Researcher helps examine puzzling Arctic Ocean ice fog

A type of cloud that forms low near Alaska’s northern coast and over the Arctic Ocean lasts far longer than scientific understanding says it should.

Associate research professor Carl Schmitt is helping a federally funded research team figure out why it’s happening.

The work is important to a variety of interests, including forecasting, shipping, defense and local communities.

“These clouds exist for three or four or five days, where theory suggests they might last just an hour or two,” Schmitt said.

Schmitt is with the Alaska Climate Research Center at the University of Alaska Fairbanks Geophysical Institute. He recently received Office of Naval Research funding to participate in the Navy’s Fog and Turbulence Interactions in the Marine Atmosphere project, or FATIMA.

FATIMA’s goal is to increase understanding of fog in marine environments, especially fog that forms over shallow seas and shelves and ice fog that forms in extremely cold conditions. The five-year project began in 2021 and is led by the University of Notre Dame, with participation by the University of Minnesota, University of Utah, Naval Postgraduate School and the Scripps Institution of Oceanography.

Schmitt and the ice particle sampler he developed will be joining the FATIMA team and its instruments at the U.S. Department of Energy atmospheric research station near Utqiaġvik for three weeks starting in mid-November.

The research target is a type of Arctic cloud known as mixed-phase, one that contains both ice crystals and liquid water droplets.

Why it matters

Arctic mixed-phase clouds and the surface influence each other in a feedback loop: The surface supplies the heat and moisture that sustain the clouds, while the clouds trap infrared radiation and warm the surface. 

Ice fog occurs 20–25% of the time during high-latitude cold seasons, according to FATIMA’s principal investigator, Harindra Joseph Fernando, engineering and geosciences professor at the University of Notre Dame.

“An understanding of the interaction between ice-nucleation aerosols, droplets, ice crystals and turbulent frigid air is imperative in quantifying conditions for ice-fog formation,” Fernando said.

In addition to posing challenges for shipping and travel, Arctic ice fog can interfere with military operations.

Fernando wrote in the FATIMA funding proposal that ice fog can sharply reduce the effectiveness of the Navy’s high-energy laser defense systems in polar regions. A laser beam striking the ice particles triggers a process that can cause the particles to absorb almost all of the laser’s energy.

Ice crystals can also damage the heat shields on supersonic and hypersonic vehicles, Fernando writes.

The science

Scientists don’t fully understand how mixed-phase clouds persist as long as they do in the Arctic.

Typically, mixed-phase clouds occur when a liquid droplet cloud forms in a below-freezing environment. Ice particles can either form within the droplet cloud or fall into the liquid cloud from above, and they tend to grow while liquid droplets evaporate. That happens because water vapor sticks more easily to ice than liquid when the temperature is below freezing. 

The Arctic has far fewer aerosols in the air that lead to the formation of ice particles — ice nuclei — than in southerly regions. In those regions, there are enough ice particles that the liquid droplets evaporate completely.  

“The whole process should lead to the collapse of the cloud,” Schmitt said.

 But not in the Arctic. The clouds hang around.

“Ice nuclei seem to be extremely rare in the clean environment up in the North,” Schmitt said. “There are sufficient ice particles to change the character of the clouds but insufficient ice particles to cause the cloud to dissipate completely like they do farther south.”

 “Where these ice particles are coming from is still somewhat of a mystery,” he said. 

Schmitt’s imager may help solve that mystery. Here’s how it works: Ice particles land on an exposed portion of a small rotating oil-coated glass disc. Particles stick to the oil and are rotated in front of the camera, which makes an image and stores it. The automated system detects particles as small as 5 microns.

Secrets of the ice

Schmitt has been interested in ice crystals for many years. In them he sees something deeper, much like a master painter’s art might reveal more than a photograph would of the same subject.

“When you look at a Monet painting, you’re looking at different sizes — brush strokes, objects, color blocks — but you see similar relationships. That’s what you get with ice crystals. 

“Large ice crystals can be made of smaller crystals that seem to be stuck together randomly, but how do you explain that randomness?” he said. “That’s always been something that’s intrigued me about ice particles.”

There is no one-size-fits-all answer, Schmitt said.

“We need to take into account the variability, that fractal nature of things, and put that into our models,” he said.