Sunspot observations by Hisako Koyama: 1945–1996

Abstract

The sunspot record is the only observational tracer of solar activity that provides a fundamental, multi-century reference. Its homogeneity has been largely maintained with a succession of long-duration visual observers. In this paper, we examine observations of one of the primary reference sunspot observers, Hisako Koyama. By consulting original archives of the National Museum of Nature and Science of Japan (hereafter, NMNS), we retrace the main steps of her solar-observing career, from 1945 to 1996.We also present the reconstruction of a full digital database of her sunspot observations at the NMNS, with her original drawings and logbooks. Here, we extend the availability 2 of her observational data from 1947-1984 to 1945-1996. Comparisons with the international sunspot number (version 2) and with the group sunspot number series show a good global stability of Koyama's observations, with only temporary fluctuations over the main interval 1947-1982. Identifying drawings made by alternate observers throughout the series, we find that a single downward baseline shift in the record coincides with the partial contribution of replacement observers mostly after 1983. We determine the correction factor to bring the second part (1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996) to the same scale with Koyama's main interval . We find a downward jump by 9% after 1983, which then remains stable until 1996. Overall, the high quality of Koyama's observations with her life-long dedication leaves a lasting legacy of this exceptional personal achievement. With this comprehensive recovery, we now make the totality of this legacy directly accessible and exploitable for future research.

Graphical evidence for the solar coronal structure during the Maunder minimum: comparative study of the total eclipse drawings in 1706 and 1715

“…These are contrasted with Ken'ichi Fujimori's paintings of the same eclipse events made without even the aid of a telescope. Fujimori is known as an experienced solar observer with long-term stability (see Mathieu et al, 2019) among the reference observers (see e.g., Hayakawa et al, 2020d). The top panel is for the eclipse of 1991 July 11 near a sunspot maximum.…”

Thaddäus Derfflinger’s Sunspot Observations during 1802–1824: A Primary Reference to Understand the Dalton Minimum

“…It is important to investigate and reconstruct solar activity of the past as it provides fundamental input for several fields such as the solar dynamo theory (Charbonneau, 2010;Atlt and Weiss, 2014;Auguston et al, 2015;Hotta et al, 2016), the solar-terrestrial relationship (Lockwood, 2013;Hayakawa et al, 2018dHayakawa et al, , 2019b, space weather (Cliver and Dietrich, 2013;Hayakawa et al, 2017Hayakawa et al, , 2018cHayakawa et al, , 2019aToriumi et al, 2017Toriumi et al, , 2019, space climate (Hathaway and Wilson, 2004;Owens et al, 2011;Barnard et al, 2011;Usoskin et al, 2015;Hayakawa et al, 2019c;Pevtsov et al 2019), terrestrial climate change (Gray et al, 2010;Lockwood, 2012;Owens et al, 2017), and for predictions of upcoming solar cycles (Svalgaard et al, 2005;Petrovay, 2010;Iijima et al, 2017;Upton and Hathaway, 2018). Excluding the solar cycle of approximately 11 years, solar activity has longer-term variations such as grand minima and grand maxima Solanki and Krivova, 2004;Usoskin et al, 2007;Clette et al, 2014;Inceoglu et al, 2015;Muscheler et al, 2016;Usoskin, 2017).…”

Reconstructing solar irradiance from historical Ca II K observations. I. Method and its validation

“…However, it is likely that it includes observations with the following settings too: [1. velopment of new techniques (Usoskin et al 2016b;Willamo et al 2017;Chatzistergos et al 2017), re-analysis of some data, as well as recovery of additional sources (e.g. Arlt et al 2013Arlt et al , 2016Vaquero et al 2016;Carrasco et al 2018Carrasco et al , 2019Carrasco et al , 2021aHayakawa et al 2020aHayakawa et al ,b, 2021Vokhmyanin et al 2020), which improved the accuracy of the sunspot number records and thus irradiance reconstructions (Kopp et al 2016). More critical for historical reconstructions is, however, the lack of accurate information on the evolution of faculae and the network.…”