On July 19, 2021, we added a new time series to our data products: extended hemispheric sunspot numbers starting in 1874. Those reconstructed numbers are based on the sunspot areas listed in the Greenwich photographic catalogue, and are calibrated on the SILSO reference hemispheric series, which starts only in 1992. This newly published series results from a collaboration between SILSO, the University of Graz (Austria) and the Skolkovo Institute of Science and Technology (Moscow, Russia).
In January 2020, the 13-month smoothed sunspot number rose for the first time since the maximum of cycle 24 (April 2014). Most probably, this indicates that the minimum between cycles 24 and 25 was passed in December 2019.
However, for now, this latest smoothed value in January 2020 is the very first point indicating a rise of the activity. So, the date of the minimum still needs a full confirmation over the coming months. For now, preliminary smoothed values, limited to less than 13 months, hint at increasing values over coming months. If the rising trend indeed continues, this date will become fully definitive.
An international panel of experts coordinated by the NOAA and NASA,to which the WDC-SILSO contributed, released a preliminary forecast for Solar Cycle 25 on April 5, 2019. Based on a compilation of more than 60 forecasts published by various teams using a wide range of methods, the panel reached a consensus indicating that cycle 25 will most likely peak between 2023 and 2026 at a maximum sunspot number between 95 and 130. This prediction is now given in the scale of sunspot number Version 2.
Starting from a collaboration with the NCEI (NOAA, Boulder USA), we implemented new 12-month ahead predictions based on the McNish and Lincoln method. This rather simple method is based on a single mean cycle profile and is thus of "climatology" type. It was used as a standard for many years at NOAA, and we now add it to our other more advanced Standard Curves and Combined methods, allowing direct comparisons. Likewise, we now also provide a Kalman-filter optimized version of these new ML predictions.
Today marked a triple transition for us:
- Uploading the new Sunspot Number archive files containing the daily, monthly and yearly re-calibrated sunspot numbers and the new Group Number series
- In our Web site, switching to the new "Data" pages giving access to the new files, to updated graphics and also to the past version of the Sunspot Number
- Adapting and running the entire monthly procedure to produce the provisional Sunspot Numbers for June 2015 and the associated 12-months forecast and EISN.
After completing the new data files themselves, we are now finalizing the design of the new sections in our data pages.
The preparation of the July 1st transition is progressing at high pace. Hundreds of lines of codes are adapted for the new sunspot number series and for the new array of data files. The corrections can be subtle changes in hard-coded formulae for our two 12-month forecast methods, as well as large-scale modifications in our data pipeline controlling the flux of new data to route them to the proper archive file and database.
Over the past 4 years a community effort has been carried out to revise entirely the historical sunspot number series. A good overview of the analyses and identified corrections is provided in the recent review paper:
Clette, F., Svalgaard, L., Vaquero, J.M., Cliver, E. W., "Revisiting the Sunspot Number. A 400-Year Perspective on the Solar Cycle", Space Science Reviews, Volume 186, Issue 1-4, pp. 35-103.
This is actually the first deep revision of the sunspot number since its creation By R. Wolf in 1849.