Plasmoids/flux ropes - last update: 27 November 1998, 1900 UT (RR)

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 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).


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