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Article Dans Une Revue Geophysical Research Letters Année : 2024

Summer Deep Depressions Increase Over the Eastern North Atlantic

Gwendal Rivière
  • Fonction : Auteur
Robert Vautard
Christophe Cassou
  • Fonction : Auteur
Dim Coumou
Tamara Happé
Aglaé Jézéquel
  • Fonction : Auteur

Résumé

Mid-tropospheric deep depressions in summer over the North Atlantic are shown to have strongly increased in the eastern and strongly decreased in the western North Atlantic region. This evolution is linked to a change in baroclinicity in the west of the North Atlantic ocean and over the North American coast, likely due to the increased surface temperature there. Deep depressions in the Eastern North Atlantic are linked to a temperature pattern typical of extreme heat events in the region. The same analysis is applied to a sample of CMIP6 model outputs, and no such trends are found. This study suggests a link between the observed increase of summer extreme heat events in the region and the increase of the number of Atlantic depressions. The failure of CMIP6 models to reproduce these events can consequently also reside in an incorrect reproduction of this specific feature of midlatitude atmospheric dynamics. Plain Language Summary Extreme temperatures events in Western Europe have been rising fast, and current global climate models are not able to reproduce this excess. There are different hypotheses to explain this discrepancy. One is that the large-scale atmospheric dynamics, responsible for the local weather, is not correctly represented by the models: indeed, the frequency and amplitude of some specific weather phenomena have been shown to be insufficiently reproduced, especially in summer. Here, we study one such phenomenon, namely the transient deep depressions, or extratropical cyclones, that travel across the Atlantic basin. A significant large increase of the number of these events is found in summer in the region of the North Atlantic off the western European coast. Depressions in that region are accompanied by high temperatures in continental western Europe. An ensemble of state of the art climate models are also analyzed and none of them is able to correctly reproduce the frequency of deep depressions nor their large trend, which suggests a common origin with the insufficient prediction of western European extreme heat events. Great caution should be used when analyzing climate change predictions in the region, and even more so when studying changes in complex dynamical phenomena.
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Dates et versions

hal-04488347 , version 1 (04-03-2024)

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Fabio d'Andrea, Jean-Philippe Duvel, Gwendal Rivière, Robert Vautard, Christophe Cassou, et al.. Summer Deep Depressions Increase Over the Eastern North Atlantic. Geophysical Research Letters, 2024, 51 (5), ⟨10.1029/2023GL104435⟩. ⟨hal-04488347⟩
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