A group of 17 scientists, led by Judith Curry of the University of Colorado, scrutinized sea ice, clouds, and local weather around the Beaufort Sea north of Canada during late September and October, as the darkening polar autumn gripped the region. The frigid Arctic is a hot spot for scientists because some global climate models predict that doubling of carbon dioxide over the next century could lead to winter warming of up to 15 degrees C in the far north, compared to 2-3 degrees C elsewhere.
Judith Curry checks out the equipment aboard the NCAR/NSF C-130. (Photo by Robert Bumpas.)
The NSF Office of Polar Programs is funding Curry's participation in the study, called the Beaufort and Arctic Seas Experiment (BASE). Other sponsors are Canada's Atmospheric Environment Service and the Institute of Ocean Sciences. BASE is a component of the Global Energy and Water Cycle Experiment, which in turn is part of the World Climate Research Program.
"The global climate models treat the sea ice and important radiation processes in the Arctic fairly crudely, so we don't know whether we can believe what the models are telling us. And there's a big difference-- especially in the Arctic--if you compare results from two or three different models," Curry explains.
To get some ground truth on the area, a Lockheed C-130 aircraft (owned by NSF and operated by NCAR) and a Canadian Convair 580 flew researchers and instruments over the Beaufort Sea north of the mouth of the Mackenzie River at the eastern edge of the remote Northwest Territories.
Working at a breakneck pace over the past year, NCAR aeronautical engineer Diana Rogers and others converted the C-130, a former Navy communications plane, into a state-of-the-art research aircraft in time for the mid-September departure to Fairbanks, Alaska, where the experiment was based. Rogers says, "Besides fabricating and mounting special racks and pods, installing 11 kilometers of electrical wire, and cutting a viewing port in the airplane's floor, we also added the basics--a toilet and a galley."
During the experiment's ten-hour flights, NCAR engineers and technicians in the aircraft's "quiet room" operated a cluster of instruments recording basic meteorological conditions--temperature, humidity, air pressure, wind gusts--while two radiometers focused on sea ice and clouds. Assistant project manager Julie Haggerty monitored colorful video displays of real-time data streaming from a microwave radiometer as it scanned the sea ice below through its custom-made viewing port in the floor. The radiometer measured sea-ice brightness temperatures; brightness temperatures at different microwave frequencies indicate the ice's thickness and age. Associate scientist Krista Laursen operated a multichannel cloud radiometer that tracked cloud-top temperatures, height, ice and liquid water content, and particle sizes from a pod under one of the aircraft's wings. Meanwhile, instruments attached to moored buoys in the Beaufort Sea recorded the ocean temperature, currents, and saltiness as well as the thickness distribution of the sea ice.
Once all the numbers have been analyzed and the models compared with the observations, scientists will be one step closer to determining whether, and how much, the Arctic sea ice might melt if the global climate warms over the next century. Sea ice in the central Arctic, which is extensive even after the usual summer melting, reflects considerable solar radiation back to space. If the thickness or area of that ice cover shrinks with greenhouse warming, it will reflect less radiation, allowing more heat to remain in the earth's system. This in turn will cause further melting--and further warming.
The key player in these spiraling feedbacks is the region's radiation balance, which depends heavily on clouds. So far Arctic clouds have been nearly impossible to observe, partly because they're thin. In the dark winter you can't see them from the ground. Although satellites have routinely scanned this region along with the rest of the globe, interpretation of Arctic cloud properties from satellite data has remained uncertain. The clouds are as cold and bright as the snow and sea ice below. This lack of contrast makes the satellite images difficult to interpret. Curry says, ̉There are some clever people working on satellite cloud retrievals for the Arctic, but until now we've had no data to check when they ask, 'Did I get it right?' So we went up there with two airplanes to get some reality into this picture."
BASE is a pilot study for a much larger effort, to begin in 1997, in which researchers will conduct a year-long field experiment from a drifting sea ice camp in the Arctic Ocean. Called SHEBA (Surface Heat Budget of the Arctic Ocean), the program is sponsored by NSF, NASA, the Office of Naval Research, and the Department of Energy (DOE). This second round of more comprehensive observations will again focus on sea ice, clouds, radiation, and their interaction with local weather. In conjunction with SHEBA, both DOE's Atmospheric Radiation Measurements program and Phase III of NASA's First International Satellite Cloud Climatology Project will be taking extensive measurements in the region.
As the data analyses are completed, one of the first to benefit from a rigorous reality check will be a high-resolution Arctic climate model being developed at the universities of Alaska, Illinois, and Colorado. This regional model will eventually be nested into the global climate models, where it can help tighten scientists' predictions of sea ice melting and temperature rises in this potentially volatile area.
Curry is working with James Maslanik, Guosheng Liu, Jeffrey Tilley, and Jeffrey Key, also of CU; and William Rossow of NASA's Goddard Institute for Space Studies. A total of eight graduate students from CU, Colorado State University, and the University of Alaska at Fairbanks participated in the study.