The comprehensive model of the near-Earth magnetic field (Langel et al., 1996) is an ongoing effort to more accurately isolate core, ionospheric, and magnetospheric magnetic fields by the simultaneous determination of these fields. The dawn and dusk maps shown here are based on equivalent source solutions. Only observations equatorward of 55 degrees dipole latitude are used in the solution because the comprehensive model does not yet include auroral features. Consequently, features in Canada and the E-W trending gradient near the Canadian border in the dusk map should not be interpreted. For comparison a previous scalar anomaly map over the United States (Arkani-Hamed et al, 1994) is included. For further details and access to the primary data set over the United States the reader should contact Michael Purucker (purucker@geomag.gsfc.nasa.gov. The Kentucky and Oklahoma-Texas anomalies are virtually unchanged in position between the new dawn and dusk maps and the previous estimate. Note however that the magnitudes in the new maps are 1.4 to 2 times larger, consistent with the absence of an along-track filter in the comprehensive model. Note that there seems to be a level shift of about 2 nT between the new dawn and dusk residual maps, with the dawn being higher. We do not yet know the source of this level shift. Four anomalies can be seen to have significantly greater N-S extent than in the previous map. These include the California- Nevada high, the Nevada-Idaho-Washington low located over an extensional tectonic regime, the Kentucky-Michigan high, and the Bahama low. One feature is missing from the new maps, the high off the Mid-Atlantic/New England shore. The maps are shown with a contour interval of 2 nT, dashed where negative. Supported by NASA RTOP 579-31-01.
Arkani-Hamed,J., R.A. Langel, and M. Purucker, Scalar magnetic anomaly maps of Earth derived from POGO and Magsat data, J. Geophys. Res, 99, 24075-24090, 1994.
Langel,R.A., T.J. Sabaka, R.T. Baldwin, and J.A. Conrad, The near-Earth magnetic field from magnetospheric and quiet-day ionospheric sources and how it is modeled, Phys. Earth Planet. Int., 98, 235-267, 1996.
Purucker, M.E., T.J. Sabaka, R.A. Langel, and N. Olsen, The missing dimension in Magsat and POGO anomaly studies, in review for Geophysical Research Letters.
