This image shows Hurricane Frances as captured by instruments onboard two
different satellites: the AIRS infrared instrument onboard Aqua, and the
SeaWinds scatterometer onboard QuikSCAT. Both are JPL-managed instruments.
AIRS data are used to create global three-dimensional maps of temperature,
humidity and clouds, while scatterometers measure surface wind speed and
direction over the ocean.
The red vectors in the image show Frances' surface winds as measured by
SeaWinds on QuikSCAT. The background colors show the temperature of clouds
and surface as viewed in the infrared by AIRS, with cooler areas pushing
to purple and warmer areas are pushing to red. The color scale on the
right gives the temperatures in degrees Kelvin. (The top of the scale,
320 degrees Kelvin, corresponds to 117 degrees Fahrenheit, and the bottom,
180 degrees K is -135 degrees F.) The powerful circulation of this storm
is evident from the combined data as well as the development of a
clearly-defined central "eye." The infrared signal does not penetrate
through clouds, so the light blue areas reveal the cold clouds tops
associated with strong thunderstorms embedded within the storm. In
cloud-free areas the infrared signal comes from Earth's surface, revealing
warmer temperatures.
The power of the SeaWinds scatterometer data set lies in its ability to
generate global maps of wind speed and direction, giving us a snapshot of
how the atmosphere is circulating. Weather prediction centers, including
the Tropical Prediction Center - a branch of NOAA that monitors the
creation of ocean-born storms, use scatterometer data to help it "see"
where these storms are brewing so that warnings can be issued and the
storms, with often erratic motions, can be tracked.
While the SeaWinds instrument isn't designed to gather hurricane data,
having difficulty seeing the surface in heavy rain, it's data can be used
in combination with other data sets to give us an insight into these
storms. In this combination image, the AIRS infrared data reveals the
temperature of the atmosphere around the storm, but doesn't tell us about
the wind direction or relative intensity. The directional vectors of the
SeaWinds data set show how the air is circulating around the storm.
Scatterometers measure surface wind speed and direction by bouncing
microwave pulses off the ocean's surface. The SeaWinds instruments measure
the backscattered radar energy from wind-generated ocean waves. By making
multiple measurements from different looks at the same location, we can
infer the vector wind averaged over each 25 km resolution cell. The
primary mission objective of the SeaWinds and QuikSCAT scatterometers is
to obtain long-term, global coverage of the ocean vector winds for
oceanographic and climate research. While not specifically designed for
detailed mapping and tracking of hurricanes, both instruments have been
found to be useful resources for operational forecasters.
The Atmospheric Infrared Sounder Experiment, with its visible, infrared,
and microwave detectors, provides a three-dimensional look at Earth's
weather. Working in tandem, the three instruments can make simultaneous
observations all the way down to the Earth's surface, even in the presence
of heavy clouds. With more than 2,000 channels sensing different regions
of the atmosphere, the system creates a global, 3-D map of atmospheric
temperature and humidity and provides information on clouds, greenhouse
gases, and many other atmospheric phenomena. The AIRS Infrared Sounder
Experiment flies onboard NASA's Aqua spacecraft and is managed by NASA's
Jet Propulsion Laboratory, Pasadena, Calif., under contract to NASA. JPL
is a division of the California Institute of Technology in Pasadena.
