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  • GEOPHYSICS  (768)
  • 1980-1984  (768)
  • 1955-1959
  • 1925-1929
  • 1984  (768)
  • 1
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    Present state of knowledge of the upper atmosphere: An assessment report (1984)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: A program of research, technology, and monitoring of the phenomena of the upper atmosphere, to provide for an understanding of and to maintain the chemical and physical integrity of the Earth's upper atmosphere was developed. NASA implemented a long-range upper atmospheric science program aimed at developing an organized, solid body of knowledge of upper atmospheric processes while providing, in the near term, assessments of potential effects of human activities on the atmosphere. The effects of chlorofluorocarbon (CFC) releases on stratospheric ozone were reported. Issues relating the current understanding of ozone predictions and trends and highlights recent and future anticipated developments that will improve our understanding of the system are summarized.
    Keywords: GEOPHYSICS
    Type: NASA-TM-87559 , NAS 1.15:87559
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Intercomparison of stratospheric/mesospheric data; Proceedings of the Topical Meeting, Graz, Austria, June 25-July 7, 1984 (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Comparative analyses of various stratospheric and mesospheric species, including aerosols, ions, ozone, and some minor species, are presented, based on measurements obtained from rocket, balloon, aircraft, and satellite missions. In addition, studies concerning temperature and density characteristics of the stratosphere and mesosphere are included, as well as discussions on the various sensing and measurement techniques. Finally, dynamics and turbulence measurements are examined; consideration is given to radar winds, solar X-ray and HF radiowave absorption, and ionization irregularities.
    Keywords: GEOPHYSICS
    Type: (ISSN 0273-1177)
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    DE-1 observations of ordinary mode and extraordinary mode auroral kilometric radiation (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Observations of auroral kilometric radiation (AKR) made with the Dynamics Explorer (DE-1) indicate the presence of both ordinary and extraordinary wave modes. Although the two modes usually occur separately, they are sometimes observed together. When both modes are present, the ordinary-mode component tends to occur at lower frequencies and with lower amplitudes than those of the accompanying extraordinary-mode component. On the other hand, the local electron gyrofrequency is an absolute lower frequency cutoff for both modes. Ordinary mode intensities are proportional to extraordinary mode intensities but less by roughly a factor of 50. Extraordinary mode ray paths are generally confined to a cone within 50 degrees of the source magnetic field direction and ordinary mode emissions are typically observed outside of this cone. This behavior suggests that both components are produced within the same source region but are then refracted differently as they escape.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 11; 1188-119
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Aerosol limb absorption (1984)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: A global observation was conducted of the vertical distribution of stratospheric aerosol and ozone using the absorption effect of the rays of the Sun by the stratospheric aerosol and ozone.
    Keywords: GEOPHYSICS
    Type: NASA-TM-77733 , NAS 1.15:77733
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    Fast collisionless tearing in an anisotropic neutral sheet (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: The collisionless tearing mode in a neutral sheet is studied in the presence of ion temperature (Ti) anisotropy, using Vlasov description for both ions and electrons. It is found that the growth rate of the instability is significantly enhanced if the ratio of Ti perpendicular to the equilibrium magnetic field to Ti parallel to the field is greater than one. For typical magnetotail parameters with modest temperature anisotropy, it is shown that the linear e-folding time is reduced to a small fraction of the time delays believed to precede the onset of reconnection. This enhancement of the growth rate is due to the Lorentz force acting on the ions that cross the neutral plane, traversing beyond the conventional electron-tearing layer.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 11; 12-15
    Format: text
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  • 6
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    Study of the system of middle atmosphere-ionosphere using remote-sensing data (1984)
    In:  CASI
    Details
    Publication Date: 2019-08-27
    Description: In the present investigation, the methods of statistical spectral analysis are employed for a study of the quasi-periodic changes of state parameters of the middle atmosphere and the ionosphere, taking into account oscillations with periods of several days. The considered oscillations are typical for planetary waves. The theory and empirical findings regarding transient planetary waves are utilized as a basis for the concepts employed in the data analysis and for the interpretation of the results. The results of the investigation show a presence of coherent variations in the time series of radiation density measurements and other state parameters for the middle atmosphere and the ionosphere. The existence of presumably dynamic coupling processes can be recognized in oscillations with periods of about 16 or 5 days.
