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

Abstract

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 Ne and Ca+ display similar descent rates of ~7 m/s at altitudes >150 km during these events.