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This summer they'll be counting raindrops in Montana

For three months this summer, in quiet southeastern Montana, hundreds of people are going to be counting raindrops. Backed by eight weather rader units, 10 specially equipped aircraft, 100 remote weather monitoring stations, and a barrage of weather balloons, an internatonal team of 300 scientists will be trying to add to the world's limited undertaking of how rain works -- or doen't work.

The immediate payoff will come through developing new techniques for predicting the approach of severe thunderstorms, high winds, hailstorms, and tornadoes. The hope is that increased understanding eventually will lead to weather-modification programs for increasing rainfall where needed while preventing unneeded rain or crop-destroying hail storms.

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This "Cooperative Convection Precipitation Experiment" is jointly managed by the National Center for Atmospheric Research and the US Interior Department's Water and Power Resources Service. Other US government agencies, along with 13 universities, the State of Montana, three commercial meteorological firms, and scientists from Canada, Britain, Italy, and Switzerland are participating in the study.

Despite a satellite communication network to gather information from the various weather observation units and sophisticated computers to analyze the largest amount of data ever collected for such a study, full analysis could take up to four years.

One man who will be following the Montana results closely is Richard Semonin. He has spent years studying rain clouds for the Institute of Natural Resources at the University of Illinois. Even though he is joint author of a thick monograph on the latest discoveries about rainfall, Dr. Semonin says meteorologists are only beginning to find out how weather works.

A sophisticated array of new tools helps Semonin and his colleagues around the world study clouds to discover their secrets. He remembers beginning his research with a room-sized computer that did far less than the hand-held model he now carries with him everywhere. So he is grateful for the latest computers designed to cope with the vast amount of weather data available from observation stations continuously checking every level of our atmosphere.

New computer power brings meteorologists a step closer to understanding how clouds work. Now, Semonin explains, he can "devide the average summer thunderstorm into cubic-meter pieces." That means dealing mathematically with 10 to the sixth or eighth power in order to cover the pieces -- and then keeping track of more than 100 variables, such as temperature, pressure, electrical charge, and size of water droplets within each separate cubic-meter piece.

Sampling many variables is done with elaborate Department of Commerce weather observation airplanes that fly directly through all types of storms. One tool for this operation is an instrument with a hole the size of the eye of a needle, used to collect samples of the minuscule water particles that make up a cloud. Since it takes perhaps 1 million droplets to form a single raindrop, collecting a stream of 10 micron droplets, says Semonin, "shows just how much of the thunderstorm is actually sampled."

At the other extreme, radar is used to study an entire 5,000-foot-diameter thunderstorm.

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Semonin hopes new equipment using laser beams will begin to fill the vast measuring gap between the extremes of the eye-of- the-needle and the radar approaches.

But even if new sampling equipment is developed to make use of the meteorologists' new computer power, says Semonin, serious legal, political, and moral problems will surround weather modification.

Recent Illinois State Water Survey studies indicate that cities have a significant impact on weather. Due to a variety of factors, communities downwind from a city experience abnormally high rainfall.

After six years of studying the St. Louis area, Semonin says he found downwind agricultural areas with high rainfall meant "the value of the farmland is higher, because corn production exceeds that of neighboring counties to an economically significant extent in spite of side effects like more hail storms."

Such benefits, the meteorologist says, can be offset by "secondary effects such as local flooding, dumping of raw sewage, and increased auto accidents directly related to abnormally high rainfall."

Currently the Illinois State Water Survey is studying the effects of the white vapor trails, or contrails, left by jet aircraft crisscrossing the skies over Illinois. Semonin points out that both in the case of cities affecting rainfall and jet contrails increasing cloudiness, "Man is influencing the weather and climate."

Because any weather change affects a wide variety of activities such as agriculture, construction, tourism, solar energy production, and heating or air conditioning, Semonin says, weather modification becomes a political question. So the meteorologists at work in Montana this summer will not only try to figure out how rain works but also must keep track of the often-conflicting needs of those affec ted by the weather in different ways.

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