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Discussion papers
https://doi.org/10.5194/acp-2018-1017
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-1017
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 27 Nov 2018

Research article | 27 Nov 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Photochemistry on the under side of the mesospheric Na layer

Tao Yuan1,2, Wuhu Feng3,4, John M. C. Plane3, and Daniel R. Marsh3,5 Tao Yuan et al.
  • 1Physics Department, Utah State University, Logan, Utah, USA
  • 2Center for Atmospheric and Space Sciences, Utah State University, Logan, Utah, USA
  • 3School of Chemistry, University of Leeds, Leeds, UK
  • 4National Centre for Atmospheric Science, University of Leeds, Leeds, UK
  • 5National Center for Atmospheric Research, Boulder, Colorado, USA

Abstract. Lidar observations of the mesospheric Na layer have revealed considerable diurnal variations particularly on the underside of the main layer where more than an order-of-magnitude increase of Na density has been observed below 80 km after sunrise. In this paper, multi-year Na lidar observations over a full diurnal cycle at Utah State University (USU) (41.8°N, 111.8°W) and a global atmospheric model of Na with 0.5km vertical resolution in the mesosphere lower thermosphere (WACCM-Na) are utilized to explore the dramatic changes of Na density on the layer underside. Photolysis of the principal reservoir NaHCO3 is shown to be primarily responsible for the increase in Na after sunrise, amplified by the increased rate of reaction of NaHCO3 with atomic H, which is mainly produced from the photolysis of H2O and the reaction of OH with O3. This finding is further supported by Na lidar observation at USU during the solar eclipse (>96% totality) event on August 21st, 2017, when a decrease and recovery of the Na density on the underside of the layer were observed. Lastly, the model simulation shows that the Fe density underside around 80km increases larger and earlier than observed Na changes during sunrise because of the considerably faster photolysis rate of its major reservoir FeOH.

Tao Yuan et al.
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The Na layer in the upper atmosphere is found to be quite sensitive to solar radiation and varies considerably during sunrise and sunset. In this paper, we use the lidar observations and an advanced model to investigate this process. We found that the variation is mostly due to the changing of several photo-chemical reactions involving Na compounds, especially NaHCO3. We also demonstrate that Fe layer in the same region changes more quickly than the Na layer, due to faster reaction rate of FeOH.
The Na layer in the upper atmosphere is found to be quite sensitive to solar radiation and...
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