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Ann. Geophys., 25, 645-659, 2007
www.ann-geophys.net/25/645/2007/
© European Geosciences Union 2007
The equatorward wall of the subauroral trough in the afternoon/evening sector
G. W. Prölss
Argelander Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
Abstract. Although ionospheric troughs are a very important feature of the subauroral
ionosphere, many of their properties remain incompletely documented and
understood. Here Dynamics Explorer-2 satellite data are used to investigate
one specific part of this complex phenomenon, namely its equatorward wall. We
find that in the afternoon/evening sector of the Northern Hemisphere the
location of this density drop depends primarily on the level of geomagnetic
activity and magnetic local time. Longitudinal variations are only of
secondary importance. A formula is derived which summarizes these variations.
The magnitude of the density drop in the trough wall depends primarily on
altitude and longitude, and to a lesser degree on local time and geomagnetic
activity. These variations are also described quantitatively. Using a
superposed epoch type of averaging procedure, a mean latitudinal profile of
the trough wall is derived. No anomalous increase in the density at the
equatorward edge of the trough is observed. There is, however, a significant
increase in the electron temperature at the location of the density drop. Our
results are important for the empirical description and numerical simulation
of ionospheric troughs. They also may be used to define the boundary between
middle and subauroral latitudes.
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