by Alessandro Bemporad
The atmosphere of the Sun, the solar corona, is made up of plasma.
The dynamics of the phenomena occurring in the solar corona is dominated by the intense magnetic fields which, starting from the solar surface, the photosphere, cross the corona forming, for example, the well-known coronal loops.
However, the measurement of these magnetic fields is very complex and requires observations that combine spectroscopy with polarimetry, techniques that require relatively long observation times and particular observation conditions. On the contrary, the measurement of coronal plasma densities is much simpler, and it is also possible from the ground with coronagraphic observations of the polarized emission in visible light, such as those acquired, for example, by the coronagraph of the Mauna Loa Observatory.
A study recently published has shown that, unexpectedly, under a suitable hypothesis never tested before, it is possible to determine a measurement of the coronal magnetic fields precisely from the distribution of the plasma densities, considering the fields not so much as a local property, but as a global property of the solar corona. The study was based on observations of the solar corona acquired during the August 21, 2017 total solar eclipse that swept across the United States, observations acquired with a common DLSR camera combined with a manually operated linear polarizing filter. Comparison with the magnetic fields predicted by one of the most advanced existing models of extrapolation from photospheric fields showed surprising agreement.
This technique therefore unexpectedly opens up new perspectives for the study of coronal magnetic fields and therefore of all plasma phenomena connected to it.
Read the article on MediaINAF (in italian).
Read the article published in ApJ: “Coronal Magnetic Fields Derived with Images Acquired during the 2017 August 21 Total Solar Eclipse” by A. Bemporad.