Scientists try to predict how the solar atmosphere would look like during the 04/12/2021 eclipse. They made a picture by running a computer programme called EUHFORIA.
The color bar at the bottom right gives the strength of the magnetic field (in Gauss) on the Sun. In a real eclipse picture, you can't see the solar surface because it is behind the moon. The color bar at the top right represents the radial velocity of the solar wind (in km/s) in the solar corona. This simulation has been performed with the COOLFluiD coronal MHD solver, which provided the input field to EUHFORIA at 0.1 AU.
Big dipole, big and less big streamers
The Sun is the blue-grey-red sphere. The colours tell you how strong the radial magnetic field is and is similar to magnetograms from the HMI instrument onboard of the satellite SDO. You can see also the positive (red) coronal hole at the solar North pole and the negative (blue) coronal hole at the solar South pole giving rise to a dipole field.The magnetic field in space shown by the white lines has indeed a dominant dipole structure. This is what we expected because we are still close to solar minimum. However, we see also intense red/blue areas at different latitudes. These are active regions that give rise to more complex magnetic structures.
The background red/blue color represents the radial velocity of the wind in km/s with blue a slow wind and red a fast wind. If we link the color scale representing the speed with the white magnetic field lines, we see the so-called streamers: magnetic closed structures extending to several solar radii that are trapping the wind and producing slow wind patches (in blue). At the poles we have open magnetic field lines allowing the wind to accelerate and generate faster wind (in red).
The EUHFORIA model predicts thus an overal dipolar magnetic structure with two big equatorial streamers and local active regions with small pseudo-streamers close to the solar surface.
Real eclipse pictures
Eclipse pictures made from Earth show the surroundings of the Sun reflecting visible light. Such pictures give an idea of the shape and orientation of the streamers which we can qualitatively compare with our picture made by running the new EUHFORIA programme.
Improved computer programme
With the old version of EUHFORIA, it was impossible to produce such pictures because we were not able to calculate the solar wind speed and the magnetic field at places far away from the Sun. The new version of EUHFORIA is a much stronger programme. The programmers also made sure that the new version was as fast as the old version. Which is crucial if we want to use EUHFORIA for forecast purposes.
Let’s ask the penguins on December 4!
