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
http://www.sec.noaa.gov and another
excellent space weather resource is
http://www.spaceweather.com .
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.