GREATER
SOLAR ACTIVITY MAY BRING U.S. MORE GRAY DAYS NASA-funded
Earth Science researchers have discovered that during periods of increased solar
activity much of the United States becomes cloudier, possibly because the jet
stream in the troposphere moves northward causing changes to regional climate
patterns.
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The
new study supports earlier findings by suggesting there is a relationship between
increased cloud cover over the United States and the solar maximum, the most intense
stage of activity on the Sun. Previous
studies have shown that during the solar maximum, the jet stream in the Northern
Hemisphere moves northward. The jet stream guides storms and plays an important
role in cloudiness, precipitation and storm formation in the United States. Dr.
Petra Udelhofen, a NASA-funded researcher at the Institute for Terrestrial and
Planetary Atmospheres at the State University of New York at Stony Brook, is the
lead author of a paper that discusses this topic, appearing in the July 1 issue
of Geophysical Research Letters. "Based
on these results and because the location of the jet stream influences cloudiness,"
said Udelhofen, "we suggest that the jet stream plays an important role in
linking solar variability and cloud cover." The
jet stream is a ribbon of fast-moving air in the upper troposphere that blows
from west to east. Storms beneath the jet stream follow its path. A shift in the
jet stream can alter the location of clouds and precipitation across the U.S. The
troposphere is the region of the atmosphere that extends from the Earth's surface
out to about 50,000 feet and is the focus of local, regional and global weather
research. The stratosphere extends above the troposphere to about 150,000 feet
and is the region where the ozone layer is formed. The
Sun's energy output varies over an 11-year cycle, sending more ultraviolet radiation
towards the Earth during times of increased activity. While the Sun's total energy
output only varies by about one-tenth of one percent between periods of low and
high solar activity, the ultraviolet radiation that affects ozone production in
the stratosphere can change by more than 10 percent. Ultraviolet
radiation is absorbed in the Earth's stratosphere and creates the protective ozone
layer. When the ozone absorbs ultraviolet radiation, it warms the stratosphere,
which may affect movement of air in the troposphere where clouds form. Solar
cycle effects of ultraviolet radiation absorption by ozone in the stratosphere,
its impact on atmospheric circulation and the location of storm tracks have been
the subject of recent Earth Science research. "Our
results show that cloudiness varies on average by about two percent between years
of solar maximum and minimum. In most parts of the U.S., cloud cover is slightly
greater in years of solar maximum," noted Udelhofen. Though
more investigation is needed to better understand just how changes in the Sun's
ultraviolet energy output is linked to atmospheric winds, the study helps people
identify potential large-scale mechanisms that affect local and regional climates. Scientists
continue to investigate mechanisms that may link solar variability with weather.
These new results support the idea of a link between stratospheric chemistry and
meteorology, and support other recent theoretical studies associated with the
impact of stratospheric chemistry on climate change and weather. "It
is important for future studies to identify and explain in detail the link between
solar variability, ozone, the atmospheric circulation and cloud cover," Udelhofen
said. This
research is part of the NASA Earth Science Enterprise program, which is dedicated
to understanding how Earth is changing and what consequences these changes have
for life on Earth. Back
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