Summer to winter variability in mesospheric calcium ion distribution and its dependence on Sporadic E at Arecibo

Abstract

We present a new investigation of the variability in the metallic calcium ion concentration near the mesopause region, and its relation to the electron concentration during summer and winter seasons at the Arecibo Observatory. During the summer months the ion layer is broader, extending to 87–88 km compared with winter months where it occurs above this altitude around midnight. The concentration maximizes to ∼200 ions cm−3 around 90–95 km close to midnight during the summer. However, for the winter months, the peak occurs during the early morning hours in thin descending layers above 98 km. Summer to winter variation in the calcium ion to electron ratio displays an average value of ∼0.15 and 0.05 during these seasons, respectively. A good correlation between them suggests that Ca+ densities are directly related to the strength of the Sporadic E, which is stronger in the summer. The average abundance of ions is 5.7 × 107 cm−2 and 4.6 × 107 cm−2 during summer and winter months respectively, while that for electrons is 1.2 × 1010 ions cm−2 and 5.8 × 109 ion cm−2 for these seasons. Both Ca+ and Ne display strong descending layers at different altitudes during summer and winter. Calcium ion lifetimes against neutralization are a factor of two lower during the summer than in the winter months around 90 km but similar at altitudes exceeding 95 km.