LIDAR OBSERVATIONS OF A LOT OF SPORADIC SODIUM LAYERS IN MIDLATITUDE

We have routinely observed mesospheric Na layers since November 1991 w ith a Na ground-based lidar above Tokyo Metropolitan University (TMU) at Hachioji, Tokyo (35.6 degrees N, 139.4 degrees E) in mid-latitude. In the past, the sporadic Na layers have been observed commonly at low - and high-latitude lidar sites [Kwon et al.. 1988; Batista et al., 19 89; von Zahn et al., 1987] but rarely observed at mid-latitude sites [ Serft et al., 1989]. Contrary to expectations, we could observe more t han 100 events of the sporadic Na layers for two years from November 1 991 until October 1993 in this mid-latitude lidar site, and the large sporadic Na layers had been observed especially during spring and summ er. Most of these events were accompanied by sporadic E layers and the most enhancement of the sporadic E layers preceded that of the sporad ic Na layers by 15 to 30 minutes.