Understanding climate
for the benefit of society

Extratropical cyclones do not last for many days, making it difficult to forecast mid-latitude weather for more than a week or two. If researchers can find links to more longlasting phenomena, they may be able to predict whether there we will be hit by more or fewer cyclones in some years. The image shows a low near Iceland in 2003. Image: Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC.

Seeking order in the atmospheric chaos

«The mid-latitudes are one big, chaotic mess”, says Camille Li.  

Camille Li
Camille Li is heading the project DYNAMITE, where scientists evaluate links between mid-latitude weather and conditions in other parts of the world.

She is talking about the weather in large parts of Europe and North America – regions where extratropical cyclones can make everything change from one day to the next.

The tropics are tidier, with shifts from rainy seasons to dry seasons, but with much less variation within each season. 

Can there still be a system in the mid-latitudinal chaos?

Camille Li is a professor at the Bjerknes Centre and the Geophysical Institute at the University of Bergen, and the leader of DYNAMITE, a project that considers whether mid-latitude storm-tracks and weather are influenced by phenomena in other regions. Possible candidates are the sea ice cover in the Arctic and sea surface temperatures in the Pacific.

This week scientists from Norway, the USA and Canada meet in Bergen to discuss ideas and results. 

Largest changes in the north

During the last decade, a strong warming and a reduced sea ice cover in the Arctic has co-occurred with several extreme winters in Europe and North America. This has led to discussion of whether the heat and the increased stretches of open water in the north may have caused the cold winters farther south. 

“Statistical correlations may be dangerous”, says Stefan Sobolowski from the Bjerknes Centre and NORCE. 

Two things occurring at the same time does not imply that one of them causes the other. To the researchers, it is vital to find physical mechanisms that explain the observed patterns. 

As energy on Earth is transported from the hot equatorial regions to the icy poles, it is not obvious how signals can be transferred in the opposite direction. One of the possible connections from Arctic sea ice to mid-latitude weather may go through the stratosphere, more than ten kilometers above the ground. 

Predictability may come from the south

Stefan Sobolowski
Stefan Sobolowski, researcher at the Bjerknes Centre for Climate Research and NORCE.

«The most well-known signals still come from the tropics», says Stefan Sobolowski. 

During El Niño events, when the sea surface temperature increases in large parts of the tropical Pacific, the weather is abnormal in many regions. Even though Europe is among the regions least affected, this connection is also something that the scientists consider. 

In some tropical regions, phenomena like El Niño makes it possible to predict whether the coming summer or winter will be wet or dry; in the mid-latitudes, such predictions are more uncertain. Cyclones do not last long, and ordinary weather forecasts are rarely issued for more than 10–15 days ahead.  

Predictions for the coming seasons, years and decades are issued, but the science behind them is relatively new. If the scientists can find robust connections between ice, oceans and storm tracks, they may be able to improve such predictions. 

“These signals are small, but understanding them is a start”, says Camille Li.