The magnetic field configuration of sunspots

The left panel shows sunspot NOAA 10933 recorded on January 5th 2007 with Hinode . The right panel shows NOAA 12049 recorded on May 3rd 2014 with GRIS. The distribution of magnetic field reversing its polarity just above the surface is shown in red. Blue regions indicate polarity reversals at higher atmospheric regions. The contours outline the penumbral boundaries and the black arrows point to the center of the solar disk.

The exact configuration of this magnetic field is important to understand the different features seen in sunspots. In the umbra, the dark center, the field is oriented perpendicular to the surface, while it is more horizontal in the penumbra, i.e. the surrounding region with narrow radially oriented filaments. Parts of the magnetic field continues into higher regions, while some of it reverses its polarity and returns back into the Sun. In the left panel of the figure we show observation with the Hinode satellite of the penumbra of a sunspot. Regions where the field returns below the surface are colored in red and blue. In the red regions, the polarity reversal is just above the surface, while it occurs in higher layers in the blue regions. The right panel show measurements with the new GREGOR Infrared Spectrograph (GRIS) at the Observatorio del Teide on Tenerife. The amount of red and blue regions in this observation is significantly less than the one found in Hinode data. The reason for this difference is subject of current studies at the KIS.

 

References:
Franz, M., Bethge, C., Collados, M. et. al. 2016 Astronomy and Astrophysics, (submitted)
Collados, M., López, R., Páez, E., et al. 2012, Astronomische Nachrichten, 333, 872