2005

Ann. Geophys.

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Abstract. Thin stable atmospheric layers cause VHF radars to receive increased echo power from near zenith. Layers can be tilted from horizontal, for instance by gravity waves, and the direction of VHF "glinting" is measurable by spatial domain interferometry or many-beam Doppler beam swinging (DBS). This paper uses the Middle and Upper atmosphere (MU) radar, Shigaraki, Japan as a volume-imaging radar with 64-beam DBS, to show tilting of layers and air flow in mountain waves. Tilt of aspect-sensitive echo power from horizontal is nearly parallel to air flow, as assumed in earlier measurements of mountain-wave alignment. Vertical-wind measurements are self-consistent from different beam zenith angles, despite the combined effects of aspect sensitivity and horizontal-wind gradients.

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“…The tilt measured with respect to the horizontal can generally be of the order of a few degrees or less, on average, (e.g. Röttger and Larsen, 1990, and references therein; Larsen and Röttger, 1991;Palmer et al, 1991Palmer et al, , 1993Palmer et al, , 1998aChau and Balsley, 1998;Worthington et al, 1999aWorthington et al, ,b, 2000aKawano et al, 2001;Hobbs et al, 2000) or much more, such as 10 degrees in extreme cases, as reported by Worthington and Thomas (1997). Worthington et al (1999a,b) also found that the zenith angle where the maximum echo power was observed is more pronounced in the troposphere than in the stratosphere.…”

Section: Azimuthal Dependence Of Echo Powermentioning

confidence: 99%

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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Evidence of tilted layers in angle of arrival and Doppler beam steering power measurements

Cited by 6 publications

References 21 publications

Aspect sensitivity in the VHF radar backscatters studied using simultaneous observations of Gadanki MST radar and GPS sonde

Aspect sensitivity in the VHF radar backscatters studied using simultaneous observations of Gadanki MST radar and GPS sonde

VHF volume-imaging radar observation of aspect-sensitive scatterers tilted in mountain waves above a convective boundary layer

Temperature sheets and aspect sensitive radar echoes

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