Lefèvre, Laure ; Mathieu, Sophie ; Clette, Frederic

Talk presented at IUGG, Montreal on 2019-07-12

Abstract: We present the determination of uncertainties and monitoring of the modern part of the sunspot series and its application to past data. Uncertainties would help improve the accurate reconstruction of the long-term evolution of solar activity, in support of multiple applications in solar physics and geo-sciences. In this context, we present results obtained by the VALUSUN project (sidc.be/valusun): they include a constant quality control and monitoring of the most recent part of the series and the inclusion of significant error bars through a complete modeling of the series. We detail the first comprehensive noise model of sunspot counts in a multiplicative framework. We estimate the distribution of errors in various regimes of solar activity and for each component of the sunspot number: the number of spots (Ns), the number of groups (Ng) and the composite (Nc=Ns+10Ng). Key results are an estimation of the short-term error distribution, and an estimation of long-term drifts specific to each observing station. Since 2018, we have progressively digitized all data gathered at the Zurich Observatory bridging the gap between the Journals of the Zurich Observatory and the database of the WDC-SILSO. The mentioned techniques developed on multiple observers from the modern part of the series can be applied to the historical part of the series. Following the recalibration of the Sunspot Number in 2015, and thanks to this data recovery campaign, we are now able to envision a reconstruction of the series from scratch, with associated statistics.

Note: Session: Advances and Upcoming Developments in Solar and Heliospheric Physics
Funding: BR/165/A3/VAL-U-SUN