SpaceWeather

Storms from the Sun

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Weather Service

Space Weather

Storms from the Sun

U.S. Department of Commerce

National Oceanic and Atmospheric Administration

National Weather Service
1 | SPACE WEATHER

WHAT IS SPACE WEATHER?

Activity on the Sun can cause space weather storms that affect us here on Earth. 

Solar storms can impact the technology we rely on everyday: Global Positioning 

Systems (GPS), satellites, and electric power grids. Just as with other types of 

weather, the National Weather Service forecasts space weather disturbances and 

serves as the official source for civilian alerts and warnings. 

Space weather is a consequence of the behavior of the Sun, the nature of Earth’s 

magnetic field and atmosphere, and our location in the solar system. There are 

various phenomena that originate from the Sun that can result in space weather 

storms. Outbursts from huge explosions on the Sun—Solar Flares and Coronal 

Mass Ejections (CME)—send space weather storms hurling outward through our 

solar system. The Sun also emits a continuous stream of radiation in the form of 

charged particles that make up the plasma of the solar wind. 

Solar Flares 

are huge explosions 

on the Sun. A flare 

appears as a sudden, 

intense brightening 

region on the Sun, 

typically lasting 

several minutes to 

hours. Flares are 

seen as bright areas 

on the Sun in optical 

wavelengths and as 

bursts of noise in radio 

wavelengths. The 

primary energy source 

of flares is the tearing 

and reconnection of 

strong magnetic fields. 

The electromagnetic 

emission produced 

during flares travels 

at the speed of light, 

taking about 

8 minutes—rapidly 

affecting the dayside 

of Earth. 

Coronal Mass 

Ejections 

are explosive 

outbursts of plasma 

from the Sun’s outer 

atmosphere, the 

Corona. The blast 

of a CME typically 

carries roughly a 

billion tons of material 

outward from the Sun 

at speeds as fast as 

hundreds of kilometers 

per second. A CME 

contains particle 

radiation (mostly 

protons and electrons) 

and powerful magnetic 

fields. In contrast to 

solar flares, CMEs are 

not particularly bright, 

may take hours to fully 

erupt from the Sun, 

and typically take 1-4 

days to travel to Earth. 

Solar Particle 

Events 

release large numbers 

of high energy 

charged particles, 

predominately protons 

and electrons, which 

are accelerated to 

large fractions of the 

speed of light. These 

particles may arrive 

at Earth between 30 

minutes and several 

hours.

A dramatic example 

of the effects of space 

weather occurred in 

March 1989 when a 

solar storm knocked out 

power in Quebec for 

up to 36 hours. The 

Hydro-Quebec electrical 

utility went from full 

operating capacity to 

blackout status in 92 

seconds. Six million 

people were plunged 

into cold and darkness.

Below is an example of a CME 

erupting from the Sun. 

Source: NASA.
SPACE WEATHER | 2

SPACE WEATHER AND THE SOLAR CYCLE

The number of sunspots on the surface of the Sun increases and decreases 

in solar cycles of approximately 11 years. Solar Minimum refers to the several 

years when the number of sunspots is lowest; Solar Maximum occurs in the 

years when sunspots are most numerous. The Sun is usually very active when 

sunspot counts are high, however, severe storms can occur anytime during the 

solar cycle. Sunspots show where the Sun’s magnetic field energy is building 

up and where it could release to cause solar flares and CMEs. The Sun gives 

off more radiation than usual during solar maximum. This extra energy creates 

changes in the Earth’s upper atmosphere. 

Sunspots

are dark, cooler areas on the solar surface that 

contain strong, constantly shifting magnetic 

fields. A moderate-sized sunspot is many times 

larger than the size of the Earth. 

Sunspots form over periods lasting from days 

to weeks, and can persist for weeks and even 

months before erupting or dissipating. 

Sunspots occur when strong magnetic fields 

emerge through the solar surface and allow the 

area to cool slightly, from a background value of 

6000°C down to about 4200°C. This cooler area 

appears as a dark spot on the Sun. As the Sun 

rotates, sunspots on its surface appear to move 

from left to right. It takes the Sun 27 days to 

make one complete rotation. 

The image below shows a large 

sunspot cluster at the center of 

the Sun, extending more than 

100,000 km from end to end. 

