Characterization of polar plumes from LASCO-C2 images in early 1996

Polar plumes or rays are characteristic ray-like structures which are well observed in the polar regions of the Sun during solar minima where they apparently outline the polar magnetic field lines. In order to better understand the nature and temporal evolution of these structures, we have analysed a set of white Light images obtained with the LASCO-C2 coronagraph aboard SOHO in April, 1996. A specific processing consisting in a polar transform followed by a radial filtering has been implemented to enhance the plumes. Their morphology can display complex forms (helicoids). They appear as recurrent structures connected to localized, miniature active:regions of the solar surface and their typical lifetime is similar to 20 hours.