Polarity reversal of the solar magnetic field during cycle 23

Abstract

Using magnetograph data, coronagraph observations, and source surface extrapolations, we examine the evolution of the photospheric magnetic field from 1996 through the 2000–2001 polarity reversal and show how this evolution is reflected in coronal holes, coronal streamers, the heliospheric current sheet (HCS), and the solar wind. The photospheric polarity reversal is completed in the more active Northern Hemisphere in late 2000 and then in the Southern Hemisphere in 2001. The polar coronal holes disappear in 2000 and start to re‐form in 2001; during this interval, most of the open magnetic flux resides in the active region latitudes, where small coronal holes with strong footpoint fields generate predominantly slow solar wind. The nondipolar nature of the large‐scale coronal field at sunspot maximum gives rise to complex streamer/HCS topologies, in which a four‐sector structure and even a secondary, detached current sheet with cylindrical geometry are sometimes present. Comparison of the potential field extrapolations with coronagraph and Ulysses observations suggests that the magnetograph measurements may have underestimated the strength of the south polar field during late 2000.