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

The multi-beam high resolution MU radar experiments, conducted in February 2000, revealed for the first lime kilometer-scale waves in the lower E-regi on over Shigaraki, Japan. The waves, occurring over a narrow height range o f 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 similar to 5 dB, are lower by about 20 dB com pared to that of the quasi-periodic echoes occurring at higher heights. The echoes occur with both negative and positive range rates, changing systema tically 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 ge nerally of the same sense as range rates, but somewhat greater in magnitude . The periodicity and wavelength of the waves seem to resemble those reveal ed in the equatorial electrojet by the high resolution Jicamarca radar obse rvations and also by the nonlocal nonlinear simulations of the gradient-dri ft instability. Behavior of the Doppler velocities, however, is found to be different from that reported for the kilometer-scale waves in the equatori al region.