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GEOPHYSICAL RESEARCH LETTERS, VOL. 29, NO. 11, 1530, doi:10.1029/2001GL014331, 2002

Low altitude quasi-periodic radar echoes observed by the Gadanki VHF radar

C. J. Pan

Institute of Space Science, National Central University, Chung-Li, Taiwan


P. B. Rao

National MST Radar Facility, Tirupati, India


Abstract

We report here on the low altitude quasi-periodic (LQP) radar echoes from low latitude sporadic E layer (Es) observed by the Gadanki (13.5°N, 79.2°E; geomagnetic latitude 6.3°N) VHF radar. The LQP echoes occurred both during daytime and nighttime and are confined to a slowly descending layer with a thickness of about 2–4 km in the height range of 90–100 km. The periods are found to range from tens of seconds to less than about 3 minutes. The Doppler velocities vary over a range of −20 to +20 m/s during daytime and 0 to 10 m/s during nighttime and are known to be sensitive to the layer height, being dominated by the effect of zonal electric field above and meridional neutral wind below a height of ∼97 km for the type 2 irregularities [ Krishna Murthy et al., 1998 ]. The spectral widths are found to be of the order of 50 to 75 m/s during daytime and 30 to 60 m/s during nighttime. The LQP echoes reported here are similar to that observed recently over midlatitudes [ Rao et al., 2000 ; Urbina et al., 2000 ], but distinctly different from the widely reported quasi-periodic (QP) echoes occurring at higher altitudes (>100 km). The observations are discussed briefly in terms of the potential source mechanisms.

Published 12 June 2002.

Index Terms: 1854 Hydrology: Precipitation (3354); 3354 Meteorology and Atmospheric Dynamics: Precipitation (1854); 3309 Meteorology and Atmospheric Dynamics: Climatology (1620); 3344 Meteorology and Atmospheric Dynamics: Paleoclimatology.

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Citation: Pan, C. J., and P. B. Rao (2002), Low altitude quasi-periodic radar echoes observed by the Gadanki VHF radar, Geophys. Res. Lett., 29(11), 1530, doi:10.1029/2001GL014331.