Each of the dark cores is larger 

than Earth. Source: NASA/SDO.

Shown is the approximately 

11 year quasi-periodic 

variation in the sunspot 

number. The polarity pattern 

of the magnetic field reverses 

with each cycle. An increase 

of solar activity, such as 

solar flares and CMEs, 

occurs frequently during the 

maximum sunspot period.
WHAT ARE THE IMPACTS OF SPACE WEATHER?

Electric Power

Large currents in the ionosphere can induce currents in power lines. Surges 

from these induced currents can cause massive network failures and 

permanent damage to electric grid components.

Navigation Systems

Disturbances in the ionosphere can cause degradation in GPS range 

measurements and in severe circumstances, loss of lock by the receiver on 

the GPS signal.

Aviation

Space weather storms can cause lost or degraded communications, radiation 

hazards to crew and passengers, unreliable navigational information, and 

problems with flight-critical electronic systems.

Human Space Exploration

Energetic particles present a health hazard to astronauts on space missions 

as well as threats to electronic systems. During space missions, astronauts 

outside spacecraft are less protected and more exposed to space radiation. 

Satellite Operations

Highly energetic ions penetrate electronic components, causing bit-flips in 

a chain of electronic signals that can result in improper commands within 

the spacecraft or incorrect data from an instrument. Less energetic particles 

contribute to a variety of spacecraft surface charging problems, especially 

during periods of high geomagnetic activity. 

Surveying

Magnetic field changes associated with geomagnetic storms directly affect 

operations that use the Earth’s magnetic field for guidance, such as magnetic 

surveys, directional drilling, or the use of magnetic compasses. Ionospheric 

disturbances cause errors in location obtained from GPS signals.

Communications

Communications at all frequencies may be affected by space weather. High 

frequency (HF) radio communications are more routinely affected because 

this frequency band depends on reflection by the ionosphere to carry signals 

great distances.

3 | SPACE WEATHER
Primary Users of Space Weather Data

Electric Power Grid Operators use geomagnetic storm detection and 

warning products to maximize power grid stability and to mitigate power grid 

component damage and large-scale blackouts. 

Spacecraft Launch Operators use radiation products to avoid electronic 

problems on navigation systems, preventing launch vehicles from going off 

course and being destroyed.

Spacecraft Operations and Design staff rely on space weather products to 

avoid electronic problems. Space weather effects on satellites vary from simple 

repairs to total mission failure.

Manned Spaceflight activities are altered to avoid or mitigate effects of 

radiation storms impacting crews and technological systems.

Navigation Systems depend on space weather information to ensure the 

integrity and safe use of electronic navigational systems, such as GPS.

Aviation Operators use crucial information on space weather impacts—

such as communication outages, potentially harmful radiation, and navigation 

errors—to adjust routes and altitudes.

Communications Operators anticipate and react to space weather activity to 

mitigate impacts occurring over a wide range of communications frequencies 

used by emergency management officials, search and rescue systems, and 

many others.

Surveying and Drilling Operations rely on accurate and timely space weather 

products for safe and efficient high-resolution land surveying and sea drilling.

A growing number of customers are realizing societal and economic benefits 

from space weather products and services. Expect this trend to continue as 

the world becomes increasingly dependent on space-based systems and other 

technologies vulnerable to hazardous space weather. 

SPACE WEATHER | 4

WHO BENEFITS FROM SPACE WEATHER FORECASTS?

Accurate and timely space weather information is vital in mitigating storm 

impacts on our technological infrastructure. Geomagnetic storms can cause 

widespread electrical blackouts, resulting in significant loss of life and a 

potential economic loss in the billions of dollars. Polar flights rerouted due to 

space weather cost airlines an average of more than $100,000 per flight. If 

airborne survey data or marine seismic data are degraded by solar activity, the 

financial impacts can range from $50,000 to $1,000,000. 

Without 

space weather 

forecasts industry 

can lose:

$100 Billion

Loss in space 

assets from a 

worst-case space 

weather storm

$1 Million

Loss to surveying 

and drilling 

companies to halt 

operations due to 

space weather

$100,000 

Cost to divert a 

polar flight due to 

space weather
5 | SPACE WEATHER

A space weather forecast begins with a thorough analysis of the Sun. 

