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| Titel |
Direct observation of magnetosheath plasma penetrating the magnetopause |
| VerfasserIn |
Herbert Gunell, Hans Nilsson, Gabriella Stenberg, Maria Hamrin, Tomas Karlsson, Rickard Lundin, Mats André |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250051530
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| Zusammenfassung |
| Plasma structures with higher density and momentum than the surrounding plasma can
penetrate magnetic field barriers through self-polarisation. As the electrons and
ions gyrate in opposite directions, space charge sheaths form on the edges of the
structure, and this causes a polarisation electric field -ăE = --ăv ÃB-ă to be set up inside.
Thus, the plasma is able to continue moving with its initial velocity by means of an
E-ă Ã-ăB-drift, as described theoretically by Schmidt (Phys. Fluids, vol. 3, p. 961,
1960).
This process has been studied rather extensively in laboratory experiments with flowing
plasmas (e.g. Baker and Hammel, Phys. Fluids, vol. 8, p. 713, 1965; Lindberg, Astrophys.
Space Sci., vol. 55, p. 203, 1978; Ishizuka and Robertson, Phys. Fluids, vol. 25, p. 2353,
1982; Hurtig, et al., Phys. Plasmas, vol. 11, p. L33, 2004). Similar behaviour has been
observed for laser produced plasmas in magnetic fields (Ripin, et al., Phys. Rev.
Lett., vol. 59, p. 2299, 1987; Mostovych, et al., Phys. Rev. Lett., vol. 62, p. 2837,
1989).
In the 1970s Lemaire suggested that inhomogeneities in the solar wind can penetrate the
magnetopause as plasma filaments through a process called impulsive penetration (Lemaire,
Planet. Space Sci., vol. 25, p. 887, 1977). Satellite based measurements have shown
evidence of magnetosheath plasma inside the magnetosphere (Woch and Lundin, J.
Geophys. Res., vol. 97, p. 1431; Lundin, et al., Annales Geophysicae, vol. 21, p. 457,
2003).
We present data from the Cluster spacecraft showing in situ observations of
magnetosheath plasma penetrating the dayside magnetopause. First, we observe
structures of magnetosheath plasma when the spacecraft are located on closed field lines
in the dayside magnetosphere. Then, as the spacecraft cross the magnetopause, a
transition region is observed in which the plasma flux is directed inwards throughout
the spacecraft crossing. Thus the penetrating plasma structure is directly observed
at the magnetopause during the penetration process. The measured plasma flux
across the magnetopause was a few per cent of the solar wind flux at the time of
penetration. |
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