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Within the plasma sheet, fast tailward plasma flows with dipolar Bz signatures (north-then-south turning of B) are called plasmoids (e.g., Hones et al., 1984). Most plasmoids have also helical magnetic field structures (large By fields), called "flux ropes" (Hughes and Sibeck, 1987; Slavin et al., 1995). Total pressure enhancement is a necessary condition for plasmoids: enhancement if the plasma (magnetic) pressure correspond to a magnetic island (flux rope) type plasmoid (Ieda et al., 1998). In the tail lobe, a travelling compression region (TCR; Maezawa, 1975; Slavin et al., 1984) is often observed, and is interpreted as a remote manifestation of a plasmoid passage (e.g., Slavin et al., 1993).

Observations of plasmoids are highly correlated with substorm onsets (Moldwin and Hughes, 1993; Nagai et al., 1994). Accordingly, their existense is considered to support substorm models based on reconnection. This is because reconnection seems to be the most obvious mechanism for plasmoid creation.

Plasmoids originate from the distance of about 20-30 Re, and have been observed up to about 200 Re downtail; tailward speeds are several hundreds of km/s (e.g., Ieda et al., 1998).

Of the heavier ions observed within the plasmoids, most of the oxygen ions are singly charged (O+, ionospheric origin), and most of the helium ions are doubly charged (He++, solar wind origin). See, e.g., Lui et al. (1998).


  • Hones, E. W., Jr., D. N. Baker, S. J. Bame W. C. Feldman, J. T. Gosling, D. J. McComas, R. D. Zwickl, J. A. Slavin, E. J. Smith, and B. T. Tsurutani, Structure of the magnetotail at 220 Re, Geophys. Res. Lett., 11, 5-7, 1984.
  • Hughes, W. J., and D. G. Sibeck, On the three-dimensional structure of plasmoids, Geophys. Res. Lett., 14, 636-639, 1987.
  • Ieda, A., S. Machida, T. Mukai, Y. Saito, T. Yamamoto, A. Nishida, T. Terasawa, and S. Kokubun, Statistical analysis of the plasmoid evolution with Geotail observations, J. Geophys. Res., 103, 4453-4465, 1998.
  • Lui, A. T. Y., D. J. Williams, R. W. McEntire, S. P. Christon, T. E. Eastman, T. Yamamoto, and S. Kokubun, Ion composition and charge state of energetic particles in flux ropes/plasmoids, J. Geophys. Res., 102, 4467-4475, 1998.
  • Maezawa, K., Magnetotail boundary motion associated with geomagnetic substorms, J. Geophys. Res., 80, 3543-, 1975.
  • Moldwin, M. B., and W. J. Hughes, Geomagnetic substorm association of plasmoids, J. Geophys. Res., 98, 81-88, 1993.
  • Nagai, T., K. Takahashi, H. Kawano, T. Yamamoto, S. Kokubun, and A. Nishida, Initial Geotail survey of magnetic substorm signatures in the magnetotail, Geophys. Res. Lett., 21, 2991-2994, 1994.
  • Slavin, J. A., et al., Substorm associated traveling compression regions in the distant tail: ISEE 3 Geotail observations, Geophys. Res. Lett., 11, 657-, 1984.
  • Slavin, J. A., M. F. Smith, E. L. Mazur, D. N. Baker, E. W. Hones Jr., T. Iyemori, and E. W. Greenstadt, ISEE 3 observations of traveling compression regions in the Earth's magnetotail, J. Geophys. Res., 98, 15425-15446, 1993.
  • Slavin, J. A., C. J. Owen, M. M. Kuznetsova, and M. Hesse, ISEE 3 observations of plasmoid with flux rope, Geophys. Res. Lett., 22, 2061-2064, 1995.
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