Linking the Solar Magnetism from the Interior to the Outer Atmosphere.

Abstract

Solar magnetic fields, produced in the interor and extending all the way into the interplanetary space, connect the Sun with the terrestrial environment. They manifest themselves on the solar surface over a wide range of scales, from ubiquitous ephemeral regions to active regions. The appearance of kilo-Gauss magnetic flux bundles on the photosphere is observationally well studied. However the physical processes that produce observed magnetic structures are yet to be well-understood, due to the lack of information below the solar surface. To illustrate the physics of sub-surface magnetic fields, we carry out numerical simulations of the emergence of magnetic flux ropes from the convection zone through the photosphere and into the corona. The spatial scale of our simulations varies from ephemeral regions to active regions. This study of the formation of magnetic structures shows the importance of the interaction of rising magnetic fields and turbulent convective motions: 1) The first simulation addresses the emergence of a flux rope and formation of an ephemeral region in a shallow convection zone. 2) In another simulation, a flux rope buoyantly rises from 10 Mm below the photosphere, interacts with convective cells of varying scales and forms a small active region with a pair of sunspots.

At the beginning, vertical motion dominates the energy transport into the corona when the flux first passes through the photosphere. After that, horizontal motions, i.e., shearing, separation of dipoles, and rotation of polarities take over the energy transport, while vertical motion transports energy back into the convection zone.

Strong shearing motions draw the magnetic field parallel to the polarity inversion line. Tether-cutting reconnection transfers the magnetic shear into the corona. Together, with the rotation of sunspots, these processes produce and transport free magnetic energy, up to 8x10^30 ergs, into the corona, providing the energy necessary for solar eruptive events.