Sunspot penumbra
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Sunspot penumbrae (3/3)
Swedish 1-m Solar Telescope
The penumbra of sunspots is a magnetized region where convective motions are not entirely inhibited. Understanding its structure, brightness, and dynamics represents a challenge, as our ability to make progress depends on improvements in the spatial resolution of the observations.
Penumbral filaments are formed by a dark core and two lateral brightenings. They carry the Evershed flow, an outward flow of several km/s extending from the umbra to the outer penumbral boundary. Its nature has been discussed for decades. According to current views, penumbral filaments are related to extended lanes of horizontal fields embedded in a more vertical and stronger magnetic background. The intensity of the magnetic field decreases with radial distance from the umbra in the two components, albeit at different paces.
The image depicts the main spot of active region NOAA 11302 as observed with the CRISP instrument at the Swedish 1-m Solar Telescope on 28 September 2011. From left to right, the three panels show maps of continuum intensity, circular polarization and velocity. Circular polarization is a proxy of magnetic fields in sunspots (white indicates fields pointing to the observer, black corresponds to fields pointing away from the observer). The velocity map show motions away from the observer in red and motions toward the observer in blue.
The movies show the evolution of the spot in continuum intensity and circular polarization for a period of 43 minutes.
To download the movie, click HERE
Movie credit: Sara Esteban Pozuelo (IAA-CSIC), Luis Bellot Rubio (IAA-CSIC), Ada Ortiz (ITA, University of Oslo)
Publication: Esteban Pozuelo et al., 2015, ApJ, 803, 93