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  • 1
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    Spatial scale of the substorm onset region determined from multi-point satellite and ground-based observations (1992)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The temporal and spatial scale of the onset of two substorm events is investigated using high resolution energetic particle and magnetic field data at synchronous orbit plus auroral and magnetic field data simultaneously taken from the ground based instrumentation. During both intervals the major expansion onset had precursor localized expansions without significant negative bay enhancement ('pseudobreakups'). Typical magnetospheric onset signatures such as tail current diversion, dipolarization, and injection were observed associated with some of the pseudobreakups. The major expansion, on the other hand, consisted of a number of rather localized injections and expansions, each of which had times scales of 5 to approximately 10 minutes, a comparable time scale to that of pseudobreakups. The number of occurrences, as well as the scale size of the magnetospheric source region, would constitute the major difference between pseudobreakup and the global expansion onset.
    Keywords: GEOPHYSICS
    Type: ESA, Substorms 1; p 353-357
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  • 2
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    A filament of energetic particles near the high-latitude dawn magnetopause (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The Geotail satelite detected a filament of tailward-streaming energetic particles spatially separated from the boundary layer of energetic particles at the high-latitude dawn magnetopause at a downstream distance of approximately 80 R(sub E) on October 27, 1992. During this event, the composition and charge states of energetic ions at energies above approximately 10 keV show significant intermix of ions from solar wind and ionospheric sources. Detailed analysis leads to the deduction that the filament was moving southward towards the neutral sheet at an average speed of approximately 80 km/s, implying an average duskward electric field of approximately 1 mV/m. Its north-south dimension was approximately 1 R(sub E) and it was associated with an earthward directed field-aligned current of approximately 5 mA/m. The filament was separated from the energetic particle boundary layer straddling the magnetopause by approximately 0.8 R(sub E) and was inferred to be detached from the boundary layer at downstream distance beyond approximately 70 R(sub E) in the distant tail.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 21; 25; p. 3011-3014
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  • 3
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    The morningside low-latitude boundary layer as determined from electric and magnetic field measurements on Geotail (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: On October 17, 1992, the Geotail satellite crossed the dawnside magnetopause approximately 41 times. At the majority of these crossings, the magnetic field and the normal component of the electric field were larger and the plasma density was smaller in a low-latitude boundary layer than they were in either the nearby magnetosheath or in the magnetosphere. These results are intepreted in terms of the Kelvin-Helmholtz instability associated with velocity shear at the magnetopause. Consistent with this interpretation, it is shown that the low-latitude boundary layer was the region where the flow decreased from its magnetosheath to magnetospheric value. Evidence is presented that the magnetopause was locally oriented within less than 20 deg of its nominal geometry on these crossings and that it moved with an amplitude of 1500-6000 kilometers. The thickness of the low-latitude boundary layer averaged 800 kilometers and the electric potential across it averaged 4 kilovolts with a spread of a factor of 2. Thus, the viscous interaction and similar processes are not significant contributors to magnetospheric convection.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 21; 25; p. 2983-2986
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  • 4
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    Geotail observations of spiky electric fields and low-frequency waves in the plasma sheet and plasma sheet boundary (1994)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Electric field data from the Geotail spacecraft provide an opportunity to extend the observations of spiky fields made by International Sun Earth Explorer-1 (ISEE-1) to a region of the magnetosphere where quasistatic electric field measurements have not previously been msde, to examine their possible importance in the dynamics of the middle and distant tail, and to test some hypotheses about their formation. In this paper, examples of large fields in the plasma sheet and its boundary at radial distances up to approximately 90 R(sub E) are presented. It is shown that three different types of large electric fields can occur: (1) spiky fields; (2) 'DC' fields; and (3) waves at frequencies comparable to the lower hybrid frequency. There is usually a gradation between (1) and (3), and often large electric field spikes are embedded in regions of lower amplitude waves. The waves tend to occur in short (few to 10's of seconds) packets whose start and stop times are not always correlated with changes in the magnetic field and/or density (as indicated by the spacecraft potential). The peak frequency is often less than but comparable to the lower hybrid frequency in agreement with theories of lower hybrid drift waves in the magnetotail. The largest spikes are not always associated with the largest changes in the spacecraft potential and/or magnetic field. It is suggested that the spiky fields may represent the nonlinear development of the waves.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 21; 25; p. 2987-2990
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  • 5
