Ultraviolet Coronagraph Spectrometer Observations of a High-Latitude Coronal Hole with High Oxygen Temperatures and the Next Solar Cycle Polarity

Citations Over TimeTop 16% of 2001 papers

Abstract

We announce the resurgence of extreme ion properties in a large, high-latitude coronal hole observed above the north heliographic pole in 2001 February at solar maximum. The observations were taken with the Ultraviolet Coronagraph Spectrometer on the Solar and Heliospheric Observatory. These observations are part of an ongoing campaign to determine the plasma properties of coronal holes during the current solar cycle. In this Letter, we compare the observations and analysis of O VI λλ1032, 1037 spectral lines of a high-latitude coronal hole in 2001 with observations of an equatorial solar maximum hole in 1999 and polar coronal holes observed near solar minimum (1996-1997). These lines provide spectroscopic diagnostics of O+5 velocity distributions and outflow velocities. The O VI line profiles show a narrow core and broad wings. The narrow core is attributed to foreground and background streamers and, possibly, dense polar plumes at the lowest observed heights. The broad wings are attributed to the coronal hole. The comparison of the coronal hole line widths shows that the O+5 perpendicular kinetic temperatures in the 2001 high-latitude hole are similar to those observed in polar coronal holes at solar minimum. These observations of extremely high ion kinetic temperatures (exceeding 108 K) at the north pole in 2001 occurred nearly simultaneously with the polarity change of the Sun's magnetic field, as seen in recent magnetogram data. This coronal hole in 2001 may represent the first manifestation of the negative polarity polar coronal holes that will dominate the Sun's open magnetic flux tubes at the next solar minimum. The reappearance of broad O VI profiles at a time when not all of the "new polarity" magnetic flux has migrated to the poles was an interesting development. The variations in coronal hole parameters with the solar cycle provide constraints on models of extended coronal heating.

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