Volume 535, November 2011
|Number of page(s)||9|
|Published online||21 November 2011|
3D MHD simulations of electric current development in a rotating sunspot: active region NOAA 8210
Max-Planck-Institut für Sonnensystemforschung (MPS), Katlenburg-Lindau, Germany
2 Laboratório Associado de Plasma, Instituto Nacional de Pesquisas Espaciais (INPE), São José dos Campos – SP, Brazil
3 Geophysical Institute, University of Alaska Fairbanks (UAF), Fairbanks, USA
Received: 27 February 2011
Accepted: 30 July 2011
Context. Active region (AR) 8210 was the host of many flares and coronal mass ejections (CMEs). Studies of its temporal evolution indicated that the clockwise rotation of a negative magnetic polarity, together with the motion of a positive polarity located close to it are a major source of magnetic energy to the corona above.
Aims. Search for the mechanisms of energy storage and release above AR8210. For this sake we locate the current system generated by the photospheric plasma motion suggested as source of coronal energy supply above AR8210 and compare it with the location of identified flaring regions.
Methods. We simulated the reaction of the corona using a three-dimensional (3D) MagnetoHydroDynamic (MHD) model. The initial coronal magnetic field is extrapolated out of the observed line-of-sight (LOS) component of the photospheric magnetic field. The corresponding photospheric plasma motion is imposed close to the bottom boundary of the simulation box. Current dependent resistivity and compressibility of the plasma are considered in the model.
Results. The horizontal plasma motion causes a current system that spatially coincides with the flaring region associated to AR8210. Particularly, the rotation of the plasma over the main negative polarity gives rise to strong currents localized over the main negative polarity, i.e. close to the position of a flare site. Above this region a strong magnetic field divergence is indicated by large differential flux tube volumes. Intense currents also form along the eastern border of a positive polarity region, over a polarity inversion line (PIL), in a site where a flare appears later. The southward motion of a positive flux concentration generates a current system extending mainly along the eastern border of it, over a polarity inversion line. Magnetic energy is deposited mainly over the main negative polarity, where the major flare activity is observed at later times.
Conclusions. The two patterns of photospheric plasma motion suggested as being responsible for the flaring activity of AR8210 generate current systems spatially coincident with the flaring area associated to this active region. These currents generate magnetic fields that contribute to the increase in magnetic energy inside the simulation volume. The transport of magnetic flux by the photospheric plasma motion also contributes to the redistribution of magnetic energy. The increase in magnetic energy occurs mainly over the main negative polarity and close to where a strong current system is formed. We conclude that in the case of AR8210 the rotation of the negative polarity region is the main contributor to its flare activity. The southward motion of a positive magnetic flux concentration plays an important role in the formation of current systems at its eastern border.
Key words: Sun: corona / Sun: flares / magnetohydrodynamics (MHD) / magnetic reconnection / methods: numerical
© ESO, 2011
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.