000005311 001__ 5311
000005311 005__ 20210301152651.0
000005311 0247_ $$2DOI$$a10.1051/swsc/2020071
000005311 037__ $$aSCART-2021-0073
000005311 100__ $$aClette, Frédéric
000005311 245__ $$aIs the F10.7cm - Sunspot Number relation linear and stable?
000005311 260__ $$c2021
000005311 520__ $$aThe F10.7cm radio flux and the Sunspot Number are the most widely used long-term indices of solar activity. They are strongly correlated, which led to the publication of many proxy relations allowing to convert one index onto the other. However, those existing proxies show significant disagreements, in particular at low solar activity. Moreover, a temporal drift was recently found in the relative scale of those two solar indices. Our aim is to bring a global clarification of those many issues. We compute new polynomial regressions up to degree 4, in order to obtain a more accurate proxy over the whole range of solar activity. We also study the role of temporal averaging on the regression, and we investigate the issue of the all-quiet F10.7 background flux. Finally, we check for any change in the F10.7–Sunspot Number relation over the entire period 1947–2015. We find that, with a 4th-degree polynomial, we obtain a more accurate proxy relation than all previous published ones, and we derive a formula giving standard errors. The relation is different for daily, monthly and yearly mean values, and it proves to be fully linear for raw non-averaged daily data. By a simple two-component model for daily values, we show how temporal averaging leads to non-linear proxy relations. We also show that the quiet-Sun F10.7 background is not absolute and actually depends on the duration of the spotless periods. Finally, we find that the F10.7cm time series is inhomogeneous, with an abrupt 10.5% upward jump occurring between 1980 and 1981, and splitting the series in two stable intervals. Our new proxy relations bring a strong improvement and show the importance of temporal scale for choosing the appropriate proxy and the F10.7 quiet-Sun background level. From historical evidence, we conclude that the 1981 jump is most likely due to a unique change in the F10.7 scientific team and the data processing, and that the newly re-calibrated sunspot number (version 2) will probably provide the only possible reference to correct this inhomogeneity.
000005311 594__ $$aSTCE
000005311 6531_ $$aSunspots
000005311 6531_ $$aSolar indices
000005311 773__ $$cid.2, 22 pp.$$pJournal of Space Weather and Space Climate$$v11$$y2021
000005311 8560_ $$ffrederic.clette@observatoire.be
000005311 85642 $$ahttps://www.swsc-journal.org/articles/swsc/full_html/2021/01/swsc200021/swsc200021.html
000005311 905__ $$apublished in
000005311 980__ $$aREFERD