Recent observations of Lithium atoms in the middle atmosphere by lidar

Ablating meteoroids form a well-known layer of metal atoms in the middle atmosphere between about 80 km and more than 100 km altitude. Some of these metals, like sodium, iron, potassium, or calcium, have been observed for decades by lidar. They are now often used for resonance lidar measurements of temperature and winds or as tracers of the middle atmosphere dynamics and the coupling with the ionosphere. Atomic lithium has rarely been observed so far because the natural abundance is very low, as is the lidar backscatter signal. Early observations in the late 1970s above southern France revealed a number density of only a few atoms per cubic centimeter, but have been suspended about 45 years ago. While lithium has a low abundance in meteoroids, it has a much higher share in space debris, i.e. satellites and upper rocket stages re-entering into the atmosphere. This makes lithium an important target for space-debris research in the mesosphere / lower thermosphere. We have set up a Li resonance lidar in 2024 at our site at Kühlungsborn/Germany (54°N, 21°E). We will show first results on the atomic Li abundance in the middle atmosphere after a 45-year observational gap, including some record-high concentrations, and describe our new lidar for regular Li monitoring.