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  • GEOPHYSICS  (289)
  • ASTRONOMY
  • Physics
  • 1990-1994  (362)
  • 1980-1984
  • 1991  (151)
  • 1990  (211)
  • 1
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    Geodetic measurement of deformation in the Loma Prieta, California earthquake with very long baseline interferometry (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: VLBI measurements were conducted immediately after the Loma Prieta earthquake and compared with VLBI gathered at Monterey, San Francisco, and Point Reyes since 1983 to obtain preearthquake deformation rates with respect to a North American reference frame. The estimated displacements at Monterey and San Francisco are consistent with the static displacements predicted on the basis of a coseismic slip model in which slip on the southern segment is shallower than slip on the northern segment of the fault rupture. Cartesian positions are presented at epoch 1990.0 of a set of VLBI fiducial stations and the three mobile sites in the earthquake's vicinity.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 1215-121
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    NASA TECHNICAL REPORTS
  • 2
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    Redistribution of reactive odd nitrogen in the lower arctic stratosphere (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: In-situ measurements of total reactive odd nitrogen NO(y), were made from the NASA DC-8 aircraft in the lower arctic stratosphere during the 1989 Airborne Arctic Stratospheric Expedition. Throughout January and February, NO(y) mixing ratios were typically between 0.5 and 3 parts per billion by volume (ppbv) at altitudes between 10 and 12.5 km. During several flights late in the mission, events of unusually light NO(y) occurred with mixing ratios up to 12 ppbv at these altitudes. Simultaneous measurements of N2O, O3, and H2O during these events suggest that large changes in NO(y) are not expected. The elevated NO(y) values are interpreted as a vertical redistribution of NO(y) in the lower stratosphere resulting from gravitational sedimentation of aerosol particles containing HNO3. No evidence of the redistribution of H2O is noted, consistent with observations of denitrification without dehydration higher in the stratosphere.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters, Supplement (ISSN 0094-8276); 17; 453-456
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  • 3
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    Asteroid radar astrometry (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Measurements of time delay and Doppler frequency are reported for asteroid-radar echoes obtained at Arecibo and Goldstone during 1980-1990. Radar astrometry is presented for 23 near-earth asteroids and three mainbelt asteroids. These measurements, which are orthogonal to optical, angular-position measurements, and typically have a fractional precision between 10 to the -5th and 10 to the -8th, permit significant improvement in estimates of orbits and hence in the accuracy of prediction ephemerides. Estimates are also reported of radar cross-section and circular polarization ratio for all asteroids observed astrometrically during 1980-1990.
    Keywords: ASTRONOMY
    Type: Astronomical Journal (ISSN 0004-6256); 102; 1490-150
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  • 4
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    Two encounters with the flank low-latitude boundary layer - Further evidence for closed field topology and investigation of the internal structure (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The structure of the flank low-latitude boundary layer (LLBL) is examined through differential energy spectra and particle angular anisotropies for traversals of the dawn flank (December 19, 1977) and dusk flank (July 7, 1978) during periods of predominantly northward magnetosheath field orientation. Spectra are presented that were obtained from combined ISEE 1 low-energy-proton and electron-differential-energy-analyzer and medium-energy-particle-instrument data extending over the 200-eV/q to 2-MeV energy range for the plasma sheet, stagnation region, outer LLBL, and magnetosheath regions. The stagnation region and the outer LLBL are each a mixture of plasma-sheet and magnetosheath populations, but the stagnation region contains a relatively higher fraction of plasma sheet particles, consistent with its placement earthward of the outer LLBL. Evidence for energization of thermal electrons appears during the dusk flank crossing. Bidirectional field-aligned ion distributions are observed with typically 5-to-1 enhancement of the flux along the magnetic field during certain portions of the dusk flank crossing.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 21
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  • 5
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    Modeling the growth phase of a substorm using the Tsyganenko model and multi-spacecraft observations - CDAW-9 (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The CDAW-9 Event C focused upon the early part of 3 May 1986 when a large substorm onset occurred at 0111 UT. By modifying the Tsyganenko 1989 magnetic field model, a model is constructed in which the near-earth current systems are enhanced with time to describe the observed development of the tail magnetic field during the growth phase. The cross-tail current intensity and the thickness of the current sheet are determined by comparison with three spacecraft in the near-earth tail. The location of the auroral bulge as recorded by the Viking imager is mapped to the equatorial current sheet. The degree of chaotization of the thermal electrons is estimated, and the consequences to the tail stability towards on tearing are discussed. It is concluded that the mapping of the brightening region in the auroral oval corresponds to the regions in the tail where the current sheet may be unstable towards ion tearing.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 18; 1963-196
