Observations of earthward and tailward propagating flux rope plasmoids: Expanding the plasmoid model of geomagnetic substorms
- Boston Univ., MA (United States)
A survey of IMP 8 magnetometer data for plasmoid signatures during magnetospheric intervals from 1981 through 1983 found 16 plasmoids and 37 traveling compression regions as well as two earthward propagating flux ropes and 19 south-north bipolar lobe signatures. The properties of these relatively near-Earth plasmoids, traveling compression regions, and earthward propagating flux ropes and a qualitative model for their formation are presented. The plasmoids have estimated sizes, durations, magnetic field signatures, downtail velocities, and substorm associations very similar to those of the plasmoids identified in ISEE 3 deep-tail observations. The occurrence frequency of these near-Earth plasma sheet plasmoids is significantly smaller than that of plasmoids found in the mid- and deep tail with ISEE 3. The earthward propagating flux ropes are characterized by a south-north bipolar turning in the GSM B[sub x] component, are localized near the noon-midnight meridional plane, and are strongly correlated with interplanetary magnetic field B[sub x] north and small isolated high latitude geomagnetic substorms. These events are also apparently very rare and/or spatially localized. The authors propose that these structures are [open quotes]proto-plasmoids,[close quotes] i.e., plasmoids for which near-Earth magnetic reconnection stopped before all the closed plasma sheet field lines were reconnected. The proto-plasmoids are than [open quotes]trapped[close quotes] inside closed magnetic field lines and propagate earthward owing to the effect of the distant X-line's earthward plasma flow. They suggest that the two different [open quotes]types[close quotes] of plasmoids are due to the different energy states of the magnetosphere during periods of southward and northward interplanetary magnetic field. 36 refs., 14 figs., 2 tabs.
- OSTI ID:
- 6720535
- Journal Information:
- Journal of Geophysical Research; (United States), Vol. 99:A1; ISSN 0148-0227
- Country of Publication:
- United States
- Language:
- English
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