Beyond the NAO : The East Atlantic Pattern's Role in Early 20th‐Century Meteorological Droughts in Western Europe

Abstract

The North Atlantic Oscillation (NAO) and the East Atlantic (EA) pattern are the primary winter modes of large‐scale atmospheric variability in the North Atlantic. While EA is generally considered secondary to NAO, recent studies have reported that during the early 20th century, EA was the leading mode of variability instead of NAO. This study builds on that finding to characterise North Atlantic winter atmospheric circulation during this period. The early 20th century was marked by an intensified Azores High coinciding with an extensive Icelandic Low (IL), which generated widespread negative SLP anomalies across the North Atlantic. This configuration elevated EA's role as a primary modulator of precipitation in Western Europe. Focusing on the Iberian Peninsula, we demonstrate that during this period, EA effectively captured precipitation variability both in the western sector—typically influenced by NAO—and in the eastern sector, where neither NAO nor EA generally exerts significant control. Our findings enhance the understanding of precipitation variability in this region and provide insights into the non‐stationary relationship between EA and NAO. Finally, this study suggests the importance of internal climate variability in shaping those North Atlantic winter dynamics. Intense volcanic activity in the late 19th century likely contributed to ocean cooling and NAO intensifying. However, the mechanisms behind the exceptionally strong IL (e.g., EA−) remain unclear. Despite remaining uncertainties, advancing knowledge in this area will be crucial for improving medium‐range weather prediction systems and long‐term climate projections.

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