Abstract The Sun's magnetic field determines the configuration of the three-dimensional heliospheric field. Measurements, inferences, and computations of the magnetic field in the corona near the Sun, extended out to 1 or 2 AU, correspond fairly well with the measurements of the interplanetary magnetic field structure. Transient and activity related events are superposed on a slowly evolving background field configuration composed primarily of dipole and quadrupole components that vary in absolute and relative intensity and in orientation during the solar cycle. The heliospheric current sheet (HCS) separates regions of the heliosphere having different interplanetary magnetic field polarity, either toward or away from the Sun. During most of the solar cycle the HCS has a fairly simple configuration: it is roughly symmetric about the solar equator, but has 2 or 4 warps of varying latitudinal extent. Near solar minimum the HCS reaches less than 20° from the equator, but during most of the cycle it extends much nearer the poles. At solar maximum the polar fields weaken and reverse; then the HCS extends all the way to the poles. During this period there may be multiple current sheets. During the declining phase of the cycle the HCS is simpler and sometimes looks like a tilted dipole. Field structures of the northern and southern hemispheres rotate at different rates in Cycle 21 and perhaps in several earlier cycles as well. Extrapolating the structure farther into the heliosphere is problematic. Small variations and perturbations of the solar wind near the Sun are amplified with increasing distance and the simple structure breaks down. Even the stability of the large-scale structure from one rotation to the next is greatly diminished at large distances.
Extending the sun's magnetic field through the three-dimensional heliosphere
Advances in Space Research ; 9 , 4 ; 141-152
1989-01-01
12 pages
Aufsatz (Zeitschrift)
Elektronische Ressource
Englisch
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