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  • 1
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    Ion cyclotron wave growth calculated from satellite observations of the proton ring current during storm recovery (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 81; May 1
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  • 2
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    The dominant mode of standing Alfven waves at the synchronous orbit (1975)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Low-frequency oscillations of the earth's magnetic field recorded by a magnetometer on board ATS 1 have been examined for the 6-month interval between January and June 1968. Using evidence from OGO 5 and ATS 5 as well as the data from ATS 1, it is argued that the dominant mode at ATS 1 must be the fundamental rather than the second harmonic of a standing Alfven wave. It is concluded that these transverse oscillations are more accurately associated with magnetically disturbed days than with quiet days. From 14 instances when oscillations of distinctly different periods occurred during the same time interval at ATS 1, it is also concluded that higher harmonics can exist. The period ratio in seven of the 14 cases corresponds to the simultaneous occurrence of the second harmonic with the fundamental, and four other cases could be identified as the simultaneous occurrence of the fourth harmonic with the fundamental.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 80; Sept. 1
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  • 3
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    An alternative analysis of low- and high-altitude observations of ring current ions during a storm recovery phase (1977)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Explorer 45 equatorial observations of ring current ions during a storm recovery phase have shown pitch angle distributions and decay rates inconsistent with proton charge exchange with neutral hydrogen. This inconsistency has led to the suggestion that recovery phase ring current ions at L less than or equal to 4 and energies not greater than 50 keV are dominated by He(+) rather than protons. The absence of He(+) on flux tubes from which H(+) and O(+) were precipitating in ion mass spectrometer measurements made during the same period by the low-altitude polar-orbiting satellite 1971-089A led Sharp et al. to suggest a source of H(+) and O(+) to L = 3 during this period. An alternative explanation, in which the magnetic field lines labeled L = 3 at the earth's surface near local midnight were mapped to about 3.7 earth radii in the equatorial plane during the storm recovery phase and during the period of enhanced activity, is proposed. If the proposed explanation is correct, the observations of Sharp et al. are not incompatible with the conclusion that the recovery phase ions at less than 50 keV were dominated by He(+) for L not greater than 3.7.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 82; June 1
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  • 4
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    Adiabatic evolution of trapped particle pitch angle distributions during a storm main phase (1977)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Equatorial pitch angle distributions of over 200-keV ions obtained near L = 4 by Explorer 45 during a storm main phase show the development of marked minima at 90 deg pitch angle in direct association with a greater-than-a-factor-of-2 reduction in the equatorial magnetic field magnitude. The evolution of these pitch angle distributions can be quantitatively explained as a result of conservation of the first two adiabatic invariants provided the magnitude of the magnetic field decrease was approximately constant along field lines.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 82; June 1
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  • 5
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    Simultaneous observations of the proton ring current and stable auroral red arcs (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Explorer 45 observed the equatorial proton ring current in the plasmapause region and Fritz Peak Observatory observed stable auroral red (SAR) arcs on Dec. 17, 1971 during a geomagnetic storm. An estimate of energy lost from the ring current was obtained by using Explorer 45 observations of pitch angle distribution transitions which are probably due to pitch angle diffusion-driven resonant interactions with ion cyclotron waves. Estimates of the equatorial loss rate yield values greater than the required SAR arc energy input rate, and the location of the peaks in these loss rates agrees with the observed location of the arcs. It is thus concluded that this energy loss is sufficient to sustain the SAR arcs.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 81; Feb. 1
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  • 6
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    Storm-associated variations of equatorially mirroring ring current protons, 1-800 keV, at constant first adiabatic invariant (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Explorer 45 observations of ring current protons mirroring near the equator, 1-800 keV, are presented at constant first adiabatic invariant mu throughout the period of the December 17, 1971, geomagnetic storm. The parameter mu is obtained from simultaneous magnetic field and particle observations. Particle deceleration in response to the storm time magnetic field decrease causes ring current measurements viewed at constant energy to underestimate the storm time increase in proton intensities at energies not exceeding 200 keV. This adiabatic deceleration also accounts for the large flux decreases observed at energies above 200 keV during the storm, in contradiction with previous results (Soraas and Davis, 1968) obtained using a model for the storm time magnetic field.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 81; Jan. 1
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  • 7
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    Trapped particles and waves, and what can be learned from multisatellite experiments (1976)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Calculations concerning the pitch-angle diffusion resulting from resonant wave-particle interactions can lead to definitive predictions of equatorial pitch-angle distributions and rates of particle loss as a function of particle energy and L-value. Thus, given simultaneous high-altitude measurements of pitch-angle distributions and low-altitude measurements of precipitating fluxes as a function of energy and L, the importance of proposed wave-particle interactions can be verified or discarded. Since many wave-particle phenomena occur over large spatial and temporal scales, exact simultaneity in longitude and time is not necessary. Simultaneous low and high altitude (preferably nearly equatorial) particle measurements could thus greatly increase our understanding of trapped particles and their effects on the ionosphere. Furthermore, given a verified pitch-angle diffusion mechanism and simultaneous low- and high-altitude measurements, accurate lowto high-altitude mappings of field lines and magnetospheric boundaries (such as the plasmapause) could be obtained.
