Other
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.p11a0944j&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #P11A-0944
Other
5420 Impact Phenomena (Includes Cratering), 5440 Magnetic Fields And Magnetism, 5480 Volcanism (8450), 6225 Mars
Scientific paper
Mars Global Surveyor measured the most strongly magnetized crust in the heavily-cratered southern hemisphere of Mars. Our analysis concentrates on the magnetic lineations or patterns centered near latitude 40oS, longitude 180oW, with a range of values ± 40o, using a rotated Cartesian coordinate system. Using Fourier transforms the magnetic field components at satellite mapping altitude can be vertically extrapolated downward to aerbobraking altitudes and the results are in excellent agreement with measurements at ˜100 km and fill in data gaps. We also construct scalar and vector potentials and a streamline function which provide a more succinct and smoother representation of the field. A model constructed with just 8 vertical dipoles accounts for 80% of the variance of the scalar potential at 400 km over the region analyzed, but 14 dipoles can account for only 64% of the variance at 100 km. More than 20 dipoles are required to model the surface field, and the fit is not as good. At any altitude, as more centers are included they begin to overlap, and the improvement in fit slows and then worsens. No obvious relation of the dipole locations and surface geology is apparent. The magnetic field can be represented as the gradient of the scalar potential or the curl of the vector potential. The vector potential can be chosen so that the vertical component is identically zero, and the horizontal components can be represented as the curl of a streamline function. We reduce the vector potential to a two component horizontal field which can be plotted on a map as a set of arrows. The observed vector potential field shows abrupt changes in direction over the analyzed region, suggesting either different stages of magnetization or local demagnetization. In the southern hemisphere region analyzed, the strongest values of the magnetization lie adjacent to ancient multi-ring basins, notably Sirenum, though not actually within its rings.
Jurdy Donna M.
Stefanick Michael
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