Reconciling North Atlantic climate modes: Revised monthly indices for the East Atlantic and the Scandinavian patterns beyond the 20th century

Climate variability in the North Atlantic sector is commonly ascribed to the North Atlantic Oscillation. However, recent studies have shown that taking into account the second and third mode of variability (namely the East Atlantic – EA – and the Scandinavian – SCA – patterns) greatly improves our understanding of their controlling mechanisms, as well as their impact on climate. The most commonly used EA and SCA indices span the period from 1950 to present which is too short, for example, to calibrate palaeoclimate records or assess their variability over multi-decadal scales. To tackle this, here, we make available seasonal (3-months) EOF-based indices of NAO, EA and SCA indices covering the period from 1851 to present (Dataset 2); and compare them with their equivalent instrumental indices calculated as standarised sea-level pressure anomalies from Valentia Observatory, Ireland and Bergen Florida, Norway (Dataset 1)