Estimations of Vertical Velocities Using the Omega Equation in Different Flow Regimes in Preparation for the High Resolution Observations of the SWOT Altimetry Mission
Alice Pietri, LPO, CNRS, Brest, France; LOCEAN-IPSL, UPMC, Paris, France, Xavier Capet, Université Pierre et Marie Curie, LOCEAN , IPSL, Paris, France, Francesco d'Ovidio, LOCEAN, Paris, France, Julien Le Sommer, Univ. Grenoble-Alpes / IGE/CNRS, Grenoble, France, Jean-Marc Molines, LGGE - Laboratoire de Glaciologie et Géophysique de l'Environnement, CNRS - Université Grenoble Alpes, Grenoble, France and Andrea Michelangelo Doglioli, Mediterranean Institute of Oceanography, 13288, Marseille, France
Abstract:
Vertical velocities (w) associated with meso and submesoscale processes play an essential role in ocean dynamics and physical-biological coupling due to their impact on the upper ocean vertical exchanges. However, their small intensity (O 1 cm/s) compared to horizontal motions and their important variability in space and time makes them very difficult to measure. Estimations of these velocities are thus usually inferred using a generalized approach based on frontogenesis theories. These estimations are often obtained by solving the diagnostic omega equation. This equation can be expressed in different forms from a simple quasi geostrophic formulation to more complex ones that take into account the ageostrophic advection and the turbulent fluxes. The choice of the method used generally depends on the data available and on the dominant processes in the region of study. Here we aim to provide a statistically robust evaluation of the scales at which the vertical velocity can be resolved with confidence depending on the formulation of the equation and the dynamics of the flow. A high resolution simulation (dx=1-1.5 km) of the North Atlantic was used to compare the calculations of w based on the omega equation to the modelled vertical velocity. The simulation encompasses regions with different atmospheric forcings, mesoscale activity, seasonality and energetic flows, allowing us to explore several different dynamical contexts. In a few years the SWOT mission will provide bi-dimensional images of sea level elevation at a significantly higher resolution than available today. This work helps assess the possible contribution of the SWOT data to the understanding of the submesoscale circulation and the associated vertical fluxes in the upper ocean.
