Seminar talk by Frédéric Clette

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  • Venue: IRSOL
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Title: The sunspot cycle, from past to future
Presenter: Frédéric Clette, Observatoire Royal de Belgique, WDC – SILSO, Brussels

After a short review of the recent re-calibration work accomplished on
the long-term series of the sunspot number and sunspot group number, I
will present the current effort to recover all original raw data that
are at the base of the sunspot number construction.
This ongoing effort revealed several gaps in the archives of the Zürich
Observatory, paradoxically in the rather recent period of the 20th
century. Quite unexpectedly, it also revealed an as-yet unnoticed break
in the composition of the Zürich observing team and of the international
network of auxiliary stations. It happens to coincide with the sharp
jump found in the scale of the original sunspot number series around
1947, a timing which eluded any clear explanation until now.
As the sunspot number forms the base for many applications including the
mid-term forecast of the solar cycle, I will also introduce the current
modernization work done on three standard prediction methods in use for
several decades at the SILSO data center in Brussels and at the NOAA
Boulder. Altogether, this illustrates how the sunspots bring together the future
and the distant past.