A Review of White Light Streamers at the End of Cycle 23

Abstract

I give a brief review of the quiescent scale visible with an emphasis on the origin, structure and role of streamers in the solar wind. The review is mostly based on results from the last 10 years of the SOHO mission and the goal is to provide a coherent picture of what is known on streamers at the end of the current cycle. This presentation is given on the occasion of a solar eclipse, one of the most spectacular natural phenomena on Earth. For ages, natural eclpses were the only way to observe with our own eyes the corona, the faint outer atmosphere of the sun. The aesthetic pleasure of the phenomenon aside, visible observations of the extended carry significant scientific value. In the last 200 years, numerous expeditions over the last 200 years have trekked into remote locations, fought against limited resourses, unpredictable weather and capricious instrumentation to obtain a limited set of images over the few minutes that a total eclipse may last Zirker (1995). But real progress in coronal physics requires long-term observations of the corona. Such observations have been made possible by specialized telescopes, called coronagraphs, that block the light from the solar disk creating an artificial eclipse. The LASCO coronagraphs Brueckner et al. 1995 aboard the SOHO mission have contributed significantly in our understanding of the over the last 10 years. We now know a great deal about the physics, morphology and evolution of the corona. It is impractical to summarize such extensive knowledge in such a short space. Interested readers can find much more information in dedicated textbooks (Golub & Pasachoff 1997; Aschwanden 2004. I will only give a brief overview of some key concepts of the scale and describe what is known about the origins and structure of the building blocks of the corona, the white light streamers, and their role in the solar wind. 1. General Properties of the Large Scale Corona Although the term large scale corona sually implies the visible corona, there exist several other coronae depending upon the mechanism responsible for their emission. The visible or K-corona is created by the reflection of the photospheric light by the coronal electrons through the Thomson scattering process. The same photospheric light is reflected by larger, dust particles to create the F-corona. The F-corona is usually a nuiscance because it dominates the K-corona signal above a few solar radii without providing any information on coronal processes. The removal of the F-corona is an integral part for coronal analysis. Those interplanetary dust particles also radiate themselves in the infrared to form the T-corona. Finally, the coronal electrons can emit radiation at several spectral lines, from X-rays to the infrared, but this so-called E-corona becomes