Aerosols and Clouds: A Complex Climate Connection
New data will help researchers examine cloud composition and resulting effects on climate cycles
Contact: Lynne Roeder, ARM Public Information Officer, 509.372.4331
Clouds are more than just interesting shapes in the sky. They modulate the atmosphere that allows us to live and breathe. But what recipe does the sky follow that combines just the right amount—and type—of clouds to keep our climate system in balance? And is this recipe changing to keep up with the pace of manmade contributions to the mix?
Different types of clouds are determined by altitude and the variety and amount of ice crystal shapes they contain. These factors affect the lifetime of clouds, whether they form rain, and how much light they reflect or absorb. (Requires Adobe® Flash® Player to display.)
To help answer these questions, scientists will use data from a month-long intensive field study that begins today in Fairbanks, Alaska. Sponsored by the U.S. Department of Energy's Office of Science, the scientists will use a heavily instrumented research aircraft based out of Fairbanks to obtain cloud and aerosol measurements in the sky over Barrow, Alaska.
"It turns out that aerosols [microscopic airborne particles from both natural and manmade sources] act as "hosts" on which clouds form," said Dr. Steven Ghan, a climate physics scientist at Pacific Northwest National Laboratory and lead scientist for the campaign.
According to Ghan, the size and density of these aerosol particles affect the type and longevity of the subsequent clouds. They also affect how much energy—or heat—is reflected back into space or absorbed by the clouds. Ultimately, all these factors contribute to the energy balance of our planet.
A key objective of this field study, called the Indirect and Semi-Direct Aerosol Campaign (ISDAC) is a data set that will allow scientists to compare and contrast Arctic aerosol and cloud properties from the spring and fall. In October 2004, a similar experiment at the North Slope of Alaska focused on obtaining microphysical data on clouds consisting of both water droplets and ice crystals, called "mixed-phase" clouds." These cloud types are prevalent in the Arctic, but due to a lack of scientific data and analyses, they are poorly represented in current climate models.
"Decades of photographic evidence showing the decline of Arctic sea ice are a clear indication of a warming trend in that region of the world," said Dr. Johannes Verlinde, a professor at Penn State University and the lead scientist for the 2004 study. "However, current climate models do a poor job of simulating these observations. To improve our confidence in the models, we need real data from the environment associated with these conditions. Clouds and aerosols are key pieces of this complex puzzle."
To obtain measurements from within the clouds, the team is using a Convair-580 research aircraft from the National Research Council of Canada. While 10 aircraft instruments were used in the 2004 fall study, the current campaign boasts more than 40.
"For many of us, this is the largest payload of cloud and aerosol probes we have ever seen integrated on a single aircraft deployment," said Dr. Beat Schmid, Technical Director of the ARM Aerial Vehicles Program, which is coordinating the campaign.
The Convair will transit from Fairbanks to Barrow, spending between two to four hours "on station" obtaining measurements at various altitudes within the clouds before returning to Fairbanks. At the same time, DOE's Atmospheric Radiation Measurement (ARM) Climate Research Facility in Barrow will collect similar atmospheric data from the ground using its permanent collection of sophisticated sensors. Several more instruments have been added at the site to obtain key data during the campaign.
The research site in Barrow has collected continuous measurements since its installation in 1994. A smaller site with a subset of instruments was established in Atqasuk, about 70 miles inland from Barrow, and has been operating continuously since 1999. Data from the sites are freely available to scientists around the world via the program's website, www.arm.gov.
"Thanks to data from DOE's research sites in Barrow and Atqasuk, scientists have access to a high-quality, continuous record of atmospheric processes in the Arctic," said Dr. Verlinde, who is also the ARM Program's site scientist for the North Slope of Alaska.
Data obtained during this campaign will help scientists improve the accuracy of climate models with more realistic Arctic cloud representations and the resulting energy feedbacks. This period was chosen because it is during the International Polar Year when many agencies are deploying observational systems that will be useful for interpreting the data.
For more information, see the ISDAC website.