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Ann. Geophys., 24, 381-392, 2006
www.ann-geophys.net/24/381/2006/
© European Geosciences Union 2006
Flux Transfer Events: 1. generation mechanism for strong southward IMF
J. Raeder
Space Science Center, University of New Hampshire, Durham, NH 03824, USA
Abstract. We use a global numerical model of the interaction of the solar wind and the interplanetary
magnetic field with Earth's magnetosphere to study the formation process of Flux Transfer Events (FTEs)
during strong southward IMF. We find that:
(i) The model produces essentially all observational features expected for FTEs, in particular
the bipolar signature of the magnetic field BN component,
the correct polarity, duration, and intermittency of that bipolar signature,
strong core fields and enhanced core pressure, and flow enhancements;
(ii) FTEs only develop for large dipole tilt whereas in
the case of no dipole tilt steady magnetic reconnection occurs at the dayside magnetopause;
(iii) the basic process by which FTEs are produced is the sequential generation of new
X-lines which makes dayside reconnection inherently time dependent
and leads to a modified form of dual or multiple X-line reconnection;
(iv) the FTE generation process in this model is not dependent on specific assumptions
about microscopic processes;
(v) the average period of FTEs can be explained by simple geometric arguments involving
magnetosheath convection;
(vi) FTEs do not develop in the model if the numerical resolution is too coarse leading to too
much numerical diffusion; and
(vii) FTEs for nearly southward IMF and large dipole tilt, i.e., near solstice, should only develop
in the winter hemisphere, which provides a testable prediction of seasonal modulation.
The semiannual modulation of intermittent FTE reconnection versus steady reconnection is also expected
to modulate magnetospheric and ionospheric convection and may thus contribute to the semiannual
variation of geomagnetic activity.
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