Cloud scientists plumb some cirrus mysteries

This "latent" heat supplies the energy the storm needs to survive, and "the distribution of that heating is pretty important for the way storms develop," Stephens says. Indeed, the knowledge could lead to more-accurate long-term weather forecasts far from the thundering heads, he suggests.

In the tropics, individual thunderstorms can organize into clusters. These clusters become systems that extend up to 2,000 miles across. These systems tend to appear in the Indian Ocean and move east across the Pacific in cycles ranging from 30 to 60 days. They can influence storm formation far to the north and south of their locations. Understanding their origins and travel habits has become something of a "holy grail" for atmospheric science.

How fast they propagate is thought to be determined in part by the altitude at which the latent heat is released. Systems that release heat at high altitudes are believed to move faster than those that release heat at low altitudes. The two satellites are expected to let scientists see where this heat is released, which could help improve forecasts of these systems and the weather patterns they affect.

Not surprisingly, these systems generate large shields of high-altitude cirrus that have their own effect on weather and climate. These clouds were the subject of a three-week field campaign this winter in Darwin, Australia. Researchers taking part in the Tropical Warm Pool International Cloud Experiment (TWP-ICE) initially hoped to have CloudSat and CALIPSO in the sky to augment their aircraft and ground measurements. Launch delays closed the door on that.

Still, the results stand to be the most comprehensive set of information ever collected on these clouds, says Charles Long, who oversees the US Department of Energy's atmospheric monitoring sites in the western Pacific.

"This is the first field program to look at tropical convection through its whole life cycle," adds Greg McFarquhar, a researcher at the University of Illinois at Urbana-Champaign who took part in the project.

Even so, because cirrus trap heat, the Australian project focused much of its effort on gathering images and other data on these tenuous, high-altitude blankets in a region that is the globe's heat engine, says James Mather, another DOE scientist who played a key role in the project.

For instance, researchers have noted that some cirrus clouds vanish within an hour or two, while others last for 12 hours or more. The team sampled ice crystals from newer and older cirrus clouds and noted a significant difference in ice-crystal shapes between the two, according to Dr. McFarquhar. Others looked at atmospheric chemistry and the role of aerosols. Indeed, some researchers found a "chemical equator" - a shifting region that separated the relatively pristine air of the Southern Hemisphere from more-polluted northern air.

Calling the data TWP-ICE gathered "a goldmine," Dr. Long anticipates it will take at least a decade for researchers to plumb its depths. Even so, researchers with both projects suggest it won't take that long for the data to begin working its way into weather and climate-change forecasts.

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