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| Titel |
Bounce-averaged Fokker-Planck diffusion equation in non-dipolar magnetic fields with applications to the Dungey magnetosphere |
| VerfasserIn |
B. Ni, R. M. Thorne, Q. Ma |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 30, no. 4 ; Nr. 30, no. 4 (2012-04-27), S.733-750 |
| Datensatznummer |
250017217
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| Publikation (Nr.) |
 copernicus.org/angeo-30-733-2012.pdf |
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| Zusammenfassung |
| We perform a detailed derivation of the bounce-averaged relativistic
Fokker-Planck diffusion equation applicable to arbitrary magnetic field at a
constant Roederer L. The form of the bounce-averaged diffusion equation is
found regardless of details of the mirror geometry, suggesting that the
numerical schemes developed for solving the modified two-dimensional (2-D)
Fokker-Planck equation in a magnetic dipole should be feasible for similar
computation efforts on modeling wave-induced particle diffusion processes in
any non-dipolar magnetic field. However, bounce period related terms and
bounce-averaged diffusion coefficients are required to be computed in
realistic magnetic fields. With the application to the Dungey magnetosphere
that is controlled by the intensity of southward interplanetary magnetic
field (IMF), we show that with enhanced southward IMF the normalized bounce
period related term decreases accordingly, and bounce-averaged diffusion
coefficients cover a broader range of electron energy and equatorial pitch
angle with a tendency of increased magnitude and peaking at lower energies.
The compression of the Dungey magnetosphere can generally produce scattering
loss of plasma sheet electrons <~4 keV and radiation belt
electrons >~100 keV on a timescale shorter than that in a dipolar
field, and induce momentum diffusion at high pitch angles closer to 90°.
Correspondingly, the strong diffusion rate drops considerably as a product
of changes in both the equatorial loss cone and the bounce period. The
extent of differences in all the parameters introduced by the southward IMF
intensification also becomes larger for a field line with higher equatorial
crossing. With the derived general formulism of bounce-averaged diffusion
equation for arbitrary 2-D magnetic field, our results confirm the need for
the adoption of realistic magnetic fields to perform accurate determination
of electron resonant scattering rates and precise multi-dimensional
diffusion simulations of magnetospheric electron dynamics. |
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