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Tailward fast plasma flows
with dipolar Bz signatures (north-then-south turning of B) observed
within plasma sheet
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
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.