Investigating features of the solar chromosphere with the EST

Our vision of magnetism in the chromosphere remains "hazy", writes Dr. Malcolm Druett from Stockholm University (Sweden). The European Solar Telescope will provide the sharp eyes needed to deepen our understanding of the chromosphere, he argues in this contribution to "The Science of EST" series. 


Temperatures at different heights from a numerical simulation of the solar atmosphere spanning from the photosphere to the chromosphere.


One of my supervisors once told me that the solar corona is “magnetism made visible”. However, our vision of this magnetism remains hazy in the chromosphere, that narrow region of dynamic change between the pressure dominated photosphere, and the magnetically dominated corona.

In the chromosphere, fibrils and spicules are observed. These are thin (around 180 km), elongated (up to 4000 km) swaying structures with waves that are seen to pass along them in intensity-only observations. To what extent do they follow magnetic field lines, and under what conditions? Where does the mass of these structures come from, and to which regions does it flow? How much of the material contained in fibrils or spicules is heated to coronal temperatures? To answer these questions and evaluate our simulations requires clearer intensity images taken with very narrow wavelength filters, and spectropolarimetric data.

With a 4-m primary mirror, the latest adaptive optics, and integral-field spectropolarimeters, the European Solar Telescope will provide the sharp eyes needed to investigate the magnetic stitch-work of the chromosphere. It will provide joined-up science, helping to link field lines and flux emerging from the photosphere to these enigmatic chromospheric structures, as well as linking others upward to the breathtaking loops and twisted flux ropes that extend through the corona.

The movie shows the temperatures of horizontal cuts from a numerical simulation of the solar atmosphere covering an area of 24000 km by 24000 km with a pixel size of 48 km. The cut heights across the solar atmosphere are 3500 km, 2900 km, and 1900 km (top row), and 1000 km, 0 km, and -200 km (bottom row). Note the long fibril structures in the chromosphere (upper row) and convection cell granulation in the photopshere (middle and right panels of the lower row). Because fibrils are generally denser and cooler than the surrounding material, the color scale in the chromospheric pictures (first 4 panels) was inverted.