In 1940 the planetary Kp peaked at 9.0 (G5) on 24 March 1940: 88 storm nights over the year, and 8.3% of its three-hour intervals at storm level.
| Month | Max Kp | Peak day | Storm nights | By class | At storm level | Avg Kp |
|---|---|---|---|---|---|---|
| January | 7.7 | 3 | 11 | G1×8G2×1G3×1G4×1 | 8.1% | 2.5 |
| February | 5.0 | 1 | 3 | G1×3 | 5.2% | 2.3 |
| March | 9.0 | 24 | 13 | G1×5G2×1G3×2G4×4G5×1 | 21.4% | 2.8 |
| April | 8.0 | 3 | 6 | G1×1G3×3G4×2 | 10.4% | 2.3 |
| May | 7.7 | 24 | 6 | G1×2G2×3G4×1 | 6.9% | 2.2 |
| June | 8.3 | 25 | 7 | G1×4G2×2G4×1 | 9.6% | 2.3 |
| July | 7.7 | 13 | 7 | G1×6G4×1 | 4.4% | 2.1 |
| August | 6.3 | 3 | 4 | G1×1G2×3 | 2.8% | 2.0 |
| September | 7.7 | 26 | 6 | G1×3G2×1G3×1G4×1 | 6.7% | 2.2 |
| October | 7.0 | 1 | 7 | G1×4G3×3 | 7.7% | 2.3 |
| November | 6.7 | 13 | 10 | G1×8G2×1G3×1 | 11.3% | 2.5 |
| December | 6.3 | 30 | 8 | G1×5G2×3 | 5.6% | 2.6 |
In the hall of storms: The Easter Sunday storm, 24 March 1940 · Kp 9.0 →
All-time record: Kp 9.0 — reached on 27 days, most recently 2024-05-11.
Ranked from the data: peak Kp, then intervals spent at 9.0. Nicknames and reach notes only where documented.
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