Good progress was maintained with LOIS (NORMS) modelling, using the 3D B-grid baroclinic model with accurate "PPM" advection. Improvements in the temperature and turbulence formulations were incorporated and the seasonal cycle of temperature during the North Sea Project survey period (1 November 1998 to 31 October 1989) was simulated on the 20 km Southern North Sea grid. The model was run for four years, cyclically repeating the surface forcing, without significant drift. Comparisons between co-located model and observed (CTD) temperatures at survey stations, provided an assessment of the model performance with minimal interpolation or averaging. Results (Figure 7) are encouraging. Point for point the correlation is 0.96, with mean and RMS deviations +0.21°C and 1.2°C, respectively. The model reproduced accurately, in magnitude and timing, the surface to bed temperature differences and thermocline depths associated with the seasonal cycle. The fit is limited mainly by the ability to predict on the 20 km grid the location of the tidal mixing front separating stratified from well mixed waters east of Flamborough Head.
The 2.4 km eddy resolving version of this model, including river inputs, was run for 6 months, reproducing the onset of stratification and realistic baroclinic features. Figure 8 show a summer distribution of computed sea bed temperature in which the Flamborough front is clearly visible with irregularities associated with baroclinic instabilities.
Future applications requiring long integrations at high resolution and with additional variables require efficient use of the most powerful computers. An implemenation of the 3D-B model for parallel computers was completed on a CRAY T3D machine with support from
the "High Performance Computing Initiative" (HPCI).
The necessary speed is achieved by domain decomposition, with computations for sub-areas of the grid carried out simultaneously on different processors.
A shelf-wide 12 km version of the parallel model is currently being coupled to ERSEM (European Regional Seas Ecosystem Model) to investigate nutrient cycling and primary production on the NW European Shelf.
Figure 7
Comparison between North Sea Project CTD temperatures and results from the 20 km baroclinic model at the time and place of the CTD stations. Four aspects of comparison are shown, averaged over all CTD stations in each cruise.
Figure 8
Sea bed temperatures on 15 August 1989 from a 6 month simulation with the 2.4 km 3D-B model.
Last updated: 12th May 1998. Please send comments to A.Lane@pol.ac.uk