Magnetic Landscape of Sun’s Polar Region

We present the magnetic landscape of the polar region of the Sun that is unprecedented in terms of high spatial resolution, large field of view, and polarimetric precision. These observations were carried out with the Solar Optical Telescope aboard Hinode. Using a Milne-Eddington inversion, we found many vertically-oriented magnetic flux tubes with field strength as strong as 1 kG that are scattered in latitude between 70 ◦ ∼ 90 . They all have the same polarity, consistent with the global polarity of the polar region. The field vectors were observed to diverge from the center of the flux elements, consistent with a view of magnetic fields that expand and fan out with height. The polar region is also covered with ubiquitous horizontal fields. The polar regions are the source of the fast solar wind channelled along unipolar coronal magnetic fields whose photospheric source is evidently rooted in the strong field, vertical patches of flux. We conjecture that vertical flux tubes with large expansion around the photospherecorona boundary serve as efficient chimneys for Alfvén waves that accelerate the solar wind. Subject headings: sun: magnetic fields, polar region, solar wind, dynamo National Astronomical Observatory, Mitaka, Tokyo, 181-8588, Japan High Altitude Observatory, National Center for Atmospheric Research, P.O. Box 3000, Boulder CO 80307-3000, USA ISAS/JAXA, Sagamihara, Kanagawa, 229-8510, Japan Kwasan and Hida Observatories, Kyoto University, Yamashina, Kyoto, 607-8471, Japan Instituto de Astrofisica de Andalucia (CSIC), Camino Bajo de Huetor, 5