Abstracts:
Francis Poulin, University of Waterloo: Mesoscale Air–Sea Interactions in a Western Boundary Current System
The Earth system is changing at an alarming rate, and quantifying these changes is of paramount importance for humankind. A key source of uncertainty lies in the exchange of physical and chemical properties between the atmosphere and the ocean through air–sea interactions. Observations and theory show that large-scale atmospheric winds drive ocean circulation, giving rise to subtropical gyres, western boundary currents (WBCs), and energetic mesoscale eddies. In contrast, the role of air–sea coupling at smaller scales remains less well understood.
At oceanic mesoscales (O(100 km)), sea surface temperature (SST) anomalies can exchange heat effectively with the atmosphere, influencing winds, cloud formation, and precipitation. However, the dynamical feedbacks between the ocean and atmosphere at these scales, particularly in regions of strong currents such as WBCs, are still not fully characterized.
In this talk, I present recent work investigating the details of mesoscale air–sea interactions in an idealized configuration consisting of a WBC in the ocean and a mean atmospheric wind. This is studied using a series of large-eddy simulations over a 24-hour period, with three configurations: (1) a dynamic ocean coupled to a static atmosphere, (2) a dynamic atmosphere over a static ocean, and (3) a fully coupled dynamic ocean–atmosphere system.
We analyze large-scale structures in potential temperature and velocity fields, along with the turbulent kinetic energy in both fluids. The results show that air–sea coupling has a relatively weak impact on atmospheric turbulence, but a strong impact on the ocean, significantly modifying the distribution of kinetic energy. These findings highlight an asymmetric coupling between the ocean and atmosphere at the mesoscale and have implications for the representation of air–sea interactions in climate and weather models.
Caroline Katsmann, Delft University of Technology: North Atlantic CLUEDO*, or how the upper and lower branches of the AMOC are connected
The Atlantic Meridional Overturning Circulation (AMOC), characterized by poleward surface currents and dense equatorward return currents, transports vast amounts of heat to high latitudes, and is largely responsible for Western Europe’s relatively mild climate. Climate models project the AMOC will weaken substantially over the 21st century, impacting weather, climate, sea level and the oceanic carbon cycle.
Until recently, our knowledge of the AMOC was based entirely on theory, numerical models and intermittent observations. Ground-breaking new observations have led to a major change in our view on the AMOC, and painfully revealed that its representation in climate models displays serious deficiencies. This obviously casts doubt on the reliability of scenarios for AMOC weakening based on such models, and discloses an underlying lack of in-depth understanding of its controlling physics.
The research presented in this seminar explores the processes that connect the upper and deep branches of the AMOC in the subpolar North Atlantic, exploiting the capabilities of both idealized and realistic model simulations. Careful analyses reveal that the regional characteristics of the AMOC at high latitudes are highly variable in space and time, and reflect the influence of multiple underlying processes.
* Controls on Light Upper ocean waters Entering the Deep Ocean
What is the Joint Oslo Seminar (JOS):
- Atmospheric and climate sciences have a stronghold in Oslo among the four institutions University of Oslo, the Meteorological Institute, CICERO and NILU.
- This joint seminar invites renowned international experts to contribute to an informal series of lectures, meant to create interaction with the Oslo atmospheric and climate science community on recent highlights and analysis in the field.
- Normally seminars will be held on Thursdays (12:15 pm -1pm).