Abstract
Abstract. In recent works, zenithal and azimuthal angle variations of echo power measured by VHF Stratosphere-Troposphere (ST) radars have been analyzed in detail using different radar multi-beam configurations. It was found that the azimuthal angle corresponding to maximum echo power is closely related to the direction of the horizontal wind shear. These properties indicate that local wind shear affects the tilt of the scatterers. Moreover, horizontal maps of echo power collected using a large set of beams steered pulse-to-pulse up to 40 degrees off zenith revealed that the power distribution pattern in the troposphere is often skewed. In this work, a three-dimensional description of echo power variations up to 24 degrees off zenith is shown for measurements in the lower stratosphere (i.e. up to approximately 20km) using a "sequential multi-beam" (SMB) configuration. Such a description was not possible above the tropopause with classical multi-beam configurations because of the loss of radar sensitivity due to the limited integration time by the use of a large number of beams. This work attempts to complete previous descriptions of the phenomenon by some observations in the lower stratosphere discussed in association with complementary balloon measurements. Key words. Meteorology and atmospheric dynamics (turbulence) – Radio Science (remote sensing)
Highlights
Flexible VHF Stratosphere-Troposphere (ST) radars such as the Middle and Upper atmosphere (MU) radar (Shigaraki, Japan, 34.85◦ N, 136.10◦ E) make it possible to volumeimage the distribution of echo power by pulse-to-pulse steering of multiple radar beams
The horizontal maps produce an image of the angular distribution of the facets’ tilts smeared by the radar volume and time averaging. This idea is quite different from the hypothesis proposed by Tsuda et al (1997), who considered a model of monochromatic gravity waves with large horizontal wavelengths to explain the azimuthal dependence of echo power at a fixed zenith angle
We propose a configuration to perform observations up to 24 degrees off zenith by using several consecutive 5-beam DBS modes at different zenith and azimuth angles, which we call the “Sequential multi beam” (SMB) configuration
Summary
From measurements performed using a multi-beam scheme with pulse-to-pulse beam steering, (e.g. Palmer et al, 1998; Worthington et al, 1999, 2000), it was clearly shown that horizontal maps of echo power are skewed and sometimes very scattered. The horizontal maps produce an image of the angular distribution of the facets’ tilts smeared by the radar volume and time averaging This idea is quite different from the hypothesis proposed by Tsuda et al (1997), who considered a model of monochromatic gravity waves with large horizontal wavelengths to explain the azimuthal dependence of echo power at a fixed zenith angle. The latter model cannot explain the skew of the distribution which can produce sinusoidal variations when considering a fixed zenith angle. The latter model cannot explain the skew of the distribution which can produce sinusoidal variations when considering a fixed zenith angle. Worthington et al (1999) proposed that the characteristics of power maps result rather from a small-scale KHI mechanism
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