Telegraph e-paper

Winds that slow down Earth key to long-range forecasts

By Sarah Knapton SCIENCE EDITOR

FASTER atmospheric winds extend the length of day on Earth and can trigger long-term changes in weather and climate, scientists have found, in a breakthrough that could improve forecasts.

Strong winds in the atmosphere are known to slow down the Earth’s 24-hour rotation by about one millisecond a day, as the planet compensates for the extra momentum.

But a team at the Met Office has discovered that when the phenomenon occurs, it sets off a wave of atmospheric fluctuations that migrate slowly towards the poles, impacting important air currents such as the jet stream.

Researchers found that the day slows down around a year before the atmospheric winds reach the jet stream – providing an early warning system of what to expect. The finding could help forecasters make predictions about cold winters or flooding far earlier than they currently can.

Prof Adam Scaife, head of long-range prediction at the Met Office, said: “The interesting bit for climate prediction is that these signatures in the atmosphere are very long-lived as they move outwards towards the mid-latitudes on the timescale of about a year, which gives us some long-range predictability.

“If you talk to anyone in this field, they will say the atmosphere only has a short memory and if you want to do a long-term forecast you have to do it using the ocean.

“But it turns out that the jet stream in the mid-latitudes is affected with a lag of about a year after the length of day first changes in the tropics. This has applications in long-range forecasting.”

Although the change in the rotation of the Earth has no direct effect on the atmosphere, the compensating change in the winds is much bigger and is strong enough to change regional weather and climate, Prof Scaife said.

The team has also shown that it is possible to predict when the day lengthening will occur, based on other predictable climate phenomena, such as El Nino, which could give an even earlier indication of jet stream changes

The findings were published in the journal

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2022-10-05T07:00:00.0000000Z

2022-10-05T07:00:00.0000000Z

https://dailytelegraph.pressreader.com/article/281917366968691

Daily Telegraph