Simultaneous measurements of dynamical structure in the mesopause region with lidars and MU radar

In order to clarify the horizontal structure of the wavelike oscillation frequently observed in the night time sodium density profile with a small Gaussian half-width in the middle of the night and a broad distribution at dusk, simultaneous observations with two lidars at Shigaraki (34.9 degrees N, 136.1 degrees E) and Hachioji (35.6 degrees N, 139.4 degrees E) and the MU radar at Shigaraki has been carried out. In the campaign of 35 nights, simultaneous observation was successful in four nights. On December 27-28, 1995, a large scale wave motion was observed by two lidars and the MU radar with meteor observation mode. Phase velocities were almost the same at the two sites and there were only slight differences in phase between the two sites. The wave motion was inconsistent with the component of the tidal wave and similar with the results of hodograph analyses. It is possible that the wave observed by lidars on December 27-28, 1995 was a gravity wave. The results of analyses suggest the possibility of gravity waves which were observed at fixed local time.