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DOE Pulse
  • Number 404  |
  • January 6, 2014

Polar impress: Scientists improve detection of Arctic clouds

A multifilter rotating shawdowband radiometer (MFRSR) measures direct and diffuse sunlight in Barrow, Alaska. Now that PNNL scientists have a new method for screening out the thin clouds prevalent at this site, MFRSR measurements of aerosol particles will be much more accurate. Photo courtesy of the ARM Climate Research Facility.

A multifilter rotating shawdowband
radiometer (MFRSR) measures direct and
diffuse sunlight in Barrow, Alaska. Now that
PNNL scientists have a new method for
screening out the thin clouds prevalent at
this site, MFRSR measurements of aerosol
particles will be much more accurate.
Photo courtesy of the ARM Climate
Research Facility.

Thin Arctic clouds can no longer hide, thanks to scientists at DOE’s Pacific Northwest National Laboratory. Atmospheric data gathered by skyward-pointing instruments can be “contaminated” by clouds so wispy that they appear to the instruments as tiny, suspended particles or aerosols, which are actually the desired target. The team showed how a simple modification to the typical methods used to detect denser clouds and remove them from the data results in more accurate measurements of aerosols. With these improvements, scientists can better understand how aerosols influence climate changes in the Arctic.

“Thin and almost uniform Arctic clouds are occasionally undetected by well-established methods,” said Dr. Evgueni Kassianov, atmospheric scientist and the study’s lead author. “Our research found a minor modification of these methods that substantially improves the detection of these clouds, thereby reducing cloud contamination of aerosol data sets.”

Kassianov and the other PNNL researchers conducted an observational study based on a multi-year and integrated dataset of aerosol and clouds collected at the high-latitude Atmospheric Radiation Measurement (ARM) Climate Research Facility’s North Slope of Alaska. Two sites provided data, one on the northern coast in Barrow, Alaska, and the second in Atqasuk, Alaska, about 100 kilometers inland from the coast. They documented occasional failures of the well-established cloud-screening methods, which had great success at other lower latitude ARM facility sites, where the clouds are thicker and more opaque. The team uncovered the main reasons for such failures: thin, wispy clouds. They proposed and evaluated an improved version of these cloud-screening methods, which in turn led to improved aerosol climatology at the ARM Alaska sites.

Next, the researchers plan to apply the improved method to similar datasets collected at ARM sites globally. These extended applications will provide important observational constraints for model-based estimates of the aerosol impact on the Earth’s radiation budget.

DOE’s Office of Science, Office of Biological and Environmental Research, ARM Climate Research Facility funded the study.

[Kristin Manke, 509.372.6011,
kristin.manke@pnnl.gov]