Lidar Soundings of the Mesospheric Nickel Layer Using Ni(³F) and Ni(³D) Transitions

Abstract

During six nights between January and March 2018 we observed the mesospheric Ni layer by lidar from Kühlungsborn, Germany (54°N, 12°E). For most of the soundings we utilized for the first time a transition from the low‐lying excited Ni(3D) state at 341 nm. For additional soundings we used the ground‐state Ni(3F) transition at 337 nm, giving similar results but a worse signal‐to‐noise ratio. We observed nightly mean Ni peak densities between ∼280 and 450 cm−3 and column abundances between 3.1·108 and 4.9·108 cm−2. Comparing with iron densities we get a Fe/Ni ratio of 38, which is a factor of 2 larger than the ratio in CI chondrites and factor of 32 larger than the Fe/Ni ratio observed by the only previous measurement of mesospheric Ni (Collins et al., 2015, https://doi.org/10.1002/2014GL062716). The underabundance of Ni compared to CI chondrites suggests that Ni is more efficiently sequestered as Ni+ or neutral reservoir species than Fe.

The Meteoric Ni Layer in the Upper Atmosphere

“…This degree of Ni enrichment seems extremely unlikely. In contrast, the Kühlungsborn measurements (Gerding et al, 2019) require the Ni MIF to be decreased by a factor of only 2.1 relative to the Fe MIF—which would be explained if the Fe:Ni ratio in the metallic phase was ~12, or the Fe‐Ni phase was ~5 wt% of the cosmic dust particles. Interestingly, a similar discrepancy was found between Fe + :Ni + measurements in the Martian thermosphere and the CABMOD‐ZoDy prediction (Carrillo‐Sánchez et al, 2020).…”

“…This might indicate a high Ni enrichment in cosmic dust particles, but that contradicts the analysis of meteoritic fragments in our laboratory (Bones et al, 2019), and the Fe:Ni ratio measured in cosmic dust particles which survived atmospheric entry (Arndt et al, 1996). The CABMOD‐ZoDy ratio is a factor of ~0.42 times smaller than the Kühlungsborn lidar‐measured ratio of 38:1 (Gerding et al, 2019), which may suggest that Ni is converted to long‐term atmospheric sinks more efficiently than Fe (Carrillo‐Sánchez et al, 2020). In comparison, the Fe + :Ni + ratio measured between 85 and 100 km, measured during eight rocket flights, is , which is close to the ratio of the Fe and Ni MIFs (Carrillo‐Sánchez et al, 2020).…”

“…After determining the optimal Ni MIF during 2 years of model spin up, WACCM‐Ni was run for a full year simulation from January to December 2012. Although the Ni observations of Gerding et al (2019) were performed in early 2018, some input files (solar input, CMIP6 emissions, and chemical species at the surface) in the released CESM2_1_1 are not yet available from 2015 onward. We therefore chose 2012 as the most recent year in which there were no major perturbations during the observational period (January–March), such as the major sudden stratospheric warming in January 2013 (Manney et al, 2015), which would have perturbed the Ni abundance in the model (Feng et al, 2017).…”

“…This surprising discrepancy prompted a further lidar study at Kühlungsborn, Germany (54°N, 12°E) on six nights between January and March 2018, using the same spectroscopic transition as Collins et al (2015), as well as the stronger Ni(a 3 D 3 ‐ 3 F 4 ) transition at λ air = 341.48 nm (Gerding et al, 2019). The Ni densities were found to be much lower, with peak densities ranging from 280–450 cm −3 and column abundances from (3.1–4.9) × 10 8 cm −2 .…”

“…However, both studies found that the Ni layer was broader than the Fe layer on the bottom‐side of the layer. The Ni layer also appeared to exhibit more short‐term variability than Fe, with the peak density of Ni varying by 55% in just 15 min (Gerding et al, 2019), compared with the Fe peak density varying by 45% over 6 hr (Bills & Gardner, 1990).…”