21.08.2017: FB1-Seminar

11 Uhr, Hörsaal West, Düsternbrooker Weg 20

Abstract:

We investigate the spatio-temporal variability of surface diffusivities using observed geostrophic velocities from AVISO to advect passive tracer fields in an idealized surface model setup.
Temporal variability in surface diffusivities is diagnosed using both Lagrangian (Effective Diffusivity) Eulerian (Osborn-Cox Diffusivity) diagnostics, both of which document high temporal variability.
The temporal changes are particularly strong in the subtropical basins of the Pacific where mean diffusivities are low on average. Here the temporal variability shows strong correlation to the El-Nino-Southern-Oscillation (ENSO) phenomenon. Diagnosed diffusivities suggest up to 100% increase in diffusivity during positive ENSO events.
These results suggest that large scale climate fluctuations modulate surface diffusivities, which might represent a partial climate feedback not currently represented in state-of-the-art climate models.
The signal in the Pacific cannot be explained by temporal variability in eddy kinetic energy (EKE), suggesting that interactions of the eddy field with the large scale flow are important to capture the temporal variability of surface eddy diffusivities. If the observed variability extends below the mixed layer this process could be important in characterizing tracer distributions and tracer uptake of e.g. heat, carbon, oxygen, nutrients etc in the upper ocean.

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