P4.5 Time Domain Analysis of solar coronal structures through Hough transform techniques

Antoine Llebaria, Philippe Lamy (LAS,CNRS,France)

Hough transform technique is applied to a series of images from the LASCO/C2 coronagraph in order to understand the temporal evolution of observed radial-like structures on the solar corona, the so-called ``polar plumes'' wich apparently ouline the polar magnetic fields lines. They may corotate with the solar corona and therefore change aspect with time due to projection effects on the plane of view. In the images these structures suddenly appear, shift, mix, and fade away on short periods of time. To better understand the motion and lifetime of these structures, we have built a Time Intensity Diagram (TID). From a long series of images ($\sim$ 100), we have determined for each image the polar intensity profile and built up the evolution of such profiles againts time. The result is a diagram where intensities are plotted with respect to time and position coordinates. Radial-like image structures appear as peak intensies in each profile and therefore as bright points in the TID. Hough transform techniques are applied to detect coherent trajectories. This technique has been applied successfully to study coronal plumes on coronal images obtained by different instruments abrord SOHO satellite.