OBSERVATION OF QUASI-PERIODIC COMPRESSIVE WAVES IN SOLAR POLAR PLUMES

On 1996 March 7, the Solar and Heliospheric Observatory spacecraft con ducted a multi-instrument campaign to observe polar plumes in the sout h polar coronal hole. Recent time-domain analyses of EUV Imaging Teles cope images from that campaign show filamentary substructure in the pl umes, on a length scale of similar to 5'', which changes on timescales of a few minutes, and coherent quasi-periodic perturbations in the br ightness of Fe IX and Fe X line emission at 171 Angstrom from the plum es. The perturbations amount to 10%-20% of the plumes' overall intensi ty and propagate outward at 75-150 km s(-1), taking the form of wave t rains with periods of 10-15 minutes and envelopes of several cycles. W e conclude that the perturbations are compressive waves (such as sound waves or slow-mode magnetosonic waves) propagating along-the plumes. Assuming that the waves are sonic yields a mechanical energy flux of 1 50-400 W m(-2) (1.5-4 x 10(5) ergs cm(-2) s(-1)) in the plumes.