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| Titel |
IMF-induced escape of molecular ions from the Martian ionosphere |
| VerfasserIn |
Y. Kubota, K. Maezawa, H. Jin, M. Fujimoto |
| 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 ; 31, no. 8 ; Nr. 31, no. 8 (2013-08-06), S.1343-1356 |
| Datensatznummer |
250086088
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| Publikation (Nr.) |
 copernicus.org/angeo-31-1343-2013.pdf |
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| Zusammenfassung |
| Since Mars does not possess a significant global intrinsic magnetic field,
the solar wind interacts directly with the Martian ionosphere and can induce
ion escapes from it. Phobos-2 and recent Mars Express (MEX) observations have shown
that the escaping ions are O+ as well as molecular O2+ and CO2+.
While O+ escape can be understood by the ion pick-up of non-thermal O
corona extended around the planet, regarding the heavy molecular O2+ and
CO2+, which are buried in the lower ionosphere, a novel escape mechanism
needs to considered. Here we attack this problem by global magnetohydrodynamic (MHD) simulations.
First, we clarify the global structure of the streamlines that result from the
interaction with the solar wind. Then, by focusing on the streamlines that dip
into the low-altitude part of the dayside ionosphere, we investigate the
escape path of the molecular ions. The effects of the interplanetary magnetic field (IMF) on the molecular ion
escape process are investigated by comparing the results with and without
IMF. IMF has little effect on O+ escape via ion pick-up mediated by solar
wind electron impact ionization of the O corona. O2+ and CO2+ are
shoveled from the low-altitude regions of the dayside ionosphere by magnetic
tension in the presence of IMF. These ions are pulled by the U-shaped field
lines to the north and south poles, and at the terminator, they are
concentrated in the noon–midnight meridian plane. These ions remain confined
to the noon–midnight plane as they are transported to the nightside to form
the tail ray. Then they escape along the streamlines open to the
interplanetary space. Under a typical solar wind and IMF condition expected
at Mars, O+, O2+ and CO2+ escape fluxes are 8.0 × 1023,
3.5 × 1023 and 5.0 × 1022 ion s−1, respectively, which are in
good agreement with the MEX observations. |
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