Mathematics – Logic
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja.....2987v&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #2987
Mathematics
Logic
Scientific paper
The spectral method for distinguishing crustal from core-source magnetic fields has been re-examined, modified, and applied to both a comprehensive geomagnetic field model and an altitude normalized magnetic map of Mars [Voorhies, Sabaka &Purucker, 2002]. The observational spectra are fairly fitted by theoretical forms expected from certain elementary classes of magnetic sources. For Earth we found fields from a core of radius 3512 +/- 64 km, in accord with the seismologic core radius of 3480 km, and a crust represented by a shell of random dipolar sources at radius 6367 +/- 14 km, near the planetary mean radius of 6371.2 km. For Mars we found no sign of a core-source field, only a field from a crust represented in same way, but at radius 3344 +/- 10 km, about 46 km below the planetary mean radius of 3389.5 km, and with sources about 9.6 +/- 3.2 times stronger. It is remarkable that the same simple theoretical form should fairly fit the crustal magnetic spectra of both worlds and return crustal-source depth estimates of plausible magnitude. Yet such estimates, at best a kind of average, depend upon both the observational spectrum fitted and the physical basis of the theoretical spectrum. Observational spectra depend on the data fitted and modeling technique. For Earth, the magnetic field model we used has since been revised [Sabaka Olsen &Langel, 2002], updated with high precision Ørsted data, and upgraded with high resolution Champ data. And there are now several fine field models for Mars [Cain et al., 2000; Connerney et al., 2001; Arkani-Hamed, 2001, 2002; Hutchinson &Zuber, 2002; Langlais et al., 2002.]. More realistic theoretical spectra, which allow for crustal thickness, oblateness, and magnetization by a planet centered dipole, were derived and discussed by Voorhies et al. [2002]. Important effects of lateral source correlations were described via an ensemble of vertically magnetized spherical caps; yet interesting complications arise from trial probability distributions for the sizes and magnetizations of extended sources. These are addressed in hopes of improving source-depth estimates, resolving joint distribution parameters, and determining whether or not the different lithospheric magnetic dichotomies of the two planets, evident in the phase information, have distinct spectral signatures.
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