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Abstract:
[...] According to the results of this thesis the following mechanism is suggested to
cause the cusp-related density anomaly: The energy input by the solar wind, as
characterised by the merging electric field, provides the power for Joule heating of
preferably neutral molecules. Soft particle precipitation in the cusp simultaneously
enhances the altitude of maximal Pedersen conductivity, thus lifting up the heated
layer in the cusp. The cusp-related density anomaly is then caused by local composition
changes in the upper atmosphere due to the differential expansion of heavier
particles. The density enhancement is more intensive during phases of high solar
activity, i.e. a larger background density favours the formation of large anomalies.
The atmospheric fountain in the cusp region affects the upper atmosphere globally.
The harmonic exitation of the fountain in 2005 caused a global density variation of
the thermosphere.
