Modelling of Meddy-topography interactions

In the description of the research project the following two main components of the research work are mentioned: (i) application of a numerical code, and (ii) a series of laboratory experiments. Here follows the text on these components as written in the project proposal.

(i) Numerical modelling

The numerical modelling of the influence of topography on Meddies will be done with a code that solves the two-dimensional (2D) viscous Navier-Stokes equation in the vorticity-streamfunction formulation using a finite difference method, i.e. using a grid in a certain domain with appropriate boundary conditions. The code, originating from a code developed by Orlandi and Verzicco (Rome), has been used successfully in simulating the evolution of several kinds of 2D vortices (monopoles, dipoles, ...) and the results compare well with those of laboratory experiments and those of other numerical methods. The code has proven to be very stable, even for inviscid flows, depending only on the size of the time step with respect to the size of the grid. Extending the existing code by implementing a topographic function can be done quite easily. Due to the use of a finite difference method only more or less smooth topographies will be possible, such as Gaussian-shaped seamounts, smooth ridge-like features or sloping bottoms. This will nevertheless lead to a better understanding of the effect of topography on the motion and evolution of Meddy-like monopolar vortices. The required smoothness of the topography that can be used is mainly determined by the resolution, i.e. the grid size, needed to show the effects being studied. There are a few additional features in the code and separate programs available to follow specific flow characteristic (such as the energy, enstrophy and circulation of the vortex) in the course of time, as well as the motion of passive tracer particles advected by the flow field.  

(ii) Laboratory experiments

In the laboratory experiments, a rotating tow-tank channel facility filled with a stratified fluid will be used to study the interactions. Such a facility is fitted with a belt arrangement that permits topographic features to be translated uniformly and horizontally at prescribed velocities along the base of the tank. In the present project, a model Meddy will be generated in the tank, using the technique developed by Carton (1994), and a topographic feature mounted on the movable belt will be translated towards and past the Meddy. The interaction between the Meddy and the topography will be monitored by the flow visualisation and direct density field measurement systems available in the host laboratory. Topographic elements matching the numerical simulations will be used, in order to make direct comparisons between the two parts of the study possible. Quantitative measurements of the velocity and density fields within the Meddy throughout its interaction with the topography will be made using the data acquisition system in Davies' laboratory. With such measurements, the nature of the topographic distortion of the density, velocity and vorticity fields within the Meddy by the topography can be determined. In addition, the small-scale mixing caused to the Meddy can be quantified and parameterised. The experiments will be designed to cover cases of direct relevance to oceanic counterparts and will investigate the topographic interactions for a range of external parameters (e.g. undisturbed Meddy vorticity, advection velocity of the Meddy, topographic height, background stratification, Coriolis parameter). Systematic parametric experiments will be carried out to study strong and weak interactions and attempts will be made to classify the different interactions that occur. The main outputs of the work will therefore be a series of flow classifications, sets of three dimensional and time-dependent velocity, vorticity and density fields for Meddy-topography interactions of varying strength and intercomparisons between laboratory model data, numerical model results and oceanic field data where available.

Back to the Post-doc. research in Dundee page.

 
Jos van Geffen -- Home  |  Site Map  |  Contact Me

last modified: 27 May 2001