Wave-mediated atmosphere-ocean-sea-ice interactions and their climatic impacts in the Nordic Seas and eastern Arctic

In this project we are studying the role of ocean surface gravity waves on climate. These waves are in the interface of the ocean-ice and atmosphere and are generated by winds. It has long been assumed that these waves are in equilibrium with the winds and all their properties are simply determined from the wind. However it has been shown that these waves are constantly changing in height and are not always aligned with the wind. The effects of waves on climate variability differ from the effects that can be captured from the surface wind alone. Since one can observe these waves affecting maritime navigation, breaking by the beach, damaging marine structures, moving and breaking sea ice, it can be easily assumed that these waves only have a local effect. Surface waves have a local and global effect in the climate system. The roughness of the surface of the ocean, caused by the presence of the waves, plays a role in air-sea transfer of momentum, heat and mass affecting the fluids above and below. In this project we have included active ocean surface waves in a climate model: Norwegian Earth System Model (NorESM) to quantify their influence. We have found that when the wave and the atmosphere communicate mutually (coupling atmosphere-wave) the atmosphere presents as a result an increased enhancement of storminess in the North Atlantic. And as a consequence there is a robust winter warming in Europe. Changes in wind-stress (the force exerted by wind on the ocean surface) in tropical and mid-latitude regions have effects that reach far beyond those regions. These effects result in warming conditions in the Arctic. We have also found that the mutual interaction between the waves and the ocean (coupling wave-ocean) mainly deepens the ocean mixed layer depth via the so-called Langmuir circulation.

The North Atlantic - Arctic Ocean is a key region of the global Northern-Hemisphere storm track, characterized by strong air-sea exchange and associated meridional flux of enthalpy and water vapour. Regionally it determines much of the climate of western Eurasia and of the Nordic Seas, with strong effects on the Arctic sea-ice cover. The ocean state in particular is affected not only by the effects of strong diabatic and mechanical forcing, but notably also by the large activity of surface waves forced by the intense storms. Even though it is expected that the presence of surface waves has an important impact on the coupling between atmosphere, ocean, and sea ice, to date there is no quantitative assessment on the implications for the climate of the European/North-Atlantic region and for its evolution under natural or anthropogenic forcing. Indeed, surface waves are at present excluded from the representation of surface interactions in Earth System Models (ESMs). To understand the implications of this, we will, for the first time, use an ESM with a fully coupled wave model covering the northern North Atlantic - Arctic domain to carry out a systematic study of the effects of full coupling between ocean surface waves, atmosphere, ocean, and sea-ice on the climate in the Nordic Seas and eastern Arctic region. The project will thereby go beyond the state of the art and provide the scientific justification for a next generation ESM with a fully coupled wave model in the global domain. The rationale for a regional focus is two-fold. The first concerns the critical role of the marginal ice zone on the Northern-Hemisphere climate, an area that is particularly exposed to the effects of global warming and intrinsically exposed to wave action. The second rationale concerns the scientific prioritization of model development paths for the next-generation Norwegian Earth System Model. Understanding regional effects is a prerequisite to evaluate potential global climate impacts.