Turbulent viscosity optimized by data assimilation

• Main Authors: Y. Leredde, J.-L. Devenon, I. Dekeyser
• Format: Article
• Language: English
• Published: Copernicus Publications 1999-11-01
• Series: Annales Geophysicae
• Online Access: https://www.ann-geophys.net/17/1463/1999/angeo-17-1463-1999.pdf

As an alternative approach to classical turbulence modelling using a first or second order closure, the data assimilation method of optimal control is applied to estimate a time and space-dependent turbulent viscosity in a three-dimensional oceanic circulation model. The optimal control method, described for a 3-D primitive equation model, involves the minimization of a cost function that quantifies the discrepancies between the simulations and the observations. An iterative algorithm is obtained via the adjoint model resolution. In a first experiment, a <i>k</i> + <i>L</i> model is used to simulate the one-dimensional development of inertial oscillations resulting from a wind stress at the sea surface and with the presence of a halocline. These results are used as synthetic observations to be assimilated. The turbulent viscosity is then recovered without the <i>k</i> + <i>L</i> closure, even with sparse and noisy observations. The problems of controllability and of the dimensions of the control are then discussed. A second experiment consists of a two-dimensional schematic simulation. A 2-D turbulent viscosity field is estimated from data on the initial and final states of a coastal upwelling event.<br><br><b>Key words.</b> Oceanography: general (numerical modelling) · Oceanography: physical (turbulence · diffusion · and mixing processes)