MU Radar observations of kilometer-scale waves in the midlatitude lower E-region

Abstract

The multi-beam high resolution MU radar experiments, conducted in February 2000, revealed for the first time kilometer-scale waves in the lower E-region over Shigaraki, Japan. The waves, occurring over a narrow height range of 92-97 km, have vertical wavelengths of 0.6 to 1.2 km and periods of 30 to 90 s. The signal intensities associated with these waves, with signal-to-noise ratio values less than ~5 dB, are lower by about 20 dB compared to that of the quasi-periodic echoes occurring at higher heights. The echoes occur with both negative and positive range rates, changing systematically from one to the other with values of about -25 m s^-1 and 20 m s^-1, respectively. The Doppler velocities, ranging -50 to 25 m s^-1, are generally of the same sense as range rates, but somewhat greater in magnitude. The periodicity and wavelength of the waves seem to resemble those revealed in the equatorial electrojet by the high resolution Jicamarca radar observations and also by the nonlocal nonlinear simulations of the gradient-drift instability. Behavior of the Doppler velocities, however, is found to be different from that reported for the kilometer-scale waves in the equatorial region.