Clouds' illusions attract ocean weather study

A TRMM (Tropical Rainfall Measuring Mission) image of Hurricane Mitch taken October 27, 1998

July 23, 1999
Web posted at: 7:06 p.m. EDT (2306 GMT)

By Robin Lloyd
CNN Interactive Senior Writer

(CNN) - Starting this weekend, dozens of scientists will look at clouds from both sides now - when a two-month study of ocean weather starts up at a remote string of coral islands in the South Pacific.

The experiment, run in tandem with a weather-watching satellite currently orbiting Earth, will undertake a simple task - identifying exactly what clouds are made of - a currently unknown fact that is key to understanding sea storms and rainfall patterns.

"We're looking for particles," says Chris Kummarow, the satellite's project scientist at NASA's Goddard Space Flight Center.

"We know about the gases, we know about the water vapor. They're really not a big role. Really, we want to know what sort of ice particles are in those clouds."

Although it certainly never snows over the string of tiny islands, an atoll called Kwajalein, even there the clouds contain ice. The Earth's atmosphere cools by 6 degrees Fahrenheit for every 1,000 feet in elevation.

At 12,000 feet above the tropics, the air temperature is at the freezing point. At 33,000 feet, thunderstorms develop in clouds that are mostly ice except for their lowest layer.

"We want to know how the particles vary by shape, by density," Kummarow says. "Are they big, heavy, round hail-type things or is it little fluffy snowflakes or is it just very tiny ice crystals?"

Those shapes and densities are thought to affect how clouds build, a factor that weather researchers want to understand for their efforts to model ocean climate processes. Eventually, scientists hope the study, called KWAJEX, will improve weather forecasting.

Planes to cruise cloud innards

A couple years ago, NASA and the Japanese National Space Development Agency launched the Tropical Rainfall Measuring Mission satellite to measure global precipitation.

By measuring tropical rainfall, scientists hope to learn more about how the sun's energy, concentrated in the tropics, is transferred from the ocean to the atmosphere, said Steve Hipskind, who heads up atmospheric chemistry at NASA's Ames Research Center.

But the satellite can only snap the big picture of cloud cover. To understand cloud composition - the innards and undersides of clouds -- scientists planned some air and ground experiments, including the one that starts this weekend in Kwajalein.

In February, scientists did a similar study over the Amazon River in Brazil, where they focused on the effect of rainforest deforestation. Those results aren't in, but they immediately saw that rainfall there was more a result of oceanic clouds than land clouds. The Kwajalein data will provide a comparison with rainfall patterns over land.

Data will come in from three planes -- a DC-8 that will fly above the clouds to calibrate with the satellite findings and to collect cloud vapor, liquid, density, temperature and motion data, and a Cessna Citation II and twin-engine Convair 580 to take measurements of particles in the clouds.

Although the rainy season will be building as the experiment concludes in September, scientists know the flight risk will be low because of a few known facts about ocean storms - for instance, they tend to knock themselves out quickly.

The experiment could shed light on why. Scientists think ocean storms stay tame because the air mass is constantly so wet.

"As soon as the storms start building, they simply start raining out and commit suicide in the process," Kummarow said. "They never get the chance to develop into massive Midwest thunderstorms. As soon as they build, they just rain."

Land storms also tend to have 100 times more lightning and taller clouds and updrafts, which makes it much more treacherous for air travel over land, but the reasons behind this are unclear.

"We don't really know the dynamics of these clouds," Kummarow says. "That's what we're really trying to accomplish -- to get a good look at them and see how they differ from the beasts that we know over land."

20 inches of rain a month in Kwajalein

Kwajalein wasn't chosen because it's an exotic destination. Rather, it's a small, flat string of coral islands with absolutely no elevation - ideal for controlling for effect that land heat can have on ocean weather.

Also, the atoll already had a small radar at a U.S. Army base, which the project upgraded for the experiment. Radar on the National Oceanic and Atmospheric Administration's Ron Brown research vessel also will be used for the experiment, overseen by NASA Ames. The radar data will be combined to give 3-D motion maps of cloud droplets, Hipskind said.

There will be no shortage of rain data - Kwajalein receives 20 inches of precipitation monthly, on average.

The setting may sound exotic, but scientists, pilots and engineers are roughing it, Kummarow says, living in small, wooden cabins with no running water.

"It's not the Holiday Inn," he says.