Table 1 Estimation of scale of space weather events with occurrence probabilities of daily to several times per year, once per year, and once per 10, 100, and 1000 years
| Phenomena | Parameter | Daily–several per year | Once per year | Once per 10 years | Once per 100 years | Once per 1000 years |
|---|---|---|---|---|---|---|
| Solar flare | X-ray peak flux | M1–X1 | X7.6 | X12 | X44 | X101 |
| Energy [erg] | < 2.0 × 1030 | 1.0 × 1031 | 1.0 × 1032 | 1.0 × 1033 | 1.0 × 1034 | |
| Coronal mass ejection (CME) | Velocity [km/s] | 250–450 | 2000 | 3000 | 3800–4500 | 4700–6600 |
| Kinetic energy [erg] | 4.4 × 1033 | 9.8 × 1033 | ||||
| Solar energetic particles (SEPs) | Fluence (≥ 10 MeV) [1010 cm−2] at GEO | ~ 0.1 | ~ 1.0 | ~ 2.4–5.1 | ~ 3.8–14 | |
| EII [%・h] | ~ 190 | ~ 6600 | ~ 223,000 | |||
| Solar radio burst [sfu] | Very high frequency (VHF, 30–300 MHz) | < 2.8 × 109 | ||||
| Ultra-high frequency (UHF, 300–3000 MHz) | < 1.2 × 107 | |||||
| GPS (1176–1602 MHz) | < 1.2 × 107 | |||||
| F10.7 (2800 MHz) | < 1.3 × 107 | |||||
| Microwave (4000–20,000 MHz) | < 3.7 × 107 | |||||
| Variations of relativistic electron flux of the outer radiation belt | Electron fluence (> 2 MeV)[1010 cm−2sr−1] at GEO | ~ 0.1 | ~ 0.6 | ~ 3.0 | ~ 10 | ~ 26 |
| Magnetic storm | Dst index [nT] | ~ − 220 | ~ − 450 ± 30 | ~ − 650 ± 110 | ~ − 930 | |
| Substorm | AL index [nT] | ~ − 3700 | ~ − 4100 | ~ − 4100 | ~ − 4200 | |
| SML index [nT] | − 460 | − 3000 | − 4000 | − 5000 | − 5900 | |
| Total electron content (TEC) | @Tokyo [TECU] | ≥ 90 | ≥ 130 | ≥ 190 | ||
| @Kagoshima [TECU] | ≥ 110 | ≥ 160 | ≥ 230 | |||
| @Hokkaido [TECU] | ≥ 70 | ≥ 105 | ≥ 150 | |||
| Dellinger phenomenon | Absorption [dB] @6.6 MHz (long-circuit) | ~ 71 | ~ 83 | ~ 93 | ~ 100 | |
| Event duration [h] | 0.6–1.3 | 1.8–3.6 | 4.0–6.8 | 7.4–11.9 | ||
|
Sporadic E-layer | Frequency propagating 1,000 km [MHz] | 100 | 110 | ≥ 130 | ||
| Frequency propagating 2,000 km [MHz] | 130 | ≥ 180 | ≥ 180 | |||
| Duration for foEs > 13.3 MHz [h] | ~ 3 | ~ 5 | ||||
| Duration for foEs > 18 MHz [h] | ~ 1–2 | ~ 3 | ||||
| Plasma bubble | Event duration [h] | 4–5 | 6 | |||
| Polar cap absorption (PCA) |
Invariant latitude, day @6.6 MHz 10 dB | 65° | 57° | 53° | 51° | 50° |
| Invariant latitude, night @6.6 MHz 10 dB | 65° | 60° | 56° | 53° | 53° | |
| Minimum duration [h] | 22 | 46 | 71 | 83 | 89 |