For Bjorn Birnir, one of the world’s leading experts on turbulence, discussing his profession often leads to a common, yet dreaded, question from his airplane seatmates: Just how dangerous is turbulence, really? This inquiry is becoming more frequent among the millions who fly daily, as severe turbulence, once a mere annoyance, is intensifying.
Recent studies highlight this growing concern. British researchers, analyzing decades of meteorological data, found that severe clear-air turbulence over the North Atlantic soared by 55 percent between 1979 and 2020. This type of turbulence, occurring without visible storms or mountains, is particularly difficult to predict, exacerbating passenger discomfort and pilot challenges.
Driven by a desire to enhance air travel comfort and safety, Dr. Birnir, who leads the Center for Complex and Nonlinear Science and chairs the mathematics department at the University of California, Santa Barbara, has unveiled what he believes is the most advanced model of turbulent motion to date. Published in the scientific journal Physical Review Research, this model promises significant benefits for aircraft design and meteorological forecasting, ultimately aiming for safer and less stressful flights.
Thomas Q. Carney, a veteran pilot and retired professor of aviation technology, echoes this sentiment, stating that improved models that more accurately capture turbulent fields lead directly to better forecasts, which are crucial tools for pilots.
While flying on American carriers remains remarkably safe, recent incidents have understandably shaken public confidence. The National Transportation Safety Board (NTSB) recently released an interim report on a Delta Air Lines flight where passengers were injured after encountering unexpected severe turbulence over Wyoming, despite pilots attempting to avoid bad weather. It’s also increasingly clear that climate change, with its effects on air pressure and wind speed, may be a contributing factor to this rising turbulence.
Turbulence has long baffled scientists, a challenge so profound that Nobel laureate Richard P. Feynman famously dubbed it ‘the most important unsolved problem of classical physics.’ Its complexity stems from a multitude of rapidly changing factors like temperature, pressure, and wind, making accurate prediction incredibly difficult, as aviation writer Patrick Smith notes on his website, Ask the Pilot. Tanner D. Harms, a former doctoral student at the California Institute of Technology, emphasizes that turbulence is inherently chaotic, with particles diverging in unpredictable ways, making its definition almost synonymous with chaos itself.
To demystify this chaos, Dr. Birnir collaborated with Luiza Angheluta-Bauer, a theoretical physicist from the University of Oslo. Together, they developed a pioneering model that integrates two distinct methods for observing turbulence: Lagrangian and Eulerian mechanics. Experts agree that neither method alone can fully capture the phenomenon.
These two frameworks offer different lenses into a turbulent system. Lagrangian mechanics observes the path of a single particle, akin to tracking a leaf drifting down a river, tossed by eddies. Eulerian mechanics, conversely, focuses on a fixed point in space, like observing how water churns around a stationary rock in the river. Lagrangian turbulence is notoriously harder to model due to the intricate, unpredictable motion of individual particles.
Understanding both perspectives is vital, much like choosing the right microscope lens. As Tomek Jaroslawski, a postdoctoral fellow at Stanford’s Center of Turbulence Research, puts it, ‘Same turbulence, different stories. Neither view is wrong — they’re just different ways of asking nature a question.’ Their combined theoretical and statistical approach marks a significant leap, as physicists previously struggled to create such a comprehensive model of turbulent motion. While some experts may have differing views, Katepalli Sreenivasan, former dean of the Tandon School of Engineering at NYU, affirms the novelty of their findings.
J. Doyne Farmer, an Oxford professor specializing in complex and chaotic systems, describes ‘fully developed turbulence’ as a state where ‘things are just crazy,’ characterized by chaotic eddies and numerous degrees of freedom. Dr. Birnir speculates that the Delta flight incident was likely a ‘typical example of severe intermittency in Eulerian turbulence.’ He believes a more refined turbulence model could have equipped pilots with the foresight to take preventative actions, such as reducing engine power, to counteract such irregular airflows.
Despite the advanced nature of the work by Dr. Birnir and Dr. Angheluta-Bauer, which Dr. Carney admits is beyond the typical pilot’s grasp, its potential is undeniable. Dr. Carney maintains confidence that their research is a valuable contribution to our collective understanding and knowledge of this complex aviation challenge.