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Wednesday, 18 December 2019

Extreme heat waves are linked to a newly discovered atmospheric model

Researchers have discovered a new link between a pattern of fluctuations of a particular type of wave in jet streams (Rossby waves) and paralyzing heat waves, which strike several regions of the world simultaneously.

They are called "Rossby waves" (or planetary waves), an atmospheric and oceanic phenomenon in which giant meanders distort the flow of currents in an undulatory model. It does not only occur on Earth, but also on other planets or stars (including the Sun). Rossby waves are particularly known for influencing the global climate.

Thanks to a recent study, the extent of this influence is becoming clearer. By analyzing the results, researchers have discovered that when certain amplified wavelengths take shape in jet streams - rapidly circulating air streams that pass through the atmosphere at high altitudes - the phenomenon is linked to the emergence simultaneous heat waves that devastate certain regions. The results were published in the journal Nature Climate Change.

Most affected regions: main agricultural producers

" We have seen a 20- fold increase in the risk of simultaneous heat waves in major agricultural regions when these global wind regimes are in place, " said Kai Kornhuber, a researcher in Earth systems at the University. Columbia. In other words, when the phenomenon occurs, it is mainly the main food producing regions that are affected.

Development of a Rossby wave along the thermal ribbon (or front). Credits: Wikipedia

Kornhuber and his team analyzed climate data from 1979 to 2018 and found that when two particular wavelengths of circonglobal Rossby waves - called wave-5 and wave-7 - scattered in the jet stream of the 'northern hemisphere, they channeled warm subtropical air into regions of North America, Europe and Asia.

Temperature spikes that can persist for weeks

Hot air produces temperature spikes that can persist for weeks: extreme weather events that threaten people and global food security, due to their widespread impact on crops.

" Two weeks or more per summer spent in wave 5 or wave 7 are associated with 4% reductions in agricultural production on average, with regional decreases of up to 11%,  " write the researchers. in the document.

And the scary effects don't stop there… Crop losses lead to higher food prices, and although researchers recognize that these prices can be affected by a host of other factors, they nevertheless believe that the impacts on the harvest due to the effects of Rossby are significant.

According to the researchers, these wave patterns appeared five times during the study period (1983, 2003, 2006, 2012 and 2018), but although it is not yet known how climate change could affect the phenomenon, the impact of these major disturbances on a mode already warming is rather worrying.

"Even if the frequency or size of the (Rossby) waves does not change, the related heat extremes will become more severe as the atmosphere as a whole heats up, " says Kornhuber. " Until now, this has only been an under-explored vulnerability of the food system ."

However, the team recognizes that more research is needed to determine how future climate projections would be affected by this discovery. Until this is done, we will not know the exact impact of Rossby waves on the world of tomorrow.


Amplified Rossby waves enhance risk of concurrent heatwaves in major breadbasket regions

Kai Kornhuber, Dim Coumou, Elisabeth Vogel, Corey Lesk, Jonathan F. Donges, Jascha Lehmann & Radley M. Horton -

Nature Climate Change (2019)

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