Flights Obtain Long-term Statistics to Improve Data Sets for Climate Models

Unlike the wispy blankets of icy cirrus clouds that appear very high in the sky, thin clouds closer to Earth’s surface contain water—but often not much. They are frequently patchy and contain small amounts of water. This combination makes them difficult for ground-based instruments to accurately measure, which decreases confidence in how these clouds are simulated in climate models.
Unlike the wispy blankets of icy cirrus clouds that appear very high in the sky, thin clouds closer to Earth’s surface contain water—but often not much. They are frequently patchy and contain small amounts of water. This combination makes them difficult for ground-based instruments to accurately measure, which decreases confidence in how these clouds are simulated in climate models.

Researchers from the U.S. Department of Energy's Atmospheric Radiation Measurement (ARM) Program discovered surprisingly large differences in the results from various techniques used to measure the properties of low-lying clouds. To increase confidence in future measurements, they decided to learn more about these clouds first-hand—from the sky.

After a year of planning and coordination by the ARM Climate Research Facility team, the Routine AVP CLOWD Optical Radiative Observations (RACORO) field campaign will obtain representative statistics of cloud properties from the Earth's surface up to an altitude of about 3.6 kilometers (12,000 feet). Using a Twin Otter aircraft, several science flights per week are planned for the duration of the campaign, ending on June 30.

Equipped with a comprehensive set of probes and sensors to measure solar and thermal radiation, cloud microphysics, aerosol properties and atmospheric state, the Twin Otter will fly over the ARM Climate Research Facility site centered near Lamont, Oklahoma.  Established in 1994, this heavily-instrumented research site operates 24/7 to obtain continuous ground-based atmospheric measurements ideally suited to climate studies. Data obtained during the RACORO field campaign will be used to validate ground-based measurements and support model simulations and studies of cloud processes.

Andrew Vogelmann
Andrew Vogelmann

"This is the first time that a long-term aircraft campaign has been undertaken for systematic in-cloud sampling of cloud field properties and will go a long way toward validating and improving the retrieval algorithms for ground-based measurements of these cloud types," said Dr. Andrew Vogelmann, a scientist from Brookhaven National Laboratory and the principal investigator for the campaign.

Clouds contain different amounts of water and ice, which affect their opacity and make them appear either thick or thin. These characteristics directly affect how much sunlight the cloud transmits to Earth or reflects back into space. This energy feedback process is a key component of climate.

In addition, low-level "thin" clouds are often tenuous and scattered, which makes their properties—such as water content and water droplet size—hard to measure accurately with ground-based or satellite instruments. Scientists rely on these measurements as input to climate models, and because these cloud types occur all over the globe, it's important that the models have accurate data.