J/A+A/601/A109 Monthly numbers of sunspot groups 1749-1996 (Willamo+, 2017)
Updated sunspot group number reconstruction for 1749-1996 using the active
day fraction method.
Willamo T., Usoskin I.G., Kovaltsov G.A.
<Astron. Astrophys. 601, A109 (2017)>
=2017A&A...601A.109W 2017A&A...601A.109W (SIMBAD/NED BibCode)
ADC_Keywords: Sun
Keywords: Sun: activity - sunspots
Abstract:
Sunspot number series are composed from observations of hundreds of
different observers that requires careful normalization of the
observers to the standard conditions. Here we present a new normalized
series of the number of sunspot groups for the period 1749-1996.
The reconstruction is based on the active day fraction (ADF) method,
which is slightly updated with respect to the previous works, and a
revised database of sunspot group observations.
Stability of some key solar observers has been evaluated against the
composite series. The Royal Greenwich Observatory dataset appears
fairly stable since the 1890s but is about 10% too low before that. A
declining trend of 10-15% in the quality of Wolfer's observation is
found between the 1880s and 1920s, suggesting that using him as the
reference observer may lead to additional uncertainties. Wolf (small
telescope) appears fairly stable between the 1860s and 1890s, without
any obvious trend. The new reconstruction reflects the centennial
variability of solar activity as evaluated using the singular spectrum
analysis method. It depicts a highly significant feature of the Modern
grand maximum of solar activity in the second half of the 20th
century, being a factor 1.33-1.77 higher than during the 18-19th
centuries.
The new series of the sunspot group numbers with monthly and annual
resolution, available also in the electronic format, is provided
forming a basis for new studies of the solar variability and solar
dynamo for the last 250 years.
Description:
The file contain the monthly numbers of sunspot groups including the
fractional year [Y], the Mean value [G_M], the low [G_l] and upper
[G_u] 1-sigma (68% bounds).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 32 2976 G-values for 1749-1996
--------------------------------------------------------------------------------
See also:
VI/138 : Sunspots catalogues, 1853-1870 (Casas+, 2013)
J/A+A/390/707 : Hemispheric Sunspot Numbers 1975-2000 (Temmer+, 2002)
J/A+A/447/735 : Hemispheric Sunspot Numbers 1945-2004 (Temmer+, 2006)
J/A+A/584/A73 : Sunspot areas and tilt angles (Senthamizh Pavai+, 2015)
J/A+A/595/A104 : Scheiner drawing sunspot areas and tilt angles (Arlt+, 2016)
Feb/28 : Group sunspot number series since 1739 (Chatzistergos+, 2017)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.3 yr Year Fractional year AD
9- 16 F8.3 ct G ?=-99 Mean G-value (G_M)
17- 24 F8.3 ct b_G ?=-99 Low 68% bound of G-value (G_l)
25- 32 F8.3 ct B_G ?=-99 Upper 68% bound of G-value (G_u)
--------------------------------------------------------------------------------
Acknowledgements:
Ilya Usoskin, ilya.usoskin[at]oulu.fi
(End) Patricia Vannier [CDS] 07-Mar-2017