The Rise of Active Region Flux Tubes in the Turbulent Solar Convective Envelope

TL;DR

This study models the buoyant rise of magnetic flux tubes in the solar convection zone, revealing how convection influences their emergence, tilt, and properties, with results aligning with observed solar active regions.

Contribution

It demonstrates how convection affects flux tube emergence, showing that mid-range field strengths produce properties consistent with solar observations.

Findings

Rise times are reduced from years to months with convection.

Emerging loops at certain field strengths follow Joy's Law.

Flux tube properties match observed active regions at 40-50 kG.

Abstract

We use a thin flux tube model in a rotating spherical shell of turbulent convective flows to study how active region scale flux tubes rise buoyantly from the bottom of the convection zone to near the solar surface. We investigate toroidal flux tubes at the base of the convection zone with field strengths ranging from 15 kG to 100 kG at initial latitudes ranging from 1 degree to 40 degrees with a total flux of 10^22 Mx. We find that the dynamic evolution of the flux tube changes from convection dominated to magnetic buoyancy dominated as the initial field strength increases from 15 kG to 100 kG. At 100 kG, the development of Omega-shaped rising loops is mainly controlled by the growth of the magnetic buoyancy instability. However, at low field strengths of 15 kG, the development of rising Omega-shaped loops is largely controlled by convective flows, and properties of the emerging loops are significantly changed compared to previous results in the absence of convection. With convection, rise times are drastically reduced (from years to a few months), loops are able to emerge at low latitudes, and tilt angles of emerging loops are consistent with Joy's Law for initial field strengths of greater than or equal to 40 kG. We also examine other asymmetries that develop between the leading and following legs of the emerging loops. Taking all the results together, we find that mid-range field strengths of approximately 40 - 50 kG produce emerging loops that best match the observed properties of solar active regions.