Seasonality and Amplification of the Sea Surface Signature of Internal Tides

We present recent results on the sea surface signature of internal tides and its seasonality using high resolution realistic simulation. The upper ocean is energetic at scales below the Rossby deformation radius owing to the existence of internal waves and submesoscale fronts and vortices. Understanding the dynamics of these different motions is crucial for separating their contribution and reconstructing the currents below the mesoscale from satellite measurements. Internal waves and submesoscale motions both undergo strong spatial and seasonal variations, driven by different mechanisms. We show that internal waves are greatly amplified near the surface in summer, mostly due to a thin mixed layer bounded by a seasonal pycnocline. This surface amplification is well captured by linear theory, provided that the stratification at the base of the mixed layer is accurately represented. In winter, the superinertial motions are not fully explained by linear theory, reflecting impacts of the more energetic submesoscale motions. The global impact of this seasonal amplification on the surface currents and surface elevation is finally addressed.