A map and graph from the study.
Top: The Rossby wavenumber-5 pattern is shown with the black line (median) and gray ribbon (full zonal range of preferred phase). The authors define the wave5-PC index to express the number of weeks within a given May-June-July season that the wave5 pattern is in a configuration likely to induce a compound extreme (e.g. hot drought) event in selected regions. The colored map shows the Pearson correlation between this index and the record of Palmer drought severity index based on tree ring records, for the period 1948-2018 CE. Significant (p ≤ 0.1) correlation is stippled or with black squares (correlations that remain significant after applying the false discovery rate (FDR) correction). Red boxes show the locations of the three regions used in the multiple linear regression model for the millennial reconstruction based on tree ring records. Bottom: Reconstructed wave5-PC index values representing the period from 1000 – 2005 CE. The box shows the period of instrumental record overlap and the blue line shows the period (1948-2018 CE) used to define the index (shown as blue line). Decadal variations are highlighted in the smoothed record (red line). Broadman et al. [2025], Figures 1(top) and 3 (bottom)
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: AGU Advances

The degree to which global warming will affect atmospheric dynamics and, therefore, extreme weather is still uncertain. Broadman et al. [2025] find a clever way to reconstruct the history of one dynamical pattern that occurs when the jet stream forms five peaks and troughs around the Northern Hemisphere (referred to as a wave5 pattern). When this pattern occurs and persists during May-June-July there is a higher likelihood of co-occurring compound climate events — for example combined heat and drought in the southeastern United States, China, and southern Europe, but wetter than normal in Northwest Canada and Spain.

The authors combine multiple lines of evidence, tree ring records, climate reanalyses and models, to reconstruct variations in the strength of the early summer wave5 pattern and extend them over the past millennium. They find decadal variations but no significant trends in the occurrence of wave5 related climate extremes. However, a demonstrated link between La Niña conditions the preceding winter could potentially help in predicting the potential in some regions for extreme weather the following summer.

Citation: Broadman, E., Kornhuber, K., Dorado-Liñán, I., Xu, G., & Trouet, V. (2025). A millennium of ENSO influence on jet stream driven summer climate extremes. AGU Advances, 6, e2024AV001621. https://doi.org/10.1029/2024AV001621

—Susan Trumbore, Editor, AGU Advances

Text © 2025. The authors. CC BY-NC-ND 3.0
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