2025-10-01 アリゾナ大学
＜関連情報＞
- https://news.arizona.edu/news/tree-ring-data-sheds-light-past-and-present-summer-climate-extremes
- https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024AV001621
ジェット気流による夏の異常気象に対するENSOの影響の1000年 A Millennium of ENSO Influence on Jet Stream Driven Summer Climate Extremes
Ellie Broadman, Kai Kornhuber, Isabel Dorado-Liñán, Guobao Xu, Valérie Trouet
AGU Advances Published: 18 August 2025
DOI:https://doi.org/10.1029/2024AV001621
Abstract
Summertime spatially compound climate extremes in the Northern Hemisphere are associated with dominant jet stream Rossby wavenumber patterns, including wavenumber5 (wave5). However, our knowledge of wave5, including its response to anthropogenic warming, is limited by the short length of instrumental records of upper-level fields. To provide a longer-term perspective, we present a 1,000-year reconstruction of a wave5 pattern that modulates summertime compound extremes, constructed by targeting drought anomalies associated with this pattern in three regions. Our results show no major trends in the occurrence of this pattern over the past millennium. We further show that La Niña winters often precede a wave5 event the following summer, evident over centuries. This pattern was exemplified by the La Niña winter of 2022–2023, which was followed by wave5-driven compound heatwaves in July. The imprint of continued anthropogenic warming on ENSO may exacerbate wave5-driven extremes, especially if the tropical Pacific becomes more La Niña-like.
Plain Language Summary
The jet stream, a band of strong winds high above the Earth’s surface, is related to atmospheric patterns that can lead to extreme climate events that occur simultaneously in multiple locations around the Northern Hemisphere during the summer. One such pattern occurs when the jet stream forms five peaks and troughs around the Northern Hemisphere (referred to as a wavenumber-5 pattern, or wave5), resulting in a higher likelihood of co-occurring extreme climate events. We use tree-ring-based data to reconstruct this wave5 pattern during the early summer months over the past millennium and find no major trends in the pattern over this time period. We also find a relationship between this wave5 pattern in the jet stream and the El Niño Southern Oscillation, where anomalously cool sea-surface temperatures in the tropical Pacific (La Niña-like winters) often precede a summer where the jet stream is commonly in a wave5 pattern, driving extreme events.
Key Points
- Rossby wavenumber-5 pattern (wave5) in the jet stream drives summertime compound climate extremes
- The frequency of these summertime wave5 driven extremes has not yet changed due to anthropogenic warming
- Over the last millennium, wave5 related extremes during the summer tend to be preceded by a La Niña winter
