Authors: John Stefan (NJIT), Alexander Kosovichev (NJIT), Andrey Stejko (NJIT)

Past studies have found strong deviations in the mean phase travel time of acoustic waves preceding the emergence of some active regions, at both shallow (10-15 Mm) and moderate (40-70 Mm) depths of the convective zone. We examine the travel time deviations produced by two numerical simulations of submerged sound speed perturbations, as a proxy for emerging flux, for depths ranging from 40 Mm to 60 Mm. We then investigate the strength and timing of the travel time deviations before and after the emergence of a collection of large active regions observed by the Helioseismic and Magnetic Imager (HMI) during Solar Cycle 24. In our investigation, we consider two different methods for obtaining the mean phase travel time deviations: the difference minimizing procedure with respect to reference Quiet Sun cross-correlations and the Gabor wavelet fitting procedure. We find that for 36 of the 46 studied active regions, the travel time anomalies are most well-correlated with the surface magnetic flux at a lag time of 24 to 48 hours. Additionally, we examine the relationship between properties of the emerged active regions and the strength of helioseismic signals prior to their emergence.