Storms of this magnitude can affect power systems and satellite operations. Such storms can also interfere with high frequency radio communications. During such storms, the aurora has been seen as low as Illinois and Oregon.

NOAA forecasters report that this storm, caused by an increase in the solar wind speed, combined with an associated interplanetary magnetic field opposite that of Earth's, struck the Earth's magnetic field on August 17 at 9:40 a.m. EDT. Forecasters issued early low-level warnings at that time, but it took almost 11 hours for the stronger characteristics of a G4 to develop.

A G4 geomagnetic storm can affect power systems with 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, which may require corrections for orientation problems. Other systems affected include satellite navigation, which may be degraded for hours, and low-frequency radio navigation can also be disrupted.

The NOAA Space Environment Center is the nation's official source of space weather alerts and warnings. SEC continually monitors and forecasts Earth's space environment.

NOAA is dedicated to enhancing economic security and national safety through the prediction and research of weather and climate-related events and providing environmental stewardship of the nation's coastal and marine resources. NOAA is part of the U.S. Department of Commerce.

Relevant Web Sites

* NOAA Solar X-ray Imager http://www.sec.noaa.gov/sxi/

* NOAA Solar X-Ray Imager -- Images http://sxi.ngdc.noaa.gov/

* NOAA Space Environment Center http://www.sec.noaa.gov/

* New Solar Storm Detector Sending Real-time Images Used to Warn of Sun's Damaging Storms; Solar X-ray Imager Onboard GOES-12 Environmental Satellite http://www.noaanews.noaa.gov/stories/s1087.htm

IMAGE CAPTION: [http://www.noaanews.noaa.gov/stories/images/sun081803-1538z.jpg (31KB)] NOAA satellite image of the sun taken on Aug. 18, 2003, at 11:38 a.m. EDT. Please credit "NOAA."

For latest view of the sun, http://www.sec.noaa.gov/sxi/latest.html