LASCO/SOHO white light observations of the solar maximum corona reveal the structure of some streamers as thin sheets of filamentary structures. We use EIT/SOHO 171Å\ observations to show the existence of bright thin sheets at very low heights in the corona. Modeling streamers as thin twisting sheets, originating from the solar surface and expanding outwards into the corona, successfully recreates the appearance of some streamers in observations. Low in the corona, the position and size of modeled sheets are dictated by the position and size of filaments (or prominences) observed in Hα on the solar disk, or by enhanced activity in EIT 171Å\ observations. Such structures can appear to a distant observer as a helmet streamer or a fan-shaped streamer depending on the latitude and alignment of the structure, and/or the solar rotation. We show that rays in a fan-shaped equatorial streamer extend directly from the brightest regions of EIT 171Å\ images, and that the apparent poleward divergence of equatorial coronal rays is a natural consequence of a twisting sheet topology. A 3D density model is constructed where sheet-like structures, originating from regions surrounding prominences, twist and merge to a height where the corona becomes radial, close to 3 R\odot. We establish that large helmet streamers may be created by the convergence of two or more sheet-like structures from widely separated regions on the Sun.
|Cyhoeddwyd - 01 Rhag 2006