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| Titel |
Evidence of strong deformation of the magnetotail under low Alfven Mach number solar wind |
| VerfasserIn |
M. N. Nishino, M. Fujimoto, T. D. Phan, T. Mukai, Y. Saito, M. Kuznetsova, L. Rastaetter |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250022724
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| Zusammenfassung |
| The density of the solar wind (SW) around the Earth’s magnetosphere at times decreases to
only several percent of the usual value, and such density extrema results in a significant
reduction of dynamic pressure and Alfven Mach number (MA) of the SW flow. While simple
expansion of the Earth’s magnetosphere by the low dynamic pressure was assumed in
previous studies, a recent simulation study predicted a remarkable dawn-dusk asymmetry of
the magnetotail in shape under low density SW and Parker-spiral IMF configuration (Nishino
et al., Phys. Rev. Lett., 2008), and thus a direct observation of the magnetotail under these
conditions has been awaited. Here we show evidence of strong deformation of the
magnetotail under low MA SW from in-situ observations by the Geotail spacecraft. In spite
of extremely low dynamic pressure in the SW, the tail magnetopause on the dusk side was
located at the usual position, which is consistent with the result of a global MHD
simulation that shows a remarkable inclination of the magnetotail toward the dawn.
In addition, an enhancement of magnetopause reconnection was detected at the
tail magnetopause in this event, which suggests that plasma transport across the
magnetopause under low density (low MA) SW can be different from one under
the normal SW density condition. The strong deformation of the magnetotail and
the enhancement of magnetopause reconnection can be universal phenomenon,
because they are attributed to the extremely low MA (low beta) SW environment that
may also take place around the Earth’s magnetosphere passed by coronal mass
ejections (CMEs) as well as around Mercury and in the interstellar medium outside the
heliopause. |
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