Satellite "radiance" data from cloudy regions in
forecast models improved hurricane monitoring
 Scientists in NESDIS
and the Environmental Modeling Center of the
National Weather Service have come a long way in assimilating satellite
data into global and regional weather forecast models. Instead of
converting what the satellite observes into quantities that the model
"knows" how to use, newer models can now assimilate what the satellite
actually measures. For example, the Community Radiative Transfer Model can
directly use measurements of radiances, a property that an instrument on a
satellite readily "sees" at a point in space, from a particular direction,
and at a moment in time. As a human eye can see the "brightness" of light
coming from a particular direction and from a region of the sky, so can an
instrument detect the radiance of electromagnetic radiation coming from a
particular direction. Radiance observations from cloudy and rainy areas
can now be assimilated into the Weather Research and Forecast model. In
the figure at right, the new technique produces a temperature field in
Hurricane Katrina that is more detailed, and that better resolves the warm
core of the hurricane. The Joint Center for Satellite Data Assimilation,
in which both NESDIS
and the NWS participate,
uses these satellite observations to enable better forecasts of severe weather.
For the first time,
observations of microwave radiances are assimilated into a weather forecast
model. Here, the radiance observations are from the Special Sensor Microwave
Imager and Sounder instrument on the Defense Satellite Meteorology Program satellite.
The new data assimilation technique improves the analysis of temperature fields
(shown in the right panels) at two levels in Hurricane Katrina, compared with the same
fields in the control run, in the left panels.
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