NASA Satellites Show How Clouds Respond to Arctic Sea Ice Changehttps://phys.org/news/2021-09-nasa-satellites-clouds-arctic-sea.htmlFor decades, scientists have assumed that losses in Arctic sea ice cover allow for the formation of more clouds near the ocean's surface. Now, new NASA research shows that by releasing heat and moisture through a large hole in sea ice known as a polynya, the exposed ocean fuels the formation of more clouds that trap heat in the atmosphere and hinder the refreezing of new sea ice.
The findings come from a study over a section of northern Baffin Bay between Greenland and Canada known as the North Water Polynya. The research is among the first to probe the interactions between the polynya and clouds with active sensors on satellites, which allowed scientists to analyze clouds vertically at lower and higher levels in the atmosphere.
Sea ice acts like a lid on a pot of boiling water, explained Linette Boisvert, a sea ice scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, who was part of the study. When the lid is removed, heat and steam escape into the air.
"We're getting more heat and moisture from the ocean going into the atmosphere because the sea ice acts like a cap or a barrier between the relatively warm ocean surface and the cold and dry atmosphere above," Boisvert said. "This warming and moistening of the atmosphere slows down the vertical growth of the sea ice, meaning that it will not be as thick, so it's more vulnerable to melt in the summer months."
Like other polynyas in the Arctic and Antarctic, the North Water Polynya forms when specific wind patterns blow in a persistent direction and tear holes in the ice. These wind patterns only exist in the winter months, and the holes open and close repeatedly, alternately exposing and insulating the ocean.
The new research shows low clouds over the polynya emitted more energy or heat than clouds in adjacent areas covered by sea ice. Those low clouds contained more liquid water, too—nearly four times higher than clouds over nearby sea ice. The increased cloud cover and heat under the clouds persisted for about a week after each occasion the polynya refroze during the time span of the study."Just because the sea ice reforms and the polynya closes up, that doesn't mean that conditions go back to normal right away," Boisvert said. "Even though the moisture sources are essentially gone, this effect of extra clouds and increased cloud radiative effect to the surface remains for a time after [the polynya freezes]."
The findings also suggest the response of the clouds to the polynya lengthened the time the hole remained open, said Patrick Taylor, a climate scientist at NASA Langley, who also was part of the study.
"They can create a thicker blanket and increase the amount of heat emitted down to the surface," Taylor said. "The emitted heat helps keep the surface of the North Water Polynya a little warmer and helps prolong the event itself."
Emily E. Monroe et al,
Arctic Cloud Response to a Perturbation in Sea Ice Concentration: The North Water Polynya,
Journal of Geophysical Research: Atmospheres (2021)
http://dx.doi.org/10.1029/2020JD034409https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020JD034409https://www.nasa.gov/feature/esnt/2021/nasa-satellites-show-how-clouds-respond-to-arctic-sea-ice-change