The Effect of Small-Scale Magnetic Structures on Inferred Solar Continuum Brightness

Share this story:
Monday, December 3, 2018

Solar irradiance models indicate that irradiance variations are dominated by changes in disk-coverage of magnetic structures, whose brightness is thought to be determined by their size and average magnetic flux density.

Graph depicting average intensity of magnetic structures as a function of width (a) and equivalent radius (b)
Average intensity of magnetic structures as a function of width (a) and equivalent radius (b). The color bar denotes the magnetic flux of the structure (average magnetic field of the element at the tau_500=1 surface). The vertical grey band represents the range of average downflow lane widths in the three simulations. Note that the downturn of the intensity corresponds roughly to the width of downflow lanes. Different line-styles indicate the average trend (and scatter) for the 3 cases with different magnetic environment in terms of mean magnetic flux.

Recent results suggest that the brightness of small-scale magnetic structures may also depend on the mean magnetic flux of the extended region surrounding them, which reduces the convective vigor of the surrounding plasma. Low spatial resolution, however, may limit the ability to isolate differences in magnetic structure size distributions from the role of the mean magnetic flux. We investigate the brightness of magnetic structures as a function of their size using high-resolution 3D MHD simulations representing three regions characterized by different mean magnetic flux. In agreement with previous results, we find a reduction in brightness with increasing mean magnetic flux when comparing the pixel-by-pixel continuum brightness as a function of magnetic field strength. Evaluating equivalently sized magnetic structures, however, we find no significant dependence of the magnetic structure brightness on the mean magnetic flux of the region in which they are embedded. These results indicate that magnetic structure size distribution dominates the observed reduction in brightness for regions with a higher mean magnetic flux, with the mean magnetic flux within the region playing negligible role.

Publication Name: Astrophysical Journal

First HAO Author's Name: Matthias Rempel