On the Sunspot Group Number Reconstruction: The Backbone Method Revisited

  • Leif Svalgaard Stanford University, USA

Abstract

We discuss recent papers very critical of the Group Sunspot Number Series (Svalgaard & Schatten [2016]). Unfortunately, we cannot support any of the concerns they raise. We first show that almost always there is simple proportionality between the group counts by different observers and that taking the small, occasional, non-linearities into account makes very little difference. Among other examples: we verify that the RGO group count was drifting the first twenty years of observations. We then show that our group count matches the diurnal variation of the geomagnetic field with high fidelity, and that the heliospheric magnetic field derived from geomagnetic data is consistent with our group number series. We evaluate the ‘correction matrix’ approach [Usoskin et al. 2016] and show that it fails to reproduce the observational data. We clarify the notion of daisy-chaining and point out that our group number series has no daisy-chaining for the period 1794-1996 and therefore no accumulation of errors over that span. We compare with the cosmic ray record for the last 400+ years and find good agreement. We note that the Active Day Fraction method (of Usoskin et al.) has the fundamental problem that at sunspot maximum, every day is an ‘active day’ so ADF is nearly always unity and thus does not carry information about the statistics of high solar activity. This ‘information shadow’ occurs for even moderate group numbers and thus need to be extrapolated to higher activity. The ADF method also fails for ‘equivalent observers’ who should register the same group counts, but do not. We conclude that the criticism of Svalgaard & Schatten [2016] is invalid and detrimental to progress in the important field of long-term variation of solar activity.

Author Biography

Leif Svalgaard, Stanford University, USA

Stanford University, USA

References

Asvestari, E., Usoskin, I. G., Kovaltsov, G. A., Owens, M. J., Krivova, N. A., Rubinetti, S., Taricco, C.: Assessment of different sunspot number series using the cosmogenic isotope 44Ti in meteorites, Monthly Notices Royal Astron. Soc. 467(2), 1608, doi:10.1093/mnras/stx190, 2017.

Balmaceda, L., Solanki, S. K., Krivova, N. A, and Foster, S.: A homogeneous database of sunspot areas covering more than 130 years, J. Geophys. Res. 114, A07104, doi:10.1029/2009JA014299, 2009.

Berggren, A.-M., Beer, J., Possnert, G., Aldahan, A., Kubik, P., Christl, M., Johnsen, S. J., Abreu, J., and Vinther, B. M.: A 600-year annual 10Be record from the NGRIP ice core, Greenland, Geophys. Res. Lett. 36, L11801, doi:10.1029/2009GL038004, 2009.

Chatzistergos, T., Usoskin I. G., Kovaltsov, G. A., Krivova, N. A., Solanki, S. K.: New reconstruction of the sunspot group number since 1739 using direct calibration and ‘backbone’ methods, Astron. & Astrophys.. 602, A69, doi:10.1051/0004-6361/201630045, 2017.

Clette, F., Cliver, E. W.,·Lefèvre, L., Svalgaard, L.,·Vaquero, J. M., and Leibacher, J. W.: Preface to Topical Issue: Recalibration of the Sunspot Number, Solar Phys. 291(9), 2479, doi:10.1007/s11207-016-1017-8, 2016.

Clette, F., Svalgaard, L., Vaquero, J. M., and Cliver, E. W.: Revisiting the Sunspot Number - A 400-Year Perspective on the Solar Cycle, Space Sci. Rev. 186, 35, doi:10.1007/s11214-014-0074-2, 2014. Cliver, E. W.: Comparison of New and Old Sunspot Number Time Series, Solar Phys. 291(9-10), 2891, doi:10.1007/s11207-016-0929-7, 2016.

Cliver, E.W. and Ling, A.G.: The Discontinuity Circa 1885 in the Group Sunspot Number, Solar Phys. 291, 2763, doi:10.1007/s11207-015-0841-6, 2016.

Friedli, T. K.: Sunspot Observations of Rudolf Wolf from 1849-1893, Solar Phys. 291(9), 2505, doi:10.1007/s11207-016-0907-0, 2016.

Herbst, K., Muscheler, R., Heber, B.: The new local interstellar spectra and their influence on the production rates of the cosmogenic radionuclides 10Be and 14C, J. Geophys. Res. (Space Physics), 122(1), 23, doi:10.1002/2016JA023207, 2017.

Hoyt D. V., Schatten K. H., and Nesmes-Ribes, E.: The one hundredth year of Rudolf Wolf’s death: Do we have the correct reconstruction of solar activity? Geophys. Res. Lett. 21(18), 2067, doi:10.1029/94GL01698, 1994.

Hoyt D. V., Schatten K. H.: Group Sunspot Numbers: A New Solar Activity Reconstruction, Solar Phys. 181(2), 491, doi:10.1023/A:1005056326158, 1998.

Muscheler, R., Adolphi, F.,·Herbst, K., Nilsson, A.: The Revised Sunspot Record in Comparison to Cosmogenic Radionuclide-Based Solar Activity Reconstructions, Solar Phys. 291(9), 3025, doi:10.1007/s11207-016-0969-z, 2016.

Lockwood, M., Nevanlinna, H., Barnard, L., Owens, M. J., Harrison, R. G., Rouillard, A. P., Scott, C. J.: Reconstruction of geomagnetic activity and near-Earth interplanetary conditions over the past 167 yr – Part 4, Annal. Geophys. 32(4), 383, doi: 10.5194/angeo-32-383-2014, 2014.

Lockwood, M., Owens, M. J., Barnard, L., and Usoskin, I. G.: Tests of Sunspot Number Sequences: 3. Effects of Regression Procedures on the Calibration of Historic Sunspot Data, Solar Phys. 291(9), 2829, doi:10.1007/s11207-015-0829.2, 2016a.

