Digitization of sunspot drawings by Spörer made in 1861–1894

Diercke, A.; Arlt, R.; Denker, C.

doi:10.1002/asna.201412138

Cited by 33 publications

(31 citation statements)

References 25 publications

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“…2.2.1). Sunspot areas can be reconstructed even before that using drawing of the sun by H. Schwabe for the years 1826-1867 Senthamizh Pavai et al 2015) and images by Spörer for the period 1861-1894 (Diercke et al 2015). In addition, some fragmentary solar drawings exist even for earlier periods, including the Maunder minimum in the seventeenth century (Ribes and Nesme-Ribes 1993;Vaquero et al 2004;Arlt 2008).…”

Section: Other Indicesmentioning

confidence: 99%

A history of solar activity over millennia

Usoskin

2017

Living Rev Sol Phys

391

241

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Presented here is a review of present knowledge of the long-term behavior of solar activity on a multi-millennial timescale, as reconstructed using the indirect proxy method. The concept of solar activity is discussed along with an overview of the special indices used to quantify different aspects of variable solar activity, with special emphasis upon sunspot number. Over long timescales, quantitative information about past solar activity can only be obtained using a method based upon indirect proxies, such as the cosmogenic isotopes 14 C and 10 Be in natural stratified archives (e.g., tree rings or ice cores). We give an historical overview of the development of the proxy-based method for past solar-activity reconstruction over millennia, as well as a description of the modern state. Special attention is paid to the verification and cross-calibration of reconstructions. It is argued that this method of cosmogenic isotopes makes a solid basis for studies of solar variability in the past on a long timescale (centuries to millennia) during the Holocene. A separate section is devoted to reconstructions of strong solar energetic-particle (SEP) events in the past, that suggest that the present-day average SEP flux is broadly consistent with estimates on longer timescales, and that the occurrence of extra-strong events is unlikely. Finally, the main features of the long-term evolution of solar magnetic activity, including the

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Section: Other Indicesmentioning

confidence: 99%

A history of solar activity over millennia

Usoskin

2017

Living Rev Sol Phys

391

241

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“…The dataset of sunspot group positions and sizes consists of three subsets: the revised version 1.3 of Schwabe data (Arlt 2011;Arlt et al 2013) for the period 1826-1867, the newly digitized Spörer data (Diercke et al 2015) for 1868-1874 (although these data are available from 1861-1894, we use them here only to fill the gap between Schwabe and RGO data), and the RGO/USAF/NOAA/SOON compilation 1 referred to collectively as the RGO data since 1875.…”

Section: Datamentioning

confidence: 99%

“…The spots were identified and measured in an automated search delivering whole-spot areas and locations for individual sunspots (Diercke et al 2015). Very few sunspots were reported in the Spörer data at the beginning of his observing period, as compared to data by Richard Carrington during a small overlapping period in 1861 (Zolotova et al 2010), but later they reached a higher more normal level.…”

Section: Datamentioning

confidence: 99%

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Wings of the butterfly: Sunspot groups for 1826–2015

Leussu

Usoskin

Pavai

et al. 2017

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The spatio-temporal evolution of sunspot activity, the so-called Maunder butterfly diagram, has been continously available since 1874 using data from the Royal Greenwich Observatory, extended by SOON network data after 1976. Here we present a new extended butterfly diagram of sunspot group occurrence since 1826, using the recently digitized data from Schwabe (1826Schwabe ( -1867 and Spörer (1866Spörer ( -1880. The wings of the diagram are separated using a recently developed method based on an analysis of long gaps in sunspot group occurrence in different latitude bands. We define characteristic latitudes, corresponding to the start, end, and the largest extent of the wings (the F, L, and H latitudes). The H latitudes (30 • -45 • ) are highly significantly correlated with the strength of the wings (quantified by the total sum of the monthly numbers of sunspot groups). The F latitudes (20 • -30 • ) depict a weak tendency, especially in the southern hemisphere, to follow the wing strength. The L latitudes (2 • -10 • ) show no clear relation to the wing strength. Overall, stronger cycle wings tend to start at higher latitudes and have a greater wing extent. A strong (5-6)-cycle periodic oscillation is found in the start and end times of the wings and in the overlap and gaps between successive wings of one hemisphere. While the average wing overlap is zero in the southern hemisphere, it is two to three months in the north. A marginally significant oscillation of about ten solar cycles is found in the asymmetry of the L latitudes. The new long database of butterfly wings provides new observational constraints to solar dynamo models that discuss the spatio-temporal distribution of sunspot occurrence over the solar cycle and longer.

