Sunspot chromosphere
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The amazing chromosphere above an active region (2/3)
Dunn Solar Telescope
Sunspots are the largest manifestation of magnetic fields in the solar photosphere. They appear darker than the surrounding photosphere, where convective heat transport takes place in the form of granulation. The details of energy transport within sunspots are still under debate. It is clear, however, that it must be of convective origin. Convective energy transport must occur even in the coolest parts of sunspots, since neither heat conduction nor radiative heat transport suffices to sustain the observed umbral temperatures.
This image shows active region 11092 as observed on 2010 August 3 with the IBIS instrument at the Dunn Solar Telescope (New Mexico, USA). It was taken in the core of the Ca II 8542 Å line to reveal the complex magnetic topology and dynamics of active regions in the mid-chromosphere. The chromospheric fibrilar structure visible in the image is much enhanced in the extended active region area. The small, roundish bright points mostly visible at the periphery of the field of view correspond to instances of acoustic shocks in the mid-chromosphere, akin to the famous Ca II bright K and H 2V grains. The brightening to the left of the spot is due to a sub-flare occurring at the time of acquisition.
Image credit: Kevin Reardon (INAF-Arcetri, NSO/AURA/NSF)
Observations by IBIS (INAF/NSO/QUB)