Comparative solar minima using the McIntosh Archive

In this paper we present the full Archive for the first time and find a hemispheric pattern of coronal hole polarity reflecting the Hale sunspot polarity pattern. In addition, we present a supplemental set of related maps created for the 2019-2020 solar minimum in support of the Whole Heliosphere and Planetary Interactions (WHPI) interval.

To facilitate this addition, we cross calibrate EUV and He-I 10,830 )1 coronal holes and study differences between the WHPI solar minimum and the earlier minima in the main Archive. We find, first, that the visibility of coronal holes in EUV introduces a bias toward larger counts of low-latitude coronal holes near solar minimum. However, the estimated lifetimes (in Carrington Rotations) of coronal hole complexes are unaffected by this fragmentation, and we find the longest-lived low-latitude coronal holes occurred during the 2008-2009 solar minimum, with 2019-2020 solar minimum lifetimes not far behind.