Space Weather Scales

“Space weather” is primarily created by solar activity. This activity is monitored by the Space Environment Center, a part of the U.S. National Oceanic and Atmospheric Administration.

In November 9, 1999 S.E.C. introduced the NOAA Space Weather Scales to provide a way of describing to the public space weather conditions and their possible effects on people and systems. See www.sec.noaa.gov/NOAAscales The wording of the effects descriptions was revised on November 1, 2000.

The scales describe the environmental disturbances for three types of events:

The descriptions of effects given below are not the official wording; they have been enlarged and edited in an attempt to increase clarity. For the official version, visit the Space Environment Center's Web site at the URL given above.

NOAA Space Weather Scale for Geomagnetic Storms
(a simplified version)
Category Effect
Physical measure¹
Average frequency
in one sunspot cycle of 11 years
Scale Descrip-
tion
G 5 Extreme Power systems: Some electrical grid systems may collapse. Transformers may be damaged.
Spacecraft operations: Surfaces of spacecraft may acquire a strong electric charge. Problems with orientation, uplink/downlink, and tracking satellites.
Other systems: Currents induced in pipelines can reach hundreds of amps. HF (high frequency) radio propagation may be impossible in many areas for 1 or 2 days. Satellite navigation may be degraded for days. Low-frequency radio navigation can be out for hours.
Aurora (the “northern lights”)²: sometimes seen as far south as Florida and southern Texas.
Kp = 9 4 events, 4 days on which there was an event
G4 Severe Power systems: The electric grid may experience widespread voltage stability problems. Protective devices may trip mistakenly, removing portions of the grid.
Spacecraft operations: may experience surface charging and tracking problems, orientation problems may require corrections.
Other systems: induced pipeline currents affect preventive measures. HF radio propagation sporadic. Satellite navigation degraded for hours. Low-frequency radio navigation disrupted.
Aurora: sometimes seen as far south as Alabama and northern California.
Kp = 8, including
 a 9-
100 events, 60 days on which there was an event
G3 Strong Power systems: Voltage corrections required. False alarms triggered on protection devices. High “gas-in-oil” transformer readings likely.
Spacecraft operations: surface charging on satellite components, increased drag on satellite, and orientation problems need corrections.
Other systems: intermittent satellite navigation and low-frequency radio navigation problems. HF radio intermittent. Aurora: seen as far south as Illinois and Oregon.
Kp = 7 200 events,
130 days on which there was an event
G 2 Moderate Power systems: High-latitude power systems affected.
Spacecraft operations: corrective actions are required by ground control. Changes in drag affect orbit predictions.
Other systems: HF radio propagation fades at higher latitudes. The aurora is seen as low as 50 degrees.
Kp = 6 600 events, 360 days on which there was an event.
G 1 Minor Power systems: Weak power grid fluctuations.
Spacecraft operations: Minor impact on satellite operations.
Other systems: Migratory animals begin to be affected.
Aurora: commonly seen in northern Michigan and Maine.
Kp = 5 1700 events,
900 days on which there was an event.

1. Kp levels measured every 3 hours, although other physical measures are also considered.

2. Our use of “south” is somewhat misleading. It depends, not on the geographic latitude, but the geomagnetic latitude. The aurora is, of course, seen in the Southern Hemisphere as well as the Northern, and in Europe as well as North America. Our apologies for the US-centric nature of the information here.

NOAA Space Weather Scale for Solar Radiation Storms
(a simplified version)
Category Effect
Physical measure:
flux level of ≥10 MeV particles (ions)¹
Average frequency
in one 11- year cycle²
Scale Descrip-
tion
S5 Extreme Biological: Unavoidable high radiation hazard to astronauts on extra-vehicular activity. Possible exposure of passengers and crew in commercial jets at high latitudes to high radiation levels (equivalent to approximately 100 chest x-rays).
Satellite operations: Satellites may be rendered useless. Damage to computer memory may cause loss of control, serious noise in image data. Star-trackers may be unable to locate sources. Permanent damage to solar panels possible.
Other systems:
Possible complete blackout of HF communications in the polar regions, and position errors make navigation operations extremely difficult.
10⁵ Fewer than 1 event
S4 Severe Biological: Unavoidable radiation hazard to astronauts on extra vehicular activity. Possible elevated radiation exposure to passengers and crew in commercial jets at high latitudes (equivalent to approximately 10 chest x-rays).
Satellite operations: memory device problems, noise on imaging systems, star-trackers cause orientation problems. Solar panels may be degraded.
Other systems: Blackout of HF radio communications through the polar regions and increased navigation errors over several days are likely.
10⁴ 3 events
S3 Strong Biological: radiation hazard avoidance recommended astronauts on EVA. Passengers and crew in commercial jets at high latitudes may receive radiation equivalent to approximately 1 chest x-ray.
Satellite operations: likely single-event upsets, noise in imaging systems. Permanent damage to exposed components/detectors. Efficiency of solar panels may be permanently reduced.
Other systems: Degraded HF radio propagation through the polar caps and navigation position errors.
10³ 10 events
S2 Moderate Biological: None.
Satellite operations: Infrequent single-event upsets possible.
Other systems: Small effects on HF propagation throughout the polar regions. Navigation at the polar caps likely to be affected.
10² 25 events
S1 Minor Biological: None.
Satellite operations: None.
Other systems: Minor impacts on high frequency radio in the polar regions.
10 50 events

1. Flux levels are 5-minute averages. Flux in particles per second-steradian-square centimeter.

2. These events can last more than one day.

NOAA Space Weather Scale for Radio Blackouts
(a simplified version)
Category Effect
Physical measure:
GOES X-ray peak brightness class
and (flux¹)
Average frequency
in one 11-year sunspot cycle
Scale Descrip-
tion
R5 Extreme HF Radio: Complete high frequency (HF) radio blackout on the entire sunlit side of the Earth lasting hours, so no HF radio contact with ships or planes en route.
Navigation: Low-frequency navigation signals 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 × 10⁻³ watts per square meter)
Less than 1 event
R4 Severe HF Radio: HF radio communication blackout for one to two hours on most of the sunlit side of Earth. 
Navigation: Outages of low-frequency navigation signals cause increased error in positioning for mariners and general aviators for one to two hours. Minor disruptions of satellite navigation possible on the sunlit side of Earth.
X10
(10⁻³ watts per square meter)
8 events, 8 days on which there was an event
R3 Strong HF Radio: Wide area blackout of HF radio communication signals. Radio contact with ships and planes lost for about an hour on Earth's sunlit side.
Navigation: Low-frequency navigation signals degraded for about an hour, affecting maritime and general aviation positioning.
X1
(10⁻⁴ watts per square meter)
175 events, 140 days on which there was an event
R2 Moderate HF Radio: Limited blackout of HF radio communication signals on sunlit side. Radio contact with ships and planes lost for tens of minutes.
Navigation: Degradation of low-frequency navigation signals for tens of minutes affecting maritime and general aviation positioning.
M5
(5 × 10⁻⁵ watts per square meter)
350 events, 300 days on which there was an event
R1 Minor HF Radio: Weak or minor degradation of HF radio communication signals on Earth's sunlit side. Radio contact with ships and planes occasionally lost.
Navigation: Low-frequency navigation signals degraded for brief intervals.
M1
(10⁻⁵ watts per square meter)
2000 events, 950 days on which there was an event

1. Flux, measured in the 0.1-0.8 nanometer range, in watts per square meter.  Other physical measures may also be considered in determining the classification.

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