2010/05/18 by M. P. Miralles, Miralles, M. P., Steven R. Cranmer +6
Physics and Astronomy · #Astro and Planetary Science #FOS: Physical sciences #Solar and Space Plasma Dynamics #Solar and Stellar Astrophysics (astro-ph.SR) #Stellar, planetary, and galactic studies #astro-ph.SR
paper · pdf · doi:10.48550/arxiv.1005.3242
8 pages (ASP style), 5 figures, in press for the proceedings of "SOHO-23: Understanding a Peculiar Solar Minimum."
arxiv created 2010/05/18 · openalex publication_date 2010/05/18 · arxiv updated 2010/05/19 · openalex created_date 2025/10/24 · openalex updated_date 2026/07/28
We have measured the physical properties of polar coronal holes from the minimum activity phase of solar cycle 23 (1996-1997) to the present minimum of solar cycle 24 (2007-2009) using the UVCS instrument on SOHO. Observations in H I Lyman alpha (121.6 nm) and O VI (103.2, 103.7 nm) provide spectroscopic diagnostics of proton and O5+ bulk outflow velocities and velocity distributions as a function of heliocentric distance above the poles of the Sun. These observations have allowed us to follow the changes in the physical properties of the polar coronal holes during solar cycle 23 and its approach to the current minimum. Recent ground- and space-based observations have reported a variety of phenomena associated with the current minimum. We present the comparison of observed oxygen line intensities, line ratios, and profiles for polar coronal holes at both minima and during solar cycle 23 and show how this new minimum manifests itself in the ultraviolet corona. The comparison of the physical properties of these two minima as seen by UVCS in the extended corona, now possible for the first time, may provide crucial empirical constraints on models of extended coronal heating and acceleration for the fast solar wind.