Solar Coronal Plumes

Polar plumes are thin long ray-like structures that project beyond the limb of the Sun polar regions, maintaining their identity over distances of several solar radii. Plumes have been first observed in white-light (WL) images of the Sun, but, with the advent of the space era, they have been identified also in X-ray and UV wavelengths (XUV) and, possibly, even in in situ data. This review traces the history of plumes, from the time they have been first imaged, to the complex means by which nowadays we attempt to reconstruct their 3-D structure. Spectroscopic techniques allowed us also to infer the physical parameters of plumes and estimate their electron and kinetic temperatures and their densities. However, perhaps the most interesting problem we need to solve is the role they cover in the solar wind origin and acceleration: Does the solar wind emanate from plumes or from the ambient coronal hole wherein they are embedded? Do plumes have a role in solar wind acceleration and mass loading? Answers to these questions are still somewhat ambiguous and theoretical modeling does not provide definite answers either. Recent data, with an unprecedented high spatial and temporal resolution, provide new information on the fine structure of plumes, their temporal evolution and relationship with other transient phenomena that may shed further light on these elusive features

Representing Solar Active Regions with Triangulations

.T he solar chromosphere consists of three classes which contribute di#erently to ultraviolet radiation reaching the earth. We describe a data set of solar images, means of segmenting the images into the constituent classes, and a novel high-level representation for compact objects based on a triangulated spatial `membership function'. Such representations are fitted in a variable-dimension Markov chain Monte Carlo scheme. Keywords.T riangulation, chromosphere, Markov chain Monte Carlo, image segmentation 1 Introduction T he solar atmosphere is comprised of several features having various characteristics, and distinct physical origin. T1 most apparent are active regions, which are associated with sunspots in the photosphere and plages in the chromosphere. T hese plages can be quite large in extent, and show themselves by their strong magnetic field and altered light emissions.T o a lesser extent, so does the chromospheric network, which is an evenly-distributed cell-patterned ..