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. © 1990 Kluwer Academic Publishers.