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Thursday 21 Nov 2019Simulating the Evolution and Eruption of Bipolar Active Regions

Dr Stephanie Yardley - University of St Andrews

Harrison 103 14:30-16:30

The coronal magnetic field evolution of 20 bipolar active regions (ARs) is simulated from their emergence to decay using the magnetofrictional relaxation technique of Mackay et al. (2011). A sequence of photospheric line-of-sight magnetograms, obtained by the Helioseismic Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) is taken for each AR and used to drive the simulations. The simulated coronal magnetic field continuously evolves through a series of nonlinear force-free equilibria and a comparison of the simulations with 171 and 193A observations taken by the Atmospheric Imaging Assembly (AIA) onboard SDO is made. The results show that it is possible to reproduce the main coronal features such as small- and large-scale coronal loops, filaments and sheared structures and evolution for 80% of the ARs. Varying the boundary and initial conditions, along with the addition of physical effects such as Ohmic diffusion, hyperdiffusion and an additional magnetic helicity injection, improves the match between the observations and simulated coronal evolution by 20%. The simulations were able to reproduce the build-up of stress and free magnetic energy in the coronal field to the point of eruption for 12 out of the 24 observed eruptions associated with the ARs. The mean unsigned time difference between the eruptions occurring in the observations compared to the time of eruption onset in the simulations was found to be approximately 5 hrs. The simulations also successfully followed the build-up of stress and energy in the coronal field to the point of eruption for all four eruptions originating from the internal polarity inversion line of the ARs. Future iterations of the model should aim to predict CME occurrence and provide advance warnings prior to eruption, which will have major consequences for space weather forecasting.

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