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A history of solar activity over millennia

“…The GSN series is more reliable and homogeneous than the WSN series before 1849. The two series are nearly identical after the 1870s (Hoyt and Schatten 1998;Letfus 1999;Hathaway and Wilson 2004). However, the GSN series still contains some lacunas, uncertainties and possible inhomogeneities (see, e.g., Letfus 2000;Usoskin et al 2003a;Vaquero et al 2012;Cliver and Ling 2016).…”

“…In addition, earlier parts of the sunspot series were "corrected" by Wolf using geomagnetic observation (see details in Svalgaard 2012), which makes the series less homogeneous. Therefore, the WSN series is a combination of direct observations and interpolations for the period before 1849, leading to possible errors and inhomogeneities as discussed, e.g, by Vitinsky et al (1986), Wilson (1998), Letfus (1999), Svalgaard (2012), Clette et al (2014). The quality of the Wolf series before 1749 is rather poor and hardly reliable (Hoyt et al 1994;Hoyt and Schatten 1998;Hathaway and Wilson 2004).…”

A History of Solar Activity over Millennia

“…However, prior to that there have been many gaps in the data that were interpolated. Therefore, the WSN series is a combination of direct observations and interpolations for the period before 1849, leading to possible errors and inhomogeneities as discussed, e.g, by Vitinsky et al (1986); Wilson (1998); Letfus (1999). The quality of the Wolf series before 1749 is rather poor and hardly reliable (Hoyt et al, 1994;Hoyt and Schatten, 1998;Hathaway and Wilson, 2004).…”

Was one sunspot cycle lost in late XVIII century?

“…Recently, a new, greatly improved and more homogeneous group sunspot number (GSN) series, R g , was introduced (Hoyt & Schatten 1998) which includes many additional early observations and covers the period since 1610. The new GSN series has been shown to be more correct than WSN for the period before 1850 (Hoyt & Schatten 1998;Letfus 1999).…”

“…The evolution of SA is distorted during the exceptionally Send offprint requests to: I. G. Usoskin, e-mail: ilya.usoskin@oulu.fi long declining phase of cycle #4 in 1791-1798, leading to the suggested phase catastroph (e.g., Vitinsky et al 1986;Kremliovsky 1994), when the phase evolution of SA was not cyclic but linear. Note that these results were obtained from the WSN series which was constructed by interpolating (without explicit notice) over sparse points, L32 I. G. Usoskin et al: Lost sunspot cycle leading to large systematic errors of up to 50 in R z units for the last decades of 18 th century (Hoyt & Schatten 1998;Letfus 1999). Since the GSN series is based on a larger observational data set and allows to study the original (not interpolated or pre-processed) data by individual observers, we use the GSN series to reanalyze solar activity in the beginning of DM.…”