New Li lidar observations and model simulation: A window to anthropogenic signatures

We present Li lidar observations in the mesopause region above Kühlungsborn, Germany (54°N, 12°E). The lithium layer is mainly formed by meteoric ablation. But lithium has a much higher relative abundance in space debris compared with meteoroids, making it a good indicator of anthropogenic influence in the upper mesosphere. Our measurements reveal a strong seasonal increase in Li abundance between August and December 2024, growing from ~1.6x106 to 4.7x106 cm-2. These values are in reasonable agreement with the first simulations based on the Whole Atmosphere Community Climate Model (WACCM6) with a newly developed Li chemistry network; however, WACCM-Li does not explain high Li abundances of up to 10.7x106 cm-2 observed in Jan/Feb 2025. This may be due to anthropogenic effects or an unidentified natural mechanism. This study highlights the potential of lithium observations for monitoring the consequences of re-entering space debris on the composition of the atmosphere.