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  • Life and Medical Sciences  (6,292)
  • GEOPHYSICS  (4,117)
  • 2020-2024
  • 1985-1989  (10,409)
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  • 11
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    Boundary layer dynamics in the description of magnetospheric substorms (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: This paper presents an analysis of eleven magnetospheric substorm events for which good-quality ground-based magnetometer data and ISEE satellite data were both available. It is shown that the magnetotail particle and field observations associated with a substorm expansive phase can be explained through the spatial movement of the boundary layers and central plasma sheet in the magnetotail. The sweeping of these regions past the satellite, even in the absence of temporal variations within the various regions, can lead to a set of plasma flow observations typical of what is observed in the magnetotail during substorm activity.
    Keywords: GEOPHYSICS
    Type: AD-A209803 , Journal of Geophysical Research (ISSN 0148-0227); 93; 14411-14
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    NASA TECHNICAL REPORTS
  • 12
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    A boundary layer model for magnetospheric substorms (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: An alternative framework for understanding magnetospheric substorm activity is presented. It is argued that observations of magnetic field and plasma flow variations in the magnetotail can be explained in terms of the passage of the plasma sheet boundary layer over the satellite detecting the tail signatures. It is shown that field-aligned currents and particle acceleration processes on magnetic field lines threading the ionospheric Harang discontinuity lead to the distinctive particle and field signatures observed in the magnetotail during substorms. It is demonstrated that edge effects of field-aligned currents associated with the westward traveling surge can lead to the negative B(z) perturbations observed in the tail that are presently attributed to observations made on the anti-earthward side of a near-earth neutral line. Finally, it is shown that the model can provide a physical explanation of both the driven system and the loading-unloading system whose combined effects provide the observed substorm perturbation pattern in the magnetosphere and ionosphere.
    Keywords: GEOPHYSICS
    Type: AD-A194400 , Journal of Geophysical Research (ISSN 0148-0227); 92; 12187-12
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  • 13
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    Plasma waves in the range of the lower hybrid frequency - ISEE 1 and 2 observations at the earth's bow shock (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: This report presents a characterization of plasma wave noise in the range of the lower hybrid frequency associated with 65 crossings of earth's bow shock observed by the ISEE 1 and 2 satellites. Wave growth generally becomes detectable at the upstream edge of the shock foot, increases at the upstream edge of the shock ramp, peaks within the ramp, and then quickly decays to steady downstream values. The upstream extent of the noise is on the same order as that of specularly reflected gyrating ions. Similar profiles were observed in subcritical and supercritical shocks, and no special behavior was associated with the first critical Mach number. Spectra in the foot and ramp were similar in shape, although the noise was 1 to 2 orders of magnitude more intense in the shock ramps than in the feet. Electric field intensities are positively correlated with solar wind speed and inversely related to electron beta and Mach number. Magnetic components are positively correlated with Mach number and beta. The results are generally consistent with suggestions that the noise consists of lower hybrid waves driven by reflected gyrating ions in the foot, and by additional instabilities, such as the cross-field current, in the shock ramp.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 9695-970
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  • 14
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    Energy spectra of plasma sheet ions and electrons from about 50 eV/e to about 1 MeV during plamsa temperature transitions (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: ISEE-1 charged-particle measurements obtained during eight plasma temperature transitions (PTTs) in 1978-1979 are compiled in tables and graphs and analyzed in detail, comparing the ion and electron differential energy spectra with the predictions of theoretical models. PTTs are defined as approximately 1-h periods of low bulk plasma velocity and steadily increasing or decreasing thermal energy. A Maxwellian distribution is found to be inadequate in describing the PTT energy spectra, but velocity-exponential and kappa distributions are both successful, the latter especially at higher energies. The power-law index kappa varies from PTT to PTT, but the high-energy spectral index and overall shape of the distribution remain constant during a PTT; both spatial and temporal effects are observed.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 2562-257
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  • 15
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    Plasma and field observations of a Pc 5 wave event (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: The particle detector and electric field data collected by the Dynamo Explorer 1 on the Pc 5 wave event encounter on July 14, 1982 are presented, yielding a nearly complete picture of the event. The overall structure of the Pc 5 seems to order the event into two distinct halves, suggesting a temporal or spatial variation of the micropulsation. Thermal plasma measurements showed that the dominant ion throughout both lobes was H(+). Significant quantities of He(+), O(+), N(+), and O(2+) were also observed to be present and rotating together in a plane normal to the magnetic field direction, due to the Pc5 E x B drift. The plasma parameters determined for the two lobes were used in theoretical calculations to predict the period of the observed resonance.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 11147-11
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  • 16
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    Cratering mechanics (1986)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: Main concepts and theoretical models which are used for studying the mechanics of cratering are discussed. Numerical two-dimensional calculations are made of explosions near a surface and high-speed impact. Models are given for the motion of a medium during cratering. Data from laboratory modeling are given. The effect of gravitational force and scales of cratering phenomena is analyzed.
