In the Arctic, a mysterious atmospheric phenomenon generates some of the oddest clouds on Earth.
Up there, streaky wisps can swiftly transform into towering thunderstorms. These strange clouds are not just visually mesmerizing. Nor are they just drivers of powerful storms. They may also play a role in the Arctic’s breakneck pace of warming, researchers say, a pace about four times as fast as that of the rest of the planet (SN: 8/11/22).
But climate simulations of the region can’t accurately incorporate the birth and evolution of these clouds: There’s simply too little known about the forces that shape them.
An international team of scientists is now confronting that uncertainty head-on. From late February to early April, the researchers repeatedly soared into the Arctic’s stormy skies, employing a heavily instrumented C-130 aircraft to study the clouds’ shape-shifting and collect a wealth of data.
Its findings, the team hopes, will be the first step to piercing a longstanding, cloudy mystery.
Swells of cold Arctic air give birth to these clouds
The Arctic clouds are the result of one of the most intense collisions of air masses on the planet.
Marine cold-air outbreaks, or MCAOs, are surges of cold, dry air that regularly whoosh seaward from the land to encounter warmer air over the oceans. In response, the ocean waters release huge amounts of heat and moisture that rise into the atmosphere and condense into clouds.
The MCAO-powered clouds have a distinct pattern. “It’s beautiful to look at in satellite imagery,” says Paquita Zuidema, an atmospheric scientist at the University of Miami’s Rosenstiel School of Marine, Atmospheric and Earth Science in Key Biscayne, Fla. These clouds are “so visually stunning,” says Zuidema, who co-led the expedition.
The first clouds to form from the MCAOs are thin rows of small, kilometer-scale “streets” that line up with the wind as they emerge just off land. Farther downwind and farther out to sea, the streaks evolve into larger, open-celled clouds, big puffs with patches of clear air at the center.
Those cells can be as much as 20 to 30 kilometers across, and up to a kilometer tall, says atmospheric scientist Bart Geerts, another co-lead on the project. Eventually, they can become towering, thick cumulonimbus clouds as tall as 5 kilometers.
Researchers have limited intel on these clouds
The cumulonimbus clouds that emerge from MCAOs are not quite like the thunderstorm-producing clouds of the lower latitudes, in that they very rarely produce lightning, says Geerts, of the University of Wyoming in Laramie. But they can produce heavy snowfall — and sometimes intense, hurricane-like storms called polar lows (SN: 1/17/23).
Compared with tropical cyclones, these cyclones are small and therefore more difficult to predict. Improving predictions of these destructive events is of intense interest to Arctic nations, Greet says — improvements that the team’s flights might help with.
Another key question the researchers hope to answer is how much liquid the clouds contain, relative to ice, and how that proportion changes as they evolve. That proportion matters, Zuidema says, because liquid clouds are brighter, reflecting more sunlight back into space than ice clouds. That means that liquid clouds can reduce warming at the surface, while ice clouds can trap more of the sun’s heat, enhancing warming.
“In the last 10 years or so, people have realized that the proportions of liquid and ice clouds are actually pretty far off in climate models,” Zuidema says. “That’s a goal for the climate modeling community.”
The trouble is that there are relatively few direct observations of the water and ice content in these Arctic clouds to help validate climate simulations of future warming. That’s in part because these phenomena occur far offshore in one of the world’s most remote regions. And the clouds, though visible to satellites, are too small for spacecraft to capture essential characteristics that help control their evolution over time, such as the small-scale vertical motions that drive upward air drafts.
What impact the region’s rapid warming is having on the rest of the planet’s weather patterns is also still unclear, she adds. “We do think that the Arctic and mid-latitude weather should be linked,” she says. But the nature of those long-range atmospheric “teleconnections” is still uncertain.
So Zuidema, Greet and colleagues have been getting up close in their tricked-out C-130.
Repeated polar flights are starting to fill in the details
During this year’s mission, the team flew eight flights over the Arctic, flying above, below and through the MCAO-spawned clouds.
The plane carried several remote sensing instruments: lidar, which uses laser pulses to measure the dimensions of clouds or land surfaces; radar, which uses radio waves for the same purpose; and radiometers, to measure fluxes of infrared radiation, or heat. The data collected by these instruments, the team says, can help assess the proportions of ice and water in the clouds. Meanwhile, the team also deployed dropsondes, metal cylinders about a third of a meter long that are attached to small parachutes. The dropsondes collect measurements of temperature, humidity and wind as they sink through the atmosphere.
The goal, Zuidema says, was to collect enough data on enough different MCAO events that scientists can begin to build a statistically robust picture of them, one that can be incorporated into computer models with confidence. The team is now beginning to analyze all their data, which they plan to present next January at the American Meteorological Society’s annual meeting in New Orleans.
This year’s fieldwork is a good start, she says. “We got some interesting case studies this time.” But more data is always better when it comes to validating computer models. “What we’re really hoping for is to develop the kind of statistics that a modeler would want.” That will likely require future flights into the stormy Arctic skies.
Source: Heart - www.sciencenews.org
