Simulated magnetic flows in the solar photosphere⋆
Max-Planck-Institut für Sonnensystemforschung,
2 School of Space Research, Kyung Hee University, Yougin, 446-701 Gyeonggi, Korea
Received: 7 March 2014
Accepted: 12 August 2014
Context. Recent Sunrise/IMaX observations have revealed supersonic magnetic flows.
Aims. Our aim is to determine the origin of these flows by using realistic magnetohydrodynamics simulations.
Methods. We simulated cancellation and emergence of magnetic flux through the solar photosphere. Our first numerical experiment started with a magnetic field of both polarities. To simulate emergence into a region with pre-existing field, we introduced a large-scale horizontally uniform sheet of a horizontal field. We followed the subsequent evolution and created synthetic polarimetric observations, including known instrumental effects of the Sunrise/IMaX and Hinode/SP instruments. We compared the simulated and observed spectropolarimetric signals.
Results. Strongly blue- and redshifted Stokes V signals are produced in locations where strong line-of-sight velocities coincide with the strong line-of-sight component of the magnetic field. The size and strength of simulated events is smaller than observed, and they are mostly associated with downflows, contrary to observations. In a few cases where they appear above a granule, single blue-lobed Stokes V are produced by strong gradients in magnetic field and velocity. No change of magnetic field sign is detected along the line of sight in these instances. More high-speed magnetised flows occurred when an emergence was simulated than when no horizontal field was added.
Conclusions. The simulations indicate that the observed events result from magnetic flux emergences in which reconnection may take place, but does not seem to be necessary.
Key words: Sun: granulation / Sun: photosphere
The movies are available in electronic form at http://www.aanda.org
© ESO, 2015