3D Global MHD Modeling of Solar Subsurface Convection

TL;DR

This study uses 3D global MHD simulations to explore how variations in near-surface convection influence solar internal dynamics and magnetic field generation, revealing significant impacts on angular momentum distribution and dynamo behavior.

Contribution

It introduces a method to modify near-surface convective transport in global MHD models and analyzes its effects on solar internal rotation and magnetic field patterns.

Findings

Increased surface convection alters angular momentum distribution below the tachocline.

Enhanced near-surface flows cause a shift from symmetric to anti-symmetric magnetic field patterns.

Changes in surface convection impact the solar dynamo cycle and magnetic field emergence.

Abstract

Various models of solar sub-surface 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.

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