Category

Effect

Physical measure

Average Frequency
(1 cycle = 11 years)

Scale

Descriptor

Duration of event will influence severity of effects

Radio Blackouts

GOES X-ray peak brightness by class (and by flux*)

Number of events when flux level was met;
(number of storm days)

R 5

Extreme

HF Radio:Complete HF (high frequency**) radio blackout on the entire sunlit side of the Earth lasting for a number of hours. This results in no HF radio contact with mariners and en route aviators in this sector.

Navigation: Low-frequency navigation signals used by maritime and general aviation systems experience outages on the sunlit side of the Earth for many hours, causing loss in positioning. Increased satellite navigation errors in positioning for several hours on the sunlit side of Earth, which may spread into the night side.

X20
(2 x 10^-3)

Less than 1 per cycle

R 4

Severe

HF Radio: : HF radio communication blackout on most of the sunlit side of Earth for one to two hours. HF radio contact lost during this time.

Navigation: Outages of low-frequency navigation signals cause increased error in positioning for one to two hours. Minor disruptions of satellite navigation possible on the sunlit side of Earth.

X10
(10^-3)

8 per cycle
(8 days per cycle)

R 3

Strong

HF Radio: Wide area blackout of HF radio communication, loss of radio contact for about an hour on sunlit side of Earth.

Navigation: Low-frequency navigation signals degraded for about an hour.

X1
(10^-4)

175 per cycle
(140 days per cycle)

R 2

Moderate

HF Radio: Limited blackout of HF radio communication on sunlit side, loss of radio contact for tens of minutes.

Navigation: Degradation of low-frequency navigation signals for tens of minutes.

M5
(5 x 10^-5)

350 per cycle
(300 days per cycle)

R 1

Minor

HF Radio: Weak or minor degradation of HF radio communication on sunlit side, occasional loss of radio contact.

Navigation: Low-frequency navigation signals degraded for brief intervals.

M1
(10^-5)

2000 per cycle
(950 days per cycle)