Solar wind expansion in a polar coronal hole: Inferences from coronal white light and interplanetary Lyman alpha observations

Abstract

Analysis of white light coronagraph observations of a polar coronal hole led Munro and Jackson (1977) to infer large solar wind speeds in the coronal hole and a consequent need for substantial energy addition to the outflow well above the coronal base. Recent interplanetary Lyman α observations by Kumar and Broadfoot (1979) and Lallement et al. (1985) indicate that the solar wind mass flux from well‐developed polar coronal holes may be considerably less than that typically observed in situ near the ecliptic plane. A reexamination of the Munro and Jackson analysis, with attention given both to the inferences drawn from the interplanetary Lyman α observations and to the uncertainties inherent in the coronal white light observations, leads to conclusions significantly different from those drawn by Munro and Jackson. Specifically, the coronal observations are found to be consistent not only with the high flow speeds and substantial energy addition inferred by Munro and Jackson, but also with much lower flow speeds and the absence of any significant energy addition in the region observed. This removal of definite observational confirmation of substantial energy addition to the coronal expansion between 1 Rs and 5 Rs has important implications for our understanding of energy balance in the solar wind.