NOMADS is a Concerted Action in the field of numerical modelling of marine systems, under the EU Marine Science and Technology ([MAST 2]) programme. The project runs for 2 years, starting February 1995.
The subject of the study is an intercomparison of advection-dispersion models for the North West European continental shelf presently available and being used at various institutes within the European Union.
The objectives are:
This focusses on the period November 1988 to October 1989 and spatially on the southern North Sea. The models are taken as they are presently used, i.e. varying from one another in the detail of included physics (2D/3D, barotropic/baroclinic, dispersion formulation), numerical solution techniques, grid sizes, calibration and underlying hydrodynamics. Thus the one constraint is that the models must all have the common spatial coverage of the North Sea basin between 51deg N and 55deg 40'N. To enable model simulations to be carried out a comprehensive [data set] has been constructed which includes bathymetry, tides, time- varying meteorology, boundary forcing and river discharge. Within the intercomparison there are four 2D models and nine 3D models, some of these are tidally-resolving (mesoscale) (9) and some are not (macroscale) (3).
Four experiments were defined:
Experiment 1 (for 2D models only): continuous release of conservative and non-conservative tracers from the six locations (see figure) for 180 days starting 1 March 1989. Parameters examined include the age and concentration of the tracer.
Experiment 2: single particle release from each location at four intervals in the year (releases at surface, mid-depth and bottom for 3D models). Parameters examined include distance travelled and relative tracer position.
Experiment 3: instantaneous release of a 1kg tracer from each location at 2 times, 1 March and 1 August 1989. Parameters examined include trajectory of the centre of mass, total mass and patch shape and area.
Experiment 4: Salinity and accumulated volume flux across 2 east-west sections at 52.5deg N and 54.5deg N (see figure). Parameters examined include time slice values and spatial variability.
The 2D models were run for the full 12 month period, the 3D models were run for either a) a six-month period, March-September 1989, or b) two 1-month periods, March and August 1989, depending on partners computational ability. Grid sizes of the models ranged from 2.4 km up to 20 km.
The experiment is the development of a fresh water eddy. A cylinder of fresher water is placed in the surface layer of an ambient fluid and allowed to mix. As the eddy forms under the influence of rotation, instabilities (secondary eddies) develop, the order of which depends on the friction (numerical and interfacial) in the system. The experiment is based on laboratory measurements (Griffiths & Linden, 1981, Journal of Fluid Mechanics, 105, 283- 316) and the numerical design of James (1996, Journal of Marine Systems, in press).
Five partners have participated in this experiment, producing 2 distinct sets of instability related to their numerical schemes.
Together, both experiments have generated more than 900 datasets for intercomparison. The intercomparison is presently in the analysis phase.
NOMADS will produce four Technical Reports:
