Published Tuesday, December 30, 2003 in the San Jose Mercury News

Space weather forecasts are tied to sun's activity
By Jan Null

The forecast: Occasional solar flares, geomagnetic storms, increasing solar winds and magnificent auroras.

While it's not a prediction you are likely to see on the daily weather page, there are forecasts made for all of these phenomena as part of a field called "space weather.'' More space physics than meteorology, it deals primarily with the interaction of the sun's energy and particles with the Earth's magnetic field and the atmosphere.

The Earth not only receives radiant energy from the sun but also sits in the path of streams of solar particles. This discharge of high-energy particles happens when gases on the extremely hot sun are stripped of their electrons and acquire enough speed to escape the sun's gravity.

Known as "plasma'' or "solar wind,'' such ions and electrons spread out in all directions, including toward the Earth, at speeds of 200 to 400 miles per second. As they near the Earth, they interact with its magnetic field in what is known as the magnetosphere. This is a region about 60 miles above the Earth where these energetic solar particles are trapped and collide with air molecules.

Some energy is transferred to these air molecules, which in turn can give off visible light that glows like neon high in the sky. This is the aurora borealis or "northern lights'' in the Northern Hemisphere and the aurora australis or "southern lights'' in the Southern Hemisphere. Each atmospheric gas has slightly different properties and its own characteristic glow -- atmospheric oxygen glows green or red while molecular nitrogen gives off reds and violets. The aurora is most common in the polar regions because this is where the lines of the Earth's magnetic field converge and concentrate this phenomenon.

Sometimes violent eruptions on the sun produce solar flares and the even more dramatic coronal mass ejection (CME), which is a large bubble of rapidly expanding solar gases. When a CME expands in the direction of the Earth, the result can be spectacular space weather or magnetic storms. These may be in the form of more spectacular and far-reaching auroras or the disruption of power grids, and radio and satellite communications.

The National Atmospheric and Oceanic Administration, which oversees the National Weather Service's earthbound forecasts, also monitors space weather. The Space Environment Center tracks solar storms and their impact upon the Earth's atmosphere. Detailed information, including the latest space weather advisories and aurora forecasts, can be found online at and another excellent space weather resource is .

Q How often are auroras seen in California? Katherine Lewis - Santa Rosa

A Historically, an aurora is visible in the Bay Area about once every five to 10 years. Because of light pollution from the metropolitan area, it takes a fairly strong aurora event to be visible. Predicting a strong aurora requires monitoring the weather on the sun, in particular the eruption of solar flares and CMEs. These forecasts are available on the Web sites listed above. Your best bet to see one would be to monitor these forecasts for increased solar activity and then head away from the city lights.

Q In reports on the fires in Southern California, reporters on TV and in newspapers call the region's hot dry winds ``the Santa Ana wind.'' Santa Ana residents don't appreciate the name. Lately, I heard one explanation for the name -- it blows through the Santa Ana Canyon. I've also read that originally the winds were called "Santanas.'' Vivian Walz - Sunnyvale

A The origin and even the original spelling of the terms for these winds are unclear, and during the past century both Santa Ana and Santana winds have been used. The term "Santana winds'' is said to have originated in Spanish California when the hot dry winds were called "devil winds.'' Other sources credit the persistence and ferocity of these winds through the Santa Ana Canyon in Orange County as the reason for their being called Santa Anas. A third reasoning has an Associated Press correspondent mistakenly identifying Santana winds as Santa Ana winds in a 1901 dispatch.

Jan Null, founder of Golden Gate Weather Services, is a retired lead forecaster with the National Weather Service. Send questions to him c/o WeatherCorner, San Jose Mercury News, 750 Ridder Park Drive, San Jose, Calif. 95190. You also can telephone questions at (510) 657-2246, fax them to (510) 315-3015 or e-mail, or fill out a form online at Please indicate in your e-mail what city you live in.