Sea Ice Outlook: How Scientists Calculate State Of Sea Ice
August 15, 2012

Sea Ice Outlook: How Scientists Calculate State Of Sea Ice

Brett Smith for - Your Universe Online

While the Sea Ice Outlook could be viewed as a non-scientific crowd sourcing on the low point of Arctic sea ice each year, an averaging of the results produces a surprisingly constant result year after year.

The U.S. government program, which emerged out of March 2008 climate change workshops in Palisades, NY, asks for regular submissions regarding the expected state of sea ice. The report generated by the program includes predictions by enthusiasts, but could also be seen as a “race to the top” that provides incentives and promotes climate researchers who submit the most accurate predictions.

"Essentially it's not for prediction but for understanding," said Jinlun Zhang, an oceanographer in the University of Washington´s Polar Science Center. "We do it to improve our understanding of sea ice processes, in terms of how dynamic processes affect the seasonal evolution of sea ice."

Working with colleague Ron Lindsay, a climatologist at the Polar Science Center, Zhang´s calculations this year were the first to include data from a new NASA program called Operation IceBridge that uses an airplane-based laboratory to measure ice at sea as well as in Arctic ice sheets.

Operation IceBridge uses different radar devices to examine the thickness and density of the entire ice column, from the surface to the bedrock below. For measuring floating ice, the scientists use gravimeters and magnetometers managed by Columbia University.

In making their calculations, Zhang and Lindsay started with a model pioneered by Zhang, known as the Pan-Arctic Ice Ocean Modeling and Assimilation System. That system combines available data with a model to track sea ice volume, which includes both ice thickness and area.

"One drawback to making predictions is historically we've had very little information about the thickness of the ice in the current year," said Lindsay.

He added that Operation IceBridge has allowed researchers that make calculations that are both more accurate and timelier.

"This is the first year they made a concerted effort to get the data from the aircraft, process it, and get it into hands of scientists in a timely manner," Lindsay said. "In the past, we've gotten data from submarines, moorings, or satellites but none of that data was available in a timely manner. It took months or even years."

The NASA program has provided a wealth of data, however the radar used by the system becomes inaccurate after the spring thaw has begun. So, to compensate for this predicament, the UW scientists have decided to use calculations based on recent history to fill in the blanks.

"Jinlun came up with the idea of using the last seven summers. Because the climate is changing so fast, only the recent summers are probably relevant," Lindsay said.

While Operation IceBridge has proven extremely valuable, it is only considered a stopgap while NASA designs and builds a new satellite system that will observe Arctic ice activity. The new system will replace a previous satellite launched by the space program that used to deliver ice thickness data but has since failed.