Nonzero azimuthal magnetic fields at the solar source surface: Extraction, model, and implications

摘要

A recent two-dimensional (radial distance r and solar longitude) model for the solar wind is driven using 1h average data from the Wind spacecraft. We extend the treatment of the Sun's magnetic field in comparison with previous models to allow a nonzero intrinsic azimuthal component B at the solar source surface, in addition to the radial component B _r. We find nonzero azimuthal magnetic fields at the source surface which dominate the variability in B (r,) at 1AU and beyond. The averages B (R _s) and B _r (R _s) | inferred over solar cycle 23 were 0.44 0.48 T (4.4 4.8 mG) and 120 30 T (1.2 0.3G) at the photosphere, respectively, where R _s equals one solar radius. While the surface magnetic field is closely radial on average as expected, it is sometimes over 20 from radial. Both B and B _r vary smoothly on periods of order of a day, with evidence for relatively narrow current sheets, and vary differently with the solar cycle: B _r (R _s) is correlated with the sunspot number while B (R _s) has a two-level behavior. The typical fields B _r (R _s) | are consistent with previous estimates. This consistency, the finding of a linear relation between the data-smoothing time period and the average transition time for each component and other arguments support the contention that the B (R _s) fields found are intrinsic. Our results and model can account naturally for non-Parker-like magnetic field directions at 1AU and all r above the source surface.