Researchers journey to Sweden to study origins of cold air outbreaks in the Great Plains

Weather researchers from the University of Oklahoma are uncovering secrets behind cold air outbreaks that can trigger rapid, dramatic temperature shifts in the Great Plains – and they traveled to the Arctic Circle to do it.

The Cold Air Outbreak Experiment in the Sub-Arctic Region (CAESAR) field campaign took research scientists from the Cooperative Institute for Severe and High-Impact Weather Research and Operations (CIWRO) in Norman, OK, to Kiruna, Sweden, for nearly two months beginning in February. Spring temperature drops by 40-50 degrees Fahrenheit within 24- to 36-hour periods, spurred by cold air outbreaks, can deliver an unexpected jolt to the growing season and place undue stress on electrical grids throughout the United States.

“The understanding gained from the collected data will ultimately aid in producing better forecasts of cold air outbreaks that occur over the Great Plains region of the United States, which have significant socioeconomic impacts,” said CIWRO Director Greg McFarquhar, who led the project with Paquita Zuidema of the University of Miami and Bart Geerts of the University of Wyoming. He said the data collected during CAESAR were unique in that both internal cloud measurements, known as in-situ, as well as remote sensing retrievals were achieved through a Lagrangian framework, a method that measures the same air masses at multiple points in time and in different locations.

Scientists trace cold air outbreaks in the United States to Arctic locations like northern Sweden. Once the cold air forms off the sea ice in the Norwegian Sea, it typically sweeps over Greenland and Canada before blowing over the Great Plains. Little is known about the origins of these cold air masses. Researchers believe that by better understanding the evolution of these clouds they can better understand the modification of the cold air masses that can eventually impact the United States.

The CAESAR campaign, sponsored by the National Science Foundation, collected extensive cloud and environmental data near the sea ice and over the open water across 10 research flights. CIWRO Research Scientist Andrew Dzambo led the in-field forecasting team. The team examined multiple models daily to produce highly detailed forecasts for the experiment domain, in the far North Atlantic Ocean and Norwegian Sea.

“To maximize participation from senior scientists to undergraduates alike, we adopted a ‘crowdsourcing’ approach where everyone contributed four to eight slides into a presentation, while focusing on one aspect of the forecast,” Dzambo said. “This allowed us to examine an incredible amount of data in a short period of time.” Through this method, the team successfully predicted verifiable cold air outbreak conditions in over 85% of all forecasts as well as every research flight.

Several OU graduate students also participated in CAESAR project activities: Nick Amundsen, Qing Niu, Yayun (Jackie) Qiao, Amanda Richter, Erika Pruitt and Saurabh Patil. All were key to forecasting and aided other research groups, including the Dropsonde and Aerosol teams.

“We were extremely impressed with the students’ ability to learn new skills quickly, especially with concepts or products they were only seeing for the first time, and to seamlessly fit into the team dynamic,” Dzambo said.

The harsh Arctic weather conditions produced challenges for researchers. Heavy snowfall caused several research flights to be cancelled.

“De-icing the plane was not an option due to issues the de-icing fluid would cause to the instruments. We needed to stay diligent watching the local radar and finding windows where the airport would be clear for one to two hours for pre-flight preparation and takeoff,” Dzambo said. To circumvent weather complications, the forecasting team and mission scientists often convened early in the morning – sometimes as early as 4 a.m. – to evaluate conditions and prepare pre-flight forecast briefings.

The next step of the project is to conduct research using the new datasets. Dzambo will work on a climatology of cloud and meteorological conditions observed in the CAESAR domain, while Amundsen will focus his master’s thesis research on the in-situ cloud observations.

“My research aims to analyze Arctic cloud properties during cold air outbreaks using novel data from CAESAR. I will investigate how these properties change with environmental factors such as vertical velocities and proximity to the sea-ice edge, among other processes,” Amundsen said. His research will be a critical component for eventual observation-model comparison studies and modeling improvements.

McFarquhar said the research from CAESAR will have a profound impact on understanding weather phenomena, which has previously been unclear to forecasters.

"There is a key challenge to modeling cold air outbreaks because they occupy a dynamic gray zone where boundary layer processes are tightly coupled and cannot be represented independently. The CAESAR data will allow these connections to be better understood and represented in models.”

The first results from the CAESAR campaign will be presented at the International Conference on Clouds and Precipitation in Jeju, South Korea, this summer.