Goodbye, ice—
hello, snow and rain
Model predicts increasing autumn precipitation for Arctic Ocean
The Arctic Ocean is losing its sea-ice blanket, but not its rain or snow. In fact, autumn precipitation is on the rise, says Julienne Stroeve of CIRES' National Snow and Ice Data Center.
Stroeve is trying to understand how thawing Arctic sea ice impacts the Northern Hemisphere climate. As the air becomes warmer and moister from that thawing, cyclones might become more frequent and intense, she says, which could make for more rain or, in the colder months, snow.
To test both theories, Stroeve used a sophisticated computer program created by NSIDC Director and CIRES Fellow Mark Serreze to track down cyclones. Into this program, she fed reanalysis data values (see sidebar at right) for sea-level pressure. The program used the data to identify when and where cyclones had occurred in the region from 1979 to 2008. Then, Stroeve then looked again at the reanalysis data to see the levels of rain and snow that accompanied the cyclones.
Applied over the Arctic Ocean, the program predicts that cyclones will become both more intense and frequent, leading to autumn
Reanalysis
In reanalysis, weather and climate researchers reconstruct past weather conditions on Earth, starting with incomplete observations. Reanalysis datasets combine real, historic observations with modern numerical weather forecast models that incorporate understanding of how the atmosphere works. The technique allows researchers to "hindcast" historical conditions for locations where no observations were taken.
downpours or snowy showers. An increase in cyclone intensity would be no surprise, Stroeve said, as the water-heavy atmosphere is ripe for the cyclones. "You just have more energy for storms," she said.
The program, however, output something unexpected: While there was a total precipitation increase for the entire region, a large proportion of this precipitation came from the North Atlantic region — a region that is always ice-free. "When you look at
the spatial patterns of where the increased precipitation is happening, it is not exactly where you would expect it to be," Stroeve said. "So that leaves you unable to conclusively attribute it to reduced sea-ice extent."
Two factors could be playing a part in this unexpected result, Stroeve said. Potentially, the loss of sea ice could be driving circulation changes, making for stronger North Atlantic storm tracks that are dumping more precipitation in the region, she said. Or it simply could be too early to detect an emerging pattern between sea ice loss and more precipitation. "These really large open water areas have only just recently happened," she said. "So the time period for a robust signal is relatively short."
Stroeve plans to continue investigating the relationship between sea ice and regional precipitation with climate models. "We hope to get at causation by using models," Stroeve said. "With models we can isolate the atmospheric and terrestrial response to depleted Arctic sea ice."
