Geomagnetic Storms

G 5 Extreme

HF radio propagation may be impossible in many areasfor one to two days, satellite navigation may be degraded for days,low-frequency radio navigation can be out for hours, and aurora hasbeen seen as low as Florida and southern Texas.

G 4 Severe

HF radio propagation sporadic, satellite navigationdegraded for hours, low-frequency radio navigation disrupted, andaurora has been seen as low as Alabama and northern California.

G 3 Strong

HF radio may be intermittent, and aurora has beenseen as low as Illinois and Oregon.

G 2 Moderate

HF radio propagation can fade at higher latitudes,and aurora has been seen as low as New York and Idaho.

G 1 Minor

Migratory animals are affected at this and higherlevels; aurora is commonly visible at high latitudes (northernMichigan and Maine).


Solar RadiationStorms

S 5 Extreme

Complete blackout of HF communications possiblethrough the polar regions, and position errors make navigationoperations extremely difficult.

S 4 Severe

Blackout of HF radio communications through the polarregions and increased navigation errors over several days are likely.

S 3 Strong

Degraded HF radio propagation through the polarregions and navigation position errors likely.

S 2 Moderate

Small effects on HF propagation through the polarregions and navigation at polar cap locations possiblyaffected.

S 1 Minor

Minor impacts on HF radio in the polar regions.


Radio Blackouts

R 5 Extreme

Complete HF radio blackout on the entire sunlit sideof the Earth lasting for a number of hours. This results in no HFradio contacts.

R 4 Severe

HF radio communication blackout on most of the sunlitside of Earth for one to two hours. HF radio contact lost during thistime.

R 3 Strong

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

R 2 Moderate

Limited blackout of HF radio communication on sunlitside, loss of radio contact for tens of minutes.

R 1 Minor

Weak or minor degradation of HF radio communicationon sunlit side, occasional loss of radio contact.