RESULTS OF A COMPARISON BETWEEN ØRSTED AND MAGSAT ANOMALY FIELDS OVER THE REGION OF THE KURSK MAGNETIC ANOMALY.
Patrick T. Taylor
Code 921, Geodynamics Branch, NASA/Goddard Space Flight Center, Greenbelt,
Ralph R. B. von Frese and Hyung Rae Kim,
Department of Earth Sciences, The Ohio State University, Columbus, OH 43210 (email@example.com) and (firstname.lastname@example.org)
The Kursk Magnetic Anomaly (KMA) of Russia (510 north, 370 east) has long been recognized as one of the largest magnetic anomalies on Earth. It is associated with the massive iron-ore formations of this region, however, model studies have revealed that the relationship between the two is not obvious. In an early effort to demonstrate the validity of Magsat data for crustal research a detailed study of the KMA, at an average altitude of 350 km, and the surrounding region was made (Taylor and Frawley, 1986). They recorded a 27 nT high and a -9 nT low giving a 37 nT peak-to-trough anomaly over the immediate area of the KMA.
Despite the much higher altitude of Ørsted (620 to 850 km) we revisited the KMA to determine if this later mission would also be able to record an associated anomalous crustal signature. We computed an Ørsted magnetic anomaly map for the same region as the original Magsat study (400 to 650 north and 150 to 450 east). The Ørsted profiles selected were from April to August 1999. From these data we chose those with an altitude range of 644 to 700 km and they were subsequently gridded, by least-squares collocation, to a mean elevation of 660 km. Both ascending and descending data were examined and signals common to both were extracted and averaged (Alsdorf et al, 1994). A correlation coefficient between these two orbit orientations of 0.82 was computed. The quadrant-swapping method of Kim et al. (1998) was applied. Removal of the main geomagnetic field was accomplished with a polynomial fitting procedure. A positive anomaly of >2.5 nT with an associated negative of <-0.5 nT for a >3 nT peak-to-trough range were computed. These Magsat and Ørsted results are consistent with the decay of a dipole field over the studied altitude range. Significant differences between these two anomaly fields are due to the greater number of orbit profiles and therefore greater number of intersecting orbits (ascending and descending) available in the Ørsted compilation. Of the four largest amplitude anomalies in the Ørsted field three are present in the Magsat map. The fourth (>2.5 nT), however, is associated with the Belorussian-Lithuanian anteclise. In the southwestern quadrant of this region the southeastern end of the TTZ is apparent in both satellite fields. This linear magnetic anomaly gradient defines the terminus of the East European Craton. Linear negative anomalies trending in a generally north-south direction cross the Black Sea; while these anomalies are apparent in both fields the paucity of Magsat orbits along the southern edge of the KMA study region makes a robust comparison less certain. Our correlation between the two different satellite anomaly fields would suggest that additional geologic information might be gained from Ørsted anomaly field mapping.