On the abundance of metal ions in the lower ionosphere

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Abstract
Height profiles of the metal ions Fe+, Mg+, Ca+, and Na+ in the lower ionosphere measured in situ in five rocket flights with a magnetic mass spectrometer are presented. The mean total column density of the ionized metals is within 4.4 ± 1.2 × 109 cm−2 in periods without special meteor shower activity. The column density increased by 1 order of magnitude during the Perseid meteor shower of August 12, 1976. The dominant metal ion in all five flights is Fe+. Its column density in the five flights is, in average, a factor 2.0 ± 0.6 larger than Mg+. A comparison of the column densities of Ni+, Al+, Ca+, Mg+, K+, and Na+, which were normalized to Fe+, to the corresponding ratios in carbonaceous chondrites type I (CI) showed a depletion in the abundance of aluminium (80%), calcium (65%), magnesium (55%), and nickel (35%). At heights above 95 km all metals under consideration should predominantly occur as ions, and no distinct mass fractionation between the different ionized metals is expected from the main loss process, the downward movement of the metal ion layers. The reduced abundance of Al, Ca, Mg, and Ni is therefore most likely an effect of a fractionation originating from partially melted micrometeorites and an associated partial evaporation retaining elements having a relatively high condensation temperature as compared to Fe, which is the case for Ni, Al, Ca, and Mg.