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  • 6
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    Relativistic electron enhancements - Simultaneous measurements from synchronous and low altitude satellites (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: This paper presents, for the first time, simultaneous measurements of trapped relativistic electron enhancements at synchronous altitude and precipitating electrons in the bounce loss cone at low altitudes. The measurements show that the daily variations in the precipitation flux for L greater than 5 correlated well with the daily variations in the total flux at high altitude, both with respect to sudden enhancements as well as flux depletions. The daily averaged precipitating flux (E greater than 1 MeV) at L = 6.1 to 7.1 was about 0.3 percent of the daily averaged directional flux (E not less than 1.5 MeV) observed at synchronous altitude, whereas within narrow spikes the precipitating directional fluxes were often within a factor of 10 of the daily averaged trapped fluxes. Strong depletions in the synchronous altitude not less than 1.5 MeV electron intensities are shown to be associated with low-altitude measurements of the equatorward movement of precipitating spikes to lower L shells.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 18; 397-400
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  • 7
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    On open and closed field line regions in Tsyganenko's field model and their possible associations with horse collar auroras (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The boundary between open and closed field lines is investigated in the empirical Tsyganenko (1987) magnetic field model. All field lines extending to distances beyond -70 R(E), the tailward velocity limit of the Tsyganenko model are defined as open, while all other field lines, which cross the equatorial plane earthward of -70 R(E) and are connected with the earth at both ends, are assumed closed. It is found that this boundary at the surface of the earth, identified as the polar cap boundary, can exhibit the arrowhead shape, pointed toward the sun, which is found in horse collar auroras. For increasing activity levels, the polar cap increases in area and becomes rounder, so that the arrowhead shape is less pronounced. The presence of a net B(y) component can also lead to considerable rounding of the open flux region. The arrowhead shape is found to be closely associated with the increase of B(z) from the midnight region to the flanks of the tail, consistent with a similar increase of the plasma sheet thickness.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 3811-381
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  • 8
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    The possible effect of solar soft X rays on thermospheric nitric oxide (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A rocket observation of nitric oxide in the lower thermosphere during a time of high solar activity is compared to the results of calculations from a one-dimensional photochemical model. A solar soft X-ray flux of 0.75 erg/sq cm/s is needed to explain the observed NO densities. This result supports the theory that the variation in the low-latitude thermospheric NO is caused by variation in solar soft X-rays.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 4311-431
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  • 9
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    The substorm event of 28 January 1983 - A detailed global study (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A comprehensive timeline of the growth, expansion, and recovery phases of a small isolated substorm with an expansion phase onset at 07:39 U.T. on January 28, 1983 is provided. The data sets examined include those from the electron-plasma, magnetometer, and energetic-particle instruments onboard ISEE-3. In addition to these data sets, a number of other spacecraft and ground-based data is utilized, including the magnetospheric energy-input rates evaluated in the upstream solar wind and imaging sequences used for examining auroral features during growth and expansion phases. Substorm energy-input and -output relationships are estimated quantitatively, and the timing and physical dimensions of the distant tail disturbance implied by global observations available are evaluated.
    Keywords: GEOPHYSICS
    Type: Planetary and Space Science (ISSN 0032-0633); 38; 1495-150
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  • 10
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    Interpretation of aircraft measurements of NO, ClO, and O3 in the lower stratosphere (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Results are presented from an October 17, 1988, flight of the NASA ER-2 stratospheric research aircraft. The flight sampled a nearly constant air mass at 20 km altitude, near 39 deg N latitude, from before sunrise until near noon. The instrumentation on board simultaneously measured NO, ClO, O3, temperature, and pressure. The measurements are combined with modeled photodissociation coefficients and known reaction kinetics to infer abundances of other important species, and the results are compared to previous estimates as a test for consistency in the understanding of the photochemical processes governing the species distributions.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 18597-18
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