"These images, combined with data from other aircraft probes, will provide us with a complete data set of detailed information about ice clouds, particularly the numbers of small ice crystals - a parameter that is poorly known and of considerable importance for understanding how clouds affect radiation and climate," said Greg McFarquhar, one of the U.S. scientists involved in the effort, which is funded by the Department of Energy's Atmospheric Radiation Measurement Program.

Team members used the Cloud Particle Imager, an instrument developed by SPEC Inc. that provides high-resolution photos of ice crystals. They obtained the images as the Proteus aircraft climbed through a thin layer of cirrus clouds. The scientists are collecting data to help determine how the properties of ice clouds, including particle size and shape, vary with temperature and altitude. Such factors influence the longevity of the cloud, and therefore the amount of heat both reaching and escaping Earth.

The Proteus is one of five instrumented research aircraft taking part in the Tropical Warm Pool International Cloud Experiment, or TWP-ICE. Jointly led by the ARM Program and the Australian Bureau of Meteorology, the effort aims to collect comprehensive cloud and atmospheric property measurements of both cirrus and deep convective (thunderstorm) clouds - the source for much of the cirrus clouds observed in the tropics - in an area approximately 120 miles (200 km) in diameter, centered on Darwin.

Other aircraft participating in the experiment include the Twin Otter, also funded by ARM; the Dimona, sponsored by the Australian Bureau of Meteorology, and the Egrett and Dornier, sponsored by the Natural Environmental Research Council in the United Kingdom. The aircraft fly at altitudes ranging as low as 30 feet (50 m) to 10 miles (17 km), and contain sensitive instruments to measure various cloud properties, aerosol properties, temperature and humidity.

"Flying the aircraft on simultaneous missions at various elevations is a critical part of the experiment,� said Jim Mather, the ARM program�s lead scientist. "We were also able to fly several of the aircraft over our ground-based instrumentation. These aircraft data will be very useful for improving the cloud properties derived from the ground-based measurements."

The ARM Program operates a permanent climate research facility in Darwin. In place since April 2002, the site collects continuous measurements of tropical cloud and atmospheric properties. Scientists installed a comparable set of instruments onboard a self-contained research vessel provided by Australia's Commonwealth Scientific Industrial Research Organisation. The ship sits at anchor in the Timor Sea, about 60 miles west of Darwin. Team members compared measurements taken by the aircraft with measurements at the Darwin facility and aboard the vessel.

The research ship also serves as one of five surface sites to launch weather balloons every three hours, for a continuous record of atmospheric observations, and it operates one of four surface flux stations to gauge the exchange of energy between Earth�s surface and atmosphere. Scientists use the measurements to try to understand how convective storms develop. The experiment concludes on February 13.

Related Links
DOE ARM Program