Photospheric and Subphotospheric Dynamics of Emerging Magnetic Flux

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.

arXiv comment21 pages, 15 figures, to appear in Space Science Reviews

References in corpus (4)

• The case for a distributed solar dynamo shaped by near-surface shear
• Acoustic tomography of solar convective flows and structures
• The Three-dimensional Evolution of Rising, Twisted Magnetic Flux Tubes in a Gravitationally Stratified Model Convection Zone
• The Interaction of New and Old Magnetic Fluxes at the Beginning of Solar Cycle 23

Cited by in corpus (22)

• Flare-productive active regions
• Mechanism of spontaneous formation of stable magnetic structures on the Sun
• Time--Distance Helioseismology Data Analysis Pipeline for Helioseismic and Magnetic Imager onboard Solar Dynamics Observatory (SDO/HMI) and Its Initial Results
• Helioseismology of Pre-Emerging Active Regions II: Average Emergence Properties
• The formation of sunspot penumbra. I. Magnetic field properties
• A low upper limit on the subsurface rise speed of solar active regions
• Local Helioseismology of Sunspots: Current Status and Perspectives (Invited Review)
• Detection of the Horizontal Divergent Flow prior to the Solar Flux Emergence
• Helioseismology of Pre-Emerging Active Regions III: Statistical Analysis
• What have we learned from helioseismology, what have we really learned, and what do we aspire to learn?
• The origin and early evolution of a bipolar magnetic region in the solar photosphere
• Development of active regions: flows, magnetic-field patterns and bordering effect
• Doubts about the crucial role of the rising-tube mechanism in the formation of sunspot groups
• Detection of Gravitational Waves through Observations of a Group of Pulsars
• Origin of Deep Acoustic Sources Associated with Solar Magnetic Structures
• Reconstruction of Solar Subsurfaces by Local Helioseismology
• Helioseismic Holography of an Artificial Submerged Sound Speed Perturbation and Implications for the Detection of Pre-Emergence Signatures of Active Regions
• Stellar magnetic cycles
• Center-limb dependence of photospheric velocities in regions of emerging magnetic fields on the Sun
• Notes about collapse in magnetohydrodynamics
• Non-linear and chaotic dynamo regimes
• Investigation of a Sunspot Complex by Helioseismology