A better way to predict extreme weather?

'Traffic jams' that form in jet streams could help reveal when devastating floods, hurricanes and droughts are about to hit

The jet stream is a narrow band of wind which keeps air flowing around the globe, but sometimes it gets clogged up in a phenomenon known as 'blocking'.

When this happens, the jet stream grinds to a halt and a huge volume of air gets stuck and the consequences can be catastrophic.

Hurricane Sandy and the deadly 2003 European heat wave were caused by this unusual event.

Scientists have known about blocking for decades, but never understood why it happens or how it impacts on the weather.

Now, researchers have discovered that these bottlenecks in the sky form in a similar way to traffic jams, and experts will now be able to predict when and where it will happen.

Research coming out of the University of Chicago used mathematical modelling to try and understand the jet stream and how it can be disrupted.

'Blocking is notoriously difficult to forecast, in large part because there was no compelling theory about when it forms and why,' said study coauthor Noboru Nakamura, a professor in the Department of the Geophysical Sciences.

Dr Nakamura conducted the research with then- graduate student Clare Huang.

The study came up with a new set of measurements to help analyse the phenomenon.

The researchers found that the equation for modelling the weather is nearly identical to one devised decades ago by transportation engineers trying to describe traffic jams.

' It turns out the jet stream has a capacity for "weather traffic," just as a highway has a traffic capacity, and when it is exceeded, blocking manifests as congestion,' said Ms Huang.

On the roads, vehicle movement slows when multiple highways converge.

Similarly, the speed of the jet stream is reduced due to topog- raphy such as mountains or coasts.

The result is a theory that not only reproduces blocking, but predicts it, said Dr Nakamura.

He called the cross- disciplinary connection ' one of the most unexpected, but enlightening moments in my research career - truly a gift from God.'

'It's very difficult to forecast anything until you understand why it's happening, so this mechanistic model should be e x t remely helpful,' Dr Nakamura said.