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. Plain Language Summary: The neutral Na atomic layers are mainly distributed from 80 to 105 km and they have been used as tracers to study atmospheric chemistry and dynamical processes. Based on four thermospheric Na layers above 130 km observed by two central middle‐latitude lidar stations simultaneously, the paper analyzes the horizontal dimension of the observed thermospheric Na layers, and reports an unprecedented layer reaching an altitude of 200 km with a peak density of 35 cm−3 and a descending rate of 9.3 m/s. The fact high peak density is possible around 150 km opens up the potential for tripling the altitude range for probing temperature and wind by a resonance fluorescence lidar, thus advancing our understanding of dynamics and chemistry in the upper atmosphere. Key Points: The first report of thermospheric Na layers above 130 km over central middle latitudesThe unprecedented thermospheric Na layer that reached highest altitude (200 km), Na density (35 cm−3), and descending speed (9.3 m/s)The first concurrent observation of thermospheric layers from two stations, revealing 3/4 cases with horizontal dimension within ~250 km [ABSTRACT FROM AUTHOR]