The Extreme Space Weather Event in February/March 1941

Abstract

This work was supported in part by JSPS Grant-in-Aids JP15H05812 and JP17J06954, JSPS Overseas Challenge Program for Young Researchers, the 2020 YLC collaborating research fund, and the research grants for Mission Research on Sustainable Humanosphere from Research Institute for Sustainable Humanosphere (RISH) of Kyoto University and Young Leader Cultivation (YLC) program of Nagoya University. We thank Mt. Wilson Observatory for providing sunspot drawings on 27 February 1941, WDC for Geomagnetism at Edinburgh for providing geomagnetic baselines and British magnetograms, WDC for Geomagnetism at Kyoto for providing the Dst index and magnetic measurements at Hermanus, San Juan, Honolulu, and Watheroo, Kakioka Event Database for providing data on the SSC and magnetic storms observed in the said observatory, WDC SILSO for providing international sunspot numbers, and Solar Science Observatory of the NAOJ for providing copies of Quarterly Bulletin on Solar Activity. Magnetograms were digitised using the WebPlotDigitizer software (https://automeris.io/WebPlotDigitizer/). SPB was supported by the NASA’s Living With a Star program (17-LWS17_2-0042). HH thanks Margaret A. Shea for her helpful advices on the historical solar proton events.