| # 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 |
| bash download.sh |
| ``` |
|
|
| The script: |
|
|
| 1. `curl`s 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. |
| |
