LIDAR OBSERVATIONS OF THE MESOSPHERIC Na LAYER OVER WUHAN: SEASONAL AND NOCTURNAL VARIATIONS

Based on the lidar observations between March 2001 and October 2002, the characteristics of background Na layer over Wuhan （30.5°N, 114.4°E） are presented and compared with other reported lidar measurements, especially with that of Ur-bana （40°N, 88°W）. The sodium abundance in Wuhan reaches a maximum value in November which is approximately 2.5 times larger than that in April. In November and May, the layer centroid height reaches its minimum and its maximum in April, September and December. The yearly averaged rms width is 4.47km. There is a variation trend in the parameters of Na layer. Especially, the layer rms width shows a semiannual variation trend. The sodium layer abundance generally increases through the night. After rapidly ascending from sunset, the layer centroid height climbs up slowly between 2000 LT and 0500 LT, then descend swiftly. The sodium layer rms width shows about 1.3km variation during the night. At first the layer rms width diminishes, after arriving at a minimum at 0035 LT, it increases steadily with time.