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

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