Physical properties of a coronal hole from a coronal diagnostic spectrometer, Mauna Loa Coronagraph, and LASCO observations during the Whole Sun Month

Abstract

Until recently [Guhathakurta and Fisher, 1998], inference of electron density distribution in the solar corona was limited by the field of view of white‐light coronagraphs (typically out to 6 Rs). Now, for the first time we have a series of white‐light coronagraphs (SOHO/LASCO) whose combined field of view extends from 1.1–30 Rs. Quantitative information on electron density distribution of coronal hole and coronal plumes/rays are estimated by using white‐light, polarized brightness (pB) observations from the SOHO/LASCO/C2 and C3 and HAO/Mauna Loa Mark III coronagraphs from 1.15 to 8.0 Rs. Morphological information on the boundary of the polar coronal hole and streamer interface is determined from the white‐light observations in a manner similar to the Skylab polar coronal hole boundary estimate [Guhathakurta and Holzer, 1994]. The average coronal hole electron density in the region 1–1.15 Rs is estimated from the density‐sensitive EUV line ratios of Si IX 350/342 Å observed by the SOHO/coronal diagnostic spectrometer (CDS). We combine these numbers with the estimate from white‐light (WL) observations to obtain a density profile from 1 to 8 Rs for the plumes and the polar coronal hole. We find that white light and spectral analysis produce consistent density information. Extrapolated densities inferred from SOHO observations are compared to Ulysses in situ observations of density. Like the density inferred from the Spartan 201–03 coronagraph, the current SOHO density profiles suggest that the acceleration of the fast solar wind takes place very close to the Sun, within 10–15 Rs. The density information is used to put constraints on solar wind flow velocities and effective temperatures. Finally, these results are compared to the recent analysis of the Spartan 201–03 white‐light observations.