Simultaneous mesosphere-lower thermosphere and thermosphericFregion observations using middle and upper atmosphere radar

Abstract

Simultaneous MLT (mesosphere-lower thermosphere) and thermospheric F region (upper thermosphere and ionosphere together) observations conducted using the middle and upper atmosphere (MU) radar (35 degrees N, 136 degrees E) in alternate meteor and incoherent scatter modes in October 2000 and March 2001 are presented. The continuous observations, each lasting more than a week, provide simultaneous zonal and meridional wind velocities at MLT altitudes (80-95 km), meridional wind velocity in the upper thermosphere (220-450 km), and electron density and peak height in the ionosphere with a time resolution of 1.5 hours. The data seem to suggest that the upper atmospheric regions could be dynamically coupled through mean winds, tides, and waves. Diurnal (24-hour) and semidiurnal (12-hour) tides and waves of periods 16-20 hours and 35-55 hours coexist at MLT and upper thermosphere altitudes, and the waves become stronger than tides at mesopause (approximate to 88 km) in both October and March. The data in these equinoctial months also show large differences in mean winds, tides, and waves in the MLT region. The amplitudes and phases of the 24-hour and 12-hour tides at MLT altitudes are compared with those predicted by the global scale wave model (GSWM). The model qualitatively predicts the observed growth of the tides with altitude but does not predict the 12-hour tide becoming stronger than the 24-hour tide at altitudes above mesopause in October.