Lefèvre, Laure ; Mathieu, Sophie ; von Sachs, Rainer ; Delouille, Véronique ; Clette, Frédéric

Talk presented at Space Climate 7, Montreal, Canada on 2019-07-09

Abstract: We present the determination of uncertainties and monitoring of the modern part of the sunspot series and possible applications to past data and previous developed techniques. 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. This new work on the behavior of sunspot counts in modern data will enable us to get new insight on how to stitch the sunspot series from past observers together. We will see how the derived statistical properties could be taken into account in different methods. Following the recalibration of the Sunspot Number in 2015 we are now able to envision a reconstruction of the series, with associated statistics.

Funding: BR/165/A3/VAL-U-SUN