The World War II-era Chicago school of meteorology that decoded weather forecasting

In the early twentieth century, Rossby was a rising star, studying in a Norwegian institute of geophysical science as the polar front theory was developed—some of the earliest large-scale studies of meteorology. The Norwegians had recently determined that enormous masses of cold dry air that descend from polar regions are the “leading players” in “weather drama,” wrote Time in a 1956 profile of Rossby. Their movements create the cold and warm fronts that appear in modern weather maps. 

In 1926, Rossby won a fellowship that placed him in the U.S. Weather Bureau to study the application of the polar front theory to American weather. During his first year in the United States, he studied turbulence and convection (the fluid-based rising of heat and sinking of cold), consulted with the booming aviation industry, and applied his mentor’s theory to U.S. weather maps.

But the Weather Bureau wasn’t “a pleasant place for the twenty-seven-year-old Swede,” wrote Horace Byers, a later student of Rossby’s who would become his longtime colleague and biographer. Rossby clashed with the bureau’s administration over a series of minor incidents that came to a head when he made an unauthorized weather forecast for Charles Lindbergh’s flight from Washington, DC, to Mexico City. Rossby left the Weather Bureau “literally persona non grata.”

Spherical cows and Rossby waves

Landing at MIT, Rossby established the first graduate program in meteorology in 1928. Using a research plane provided by the school and a new remote-sensing device carried by helium balloons, Rossby was able to access the upper atmosphere, where he detected the large-scale flow patterns that directly influence weather. These were planetary waves, now called Rossby waves, that naturally occur in rotating fluids. If polar air masses are weather stars, then Rossby waves are the producers.

Rossby’s research laid “the fundamental groundwork for our understanding of the mid-latitude atmosphere, between the tropics and the poles,” says Tiffany Shaw, associate professor in geophysical sciences at UChicago, whose research focuses on the physics of Earth’s current and future climate. “What was beautiful about his work was that he was using a very simple model. Starting with the complicated laws of physics, he had to make assumptions and came out with this emergent property of weather waves.”

Shaw, a physicist by training, invokes the “spherical cow” metaphor to explain why physicists like Rossby tend to simplify models. The joke goes, a dairy farmer asks for help increasing milk production. A theoretical physicist replies, “I have a solution, but it only works for spherical cows in a vacuum.”

A classic approach for theoretical physicists is to simplify models for complex systems. If you want to model the motion of a thrown ball as accurately as possible, you must consider the ball’s shape, texture, surrounding air density—countless considerations that affect the physics of the trajectory. Not only does that make solving complex problems daunting, it also leads to models that accurately predict the motion of footballs thrown in high humidity, but not baseballs thrown in dry heat. But if you consider only mass, you can predict the motion, imperfectly but well enough, for different scenarios.

This is what Rossby did with his planetary waves; he modeled their motion in two dimensions instead of three, neglecting aspects such as water vapor and vertical motion. His simplified model could then be studied via atmospheric observations or laboratory experiments. They also made future atmospheric science discoveries possible.

Soon after Rossby’s waves were discovered, he joined the University of Chicago to lead its brand-new institute.

War, waves and weather

The Second World War was a driving force in the founding of UChicago’s Institute of Meteorology. Arthur Holly Compton championed the program, calling it an “essential part of the contribution we can make to the national defense.” He argued that the University was already conducting groundbreaking research in physics, geography, and math. Second, it favored fundamental research, and third, it was located in a region with distinctive weather and in need of meteorologists for aviation, agriculture and industry.

The Institute of Meteorology opened in 1940 as part of the physics department. Rossby was called to lead the institute, with Byers as his right hand. That year, President Franklin Roosevelt called for the construction of 50,000 military aircraft, requiring 10,000 meteorology-trained officers; Rossby’s academic instruction quickly pivoted to military-based cadet training.

As students left Hyde Park to go to war after Pearl Harbor was bombed in late 1941, cadets took their place. “By 1942 all available dormitory space had been consigned to military programs,” writes College dean John W. Boyer in The University of Chicago: A History. International House was filled with meteorology cadets and Red Cross volunteers, and the Reynolds Club became the institute’s headquarters.

The curriculum, which crammed two years of material into a nine-month course, included common wisdom from old meteorology, but it was grounded in fluid dynamics. “Rossby was very much in the philosophy of training the next generation of meteorologists based on physics,” says Noboru Nakamura, a professor in geophysical sciences who studies the jet stream. Rossby wanted to teach these students not simply how to read a weather map, but how to analyze data (often collected by Air Force pilots) and recognize global patterns.

By the end of World War II, Chicago had trained more than 1,700 meteorologists.

