Simulated magnetic flows in the solar photosphere

Abstract

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.

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