Forecasters use many different types of solar images to analyze active solar 

regions, localized areas that typically contain enhanced magnetic fields and 

sunspots. Sunspot groups can be many times the size of Earth and contain 

complex magnetic structures. Forecasters analyze the size of active regions, 

assess their magnetic complexity, and evaluate growth and decay. Following this 

analysis, forecasters will predict the probability of a solar flare.

Forecasters use a number of computer models 

to determine the likely effects of solar events on 

Earth’s atmosphere and magnetosphere. These 

models help forecasters estimate when the 

effects will begin, how long they will last, and 

how severe the event will be. Space weather 

forecasters also analyze the 27-day recurrent 

pattern of solar activity. Based on a thorough 

analysis of current conditions, compared to past 

conditions, forecasters use numerical models to 

predict space weather on times scales ranging 

from hours to weeks. 

NOAA’s Space Weather Prediction Center 

(SWPC), located in Boulder, Colorado, operates 

24 hours a day and 7 days a week. SWPC 

continuously monitors conditions on the Sun 

using data received from spacecraft and ground-based observatories around 

the globe. SWPC leverages space weather observations, as well as research 

and development supported by the National Science Foundation and National 

Aeronautics and Space Administration (NASA), the Department of Defense and 

the U.S. Geological Survey. 

SWPC works closely with the Air Force Weather Agency to ensure forecast 

coordination and product compatibility between the civil and military sectors. 

In addition to being the official source of U.S. civilian space weather alerts and 

warnings, SWPC serves as the World Warning Agency for the 14 Regional 

Warning Centers of the International Space Environment Services (ISES): 

Australia, Belgium, Brazil, Canada, China, Czech Republic, India, Japan, Korea, 

Poland, Russia, South Africa, and Sweden. 

SWPC forecasters communicate current and future space weather conditions 

and the possible effects using a variety of products. Some of the products 

reference the NOAA Space Weather Scales. These scales are similar to those 

describing hurricanes (e.g., Category 4), tornadoes (e.g., EF-5), and earthquakes 

(e.g., 7 on the Richter Scale). Space weather scales describe radio blackouts 

(R1-5), solar radiation storms (S1-5), and geomagnetic storms (G1-5). The 

scales list possible impacts for each level (see Pages 9-11). The scales also 

indicate how often such events happen and give a measure of the intensity of the 

physical causes (i.e., x-ray flares, proton fluxes, or magnetic disturbances).

HOW IS SPACE WEATHER PREDICTED?

NOAA Space Weather Prediction 

Center Forecast office. 

Source: NOAA. 
SPACE WEATHER | 6

SPACE WEATHER STORMS

Radio Blackouts

Radio Blackouts are caused by bursts of X-ray and Extreme Ultra Violet radiation 

emitted from solar flares. Radio blackouts primarily affect High Frequency (HF) 

(3-30 MHz) communication, although fading and diminished reception may spill 

over to Very High Frequency (VHF) (30-300 MHz) and higher frequencies. These 

storms are a consequence of enhanced electron densities caused by solar flare 

emissions. The emissions ionize the sunlit side of Earth, which increases the 

amount of energy lost as radio waves pass through this region.

Radio blackouts are among the most common space 

weather events to affect Earth. Minor events occur, 

on average, 2000 times each solar cycle. Blackouts 

are by far the fastest to impact our planet. The 

X-rays creating radio blackouts arrive at the speed of 

light–8 minutes from Sun to Earth, making advance 

warnings difficult. When flares occur, however, 

SWPC measures their intensity and forecasts their 

duration. Usually the radio blackouts last for several 

minutes, but they can last for hours.

The impacts of Radio Blackouts are felt by industries 

relying on HF radio communication and low 

frequency signals, primarily the aviation and marine 

industries. 

Solar Radiation Storms

Solar radiation storms occur when large quantities 

of charged particles, protons and electrons, are accelerated by processes at or 

near the Sun. When these processes occur, the near-Earth satellite environment 

is bathed with high energy particles. Earth’s magnetic field and atmosphere offer 

some protection from this radiation, but the amount of protection is a function of 

altitude, latitude, and magnetic field strength. The polar regions are most affected 

by energetic particles because the magnetic field lines at the poles extend 

vertically downwards, allowing the particles to spiral down the field lines and 

penetrate into the atmosphere, increasing ionization.

