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

TL;DR

This study uses helioseismic holography to identify statistically significant subsurface flow and wave speed signatures that precede active region emergence on the Sun, providing constraints for models of solar magnetic activity.

Contribution

It presents the first large-scale statistical analysis of pre-emergence subsurface properties, revealing measurable signatures that occur before active regions become visible.

Findings

Significant subsurface flow signatures precede active region emergence.

No large-scale flows exceeding 15 m/s are detected in the 20 Mm below the surface.

Results constrain theoretical models of active region formation.

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.