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  • GEOPHYSICS  (26)
  • 1980-1984  (26)
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  • 1
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    Observations of the dynamics of the polar thermosphere (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The dynamics of the polar thermosphere are examined by using observations made from the Dynamics Explorer 2 satellite. The results used in this study were obtained primarily from the Fabry-Perot interferometer (FPI) and the wind and temperature spectrometer (WATS) during the time period from September 1981 through January 1982. Two primary geophysical conditions were examined: these were the southern summer and the northern winter polar regions. The results support the conclusion that above 60 degrees of latitude the neutral winds are strongly controlled by ion/neutral frictional momentum transfer resulting from magnetospheric convection. This implies that the natural coordinate system within which to display the neutral winds in the high polar thermosphere is magnetic. The collected observations of this study were used to assess the validity of two of the large thermospheric general circulation models. The result of this assessment was that the models reasonably represent the vector winds at high altitudes but do not, at present, accurately simulate the thermodynamics of that regime.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 89; 5597-561
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  • 2
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    Geocoronal imaging with Dynamics Explorer - A first look (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The ultraviolet photometer of the University of Iowa spin-scan auroral imaging instrumentation on board Dynamics Explorer-1 has returned numerous hydrogen Lyman alpha images of the geocorona from altitudes of 570 km to 23,300 km (1.09 R sub E to 4.66 R sub E geocentric radial distance). The hydrogen density gradient is shown by a plot of the zenith intensities throughout this range, which decrease to near celestial background values as the spacecraft approaches apogee. Characterizing the upper geocorona as optically thin (single-scattering), the zenith intensity is converted directly to vertical column density. This approximation loses its validity deeper in the geocorona, where the hydrogen is demonstrated to be optically thick in that there is no Lyman alpha limb brightening. Further study of the geocoronal hydrogen distribution will require computer modeling of the radiative transfer. Previously announced in STAR as N83-20889
    Keywords: GEOPHYSICS
    Type: AD-A132344 , Geophysical Research Letters (ISSN 0094-8276); 10; July 198
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  • 3
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    Energetic magnetosheath ions and the interplanetary magnetic field orientation (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Times when energetic ions are absent and present in ISEE 1 magnetosheath plasma spectrograms are correlated with ISEE 3 IMF orientation measurements. The study indicates that when the plasma at the spacecraft is traced along a streamline to the bow shock surface, the angle between the surface normal at that point and the IMF is greater than 60 deg when the energetic ions are absent and less than 60 deg when they are present. The pattern is consistent with the ions coming from the same regions of the bow shock where intermediate and diffuse ions are found on the upstream side. The 60 deg criterion is used to draw schematic patterns of the location of energetic ions in the magnetosheath as a function of IMF orientation. Some orientations result in layers adjacent to the magnetopause and other orientations give layers adjacent to the bow shock.
    Keywords: GEOPHYSICS
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  • 4
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    Plasma rest frame distributions of suprathermal ions in the earth's foreshock region (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The paper presents rest frame ion distributions computed from three-dimensional observations of upstream suprathermal ions made by the University of Iowa Quadrispherical Lepedea on ISEE-1. The observations are for a single inbound midmorning pass starting upstream from the ion foreshock and continuing across the quasi-spherical bow shock into the magnetosheath. The crossing of the ion foreshock boundary is marked by a several-minute burst of ions of temperature 100-200 eV moving along the IMF away from the bow shock at 500 km/s relative to the solar wind. The observation of these reflected ions is followed by an extended interval of diffuse ions of temperatures 2-3 keV flowing at about 250 km/s relative to the solar wind and persisting until the bow shock is crossed. Both types of suprathermal ions constitute roughly 2% of the total ion density and carry a parallel heat flux of 0.01 ergs/sq cm-s.
