Observation of Quasi-periodic Compressive Waves in Solar Polar Plumes

On 1996 March 7, the Solar and Heliospheric Observatory spacecraft conducted a multi-instrument campaign to observe polar plumes in the south polar coronal hole. Recent time-domain analyses of EUV Imaging Telescope images from that campaign show filamentary substructure in the plumes, on a length scale of ∼50, which changes on timescales of a few minutes, and coherent quasi-periodic perturbations in the brightness of Fe ix and Fe x line emission at 171 Å from the plumes. The perturbations amount to 10%–20% of the plumes’ overall intensity and propagate outward at 75–150 km s, taking the form of wave trains with periods of 10–15 minutes and envelopes of several cycles. We 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 150–400 W m (1.5– ergs cm s) in the plumes. 5 4 # 10 Subject headings: Sun: corona — Sun: solar wind — Sun: UV radiation