The Arctic is warming rapidly. These clouds may hold clues as to why

An international team of scientists is now confronting this uncertainty head-on. From late February to early April, the researchers soared repeatedly into stormy Arctic skies, using a heavily instrumented C-130 aircraft to study changing cloud shape and collect a wealth of data. .

Its findings, the team hopes, will be the first step in unraveling a long and murky mystery.

Blows of cold Arctic air give rise to these clouds

Arctic clouds are the result of one of the most intense collisions of air masses on the planet.

Marine Cold Air Outbursts, or MCAOs, are waves of cold, dry air that regularly cycle seaward from land to meet warmer air over the oceans. In response, ocean waters release large amounts of heat and moisture that rise into the atmosphere and condense into clouds.

Clouds powered by MCAO have a distinctive pattern. “It’s beautiful to look at in satellite images,” says Paquita Zuidema, an atmospheric scientist at the University of Miami’s Rosenstiel School of Marine, Atmospheric and Earth Sciences in Key Biscayne, Fla. These clouds are “so visually stunning,” says Zuidema. who co-led the expedition.

The first clouds that form from MCAOs are thin rows of small, kilometer-scale “streets” that line up with the wind as they rise off the ground. Farther downwind and farther offshore, the bands evolve into larger, open-celled clouds, large puffs with patches of fresh air in the center.

These cells can be up to 20 to 30 kilometers wide and up to a kilometer long, says atmospheric scientist Bart Geerts, another co-leader of the project. Eventually, they can become high and thick cumulonimbus clouds up to 5 kilometers high.

Researchers have limited information on these clouds

Cumulonimbus clouds that emerge from the MCAO are not quite like the thunderstorm-producing clouds of 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 strong, hurricane-like storms called polar lows (SN: 17.01.23).

Compared to tropical cyclones, these cyclones are small and therefore more difficult to predict. Improving forecasts of these devastating events is of great interest to Arctic nations, Greet says — improvements that the team’s flights can help with.

Another key question the researchers hope to answer is how much liquid clouds contain, relative to ice, and how this ratio changes as they evolve. This ratio matters, Zuidema says, because liquid clouds are brighter, reflecting more sunlight into space than ice clouds. This means that liquid clouds can reduce surface heating, while ice clouds can block more of the sun’s heat, increasing warming.

“In the last 10 years or so, people have realized that the proportions of liquid clouds and ice are actually very far off in climate models,” says Zuidema. “This is a goal for the climate modeling community.”

The problem 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. This is partly because these phenomena occur far from the sea in one of the most remote regions of the world. And clouds, although visible to satellites, are too small for the spacecraft to capture crucial features that help control their evolution over time, such as the small-scale vertical motions that direct air currents aloft. .

What impact the region’s rapid warming has on the weather patterns of the rest of the planet is also still unclear, she adds. “We think Arctic and midlatitude weather should be linked,” she says. But the nature of those long-range atmospheric “teleconnections” is still uncertain.

So Zuidema, Greet and colleagues have approached in their tricked-out C-130.

Repeated polar flights are beginning to fill in the details

During this year’s mission, the team flew eight flights over the Arctic, flying above, below and through clouds created by the MCAO.

The aircraft carried several remote sensing instruments: lidar, which uses laser pulses to measure the size 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 estimate the extent of ice and water in clouds. Meanwhile, the team also deployed rockets, metal cylinders about a third of a meter long that are attached to small parachutes. Dropsondes collect measurements of temperature, humidity and wind as they plunge through the atmosphere.

The goal, Zuidema says, was to collect enough data on enough different MCAO events that scientists could begin to build a statistically consistent picture of them that could be fed into computer models with confidence. The team is now starting to analyze all of their data, which they plan to present next January at the annual meeting of the American Meteorological Society in New Orleans.

This year’s fieldwork is off to 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.” This will likely require future flights into stormy Arctic skies.