The First Concurrent Observations of Thermospheric Na Layers From Two Nearby Central Midlatitude Lidar Stations

In 2011, Chu et al. reported the observation of neutral Fe layers reaching 155 km. Since then, there are five additional reports of layers extending above 130 km to as high as 170 km, none from central middle latitudes (35°-55°), a large atmospheric region of considerable importance. Here we report the first concurrent observations of thermospheric Na layers from two nearby lidar stations so located, Yanqing (40.5°N, 116.0°E) and Pingquan (41.0°N, 118.7°E). From one-year data set, we found four such layers, including an unprecedented one reaching 200 km with highest density of 35 cm^-3 and fastest descending rate. While the main Na layers were comparable, in three nights, these thermospheric layers were observed only in one station (Yanqing), suggesting that these layers often occur locally with a horizontal scale less than 250 km. We tabulate, compare, and discuss the principle characteristics of all the reported thermospheric layers.