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Graeme Stephens describes satellite’s look at Earth’s water cycle

Stephens said that when scientists learn how clouds interact with other forces in the atmosphere, models predicting future climate will become much more accurate.

Graeme Stephens is principal investigator of NASA’s CloudSat Mission. CloudSat is a satellite designed to investigate how clouds affect Earth’s water cycle – that is, the movement of water on, in, and above the Earth.

Graeme Stephens: We’re really beginning to understand the water cycle of our planet at a level that’s important to make predictions about how this water cycle might change.

CloudSat is equipped with radar that is 1,000 times more sensitive than weather radar. CloudSat’s radar can detect the tiny particles of liquid water and ice that make up clouds, which other satellites can’t see. It orbits the Earth along with NASA’s Aqua satellite, and their data is often combined to make unique and important observations, said Stephens.

Graeme Stephens: We can actually use the observations of CloudSat to basically weigh clouds, and work out how much rain is in the clouds.

Stephens said that scientists want to know how much water is suspended in the atmosphere, and how it converts into rainfall. He said that’s important because climate scientists try to accurately predict how global warming might alter future precipitation.

Graeme Stephens:
We find, for example, that the conversion of cloudwater to rainwater is much slower than expected, and much slower than is predicted in climate models.

Stephens said that these findings could reshape the way climate models are created.

Graeme Stephens: These observations are truly unique. And this has been a unique period in Earth observation with this constellation of satellites.

CloudSat is part of what NASA calls a “constellation” of satellites, orbiting the planet together. Dubbed the “A-Train,” these satellites are intended to improve scientific understanding of the climate system and the potential of climate change. The other satellites include Aqua, Aura, Calypso and PARASOL. Stephens explained the usefulness of this constellation.

Graeme Stephens: Cloudsat makes the measurements from this radar, and we use measurements from Aqua from other sensors. We tie them together, and that gives us an absolutely unique way of observing the Earth’s atmosphere, and the processes that shape the flow of water through the atmosphere.

He added that clouds are one of the most complicated aspects of studying the atmosphere.

Graeme Stephens:
Clouds are a lot more complicated than carbon dioxide in the atmosphere because they affect sunlight, they affect infrared radiation and the greenhouse effect. These effects are very complicated and in many ways, they compensate each other. It’s been a puzzle as to what clouds really do. The observations we’ve had over last 20 to 30 years, global observations, weren’t precise enough to give us clues as to how greenhouse effects of clouds might compensate albedo effect on clouds – that is, how sunlight is reflected from them.

Stephens said that when scientists learn how clouds interact with other forces in the atmosphere, models predicting future climate will become much more accurate.

Our thanks today to NASA’s Aqua Mission, improving our knowledge of our home planet through satellite observations.

Lindsay Patterson

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