INCOHERENT-SCATTER RADAR OBSERVATIONS OF AGW TID EVENTS GENERATED BY THE MOVING SOLAR TERMINATOR/

Observations of traveling ionospheric disturbances (TIDs) associated w ith atmospheric gravity waves (AGWs) generated by the moving solar ter minator have been made with the Millstone Hill incoherent scatter rada r. Three experiments near 1995 fall equinox measured the AGW/TID veloc ity and direction of motion. Spectral and cross-correlation analysis o f the ionospheric density observations indicates that ST-generated AGW s/TIDs were observed during each experiment, with the more-pronounced effect occurring at sunrise. The strongest oscillations in the ionosph eric parameters have periods of 1.5 to 2 hours. The group and phase ve locities have been determined and show that the disturbances propagate in the horizontal plane perpendicular to the terminator with the grou p velocity of 300-400 m s(-1) that corresponds to the ST speed at iono spheric heights. The high horizontal group velocity seems to contradic t the accepted theory of AGW/TID propagation and indicates a need for additional investigation.