Coronal Magnetic Field Evolution from 1996 to 2012: Continuous Non-potential Simulations
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Coronal Magnetic Field Evolution from 1996 to 2012: Continuous Non-potential Simulations A.R. Yeates
Received: 23 August 2012 / Accepted: 4 April 2013 © Springer Science+Business Media Dordrecht 2013
Abstract Coupled flux transport and magneto-frictional simulations are extended to simulate the continuous magnetic-field evolution in the global solar corona for over 15 years, from the start of Solar Cycle 23 in 1996. By simplifying the dynamics, our model follows the build-up and transport of electric currents and free magnetic energy in the corona, offering an insight into the magnetic structure and topology that extrapolation-based models cannot. To enable these extended simulations, we have implemented a more efficient numerical grid, and have carefully calibrated the surface flux-transport model to reproduce the observed large-scale photospheric radial magnetic field, using emerging active regions determined from observed line-of-sight magnetograms. This calibration is described in some detail. In agreement with previous authors, we find that the standard flux-transport model is insufficient to simultaneously reproduce the observed polar fields and butterfly diagram during Cycle 23, and that additional effects must be added. For the best-fit model, we use automated techniques to detect the latitude–time profile of flux ropes and their ejections over the full solar cycle. Overall, flux ropes are more prevalent outside of active latitudes but those at active latitudes are more frequently ejected. Future possibilities for space-weather prediction with this approach are briefly assessed. Keywords Coronal mass ejections, theory · Magnetic fields, corona · Magnetic fields, models · Magnetic fields, photosphere · Solar cycle, models 1. Introduction Modelling the Sun’s coronal magnetic field over the full solar cycle is important because it acts as a driver of space-weather events, and changes significantly over the cycle, as well as from one cycle to the next. It is fundamentally time-dependent, as manifested in the
Solar Origins of Space Weather and Space Climate Guest Editors: I. González Hermández, R. Komm, and A. Pevtsov A.R. Yeates () Department of Mathematical Sciences, Durham University, Durham, DH1 3LE, UK e-mail: [email protected]
A.R. Yeates
variations of almost all observed properties of the Sun, including sunspot number, magnetic flux, rates of flares and coronal mass ejections (CMEs), and even the total solar irradiance (Willson and Hudson, 1991). The coronal magnetic field is driven by activity in the solar interior, including large-scale flows and convection in the photosphere as well as the periodic emergence of new active regions. Previous studies of the coronal magnetic evolution over months to years have mostly used potential-field extrapolations (Altschuler and Newkirk, 1969; Schatten, Wilcox, and Ness, 1969). From the space-weather viewpoint, these models give a first approximation of the Sun’s open flux (Wang and Sheeley, 2002) and the heliospheric current sheet (Hoeksema, Wilcox,
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