Magneto-Rotational Instability in the Sun? Global Radiation-MHD Simulations of the Near-Surface Shear Layer

The proposed work will address the origins of the Sun’s magnetic activity along with Science Goal #1 of the Heliophysics Decadal Survey, to “Determine the origins of the Sun’s activity and predict the variations in the space environment.” In particular: • The project will consider the novel approach that the seat of global solar magnetic activity resides mostly within Near-Surface-Shear Layer (NSSL, the out 5-10% of the solar radius) • We also consider the likelihood the Magnetorotational Instability (MRI) is a major influence, and possibly cause of dynamo action within the NSSL. Our investigation is motivated by several important observations. (i ) Sunspots emergence, and their migration pattern, correlate highly with the observed Torsional Oscillations, the axisym- metric flow pattern which migrates equator-ward through the solar cycle. (ii ) As a function of depth, the Torsional Oscillations reach down mostly to the bottom of the NSSL, and exhibit a latitudinal mode-like structure. (iii ) Helioseismic inversions show the NSSL contains the strongest shear anywhere in the solar interior, and the flow is inwardly increasing as a function of depth. (iv ) The torsional oscillations do not show any significant signal at the base of the convection zone, i.e., in the tachocline, except at high latitudes where the flow is inwardly increasing to the base of the convection zone. (v ) Inwardly increasing shear flow characterizes the MRI. For solar parameters, the MRI is likely operating in a three-dimensional regime, and therefore can interact with a dynamo field.