Modeling 1 AU solar wind observations to estimate azimuthal magnetic fields at the solar source surface

Details Modeling 1 AU solar wind observations to estimate azimuthal magnetic fields at the solar source surface Modeling 1 AU solar wind observations to estimate azimuthal magnetic fields at the solar source surface

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011georl..3824101s&link_type=abstract

Geophysical Research Letters, Volume 38, Issue 24, CiteID L24101

Astronomy and Astrophysics

Astrophysics

Interplanetary Physics: Interplanetary Magnetic Fields, Interplanetary Physics: Solar Wind Sources, Solar Physics, Astrophysics, And Astronomy: Magnetic Fields, Solar Physics, Astrophysics, And Astronomy: Photosphere, Solar Physics, Astrophysics, And Astronomy: Solar Activity Cycle (2162)

Scientific paper

A recent two-dimensional (radial distance r and solar longitude ϕ) model for the solar wind is driven using 1-hour average data from the Wind spacecraft. We extend the treatment of the Sun's magnetic field to allow a nonzero azimuthal component Bϕ at the source surface, assumed to be at the photosphere where r = Rs, in addition to the radial component Br. We find nonzero azimuthal magnetic fields at the source surface with important consequences for the more distant heliosphere. The averages ∣Bϕ(Rs)∣ and ∣Br(Rs)∣ inferred over solar cycle 23 are 0.44 ± 0.48 μT (4.4 ± 4.8 mG) and 120 ± 30 μT (1.2 ± 0.3 G) at the photosphere, respectively. Both components vary with time by more than an order of magnitude, with ∣Bϕ(Rs)∣ ≤ ∣Br(Rs)∣. While the surface magnetic field is closely radial on average it is sometimes 20° from radial. Both Bϕ and Br vary smoothly on periods of 10 hours, with evidence for relatively narrow current sheets, and vary with the solar cycle: Br(Rs) is correlated with the sunspot number, but with a time lag of 20 months, while Bϕ(Rs) has a two level behavior, decreasing near solar maximum and increasing near solar minimum. Our results and model can account naturally for non-Parker-like magnetic field directions at 1 AU since the Bϕ fields inferred at the source surface lead to the Bϕ and Br fields at 1 AU having similar average magnitudes and large variability.

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