Magnetic field measurements with the IMP 2 satellite

The IMP 2 satellite was launched on October 4, 1964, with apogee at 15.9 RE near the earth-sun line. Two onboard monoaxial fluxgate magnetometers measured magnetic fields in interplanetary space, the magnetosheath, and the magnetosphere during the time interval between launch and April 7, 1965. Analysis of over 325 hours of interplanetary data distributed throughout the first two months of operation revealed structuring of the interplanetary magnetic field into four recurring sectors of approximately equal size. Average fields within each sector were directed either toward or away from the sun near the theoretical spiral angle. High magnitudes and increased geomagnetic activity tended to occur early in the sectors and lower fields and quiet conditions at the end. Field directions in the magnetosheath were found to be highly dependent on the sector direction. Results suggest that fields convected through the bow shock front undergo compression and an angle change at the shock and subsequently tend to become aligned tangent to the magnetopause. Frequently both the shock front and the magnetopause were observed to move back and forth past the satellite. Comparisons with onboard plasma detectors showed very good agreement in identifying the magnetosheath. Several passes were notable for the lack of a clear magnetopause, in both plasma and field data. The average magnetic field topology in the magnetosphere between approximately 9 and 16 RE in the dawn-to-midnight region was definitively mapped. Results demonstrate solar wind distortion of the magnetosphere and the gradual formation of the magnetic tail in the dawn-to-midnight region.