How does the ocean influence temperature over land?

Norway is much warmer than most other places at similar latitudes. The picture below shows fishing activity in northern Norway in winter; this could not have been possible without the warm Norwegian Atlantic Current, which brings warm water masses from the south throughout the year.

“Vinter i Lofoten” (1886), painted by Otto Sinding

In a new paper, Marius Årthun, Noel Keenlyside and Erik Kolstad from our project group and colleague Tor Eldevik from the Bjerknes Centre for Climate Research investigate the causes of European temperature variations on long time scales. For instance, we know that the temperature in parts of Scandinavia fluctuates with a period of 14 years. The paper shows that this is probably because the sea surface temperatures in the Nordic Seas also fluctuate on the same time scale. The mean westerly winds then transport air masses form over the ocean to over land, and thus the connection between the ocean and land is mediated. We can use this information to predict variations between colder-than-normal and warmer-than-normal, potentially several years ahead.

The title of the paper is Time scales and sources of European temperature variability, and it has now been accepted for publication in Geophysical Research Letters (GRL). Here is the abstract:

Skillful predictions of continental climate would be of great practical benefit for society and stakeholders. It nevertheless remains fundamentally unresolved to what extent climate is predictable, for what features, at what time scales, and by which mechanisms. Here we identify the dominant time scales and sources of European surface air temperature (SAT) variability during the cold season using a coupled climate reanalysis, and a statistical method that estimates SAT variability due to atmospheric circulation anomalies. We find that eastern Europe is dominated by sub-decadal SAT variability associated with the North Atlantic Oscillation, whereas interdecadal and multi-decadal SAT variability over northern and southern Europe are thermodynamically driven by ocean temperature anomalies. Our results provide evidence that temperature anomalies in the North Atlantic Ocean are advected over land by the mean westerly winds, and, hence, provide a mechanism through which ocean temperature controls the variability and provides predictability of European SAT.

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