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National Severe Storms Laboratory Hosts International H₂0 Project

by Keli Tarp

Meteorological researchers from around the World have gathered in central Oklahoma for one of the largest weather-related studies in U.S. history, hosted by the National Oceanic and Atmospheric Administration's National Severe Storms Laboratory.

From May 13 to June 25, during IHOP 2002 (International H20 Project), NSSL scientists known for their research on tornadoes are pursuing a different atmospheric phenomena, hoping to unlock the secrets behind some of nature's most destructive storms. Researchers are tracking the nearly invisible swaths of moisture that fuel severe thunderstorms and heavy rain across the southern Great Plains from Texas to Kansas. Scientists hope analyzing water vapor will be the key to better predictions of when and where thunderstorms will form and how intense they will be.

More than 100 scientists and technicians scattered across the plains are aiming radars and other sensors at water vapor well ahead of the day's first raindrops. On the ground, an armada of 30 weather-tech vehicles, including four Doppler radars on flatbed trucks, comb the rural roadways of Oklahoma, Kansas and Texas. They are measuring temperature, humidity, wind and other variables in the lower atmosphere. Six aircraft from the United States and Germany are traversing the core study area, some flying as low as 100 feet above the surface. A futuristic, semi-autonomous research craft—the Proteus, sponsored by the National Aeronautics and Space Administration—carries instruments up to 45,000 feet.

The National Science Foundation is providing the bulk of the project's $7 million funding, with additional support from NOAA, the National Centers for Atmospheric Research (NCAR), NASA, and U.S. Department of Energy. In addition, scientists from France, Germany, the Netherlands and Canada are participating.

Rather than trying to capture episodic events like tornadoes or other severe weather as in previous studies, IHOP is homing in on the water vapor that feeds thunderstorms, and the wind convergence bands that help spawn the storms. Where, when and how hard it will rain are the most difficult elements to nail down in weather forecasting, especially in spring and summer. Better precipitation outlooks are a key goal of the U.S. Weather Research Program, which has organized a number of agencies in support of IHOP. Researchers hope their findings will reveal a pattern to help them identify conditions necessary for a storm's formation. In addition, they hope the project will help improve estimates of how much rainfall a particular storm will produce.

"We are confident the project will bring us closer to identifying thunderstorms before their clouds form, helping forecasters improve their timing, accuracy and precision," said Conrad Ziegler, NOAA researcher and a lead investigator in the project. "Lessons learned will have applications for better forecasts."

NOAA scientists are operating a new mobile radar, called the SMART-Radar (Shared Mobile Atmospheric Research and Teaching-Radar), canvassing the study region, scanning the skies from off-road positions. Built with partners Texas A&M University, Texas Tech University and the University of Oklahoma, the SMART-Radar is the first mobile 5 cm radar in the United States. It was designed using the latest computer and radar signal processing hardware and software. With the capability to see through an entire thunderstorm or hurricane, it can observe precipitation over a larger area than other mobile radars.

In addition, NOAA researchers are coordinating vehicles with roof-mounted weather stations that monitor local conditions. These mobile mesonet vehicles drive across wind convergence bands, called "boundaries," whose vertical air motions frequently initiate clouds and storms. By mapping the contrasting weather conditions across boundaries with mobile mesonets, NOAA researchers will learn what weather contrasts are associated with storm formation.

Some 800 radiosondes will be launched during IHOP2002, many twice each day from National Weather Service offices in Dodge City, Kan., Norman, Okla., and Wichita, Kan., and from Liberal, Kan. Others will be launched from vehicles positioned in and near regions of expected storm development.

Heavy rain depends on an ample supply of moisture, so the current 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, a network of earth-orbiting satellites used for precise position-finding in surveying and navigation) and other sources. Special high-end radiosondes will be launched for comparison with other data.

In effect, the NOAA scientists involved in IHOP hope the data gathered this spring will provide clues to thunderstorm formation that will eventually help save lives and property through better forecasts.

[5/20/02]

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