    Keywords: GEOPHYSICS
    Type: The scientific satellite programme during the International Magnetospheric Study; Jun 10, 1975 - Jun 13, 1975; Vienna; Austria
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  • 8
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    Explorer 45 observations of the proton ring current (1976)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Explorer 45 satellite data on the stormtime proton ring current are reported and analyzed. Storm-associated variations of equatorially mirroring protons, interactions between the ring current and the plasmapause, and storm recovery phase behavior are discussed. Pitch-angle distributions are plotted as a function of proton energy and radial distance, the structure implying domination of pitch-angle diffusion of ring-current protons in the plasmapause region by resonant interactions with ion cyclotron waves during storm recovery. The anisotropic precipitation in the plasmapause region and the more poleward isotropic precipitation observed at low altitudes outside the plasmapause are compared and distinguished.
    Keywords: GEOPHYSICS
    Type: Magnetospheric particles and fields Summer Advanced Study School; Aug 04, 1975 - Aug 15, 1975; Graz; Austria
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  • 9
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    The dominant mode of standing Alfven waves at synchronous orbit (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Low-frequency oscillations of the earth's magnetic field recorded by the UCLA magnetometer on board ATS-1, have been examined for the six-month interval, January-June, 1968. The initial interpretation, that these oscillations represent the second harmonic of a standing Alfven wave, has been re-examined, and it is concluded that this hypothesis must be withdrawn. Using evidence from OGO-5 and ATS-5, as well as the data from ATS-1, it is argued that the dominant mode at the synchronous orbit must be the fundamental rather than the second harmonic. From 14 instances when the oscillations of distinctly different periods occurred during the same time interval at ATS-1 it is concluded that higher harmonics can exist. The period ratio in 7 of the 14 cases corresponds to the simultaneous occurrence of the second harmonic with the fundamental, and 4 other cases could be identified as the simultaneous occurrence of the fourth harmonic with the fundamental.
    Keywords: GEOPHYSICS
    Type: NASA-CR-142030
    Format: application/pdf
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  • 10
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    The inconsistency between proton charge exchange and the observed ring current decay (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The equatorial pitch-angle distributions of ring-current ions observed during a storm recovery phase at L values between 3 and 4 are compared with the pitch-angle distributions predicted by proton charge exchange with neutral hydrogen. Large disagreements are found, and three alternative explanations are explored. (1) A strong proton source acts to mask the effects of charge exchange. It is believed that the required strong continual source with a unique pitch-angle and energy dependence is unrealistic at these low L values. (2) Presently accepted neutral hydrogen density models have densities well over an order of magnitude too large for a storm recovery phase. No evidence is known to support the required large errors in the densities. (3) The ring current at particle energies not exceeding 50 keV was dominated by some ion species other than protons during the storm recovery phase. Such ions must have much longer lifetimes for charge exchange with hydrogen than do protons. This alternative is strongly favored, with He(+) being an attractive candidate.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 81; Dec. 1
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