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    Observations of plasmas associated with the magnetic signature of a plasmoid in the distant magnetotail (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The three-dimensional electron and positive ion velocity distributions were examined for four events for which the magnetic signature of plasmoids occurred at the Geotail spacecraft position in Earth's distant magnetotail. The proton bulk parameters and the electron velocity distributions for one of the events are presented in order to characterize the qualitative character of the set of events. The north-to-south turnings of the magnetic field that were taken for evidence of the passage of a plasmoid were often accompanied by a significant strong core of B(sub y) that was centered on the transition of B(sub z) from north to south. The magnetic signatures thus appeared to be more indicative of flux ropes than of classical plasmoids with weak core fields. The proton and electron bulk velocities in these magnetic structures are not equal, a situation that provides an earthward current. The plasma beta was typically one or greater. Counterstreaming of low-energy electrons was often found on the magnetic field lines around the central magnetic core and suggested the existence of a closed field line topology in these regions. These events appeared to be the tailward flowing debris from acceleration processes occuring in the vicinity of a separator positioned nearer to Earth.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 21; 25; p. 2967-2970
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  • 6
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    Direct entry of dense flowing plasmas into the distant tail lobes (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Electric field, magnetic field, and spacecraft potential measurements on the Geotail satellite have confirmed earlier observations of relatively dense flowing plasmas in the magnetotail lobes. Within these flowing plasmas, density discontinuities of factors of 2 to 4 were observed. At least 15 of the 18 magnetopause crossings that occurred during a 24-hour interval when the spacecraft was at GSM coordinates near X = -140 R(sub e), Y = 0, and Z = 15 R(sub e), were rotational discontinuities across which the magnetosheath plasma had direct entry into the tail lobes. Within the lobes near the rotational discontinuities, the spacecraft typically crossed a second boundary at which the plasma density decreased from its magnetosheath value by a typical factor of 1.5 to 3 while the magnetic field strength and flow speed increased. Equatorward of this density discontinuity, the plasma density and flow remained appreciable. At least 2 of the 18 magnetopause crossings may have been tangential discontinuities across which the density and magnetic field strength both changed. Within the lobes near these tangential discontinuities, significant densities of flowing plasma were observed. Since 11 of the 18 discontinuities were crossed within a time interval of less than 7 seconds, the bondary current layer was well-defined and very thin.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 21; 25; p. 2959-2962
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  • 7
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    Quasi-periodic oscillations of the magnetopause during northward sheath magnetic field (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The Geotail satellite quasi-periodically crossed the dawn flank of magnetopause more than ten times during an interval of 1.5 hours on November 4, 1992. Magnetopause crossings were characterized by quasi-periodic pulses of a sawtooth wave form in the magnetic field and the plasma flow components tangential to the magnetopause. The magnetic field strength in the magnetosheath was larger than that in the magnetosphere. The direction of magnetic field outside the magnetopause current layer was northward with antisunward tilt, indicating the draping of magnetic field on the magnetopause. Boundary normals of wavy magnetopause systematically incline sunward on the upstream side, while they tend to incline antisunward with considerable deviation on the downstream side. Comparison with other multiple crossing events suggests that the November 4 event exhibits wavy structure of the dawn flank magnetopause associated with the northward interplanetary magnetic field (IMF).
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 21; 25; p. 2883-2886
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  • 8
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    ISEE 1 and Geotail observations of low-frequency waves at the magnetopause (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Observations of waves at frequencies below approximately 200 Hz obtained near the magnetopause are presented. For one case identified in the ISEE 1 data as a period when steady state reconnection was occurring, there were waves below the lower hybrid frequency with amplitudes up to approximately 7 mV/m. Intense low-frequency waves with amplitudes up to approximately 20 mV/m at the subsolar magnetopause have also been observed by the Geotail electric field instrument. In some cases, large spiky fields were embedded in the waves. The waves observed by ISEE 1 and Geotail were large enough to provide the dissipation required for reconnection to occur.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 100; A7; p. 11,823-11,829
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  • 9
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    Cross-tail magnetic flux ropes as observed by the GEOTAIL spacecraft (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Ten transient magnetic structures in Earth's magnetotail, as observed in GEOTAIL measurements, selected for early 1993 (at (-) X(sub GSM) = 90 - 130 Earth radii), are shown to have helical magnetic field configurations similar to those of interplanetary magnetic clouds at 1 AU but smaller in size by a factor of approximately = 700. Such structures are shown to be well approximated by a comprehensive magnetic force-free flux-rope model. For this limited set of 10 events the rope axes are seen to be typically aligned with the Y(sub GSM) axis and the average diameter of these structures is approximately = 15 Earth radii.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 22; 10; p. 1193-1196
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  • 10
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    Attenuation distance of low frequency waves upstream of the pre-dawn bow shock: GEOTAIL and ISEE 3 comparison (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: We have made a statistical study of the spatial distribution of low frequency waves (approx. 0.01-0.1 Hz) in the region upstream of the pre-dawn to dawn side bow shock (-50 Re less than X less than 15 Re) using both GEOTAIL and international sun earth explorer 3 (ISEE-3) magnetometer data. We have found that the wave amplitude dependence on D and X(sub s), where D is the distance from the bow shock and X(sub s) the x-coordinate position of shock foot point of the IMF, can be described by a functional form of A exp (X(sub s)/L(sub X)-D/L(sub D), with the characteristic attenuation distances, L(sub X) = 62 +/- 12 Re and L(sub D) = 59 +/- 38 Re.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 22; 2; p. 81-84
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