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

We report on simultaneous, common-volume observations of Ca add 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 Rugen (55 degrees N, 13 degrees E). We observed a permanent Ca layer with an average peak density of 31 atoms/cm(3) at 87 km altitude. The average Ca column abundance was 2.2 x 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/cm(3). We demonstrate the interesting possibilities of groundbased simultaneous common-volume observations of neutral and ionized calcium in the lower thermosphere.