- New research shows that stalled atmospheric events linked to heatwaves, floods, and wildfires—driven by a phenomenon called quasi-resonant amplification (QRA)—have nearly tripled since the 1950s.
- QRAs occur when large planetary waves in the jet stream become amplified and trapped, causing extreme weather to persist over one region for longer periods.
- Today’s climate models struggle to capture QRAs accurately, meaning they may underestimate the likelihood and severity of prolonged extreme weather events.
Presidential Distinguished Professor in Penn’s Department of Earth and Environmental Science Michael E. Mann, postdoctoral researcher Xueke Li, and other researchers offer fresh insight into the atmospheric mechanics behind these extremes—and troubling evidence that they’re becoming more common.
Published in Proceedings of the National Academy of Sciences , the paper shows that a specific and destructive jet stream behavior, known as quasi-resonant amplification (QRA), is happening more frequently and is tightly linked to human-caused climate change.
Michael Wehner, a senior scientist at Lawrence Berkeley National Laboratory and co-author on the study, notes that while the thermodynamic effects of climate change—such as increased temperatures—are well understood, “the effects of climate change on the dynamical processes that cause certain types of extreme weather is a more difficult problem. This paper detects an important change in one of these complex aspects of atmospheric motion.”
What is quasi-resonant amplification?
QRA occurs when large, slow-moving planetary waves in the jet stream—a high-altitude air current that guides weather systems—intensify and become stalled, Li explains. This “trapping” effect causes weather such as heat domes or rainstorms to remain over one region. “This resonance increases the waves’ strength and persistence, often leading to extended extreme weather,” Li says
The team previously studied the 2021 Pacific Northwest heat dome, one of the most extreme heat events on record. Their analysis traced that event to QRA dynamics that amplified a planetary wave and dried out regional soils, which in turn fed extreme surface warming.
“This latest study builds on that by providing the first observational evidence that such QRA events are becoming more frequent in a warming climate,” Mann says. “And it’s the first study to demonstrate a historical increase, taking advantage of the more reliable atmospheric ‘reanalysis’ observations that are available today.”
The observed rise in QRA events, Mann notes, isn’t due solely to more powerful waves, but to the rare alignment of two necessary conditions: wave amplitude and wave phase.
“For a QRA event to occur,” he explains, “high-amplitude waves must also be in just the right phase, meaning they are positioned in the atmosphere in a way that allows them to become trapped and resonate. Without that precise alignment, even strongly amplified waves may simply move along and fail to lock into place.”
Li adds that the trend is closely tied to “polar amplification of warming and increased land/ocean thermal contrast,” both of which can be tied to the pattern of human-caused warming.