Spectral characteristics and scatter cross-section of low latitude mesospheric echoes measured by the Indian MST radar at Gadanki

E Belova,T Sergienko,S Satheesh Kumar,T Narayana Rao,S Kirkwood

doi:10.5194/angeo-30-983-2012

Abstract

Abstract. In November 2008 and in March and April 2009 the Indian MST radar (53 MHz) at Gadanki was operated during the daytime in a special experiment, with 600 m altitude resolution, for understanding the characteristics of low-latitude mesospheric echoes (LLME). The data of three days when the echoes were strongest have been analysed in terms of spectral widths and radar volume reflectivities. Spectral widths of LLME show some decrease with altitude, with median values of 4–6 m s−1 at 69–72 km and of 2–4 m s−1 at 73–78 km. This corresponds to 20–200 mW kg−1 turbulent energy dissipation rates. It has been shown that stronger echoes have broader spectra consistent with a turbulent scattering mechanism. For the first time, the volume reflectivities for the strong LLME for Gadanki have also been calculated. They are in the range of 10−17–10−15 m−1, so LLME at Gadanki are somewhat stronger than those reported so far from Jicamarca, Peru (Lehmacher et al., 2009).

Highlights

Radar echoes from the mesosphere are a very common phenomenon observed by MST radars located over a wide range of latitudes, from the polar regions in both hemispheres to the tropics (e.g. Woodman and Guillen, 1974; Czechowsky et al, 1979; Ecklund and Balsley, 1981; Reid, 1990; Morris et al, 2004; Kirkwood et al, 2007; Smirnova et al, 2010)
During the last three decades scientific interest has concentrated on strong radar returns from the mesopause region (80–90 km altitudes) observed in the summer months at polar latitudes, which have been termed polar mesosphere summer echoes (PMSE)
We presented the results of the calculations of spectral widths of LLME power spectra for three experiments in Figs. 1, 4 and 6

Summary

Introduction

Radar echoes from the mesosphere are a very common phenomenon observed by MST radars located over a wide range of latitudes, from the polar regions in both hemispheres to the tropics (e.g. Woodman and Guillen, 1974; Czechowsky et al, 1979; Ecklund and Balsley, 1981; Reid, 1990; Morris et al, 2004; Kirkwood et al, 2007; Smirnova et al, 2010). It has been suggested that MSE are related to the presence of ice particles either advected by the wind from the cold polar mesopause (Berger and von Zahn, 2007) or formed locally, e.g. during the cold phase of planetary waves (Zeller et al, 2009). At high latitudes another type of strongly enhanced radar return, different from PMSE, is sometimes found at altitudes below 80 km, in the winter and equinox seasons. The mechanism of PMWE generation is still unclear though both turbulent (Lubken et al, 2006) and nonturbulent (Kirkwood et al, 2006) hypotheses have been suggested

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Discussion

Conclusion