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  • 1
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    Centrifugal trapping in the magnetotail (1995)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Particles leving the neutral sheet in the distant magnetotail at times display adiabatic trajectory sequences characterized by an inflection toward the equator and subsequent mirroring in its vicinity. We demonstrate that this low-latitude mirroring results primarily from a centrifugal deceleration due to the fast direction-changing E x B drift. This effect which we refer to as 'centrifugal trapping' appears both in guiding centre and full particle treatments. It thus does not directly relate to nonadiabatic motion. However, pitch angle scattering due to nonadiabatic neutral sheet interaction does play a role in reducing the parallel speed of the particles. We show that centrifugal trapping is an important mechanism for the confinement of the slowest (typically below the equatorial E x B drift speed) plasma sheet populations to the midplane vicinity.
    Keywords: GEOPHYSICS
    Type: Annales Geophysicae (ISSN 0992-7689); 13; 3; p. 242-246
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  • 2
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    Polar wind ion dynamics in the magnetotail (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The circulation of polar wind ions from the high-latitude ionosphere to the plasma sheet is investigated. Single-particle trajectory simulations for the geomagnetic tail show, in addition to the breaking of adiabaticity, the possible creation of new high-altitude mirror points. This trajectory feature results from an intense parallel deceleration imparted by the magnetic field rotation during fast ExB transport. This centrifugal deceleration yields a critical parallel velocity which depends on the magnitude of the convection electric field and below which ions remain trapped inside the neutral sheet.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; A6; p. 9155-9169.
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  • 3
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    Cleft contribution to ring current formation (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The storm time transport of ionospheric plasma from the 'cleft fountain' to the plasma sheet and ring current is investigated by means of three-dimensional trajectory codes. Using observations to define the source location and flow rate, test particles are traced during a 'taillike' to 'dipolelike' reconfiguration of the geomagnetic field. Emphasis is placed on the behavior of heavy ions of low charge state, O(+). As a result of their long periods of gyration, these ions are highly sensitive to rapid field variations and possibly display transient nonadiabatic motions. It is demonstrated that O(+) which have originated in the high-latitude ionosphere but which find themselves in the vicinity of the equator at substorm onset can experience considerable energization (from several keV up to several hundred keV) and pitch angle increase leading to trapping, as an effect of the induced electric field.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 20937-20
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  • 4
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    A survey of upwelling ion event characteristics (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Quasi-static electric field data collected by the DE-1 spacecraft were used to study ionospheric ion upwelling events observed in the vicinity of the dayside cleft. Bulk plasma parameters such as ion-species density and field-aligned bulk velocity and flux were derived at points within several upwelling ion events for the H(+), He(+), O(+), and O(2+), and the ion-species bulk parameters near the source altitude were compared. It was found that O(+) ions comprise about 90 percent of the upwelling particle density, followed by H(+) at less than 10 percent; He(+) and O(2+) contribute about 1 percent each. The upwelling O(+) flux is also dominant, followed by upward H(+) flux, which is relatively more significant than the fractional H(+) density, due to its high upward flow velocity.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 18969-18
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  • 5
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    Low-energy bouncing ions in the magnetosphere - A three-dimensional numerical study of Dynamics Explorer 1 data (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 1859-187
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  • 6
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    Observations of coherent transverse ion acceleration (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: DE-1 retarding ion mass spectrometer (RIMS) observations of transverse O(+) acceleration in the topside ionosphere are reported and analyzed. The operation and capabilities of RIMS are reviewed, and the data are presented graphically and characterized in detail. Torus or ring O(+) distributions with radii 10 km/s are observed, consistent with coherent transverse acceleration to 10-eV energies in the bulk-plasma reference frame, and conical hot tails at energies above the 50-eV RIMS maximum are noted. Possible mechanisms for these phenomena are discussed.
    Keywords: GEOPHYSICS
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  • 7
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    Low-energy ion outflows from the ionosphere during a major polar cap expansion - Evidence for equatorward motion of inverted-V structures (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: GEOPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 6; 3, 19
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  • 8
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    Ion energization in upwelling ion events (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A source of H(+), He(+), O(+), and N(+) outflow from the ionosphere has been identified near the polar cusp/cleft using the Dynamics Explorer/retarding ion mass spectrometer data set. This ion outflow termed 'upwelling ions' is characterized by large outfluxes of H(+) and O(+) ions and high transverse ion temperatures. This paper reports on the associated particle and field characteristics of one such upwelling ion event on March 12, 1982. Field-aligned currents and strong E x B convection channels are associated with the event as well as strong broadband plasma wave emission. One or all of these sources may play an important role in the ion energization in this region.
    Keywords: GEOPHYSICS
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  • 9
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    Contribution of low-energy ionospheric protons to the plasma sheet (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The magnetospheric transport of low-energy ionospheric ions is examined by means of three-dimensional particle codes. Emphasis is placed on the behavior of polar wind and cleft originating protons. It is demonstrated that, via nonadiabatic motion inside the neutral sheet, these ions can significantly contribute to the populations of the plasma sheet. The importance of this contribution is found to depend critically upon the dynamics of particles originating from the highest latitudes, as these possibly have access to the distant tail. Hence it is shown that polar wind H(+) expelled into the magnetosphere at very low energies (in the electron volt range) preferentially feed the plasma sheet during quiet times, experiencing accelerations up to several kiloelectron volts upon return into the inner magnetosphere. In contrast, during disturbed times, the intensifying magnetospheric convection confines this population to low L shells where it travels in a nearly adiabatic manner. As for the protons originating from the cleft fountain, the simulations reveal that they can be transported up to the vicinity of the distant neutral line in the nightside sector. Via interaction with the neutral sheet, these ionospheric ions are rapidly raised to the characteristic plasma sheet energy range. The density levels contributed by these populations are quite substantial when compared to those measured in situ. These simulations establish an active role of low-energy ionospheric ions in the overall magnetospheric dynamics.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; A4; p. 5681-5689
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  • 10
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    Auroral zone effects on hydrogen geocorona structure and variability (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The effect of diurnal and magnetospheric modulations on the structure of the hydrogen geocorona is analyzed on the basis of recent observations. Particular attention is given to the enhancement of neutral escape by plasma effects, including the recently observed phenomenon of low-altitude ion acceleration. It is found that, while significant fluxes of neutral H should be produced by transverse ion acceleration in the auroral zone, the process is probably insufficient to account for the observed polar depletion of hydrogen atoms. Analysis of recent exospheric temperature measurements from the Dynamics Explorer-2 satellite suggest that neutral heating in and near the high latitude cusp may be the major contributor to depleted atomic hydrogen densities at high latitudes. Altitude profiles of the production rates for escaping neutral hydrogen atoms during periods of maximum, minimum, and typical solar activity are provided.
    Keywords: GEOPHYSICS
    Type: Planetary and Space Science (ISSN 0032-0633); 33; 499-505
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