Abstract
Recent spectroscopic measurements from instruments on the Solar and Heliospheric Obser vatory (SOHO) find that the coronal composition above a polar coronal hole is nearly photospheric. However, similar SOHO observations show that in coronal plasmas above quiet equatorial regions low-PIP elements are enhanced by a factor of ~ 4. In addition, the process of elemental settling in coronal plasmas high above the solar surface was shown to exist. Measurements by the Ulysses spacecraft, which are based on non-spectroscopic particle counting techniques, show that, with the exception of He, the elemental composition of the fast speed solar wind is similar to within a factor of 1.5 to the composition of the photosphere. In contrast, similar measurements in the slow speed wind show that elements with low first ionization potential (FIP< 10 eV) are enhanced, relative to the photosphere, by a factor of 4-5. By combining the SOHO and Ulysses results, ideas related to the origin of the slow speed solar wind are presented. Using spectroscopic measurements by the Solar Ultraviolet Measurement of Emitted Radiation (SUMER) instrument on SOHO the photospheric abundance of He was determined as 8.5 ± 1.3% (Y = 0.248).
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
