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  • 1
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In Parker's original model, the solar wind is represented as a spherically symmetric hydrodynamic flow. The velocity is radially directed and decoupled from the magnetic field. The simple extension of this model to include a dependence on the polar angle, θ, is shown to be invalid for radial flow and radial magnetic field. This work demonstrates how ad hoc symmetry conditions imposed to simplify a non-linear problem can be incompatible with the basic hydromagnetic equations.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The high spatial-temporal resolution of instrumentation on the polar-orbiting S3-2 satellite has allowed a wide variety of measurements of the electrodynamic characteristics of both large- and small-scale structures at high latitudes. Analyses of large scale features observed by S3-2 have shown that: (i) The IMF B ydependence of polar cap convection, first observed in June 1969 by OGO-6 persists in other seasons. During periods of northward IMF B zextensive regions of sunward convection may be found in the sunlit polar cap. (ii) In the dawn and dusk MLT sectors 〉90% of the region 1 currents lie equatorward of the convection reversal line. Potentials across the ionospheric projection of the low-latitude boundary layer are typically a few kV. (iii) The location of ‘extra’ field-aligned currents, near the dayside cusp and poleward of the region 1 current sheet is dependent on the IMF B ycomponent. (iv) Simultaneous observations by TRIAD and S3-2 show that sheets of field-aligned current extend uniformly for several hours in MLT, but may have an altitude dependence in the 1000–8000 km range. (v) During magnetic storms ionospheric irregularities occur in regions of poleward density gradients and downward field-aligned currents near the equatorward boundary of diffuse auroral precipitation. In the winter polar cap, density irregularities were also found in regions of highly structured electric fields and soft electron precipitation. (vi) During an intense magnetic storm the auroral zone height-integrated Pederson conductivity was calculated to be in the range 10–30 mho and downcoming energetic electron fluxes accounted for between 50% and 70% of the upward Birkeland currents. Analysis of small-scale structures (latitudinal width 〈 1°), observed by S3-2, have shown that: (i) Intense meridional electric fields (50–250 mV m-1) generated by charge separation near the inner edge of the plasma sheet drive intense subauroral convection and are associated with field-aligned currents, on the order of 1–2 μA m-2. (ii) Case studies of discrete arcs in the auroral oval have shown that arcs are associated with pairs of small-scale, field-aligned currents embedded in the large-scale region 1/region 2 field-aligned current sheets. The maximum observed field-aligned current was an upward current of 135 μA m-2, confined to a latitudinal width of ∼ 2km and carried by field-aligned accelerated electrons. Return (downward) currents associated with arcs are limited to intensities of 10–15 μA m-2. At this limit the ionospheric plasma becomes marginally stable to the onset of ion-cyclotron turbulence. Two instances of plasma vortices, characteristic of auroral curls, have been observed in the region between the paired current sheets. (iii) Sun-aligned arcs in the polar cap are found in a region of negative electric field divergence, embedded in an irregular electric field pattern. The electrons producing the arcs have a temperature of ∼ 200 eV and have been accelerated through potential drops of ∼ 1 kV along the magnetic field. Return currents may appear on both sides of polar-cap arcs.
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  • 3
    Publication Date: 2013-08-31
    Description: The dosimeter on board the low altitude polar orbiting DMSP/F7 satellite makes dose and flux measurements for electrons with energies greater than 1.0, 2.5, 5.0 and 10.0 MeV; and for protons with energies greater than 20, 35, 51, and 75 MeV. The characteristics and performance of the dosimeter are illustrated by presenting dose and flux data taken during the solar flare proton events of February 16 and April 26, 1984.
    Keywords: SOLAR PHYSICS
    Type: Alabama Univ., Huntsville. STIP Symposium on Physical Interpretation of Solar(Interplanetary and Cometary Intervals; p 5
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  • 4
    Publication Date: 2016-06-07
    Description: An electron beam system was operated over a wide range of beam currents and energies for periods both in sunlight and in eclipse. Complex pitch angle modulations of the electron spectra are separately decomposed for each beam operation. When electrons are emitted perpendicular to the magnetic field with an energy of 3 keV and a current of 0.10 mA they return as a coherent beam only to the parallel detector. Throughout the beam operations the pitch angle distributions show electrons with energy less than beam energy streaming along the field line. Analytic expressions for the satellite electric field are constructed and particle trajectories are determined.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA. Lewis Research Center Spacecraft Charging Technol., 1980; p 642-664
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  • 5
    Publication Date: 2016-06-07
    Description: The precipitation electrons in the auroral environment are highly variable in their energy and intensity in both space and time. As such they are a source of potential hazard to the operation of the Space Shuttle and other large spacecraft operating in polar orbit. In order to assess these hazards both the average and extreme states of the precipitating electrons must be determined. Work aimed at such a specification is presented. First results of a global study of the average characteristics are presented. In this study the high latitude region was divided into spatial elements in magnetic local time and corrected geomagnetic latitude. The average electron spectrum was then determined in each spatial element for seven different levels of activity as measured by K sub p using an extremely large data set of auroral observations. Second a case study of an extreme auroral electron environment is presented, in which the electrons are accelerated through field aligned potential as high as 30,000 volts and in which the spacecraft is seen to charge negatively to a potential approaching .5 kilovolts.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA. Lewis Research Center Spacecraft Environ. Interactions Technol., 1983; p 131-153
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  • 6
    Publication Date: 2019-07-12
    Description: Akasofu and Tsurutani (1984) have observed very unusual auroral activity on January 10-11, 1983. They employed visible line scan imagery from the Defense Meteorological Satellite Program (DMSP) F6 satellite to monitor auroral activity over the northern (winter) polar region. Magnetometer data from the ISEE 3 and IMP 8 spacecraft were used to monitor the interplanetary magnetic field (IMF) orientation. A number of auroral features which occurred in coincidence with changes in the IMF orientation were noted. The present paper is mainly concerned with the specific occurrence of a broad transpolar are later on January 11, 1983. During this occurrence, the IMF B(z) and B(y) components were positive and stable in time. This report has the objective to use a fortunate orbital configuration of three low-altitude polar orbiting spacecraft to probe the distribution of precipitating plasma responsible for the arc.
