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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