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MAGSAT crustal anomalies for Africa; dawn and dusk data differences and a combined data set



MAGSAT crustal anomalies for Africa; dawn and dusk data differences and a combined data set



Physics of the Earth and Planetary Interiors 67(3-4): 0-250



A new crustal magnetic anomaly map of Africa using both local time (dawn and dusk) MAGSAT data sets is presented. MAGSAT data include the external field (magnetospheric field) and internal fields (main core field, crustal field, induction field, and ionospheric field). The crustal field is extracted by removing the undesired external and internal components with the least possible effect on the crustal signature. The effects of external and internal fields can be reduced by filtering along track, calculating a mean ionospheric field correction for both the equatorial electrojet and solar daily quiet variation (Sq) currents, removing a thirteenth-degree and -order spherical harmonic model of the main field, and eliminating observations associated with large values of magnetic field indices (Kp, Dst, AE). An important consideration in selecting the appropriate long-wavelength cutoff for the along-track filter is how to minimize attenuation of the true crustal field. Power spectra, coincident passes, standard error maps, and differences in scalar anomalies for local time maps are examined to determine the best choice. After filtering each local time separately, dawn and dusk data can be averaged in 2° equal-area bins to produce a combined average scalar map. Using the equivalent source method, the crustal anomalies are presented at a common altitude (400 km) and in reduced-to-pole representation.

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Accession: 019348650

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DOI: 10.1016/0031-9201(91)90021-9


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