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Study looks back over 20,000 years to find what drives monster storm systems

Mesoscale convective systems are groups of storms that can cover whole states, bringing floods, tornadoes and hail to the Great Plains.

A new study in the journal Nature Geoscience helps explain their behavior — and the long-term forces that drive them.

Relating 20,000 years of sedimentary evidence from a Texas cave with data from computer models, the team found that springtime surface warming feeds the monster storms by drawing in more moisture from the Gulf of Mexico.

"If you come to this region, whenever the wind blowing from the south, you will immediately know it, because it's so humid. And those humid winds, they help to grow and sustain those thunderstorms known as MCSs," said lead author Chijun Sun, a postdoctoral researcher at the National Center for Atmospheric Research.

The storm patterns and intensity also varied over the past 20 millennia as continental glaciers advanced and retreated. 

"During the past 20,000 years, there is a big global climate change of transitioning from the glacial world to the interglacial world," said Sun.

Co-author Nick McKay is an associate professor in NAU's School of Earth and Sustainability. He says uniting climate models with chemical and geological data to ask big questions shows where the field is headed.

"Not just, 'Was it wetter or drier?' or 'Was it colder or warmer?' but 'How are these large-scale dynamical climate features changing, and why?'" McKay said. 

Springtime warming steepens regional pressure differences, intensifying a stream of air called the low-level jet, which brings moisture from the south and strengthens the storms.

Sun, who worked on the research while at the University of Texas at Austin, says the past is prologue: In the future, a warming Earth likely will drive warmer surface temperatures and, with it, a stronger southerly jet.

"It would sustain even stronger mesoscale convective systems, making larger rainfall and potentially more damages in the future," Sun said. 

Nicholas Gerbis joined KJZZ’s Arizona Science Desk in 2016. A longtime science, health and technology journalist and editor, his extensive background in related nonprofit and science communications inform his reporting on Earth and space sciences, neuroscience and behavioral health, and bioscience/biotechnology.Apart from travel and three years in Delaware spent earning his master’s degree in physical geography (climatology), Gerbis has spent most of his life in Arizona. He also holds a master’s degree in journalism and mass communication from Arizona State University’s Cronkite School and a bachelor’s degree in geography (climatology/meteorology), also from ASU.Gerbis briefly “retired in reverse” and moved from Arizona to Wisconsin, where he taught science history and science-fiction film courses at University of Wisconsin-Eau Claire. He is glad to be back in the Valley and enjoys contributing to KJZZ’s Untold Arizona series.During the COVID-19 pandemic, Gerbis focused almost solely on coronavirus-related stories and analysis. In addition to reporting on the course of the disease and related research, he delved into deeper questions, such as the impact of shutdowns on science and medicine, the roots of vaccine reluctance and the policies that exacerbated the virus’s impact, particularly on vulnerable populations.