    Keywords: GEOPHYSICS
    Type: AD-A170918 , AFGL-TR-86-0153 , Journal of Geophysical Research (ISSN 0148-0227); 91; 339-346
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  • 7
    Publication Date: 2019-07-12
    Description: The statistical occurrence of spacecraft charging at near-geosynchronous orbit in daylight is studied with reference to results of an experiment conducted on the SCATHA satellite. In particular, it is found that: (1) the external current that creates high negative satellite frame potentials is the high-energy electron current from the electron population with energies greater than about 30 keV; (2) the electron current to the satellite from particles with energies less than about 30 keV neither drives the frame potential nor provides the current to balance the high-energy populations; and (3) the ion current provided from the entire range of measured ions is also not the primary source of the balancing current.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AD-A165444 , AFGL-TR-86-0057 , Journal of Geophysical Research (ISSN 0148-0227); 91; 1474-149
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  • 8
    Publication Date: 2019-08-28
    Description: Instruments on the SCEX 3 rocket payload were used to study charging during electron beam emissions. The data show that electrostatic analyzers can be used to measure vehicle charging and direct beam return currents in dense plasma conditions. The data also show return current dependencies on pitch angle, beam current and beam energy. It is found that if the proper care is taken, ESAs can be used to detect charging on vehicles in low altitude orbits which are contaminated with high levels of outgassing and in dense plasma regimes. These results are particularly important for the TSS-1 electrodynamic tether program where ESAs are being used to determine Shuttle charging levels during tether employment and to look for high fluxes of directly returning electrons during electron generator operations to balance the Shuttle charging.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: IEEE Transactions on Nuclear Science (ISSN 0018-9499); 38; 1622-162
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  • 9
    Publication Date: 2019-07-13
    Description: We compare equatorward/earthward boundaries of convection electric fields and auroral/plasma sheet electrons detected by the DMSP F8 and CRRES satellites during the June 1991 magnetic storm. Measurements come from the dusk magnetic local time sector where the ring current penetrates closest to the Earth. The storm was triggered by a rapid increase in the solar wind dynamic pressure accompanied by a southward turning of the interplanetary magnetic field (IMF). Satellite data show the following: (1) all particle and field boundaries moved equatorward/earthward during the initial phase, probably in response to the strong southward IMF turning; (2) electric field boundaries were either at lower magnetic L shells or close to the inner edge of ring current ions throughout the main and early recovery phases. Penetration earthward of the ring current occurred twice as the polar cap potential increased rapidly; (3) electric potentials at subauroral latitudes were large fractions of the total potentials in the afternoon cell, twice exceeding 60 kV; and (4) the boundaries of auroral electron precipitation were more variable than those of electric fields and mapped to lower L shells than where CRRES encountered plasma sheet electrons. Observations qualitatively agree with predictions of empirical models for auroral electron and electric field boundaries.
    Keywords: Geophysics
    Type: Paper-98JA02197 , Journal of Geophysical Research (ISSN 0148-0227); 103; A12; 29,399-29,418
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  • 10
    Publication Date: 2019-07-12
    Description: Data from the low-altitude DMSP spacecraft were used to compare polar rain electron intensities, energy spectra, and time variations at low altitudes with concurrent bidirectional electron properties in the magnetotail measured by ISEE 3. The DMSP-measured polar rain phase space densities near the polar cap agreed well with the field-aligned magnetotail lobe electron phase space densities above about 200 eV. Below 100-200 eV, a thermal electron population was observed (by ISEE) in the distant tail which is absent at the DMSP altitudes. The results suggest that the suprathermal tail lobe electrons can move freely along field lines to form polar rain, whereas the thermal electrons are bound to the tailward flowing lobe ion population far down the tail and thus cannot reach the polar cap regions.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 92; 13547-13
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