Characterization of the polar plumes from high cadence LASCO-C2 observations

In order to understand the spatio-temporal characteristics of polar plumes, we analyzed a sequence of continuous observations obtained with the SOHO/LASCO-C2 coronagraph over a period of 3 days with a time resolution of 10 minutes. We generated the time intensity diagram (TID) where the radiance of the plumes is displayed as a function of their angular positions and time. The derivatives of the TID with respect to the phase angle on the one hand and to time on the other hand allow us to define the trajectories of individual plumes and their temporal variations. This confirms that polar plumes are enduring structures that are only transiently lit, as we found before, but the present analysis reveals that the blinking takes place on time scales as short as 2 hours. This is confirmed by the radial intensity diagrams (RID) which track each individual plume by displaying its radiance as a function of time and distance. These diagrams also indicate a constant speed of expansion with a mean value of 460 km/sec. (C) 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.