Magnetic anomaly maps obtained by means of the mean ionospheric field correction

The advantage of Mean Ionospheric Field Correction (MIFC) over the MAGSAT data is described in order to obtain crustal magnetic anomalies, the magnitude of which is in many cases comparable to or smaller than that of electric currents in the magnetosphere and ionosphere. In the past, the correction for non-crustal fields has been empirical without sound physical meaning, so that the non-crustal fields remain almost uneliminated in the geomagnetic anomaly maps, or the crustal anomalies are too reduced by some artificial corrections. Recently, it was proposed to calculate the Mean Ionospheric Field (MIF) separately for the dawn side and dusk side and subtract it, in order to obtain the magnetic anomalies of crustal origin (YANAGISAWA, 1983; YANAGISAWA and KONO, 1984). In this paper, we derive the magnetic anomaly maps of crustal origin for regions over the western Pacific and South America, taking the longitudinal inequality of MIF into consideration. (author)