Energetic protons reach Earth a half hour to several hours after a solar eruption. 

Solar radiation storms can last from a few hours to days, depending on the 

magnitude of the eruption. Solar radiation storms can occur at any time during 

the solar cycle but tend to be most common around solar maximum.

Solar radiation storm impacts include loss of HF radio communications through 

the polar regions, navigation position errors, elevated radiation exposure to 

astronauts, and to passengers and crew in aircraft at high altitudes and latitudes, 

and damage to satellite systems.

Above is an example of a solar 

flare. Flares can result in lost 

or degraded communications 

and navigation position errors. 

Source: NOAA/GOES-15.
Geomagnetic Storms 

Geomagnetic storms, strong disturbances to Earth’s magnetic field, pose 

problems for many activities, technological systems, and critical infrastructure. 

The Earth’s magnetic field changes in the course of a storm as the near-Earth 

system attempts to adjust to the jolt of energy from the Sun carried in the solar 

wind. CMEs and their effects can disturb the geomagnetic field for days at a time.

The most visible attribute of a geomagnetic storm is the aurora, which 

becomes brighter and moves closer to the equator. This heightened aurora 

signals the vigorous electrodynamic processes at play as they respond to 

the burst of energy. 

Geomagnetic storms usually last a few hours to days. The strongest storms 

may persist for up to a week. A string of CMEs may cause prolonged disturbed 

periods related to the additional energy being pumped into Earth’s magnetic 

field. The frequency of geomagnetic storms, in general, depends on where 

we are in the solar cycle–with most storms occurring near solar maximum; 

however, these storms are also common in the declining phase due to highspeed solar wind streams.

Geomagnetic storms induce currents that can have significant impact on 

electrical transmission equipment. Electric power companies have procedures 

in place to mitigate the impact of geomagnetic storms. 

7 | SPACE WEATHER

Example of an Aurora Borealis 

or Northern Lights. Source: 

U.S. Air Force.
NOAA Space Weather Scale: Geomagnetic Storms

*Based on this measure but other physical measures are also considered.

**For specific locations around the globe, use geomagnetic latitude to determine likely sightings

SPACE WEATHER | 8

Category Effect Physical

Measure

Average 

Frequency

(1 cycle=

11 years)

Scale/

Descriptor

Duration of Event Influences 

Severity of Effects 

Kp values*

determined 

every 3 hours

Events when Kp 

level met; 

(# of storm days)

G5 

Extreme

Power systems: widespread voltage control problems and protective 

system problems can occur, some grid systems may experience complete 

collapse or blackouts. Transformers may experience damage.

Spacecraft operations: may experience extensive surface charging, problems with orientation, uplink/downlink and tracking satellites. 

Other systems: pipeline currents can reach hundreds of amps, HF radio 

propagation may be impossible in many areas for one to two days, satellite 

navigation may be degraded for days, low-frequency radio navigation can 

be out for hours, and aurora has been seen as low as Florida and southern 

Texas (typically 40° geomagnetic lat.).** 

Kp=9 4 per cycle

(4 days per 

cycle)

G4 

Severe

Power systems: possible widespread voltage control problems and some 

protective systems will mistakenly trip out key assets from the grid.

Spacecraft operations: may experience surface charging and tracking 

problems, corrections may be needed for orientation problems.

Other systems: induced pipeline currents affect preventive measures, HF 

radio propagation sporadic, satellite navigation degraded for hours, lowfrequency radio navigation disrupted, and aurora has been seen as low as 

Alabama and northern California (typically 45° geomagnetic lat.).** 

Kp=8 100 per cycle

(60 days per 

cycle)

G3 

Strong

Power systems: voltage corrections may be required, false alarms triggered on some protection devices.

Spacecraft operations: surface charging may occur on satellite components, drag may increase on low-Earth-orbit satellites, and corrections may 

be needed for orientation problems.

Other systems: intermittent satellite navigation and low-frequency radio 

navigation problems may occur, HF radio may be intermittent, and aurora 

has been seen as low as Illinois and Oregon (typically 50° geomagnetic 

lat.).** 

Kp=7 200 per cycle

(130 days per 

cycle)

G2 

Moderate

Power systems: high-latitude power systems may experience voltage 

alarms, long-duration storms may cause transformer damage.

