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  • 1
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    The contribution of flux transfer events to convection (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: It is shown from flux transfer event (FTE) occurrence statistics, observed as a function of MLT by the ISEE satellites, that recent 2-dimensional analytic theories of the effects of pulsed Petschek reconnection predict FTEs to contribute between 50 and 200 kV to the total reconnection voltage when the magnetosheath field points southward. The upper limit (200 kV) allows the possibility that FTEs provide all the antisunward transport of open field lines into the tail lobe. This range is compared with the voltages associated with series of FTEs signatures, as inferred from ground-based observations, which are in the range 10-60 kV. We conclude that the contribution could sometimes be made by a series of single, large events; however, the voltage is often likely to be contributed by several FTEs at different MLT.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 22; 10; p. 1185-1188
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  • 2
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    The response of ionospheric convection in the polar cap to substorm activity (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We report multi-instrument observations during an isolated substorm on 17 October 1989. The European Incoherent Scatter (EISCAT) radar operated in the SP-UK-POLI mode measuring ionospheric convection at latitudes 71 deg Lambda - 78 deg Lambda. Sub-Auroral Magnetometer Network (SAMNET) and the EISCAT Magnetometer Cross provide information on the timing of substorm expansion phase onset and subsequent intensifications, as well as the location of the field aligned and ionospheric currents associated with the substorm current wedge. Interplanetary Monitoring Platform-8 (IMP-8) magnetic field data are also included. Evidence of a substorm growth phase is provided by the equatorward motion of a flow reversal boundary across the EISCAT radar field of view at 2130 MLT, following a southward turning of the interplanetary magnetic field (IMF). We infer that the polar cap expanded as a result of the addition of open magnetic flux in the tail lobes during this interval. The flow reversal boundary, which is a lower limit to the polar cap boundary, reached an invariant latitude equatorward of 71 deg Lambda by the time of the expansion phase onset. We conclude that the substorm onset region in the ionosphere, defined by the westward electrojet, mapped to a part of the tail radially earthward of the boundary between open and closed magnetic flux, the distant neutral line. Thus the substorm was not initiated at the distant neutral line, although there is evidence that it remained active during the expansion phase.
    Keywords: GEOPHYSICS
    Type: Annales Geophysicae (ISSN 0992-7689); 13; 2; p. 147-158
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  • 3
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    Heikkila's mechanism for impulsive plasma transport through the magnetopause - A reexamination (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper reexamines arguments formulated and restated by Heikkila to the effect that a magnetosheath plasma cloud having 'excess' momentum which impinges on the dayside magnetopause boundary is able to flow continuously through the boundary onto both open and closed flux tubes in the interior. It is shown that the argument used to arrive at this conclusion is not correct. The error in the argument concerns the nature of the flow which is associated with the induction electric field produced by the perturbed current layer, which was assumed by Heikkila to be such as to keep the plasma jet just moving with the boundary. Heikkila's argument, correctly applied, does not lead to 'impulsive transport' of plasma through the magnetopause.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 5565-557
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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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    Pitch angle distributions of energetic ions in the lobes of the distant geomagnetic tail (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A model is presented which accounts for observed pitch angle distributions of energetic ions in the lobes of the deep geomagnetic tail. Energetic (greater than 35 keV) ion data from the ISEE-3 spacecraft obtained during 1982-1983, when the spacecraft made a series of transversals of the distant geomagnetic tail (X sub GSE greater than -238 R sub E) is considered. Analysis indicates that under usual conditions the lobe pitch angle distribution is highly peaked at pitch angles closely perpendicular to the magnetic field direction while also showing a small downtail anisotropy. It is noted, however, that during periods of solar particle enhancements the lobe distributions become much more clearly isotropic. The proposed model successfully reproduces these features of the data and also accounts for the more isotropic ion population observed in the lobe during solar particle events, when the terrestrial component of the magnetosheath source may be considered negligeable in comparison to the enhanced solar component.
