NSF PR 02-25 - April 16, 2002
Complex Weather Study to Target Summer Storm Forecasting
One of the largest weather-related studies in U.S.
history will track the nearly invisible swaths of
moisture that fuel heavy rain across the southern
Great Plains from Texas to Kansas. Scientists hope
that analyzing water vapor will help to better predict
the timing, location, and intensity of summer storms.
Led by scientists from the National Center for Atmospheric
Research (NCAR) in Boulder, Colorado, the International
H2O Project (IHOP2002) will be based in central Oklahoma
from May 13 to June 25. The National Science Foundation
(NSF), NCAR's primary sponsor, is providing the bulk
of the project's $7 million funding, with additional
support from other agencies.
"NSF is excited about IHOP, as it's one of the most
complex and potentially scientifically rewarding field
projects we have implemented," said James Huning,
program director in NSF’s division of atmospheric
sciences.
Six aircraft from the United States and Germany will
traverse the core study area, some flying as low as
100 feet above the surface. A futuristic, semi-autonomous
research craft- -the Proteus, sponsored by NASA --
will carry instruments up to 45,000 feet. On the ground,
an armada of 30 weather-tech vehicles, including four
Doppler radars on flatbed trucks, will comb the rural
roadways of Oklahoma, Kansas and Texas. More than
100 scientists and technicians scattered across the
plains will aim radars and other sensors at water
vapor well ahead of the day's first raindrops.
Unlike other weather studies undertaken in this region,
IHOP will study the water vapor that feeds showers
and thunderstorms, rather than trying to capture episodic
events like tornadoes or other severe weather.
"We're hoping to actually see how the water vapor moves,"
says NCAR's Tammy Weckwerth, one of IHOP's two lead
scientists. "That's never been done before." Cloud
cover may impede some of the more sensitive instruments,
Weckwerth adds. "The ideal day will start out cloud
free, yet humid."
A number of agencies support IHOP under the U.S. Weather
Research Program. The study aims to improve forecasts
from one to 12 hours ahead of heavy rain, which could
help in flash-flood safety and other applications.
"Right now the lead time for flash-flood forecasts
is well under an hour," says NCAR's David Parsons,
co-lead scientist on the study. "If you can extend
forecasts of heavy rainfall out a few hours, you're
doing great."
Heavy rain depends on an ample supply of moisture,
so the lack of water-vapor data is a major forecast
impediment. Currently, no device can track tiny molecules
of water vapor minute by minute over large areas.
Weather balloons (radiosondes) provide most of the
water-vapor data used in forecasting; however, their
high cost reduces the frequency and spacing of balloon
launches. Lidar (laser-based radar) provides more
detail than radiosondes, but it can only sample across
a few miles, and clouds reduce that range further.
Satellite sensors, which cover much of the globe,
haven't yet furnished the high- resolution measurements
needed in the lower atmosphere for storm prediction.
By mixing older and newer sensors, IHOP2002 will examine
how the latest technology can bridge the gaps in water-vapor
sensing. Four of the IHOP aircraft will carry state-of-the-art
systems that produce vertical profiles of water vapor.
These will be used to help calibrate new, higher-precision
instruments aboard satellites. Other sensors on the
ground will analyze signals from the Global Positioning
System (GPS) and other sources. Special high-end radiosondes
will be launched for comparison with other data.
Meanwhile, forecasters from several labs and universities
will use high-performance computer models to predict
each day's weather. Rather than simply assigning a
chance of rain, the meteorologists will specify rainfall
amounts across the study area. Such forecasts are
now limited in accuracy, but with the IHOP data at
hand, scientists are hoping to improve their skills.
Additional support for IHOP is from the National Aeronautics
and Space Administration (NASA), the National Oceanic
and Atmospheric Administration (NOAA), and the U.S.
Department of Energy (DOE).
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