|
|
 |
|
|
Ann. Geophys., 24, 173-185, 2006
www.ann-geophys.net/24/173/2006/
© European Geosciences Union 2006
The F-region trough: seasonal morphology and relation to interplanetary magnetic field
M. Voiculescu1, I. Virtanen2, and T. Nygrén2
1Department of Physics, Faculty of Sciences, University “Dunărea de Jos" Galati, St. Domnească, No. 47, 800008 Galati, Romania
2Department of Physical Sciences, University of Oulu, P.O. Box 3000, FIN-90014, Finland
Abstract. We present here the results of a statistical study of the
ionospheric trough observed in 2003 by means of satellite
tomography. We focus on the seasonal morphology of the trough
occurrence and investigate the trough latitude, width and the
horizontal gradients at the edges, at different magnetic local
times, as well as their relations to geomagnetic activity and
the interplanetary magnetic field. A seasonal effect is noticed in the
diurnal variation of the trough latitude, indicating that summer
clearly differs from the other seasons. In winter the troughs seem
to follow the solar terminator. The width of the trough has a
diurnal variation and it depends on the season, as well. The
broadest troughs are observed in winter and the narrowest ones in
summer. A discontinuity in the diurnal variation of the trough
latitude is observed before noon. It is suggested that this is an
indication of a difference between the generation mechanisms of
morningside and eveningside troughs. The density gradients at the
edges have a complex dependence on the latitude of the trough and
on geomagnetic activity. The photoionization and the auroral
precipitation are competing in the formation of the trough walls
at different magnetic local times. An important finding is that
the interplanetary magnetic field plays a role in the occurrence
of the trough at different levels of geomagnetic activity. This is
probably associated with the topology of the polar cap convection
pattern, which depends on the directions of the IMF components By
and Bz.
Full Article in PDF (581 KB) |
|
|