    Keywords: GEOPHYSICS
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  • 5
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    Relationship between energetic particles and plasmas in the distant plasma sheet (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Measurements of ions from three different instruments on the IMP-7 and 8 spacecraft are combined to yield the differential energy spectra of ions over the entire energy range of 100 eV to 4 MeV in the earth's distant (30 to 40 earth radii) plasma sheet. These spectra, obtained during times of relatively small bulk flow velocities, span the intensity range from 10 to the -5th to 10 to the 5th per sq cm-sec-sr-keV, varying smoothly over the entire energy range both when the plasma is cold (about 1 keV) and hot (about 9 keV). Overall, the shape of the spectrum resembles a Maxwellian but with a high energy (not less than 50 keV) tail described well by a power law. The high energy tail is displaced in a parallel fashion to higher or lower intensities when the plasma is hot or cold, respectively. It is found that the energetic particle populations in the plasma sheet appear to be directly related to the mean thermal energies of the corresponding plasmas.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters; 8; Apr. 198
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  • 6
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    Temperature variation of the plasma sheet during substorms (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The temperature and density of the plasma in the earth's distant plasma sheet at downstream distances of about 20-25 earth radii, are examined during a high geomagnetic disturbance period. It is shown that the plasma sheet cools when magnetospheric substorm expansion is indicated by the AE index. During cooling, the plasma sheet temperature, T, and the number density, N, are related by T proportional to N to the 2/3 power (adiabatic process) in some instances, while by T proportional to 1/N (isobaric process) in other cases. The total plasma and magnetic pressure decreases when T is proportional to 1/N and increases when T is proportional to 1/N. Observation also indicates that the dawn-dusk component of plasma flow is frequently large and comparable to the sunward-tailward flow component near the central plasma sheet during substorms.
    Keywords: GEOPHYSICS
    Type: Planetary and Space Science; 29; Aug. 198
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  • 7
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    Observations of a free-energy source for intense electrostatic waves (1980)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Significant progress has been made in understanding intense electrostatic waves near the upper hybrid resonance frequency in terms of the theory of multiharmonic cyclotron emission using a classical loss-cone distribution function as a model. Recent observations by Hawkeye 1 and GEOS 1 have verified the existence of loss-cone distributions in association with the intense electrostatic wave events, however, other observations by Hawkeye and ISEE have indicated that loss cones are not always observable during the wave events, and in fact other forms of free energy may also be responsible for the instability. Now, for the first time, a positively sloped feature in the perpendicular distribution function has been uniquely identified with intense electrostatic wave activity. Correspondingly, we suggest that the theory is flexible under substantial modifications of the model distribution function.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters; 7; May 1980
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  • 8
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    Characteristics of the ULF waves associated with upstream ion beams (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A new class of upstream wave is reported with relatively high frequencies of about 1 Hz and small amplitudes compared to the more common larger amplitude, low-frequency (0.03 Hz) upstream wave. The waves were first noted in association with beams of ions reflected back upstream at the bowshock, and although beam presence appears to be a necessary condition for the observation of the waves, it is not a sufficient condition for the existence of the waves. Magnetometer measurements are used to determine intrinsic properties of the waves, and simultaneous two point measurements are used to calculate and eliminate Doppler shifting effects. Results indicate that the waves are right-hand elliptically polarized whistler mode waves with plasma rest frame frequencies of about 20-100 times the proton gyrofrequency and wavelengths of about 100 km.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 87; Feb. 1
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  • 9
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    Field-aligned currents in the earth's magnetotail (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Direct measurements of the plasma velocity distributions and simultaneous observations of magnetic fields are used to examine the character of field-aligned currents in the earth's magnetotail during the recovery phase of a magnetic substorm. Three contiguous field-aligned current sheets are identified at the interface between the magnetotail lobe and plasma sheet. Average current densities within these three current sheets are, in order of decreasing distance to the plasma sheet, +3.3 x 10 to the -9th, -1.3 x 10 to the -8th, and +1.1 x 10 to the -8th A/sq m, respectively.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 86; Feb. 1
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  • 10
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    Observations of ion streaming during substorms (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The ion beam phenomenon at the plasma sheet boundary is examined for individually identifiable substorms, and the substorm-associated particle phenomena are evaluated in terms of the energy-angle distributions of the plasma population and three-dimensional energetic ion distributions. In all seven cases studied it is found that ion beams streaming earthward and/or tailward are always present at the edge of the plasma sheet adjacent to the tail lobe. Ion beams penetrating into the plasma sheet region with no detectable density gradient are also observed. Beams at tens to hundreds of eV often stream tailward and are often long lasting, suggesting that they may be related to ionospheric sources. Both tailward and earthward streaming beams are detected for ion beams above 1 keV, consistent with an origin from the distant tail, propagation toward earth, and mirroring back under single particle motions.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 88; Oct. 1
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