AUTHOR=Lockwood Mike , Owens Mathew J. , Yardley Stephanie L. , Virtanen Iiro O. I. , Yeates Anthony R. , Muñoz-Jaramillo Andrés TITLE=Application of historic datasets to understanding open solar flux and the 20th-century grand solar maximum. 2. Solar observations JOURNAL=Frontiers in Astronomy and Space Sciences VOLUME=9 YEAR=2022 URL=https://www.frontiersin.org/journals/astronomy-and-space-sciences/articles/10.3389/fspas.2022.976444 DOI=10.3389/fspas.2022.976444 ISSN=2296-987X ABSTRACT=
We study historic observations of solar activity from the 20th-century rise towards the peak of the Modern Grand Solar Maximum (MGSM) and compare with observations of the decline that has occurred since. The major difference in available solar observations of the rise and of the fall are accurate magnetograms from solar magnetographs: we here use synthetic magnetograms to interpret the rise and employ historic observations of Polar Crown Filaments to test them and verify their use. We show that eclipse images at sunspot minimum reveal the long-term variation of open flux deduced from geomagnetic observations in Paper 1 (