FYI: Introducing the A-Train Satellites, A New Tool For Investigating Changing Climate

[Henk Elegeert]

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FYI:

 *Introducing the A-Train Satellites, A New Tool For Investigating Changing
Climate*<http://beforeitsnews.com/story/238/273/Introducing_the_A-Train_Satellites,_A_New_Tool_For_Investigating_Changing_Climate.html>


Mention the "A-*Train*" and most people probably think of the jazz legend
Billy Strayhorn or perhaps *New York City subway trains* — not climate
change. However, it turns out that a convoy of "A-Train" satellites has
emerged as one of the most powerful tools scientists have for understanding
our planet's changing climate.


Artist's Concept of the A-Train constellation of satellites [image: artists
concept of the A-Train with labels]

http://www.nasa.gov/images/content/490639main_A-Train670.jpg
*Credit*:  NASA

The formation of satellites — which currently includes Aqua, CloudSat,
Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO)
and Aura satellites — barrels across the equator each day at around 1:30
p.m. *local* time each afternoon, giving the constellation its name; the "A"
stands for "afternoon."

Together, these four satellites contain 15 *separate* scientific instruments
that observe the same path of Earth's atmosphere and surface at a broad
swath of wavelengths. At the front of the train, Aqua carries instruments
that produce measurements of temperature, water vapor, and rainfall. Next in
line, CloudSat, a cooperative effort between NASA and the Canadian Space
Agency (CSA), and CALIPSO, a joint effort of the French space agency Centre
National d'Etudes Spatiales (CNES) and NASA, have high-tech laser and radar
instruments that offer three-dimensional views of clouds and airborne
particles called aerosols. And the caboose, Aura, has a suite of instruments
that produce high-resolution vertical maps of greenhouse gases, among many
other atmospheric constituents.

In coming months, the A-Train will expand with the launch of NASA's
aerosol-sensing Glory satellite and the carbon-tracking Orbiting Carbon
Observatory 2 (OCO-2) satellite. In 2010, the Japan Aerospace Exploration
Agency (JAXA) plans to launch the Global Change Observation Mission-Water
(GCOM-W1), which will monitor ocean circulation. Meanwhile, a fifth
satellite, France's Polarization and Anistropy of Reflectances for
Atmospheric Science coupled with Observations from a Lidar (PARASOL), which
studies aerosols, is easing out of an A-Train orbit as its fuel supplies
dwindles.

*Accidental Origins*

This multi-sensor view allows scientists to simultaneously observe changes
in key environmental phenomenon – such as clouds or ice sheets – from
numerous perspectives. And it helps skirt around engineering obstacles that
would have made it impossible to *cluster* all 15 instruments on one large
spacecraft.

But it wasn't necessarily planned that way. Formation flying is a fairly
novel concept, and it came to the fore partly by accident. The concept of an
A-Train first emerged when scientists and engineers were hashing out the
orbit of Aura, which launched in 2004. At the time, rather than calculating
a whole new orbital plan for Aura, flight engineers realized they could
simply model its orbit after Aqua, a sister satellite NASA had launched in
2002.

They went forward with that plan, but limitations in data transmissions
rates, meant that the two satellites ended up flying much closer to each
other than originally planned. In the end, they decided that Aura would fly
about 6,300 kilometers – a mere 15 minutes *of flight* – behind Aqua.

Meanwhile, two additional satellites that study minute airborne particles
called aerosols and clouds – the CALIPSO and CloudSat – without realizing it
had requested nearly identical orbits near Aura because the scientists
involved with these missions wanted to compare their results with the
humidity and cloud measurements coming from Aura. In 2006, CloudSat and
CALIPSO eased into the train behind Aura just 93 kilometers – about 12.5
seconds – from one another. As a *result*, CALIPSO's lidar beam and
CloudSat's radar have coincided at Earth's surface about ninety percent of
the time they have been in orbit.

*Reaping the Rewards*

The longer the A-Train has existed, the more scientists have begun to
appreciate its potential. Indeed, scientists representing all the A-Train
satellites are meeting this week in New Orleans to compare notes and to
sketch out plans for future cross-satellite collaboration. Leading earth
scientists from three national space agencies, including the *director* of
NASA's Earth Science Division Michael Freilich, Didier Renaut from CNES and
Haruhisa Shimoda of JAXA, are giving talks about A-Train science. And
scientists from dozens of institutions are *presenting* research on topics
ranging from air quality, to the carbon cycle, to cloud dynamics.

There is a great deal to discuss. Multi-sensor measurements from the
A-Train, for example, have proven critical in working out why the summer of
2007 experienced the greatest loss of Arctic sea ice in history. A-Train
sensors captured environmental conditions during the loss – which was far
greater than climate models had predicted – allowing scientists to go back
after the fact to pinpoint its causes. By now, they have proven that some
unexpected factors, such as anomalously high winds and an sharp decrease in
cloudiness, fueled the rapid loss, in addition to more predictable culprits
such as high air temperatures and low humidity.

Likewise, synergistic A-Train measurements have yielded great insight into
aerosols – small airborne particles such as dust, sea salt, and soot.
Depending on their composition, aerosols can scatter and or absorb the sun's
heat, and can thus both warm and cool the planet. Some types of aerosols
also seed clouds, A-Train sensors have helped reveal, and can change cloud
behavior. A-Train instruments aboard Aura and Aqua, for example, produced
groundbreaking insight about aerosols and ice clouds, making it possible for
scientists to prove that polluted ice clouds have smaller particles and are
therefore much less likely to produce rain.

Still, pressing questions about our climate remain. What is the overall
affect of aerosols and clouds on climate? How much carbon is absorbed by
forests? How will the monsoon cycle react to a warming world? To what extent
will a changing climate change the size and strength of hurricanes? And what
feedback cycles will encourage or discourage climate change? These and many
more questions still need answers, and now that the power of formation
flying is clear, it is a good bet that A-Train satellites will play a key
role in answering them.

Contacts and sources:
Adam Voiland <avoiland at sesda2.com>
NASA/Goddard Space Flight Center <http://www.nasa.gov/goddard>
NASA's Earth Science News
Team<http://www.nasa.gov/mission_pages/a-train/a-train.html>
"

Henk Elegeert

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