Interpolated polar field for CR1914: 7 Methods

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Interpolated polar field for CR1914 7 Methods
Synoptic Maps of Magnetic Field from MDI
Magnetograms Polar Field Interpolation.Y. Liu,
J. T. Hoeksema, X. P. Zhao, R. M. Larson
Stanford University
Question How best to infer the polar field?

This poster compares seven methods for
interpolation of the polar magnetic field for the
MDI synoptic charts. By examining the coronal and
heliospheric magnetic field computed from the
synoptic charts based on a Potential Field Source
Surface model (PFSS), and by comparing the
heliospheric current sheets and footpoints of
open fields with the observations, we conclude
that the coronal and heliospheric fields
calculated from the synoptic charts are sensitive
to the polar field interpolation, and a
time-dependent interpolation method (Method 5)
using the observed polar fields is the best among
the seven methods investigated.

• Discussion Conclusion
• Method 1 This method is bad because closed
  fields are computed in polar regions in solar
  minimum
• Method 2 This method is based on Method 1 (bad)
• Method 3 Improved but questionable during polar
  field reversal. When trailing field reaches high
  latitude but the polar field is not reversed, the
  interpolated polar field might already give a
  reversed polar field because this method uses low
  latitude data to interpolate polar field (see
  CR1967)
• Method 4 generally is good, but might be
  questionable in solar maximum because no evidence
  has been presented to show this model is still a
  good approximation in solar maximum
• Method 5 might be the best
• Method 6 also uses the low latitude data to fill
  in the polar regions. It may be questionable
  during polar field reversal (see CR1967)
• Method 7 strongly depends on flux transportation
  model that would be very complicated. Also show
  earlier polar field reversal (CR1967).