The storm began somewhere between Iceland and Greenland, as disturbances high and low in the atmosphere united into a full-fledged cyclone. One day later, the vast spiral of winds had grown nearly as big as Mongolia. It was on a beeline for Svalbard, the archipelago between Norway and the North Pole, and heading for the thin floes girding the Arctic’s vulnerable pack of summer sea ice. And that made John Methven very, very happy.
Last week, Methven, an atmospheric dynamicist at the University of Reading, flew through the storm as part of an airborne campaign based out of Svalbard’s Longyearbyen, the world’s northernmost town. As his Twin Otter plane shuddered through tropical storm–force winds of 100 kilometers per hour, flying just 15 to 30 meters above the sea surface, Methven and the crew took measurements of the ice, water, and air before returning to a bumpy landing on Svalbard. It was the third, and strongest, cyclone that U.K., U.S., and French teams had captured in a monthlong effort.
“It’s really exciting to get this sequence [of cyclones],” says Methven, leader of the U.K. component of the Thin Ice campaign, the first airborne project to study how these summertime storms affect sea ice. “People are going to be pretty pleased.”
With data from the ice-skimming plane, a second aircraft flying through the tops of the storms, and dozens of weather balloons, the Thin Ice teams hope to learn how these common but poorly understood storms form, function, and chew up sea ice. They also plan to gauge how the properties of the sea ice—smooth, rough, or missing—feed back into the storms themselves. The data should help improve Arctic weather models and sharpen the picture of how summer cyclones may be accelerating the retreat of Arctic sea ice, already on the run because of global warming.
The storms whip up waves that menace Arctic fishing vessels and send storm surges into coastal villages. “A lot of these communities are having to move,” says Julienne Stroeve, a polar scientist at the University of Manitoba (U of M). “They’re falling into the ocean.” The cyclones also threaten the cargo and cruise ships rushing to take advantage of newly ice-free passages in the summer. Better models will “make it safer” to travel the region, says Alex Crawford, an Arctic climate scientist at U of M. “You’ll have a better clue to stay in port or go on.”
Summertime Arctic cyclones are very different beasts from tropical cyclones: not as powerful but sometimes larger. The aptly named Great Arctic Cyclone of 2012 stretched 5000 kilometers across, spanning the entire Arctic Ocean. With little topographic relief to disrupt them, the storms can wander around the Arctic Ocean for weeks on end. “There’s nothing to get rid of them,” Methven says.
Hurricanes are fueled by the energy in water vapor rising from a warm ocean, but Arctic cyclones get their spark from horizontal temperature differences. At high altitude, kinks in the polar vortex, a collar of winds 5 to 8 kilometers up that keeps warm midlatitude air separated from cold Arctic air, can start air spinning. Near the surface, temperature differences between the ocean and the ice front or between land and the ocean can do the same. When a low-level spin-up meets up with one at the top, they intensify into a cyclone. Other Arctic cyclones are imports—storms from lower latitudes that wind up in the “garbage bin” of the Arctic, Crawford says.
Unlike hurricanes, Arctic cyclones blow across an ocean partly covered by sea ice—with complex consequences for both winds and ice. Early in the summer, the storms’ cloud cover can inhibit melting. But by August, as ice thins near the edge of the pack, cyclones can speed melting by pushing floes to warmer waters, breaking up ice into smaller floes that melt more easily, and creating waves that stir up warmer waters. Meanwhile, the rough surface of the ice can act as a brake on the winds. Yet the friction can also help the storm persist by keeping its core stable, Methven says.
Weather and climate models struggle to forecast both the storms and their interactions with sea ice. In early August, two leading models differed by a full day in when they predicted a major storm would arrive, says Jim Doyle, an atmospheric scientist at the Naval Research Laboratory and the leader of the U.S. component of Thin Ice. Methven says the U.K. Met Office’s model creates storms that tend to melt summer ice too fast, whereas the model at the European Centre for Medium-Range Weather Forecasts leaves too much ice lingering.
The models perform poorly in part because data on Arctic conditions are relatively scant, with few weather stations. The models also struggle with the physics of Arctic clouds, which often contain a mix of frozen and liquid droplets. “Getting the balance between the liquid and ice phase is really, really hard,” says Ian Renfrew, a meteorologist at the University of East Anglia. Thin Ice’s high-flying aircraft will help tune models by gathering detailed cloud data from within the storm.
Modelers are also eager for surface-level data, especially along the rough, busted-up perimeter of the ice pack, a region called the marginal ice zone. In the past few years, Renfrew says, a few models have begun to include a parameter to account for the roughness of the marginal ice instead of treating it as uniformly smooth. That seems to improve the models’ forecasts of cyclones and ice loss, but researchers don’t know whether their parameter matches reality. By directly measuring the roughness of the ice and how its friction pushes back on storms, the ice-skimming flights should help models forecast the complex interplay of winds and ice.
The storms are a major driver of sea-ice retreat. The 2012 Great Arctic Cyclone destroyed 500,000 square kilometers of ice—an area the size of Spain, says Steven Cavallo, an atmospheric scientist at the University of Oklahoma, Norman. Cyclones routinely destroy a couple hundred thousand square kilometers of ice and could be ultimately responsible for up to 40% of annual ice losses, he says. “We think it’s pretty significant. And it’s growing.”
Doyle doesn’t see any sign that climate change is creating stronger or more frequent summertime storms, in recent decades at least. But he says warming makes the ice more vulnerable to the regular parade of cyclones. “The ice is thinning, and so the Arctic cyclones are having a much bigger impact.”
Models suggest the Arctic will lose all its summer sea ice by 2050, if not sooner. How that will affect the summer storms is “the million-dollar question,” says Elina Valkonen, an atmospheric scientist at Colorado State University. Competing forces are at work. The open, warmer ocean is expected to provide more moisture and fuel for storms, but it would also reduce the low-level spin-ups that spark many storms, by eliminating temperature gradients at what was once the ice front and diminishing gradients between ocean and land.
In unpublished work, Valkonen and colleagues looked at scenarios for the year 2100 from a set of models tuned for an ice-free Arctic. They found no change in the predicted pressure for the summer storms, which defines their strength. And although the number of storms rose slightly, that was only due to imported storms from lower latitudes, not cyclones generated in the Arctic. Still, it might not all be good news. Without rough ice to slow them, the storms tended to be longer lasting, with faster winds, Valkonen says. “When you’re a fisherman in the Arctic, that’s what you care about.”