    Keywords: GEOPHYSICS
    Type: NASA-TM-77764 , NAS 1.15:77764
    Format: application/pdf
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  • 7
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    Subcritical Fracture Propagation in Rocks: an Examination Using the Methods of Fracture Mechanics and Non-Destructive Testing (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-08-14
    Description: An experimental investigation of tensile rock fracture is presented with an emphasis on characterizing time dependent crack growth using the methods of fracture mechanics. Subcritical fracture experiments were performed in moist air on glass and five different rock types at crack velocities using the double torsion technique. The experimental results suggest that subcritical fracture resistance in polycrystals is dominated by microstructural effects. Evidence for gross violations of the assumptions of linear elastic fracture mechanics and double torsion theory was found in the tests on rocks. In an effort to obtain a better understanding of the physical breakdown processes associated with rock fracture, a series of nondestructive evaluation tests were performed during subcritical fracture experiments on glass and granite. Comparison of the observed process zone shape with that expected on the basis of a critical normal principal tensile stress criterion shows that the zone is much more elongated in the crack propagation direction than predicted by the continuum based microcracking model alone.
    Keywords: GEOPHYSICS
    Format: text
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  • 8
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    Correlated low-frequency electric and magnetic noise along the auroral field lines (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-08-13
    Description: Dynamics Explorer 1 measurements of intense low-frequency electric and magnetic noise observed at low altitudes over the auroral zone are described. The intensity of both the electric and magnetic fields decreases rapidly with increasing frequency. Most of the energy is at frequencies below the O(+) cyclotron frequency, and some evidence is found for a cutoff or change in spectral slope near that frequency. The magnetic to electric field ratio decreases rapidly with increasing radial distance and also decreases with increasing frequency. The polarization of the electric field in a plane perpendicular to the earth's magnetic field is essentially random. The transverse electric and magnetic fields are closely correlated, with the average Poynting flux directed toward the earth. The total electromagnetic power flow associated with the noise is substantial. Two general models are discussed to interpret these observations, one based on static electric and magnetic fields imbedded in the ionosphere and the other based on Alfven waves propagating along the auroral field lines.
    Keywords: GEOPHYSICS
    Type: AD-A150627 , Journal of Geophysical Research (ISSN 0148-0227); 89; 8971-898
    Format: text
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    NASA TECHNICAL REPORTS
  • 9
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    Externally driven magnetic reconnection (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A model is presented in which externaly driven reconnection is simulated by solving the MHD equations in an initially plane current sheet. Magnetic reconnection in the earth's magnetotail is widely believed to be the direct cause of magnetospheric substorms. Both 2-D and 3-D versions of the model have been developed. It is postulated that connection in the tail is triggered by a local compression of the plasma sheet which results from an invasion of the solar wind into the magnetotail. Thus, the simulation is started by introducing flow from the lobes normal to the plasma sheet. When resistivity is generated in a local region of the neutral sheet, reconnection develops and magnetic energy is converted into plasma bulk flow. Although the driven reconnection model is highly simplified, it can aid in understanding many features of substorms in the tail; in particular, results show that rapid flows both earthward and tailward of the neutral line and the nightside substorm current system are natural consequences of driven magnetic reconnection.
    Keywords: GEOPHYSICS
    Type: Magnetic reconnection in space and laboratory plasmas; Oct 03, 1983 - Oct 07, 1983; Los Alamos, NM
    Format: text
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    NASA TECHNICAL REPORTS
  • 10
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    Boundary layers of the earth's outer magnetosphere (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The magnetospheric boundary layer and the plasma-sheet boundary layer are the primary boundary layers of the earth's outer magnetosphere. Recent satellite observations indicate that they provide for more than 50 percent of the plasma and energy transport in the outer magnetosphere although they constitute less than 5 percent by volume. Relative to the energy density in the source regions, plasma in the magnetospheric boundary layer is predominantly deenergized whereas plasma in the plasma-sheet boundary layer has been accelerated. The reconnection hypothesis continues to provide a useful framework for comparing data sampled in the highly dynamic magnetospheric environment. Observations of 'flux transfer events' and other detailed features near the boundaries have been recently interpreted in terms of nonsteady-state reconnection. Alternative hypotheses are also being investigated. More work needs to be done, both in theory and observation, to determine whether reconnection actually occurs in the magnetosphere and, if so, whether it is important for overall magnetospheric dynamics.
    Keywords: GEOPHYSICS
    Type: Magnetic reconnection in space and laboratory plasmas; Oct 03, 1983 - Oct 07, 1983; Los Alamos, NM
    Format: text
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