Photospheric and Subphotospheric Dynamics of Emerging Magnetic Flux

TL;DR

This paper investigates the dynamics of emerging magnetic flux on the Sun, analyzing surface and subsurface flows, tilt angles, and helioseismic data to understand magnetic flux emergence and structure formation.

Contribution

It provides new insights into the subsurface properties of magnetic flux emergence, including tilt angle behavior and flow patterns, using helioseismology and observational data.

Findings

Tilt angles are likely established below the surface.

Localized upflows and downflows occur during emergence.

Strong diverging flows are observed during flux emergence.

Abstract

Magnetic fields emerging from the Sun's interior carry information about physical processes of magnetic field generation and transport in the convection zone. Soon after appearance on the solar surface the magnetic flux gets concentrated in sunspot regions and causes numerous active phenomena on the Sun. This paper discusses some properties of the emerging magnetic flux observed on the solar surface and in the interior. A statistical analysis of variations of the tilt angle of bipolar magnetic regions during the emergence shows that the systematic tilt with respect to the equator (the Joy's law) is most likely established below the surface. However, no evidence of the dependence of the tilt angle on the amount of emerging magnetic flux, predicted by the rising magnetic flux rope theories, is found. Analysis of surface plasma flows in a large emerging active region reveals strong localized upflows and downflows at the initial phase of emergence but finds no evidence for large-scale flows indicating future appearance a large-scale magnetic structure. Local helioseismology provides important tools for mapping perturbations of the wave speed and mass flows below the surface. Initial results from SOHO/MDI and GONG reveal strong diverging flows during the flux emergence, and also localized converging flows around stable sunspots. The wave speed images obtained during the process of formation of a large active region, NOAA 10488, indicate that the magnetic flux gets concentrated in strong field structures just below the surface. Further studies of magnetic flux emergence require systematic helioseismic observations from the ground and space, and realistic MHD simulations of the subsurface dynamics.