Mathematics – Logic
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmgp42a..03v&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #GP42A-03
Mathematics
Logic
5440 Magnetic Fields And Magnetism, 6225 Mars, 1507 Core Processes (8115), 1517 Magnetic Anomaly Modeling, 1545 Spatial Variations (All Harmonics And Anomalies)
Scientific paper
The spectral method for distinguishing crustal from core source magnetic fields is re-examined, modified, and applied to both a comprehensive geomagnetic field model and an altitude normalized magnetic map of Mars. The observational spectra are fairly fitted by theoretical forms expected from certain elementary classes of magnetic sources. For Earth we find 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 find 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. Spectral effects of source layer thickness, oblateness, polarization, and correlation are understood and addressed. Mars' spectrum clearly shows the need to modulate an exponential form along lines developed for Earth's crustal-source field. Similarly, Earth's low degree spectrum shows an unmodulated exponential form is not a reliable indicator of core radius, unlike the expected core field spectrum. Both planetary spectra show significant scatter about the theoretical forms, albeit less than anticipated. These deviations are attributed to physically significant fluctuations in Earth's core-source field and to correlated sources in the magnetic lithospheres of Earth and of Mars.
Purucker Michael
Sabaka Terence J.
Voorhies Coerte V.
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