p-mode absorption in the giant active region of 10 March, 1989

A time series of velocity oscillations is observed in the vicinity of NOAA region 5395 with the Kitt Peak vacuum telescope for 6.8 hours on 1989 March 10 as part of a program to study the interaction of solar p-mode oscillations with solar active regions. The data is transformed in a cylindrical coordinate system centered on the visible sunspot, then Hankel- and Fourier-transformed to produce the power spectra of in- and outgoing acoustic waves. It is observed that a maximum of nearly 70% of the power of incident high-degree modes is absorbed by this unusually large sunspot group. The absorptive properties of this active region are compared with those of more typical regions studied previously.A major flare occurred within this region during the observing sequence, providing a rare opportunity to test the hypothesis that flares may excite acoustic waves in the photosphere. A comparison is made of the amount of outgoing p-mode power in equal 200 min time intervals before and after the time of the flare. No significant difference in outgoing acoustic waves is observed within a one-sigma error of about 5% averaged over the interval. A search for acoustic pulses emanating from the flare is made by filtering the data and performing appropriate inverse transforms. No such pulses were detected to a level of about 20% of the background power.NAS-NRC Resident Research Associate.