Helioseismology of Pre-Emerging Active Regions II: Average Emergence Properties

Abstract

We report on average subsurface properties of pre-emerging active regions as compared to areas where no active region emergence was detected. Helioseismic holography is applied to samples of the two populations (pre-emergence and without emergence), each sample having over 100 members, which were selected to minimize systematic bias, as described in Leka et al. We find that there are statistically significant signatures (i.e., difference in the means of more than a few standard errors) in the average subsurface flows and the apparent wave speed that precede the formation of an active region. The measurements here rule out spatially extended flows of more than about 15 m/s in the top 20 Mm below the photosphere over the course of the day preceding the start of visible emergence. These measurements place strong constraints on models of active region formation.

15 pages, 10 figures, ApJ (published)

References in corpus (4)

• The case for a distributed solar dynamo shaped by near-surface shear
• 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

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• Helioseismology of Pre-Emerging Active Regions I: Overview, Data, and Target Selection Criteria
• Average motion of emerging solar active region polarities II: Joy's law
• Time-Distance Helioseismology of Two Realistic Sunspot Simulations
• Issues with time--distance inversions for supergranular flows
• Properties of $p$- and $f$-modes in hydromagnetic turbulence
• Impact of subsurface convective flows on the formation of sunspot magnetic field and energy build-up
• Local Helioseismology of Emerging Active Regions: A Case Study
• Pre-emergence Signatures Of Horizontal Divergent Flows In Solar Active Regions
• Investigating toroidal flows in the Sun using normal-mode coupling