Extension of coronal structure into interplanetary space

Publisher Website
Google Scholar
Abstract
We investigate the extension and evolution of the solar corona into interplanetary space by comparing 1995 Ulysses radio occultation measurements of path‐integrated electron density and density fluctuations measured between 21 and 32 Ro, with simultaneous white‐light measurements made by the HAO Mauna Loa K‐coronameter below 2.5 Ro. The surprising picture of the extended corona to emerge from this comparison is one in which stalks of streamers, occupying a small fraction of volume in interplanetary space, are superimposed on a background corona distinguished by a plethora of ray like structures, often referred to as plumes in polar coronal holes. The radial preservation of the boundary between polar coronal holes and the base of streamers implies that the solar wind from polar coronal holes expands radially rather than undergoing any significant divergence as previously thought. Combining this picture of the extended corona with in situ velocity measurements made by Ulysses throughout its two polar passages, we conclude that the raylike structures, except for the stalks of streamers, seem to be the source of the fast wind. The existence of the fast wind at low latitudes can be attributed to these raylike structures, rather than the expansion of the boundaries of polar coronal holes to low latitudes.