Lidar soundings of the mesospheric nickel layer using Ni(³F) and NI(³D) transitions

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.