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Ann. Geophys., 23, 3389-3398, 2005
www.ann-geophys.net/23/3389/2005/
© European Geosciences Union 2005
Electron dynamics during substorm dipolarization in Mercury's magnetosphere
D. C. Delcourt1, K. Seki2, N. Terada2,*, and Y. Miyoshi2
1CETP-CNRS-IPSL, Saint-Maur des Fossés, France
2STEL, Nagoya University, Toyokawa, Japan
*now at: NIICT, Tokyo and CREST-JSTA, Saitama, Japan
Abstract. We examine the nonlinear dynamics of electrons during the
expansion phase of substorms at Mercury using test particle simulations. A
simple model of magnetic field line dipolarization is designed by rescaling
a magnetic field model of the Earth's magnetosphere. The results of the
simulations demonstrate that electrons may be subjected to significant
energization on the time scale (several seconds) of the magnetic field
reconfiguration. In a similar manner to ions in the near-Earth's
magnetosphere, it is shown that low-energy (up to several tens of eV)
electrons may not conserve the second adiabatic invariant during
dipolarization, which leads to clusters of bouncing particles in the
innermost magnetotail. On the other hand, it is found that, because of the
stretching of the magnetic field lines, high-energy electrons (several keVs
and above) do not behave adiabatically and possibly experience meandering
(Speiser-type) motion around the midplane. We show that dipolarization of
the magnetic field lines may be responsible for significant, though
transient, (a few seconds) precipitation of energetic (several keVs) electrons onto the
planet's surface. Prominent injections of energetic trapped electrons toward
the planet are also obtained as a result of dipolarization. These injections,
however, do not exhibit short-lived temporal modulations, as observed by
Mariner-10, which thus appear to follow from a different mechanism than a
simple convection surge.
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