Colorado State University Scientists Lead Team Studying Precipitation in Higher-Latitude Clouds

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Scientists have gained a much better picture of how much precipitation comes from clouds thanks to CloudSat, NASA’s first cloud-profiling radar in orbit designed in part by former Colorado State University researcher Graeme Stephens.

Even the best technology in the world needs a backup plan: Scientists need to check the measurements from CloudSat against actual observations in the sky to ensure that their predictions and models are working.

Tristan L’Ecuyer, a Colorado State research scientist and one of the original crew working on CloudSat with NASA’s Jet Propulsion Laboratory, spent five weeks in September and October flying over Helsinki, Finland, to measure precipitation in clouds at higher latitudes. These clouds produce light, steady rainfall that makes up a large fraction of the fresh water that supports life at higher latitudes. Helsinki gets extended periods – usually two months – of this type of light rainfall, L’Ecuyer said.

L’Ecuyer flew in a specially equipped plane – owned by the University of Wyoming – to compare measurements of cloud particles and raindrops against precipitation models and CloudSat observations.

The experiment, known as the Light Precipitation Validation Experiment, provided some of the first observational data on these types of clouds. Also working on the project were research scientist Matt Lebsock and graduate student Norm Wood, both from Colorado State, as well as scientists from the Finnish Meteorological Institute, the University of Helsinki, Environment Canada and the University of Wyoming, which hosts the plane.

“Light rainfall at higher latitudes is an important source of fresh water that could be susceptible to climate change. 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,” L’Ecuyer said. “We’re trying to measure the whole vertical profile of the cloud that produces precipitation to help explain what we see from space with CloudSat. The CloudSat observations can then be used to test climate models globally.”

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.

“We watched the ice crystals melt as we flew down through the clouds – you can’t see that with the naked eye,” L’Ecuyer said. “We’re studying the properties of the air, the humidity, temperature and the water content as well as how much rainfall actually landed.”

Funding for the project was provided through CloudSat and JPL.

Stephens, formerly at CSU and now at JPL, is the principal investigator on NASA CloudSat mission, which is one of the few university-led Earth science missions. 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 NOAA – collects and distributes data from CloudSat to scientists across the globe.