NASA: Quiet Sun Means Cooling

NASA Press Release 12-16-09:

NASA SHOWS QUIET SUN MEANS COOLING OF EARTH'S UPPER ATMOSPHERE


HAMPTON, Va. -- New measurements from a NASA satellite show a dramatic
cooling in the upper atmosphere that correlates with the declining
phase of the current solar cycle. For the first time, researchers can
show a timely link between the Sun and the climate of Earth's
thermosphere, the region above 100 km (roughly 60 miles), an
essential step in making accurate predictions of climate change in
the high atmosphere.
Scientists from NASA's Langley Research Center and Hampton University
in Hampton, Va., and the National Center for Atmospheric Research in
Boulder, Colo., will present these results at the fall meeting of the
American Geophysical Union in San Francisco from Dec. 14 to 18.

Earth's thermosphere and mesosphere have been the least explored
regions of the atmosphere. The NASA
Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED)
mission was developed to explore the Earth's atmosphere above 60 km
altitude and was launched in December 2001. One of four instruments
on the TIMED mission, the Sounding of the Atmosphere using Broadband
Emission Radiometry (SABER) instrument, was specifically designed to
measure the energy budget of the mesosphere and lower thermosphere.
The SABER dataset now covers eight years of data and has already
provided some basic insight into the heat budget of the thermosphere
on a variety of timescales.

The extent of current solar minimum conditions has created a unique
situation for recent SABER datasets. The end of solar cycle 23 has
offered an opportunity to study the radiative cooling in the
thermosphere under exceptionally quiescent conditions.

"The Sun is in a very unusual period," said Marty Mlynczak, SABER
associate principal investigator and senior research scientist at
NASA Langley. "The Earth's thermosphere is responding remarkably --
up to an order of magnitude decrease in infrared emission/radiative
cooling by some molecules."

The TIMED measurements show a decrease in the amount of ultraviolet
radiation emitted by the Sun. In addition, the amount of infrared
radiation emitted from the upper atmosphere by nitric oxide molecules
has decreased by nearly a factor of 10 since early 2002. These
observations imply that the upper atmosphere has cooled substantially
since then. The research team expects the atmosphere to heat up again
as solar activity starts to pick up in the next year.

While this warming has no implications for climate change in the
troposphere, a fundamental prediction of climate change theory is
that the upper atmosphere will cool in response to increasing carbon
dioxide. As the atmosphere cools the density will increase, which
ultimately may impact satellite operations through increased drag
over time.

The SABER dataset is the first global, long-term, and continuous

record of the Nitric oxide (NO) and Carbon dioxide (CO₂)

emissions from the thermosphere.



"We suggest that the dataset of radiative cooling of the thermosphere

by NO and CO₂ constitutes a first climate data record for

the thermosphere," says Mlynczak.



The TIMED data provide a fundamental climate data record for

validation of upper atmosphere climate models which is an essential

step in making accurate predictions of climate change in the high

atmosphere. SABER provides the first long-term measurements of

natural variability in key terms of the upper atmosphere climate. As

the TIMED mission continues, these data derived from SABER will

become important in assessing long term changes due to the increase

of carbon dioxide in the atmosphere.


TIMED is the first mission in the Solar Terrestrial Probes Program
within the Heliophysics Division in NASA's Science Mission
Directorate in Washington.

For more information:
http://stp.gsfc.nasa.gov/missions/timed/timed.htm