    Keywords: GEOPHYSICS
    Type: Planetary and Space Science (ISSN 0032-0633); 38; 851-882
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  • 6
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    The ionospheric signature of flux transfer events (1991)
    In:  Other Sources
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    Publication Date: 2013-08-29
    Description: The effects at ionospheric heights which take place when transient reconnection events (i.e., Flux Tranfer Events (FTEs)) occur at the dayside magnetopause are considered. The nature of the FTE related ionospheric flows, the associated current systems, and the plasma precipitation, are discussed. In particular, the nature of the time dependent cusp precipitation which occurs on this case is outlined and expectations are compared with those based on steady magnetopause reconnection.
    Keywords: GEOPHYSICS
    Type: ESA, Cluster Dayside Polar Cusp; p 105-112
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  • 7
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    The ionospheric signatures of flux transfer events and solar wind dynamic pressure changes (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Recent observations of vortical flow patterns in the dayside auroral ionosphere are discussed in terms of two alternative mechanisms: (1) the time-dependent magnetic reconnection in 'flux transfer events' (FTEs); and (2) the action of solar wind dynamic pressure changes at the magnetopause. It is argued that the ionospheric flow signature of an FTE should be a twin vortex, with the mean flow velocity in the central region of the pattern being equal to the velocity of the pattern as a whole. On the other hand, the pulse of enhanced or reduced dynamic pressure is also expected to produce a twin vortex, but with the central plasma flow being generally different in speed from (and almost orthogonal to) the motion of the whole pattern. It is found that, while none of the events discussed here are consistent with the theories of the effects of the dynamic pressure changes, all are well explained in terms of the ionospheric signatures of FTEs.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 17113-17
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  • 8
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    ISEE 3 observations during the CDAW 8 intervals - Case studies of the distant geomagnetic tail covering a wide range of geomagnetic activity (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Observations made by the ISEE 3 spacecraft in the distant geomagnetic tail during the eight CDAW 8 intervals are discussed, along with their relation to concurrent geomagnetic activity. This extensive multiinstrument case study of distant tail data covers a wide range of geomagnetic conditions from extended intervals of magnetic quiet with isolated substorms to prolonged periods of intense disturbance. Plasmoids are observed in the distant tail following disturbance enhancements, the time of their appearance being generally consistent with disconnection from the near-earth region at the time of the enhancement. Their structure is entirely consistent with the neutral line model. However, not all enhancements in geomagnetic activity result in the observation of plasmoids. In particular, the CDAW 8 data suggest that, during extended intervals of strong activity, a continuous neutral line may reside in the near-earth tail and some disturbance enhancements may then relate to an increase in the reconnection rate at a preexisting neutral line, rather than to new neutral line and plasmoid formation.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 94; 15189-15
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  • 9
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    Magnetospheric and ionospheric plasmas; Proceedings of the Ninth Symposium and Topical Meeting, Graz, Austria, June 25-July 7, 1984 (1985)
    In:  Other Sources
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    Publication Date: 2016-03-09
    Description: Papers are presented on the physics of the magnetosphere-ionosphere connection, with attention given to theory and modeling, auroras, plasma dynamics and irregularities, waves and electron beams, the dynamics of the thermosphere, and planetary plasmas. Plasma circulation in the magnetosphere is also discussed; consideration is given to observations of magnetospheric convection from low altitudes, the structure and properties of the earth's plasmasphere, and the circulation of energetic ions of terrestrial origin in the magnetosphere.
    Keywords: GEOPHYSICS
    Type: (ISSN 0273-1177)
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  • 10
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    The magnetic field investigation on Cluster (1988)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: The magnetic field investigation of the Cluster four-spacecraft mission is designed to provide intercalibrated measurements of the B magnetic field vector. The instrumentation and data processing of the mission are discussed. The instrumentation is identical on the four spacecraft. It consists of two triaxial fluxgate sensors and of a failure tolerant data processing unit. The combined analysis of the four spacecraft data will yield such parameters as the current density vector, wave vectors, and the geometry and structure of discontinuities.
    Keywords: GEOPHYSICS
    Type: ESA, The Cluster Mission: Scientific and Technical Aspects of the Instruments; p 15-20
    Format: application/pdf
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