Preprints
https://doi.org/10.5194/wcd-2021-69
https://doi.org/10.5194/wcd-2021-69

  19 Oct 2021

19 Oct 2021

Review status: this preprint is currently under review for the journal WCD.

Past Evolution and Recent Changes in Western Europe Large-scale Circulation

Antoine Blanc, Juliette Blanchet, and Jean-Dominique Creutin Antoine Blanc et al.
  • Univ. Grenoble Alpes, CNRS, IRD, Grenoble INP, IGE, 38000 Grenoble, France

Abstract. Detecting trends in regional large-scale circulation (LSC) is an important challenge as LSC is a key driver of local weather conditions. In this work, we investigate the past evolution of Western Europe LSC based on the 500 hPa geopotential height fields from 20CRv2c (1851–2010), ERA20C (1900–2010) and ERA5 (1950–2010) reanalyses. We focus on the evolution of large-scale circulation characteristics using three atmospheric descriptors that are based on analogy – characterizing the geopotential shape stationarity and how well a geopotential shape is reproduced in the climatology – together with a non-analogy descriptor accounting for the intensity of the centers of action. These descriptors were shown relevant to study precipitation extremes and variability in the Northwestern Alps in previous studies. Even though LSC characteristics and trends are consistent among the three reanalyses after 1950, we find major differences between 20CRv2c and ERA20C from 1900 to 1950 in accordance with previous studies. Notably, ERA20C produces flatter geopotential shapes in the beginning of the 20th century and shows a reinforcement of the meridional pressure gradient that is not observed in 20CRv2c. We then focus on the recent changes in LSC from 1950 to 2019 using ERA5. We combine the four atmospheric descriptors with an existing weather pattern classification to study the recent changes in the main atmospheric influences over France and Western Europe (Atlantic, Mediterranean, Northeast, Anticyclonic). We show that little changes are found in Northeast circulations. However, we show that Atlantic circulations (zonal flows) tend to become more similar to known Atlantic circulations in winter. Anticyclonic conditions tend to become more stationary in summer – a change that can potentially affect summer heatwaves. Furthermore, Mediterranean circulations tend to become more stationary, more similar to known Mediterranean circulations and associated with stronger centers of action in autumn, which could have implications for autumn extreme precipitation in the Mediterranean-influenced regions of the Southwestern Alps.

Antoine Blanc et al.

Status: open (until 30 Nov 2021)

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Antoine Blanc et al.

Antoine Blanc et al.

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Short summary
Local weather is governed by the atmospheric circulation, which can be viewed as the air flow on a large scale and at high elevation. In this work, we show some recent evolutions of the air flows coming from the Atlantic ocean and from the Mediterranean Sea to Western Europe, but also for Anticyclonic conditions (reflecting no air flow). These recent evolutions could have implications for temperature and precipitation variability and extremes over Western Europe.