COHERENS
North Sea case study
The program has been applied in previous projects to the study of
physical and biological processes in coastal areas with an important
river input and for the simulation of the advection and dispersion of
contaminants in the North Sea. An important objective is to
demonstrate its scientific usefulness by simulating a full annual
cycle in typical shelf seas and comparing the results with
observational data sets.
The area, selected for the study is the part of the North Sea between
4°W and 57°N including the Channel, the southern Bight and the
central North Sea. A fine resolution ((6-7 km) grid is adopted in the
horizontal allowing a realistic simulation to be made and to study the
impact of frontal processes on the biological system. The simulation
starts at 1 January 1989 when the water column is vertically mixed and
ends at 31 December 1989 covering the formation and erosion of the
thermocline and the spring and autumn blooms of plankton. The
evolution of the salinity field is simulated including input of the
most important river discharges and fluxes at the open boundaries.
The model results are compared with the North Sea Project data
collected at more than 120 stations in the southern and central North
Sea. The data set consists of vertical profiles of temperature and
salinity taken at approximatively monthly intervals. Concentrations of
chlorophyll, nitrate and suspended sediment concentrations are
available for three depths at most of the stations.
click on image to
view the full figure
Results from a first run with the model for the year 1989. The first
figure shows the depth of the thermocline in August, taken as the
depth where the temperature difference with the surface value first
equals 0.5°C and taken to be zero if the surface-bottom temperature
difference is lower than 0.5°C. The boundary between the
(thermally) stratified and mixed areas is marked by a sharp front
which extends eastwards from the British coast upto the central North
Sea, then curves upwards first northeastwards and finally northwards
parallel to the Danish coast. The transition between the mixed and
stratified regime occurs at a water depth of ~40 m as can be observed
in the temperature contour plot along a vertical transect at 4.5°E.
click on image to
view the full figure
The model results will be compared with the data of the North Sea
Project. The locations of the data stations are indicated with a
"+". A preliminary comparison has been made at station CS (55°30'N,
0°55'E). The time series plot represents the surface and bottom
temperatures. Data values are indicated by diamonds (surface) and
squares (bottom). Although the initial temperatures are too low, the
onset of stratification is well predicted while model and data are
afterwards in good agreement upto July. In the late summer and the
autumn vertical stratification is underestimated by the model with
lower surface and higher bottom temperatures. This may be due to
dvective processes which need to be further investigated.
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