New Lidar Observations of Ca+ in the Mesosphere and Lower Thermosphere Over Arecibo

This paper presents the first high-resolution resonance lidar measurements of calcium ion (Ca+) layers in the F region valley (140-180 km) over Arecibo. Unique, simultaneous Ca+, neutral sodium (Na), and potassium (K) lidar observations, along with incoherent scatter radar electron concentration (Ne) covering 80- to 180-km altitudes for three consecutive nights, are reported here. At E region altitudes, the Ca+ distribution follows sporadic E activity on these nights. Thin Ca+ layers (widths < 150 m) imply wind reversals to be occurring over this short height range. Ca+ above 140 km do not always correspond to Ne layers but are detected only during presunrise hours. The average Ca+ column abundance below 120 km is highly variable but during high-altitude Ca+ event decreases by a factor of 2 above 120 km. Both N-e and Ca+ display similar descent rates of similar to 7 m/s at altitudes >150 km during these events. Plain Language Summary Metals and their ions are deposited in the Earth's mesosphere and lower thermosphere region due to meteoroid sputtering and ablation. These long-lived metal ions converge to form thin descending layers in the ionosphere, where they are often observed by ionosondes, incoherent scatter radar, etc. The neutralization of these metal ions results in enhanced neutral metal layers at altitudes below 100 km. Resonance lidars play an important role in investigating the structures of the neutral metal layers. The only metal ion that can be observed from ground is Ca+, which can be studied using the Arecibo Observatory resonance lidar. We report unique, common-volume lidar/incoherent scatter radar metals and electron concentration observations over 80- to 180-km altitudes. Previous in situ measurements have revealed molecular ions (NO+) to be dominant in the descending layers at altitudes >150 km. Such measurements promise new insights into ion transport processes and meteoroid ablation/sputtering processes.