The meandering waves that link jet streams to global warming

Extra waves can be great for surfers, but they can lead to rough weather when they start showing up in jet streams.

Indeed, jet streams — blowing ribbons of wind that encircle the land — play a critical role in the location and severity of weather events, such as the recent floods that devastated Kentucky. Even a slight change in the “ripple” of the polar or subtropical jet stream can cause dramatic climate changes in mid-latitude regions from northern California to Moscow.

The past few decades have seen such an increase in jet stream waves, leading scientists to ask the question: Are these windy wanderings caused by a warming planet?

A renowned Yale scientist and a team of international colleagues say yes – and in a new study, published in the journal Proceedings of the National Academy of Sciences, they offer a theory to prove it.

As the planet warms, we expect the land-ocean contrast of atmospheric warming to enhance the meanderings of the jet stream and that involves more of these extreme weather events, like what we experienced this summer in Kentucky “, said John WettlauferProfessor AM Bateman of Geophysics, Mathematics and Physics at Yale, the co-corresponding author of the study.

A certain ripple has always been a characteristic of jet streams. Swedish-American meteorologist Carl-Gustaf Rossby predicted the atmospheric wave concept in the late 1930s; since then meanders are commonly referred to as “Rossby waves”.

Over the past 30 years, scientists have observed an intensification of waves, coinciding with increased global warming. More ripple in the jet stream means that rain and wind stay in an area longer than if the jet stream simply moved east without detours.

Various researchers have correlated climate change with greater ripple in jet streams, however, the mechanism to explain the connection has been debated.

In the new study, Wettlaufer and his colleagues developed a mathematical theory that explains the waviness of the jet stream, then created a simulation of atmospheric circulation under warming conditions to test their theory.

Because the polar regions of the planet are warming faster than the mid-latitudes, the typical north-south temperature difference is smaller,” Wettlaufer said. As this temperature difference decreases, it causes a slight drop in zonal winds in the jet stream, which, in turn, leads to more meandering of the jet stream.

This means that cyclones and anticyclones associated with meandering are more stationary – there are ‘parked’ weather systems over a place on the planet,” Wettlaufer said. “So if a low pressure system sits over eastern Kentucky for a long time, the moisture is just concentrated there until the meanders start to shift and the weather system moves eastward. is.”

The first author of the study is Woosok Moon from Stockholm University. The co-authors are Baek-Min Kim and Gun-Hwan Yang from National Pukyong University.

Teresa H. Sadler