|Changes of the Magnetic Field during Flares|
|The photospheric magnetic field has been
found to change during flares in many observations. It
is however unclear which mechanism transports the required
energy through the solar atmosphere. In contrast,
chromospheric magnetic fields are very difficult
to measure, both because of the lower signal and
because of the more complex interpretation due to
non-local thermal equilibrium. |
We obtained the first high-resolution chromospheric polarimetric flare data and found stepwise chromospheric magnetic field changes during a flare (Kleint, 2017). The chromospheric changes are stronger and occur in a larger area. They are located near footpoints of loops, in contrast to photospheric changes which predominantly occur near neutral lines. A surprising result was a difference in timing, sign, and size of the changes when comparing the two atmospheric layers. Another surprise was that a model of contracting loops is not compatible with the observed direction of changes. Instead, we rather interpret the changes as an untwisting of loops, but future vector magnetic field measurements will need to verify this hypothesis.
Left: Photosphere (background) with color-coded photospheric magnetic field changes and contours of hard X-ray radiation. Right: Chromospheric magnetic field changes. From (Kleint, 2017).
|Dissipation of Flare Energy: Continuum Emission|
|Intensities of several pixels before (left) and during the flare (right). The enhancement is largest in the NUV because of the contribution of the Balmer continuum. A simple blackbody-fit, as is often used, is not a good fit for flare enhancements. From (Kleint et al., 2016)|
|The best-ever observed flare|
|Photosphere (background) and chromosphere (inset) during the X1 flare on 2014-03-29 taken at the DST.|