Upper atmosphere Ca and Ca⁺ at mid‐latitudes: First simultaneous and common‐volume lidar observations

We report on simultaneous, common‐volume observations of Ca and Ca + layers in the 80 to 125 km altitude range by groundbased resonance lidar. The measurements were carried out during 9 nights in summer 1995 on the German island Rügen (55°N, 13°). We observed a permanent Ca layer with an average peak density of 31 atoms/cm³ at 87 km altitude. The average Ca column abundance was 2.2×10 7 cm; −2 . No permanent Ca + layer was found, but sporadic Ca + layers occured frequently in the altitude range 90–120 km. Peak densities of these thin layers varied between 65 and 3900 atoms/cm³. We demonstrate the interesting possibilities of groundbased simultaneous common‐volume observations of neutral and ionized calcium in the lower thermosphere.