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  • GEOPHYSICS  (3)
  • perturbation theory
  • 1980-1984  (3)
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  • 1
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    Unknown
    Minimal upper mantle temperature variations consistent with observed heat flow and plate velocities (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Heat-flow and plate-velocity measurements are used to model upper-mantle temperature variations; the results are intended to form the basis for a gravity-field-variation model and are also applicable to the interpretation of petrological and seismological data. A 5-deg grid is used, a depth of 280 km is chosen as the fully convecting level, and it is assumed that 85 percent of the global heat production (4.0 x 10 to the 13th W) comes from below this level. The velocity field is calculated by integrating the momentum equations down to 280 km (assuming laterally homogeneous viscosity and density) and then used to determine the temperature fields. The results are presented in graphs, tables, and maps. The largest lateral temperature differences are about 1500 C and occur in the top 20 km, where the largest (about 200 C/Myr) nonlinear terms of the energy equation are also found. Below 50 km, heat transfer becomes more convective than conductive, and the most significant temperature variation appears in the form of negative 'tongues' as cold as -825 C at about 100 km. Temperature variations of at least + or - 180 C are calculated at the fully convecting level.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 88; 10323-10
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
    facet.materialart.
    Unknown
    Material properties for mantle convection consistent with observed surface fields (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: An attempt is made to derive constraints on mantle convection from observed surface fields: plate velocities, gravity, topography and heat flow. The spherical harmonic spectra of the fields are expressed in terms of a spectral magnitude and slope, and requirements for the minimal representation of the equations for mantle convection are discussed. The effects of the boundary layer represented by the surface fields on convection at the mantle surface and at deeper levels are then examined, and a mean value of the effective mantle viscosity of approximately 10 to the 23rd g/cm per sec is obtained, together with values of 10 to the 8th and 10 to the 7th for the Rayleigh numbers of whole mantle and upper mantle convection, respectively. Consideration is then given to the compositional, thermal and rheological aspects of mantle convection, and it is pointed out that constraints on the depth and other properties of convection will require more detailed modeling using the relationships between the harmonic coefficients of the surface fields.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 85; Dec. 10
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Unknown
    Inference of variations in the gravity field from satellite-to-satellite range rate (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: An analytic scheme for inferring variations of the gravity field from satellite-to-satellite range rate (low-low) is developed. As a test, it is applied to a pair of satellites in polar orbit, at altitude 160 km and spacing 100 km, with 72 data points per revolution. An assumed gravity field of tesseral spherical harmonics up to the eighth degree is completely recovered in three iterations over 64 revolutions. It is apparent that data points at regular intervals enable the use of data analysis techniques that avoid massive matrix inversions.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 88; Oct. 10
    Format: text
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    NASA TECHNICAL REPORTS
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