benchmarks/dynamical_systems/sidc_sunspot/data/README.md

data/ — SIDC SILSO Monthly Mean Total Sunspot Number

Source

• Provider: SIDC — Solar Influences Data Analysis Center, Royal Observatory of Belgium
• Data URL: https://www.sidc.be/SILSO/INFO/snmtotcsv.php
• Version: International Sunspot Number v2.0 (ISN v2, recalibrated; Clette et al. 2016, 2021)
• Coverage: Monthly values from January 1749 to present (~3300+ observations)
• Definition: Monthly mean of daily total international sunspot number (ISN), counting both sunspot groups and individual spots weighted by a standard formula.

License

CC-BY-NC-4.0 — Creative Commons Attribution–NonCommercial 4.0 International. https://creativecommons.org/licenses/by-nc/4.0/

Attribution: SIDC, Royal Observatory of Belgium, "SILSO Monthly Mean Total Sunspot Number." Non-commercial use only. If this benchmark is used commercially, a separate data agreement with SIDC is required.

How to rebuild data.csv

bash download.sh

The script:

1. curls the SILSO semicolon-separated CSV (snmtot_raw.csv).
2. Parses columns: year;month;decimal_year;ssn;ssn_std;n_obs;provisional.
3. Drops rows where ssn < 0 (SILSO missing-value sentinel is −1).
4. Computes t_year = year + (month − 0.5) / 12 (mid-month decimal year).
5. Emits data.csv with col 0 = ssn (output).

snmtot_raw.csv and data.csv are both gitignored; only download.sh and this README.md are committed. Rebuild from the script on a fresh clone.

Column meanings

index	name	role	units	description
0	ssn	output	dimensionless	Monthly mean total international sunspot number (ISN v2). Mean of daily totals within the calendar month.
1	t_year	input	decimal year	Decimal year at the midpoint of the month, e.g. 1818.042 for January 1818. Continuous time coordinate.
2	year	input	integer year	Integer calendar year.
3	month	input	integer 1–12	Calendar month. Captures any intra-annual cycle in sunspot activity.
4	ssn_std	input	dimensionless	Standard deviation of daily SSN values within the month. Higher values indicate more day-to-day variability. Not used by current ground_truth.

Shape

3327 rows × 5 columns (as of 2026-04-22; monthly observations from January 1749 to present, after filtering missing values). Benchmark entries typically focus on the more reliable instrumental record from 1818 onward.

Notes

• ISN v2.0: The SILSO v2 recalibration (Clette & Lefevre 2016) rescaled the historical series by a factor of ~1.5 relative to the old v1 (Zürich) series. Always check which version is used when comparing to published solar-cycle analyses.
• Solar cycles: The ~11-year Schwabe cycle (sunspot number) and ~22-year Hale cycle (magnetic polarity) dominate the power spectrum. Cycle length varies between ~9 and ~14 years. No accepted closed-form formula captures this variability.
• Provisional values: Recent months may be marked as provisional (provisional column); these are included but may be revised in future SILSO updates.