CSU cloud-profiling team studies precipitation from space

When severe flooding hit Queensland, Australia, in late 2010 and early 2011, and three quarters of the state was declared a disaster zone, CloudSat captured the activity. When a powerful snow storm blanketed the U.S. east coast in late December, dumping 32 inches of snow, CloudSat profiled the storm.

CloudSat, a NASA satellite co-designed by former Colorado State researcher Graeme Stephens, uses radar to study clouds and precipitation from space. Clouds exert an enormous influence on weather and climate, and scientists track the precipitation from clouds with the satellite.

Scientists check measurements from CloudSat against actual observations in the sky to ensure that their predictions and models are working. CloudSat is the first radar of its kind in orbit and one of the few university-led Earth-science missions. Scientific support and data processing operations are based at Colorado State University.

Tristan L'Ecuyer, a CSU research scientist working with CloudSat and NASA's Jet Propulsion Laboratory, spent five weeks in September and October flying in a specially equipped plane over Helsinki, Finland, to measure precipitation in clouds at higher latitudes. These clouds produce light, steady rainfall that makes up much of the fresh water there.

The project, known as the Light Precipitation Validation Experiment, provided some of the first observational data on these types of clouds. The researchers are measuring the vertical profile of the cloud that produces precipitation, says L'Ecuyer. The CloudSat observations can then be used to test climate models globally.

Light rainfall at higher latitudes is an important source of fresh water that could be susceptible to climate change, explains L'Ecuyer. "It's really important to be able to verify whether our model of future changes in light rainfall are on the right track or not."

Measurements collected during the experiment show how these high-latitude clouds produce precipitation. Small ice particles at the top of the cloud collect into snow crystals just above the freezing mark. As those particles start to fall and the temperature warms above freezing, they collapse and turn into rain drops.

The research team is studying the properties of the air, humidity, temperature, and water content as well as how much rainfall actually landed. "We watched the ice crystals melt as we flew down through the clouds – you can’t see that with the naked eye," L'Ecuyer says.

Stephens, formerly at CSU and now the director of the Center for Climate Sciences at the Jet Propulsion Lab, is the principal investigator on the NASA CloudSat mission. CloudSat launched from Vandenberg Air Force Base near Santa Barbara, Calif., and reached its destination 438 miles above Earth in April 2006. Colorado State's Cooperative Institute for Research in the Atmosphere — a partnership with the National Oceanic and Atmospheric Administration — collects and distributes data from CloudSat to scientists around the world.