28 Feb 2022
28 Feb 2022
Status: a revised version of this preprint is currently under review for the journal ACP.

Significant enhancements of the mesospheric Na layer bottom below 75 km observed by a full-diurnal-cycle lidar at Beijing (40.41 °N, 116.01 °E), China

Yuan Xia1,2, Jing Jiao2, Satonori Nozawa3, Xuewu Cheng4, Jihong Wang2, Lifang Du2, Yajuan Li1, Haoren Zheng2, Faquan Li4, and Guotao Yang2 Yuan Xia et al.
  • 1School of Electronic Engineering, Nanjing Xiaozhuang University, Nanjing, 211171, China
  • 2State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing, 100190, China
  • 3Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, 464-8601, Japan
  • 4Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan, 430071, China

Abstract. Based on the full-diurnal-cycle sodium (Na) lidar observations at Beijing (40.41 °N, 116.01 °E), we firstly report pronounced downward extensions of the Na layer bottomside to below 75 km near mid-December, 2014. Considerable Na atoms were observed even as low as ~72 km, where Na atoms is short-lived. To our knowledge, this represents the lowest altitude where considerable Na atoms have ever been detected by Na lidar. More interestingly, an unprecedented Na density of ~2500 atoms/cm3 around 75 km was observed on December 17, 2014. Such high Na atoms concentration was two orders of magnitude larger than that normally observed at the similar altitude region. The variations of Na density on the layer bottom were found to be accompanied by warming temperature anomalies and considerable perturbations of minor chemical species (H, O, O3) in the upper mesosphere. Different from the previous reported metal layer bottom enhancements mainly contributed by photolysis after sunrise, these observational results suggest more critical contributions were made by the Na neutral chemical reactions to the Na layer bottom extensions reported here. The time-longitudinal variations of background atmospheric parameters in the upper mesosphere and stratosphere from global satellite observations and ERA reanalysis data indicated that the anomalous structures observed near the lidar site in mid-December, 2014 were associated with planetary wave (PW) activities. The anomalies of temperature and O3 perturbation showed opposite phase in the altitude range of 70~75 km and 35~45 km. This implied that the vertical coupling between the mesosphere and stratosphere, possibly driven by the interactions of PW activities with background atmosphere, contributed to the perturbations of background atmosphere. Furthermore, the bottom enhancement on December 17, 2014 was also accompanied by clear wavy signatures in the main layer. The wavy structures had downward phase propagations and agreed well with the variation of zero zonal wind measured by a nearby meteor radar, suggesting the downward transportation of Na species from above 80 km to below further promotes the formation of the unprecedented Na layer bottom enhancement on December 17, 2014. These results provide a clear observational evidence for the Na layer bottom response to the planetary-scale atmospheric perturbations which modulated Na chemical reactions. The results of this paper also have implications for the response of the metal layer to vertical coupling between the lower atmosphere and the mesosphere.

Yuan Xia et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-112', Anonymous Referee #1, 11 Mar 2022
    • AC1: 'Reply on RC1', Yuan Xia, 21 May 2022
  • RC2: 'Comment on acp-2022-112', Anonymous Referee #2, 12 Apr 2022

Yuan Xia et al.

Yuan Xia et al.


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Short summary
The layer of sodium atoms is generally located above 80 km. This study reports the significant enhancements of the sodium layer below 75 km where sodium atoms are short-lived. The neutral chemical reactions were suggested making a critical contribution. The reported results provide a clear observational evidence for the role of planetary waves in the variation of metal layers, and have implications for the response of the metal layers to perturbations in lower atmosphere.