It rained gobs at Biosphere 2

Talk about a microburst.

Scientists dropped a whopping 2.5 inches of rain in less than two hours Monday on the "ocean" at Columbia University's Biosphere 2 Center near Oracle.

They're studying how rain affects the exchange of gases like carbon dioxide across ocean surfaces. Understanding how carbon dioxide is stored, taken in and released in oceans is of critical importance, said John Adams, Biosphere 2's associate director of pubic outreach.

"Carbon dioxide is a major greenhouse gas, and oceans are where the greatest amount of carbon dioxide is stored," Adams said. "So figuring out how this gas is taken in and released is really important for understanding future global climate change."

Industrialization and automobiles have increased greenhouse gases held by the Earth's atmosphere, and many scientists say this has already warmed the Earth. Biosphere 2, with its miniature ocean and other biomes built in a 3-acre greenhouse, is uniquely suited to helping scientists study whether global warming is indeed happening and what can be done about it.

A fleet of experiments bobbed Monday in the million-gallon ocean, measuring its temperature and gas levels at different depths, the amount of rainfall in different areas, and taking hi-tech pictures of raindrops.

Rain affects the exchange of gases in different ways, said David Ho, a Columbia geochemist.

Rain is fresh water, which is less dense than sea water, so it initially forms a distinct layer above the sea water, like oil and water, he said. In some conditions, this could slow the exchange rate down, but in others, the freshwater level could act as a kind of lens, increasing the exchange, he said.

Raindrops hitting the surface of the ocean also mess with the exchange rate, because as they bombard the surface, they lessen the energy needed for gas to go back and forth through the surface, Ho said.

Using Biosphere 2's ocean not only allows the scientists to control when and where the rain falls, but also saves a tremendous amount of money, Ho said.

"It would be really expensive to do this in a real ocean," he said. "You set all this stuff up and it might not rain enough, or rain at all."

Ho conducted a similar experiment last year at Biosphere 2, but the commercial sprinkler heads used to bring the rain down some 40 feet to the ocean didn't make big enough drops.

The challenge for this year's experiment was to find a way to get drops as big as real rain drops and still distribute them evenly and densely over the ocean.

The job fell to Allen Wright, director of research operations at Biosphere 2.

"I had tried a bunch of things that didn't work, and one day, on the shuttle, I just told everyone I was out of ideas and I needed help," Wright said.

To the rescue came marine technician Burton Shank, who remembered a backyard toy - the Water Wiggle - that danced around yards squirting water from tubes fed from a garden hose.

Wright seized the idea and used commercial irrigation parts to invent round fixtures with flexible tubes about 4 inches long. The tubes are just the right strength and length to bob around wildly when pressurized water flows through them, spraying the right-sized drops with the right frequency and distribution to accurately simulate rain.

On behalf of NASA, Larry Bliven, an oceanographer with the Laboratory for Hydrospheric Processes at NASA's Goddard Space Flight Center, operated a special camera that measured the size and shape of rain drops falling from Wright's fixtures 42 feet above the ocean.