The agency on Wednesday released three "Space Weather Scales" modeled on the well-understood scales used for tornadoes or earthquakes, that NOAA will use to broadcast solar storm warnings.

"We are more vulnerable today because we have more satellites flying," said NOAA Administrator D. James Baker. "All of these will have some vulnerability to solar flares."

The largest threat is to the nation's power grid. As local power systems become increasingly interconnected for better resource management, the whole continent's network of transformers becomes one big antenna for the geomagnetic storms that solar storms can touch off.

"Ironically what has made us strong for terrestrial weather has inadvertently become a vulnerability as regards space weather," said John Kappenman, senior engineer for Metatech, a company that predicts solar weather for power companies. "We are weaker today than we were 10 years ago."

Using sun-observing satellites such as SOHO, NOAA can provide up to three hours warning before the effects of solar storms hit Earth. SOHO, a joint NASA-European Space Agency satellite orbits a million miles out from Earth at one of the gravitational balance points between the sun and our planet called Lagrangian point 1 (L-1).

SOHO and another satellite called ACE, which monitors high-energy particles at the L-1 point, provide NOAA with information in enough time to provide warnings for satellite operators and power companies.

The warnings will be displayed on NOAA's Space Environment Center website.

Emergency advisories will also be available through automatic faxing, e-mail notices and paging services. NOAA plans to use some of the other warning systems now employed by the National Weather Service, such as dedicated radio broadcasts of space weather news.

NOAA's new scale involves ranking storms from S-1 to S-5, with the highest number being the most threatening. Fifty S-1 storms are expected in a typical 11-year cycle and would have "minor impacts on high-frequency radio in the polar regions."

An S-5 storm, by contrast, would make radio communication impossible at Earth's poles, effectively destroy some satellites and seriously damage others by frying their on-board computer. It would also deliver radiation doses equivalent to a chest X-ray to passengers in high-flying aircraft at high latitudes. Less than one S-5 event occurs per cycle on average.

"We can expect six to 12 major storms during the three-year period centered on the year 2000," Baker said.

Underlining the potential need for NOAA's plans, the agency's Space Environment Center issued a report Tuesday of a minor "geomagnetic" or solar storm that started Sunday and was associated with a coronal hole now rotating across the face of the sun.

Coronal holes, as shown in the image at the top of this story, are gaps in the sun's outer layer, or corona, which usually acts as a blanket to absorb much of the charged-particle radiation emitted by the sun's inner layers.

A gap in the corona allows high-speed winds of particles to stream into space. If those particles shoot out in the direction of Earth, they cause electromagnetic disturbances that can affect satellites and power generation systems.

Space weather forecasters at the NOAA's Space Environment Center in Boulder, Colo., predict that the storm's effects will be similar to those caused by the same hole when it faced Earth a month ago.

It may cause weak power grid fluctuations, as well as brighter-than-normal aurora displays at high latitudes for the rest of the week. Surface features like coronal holes, sunspots and flares are carried around the solar sphere as the sun completes one rotation every 28 days.