The weakening summer circulation in the Northern Hemisphere mid-latitudes

Dim Coumou*, Jascha Lehmann, Johanna Beckmann

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

Rapid warming in the Arctic could influence mid-latitude circulation by reducing the poleward temperature gradient. The largest changes are generally expected in autumn or winter, but whether significant changes have occurred is debated. Here we report significant weakening of summer circulation detected in three key dynamical quantities: (i) the zonal-mean zonal wind, (ii) the eddy kinetic energy (EKE), and (iii) the amplitude of fast-moving Rossby waves. Weakening of the zonal wind is explained by a reduction in the poleward temperature gradient. Changes in Rossby waves and EKE are consistent with regression analyses of climate model projections and changes over the seasonal cycle. Monthly heat extremes are associated with low EKE, and thus the observed weakening might have contributed to more persistent heat waves in recent summers.

Original languageEnglish
Pages (from-to)324-327
Number of pages4
JournalScience
Volume348
Issue number6232
DOIs
Publication statusPublished - 17 Apr 2015

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