1. ISSI Team: Recalibration of the Sunspot Number Series
Kick-off meeting, 22 Jan 2018
Welcome!

2. Who we are Co-Leaders: Frédéric Clette (Belgium), Mathew Owens (UK)
Team members: Rainer Arlt (Germany), Ed Cliver (USA), Thierry Dudok de Wit (France), Greg Kopp (USA), Laure Lefèvre (Belgium), Mike Lockwood (UK), Andrés Muñoz-Jaramillo (USA), Ilya Usoskin (Finland), Lidia van Driel-Gesztelyi (UK/France/Hungary), José Vaquero (Spain) Young scientist: Theodosios Chatzistergos (Germany) Self-supported experts: Thomas Friedli (Switzerland), Dean Pesnell (USA) and Alexei Pevtsov (USA).

3. What we promised (!)
“…resolve the uncertainties related to the sunspot series and to produce a consensus new-generation series, based on the modern methods and knowledge of physical processes leading to sunspot variability.”
“… provide a consensus "best" sunspot number reference(s), including accurate estimates of the uncertainties, for use by the whole scientific community”

4. Aims of this first meeting
Understand the series and underlying data/techniques used thus far
Identify best practice
Uncertainty estimation
Quality assurance versus quality control
Identify/quantify problem points in the observational records
Discuss possible solutions
Non-sunspot data: Verification/validation/calibration?
Physical understanding of sunspots? E.g., spot-to-group ratios, etc.

5. Expected outputs
Short term, possible: Concise review of the current state of play regarding the sunspot records
Medium term: Repository of “raw” sunspot and group data. Possible inclusion of associated code.
On going: Processing and recovery of new data sources
Long term: Construction of new series using agreed technique(s)
Include comprehensive estimate of uncertainty incorporating both data and technique errors
Long term: Publication of new series and uncertainty estimates

6. Rules of the road None…? Recommendations of the road Post ISSI:
Do interrupt! The aim is discussion
Don’t worry about too much about over-running.
Post ISSI:
Would be advantageous to avoid further “splintering” of the records
Nevertheless, useful to see how a different technique/dataset affects the resultant series
Would be sensible to collaborate as far as possible
But obviously everyone free to pursue their own research lines
Nice to keep the team informed of developments (we can add to ISSI webpage)
Acknowledge ISSI if appropriate

7. Schedule
Monday a.m.
– Welcome, administration, meeting goals & ground rules (Matt, Frédéric) – Friedli (Thomas) – Sunspot number overview & historical context (Laure) “Triad” debrief – Clette & Lefévre and Lockwood et al. (Greg) – Svalgaard & Schatten and Chatzistergos et al. (Mike, Ed)
Monday p.m. Methods 1825-present (1) – Expectation maximization (Thierry) – Wolf number from scratch (Frédéric)
Tuesday a.m. Methods 1825-present (2)
– Backbones (Theo) – Active day fractions (Ilya) – Usoskin et al. (Andrés, Laure)
Tuesday p.m. Data base
– Recent developments for Vaquero et al. data base (José) – Data/software repository (Frédéric, Andrés) – Series release: IAU sanctioning, procedure for updates (Alexei, Frédéric)
Wednesday a.m.
– Open discussion of best practices; analyses needed before ISSI-2(Frédéric, Matt)
Wednesday p.m.
– Working group meetings
Thursday a.m.
– Pre-Schwabe (2) 17th century & Maunder Minimum (Ilya, José, Matt, Andrés)
Thursday p.m.
– Pre-Schwabe (1) 18th century (Rainer, Ilya, Ed) – Open discussion (Lidia)
Friday a.m.
– Uncertainties (Thierry, Laure, Andrés) – Meeting Summary (Lidia, Dean, Alexei) – ISSI-2 (Matt, Frédéric)
Friday p.m.
– Travel, subgroup meetings, etc.

8. “Absolute calibration”
Spot-to-group ratio…
Active-day fraction…
…any statistical property of spots
Rainer: “Any absolute calibration rests on the principle that a given property is constant for every cycle… …That a cycle in the past is similar to the modern period, just scaled up or down.”
Clearly this may not always be true. E.g., Dalton or Maunder minima
But that’s ok!
Need a measure of how valid this assumption is
E.g., is distribution of corrected groups the same as modern period?
If not, use alternative method
E.g., daisy-chaining, with abs. cal. as anchor points.
Just a pinch of heresy

9. The composite series
General agreement that different techniques will be required at different times
How do we (objectively) decide what to use, when?
Figure of merit?
Minimise uncertainty?
Quantitatively compare uncertainties from different methods

10. Final day Group photo! Sign the book Fill in the doodle poll
Meeting summary
Send me your presentations
Future work