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Ann. Geophys., 19, 47-58, 2001
www.ann-geophys.net/19/47/2001/
© European Geosciences Union 2001
Sporadic Ca and Ca+ layers at mid-latitudes: Simultaneous observations and implications for their formation
M. Gerding*, M. Alpers, J. Höffner, and U. von Zahn
Leibniz-Institute of Atmospheric Physics, Schloss-Straße 6, D–18225 Kühlungsborn, Germany
*Now at Alfred Wegener Institute for Polar and Marine Research, Research Department Potsdam, Telegrafenberg A43, D–14473 Potsdam, Germany
Abstract. We report on the
observations of 188 sporadic layers of either Ca atoms and/or Ca ions that we
have observed during 112 nights of lidar soundings of Ca, and 58 nights of Ca+
soundings, at Kühlungsborn, Germany (54° N, 12° E). The Ca+
soundings have been performed simultaneously and in a common volume with the Ca
soundings by two separate lidars. Correlations between sporadic neutral and
ionized metal layers are demonstrated through four case studies. A systematic
study of the variations of occurrence of sporadic Ca and Ca+ layers reveals
that neutral and ionized Ca layers are not as closely correlated as expected
earlier: (a) The altitude distribution shows the simultaneous occurrence of both
sporadic Ca and Ca+ layers to be most likely only in the narrow altitude range
between 90 and 95 km. Above that region, in the lower thermosphere, the sporadic
ion layers are much more frequent than atom layers. Below 90 km only very few
sporadic layers have been observed; (b) The seasonal variation of sporadic Ca
layers exhibits a minimum of occurrence in summer, while sporadic Ca+ layers do
not show a significant seasonal variation (only the dense Ca+ layers appear to
have a maximum in summer). At mid-latitudes sporadic Ca layers are more frequent
than sporadic layers of other atmospheric metals like Na or K. For the
explanation of our observations new formation mechanisms are discussed.
Key words. Ionosphere (ion chemistry and composition;
ionosphere-atmosphere interactions; mid-latitude ionosphere)
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