AN EXAMINATION OF DIRECTIONAL DISCONTINUITIES AND MAGNETIC POLARITY CHANGES AROUND INTERPLANETARY SECTOR BOUNDARIES USING E-GREATER-THAN-2 KEV ELECTRONS

Past studies of interplanetary magnetic sector boundaries have been based on the assumption that one can determine the field polarities by comparing the field directions with those of the nominal Parker spiral angles. Previous investigators have found evidence for decreases of \B\, the magnitude of the magnetic field B, and increases of Theta, the angle between B and the ecliptic plane, at sector boundaries. Others have argued that the characteristic thickness of sector boundaries exceeds that of tangential discontinuities, making sector boundaries a separate class of structures. We use a simple technique for inferring the polarities of interplanetary magnetic fields based on the assumption that E > 2 keV electrons are always flowing along the magnetic field away from the Sun. Electron data from the UC Berkeley experiment on the ISEE-3 spacecraft are used to examine periods around several apparent sector boundaries in 1978 and 1979. We compare properties of (a) boundaries with field polarity changes and (b) large-angle (omega > 60 degrees) directional discontinuities with no field polarity changes. We find no significant differences between the sector boundaries and the directional discontinuities in terms of associated decreases in \B\ or of values of Theta. These results suggest no significant difference between sector boundaries and directional discontinuities other than the change in field polarities. Within limited statistics we find that about half the polarity changes would not have been identified using a requirement that omega > 90 degrees and that half of the omega > 120 degrees discontinuities would have been misidentified as polarity changes.