Emergence of magnetic flux generated in a solar convective dynamo I

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Friday, August 25, 2017

Formation of Sunspots and Active regions, and Origin of Their Asymmetries—We present a realistic numerical model of sunspot and active region formation based on the emergence of flux bundles generated in a solar convective dynamo.

Evolution of the vertical component of the magnetic field image
Evolution of the vertical component of the magnetic field at the surface of the Sun in the simulation. It clearly shows that the leading polarity spot (e.g., C1) in a bipolar sunspot pair forms earlier than the following spot (e.g., C2). The leading spot is more coherent in shape and has stronger magnetic field strength.

To this end we use the magnetic and velocity fields from a solar convective dynamo simulation to drive realistic radiative MHD simulations of the upper most layers of the convection zone.

The emerging flux bundles rise with the mean speed of convective upflows, and fragment into small-scale magnetic elements that further rise to the photosphere. In this process the large-scale flow pattern does not seem to be impacted by the emerging flux bundles. Sunspots form in the photosphere through combination of small-scale magnetic elements. A well formed sunspot is a mostly monolithic magnetic structures that is anchored in a persistent deep-seated downdraft lane.

The sunspots successfully reproduce the fundamental properties of the observed solar active regions, including the more coherent leading spots with a stronger field strength, and the correct tilts of bipolar sunspot pairs. These asymmetries can be linked to the intrinsic asymmetries in the magnetic and flow fields adapted from the convective dynamo simulation.

This paper is accepted for publication in ApJ: https://arxiv.org/abs/1704.05999.