Home North pole ice Arctic Storm Chasers Brave Giant Cyclones to Understand How They Chew Sea Ice | Science

Arctic Storm Chasers Brave Giant Cyclones to Understand How They Chew Sea Ice | Science


The storm began somewhere between Iceland and Greenland, as disturbances high and low in the atmosphere coalesced into a full-fledged cyclone. A day later, the vast spiral of winds had become almost as big as Mongolia. It was heading for Svalbard, the archipelago between Norway and the North Pole, and heading for the thin floes surrounding the vulnerable Arctic sea ice in summer. And that made John Methven very, very happy.

Last week, Methven, an atmospheric dynamizer from the University of Reading, flew through the storm as part of an aerial campaign based in Longyearbyen, Svalbard, the world’s northernmost town. As his Twin Otter aircraft shivered 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 most powerful cyclone that the British, American and French teams had captured in a month.

“It’s really exciting to have this streak [of cyclones]says Methven, head of the UK component of the Thin Ice campaign, the first airborne project to study how these summer storms affect sea ice. “People are going to be pretty happy.”

With data from the ice-skimming plane, a second plane flying through storm tops, and dozens of weather balloons, Thin Ice teams hope to learn how these common but poorly understood storms form, function, and chew. sea ​​ice. They also plan to assess how the properties of sea ice — smooth, rough, or lacking — affect the storms themselves. The data should help improve Arctic weather models and better understand how summer cyclones could accelerate the retreat of Arctic sea ice, already on the run due to global warming.

Storms stir up waves that threaten Arctic fishing vessels and send storm surges into coastal villages. “A lot of these communities have to move,” says Julienne Stroeve, a polar scientist at the University of Manitoba (U of M). “They fall into the ocean.” Cyclones also threaten freighters and cruise ships that rush to take advantage of the newly ice-free passages in summer. Better models will “make it safer” to travel in the region, says Alex Crawford, arctic climatologist at the U of M. “You’ll have a better idea of ​​staying in port or moving on.”

Summer arctic cyclones are very different beasts from tropical cyclones: not as powerful but sometimes bigger. The aptly named Great Arctic Cyclone of 2012 was 5,000 kilometers in diameter, covering the entire Arctic Ocean. With little topographic relief to disturb them, storms can wander around the Arctic Ocean for weeks. “There’s nothing to get rid of,” Methven says.

Hurricanes are powered by the energy of water vapor rising from a warm ocean, but Arctic cyclones get their spark from horizontal differences in temperature. At high altitudes, the nodes of the polar vortex, a 5-8 kilometer collar of winds that separates warm mid-latitude air from cold Arctic air, can begin to spin the air. Near the surface, temperature differences between the ocean and the ice front or between the land and the ocean can have the same effect. When a low-level spin-up encounters one at the top, they escalate into a cyclone. Other Arctic cyclones are imports — storms from lower latitudes that end up in the Arctic “trash,” Crawford says.

On July 29, British scientists kicked off the Thin Ice campaign with a skimming flight from Longyearbyen in Svalbard, the world’s northernmost town.John Methven

Unlike hurricanes, Arctic cyclones cross an ocean partially covered in sea ice, with complex consequences for winds and ice. In early summer, cloud cover from storms can prevent melting. But in August, as the ice thins near the edge of the pack, cyclones can accelerate melting by pushing floes toward warmer waters, breaking ice into smaller floes that melt more easily, and creating waves. which agitate warmer waters. During this time, the rough surface of the ice can act as a brake on the winds. Yet friction can also help the storm persist by keeping its core stable, Methven says.

Weather and climate models struggle to predict both storms and their interactions with sea ice. Jim Doyle, an atmospheric scientist at the Naval Research Laboratory and head of the U.S. component of Thin Ice. Methven says the UK Met Office model creates storms that tend to melt summer ice too quickly, while the European Center for Medium-Range Weather Forecast model lets too much ice linger.

The models perform poorly in part because data on Arctic conditions is relatively sparse, with few weather stations. The models also struggle with the physics of Arctic clouds, which often contain a mixture of frozen and liquid droplets. “Getting the balance between the liquid phase and the ice phase is really, really difficult,” says Ian Renfrew, a meteorologist at the University of East Anglia. Thin Ice’s high-flying aircraft will help tune the models by collecting detailed cloud data inside the storm.

Modelers are also hungry for surface-level data, especially along the rough, splintered perimeter of the pack ice, a region called the marginal ice zone. In recent years, Renfrew says, a few models have begun to include a parameter to account for marginal ice roughness instead of treating it as uniformly smooth. This appears to improve model predictions of cyclones and ice loss, but researchers aren’t sure if their parameter matches reality. By directly measuring the roughness of the ice and how its friction repels storms, skimming flights should help models predict the complex interaction of winds and ice.

A global weather balloon is launched from Svalbard
Thin Ice aircraft campaigns were supplemented by dozens of weather balloons that drifted up to 20 kilometers. carried by the wind

Storms are a major factor in sea ice retreat. The Great Arctic Cyclone of 2012 destroyed 500,000 square kilometers of ice, an area the size of Spain, Steven Cavallo, an atmospheric scientist at the University of Oklahoma, told Norman. Cyclones regularly destroy a few hundred thousand square kilometers of ice and could be responsible for up to 40% of annual ice loss, he says. “We think it’s quite important. And it’s growing. »

Doyle sees no sign that climate change is creating stronger or more frequent summer storms, at least in recent decades. But he says the warming makes the ice more vulnerable to the regular parade of cyclones. “The ice is thinning, so Arctic cyclones have a much bigger impact.”

Models suggest that the Arctic will lose all of its summer sea ice by 2050, if not sooner. How this will affect 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 should provide more moisture and fuel for storms, but it would also reduce the low-level spin-ups that trigger many storms, by eliminating temperature gradients across what was once the front of ice and decreasing the gradients between ocean and land.

In unpublished work, Valkonen and his colleagues examined scenarios for the year 2100 from a set of models tuned for an ice-free Arctic. They found no change in predicted pressure for summer storms, which defines their strength. And although the number of storms increased slightly, this was only due to storms imported from lower latitudes, and not to cyclones generated in the Arctic. However, all may not be good news. Without rough ice to slow them down, storms tended to last longer, with faster winds, Valkonen says. “When you’re a fisherman in the Arctic, that’s what matters to you.”