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Ann. Geophys., 22, 63-72, 2004
www.ann-geophys.net/22/63/2004/
© European Geosciences Union 2004
Evaluation of the geometry of ionospheric current systems related to rapid geomagnetic variations
S. V. Apatenkov1, V. A. Sergeev1, R. Pirjola2, and A. Viljanen2
1Institute of Physics, St. Petersburg State University, Ulyanovskaya 1, Petrodvoretz, 198504, St.Petersburg, Russia
2Finnish Meteorological Institute, Geophysical Research Division, P.O. Box 503, FIN-00101 Helsinki, Finland
Abstract. To learn about the geometry and sources of the ionospheric current
systems which generate strong geomagnetically induced currents, we
categorize differential equivalent current systems (DEC) for
events with strong dB/dt by decomposing them into the
contributions of electrojet-type and vortex-type elementary
systems. By solving the inverse problem we obtain amplitudes and
locations of these elementary current systems. One-minute
differences of the geomagnetic field values at the IMAGE
magnetometer network in 1996–2000 are analysed to study the
spatial distributions of large dB/dt events. The relative
contributions of the two components are evaluated. In particular, we
found that the majority of the strongest dB/dt events (100–1000nT/min) appear to be produced by the vortex-type current
structures and most of them occur in the morning LT hours, probably
caused by the Ps6 pulsation events associated with auroral omega
structures. For strong dB/dt events the solar wind parameters are
shifted toward strong (tens nT) southward IMF, enhanced velocity
and dynamic pressure, in order for the main phase of
the magnetic storms to occur. Although these events appear mostly during
magnetic storms when the auroral oval greatly expands, the area of
large dB/dt stays in the middle part of the auroral zone;
therefore, it is connected to the processes taking part in the
middle of the magnetosphere rather than in its innermost region
populated by the ring current.
Key words.
Geomagnetism and paleomagnetism (rapid time variations) –
Ionosphere (auroral ionosphere; ionospheric disturbances)
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