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On the factors determining the eruptive character of solar flares View all abstracts by submitter

Julia K. Thalmann   Submitted: 2017-12-19 01:24

We investigated how the magnetic field in solar active regions (ARs) controls flare activity, i.e., whether a confined or eruptive flare occurs. We analyzed 44 flares of GOES class M5.0 and larger that occurred during 2011-2015. We used 3D potential magnetic field models to study their location (using the flare distance from the flux-weighted AR center dFC) and the strength of the magnetic field in the corona above (via decay index n and flux ratio). We also present a first systematic study of the orientation of the coronal magnetic field, using the orientation φ of the flare-relevant polarity inversion line as a measure. We analyzed all quantities with respect to the size of the underlying dipole field, characterized by the distance between the opposite-polarity centers, dPC. Flares originating from underneath the AR dipole (dFC/dPC<0.5) tend to be eruptive if launched from compact ARs (dPC≤60 Mm) and confined if launched from extended ARs. Flares ejected from the periphery of ARs (dFC/dPC>0.5) are predominantly eruptive. In confined events the flare-relevant field adjusts its orientation quickly to that of the underlying dipole with height (Δφ≳40∘ until the apex of the dipole field), in contrast to eruptive events where it changes more slowly with height. The critical height for torus instability, hcrit=h(n=1.5), discriminates best between confined (hcrit≳40 Mm) and eruptive flares (hcrit≲40 Mm). It discriminates better than Δφ, implying that the decay of the confining field plays a stronger role than its orientation at different heights.

Authors: Christian Baumgartner, Julia K. Thalmann, Astrid M. Veronig
Projects: None

Publication Status: Accepted for publication in ApJ
Last Modified: 2017-12-20 10:33
Go to main E-Print page  A Hydrodynamic Model of Alfv?nic Wave Heating in a Coronal Loop and its Chromospheric Footpoints  Reconnection fluxes in eruptive and confined flares and implications for superflares on the Sun  Edit Entry  Download Preprint  Delete Entry 

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