Lockwood, M., Owens, M. J., Barnard, L., and Usoskin, I. G.: An Assessment of Sunspot Number Data Composites over 1845–2014, Astrophys. Journal 824(1), doi:10.3847/0004-637X/824/1/54, 2016b.

Owens, M. J., Cliver, E. W., McCracken, K. G., Beer, J., Barnard, L., Lockwood, M., Rouillard, A., Passos, D., Riley, P., Usoskin, I. G., and Wang, Y.-M.: Near-Earth heliospheric magnetic field intensity since 1750: 1. Sunspot and geomagnetic reconstructions. J. Geophys. Res. (Space Physics) 121, 6048, doi: 10.1002/2016JA022550, 2016.

Schrijver, C. J., Livingston, W. C., Woods, T. N., and Mewaldt, R. A.: The minimal solar activity in 2008–2009 and its implications for long–term climate modeling, Geophys. Res. Lett. 38, L06701, doi:10.1029/2011GL046658, 2011.

Schwabe, S. H.: Sonnenbeobachtungen im Jahre 1843, Astron. Nachrichten 21, 233, 1844.

Svalgaard, L.: Correction of errors in scale values for magnetic elements for Helsinki, Ann. Geophys. 32, 633, doi:10.5194/angeo-32-2014, 2014.

Svalgaard, L.: Reconstruction of Solar Extreme Ultraviolet Flux 1740-2015, Solar Phys. 291(10), 2981, doi:10.1007/s11207-016-0921-2, 2016.

Svalgaard, L., Cliver, E. W., and Le Sager, P.: Determination of Interplanetary Magnetic Field Strength, Solar Wind Speed, and EUV Irradiance, 1890-Present. International Solar Cycle Studies Symposium, June 23-28, 2003, Tatranska Lomnica, Slovak Republic, Proceedings (ESA SP-535), 15, ed. A. Wilson, Noordwijk, ISBN:92-9092-845-X, 2003.

Svalgaard, L. and Cliver, E. W.: The IDV index: Its derivation and use in inferring long-term variations of the interplanetary magnetic field strength, J. Geophys. Res. 110, A12103, doi:10.1029/2005JA011203, 2005.

Svalgaard, L. and Cliver, E. W.: Interhourly variability index of geomagnetic activity and its use in deriving the long-term variation of solar wind speed, J. Geophys. Res. 112, A10111, doi:10.1029/2007JA012437, 2007.

Svalgaard, L. and Cliver, E. W.: Heliospheric magnetic field 1835–2009, J. Geophys. Res. 115, A09111, doi:10.1029/2009JA015069, 2010.

Svalgaard, L., and Schatten, K. H.: Reconstruction of the Sunspot Group Number: the Backbone Method, Solar Phys. 291(10), 291(9), 2653, doi:10.1007/s11207-015-0815-8, 2016.

Usoskin, I. G., Arlt, R., Asvestari, E., Hawkins, E., Käpylä, M., Kovaltsov, G. A., Krivova, N., Lockwood, M., Mursula, K., O’Reilly, J., Owens, M. J., Scott, C. J., Sokoloff, D. D., Solanki, S. K., Soon, W., Vaquero, J. M.: The Maunder minimum (1645–1715) was indeed a Grand minimum: A reassessment of multiple datasets, Astron.&Astrophys. 581, A95, doi:10.1051/0004-6361/201526652, 2015.

Usoskin, I. G., Kovaltsov, G. A., Lockwood, M., Mursula, K., Owens, M. J., Solanki, S. K.: A New Calibrated Sunspot Group Series Since 1749: Statistics of Active Day Fractions, Solar Phys. 291(9), 2685, doi:10.1007/s11207-015-0838-1, 2016.

Vaquero, J. M.: Presentation at 2nd- Sunspot Number Workshop, Brussels, Belgium, http://www.leif.org/research/SSN/Vaquero2.pdf, 2012.

Vaquero, J. M., Trigo, R. M., and Gallego, M. C.: A Simple Method to Check the Reliability of Annual Sunspot Number in the Historical Period 1610 – 1847, Solar Phys. 277(2), 389, doi:10.1007/s11207-011-9901-8, 2012.

Vaquero, J. M., Svalgaard, L., Carrasco, V. M. S., Clette, F., Lefèvre, L., Gallego, M. C., Arlt, R., Aparicio, A. J. P., Richard, J-G., Howe, R.: A Revised Collection of Sunspot Group Numbers, Solar Phys. 291(10), 3061, doi:10.1007/s11207-016-0982-2, 2016.

Wang, Y.-M. and Sheeley Jr, N. R.: On the fluctuating component of the Sun’s large‐scale magnetic field, Astrophys. J. 590, 1111, doi:10.1086/375026, 2003.

Wang, Y.-M., Lean, J. L., and Sheeley Jr, N. R.: Modeling the Sun’s magnetic field and irradiance since 1713, Astrophys. J. 625, 522,doi:10.1086/429689, 2005.

Weise, W., Dorschner, J., and Schielicke, R. E.: Wilhelm Winkler (1842-1910) - a Thuringian private astronomer and maecenas, Acta Historica Astron. 3, 95, 1998.

Willamo, T., Usoskin, I. G., and Kovaltsov, G. A.: Updated sunspot group number reconstruction for 1749–1996 using the active day fraction method, Astron. & Astrophys. 601, A109, doi:10.1051/0004-6361/201629839, 2017.

Wolf, J. R.: Astronomische Mittheilungen, LXXXII, 58, 1893.

Published
2018-08-29
Section
Research Articles