Evidence of kilometer-scale waves in the lower E region from high resolution VHF radar observations over Gadanki

Abstract

High resolution VHF radar observations made at Gadanki revealed the kilometer-scale waves in the low latitude lower E region. These waves are found to occur in a narrow altitude range of 92-97 km and have vertical wavelengths of ~0.5 km and wave periods of ~40 seconds. They resemble quite closely to that reported recently for midlatitude using the MU radar. The signal intensities associated with these waves, shown in SNR, are found to be as high as 25 dB, quite comparable to that observed at higher altitudes. It is in contrast to the much weaker midlatitude lower E region echoes reported by the MU radar. The wave structures show both positive and negative altitude rates with values in the range of 15-20 ms^-1, which are in good agreement with the observed Doppler velocities. The spectral widths are found to be relatively lower, implying the lower E region wave structures to be less turbulent compared to their counterpart at higher altitudes. The observed wave structures bear remarkable resemblance to that simulated for the equatorial E region through nonlocal nonlinear gradient drift instability.