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.

A 3D rendering of the prominence density with magnetic field lines, approximately 400 minutes after the formation of the prominence started. The colorscale shows the logarithmic density and is adjusted such that the chromosphere and the prominence are well visible: opacity values for rho < 10-14 are set to 0 (the surrounding coronal density is not visible). The field line colorscale shows the vertical component of the magnetic field: the prominence sits in the magnetic dips of the configuration, where the white field lines indicate a mostly horizontal field. This snapshot shows the prominence in a vertical state, but due to its dynamics, the appearance of the prominence can vary a lot. — A 3D rendering of the prominence density with magnetic field lines, approximately 400 minutes after the formation of the prominence started. The colorscale shows the logarithmic density and is adjusted such that the chromosphere and the prominence are well visible: opacity values for rho < 10^-14 are set to 0 (the surrounding coronal density is not visible). The field line colorscale shows the vertical component of the magnetic field: the prominence sits in the magnetic dips of the configuration, where the white field lines indicate a mostly horizontal field. This snapshot shows the prominence in a vertical state, but due to its dynamics, the appearance of the prominence can vary a lot.

A 3D rendering of the prominence density with magnetic field lines, approximately 400 minutes after the formation of the prominence started. The colorscale shows the logarithmic density and is adjusted such that the chromosphere and the prominence are well visible: opacity values for rho < 10^-14 are set to 0 (the surrounding coronal density is not visible). The field line colorscale shows the vertical component of the magnetic field: the prominence sits in the magnetic dips of the configuration, where the white field lines indicate a mostly horizontal field. This snapshot shows the prominence in a vertical state, but due to its dynamics, the appearance of the prominence can vary a lot.

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.