Trapped Jet Stream Waves, Which Drive Summer Weather Extremes And Records, Have Tripled Since 1950s
WASHINGTON (AP) — Climate change has tripled the frequency of atmospheric wave events linked to extreme summer weather in the last 75 years and that may explain why long-range computer forecasts keep underestimating the surge in killer heat waves, droughts and floods, a new study says.
In the 1950s, Earth averaged about one extreme weather-inducing planetary wave event a summer, but now it is getting about three per summer, according to a study in Monday’s Proceedings of the National Academy of Sciences. Planetary waves are connected to 2021’s deadly and unprecedented Pacific Northwest heat wave, the 2010 Russian heatwave and Pakistan flooding and the 2003 killer European heatwave, the study said.
“If you’re trying to visualize the planetary waves in the northern hemisphere, the easiest way to visualize them is on the weather map to look at the waviness in the jet stream as depicted on the weather map,” said study co-author Michael Mann, a University of Pennsylvania climate scientist. Planetary waves flow across Earth all the time, but sometimes they get amplified, becoming stronger, and the jet stream gets wavier with bigger hills and valleys, Mann said. It’s called quasi-resonant amplification or QRA.
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“This study shines a light on yet another way human activities are disrupting the climate system that will come back to bite us all with more unprecedented and destructive summer weather events,” said Jennifer Francis, a climate scientist at the Woodwell Climate Research Center who wasn’t involved in the research. “Wave resonance does appear to be one reason for worsening summer extremes. On top of general warming and increased evaporation, it piles on an intermittent fluctuation in the jet stream that keeps weather systems from moving eastward as they normally would, making persistent heat, drought, and heavy rains more likely,” Francis said.
This is different than Francis’ research on the jet stream and the polar vortex that induces winter extremes, said Mann.
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https://apnews.com/article/extreme-weather-climate-change-heatwave-flooding-drought-cc4c3d93e178b6f4ab13cb7788998801
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Time series of the boreal summer QRA event counts from 1950 to 2024. The annual QRA counts (unitless) based on ERA5 reanalysis data are represented by the blue line, while the series of QRA fingerprints (unitless)—an anomalous meridional temperature “fingerprint” associated with QRA-favorable conditions—using the three series of observational surface temperatures (GISTEMP, HadCRUT4, and Cowtan and Way datasets) are indicated by the green, orange, and red lines, respectively. The QRA fingerprint series (which are available from 1950 to 2016) are centered and rescaled to dimensionally match the annual QRA count series (Eq. 6 in Materials and Methods), allowing for direct comparison of the two series. The linear trends for each series during the period of overlap are depicted by thick dashed lines, with the respective slopes shown in brackets within the legend. The linear trend is also shown for the full QRA event count series through 2024 (thin dashed line). The trends are statistically significant at the P = 0.01 level using either a two-tailed Student’s t test or a nonparametric Mann-Kendall test (39) and the slopes are statistically indistinguishable. Gray vertical dashed lines denote the years when El Niño becomes mature based on the Oceanic Niño Index (ONI) (Materials and Methods). Strong to very strong events are represented by large triangles, while weak to moderate ones are indicated by small triangles (see also SI Appendix, Table S1).
