Dependence of the IMF sector structure on the solar dipole tilt angle

摘要

The quasiperiodic variations of the interplanetary magnetic field (IMF) sector structure at the ACE satellite (L1) are investigated using power spectrum analysis. It appears that the two-sector structure of the IMF dominates during the solar maximum, lasting 3 years from 2000 through 2003, and the four-sector structure dominates during the solar activity minimum. A possible explanation is introduced for this phenomenon in which the IMF sector structures vary with the tilt angle of the heliospheric current sheet (HCS) with respect to the solar rotation axis. During the solar activity maximum, the HCS is perpendicular to the ecliptic plane. Therefore the spacecrafts at L1 point are expected to pass through the HCS only twice in one solar rotation, which gives rise to the observed two-sector structure of the IMF. On the other hand, during the solar activity minimum, the HCS is nearly parallel to the ecliptic plane, and the polarity of IMF Bx changes several times in one solar rotation due to the wavy nature of the HCS, which may lead to the observed four-sector structure.