A Comparison of the Midlatitude Nickel and Sodium Layers in the Mesosphere: Observations and Modeling

• Published in: Journal of geophysical research. Space physics 2022-02, Vol.127 (2), p.n/a
• Main Authors: Jiao, Jing, Feng, Wuhu, Wu, Fang, Wu, Fuju, Zheng, Haoran, Du, Lifang, Yang, Guotao, Plane, John
• Format: Article
• Language: English
• Subjects: cosmic dust; lower thermosphere; mesosphere; meteoric ablation; nickel layer; sodium layer
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2021JA030170

A dual‐wavelength resonance fluorescence lidar facility, operating at 341 and 589 nm, was used to observe simultaneously the Ni and Na layers in the upper atmosphere over Yanqing station, Beijing (40.41°N, 116.01°E). Lidar measurements were performed on 126 nights (1090 hr in total) from April 2019 to March 2020 and April 2021 to August 2021, so that the full seasonal cycle of the Ni layer was observed for the first time. The Ni and Na layers exhibit a similar annual cycle, increasing by a factor of ∼3 from a mid‐summer minimum to a midwinter maximum. The annual mean column densities of Ni and Na are 3.1 × 108 and 2.5 × 109 cm−2, respectively, giving a mean Na:Ni ratio of 8.1, which is significantly larger than their CI chondritic ratio of 1.2. This is explained by the more efficient ablation of Na from cosmic dust particles by a factor of 3, and the more rapid neutralization of Na+ between 90 and 100 km, where the measured Na+:Ni+ ratio is only 2.2. The Ni layer peak occurs around 84 km, 8 km below that of Na. These features are simulated satisfactorily by the Whole Atmosphere Community Climate Model (WACCM) and are explained by significant differences in the neutral chemistry of the two metals below 90 km and their ion‐molecule chemistry between 90 and 100 km. Plain Language Summary Layers of metal atoms are produced in the upper atmosphere by the ablation of cosmic dust particles, which enter the atmosphere at hyperthermal speeds, so that a significant fraction of them melt and evaporate. A layer of sodium atoms has been observed for more than 40 years both from the ground and space. In contrast, a layer of nickel atoms was only discovered 6 years ago. Ni is of interest because it occurs in an iron‐nickel‐sulfide phase in cosmic dust, whereas sodium occurs in the bulk metal silicate phase. Also, the Ni layer extends lower in the atmosphere than the other metals, such as Na, Fe, and Mg. This study reports the first observations of the seasonal behavior of Ni along with simultaneous Na measurements. Although the seasonal behavior of the two metals is similar (maximum in winter and minimum in summer), the Ni layer peaks 8 km below the Na layer as a result of important differences in the atmospheric chemistry, which controls the layers. There is about 8 times as much Na as Ni compared with a ratio of 1.2 in carbonaceous meteorites. All these features are simulated satisfactorily by a global chemistry‐climate model. Key Points First simultaneous observations