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

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. In our investigation, we consider two different procedures for obtaining the mean phase travel time, by minimizing the differ...

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Bibliographic Details
Published in:The Astrophysical journal 2023-05, Vol.948 (1), p.1
Main Authors: Stefan, John T., Kosovichev, Alexander G.
Format: Article
Language:English
Subjects:
Acoustic waves
Anomalies
Astrophysics
Correlation
Cross correlation
Deviation
Fluctuations
Helioseismology
Lag time
Magnetic fields
Morlet wavelet
Perturbation
Quiet Sun
Solar active regions
Solar cycle
Solar magnetic flux emergence
Time lag
Travel time
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Summary: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. 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 24–48 hr prior to the flux emergence. Additionally, we examine the relationship between the properties of the emerged active regions and the strength of helioseismic signals prior to their emergence.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/acc836