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“…In regard to the GSN, the Sunspot Number Workshops drew attention to the inhomogeneity in the early RGO series responsible for the~1885 discontinuity (Svalgaard 2010;Clette et al 2014;Cliver & Ling 2016), the 1874-1976 interval used to scale GSN to WSN which was affected by both the RGO inhomogeneity and the Waldmeier discontinuity (Clette et al 2014), and the RGO-ISOON transition after 1975 (Clette et al 2014). Both series have benefitted from the important ongoing work of Vaquero, Arlt, and others (e.g., Vaquero 2007;Arlt 2008Arlt , 2009Arlt , 2011Vaquero et al 2011Vaquero et al , 2012Carrasco et al 2013;Vaquero & Gallego 2014, Diercke et al 2015Vaquero et al 2016) to both critically evaluate and increase the sunspot Hoyt & Schatten (1998a, 1998b group number database, including digitization, archival, and accessibility. In addition, have specified a constant non-linear relationship between the sunspot number and group counts.…”

Section: Discussionmentioning

confidence: 99%

Sunspot number recalibration: The ~1840–1920 anomaly in the observer normalization factors of the group sunspot number

Cliver¹

2017

J. Space Weather Space Clim.

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We analyze the normalization factors (k 0 -factors) used to scale secondary observers to the Royal Greenwich Observatory (RGO) reference series of the Hoyt & Schatten (1998a, 1998b group sunspot number (GSN). A time series of these k 0 -factors exhibits an anomaly from 1841 to 1920, viz., the average k 0 -factor for all observers who began reporting groups from 1841 to 1883 is 1.075 vs. 1.431 for those who began from 1884 to 1920, with a progressive rise, on average, during the latter period. The 1883-1884 break between the two subintervals occurs precisely at the point where Hoyt and Schatten began to use a complex daisy-chaining method to scale observers to RGO. The 1841-1920 anomaly implies, implausibly, that the average sunspot observer who began from 1841 to 1883 was nearly as proficient at counting groups as mid-20th century RGO (for which k 0 = 1.0 by definition) while observers beginning during the 1884-1920 period regressed in group counting capability relative to those from the earlier interval. Instead, as shown elsewhere and substantiated here, RGO group counts increased relative to those of other long-term observers from 1874 to~1915. This apparent inhomogeneity in the RGO group count series is primarily responsible for the increase in k 0 -factors from 1884 to 1920 and the suppression, by 44% on average, of the Hoyt and Schatten GSN relative to the original Wolf sunspot number (WSN) before~1885. Correcting for the early ''learning curve'' in the RGO reference series and minimizing the use of daisy-chaining rectifies the anomalous behavior of the k 0 -factor series. The resultant GSN time series (designated GSN*) is in reasonable agreement with the revised WSN (S N *; Clette & Lefèvre 2016) and the backbone-based group sunspot number (R GS ; Svalgaard & Schatten 2016) but significantly higher than other recent reconstructions (Friedli, personal communication, 2016;Lockwood et al. 2014aLockwood et al. , 2014bUsoskin et al. 2016a). This result is substantiated by a ''correction-factor'' (CF) time series defined as the ratio of annual group counts of the Hoyt & Schatten (1998a, 1998b series to the average raw (unscaled) group counts of all observers, as well as by a comparison of the GSN and GSN* time series with a recent reconstruction of solar wind B from 1845 to the present. The~1840-1920 k 0 -factor anomaly and its impact on the Hoyt and Schatten GSN are discussed in the context of the ongoing effort to recalibrate the sunspot number time series.

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Digitization of sunspot drawings by Spörer made in 1861–1894

Cited by 33 publications

References 25 publications

A history of solar activity over millennia

A history of solar activity over millennia

Wings of the butterfly: Sunspot groups for 1826–2015

Sunspot number recalibration: The ~1840–1920 anomaly in the observer normalization factors of the group sunspot number

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