Astronomy and Astrophysics – Astronomy
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009spd....40.3708y&link_type=abstract
American Astronomical Society, SPD meeting #40, #37.08; Bulletin of the American Astronomical Society, Vol. 41, p.871
Astronomy and Astrophysics
Astronomy
Scientific paper
We have developed new simulations of the global magnetic field evolution in the solar corona. Using a coupled surface flux transport and magnetofrictional model, we can follow, for the first time, the build-up of magnetic helicity and shear on a global scale over many solar rotations. The evolution is driven by surface motions and by flux emergence, with properties of new active regions determined from synoptic normal-component photospheric magnetograms from NSO/Kitt Peak. As a first application we compare the model to observations of sheared magnetic fields in filaments (aka. prominences), over a 6-month period. We have unprecedented success in reproducing the chirality (axial magnetic field direction) of filaments. Depending on the sign of helicity in newly-emerging regions, the correct chirality is simulated for up to 96% of filaments tested. On the basis of these simulations, an explanation for the observed hemispheric pattern of filament chirality is put forward, including why exceptions occur for filaments in certain locations. When too much axial magnetic flux builds up in filament channels, magnetic flux ropes lose equilibrium and are ejected from the simulation. Using automated techniques for detecting flux ropes and their ejection in the global simulations, we find that the number of ejections depends on both the magnitude and sign of the emerging helicity. For reasonable parameter choices, loss of equilibrium of magnetic flux ropes formed by quasi-static flux cancellation produces about 50% of the observed CME rate.
Mackay Duncan H.
van Ballegooijen Adriaan A.
Yeates Anthony R.
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