First Simultaneous Lidar Observations of Thermosphere‐Ionosphere Sporadic Ni and Na (TISNi and TISNa) Layers (∼105–120 km) Over Beijing (40.42°N, 116.02°E)

• Published in: Geophysical research letters 2022-08, Vol.49 (16), p.n/a
• Main Authors: Wu, Fuju, Chu, Xinzhao, Du, Lifang, Jiao, Jing, Zheng, Haoran, Xun, Yuchang, Feng, Wuhu, Plane, John M. C., Yang, Guotao
• Format: Article
• Language: English
• Subjects: Ablation; Abundance; Altitude; Atmosphere; Atmospheric particulates; Atoms & subatomic particles; Coefficients; Correlation coefficient; Correlation coefficients; Cosmic dust; direct recombination; Dust; Dust particles; E region; Electron-ion recombination; Electrons; Heavy metals; Interplanetary dust; Ionosphere; Lidar; Lidar observations; Lower thermosphere; Metal ions; metal layer; Metals; Neutralization; Nickel; Ratios; Recombination; Sodium; sporadic E layer; sporadic metal layers; Thermosphere; thermosphere‐ionosphere; Upper atmosphere
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2022GL100397

We report the first simultaneous lidar observations of thermosphere‐ionosphere sporadic nickel and Na (TISNi and TISNa) layers in altitudes ∼105–120 km over Yanqing (40.42°N, 116.02°E), Beijing. From two years of data spanning April 2019 to April 2020 and July 2020 to June 2021, TISNi layers in May and June possess high densities with a maximum of 818 cm−3 on 17 May 2021, exceeding the density of main layer peak (∼85 km) by ∼4 times. They correlate with strong sporadic E layers observed nearby. TISNa layers occur at similar altitudes as TISNi with spatial‐temporal correlation coefficients of ∼1. The enrichment of Ni in TISNi is evident as the [TISNi]/[TISNa] column abundance ratios are ∼1, about 10 times the main layer [Ni]/[Na] ratios. These results are largely explained by neutralization of converged Ni+ and Na+ ions via recombination with electrons. Calculations show direct recombination dominating over dissociative recombination above ∼105 km. Plain Language Summary The metal layers in the Earth's middle and upper atmosphere originate from cosmic dust (i.e., interplanetary dust particles), and they are also called meteoric metal layers. Tons of cosmic dust particles enter the atmosphere each day. Some of these particles heat up during entry to the point where they melt and their metallic constituents begin to vaporize. Na (sodium) is a relatively volatile metal compared to Ni (nickel), so tends to ablate more efficiently. Cosmic dust ablation gives rise to permanent (main) layers of neutral metal atoms which occur globally around 80–100 km in altitude. The Ni layer was observed recently for the first time, and the Ni/Na abundance ratio shown to be ∼0.1. In the present study we report the very surprising observations that sporadic layers of these metal atoms, which occur intermittently in the lower thermosphere and ionosphere between 105 and 120 km, have Ni/Na relative abundances which are 10 times larger. We demonstrate that this is likely due to the formation of neutral metals at this height through the process of direct (radiative) recombination of metal ions Ni+ and Na+ with electrons. This process is significantly faster for Ni+ ions. Key Points First simultaneous observations of thermosphere‐ionosphere sporadic Ni and Na layers (105–120 km) show close correlations and Ni enrichment High‐density thermosphere‐ionosphere sporadic Ni mainly occur in May–June with a maximum of 818 cm−3 being 4 times the main Ni peak and correlate well with sporadic E A