+ Play
Audio
|
+ Download Audio | +
Email to a friend | +
Join mailing list
July
18, 2008: Sometimes seconds count. If a furious,
tornado-spitting thunderstorm was bearing down on your home
town, a few moments might make all the difference in the world.
Will
McCarty, a graduate student at the National Space Science
and Technology Center, is working with data from NASA's Aqua
satellite to improve short-term weather predictions--the kind
that could help you dodge that thunderstorm.
Above:
Severe weather over DeWitt, Michigan, on June 14, 2008. Photo
credit and copyright: Daniel O'Malley.
Guided
by his NASA mentor, Gary Jedlovec, McCarty has already learned
how to improve 48-hour forecasts by 3 hours. "That may
not sound like a big deal, but tell that to someone who escaped
a weather disaster by the skin of their teeth," says
McCarty.
They
accomplished the improvement by entwining measurements from
Aqua's Atmospheric Infrared Sounder (AIRS), into weather models.
To
understand how AIRS works its magic, let's first take a look
at how forecasts are made:
Twice
a day, all over the world, weather balloons measure temperature,
wind, air pressure and humidity. These balloons sample the lowest
7 to 10 miles of Earth's atmosphere, where weather happens.
More measurements are made by surface observing stations, aircraft,
and weather radars. All these data form a "snapshot"
of the weather over the land at one point in time, every 12
hours.
Next,
the measurements are plugged into forecast models--computer-coded
equations that describe the interactions among the weather-influencing
variables mentioned above, plus others. A forecaster interprets
the model output to make his local weather prediction.
Sometimes
lives ride on this mundane sounding process.
"The
better we make the model output, the more the forecaster can
trust it and use it as a tool for forecasting, and the more
accurate forecasts the public receives," says McCarty.
AIRS
improves the model output by improving its input: Riding on
NASA's Aqua spacecraft and viewing the atmosphere through
nearly 2,400 different spectral channels, AIRS creates an
accurate global 3-D map of atmospheric temperature, water
vapor, clouds and greenhouse gases.
Right:
Will McCarty of the National Space Science and Technology
Center in Huntsville, Alabama. [more]
"AIRS
has finer resolution than previous instruments, so it can
make more detailed measurements," says McCarty. "This
makes analyses sharper, which improves the forecasts based
on them."
McCarty
and Jedlovec are most interested in AIRS infra-red "radiances,"
i.e., measurements of thermal energy emitted by the Earth's
surface and atmosphere. The researchers look at radiances
because they provide large scale measurements of the temperature
and water vapor patterns in the atmosphere.
"Radiance
measurements, in general, allow the observation of many places,
particularly over the oceans, that are sparsely measured directly
by traditional means, if at all," explains McCarty. "AIRS
gives us the best picture of the vertical temperature and
moisture structures ever made from space."
AIRS'
claim to fame, then, is its capacity to increase both the
area of Earth's atmosphere measured and the detail of those
measurements.
Above:
A typical AIRS infra-red weather snapshot. This is typhoon
Nakri, which Aqua flew over on May 28, 2008. [more]
What's
the next step? "Dealing with clouds," says McCarty.
"Infrared energy doesn't penetrate clouds well. When
clouds are around, the instrument is really only seeing the
tops of clouds."
When
clouds are low, however, there's still some good data from
the air above them because most of the atmosphere is still
being measured. These data have been wasted up to now – thrown
out in the bathwater along with all the other cloud-contaminated
data.
McCarty
is now working on an algorithm to identify which channels
are truly useless and which are valid. His method will help
identify what is good, useful data and increase the amount
of data collected, making even better forecasts possible.
He will soon plug his data into a forecast model to find out
just how much better.
A
3-hour improvement may be just the beginning.
SEND
THIS STORY TO A FRIEND
Author: Dauna Coulter
| Editor:
Dr. Tony Phillips | Credit: Science@NASA
|