Space Climate 7 Meeting Abstract
Reconstructing the full sunspot number database
Frédéric Clette (Observatoire Royal de Belgique)
The current re-calibrated version of the sunspot number is still entirely based on the Wolf numbers of the Zurich reference station for the period before 1980. Further improvements to the series will require a broader statistical analysis exploiting the entire set of raw sunspot data from all past sunspot observers. This includes the personal raw numbers by the Zurich primary observers and all their assistants, as well as all auxiliary data from external observers, of which only a small part was used in the past production of the Zurich sunspot number. Therefore, since 2017, we undertook the full digitization of all data gathered at the Zurich Observatory since 1849. Here, we report about the completion of all raw sunspot and group counts published in the Mittheilungen of the Zurich Observatory, from 1856 to 1945. We derive some overall statistics and timelines of the observers contained in this database. As most of the collected data were not published anymore in printed form after 1919, we recently started a search for the original source data in the Zurich archives. Thanks to this work, we can now announce the recovery of long-lost data tables containing all data between 1945 and 1980. We describe the information included in those detailed tables that bridge the gap between the Zurich Mittheilungen and the current database of the World Data Center SILSO that starts in 1980, a key missing link connecting the historical series with the current international sunspot index. We conclude on the new unique insights that can and will be extracted from this mass of data, in order to further improve the calibration of the sunspot number time series and solve key pending issues like the Schwabe-Wolf and Wolf-Wolfer transitions in the chain of former reference observers.
Mode of presentation: oral (Need to be confirmed by the SOC)