Extreme events and planetary waves: new index approach

09/22/2016 - Both heat waves like 2010 in Russia or cold spells like 2014 in the US have a common feature – they appeared together with certain patterns of gigantic airstreams in the atmosphere. This so called jetstream circles around the globe in waves swinging up and down between the Tropics and the Arctic. These large meandering planetary waves can have huge impacts – the economic damages of the 2014 cold spell at the US east coast with record-breaking cold temperatures for instance were estimated up to 5 billion Dollars.
Extreme events and planetary waves: new index approach
Coldspell in the US East Coast in 2014. Photo: see study

Scientists of the Potsdam Institute for Climate Impact Research now analyzed if these airstream patterns actually changed in the last 35 years. Using a novel index approach, they found that there have indeed been changes in the middle tropospheric circulation waviness. They found a greater meandering in autumn/early winter, meaning that the general circulation has become “wavier” in this season. "In contrast, we found a decrease in meandering in summer – which is consistent with an earlier reported weakening of storm tracks in summer", Giorgia Di Capua explains.

The open question remains why the planetary waves changed – possible drivers might include rapid warming in the Arctic, changes in the sea surface temperatures in the tropics or internal atmospheric variability. "However, since extreme weather events and planetary waves are closely linked, changes in the airstream patterns can have major implications for the occurrence of weather extremes and the consequences for society", Dim Coumou adds.

Article: Di Capua, G., Coumou, D. (2016): Changes in meandering of the Northern Hemisphere circulation. Environmental Research Letters [DOI: 10.1088/1748-9326/11/9/094028]

Weblink to the article: http://iopscience.iop.org/article/10.1088/1748-9326/11/9/094028

Video abstract: https://youtu.be/tzMrHcWE1rU

Weblink to earlier research on summer storm weakening and more persistend heat extremes: https://www.pik-potsdam.de/news/press-releases/summer-storm-weakening-leads-to-more-persistent-heat-extremes