A persistent atmospheric pressure mode governs western Europe’s seasonal climate
Abstract
The North Atlantic Oscillation (NAO) is widely recognised as the leading mode of atmospheric variability over the North Atlantic (90°W-40°E, 20°-80°N). However, its broad-scale dipole fails to fully explain climate variability at mid-latitudes around Western Europe, where coastal storm and hydroclimatic impacts remain poorly captured. Here, using monthly mean sea-level pressure (SLP) from the ERA5 reanalysis (1950-2024), we apply empirical orthogonal function (EOF) analysis to identify dominant regional pressure modes across the Eastern part of the North Atlantic sector (25°W-15°E, 20°-65°N). The leading mode corresponds to the West Europe Pressure Anomaly (WEPA), while the second reproduces the canonical NAO pattern. Together, these modes explain between 67% and 78% of the seasonal SLP variance. The WEPA exhibits a remarkably stable spatial structure throughout the annual cycle and is strongly correlated with precipitation, near-surface wind speed and significant wave height along the Atlantic coast of Western Europe, demonstrating that it represents a persistent regional mode of atmospheric variability rather than a winter-specific empirical index. Future projections based on CMIP6 simulations indicate only modest changes in WEPA under the SSP2-4.5 scenario. Although a weak decrease in the ensemble-mean index is detected when all ensemble members are considered, this trend is not reproduced when analyses are performed using one ensemble member per model, suggesting limited evidence for a robust multi-model climate response. These results establish WEPA as a fundamental mode of atmospheric variability governing Western European climate while indicating that its future evolution remains uncertain relative to the large internal variability of the climate system.
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BibTeX
@article{alkama2026persistent,
title = {{A persistent atmospheric pressure mode governs western Europe’s seasonal climate}},
author = {Ramdane Alkama and Didier Swingedouw and Bruno Castelle and Christophe Cassou and Joanne Couallier and Theodore Raymond and Jérôme Ogée},
journal = {Climate Dynamics},
year = {2026},
month = oct,
doi = {10.1007/s00382-026-08420-9},
url = {https://hal.science/hal-05843944v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - A persistent atmospheric pressure mode governs western Europe’s seasonal climate
AU - Ramdane Alkama
AU - Didier Swingedouw
AU - Bruno Castelle
AU - Christophe Cassou
AU - Joanne Couallier
AU - Theodore Raymond
AU - Jérôme Ogée
PY - 2026
DA - 2026/10/29
JO - Climate Dynamics
DO - 10.1007/s00382-026-08420-9
UR - https://hal.science/hal-05843944v1
AB - The North Atlantic Oscillation (NAO) is widely recognised as the leading mode of atmospheric variability over the North Atlantic (90°W-40°E, 20°-80°N). However, its broad-scale dipole fails to fully explain climate variability at mid-latitudes around Western Europe, where coastal storm and hydroclimatic impacts remain poorly captured. Here, using monthly mean sea-level pressure (SLP) from the ERA5 reanalysis (1950-2024), we apply empirical orthogonal function (EOF) analysis to identify dominant regional pressure modes across the Eastern part of the North Atlantic sector (25°W-15°E, 20°-65°N). The leading mode corresponds to the West Europe Pressure Anomaly (WEPA), while the second reproduces the canonical NAO pattern. Together, these modes explain between 67% and 78% of the seasonal SLP variance. The WEPA exhibits a remarkably stable spatial structure throughout the annual cycle and is strongly correlated with precipitation, near-surface wind speed and significant wave height along the Atlantic coast of Western Europe, demonstrating that it represents a persistent regional mode of atmospheric variability rather than a winter-specific empirical index. Future projections based on CMIP6 simulations indicate only modest changes in WEPA under the SSP2-4.5 scenario. Although a weak decrease in the ensemble-mean index is detected when all ensemble members are considered, this trend is not reproduced when analyses are performed using one ensemble member per model, suggesting limited evidence for a robust multi-model climate response. These results establish WEPA as a fundamental mode of atmospheric variability governing Western European climate while indicating that its future evolution remains uncertain relative to the large internal variability of the climate system.
SN - 0930-7575
SN - 1432-0894
ER -