Abstract
Northern European sea levels show a non-stationary link to the North Atlantic Oscillation (NAO). The location of the centers of the NAO dipole, however, can be affected through the interplay with the East Atlantic (EAP) and the Scandinavian (SCAN) teleconnection patterns. Our results indicate the importance of accounting for the binary combination of the NAO with the EAP/SCAN for better understanding the non-stationary drivers inducing sea level variations along the European coasts. By combining altimetry and tide gauges, we find that anomalously high monthly sea levels along the Norwegian (North Sea) coast are predominantly governed by same positive phase NAO+/EAP+ (NAO+/SCAN+) type of atmospheric circulation, while the Newlyn and Brest tide gauges respond markedly to the opposite phase NAO−/EAP+ combination. Despite these regional differences, we find that coherent European sea level changes project onto a pattern resembling NAO+/SCAN+, which is signified by pressure anomalies over Scandinavia and southern Europe forcing winds to trace the continental slope, resulting in a pile-up of water along the European coasts through Ekman transport. We conclude that taking into consideration the interaction between these atmospheric circulation regimes is valuable and may help to understand the time-varying relationship between the NAO and European mean sea level.
Highlights
Global mean sea level has been accelerating from rates of 1.1 to 2 mm/year before 1990 [1] towards unprecedented high rates of 3.3 ± 0.4 mm/year afterwards [2] and is expected to continue its acceleration in a warming climate primarily as a result of melting ice and ocean thermal expansion [3,4] giving rise to significant socioeconomic and environmental consequences on the coastal zones [5]
The location of the centers of action associated with the North Atlantic meridional pressure dipole, can be affected through the interplay with the East Atlantic Pattern (EAP) and SCAN teleconnections, potentially explaining the temporally-varying relationship between sea level variability and the North Atlantic Oscillation (NAO)
Our results indicate that it is important to account for the binary interaction of the NAO with EAP/SCAN to better understand the drivers inducing anomalous sea level periods along the European coast
Summary
Global mean sea level has been accelerating from rates of 1.1 to 2 mm/year before 1990 [1] towards unprecedented high rates of 3.3 ± 0.4 mm/year afterwards [2] and is expected to continue its acceleration in a warming climate primarily as a result of melting ice and ocean thermal expansion [3,4] giving rise to significant socioeconomic and environmental consequences on the coastal zones [5]. Our findings suggest that the NAO alone is not always sufficient as a forcing mechanism (see, e.g., Dangendorf et al [13], Kolker and Hameed [42], Ullmann and Monbaliu [43]), and that it is essential to take into account all three leading modes of North Atlantic atmospheric variability to explain the anomalous periods of the European sea level, not least since there are regional differences with a preference toward a specific atmospheric pattern that can only be formed by the linear combination of these teleconnections [14].
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