Slow appearance of sunspots challenges theory

Thursday, July 21, 2016

HAO along with researchers from the Max Planck Institute for Solar System Research, The University of Göttingen, and NorthWest Research Associates have now shown that magnetic flux concentrations forming active regions on the sun emerge at a rate much slower than predicted by the prevailing current model.

HAO flux emergence simulation image
Example of a flux emergence simulation performed by HAO scientist Matthias Rempel. The top panels show intensity (left) and the vertical component of the magnetic field (right), the bottom panels the vertical flow velocity (left, upflows red, downflows blue) as well as the subsurface field strength (right) on a vertical slice through the center of the simulation domain. Flux emergence simulations were compared to observational constraints in order to infer the maximum permissible sub-photospheric flux emergence velocity. Computing time was provided by the NASA High-End Computing (HEC) Program through the NASA  Advanced Supercomputing (NAS) Division at Ames Research Center under projects s1325 and s1326.

For their study, which was published July 13 in the journal Science Advances, they compared satellite observations from the NASA Solar Dynamics Observatory (SDO) and computer simulations performed by HAO scientist Matthias Rempel. It was found that typical emergence velocities cannot exceed 150 m/s in a depth of 20,000 km beneath the solar photosphere, which is a velocity comparable to convective motions. This shows that convection in the solar interior plays a crucial role even for active region scale flux emergence.