TIME-DISTANCE SUNSPOT SEISMOLOGY WITH GONG DATA

We present time-distance analyses of several active regions and a regi on of quiet Sun observed with the Global Oscillation Network Group (GO NG). Analyzing temporal correlations between the p-mode oscillation si gnal observed within the sunspots with the signals integrated within s urrounding annuli, we confirm the recent finding of Duvall and his col leagues that travel times (tau(+)) for outward propagating p-modes are smaller by approximately 1 minute than corresponding inward travel ti mes (tau(-)). We also analyze correlations of the oscillation signal i ntegrated within annuli of different radii. By varying the radius of t he inner annulus (that which is closer to the target) we show that the radial extent of the region giving rise to the travel time perturbati ons is coincident with the outer boundary of the sunspot penumbrae. A comparison of independent methods designed to determine the mean trave l time perturbations of p-modes passing through the sunspots is made. We find the surprising result that time-distance correlations that do not utilize the signal within the sunspot itself (employing ''two-skip '' trajectories) yield mean travel times that differ substantially fro m the average of tau(+) and tau(-) and that are significantly closer i n agreement with times predicted from scattering phase shifts measured by Hankel decomposition techniques. These observations suggest that i t unlikely that Doppler shifts caused by subsurface flows are responsi ble for the travel time differences determined from center-annuli corr elations targeted on sunspots.