Coupling of scales in the solar photosphere

August 01, 2017

Radiative magnetohydrodynamic simulations for the Sun

The evolution of magnetic fields on the solar surface on small scales is well captured by detailed comprehensive simulations including compressibility, stratification, radiative energy transport, effects of partial ionization on the equation of state as well as magnetic fields. On large scales the evolution is observed to follow the Surface Flux Transport model, which assumes that the field evolution at the surface, after emergence, is decoupled from the subsurface magnetic field dynamics. How the small and large scale evolution are coupled is poorly understood.

This project will first answer the question of why the Surface Flux Transport model arises from the physics included in the comprehensive simulations. That is, how do the small-scale flows affect the large-scale magnetic field. To this end a number of comprehensive numerical experiments will be ran using the MURaM code and analyzed.

Snapshot from a simulation of solar convective flows. The green volume rendering indicates swirling flows near the optical solar surface, which is color-coded with vertical flow velocity (downflows in red and upflows in blue). The size of the box shown is 4800 km × 4800 km horizontally and 1400 km in depth. The optical surface is hidden in the lower right quadrant, uncovering the swirling structure in the subsurface layers.

The second side of the coin is to investigate the driving of large scale flows by small-scale magnetic fields. These large-scale flows are observed and are important for the evolution of the large scale magnetic field. They are however not particularly well understood theoretically. To better understand them comprehensive numerical simulations will be set up with the goal of self-consistently driving these inflows.

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