Volume 649, May 2021
|Number of page(s)||9|
|Section||The Sun and the Heliosphere|
|Published online||26 May 2021|
Relative field line helicity of a large eruptive solar active region
Physics Department, University of Ioannina, Ioannina 45110, Greece
Accepted: 4 March 2021
Context. Magnetic helicity is a physical quantity of great importance in the study of astrophysical and natural plasmas. Although a density for helicity cannot be defined, a good proxy for this quantity is field line helicity. The appropriate quantity for use in solar conditions is relative field line helicity (RFLH).
Aims. This work aims to study in detail the behaviour of RFLH, for the first time, in a solar active region (AR).
Methods. The target AR is the large, eruptive AR 11158. In order to compute RFLH and all other quantities of interest, we used a non-linear force-free reconstruction of the AR coronal magnetic field of excellent quality.
Results. We find that the photospheric morphology of RFLH is very different than that of the magnetic field or electrical current, and this morphology is not sensitive to the chosen gauge in the computation of RFLH. The value of helicity experiences a large decrease, that is ∼25% of its pre-flare value, during an X-class flare of the AR; this change is also depicted in the photospheric morphology of RFLH. Moreover, the area of this change coincides with the area that encompasses the flux rope, which is the magnetic structure that later erupted.
Conclusions. The use of RFLH can provide important information about the value and location of the magnetic helicity expelled from the solar atmosphere during eruptive events.
Key words: Sun: fundamental parameters / Sun: magnetic fields / Sun: flares / magnetohydrodynamics (MHD) / methods: numerical
© ESO 2021
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.