Early Detection of Emerging Magnetic Flux

We employ a time-distance measurement procedure, similar to the one used by Ilonidis et al in their 2013 work, to detect solar subsurface structures associated with emerging magnetic flux. We compute the spatially-averaged cross-covariance of Dopplergram signals, and fit to a Gabor wavelet so that the phase travel time of acoustic waves can be extracted. Deviations from the mean phase travel time are interpreted as fluctuations in density and gas pressure. We independently confirm the analysis of AR10488 from Stathis et al (2013), a result that was hotly debated after publishing. We also calibrate this time-distance method using numerical models provided by Hartlep et al (2011) and Stejko et al (2020, this meeting). Based on this calibration, we propose an estimate for the magnitude of local sound-speed perturbations necessary to produce the observed signal.