A question of scale

After the war ended, the institute returned to its original focus on fundamental research, forming what would become known as the Chicago school of meteorology, with a heavy emphasis on physics, mathematics, and modeling. It was an exciting time, rife with “untested theories that needed a proof of concept,” says Nakamura. Data were flying in, ready to be applied to theoretical equations to see if they held up in practice.

Guided by wartime-gathered observations, Rossby’s team revisited his planetary waves. After bombing missions in Japan, B-29 pilots reported winds as high as 230 miles per hour at cruising altitudes. The winds caused bombs to miss targets and, when positioned as headwinds, burned extra fuel, draining the aircraft. Rossby thought these winds must be associated with his high-altitude waves and developed a mathematical theory to predict their behavior. He named these fast-moving rivers of wind “jet streams,” and they are now used in both weather forecasting and aviation planning.

The Norwegians, who approached weather from a comprehensive point of view, prioritized large movements and trends over localized phenomena: polar air masses, as well as low-pressure cyclones and hurricanes. Rossby went bigger; jet streams are part of global-scale meteorology, incorporating models of circulation around the planet. But research at UChicago also went smaller, into the meso, or middle, scale. This subfield of meteorology includes thunderstorms and tornadoes, and it blossomed after the war.

A significant contribution to mesometeorology came from the Congress-mandated and funded Thunderstorm Project. A collaboration among the Weather Bureau, the Army Air Force, the Navy, and NASA’s predecessor, the project studied storm causes and characteristics. Byers was appointed director. The project, which began almost immediately after the war ended, had access to airplanes, weather instruments, and an enormous cadre of trained personnel. It also had radar—previously highly classified technology used to monitor enemy aircraft—that was capable of tracking thunderstorms and visualizing precipitation structure within the clouds.

The Thunderstorm Project sent pilots through storms in radar-outfitted Black Widow warplanes, flying in a vertical stack at different altitudes to gather data on the storms’ traits and evolution. Then UChicago scientists analyzed the massive data sets by hand in a two-year effort. The discoveries made during the Thunderstorm Project provided foundational knowledge for severe weather research: for example, the discovery and characterization of a storm’s three-stage life cycle.

During this time, another man was climbing a mountain in Japan to collect his own data. They both arrived at similar conclusions about the nature of storms. Impressed that one individual with so few resources could achieve so much, Byers invited Tetsuya Theodore Fujita to Chicago, where he soon became director of the Mesometeorology Research Project. 

Fujita went on to conduct his own wide-scale, data-driven investigations into tornadoes. His unconventional approach was long rejected by the meteorological community, says Nakamura, who counts Fujita as one of his heroes. “But our university has traditionally been nurturing to unconventional, creative approaches to science,” he says, “and supportive of the scientists doing work that may not have been possible elsewhere.”

Geophysical sciences

Over the next few years, the expansion of meteorology into planetary science took hold across the field. In 1961, UChicago’s meteorology department merged with geology and became the Department of Geophysical Sciences.

Today the department focuses on Earth’s atmosphere, oceans, glaciers, and climate; surface, interior, and evolution; and biosphere. Researchers in the department also look to space, studying exoplanets and cosmochemistry. 

“The vision of the department from the outset was to approach Earth science from the system point of view,” says Nakamura, “not just from individual disciplines but with a holistic view of Earth’s environment.”

Nakamura’s recent research concerns how and why jet streams can get disrupted, and how that can lead to anomalous weather. He compares jet streams to highways that weather systems travel on, but they’re not straightaways—they meander. And large-scale features, such as mountains, land-sea transitions, or expansive land masses, change the streams’ internal dynamics, like changing the speed limit along a highway. At lower speeds, traffic can jam up. Nakamura uses fluid mechanics to explain why this happens, simplifying as much as possible, the way Rossby did with his waves. In doing so, he’s been able to draw mathematical connections to automobile traffic flow.

“I’m more interested in the short term,” says Nakamura, from a few days to a few weeks—the timescale for weather variability. 

Longer term analysis starts moving into climate science. For example, Assoc. Prof. Tiffany Shaw’s climate work involves testing theories about the way the world works using numerical simulations as well as making observations to look for emergent patterns. 

“My research focuses on large-scale features, whether it’s Rossby waves or the jet stream or the Hadley circulation, which dominates how air moves in the tropics,” says Shaw. One question she seeks to answer is how such features respond to climate change.

For theoretical physicists, the questions always arise: What are the minimal physical ingredients required to explain emergent patterns in response to climate change? Can climate behavior be understood on a more fundamental level using simpler tools?

“We have a big model with all the bells and whistles,” says Shaw, “and then we strip away the extra, leaving only the essential, the way Rossby did.” If the theories are sound, they should be able to explain the continuum of a changing climate. “And that’s how we build our confidence in future projections of Earth’s climate for the next hundred years.”

—Adapted from a story originally published by the University of Chicago Magazine.