Polar regions
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The North Pole of the Sun (1/4)
Hinode Spectropolarimeter
These images show the magnetic activity of the north polar region of the Sun as recorded by the spectropolarimeter (SP) aboard the Japanese Hinode satellite. The pictures display seeing-free observations of the solar surface in intensity (I), linear polarization (Q and U) and circular polarization (V) with the highest magnetic sensitivity and spatial resolution achievable nowadays.
Near the border of the solar disk (the limb), linear polarization measurements reveal vertical magnetic fields on the surface of the Sun, while circular polarization measurements sample horizontal magnetic fields. A comparison of the various maps shows that the polar regions of the Sun are covered by very weak small-scale magnetic fields which are horizontal for the most part. These fields are short lived. In addition, the linear polarization maps reveal the presence of localized patches of vertical magnetic fields which are more intense, corresponding to the so-called polar faculae.
Studying the magnetism of the poles is important to understand the origin of the weak magnetic fields that populate the quiet Sun. Those regions are devoid of sunspots and pores, and therefore the fields observed there must be produced by a local dynamo or be the remnants of decaying active regions transported to the poles by meridional flows. Are their properties different from those observed at lower latitudes where active regions are usually seen? We still do not know. Characterizing polar magnetic fields is difficult because of large projection effects, which make the signals much smaller and difficult to interpret. With its superb spatial resolution, EST will measure polar magnetic fields with unprecedented accuracy, allowing comparative studies of polar and equatorial regions to be carried out for the first time.
Image credit: Luis Bellot Rubio (IAA-CSIC)
Observations: Hinode (ISAS/JAXA, NAOJ, NASA, STFC, ESA)