A low upper limit on the subsurface rise speed of solar active regions

Abstract

Magnetic field emerges at the surface of the Sun as sunspots and active regions. This process generates a poloidal magnetic field from a rising toroidal flux tube, it is a crucial but poorly understood aspect of the solar dynamo. The emergence of magnetic field is also important because it is a key driver of solar activity. We show that measurements of horizontal flows at the solar surface around emerging active regions, in combination with numerical simulations of solar magnetoconvection, can constrain the subsurface rise speed of emerging magnetic flux. The observed flows imply that the rise speed of the magnetic field is no larger than 150 m/s at a depth of 20 Mm, that is, well below the prediction of the (standard) thin flux tube model but in the range expected for convective velocities at this depth. We conclude that convective flows control the dynamics of rising flux tubes in the upper layers of the Sun and cannot be neglected in models of flux emergence.

Published in Science Advances. DOI: 10.1126/sciadv.1600557

References in corpus (8)

• The case for a distributed solar dynamo shaped by near-surface shear
• Numerical simulations of quiet Sun magnetism: On the contribution from a small-scale dynamo
• On the Formation of Active Regions
• Helioseismology of Pre-Emerging Active Regions II: Average Emergence Properties
• Surface-focused Seismic Holography of Sunspots: I. Observations
• Photospheric and Subphotospheric Dynamics of Emerging Magnetic Flux
• Helioseismology of Pre-Emerging Active Regions I: Overview, Data, and Target Selection Criteria
• Time-Distance analysis of the Emerging Active Region NOAA 10790

Cited by in corpus (14)

• SDO/HMI survey of emerging active regions for helioseismology
• Average motion of emerging solar active region polarities II: Joy's law
• Magnetic concentrations in stratified turbulence: the negative effective magnetic pressure instability
• Average motion of emerging solar active region polarities I: Two phases of emergence
• Flows around Averaged Solar Active Regions
• Imaging the Sun's near-surface flows using mode-coupling analysis
• Exploring the Connection between Helioseismic Travel Time Anomalies and the Emergence of Large Active Regions during Solar Cycle 24
• Coriolis force acting on near-surface horizontal flows during simulations of flux emergence produces a tilt angle consistent with Joy's law on the Sun
• Average solar active region: I. Intensities, velocities, and the photospheric magnetic field
• Observed Joys law of Bipolar Magnetic Region tilts at the emergence supports the thin flux tube model
• Evolution of the magnetic field and flows of solar active regions with persistent magnetic bipoles before emergence
• Solar active region scaling laws revisited
• Solar Interior
• Evolution of solar surface inflows around emerging active regions