A new study confirms a long-held theory that large solar storms rain
electrically charged particles down on Earth’s atmosphere and deplete the
upper-level ozone for weeks to months thereafter. New evidence from NASA and
NOAA satellites is helping scientists better understand how man and nature
both play a role in ozone loss.

The study, appearing in the August 1 issue of Geophysical Research Letters,
examined impacts of a series of huge solar explosions on the atmosphere in
the Northern Hemisphere. A solar flare with an associated coronal mass
ejection sent positively-charged protons streaming to Earth from July 14 to
16th, 2000. The bombardment of protons, called a solar proton event, was the
third largest in the last 30 years.

Solar storms consist of coronal mass ejections and solar flares. Coronal
mass ejections are huge bubbles of gas ejected from the Sun and are often
associated with these flares. Solar flares are explosions on the Sun that
happen when energy stored in twisted magnetic fields (usually above
sunspots) is suddenly released.

When protons like these bombard the upper atmosphere, they break up molecules
of gases like nitrogen and water vapor, and once freed, those atoms react
with ozone molecules and reduce the layer.

“A lot of impacts on ozone are very subtle and happen over long periods
of time,” said Charles Jackman, a researcher at NASA Goddard Space Flight
Center’s Laboratory for Atmospheres and lead author of the study. “But when
these solar proton events occur you can see immediately a change in the
atmosphere, so you have a clear cause and effect.”

The study’s investigators used measurements from the Halogen Occultation
Experiment (HALOE) instrument aboard the Upper Atmosphere Research Satellite
(UARS) and the Solar Backscatter Ultraviolet (SBUV/2) instrument aboard the
NOAA-14 satellite to obtain data on amounts of atmospheric gases like ozone
and oxides of nitrogen in different layers of the atmosphere in the Northern
Hemisphere. The investigators then compared readings before and during the
event.

When the sun’s protons hit the atmosphere they break up molecules of
nitrogen gas and water vapor. When nitrogen gas molecules split apart, they
can create molecules, called nitrogen oxides, which can last several weeks
to months depending on where they end up in the atmosphere. Once formed,
the nitrogen oxides react quickly with ozone and reduce its amounts. When
atmospheric winds blow them down into the middle stratosphere, they can
stay there for months, and continue to keep ozone at a reduced level.

Protons similarly affect water vapor molecules by breaking them up into
forms where they react with ozone. However, these molecules, called hydrogen
oxides, only last during the time period of the solar proton event. These
short-term effects of hydrogen oxides can destroy up to 70 percent of the
ozone in the middle mesosphere. At the same time, longer-term ozone loss
caused by nitrogen oxides destroys a maximum of about nine percent of the
ozone in the upper stratosphere. Only a few percent of total ozone is in
the mesosphere and upper stratosphere with over 80 percent in the middle
and lower stratosphere.

“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,” Jackman said.

While impacts to humans are minimal, the findings are important scientifically.

“Solar proton events help us test our models,” Jackman said. “This is an
instance where we have a huge natural variance. You have to first be able to
separate the natural effects on ozone, before you can tease out human-kind’s
impacts.”

Chlorine and bromine are major culprits in ozone decline. Most of the
chlorine and bromine comes from human-produced compounds such as
chlorofluorocarbons (CFCs) and halon gas.

NASA’s HALOE was launched on the UARS spacecraft September 15, 1991 as part
of the Earth Science Enterprise Program. Its mission includes improvement of
understanding stratospheric ozone depletion by measuring vertical profiles
of ozone, hydrogen chloride, hydrogen fluoride, methane, water vapor, nitric
oxide, nitrogen dioxide, aerosols, and temperature. The SBUV/2 instrument
was launched aboard the NOAA-14 satellite on December 30, 1994 and its
mission is to observe the ozone layer.

For more information, please visit:
http://www.gsfc.nasa.gov/topstory/20010801solarproton.html