Spacecraft operations: corrective actions to orientation may be required 

by ground control; possible changes in drag affect orbit predictions.

Other systems: HF radio propagation can fade at higher latitudes, and 

aurora has been seen as low as New York and Idaho (typically 55° geomagnetic lat.).** 

Kp=6 600 per cycle

(360 days per 

cycle)

G1 

Minor

Power systems: weak power grid fluctuations can occur. 

Spacecraft operations: minor impact on satellite operations possible. 

Other systems: migratory animals are affected at this and higher levels; aurora is commonly visible at high latitudes (northern Michigan and 

Maine).** 

Kp=5 1700 per 

cycle

(900 days per 

cycle)
9 | SPACE WEATHER

Category Effect Physical

Measure

Average Frequency

(1 cycle=11 years)

Scale/

Descriptor

Duration of Event Influences 

Severity of Effects

Flux level of 

> 10 MeV 

particles 

(ions)* 

Number of events 

when flux level 

was met 

(# of storm days**)

S5

Extreme

Biological: unavoidable high radiation hazard to astronauts on 

EVA (extra-vehicular activity); passengers and crew in high-flying 

aircraft at high latitudes may be exposed to radiation risk. ***

Satellite operations: satellites may be rendered useless, memory impacts can cause loss of control, may cause serious noise 

in image data, star-trackers may be unable to locate sources; 

permanent damage to solar panels possible.

Other systems: complete blackout of HF (high frequency) communications possible through the polar regions, and position 

errors make navigation operations extremely difficult.

105 Fewer than 1 per 

cycle

S4

Severe

Biological: unavoidable radiation hazard to astronauts on EVA; 

passengers and crew in high-flying aircraft at high latitudes may 

be exposed to radiation risk.***

Satellite operations: may experience memory device problems 

and noise on imaging systems; star-tracker problems may 

cause orientation problems, and solar panel efficiency can be 

degraded.

Other systems: blackout of HF radio communications through 

the polar regions and increased navigation errors over several 

days are likely.

104 3 per cycle

S3

Strong

Biological: radiation hazard avoidance recommended for astronauts on EVA; passengers and crew in high-flying aircraft at high 

latitudes may be exposed to radiation risk.***

Satellite operations: single-event upsets, noise in imaging systems, and slight reduction of efficiency in solar panel are likely.

Other systems: degraded HF radio propagation through the 

polar regions and navigation position errors likely.

103 10 per cycle

S2 

Moderate

Biological: passengers and crew in high-flying aircraft at high 

latitudes may be exposed to elevated radiation risk.*** 

Satellite operations: infrequent single-event upsets possible.

Other systems: effects on HF propagation through the polar 

regions and navigation at polar cap locations possibly affected. 

102 25 per cycle

S1

Minor

Biological: none.

Satellite operations: none.

Other systems: minor impacts on HF radio in the polar regions. 

10 50 per cycle

* Flux levels are 5 minute averages. Flux in particles·s-1·ster-1·cm-2. Based on this measure, but other physical measures are also 

considered. 

** These events can last more than one day.

*** High energy particle measurements (>100 MeV) are a better indicator of radiation risk to passenger and crews. Pregnant women 

are particularly susceptible.

NOAA Space Weather Scale: Solar Radiation Storms
SPACE WEATHER | 10

Category Effect Physical

Measure

Average Frequency

(1 cycle=11 years)

Scale/

Descriptor

Duration of Event Influences 

Severity of Effects

GOES 

X-ray peak 

brightness by 

class and by 

flux*

Number of events when 

Flux level was met;

(# of storm days)

R5

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

(2x10-3)

Less than 1 per cycle

R4

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. 

X1

(10-3)

8 per cycle

(8 days per cycle)

R3

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)

R2

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. 

M1

(5x10-5)

350 per cycle

(300 days per cycle)

R1

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)

* Flux, measured in the 0.1-0.8 nm range, in W·m-2. Based on this measure, but other physical measures are also considered. 

** Other frequencies may also be affected by these conditions. 

NOAA Space Weather Scale: Radio Blackouts

NOAA Space Weather Scales are online at www.spaceweather.gov
For the latest information on space 

weather events, please visit: 

www.spaceweather.gov

For the latest information on space 

weather events, please visit: 

www.spaceweather.gov