Improved marine predictions for UK waters

May 2012 - The Met Office makes daily predictions of the temperatures, currents, nutrients and plankton in the seas around the UK. Major improvements to these predictions were introduced at the end of March 2012.

Marine predictions for the north-west European shelf

The waters of the continental shelf around the UK are shallow and strongly affected by the tides. An ocean forecasting system for this region has been operated at the Met Office since 2000. Each day this predicts the evolution of the three-dimensional structure of the temperatures, salinities, tides and other currents over the next five days. This system includes a bio-geochemical model which simulates the evolution of the sediments, nutrients, phyto-plankton and zoo-plankton.

Recent Improvements made

The new system uses the NEMO physical ocean model (in place of POLCOMS). Table 1 shows that the root mean square errors in the amplitudes and phases of the main tides is much improved (M2 and S2 are the lunar and solar semi-diurnal tides). When enlarged the figure above shows that the locations of the tidal mixing fronts during the summer period (June - August) is also much improved. The tidal mixing front is where the difference between the temperature of the water at the surface and the bottom equals 0.5 °C. The red lines show the location of the tidal mixing fronts according to the ICES climatology which is based on in situ measurements. The white and yellow lines show the tidal mixing fronts as simulated in 2008 by the old and new systems (POLCOMS and NEMO) respectively. These improvements are the result of wide-ranging developments to the NEMO model to make it suitable for tidal continental shelves (O'Dea et al. 2012).

Table 1: Root mean square (RMS) differences between the model and tide gauge values for the amplitude and phase of the lunar (M2) and solar (S2) semi-diurnal tides

Amplitude (cm)

Phase (°)

Old New Old New
M2 12.0 10.3 21.1 14.7
S2 6.1 3.7 14.3 12.8

The simulation of nitrates (top) and phosphates (bottom) at the L4 mooring site near Plymouth in 2007. Red crosses are in situ measurements; blue line the old simulation; black line the new simulation. Figure 2: The simulation of nitrates (Enlarge to see phosphates) at the L4 mooring site near Plymouth in 2007. (see text for details)
The simulation of the seasonal cycle of nutrients by the new system is also much better in the new system than the old one. When enlarged, figure 2 illustrates the simulation of nitrates (top) and phosphates (bottom) at the L4 mooring site near Plymouth in 2007. Red crosses show in situ measurements; blue lines the old simulation and black lines the new simulation. The improvements result from better specification of nutrients at the boundaries, better initialisation of the benthic ecosystem and various corrections.

Figure 3 shows the impact of the improved boundary conditions on the near-surface nitrate in winter. When enlarged, the World Ocean Atlas climatology in the middle panel is to be compared with the simulation using the original, no flux, The impact of the boundary conditions on the near-surface mean nitrate in winter (Dec – Jan). Figure 3: The impact of the boundary conditions on the near-surface mean nitrate in winter (Dec - Jan). (See text for details of the different panels) boundary condition on the left and the new climatology boundary conditions on the right. The sediments in the new system have also been considerably improved recently (Sykes and Barciela 2012). 

Further information

More details on these improvements are available from the NCOF successes page . They were only made possible by close collaborations with the National Oceanographic Centre and Plymouth Marine Laboratory under the umbrella of the NCOF consortium.

The north-west European shelf forecasting system described above is part of the MyOcean system, which is making forecasts available from this and other European systems.

The Met Office and NCOF also predict surface waves , tides and storm surges , the temperatures, salinities and currents in the deep ocean and monitor global sea surface temperatures and sea-ice .

References

O'Dea, E. J., J. While, R. Furner, A. Arnold, P. Hyder, D. Storkey, K. P. Edwards, J. R. Siddorn, M. J. Martin, H. Liu, J. T. Holt, 2012, An operational ocean forecast system incorporating SST data assimilation for the tidally driven European North-West European shelf. Journal of Operational Oceanography, Volume 5, Number 1, pp. 3-17(15)

Edwards, K. P., R. M. Barciela, M. Butenschon, 2012, Validation of the NEMO-ERSEM operational ecosystem model for the North West European Continental Shelf, submitted to Ocean Sciences (under open review)

Sykes, P. A., and R. M. Barciela, 2012, Assessment and development of a sediment model within an operational system. J. Geophys. Res., 117, C04036, doi:10.1029/2011JC007420.

Last updated: 14 August 2014