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Listen to this story (requires RealPlayer) Sept. 5, 2000 -- For many Americans, Labor Day weekend was the last chance to hit the beach during the Summer of 2000. With autumn just around the corner and school starting around the country, droves of sunbathers spent their holiday perfecting a last-minute tan. But was it safe? After all, the Sun is near the peak of its 11-year activity cycle. There are more sunspots, solar flares and UV rays from the Sun than at any time since 1989. "We're in the maximum phase of the solar cycle now," says Dr. David Hathaway, a solar physicist at the NASA Marshall Space Flight Center, "and it will probably persist for another year or more. This one is somewhat smaller than the last two maxima in 1989 and 1979, but it's definitely bigger than average." Above: The sunspot number is soaring in the year 2000, which marks the peak of another 11-year sunspot cycle. A white curve displaying monthly-averaged International Sunspot Numbers is overlaid on an x-ray image of the Sun. [more information] Fortunately for beach-goers, elevated levels of solar activity
around the peak of the sunspot cycle do not substantially
increase the risk of sunburns on Earth. Our planet's atmosphere
acts as a shield against the most harmful forms of radiation
-- and the shielding actually increases slightly near the peak
of the solar cycle. So, if you failed to buy any super-protective
Solar Max Sunscreen for your Labor Day on the beach, you
can relax. There was nothing to worry about beyond the usual
forms of skin
cancer and exposure-related maladies.
Ultraviolet (UV) radiation comes from the Sun in a range of
wavelengths; some are completely blocked by the atmosphere, while
others pass through to the Earth's surface. Above: This image, courtesy of Dr. Judith Lean at the
US Naval Research Laboratory, shows three extreme ultraviolet
(30 nm) pictures of the Sun captured by the ESA/NASA Solar and
Heliospheric Observatory at different times during the current
solar cycle. In 1996, near solar minimum, the extreme ultraviolet
Sun was nearly featureless. Near the peak of the cycle, the Sun
is dotted by fiery regions of hot gas trapped in magnetic fields
above sunspots and plages. These active regions produce copious
numbers of extreme ultra-violet and X-ray photons that are absorbed
in outer layers of our atmosphere before they reach Earth's surface.
Heightened levels of solar ultraviolet radiation can actually
strengthen the shielding capacity of Earth's atmosphere by a
slight amount. Spaceborne TOMS instruments are able to monitor erythemal UV radiation levels on the ground. Every day a new map is published at the TOMS web site. In areas of the globe marked by red, yellow or pink (see above), prolonged exposure to the Sun can be dangerous. Above: Daily updates of erythemal UV exposure around
the world can be found on the TOMS Web site. Colors indicate
the intensity of solar ultraviolet radiation reaching plant and
animal life after it has been filtered through stratospheric
ozone, clouds and aerosols multiplied by its biological damage
potential. Red, yellow and pink denote levels that can be especially
dangerous with prolonged exposure. [more
information] "The day of the year is also important because the largest
variation of UV irradiance (after clouds) is caused by the slant
path of the radiation through the atmosphere. The slant path
is at a minimum around the time of the summer solstice,"
which leads to the largest UV exposure, explained Herman. Right:
Readers with an internet connection can monitor ozone concentrations
for themselves, thanks to near-realtime global maps of ozone
column density published at the Earth Probe TOMS web site. In
this map, completed on Sept 4, 2000, the Antarctic
ozone hole is prominent as a purple region surrounding the
south pole. [more
information] TOMS-EP and other ozone-measurement programs are important parts of a global environmental effort of NASA's Earth Science enterprise, a long-term research program designed to study Earth's land, oceans, atmosphere, ice, and life as a total integrated system. |
Web Links |
TOMS
Web Site
-- data and information about the Total Ozone Mapping Spectrometer
(TOMS) instrument aboard NASA's Earth Probe (TOMS-EP) satellite. Solar S'Mores -- As a result of the solar maximum, Earth's atmosphere is "puffed up" like a marshmallow over a campfire leading to extra drag on Earth-orbiting satellites. Sunspot Cycle Predictions -- from the NASA Marshall Space Flight Center Stratospheric Ozone: An Electronic Textbook -- a comprehensive tutorial about the chemistry and dynamics of the ozone layer The Solar Backscatter Ultraviolet (SBUV) instrument on NASA's Nimbus-7 satellite --Operating from November 1978 to June 1990, the SBUV sensor measured the intensities of various UV wavelengths backscattered from the Earth's atmosphere over the course of approximately one solar cycle. Based on SBUV data scientists concluded that over the course of an 11-year solar cycle, most of the variation in radiation intensity occurs at wavelengths shorter than 280 nm. |
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