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.