Search

We report 19 coobserved enhanced sodium layers, including sporadic sodium layers (SSLs) and thermospheric enhanced sodium layers (TeSLs), over Hefei (31.8°N, 117.3°E) and Wuhan (30.5°N, 114.4°E) from 2011 to 2018. The total coobservation time at Hefei and Wuhan was 387.24 hr, and the average occurrence rates were 0.038 hr−1 and 0.028 hr−1 for the SSLs and TeSLs, respectively. The SSL and TeSL occurrence rates in summer were 0.078 and 0.039 hr−1, respectively, which were considerably higher than those in other seasons. Among all 19 cases, 16 cases, including 9 SSL cases and 7 TeSL cases, occurred almost simultaneously over Hefei and Wuhan without a time delay. Seven TeSLs and four out of the nine SSLs were accompanied by ionospheric sporadic E (Es), suggesting that an "Es‐SSL (TeSL)" chain formed via the wave‐induced wind shear mechanism. Three SSLs were modulated by waves and the two other cases were related with gravity wave overturning. In general, the correlation coefficients between Hefei and Wuhan for long‐duration cases (more than 2 hr) were high due to some large‐scale mechanism, and the short‐duration cases (less than 2 hr) had poor correlation due to different local characteristics. In addition, three cases were observed with an apparent time delay over Hefei and Wuhan, which might indicate the possible existence of long‐distance transport processes. Key Points: Enhanced sodium layers observed between Hefei and Wuhan showed the consistency of the overall propagating and the difference in detailMost of the enhanced sodium layers were related with ionospheric sporadic E, one of which extended horizontally for nearly 1,000 kmFive sporadic sodium layer cases in the upper mesosphere, instead of relate with Es, are mainly generated by neutral dynamic process [ABSTRACT FROM AUTHOR]

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]