The Sun plays a role in another environmental
issue that human activity influences.
As the Sun winds down its activity, it
delivers less frequent and less punishing blows
of various forms of radiation to Earth's
atmosphere. That's good news for ozone, which
gets zapped by the Sun's high-energy storms.
Ozone occurs naturally in the stratosphere
and filters out much of the Sun's ultraviolet
In a study released in the August 1 issue of
Geophysical Research Letters, researchers
presented new evidence confirming a long-held
theory that large solar storms deplete the
upper-level ozone for weeks to months.
NASA researchers studied the effects of a
solar storm that hit Earth between July 14 and
16 last year, smack in the middle of the solar
cycle's peak. During such storms, protons
bombarded the upper atmosphere, breaking up
molecules of gases like nitrogen and water
vapor. Once freed, those atoms react with ozone
molecules and break them down into other
Using satellites to examine ozone before and
after the event, the researchers found a small
but measurable effect.
"If you look at the total atmospheric column,
from your head on up to the top of the
atmosphere, this solar proton event depleted
less than one percent of the total ozone in the
Northern Hemisphere," said Charles Jackman, a
researcher at NASA's Goddard Space Flight Center
Laboratory and lead author of the study.
That hole above our heads
Jay Herman, another Goddard scientist, also
uses satellites to study ozone. Herman said the
11-year solar cycle alters the amount of ozone
roughly 2 percent from the peak to the low point
Other causes, such as Earth's seasons and the
resulting change in sunlight at the poles,
create greater fluctuations.
"To put this in perspective, the global
average seasonal variation is 5-8 percent,"
Herman said. And in both the Northern and
Southern hemispheres, where seasonal holes
develop above the poles, ozone can vary as much
as 25 percent each year.
The ozone holes are bounded by rings of
high-altitude winds that circle each pole.
"There always has been a springtime reduction
of ozone in the Antarctic," Herman said. "In
recent years, the ozone hole has expanded to
fill in the maximum area available within the
polar vortex winds and has removed almost all of
the ozone that is possible."
Last year, the hole above Antarctica reached
Herman said it's too early to tell what will
happen this year.
The relatively small populations of humans
who live beneath the thinned layers of ozone can
be exposed to higher doses of ultraviolet
radiation, which studies suggest can lead to
cancer and premature aging of the skin. Most
researchers agree that the increased depletion
is caused by the human production of
chlorofluorocarbons, which means the human
impact far exceeds that of the solar cycle.
But even this relationship is not so simple.
Last year, researchers learned that the
planet's surface temperature might affect ozone
levels. Scientists at NASA's Jet Propulsion
Laboratory found that the unusually cold
temperatures in the stratosphere, 10 to 30 miles
(16 to 48 kilometers) up, are related to balmy
winters at ground level. The cold stratosphere
was in turn blamed for fueling ozone
Relief for astronauts, satellites, power
The reduced solar activity also means less
radiation that would threaten astronauts on
spacewalks. And in coming years, fewer storms
will bombard satellites, which can be damaged by
severe space weather.
Even power grids on Earth can be affected, as
happened in 1989 when a power surge triggered by
solar energy damaged transformers of the
Hydro-Quebec power system, leaving 6 million
people in Canada and the Northeast United States
without power for more than nine hours. No such
damage has occurred during this peak, part of
what scientists call Sunspot Cycle
But experts caution that even though the peak
is past, severe solar storms can still crop up.
In fact, the strongest solar flare of this
after the peak, in April 2001.
And the Sun's rhythm guarantees that another
peak is roughly three presidential elections
With more and more satellites in space, and
Earth's power grids operating under greater
stress all the time, scientists and engineers
are eager to know how strong the next maximum
will be, and when it is due (the roughly 11-year
cycle has been known to range anywhere from
eight to 15 years).
Given recent predictability, it's a fair bet
the next peak will occur around 2012. But its
potential impact is unknown.
"It is still too early to reliably predict
the size of the next cycle," says Hathaway, the
solar physicist. "We won't have good estimates
until near solar minimum, around
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