Magnetic Landscape of Sun's Polar Region

TL;DR

This paper provides unprecedented high-resolution observations of the Sun's polar magnetic fields, revealing strong vertical flux tubes and horizontal fields, and discusses their role in solar wind acceleration.

Contribution

It offers the first detailed high-resolution magnetic landscape of the Sun's polar region, highlighting the structure and potential role of flux tubes in solar wind acceleration.

Findings

Presence of strong, vertically-oriented magnetic flux tubes with 1 kG field strength.

Ubiquitous horizontal magnetic fields in the polar region.

Vertical flux tubes may act as chimneys for Alfvén waves that accelerate the solar wind.

Abstract

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 \emph{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 degree. 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 photosphere-corona boundary serve as efficient chimneys for Alfven waves that accelerate the solar wind.