Spherical harmonic analysis of earth’s conductive heat flow |
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| Authors: | V M Hamza R R Cardoso C F Ponte Neto |
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| Institution: | (1) Observatório Nacional, Rua General José Cristino, 77, Rio de Janeiro, Brazil |
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| Abstract: | A reappraisal of the international heat flow database has been carried out and the corrected data set was employed in spherical
harmonic analysis of the conductive component of global heat flow. Procedures used prior to harmonic analysis include analysis
of the heat flow data and determination of representative mean values for a set of discretized area elements of the surface
of the earth. Estimated heat flow values were assigned to area elements for which experimental data are not available. However,
no corrections were made to account for the hypothetical effects of regional-scale convection heat transfer in areas of oceanic
crust. New sets of coefficients for 12° spherical harmonic expansion were calculated on the basis of the revised and homogenized
data set. Maps derived on the basis of these coefficients reveal several new features in the global heat flow distribution.
The magnitudes of heat flow anomalies of the ocean ridge segments are found to have mean values of less than 150 mW/m2. Also, the mean global heat flow values for the raw and binned data are found to fall in the range of 56–67 mW/m2, down by nearly 25% compared to the previous estimate of 1993, but similar to earlier assessments based on raw data alone.
To improve the spatial resolution of the heat flow anomalies, the spherical harmonic expansions have been extended to higher
degrees. Maps derived using coefficients for 36° harmonic expansion have allowed identification of new features in regional
heat flow fields of several oceanic and continental segments. For example, lateral extensions of heat flow anomalies of active
spreading centers have been outlined with better resolution than was possible in earlier studies. Also, the characteristics
of heat flow variations in oceanic crust away from ridge systems are found to be typical of conductive cooling of the lithosphere,
there being little need to invoke the hypothesis of unconfined hydrothermal circulation on regional scales. Calculations of
global conductive heat loss, compatible with the observational data set, are found to fall in the range of 29–34 TW, nearly
25% less than the 1993 estimate, which rely on one-dimensional conductive cooling models. |
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| Keywords: | Global heat flow Spherical harmonic analysis Conduction heat transfer |
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