Exploring the Connection between Helioseismic Travel Time Anomalies and the Emergence of Large Active Regions during Solar Cycle 24

TL;DR

This study analyzes helioseismic travel time anomalies to predict the emergence of large active regions on the Sun during Solar Cycle 24, revealing that travel time deviations can precede magnetic flux emergence in many cases.

Contribution

It introduces a comparative analysis of two methods for detecting travel time anomalies and links these anomalies to active region emergence, enhancing predictive capabilities.

Findings

Travel time anomalies often precede flux emergence by 24-48 hours.

The difference minimization procedure's lag times correlate with flux emergence rates.

Only some active regions show significant travel time deviations prior to emergence.

Abstract

We investigate deviations in the mean phase travel time of acoustic waves preceding the emergence of 46 large active regions observed by the Helioseismic and Magnetic Imager (HMI). In our investigation, we consider two different procedures for obtaining the mean phase travel time, by minimizing the difference between cross-correlations and a reference, as well as the Gabor wavelet fitting procedure. We cross-correlate the time series of mean phase travel time deviations with the surface magnetic field and determine the peak correlation time lag. We also compute the perturbation index--the area integrated mean phase travel time deviations exceeding quiet sun thresholds--and compare the time of peak perturbation index with the correlation time lag. We find that the lag times derived from the difference minimization procedure precede the flux emergence for 36 of the 46 active regions, and that this lag time has a noticeable correlation with the maximum flux rate. However, only 28 of the active regions have peak perturbation index times in the range of 24 to 48 hours prior to the flux emergence. Additionally, we examine the relationship between properties of the emerged active regions and the strength of helioseismic signals prior to their emergence.