3D MHD Modeling of the Impact of Subsurface Stratification on the Solar Dynamo

TL;DR

This study uses 3D MHD simulations to explore how subsurface stratification and near-surface convection influence the solar dynamo, revealing significant impacts on angular momentum distribution and magnetic field patterns.

Contribution

It introduces a novel approach by systematically altering near-surface stratification in global MHD models to study its effects on solar dynamo behavior.

Findings

Increased surface convection alters angular momentum distribution.

Enhanced near-surface flow shifts magnetic field patterns.

Dynamo cycle transitions are influenced by subsurface stratification.

Abstract

Various models of solar subsurface stratification are tested in the global EULAG-MHD solver to simulate diverse regimes of near-surface convective transport. Sub- and superadiabacity are altered at the surface of the model ($ r > 0.95~R_{\odot}$) to either suppress or enhance convective flow speeds in an effort to investigate the impact of the near-surface layer on global dynamics. A major consequence of increasing surface convection rates appears to be a significant alteration of the distribution of angular momentum, especially below the tachocline where the rotational frequency predominantly increases at higher latitudes. These hydrodynamic changes correspond to large shifts in the development of the current helicity in this stable layer ($r<0.72R_{\odot}$), significantly altering its impact on the generation of poloidal and toroidal fields at the tachocline and below, acting as a major contributor towards transitions in the dynamo cycle. The enhanced near-surface flow speed manifests in a global shift of the toroidal field ($B_{\phi}$) in the butterfly diagram - from a North-South symmetric pattern to a staggered anti-symmetric emergence.