The timing structure of extreme precipitation reveals how climate systems connect globally

According to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change published in February 2022, extreme precipitation is very likely to become more frequent in most places. a global scale is elevated to an issue of great societal importance.

In Chaosfrom AIP Publishing, German researchers propose to use a complex network-based clustering workflow to search for synchronized structures of extreme precipitation events in the context of atmospheric chaos.

In doing so, they were able to reconstruct a functional climate network to encode the underlying interaction of the climate system. Clusters on the network revealed regions with similar climatological behavior.

For example, monsoons describe seasonal changes in atmospheric circulation, and although they are distributed across different continents, their occurrences are usually accompanied by extreme rainfall.

“Although the global atmospheric circulation in the tropics and subtropics forms links between different monsoons, they are essentially driven, synchronized and coordinated by the annual cycle of solar radiation,” said Zhen Su of the Institute of Potsdam Climate Impact Research and Humboldt University zu Berlin. “Synchronization can also occur between extreme rainfall events, even when they do not occur in monsoon regions.”

This means that precipitation extremes at different locations are not independent of each other, but have some degree of similarity.

“In this regard, it is still unclear what the global-scale synchronization pattern of extreme precipitation will look like, for example, during the Northern Hemisphere summer season,” Su said. “We aim to find the answer from rainfall observation data.”

The global synchronization of extreme precipitation has two main distributions with independent temporal and spatial characteristics. “One mainly occurs from early June to mid-July,” Su said. “The other occurs mainly from mid-July to late August.”

Between these periods, a monsoon “jump” occurs – a northward movement of the monsoon rain belt over time. With this monsoon shift, the spatial distribution of synchronization also undergoes a northward shift. The researchers noticed that the two spatial distributions cover monsoon regions as well as oceanic and inland areas.

“The timing pattern of extreme precipitation tells us how the climate system is globally interconnected,” Su said. “It also provides information to improve the corresponding interaction processes in general circulation models, which are mainly used to estimate the state of our future climate.”

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Materials provided by American Institute of Physics. Note: Content may be edited for style and length.

Maria R. Newman