Demystifying the complex nature of Arctic clouds

With dancing ribbons of light visible in the sky, a team of researchers flew into the cold unknown on a series of scenic and sometimes stormy flights, trying to learn more about why one of the frigidest places on Earth is moving at a feverish pace. warms up.

The researchers – an atmospheric scientist from the University of Miami and her two Ph.D. students – took the flights as part of a nearly two-month field campaign aimed at investigating the extent to which clouds generated by marine cold air outbreaks (MCAOs) reflect and potentially contribute to rapid Arctic warming, while also mitigating more extreme weather events in that Arctic region.

“The Arctic is changing rapidly and warming two to four times faster than the global average,” said Paquita Zuidema, professor and chair of atmospheric sciences at the Rosenstiel School of Marine, Atmospheric, and Earth Science and principal investigator of CAESAR. , or Cold Air Outbreak Experiment in the Subarctic Region. “There is still no consensus on why and how this is happening, and questions remain about how clouds contribute to or simply respond to these changes. The more we can learn now about the behavior of Arctic clouds, the better we can predict the Arctic of the future. Either way, as the Arctic becomes more accessible, we will need to improve Arctic weather forecasts in one of the worst observed regions on Earth.”

MCAOs, which can affect weather patterns around the world, form when cold, dry air moves over warm ocean waters, with the difference in air and sea temperatures causing the ocean to release large amounts of heat and moisture into the air. As part of that extreme air-sea energy exchange, an extensive boundary layer of convective clouds forms, sometimes producing intense hurricane-like polar lows.

These clouds are complex in nature and consist of both ice and liquid. But little is known about how they arise and evolve. “Understanding how those clouds distribute their moisture between liquid and ice is still not well represented in models,” says Zuidema. “And that’s becoming a big problem, because liquid clouds reflect a lot of sunlight. Ice clouds tend to just snow on the ground or in the ocean. So we want to know, in very cold clouds, how much of that moisture is liquid and how much is ice, and why and how that change occurs?

And that’s where CAESAR comes into the picture. During the recent field camp hosted by the National Science Foundation’s National Center for Atmospheric Research, students Sam Ephraim and Tyler Tatro of the Zuidema and Rosenstiel School from Kiruna, Sweden, flew aboard a C-130 Hercules aircraft . , which involved traveling to the Arctic sea ice edge off the coast of Greenland and using a suite of instruments that collected a wealth of data.

Dropsondes released by the C-130 recorded in-situ wind, temperature and humidity data as they traveled vertically through the atmosphere. Lidars, radars and radiometers on the plane determined the proportion of ice and water in clouds. Instruments mounted on the plane’s wings sampled cloud properties, while air intakes collected aerosols for analysis.

Scientists from eight other universities in the United States and from Stockholm University in Sweden, the University of Oslo in Norway and the US Naval Research Laboratory also participated in the field campaign. They investigate how aerosols, air from the stratosphere and small-scale dynamics influence the development of clouds. Model builders were also brought in to facilitate faster knowledge transfer.

For Ephraim, who flew on four of the eight CAESAR flights, the campaign was more than an opportunity to observe senior scientists at work. He played a crucial role in the success of the mission by operating the radiometer that measures the amount of radiation emitted by water vapor and liquid water in the air. In addition, he helped conduct weather forecast briefings for the team of scientists who determined whether flights would take off or remain on the ground on each day of the campaign.

“It’s one thing to sit in a classroom or in front of a computer and look at cold air outbreak data that other people have collected in other field campaigns, but it’s another thing to actually be able to see it with your own eyes and see it play out an active role in the investigation,” says Ephraim, who as a young boy decided he wanted a career in meteorology after watching several hours of Weather Channel coverage.

“Our whole effort was great,” he continued. “We saw the Northern Lights a lot. They were very active during the period we were there. And on the flights it was remarkable to see the transition from clear, sunny skies over the sea ice to stormy conditions.”

Tatro, who studies biomass burning and interactions with aerosol clouds over Africa, also assisted in operating the radiometer and helped plan some flights. For him, the campaign was ‘science from textbooks brought to life’.

“I got a sense of how much community there is in atmospheric science,” he said. “I have seen the names of famous scientists in books and on research papers. Seeing them in action and working with them gave me a sense of how passionate they are about their work.”

Preliminary analysis of the CAESAR data is now underway, with a special session on the proposed campaign for an upcoming meeting of the American Meteorological Society, Zuidema said.