Observations of the Earth's Polar Cleft at Large Radial Distances with the Hawkeye 1 Magnetometer.

摘要

Based on 364 spacecraft passes through the dayside region, the position of the polar cleft at large radial distances was determined with the magnetometer flown on Hawkeye 1. This data set represents one of the largest to investigate the high-latitude region at large radial distances, making it ideal for study of the cusp and cleft region. Identification of the cleft depended on noting strong negative deviations of the magnetic field strength in the region from that of the dipole field. In solar magnetic coordinates, cleft observations were found between 40 deg and 70 deg lat. and + or - 75 deg long., while in geocentric magnetospheric coordinates, these observations were found between 20 deg and 75 deg lat. and + or - 75 deg long. The extreme longitudinal extent of 150 deg is larger than those reported in some previous studies. Large magnetic depressions associated with the cleft extend out to 12 earth radii. Beyond this point, low model dipole field strengths make the determination of the cleft based on magnetic depressions unreliable. The cleft occurrences fall within an oval in magnetic latitude and longitude, but this oval is of a statistical nature and cannot be interpreted as the shape of the region at a given moment. (edc)