    Keywords: GEOPHYSICS
    Type: NASA-TM-88477 , NAS 1.15:88477
    Format: application/pdf
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  • 17
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    The planning and execution of ER-2 and DC-8 aircraft flights over Antarctica, August and September 1987 (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: The significant ozone loss in the lower stratosphere over Antarctica during recent austral springs was studied by instrumented ER-2 and DC-8 aircraft. Data on the homogeneous gas composition, polar stratospheric clouds, and on tracers for dynamic motion are provided. The mission design is described, the aircraft and their payloads are documented, and the flight tracks are specified.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 94; 11181-11
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  • 18
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    Plasma flows near the neutral sheet of the magnetotail (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: The Lepedea on board ISEE 1 is used to investigate the bulk flow plasma in the neutral sheet region (defined as the area where BX approx = O) of the magnetotail. For the majority of crossings there is no appreciable change in the macroscopic plasma parameters, i.e., the density, temperature and velocity of the plasma remain constant through the neutral sheet. This is true even during active periods, when AE is somewhat greater than 100nT. However, for a small number of crossings, all during disturbed times, large plasma bulk velocities abs. val V is greater than or = 300 km/s are observed. The velocity distributions during these events are qualitatively similar to those of the plasma sheet boundary layer that is usually observed at higher latitudes. The acceleration mechanism which creates the plasma sheet boundary layer extends to relatively small radial distances during these active periods.
    Keywords: GEOPHYSICS
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  • 19
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    NASA's geodynamics program (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: The NASA geodynamics program covers dynamics of the core; dynamics and structure of the mantle; dynamics and structure of the lithosphere; evolution and composition of the Earth; and comparative planetology. Projects include crustal dynamics/Earth observations; gravity field modelling; and magnetic field studies. Planned space flights include global gravity and magnetic field mapping; magnetic field secular changes; gravity gradiometer mission; LAGEOS-2; and Earth Observing System.
    Keywords: GEOPHYSICS
    Type: ESA, Proceedings of an ESA-NASA Workshop on a Joint Solid Earth Program; p 11-16
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  • 20
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    Causes and effects of a hole (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Preliminary results from the U.S. National Ozone Expedition (NOZE) to Antarctica are reviewed. The NOZE ozonesonde measurements showed significant vertical structure in the hole, with 80 percent depletion in some of the 1 km layers but only 20 percent in adjacent layers. The depletion was confined to the 12-20 km region, beginning first at higher altitude and progressing downward. This is strong evidence against the theory that the ozone hole is due to solar activity producing odd nitrogen at high altitudes which is transported downwards, leading to enhanced odd-nitrogen catalytic cycles that destroy ozone. Nitrous oxide data show unusually low concentrations within the polar vortex, which is evidence against the theory that the hole is caused by a purely dynamical mechanism in which rising air motions within the polar vortex lead to reduced column densities of ozone. It is tentatively concluded that a chemical mechanism involving man-made chlorofluorocarbons is the likely cause of ozone depletion in the hole.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 325; 297
    Format: text
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