Polar Magnetic Fields Observed During the Last Four Solar Minima

Details Polar Magnetic Fields Observed During the Last Four Solar Minima Polar Magnetic Fields Observed During the Last Four Solar Minima

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsh51a1589s&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #SH51A-1589

Other

7511 Coronal Holes, 7524 Magnetic Fields, 7529 Photosphere, 7536 Solar Activity Cycle (2162)

Scientific paper

The Sun's polar fields during the current minimum are the weakest in at least four solar cycles. The field strengths are fairly symmetric, unlike at least the two previous minima. We compare data from the Wilcox Solar Observatory (WSO) and Michelson Doppler Imager (MDI) to follow the polar field changes since 1976. The polar field is never observed well from Earth because the ecliptic lies near the Sun's equator, and each year the view of the north (south) is completely hidden for several months around March 7 (September 7). Analysis of the most favorably oriented MDI synoptic maps each year allows us to derive the fairly slowly evolving large-scale polar magnetic field pattern from 1996 to the present. We account for differential rotation and other geometric effects. The analysis allows us to provide a useful interpolated or extrapolated correction that can be smoothly incorporated into the global synoptic or synchronic maps above about 70 degrees latitude. The polar field is important in modeling the large-scale coronal and heliospheric field, particularly at minimum. Even though there has been extremely little solar activity over the last several months, at the current solar minimum the structure of the corona is much less equatorial than usual, in part because the polar fields are relatively weak.

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