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  • 1
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    A detailed examination of a X-line region in the distant tail: ISEE-3 observations of jet flow and B(sub z) reversals and a pair of slow shocks (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We report an observation of Petschek-type magnetic reconnection at a distant neutral line (X = -230 R(sub e)) with a full set of signatures of the magnetic merging process. These features include a reversal of plasma flows from earthward to tailward, a pair of slow shocks and the magnetic field X-type line. These two slow shocks are shown to satisfy the shock criteria used by Feldman et al. (1987). The spacecraft first crosses a slow shock to enter the earthward flowing plasmasheet with velocity of about 440 km/s. The embedded magnetic field has a positive B(sub z) component. The spacecraft next enters a region of tailward plasma flow with speed approximately 670 km/s and an embedded negative B(sub z), indicating entry into the plasmasheet tailward of the X-line. These observed velocities are comparable to calculated velocities based on Rankine-Hugoniot conservation relationships. The spacecraft subsequently returns into the south tail lobe by crossing another slow shock. Coplanarity analyses shows that the two slow shocks have orientations consistent with that predicted by the Petschek reconnection model. We note that this event occurs during northward interplanetary magnetic fields. Thus, a magnetic stress built-up in the distant tail may be responsible for this reconnection process.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 21; 25; p. 3031-3034
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  • 2
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    The semiannual variation of great geomagnetic storms and the postshock Russell-Mcpherron effect preceding coronal mass ejecta (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Recent results indicate that the intense southward interplanetary magnetic fields (IMFs) responsible for great storms can reside in the postshock plasma preceding the driver gas of coronal mass ejections (CMEs) as well as in the driver gas itself. It is proposed here that strong southward fields in the postshock flow result from a major increase in the Russell-McPherron polarity effect through a systematic pattern of compression and draping within the ecliptic plane. Differential compression at the shock increases the Parker spiral angle and, consequently, the azimuthal field component that projects as a southward component onto earth's dipole axis. The resulting prediction is that southward fields in the postshock plasma maximize at the spring (fall) equinox in CMEs emerging from toward (away) sectors. This pattern produces a strong semiannual variation in postshock IMF orientation and may account at least in part for the observed semiannual variation of the occurrence of great geomagnetic storms.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 19; 429-432
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  • 3
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    Geomagnetic sudden impulses and storm sudden commencements - A note on terminology (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The definitions of and distinctions between storm sudden commencements (SSCs) and geomagnetic sudden impulses (SIs) are examined and present definitions of SIs and SSCs are modernized. Quantitative definitions of the two terms are recommended.
    Keywords: GEOPHYSICS
    Type: EOS (ISSN 0096-3941); 71; 1808
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  • 4
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    Theory and observation of energetic ions in the lobes of the geomagnetic tail (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The Owen et al. (1990) model, which attempts to explain the nature of the pitch angle distributions of energetic ions within the lobes of the distant geomagnetic tail is briefly reviewed. Energetic ion data from the ISEE-3 spacecraft obtained during early 1983, when the spacecraft made several traversals of the distant geomagnetic tail are then presented. The data demonstrate that during quiet periods in which the spacecraft is continuously located in the tail lobes, the pitch angle distribution is observed to be highly anisotropic, being peaked closely perpendicular to the magnetic field direction, but with a small net flow in the antisunward direction, in agreement with the model results. Further predictions of the model, concerning the variation of the lobe energetic ion distributions with position in the lobes, are compared to observations made as the spacecraft performed a traversal of the lobe. Finally, since the model indicates that a more isotropic distribution should exist in the tail lobe during solar particle events, data is presented from such a period for further comparison. In all the above cases, good agreement is demonstrated between the data and the expections of the model.
    Keywords: GEOPHYSICS
    Type: Planetary and Space Science (ISSN 0032-0633); 39; 761-775
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  • 5
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    A review of the ISEE-3 geotail magnetic field results (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This review presents a summary of past work on the ISEE-3 distant tail magnetic field observations. An attempt has been made to bring the many results together as a coherent whole, in the hope that the reader can envision the direction of future research necessary to achieve an understanding of the dynamics of the magnetotail from 60 to 240 earth radii and perhaps beyond.
