The source of space weather, our dynamic sun, shown with a coronal mass ejection that will interact with the terrestrial magnetosphere producing geospace storms. Credit: NASA

Everyone is familiar with changes in the weather on Earth. But "weather" also occurs in space. Just as it drives weather on Earth, the sun is responsible for disturbances in our space environment.

Besides emitting a continuous stream of plasma called the solar wind, the sun periodically releases billions of tons of matter in what are called coronal mass ejections. These immense clouds of material, when directed towards Earth, can cause large magnetic storms in the space environment around earth, the magnetosphere and the upper atmosphere.

The term space weather generally refers to conditions on the sun, in the solar wind, and within Earth's magnetosphere, ionosphere and thermosphere that can influence the performance and reliability of space-borne and ground-based technological systems and can endanger human life or health.

Magnetic storms produce many noticeable effects on and near Earth:

• Aurora borealis, the northern lights, and aurora australis, the southern lights
• Communication disruptions
• Radiation hazards to orbiting astronauts and spacecraft
• Current surges in power lines
• Orbital degradation
• Corrosion in oil pipelines

Forecasting Space Weather Is a Complex Business

• Space weather forecasts are important because radiation from particles from the sun associated with large solar flares can be hazardous to unprotected astronauts, airplane occupants and satellites.
• Scientists recently reported improved methods of forecasting periods of low flare probability.
• Flares are often cause for concern as they can foretell of intense effects at Earth.

• Detecting phenomena occurring on the surface of the sun allows us to monitor solar activity, but knowing that something is heading towards Earth is a key measurement.
• Images of eruptions in the solar corona from NASA's SOHO spacecraft have provided invaluable monitoring capabilities of approaching coronal mass ejections - energetic eruptions on the Sun and primary cause of major geomagnetic storms.

Artist's concept of the twin STEREO observatory studying the sun.
Credit: NASA/JHU Applied Physics Laboratory
Click on image above to enlarge.

Stereoscopic Imaging Will Provide an Extra Dimension for Forecasting

A major advance in space weather forecasting will come from our ability to determine the speed at which the phenomenon is moving. This will be achieved with stereoscopic views of the sun from NASA's Solar TErrestrial RElations Observatory (STEREO) spacecraft. This pair of spacecraft will use 3-D vision to construct a global picture of the sun and its influences.

Solar Signatures Are Just One Way to Monitor Space Weather

Sometimes dramatic events on the sun can be the precursor of huge storms in geospace - Earth's near space environment - but at other times they can have little or no effect. Understanding how this geospace region responds to a variety of solar drivers is the key to predicting space weather.

Similar solar events can cause the Earth's Northern Lights to glow or remain dim.

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July 2000

Solving the Chain - One Link at a Time

• Predicting space weather is a complex problem, because of the intricate interactions between many systems - the Sun, solar wind, Earth's magnetic field, and Earth's atmosphere. Periods of intense activity at Earth can occur during so called "quiet times" on the sun.
• Space weather is a complicated series of events. This improved ability to predict solar quiet times is the first link.
• Just as no one would expect to be able to predict weather in the lower atmosphere solely by observing the Sun, understanding the upper atmosphere of the Earth requires an understanding of how Earth 's atmosphere responds to changes in the space environment.
• Programs, such as NASA's Living With a Star-Geospace mission will provide us with the vital information needed to allow full understanding of the space weather chain.