    Keywords: GEOPHYSICS
    Type: Planetary and Space Science (ISSN 0032-0633); 34; 931-960
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  • 6
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    What is a geomagnetic storm? (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: After a brief review of magnetospheric and interplanetary phenomena for intervals with enhanced solar wind-magnetosphere interaction, an attempt is made to define a geomagnetic storm as an interval of time when a sufficiently intense and long-lasting interplanetary convection electric field leads, through a substantial energization in the magnetosphere-ionosphere system, to an intensified ring current sufficiently strong to exceed some key threshold of the quantifying storm time Dst index. The associated storm/substorm relationship problem is also reviewed. Although the physics of this relationship does not seem to be fully understood at this time, basic and fairly well established mechanisms of this relationship are presented and discussed. Finally, toward the advancement of geomagnetic storm research, some recommendations are given concerning future improvements in monitoring existing geomagnetic indices as well as the solar wind near Earth.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; A4; p. 5771-5792
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  • 7
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    Observations of a gradual transition between Ps 6 activity with auroral torches and surgelike pulsations during strong geomagnetic disturbances (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper describes a long-lasting large-amplitude pulsation event, which occurred on January 10, 1983 in the ionosphere and magnetosphere and was characterized by Steen and Rees (1983). Over the 4-h period (0200-0600 UT), the characteristics of the pulsations in the ionosphere changed from being Ps 6 auroral torches toward substorms and back to Ps 6. At GEO, the corresponding characteristics were a modulation of the high-energy particle intensity and plasma dropouts. Based on the ideas presented by Rostoker and Samson (1984), an interpretation of the event is offered, according to which the pulsations are caused by the Kelvin-Helmholtz instability during an interval of strong magnetospheric convection. On the basis of this explanation, a new interpretation of the substorm time sequence is proposed.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 8713-873
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  • 8
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    Substorm associated traveling compression regions in the distant tail - ISEE-3 geotail observations (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: While in the lobes of the distant magnetotail, ISEE-3 encountered regions of compressed magnetic field at a rate of several per day. The duration of these events was 5 to 20 minutes and they were observed 10 to 30 minutes following the onset of substorm activity near the earth. During each event, the lobe magnetic field tilted first northward and then southward with the inflection point near the time of peak field strength. Following the compression events, the lobe field weakened and retained a southward component for 20 to 40 minutes. It is suggested that these traveling compression regions are the lobe signatures of plasmoids moving rapidly down the tail in the plasma sheet. Comparison of ISEE-3 compression event times with substorm onset times yielded propagation speeds of 350 to 750 km/s.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 11; 657-660
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  • 9
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    Magnetic structure of the distant geotail from -60 to -220 earth radii - ISEE-3 (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: ISEE-3 magnetic-field measurements in the region of the geomagnetic tail from -80 to -220 earth radii are reported and discussed. A well-ordered field structure is found, comprising two 7-8-nT lobes separated by a plasma sheet, an embedded neutral sheet with significant By fields, and an intermittent plasma-sheet boundary layer with 5-nT-amplitude (peak-to-peak) electromagnetic waves. The plasma-sheet Bz distribution changes from principally northern orientation near the earth to an approximately equal north-south distribution at 200-220 earth radii. These findings are considered to be in general agreement with magnetic-reconnection models of the magnetosphere, with reconnection either throughout the region observed (in tearing-mode or plasmoid-formation models) or at a constant (about 220-earth-radii) or variable (40-80 to 220-earth-radii) X line (in X-line models).
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 11; 1-4
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  • 10
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    Structure of the magnetotail at 220 earth radii and its response to geomagnetic activity (1984)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Using plasma electron and magnetic field measurements from ISEE 3, 220 earth radii from earth, it is found that the magnetotail at that distance is a coherent structure that evidently waves about through distances comparable to its own lateral scale size. For about one-third of the time it was inside the magnetotail, ISEE 3 was in the plasma sheet. During quiet times the plasma sheet is apparently quite thin, but in response to geomagnetic activity it expands, becoming filled with hot plasma flowing tailward at speeds sometimes exceeding 1000 km/sec, and forces the magnetotail cross-section itself to expand. The plasma sheet's expansion is delayed typically by about 30 minutes from the onset of the associated geomagnetic activity (often a clearly identified isolated substorm). The magnetic field in the newly-expanded plasma sheet usually exhibits a few-minute steep northward excursion followed by a more prolonged (and often steep) southward excursion. These are believed to be the signatures of arrival of a plasmoid formed and released near the earth at the onset of the corresponding geomagnetic activity. The discreteness of these plasma releases through the magnetotail and their close association with onsets of geomagnetic activity at earth suggest that they are consequences of spontaneous release, probably by magnetic reconnection, of energy and plasma earlier stored in the magnetotail.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 11; 5-7
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