54
It is worth pointing out that the pathological behaviour of the standard closure does not seem
to be directly related to the mesh size. For instance, with /',.z = 2 m and /',.z = 0.5 m, the level
2.5 model still exhibits unacceptable oscillations, whereas the quasi-equilibrium version
produces results free of unphysical noise (Deleersnijder and Luyten, 1994). With non zero
Coriolis factor if -:t:: 0), the rate of deepening of the turbulent layer is considerably slower
(Mellor and Strub, 1980), but the level 2.5 model's results are still significantly less acceptable
than those of the quasi-equilibrium model (Deleersnijder and Luyten, 1994).
Conclusion. The numerical experiments described above clearly show that ensuring the
physical well-foundedness of a given parameterization is not sufficient. The stability functions
tested, which seemingly are a small detail in the governing equations, may be deemed equally
valid from a physical point of view, but lead to significantly different model results. One should
always investigate the influence of every parameterization on the behaviour of the whole model.
In general, this is not an easy task, which is no excuse for disregarding it...
5. Interpretation of the results of a three-dimensional marine model
In this Section, we address the problem of interpreting the large amount of information
generated by a marine model. The study concentrates on the understanding of the vertical
velocity field of a three-dimesional model of the region of the Berig Strait.
The Pacific and Arctic Oceans exchange mass, momentum and energy through the Bering
Strait only (Fig. 6). The region of the Bering Strait exhibits some of the most intense biological
productivity ever measured in the sea (Sambrotto et aI., 1984), with peak values that can be of
the order of 10- 2 kg C m- 2 day-I. From a physical and biological point of view, this region is
thus of great importance.
The monthly flow through the Bering Strait, which is of order 1 Sverdrup (= 10 6 m 3 s-I), is
directed to the North, i.e., from the Pacific to the Arctic. Since Coachman and Aagaard (1966),
it seems clear that this northward flow is primarily induced by the water level difference
between the Pacific and the Arctic. It is also believed that the variability of the flow mainly
results from the wind forcing (Coachman and Aagaard, 1988). On average, two thirds of the
flow pass through the Anadyr Strait.
In the domain of interest the salinity variations are predominantly horizontal, whereas the
temperature contrasts are mostly observed in the vertical direction, with a marked thermocline
(Coachman et al., 1975). Satellite infra-red pictures show that a plume of cold water originates
in the Anadyr Strait, near the Siberian coast. Although its extent depends on meso-scale
phenomena, the cold water plume seems to be a permanent hydrodynamic feature (Fig. 7).
All in situ data analysed by Brasseur (1991) and Brasseur and Haus (1991) confirm the
existence and persistence of a plume of cold water downstream of the Anadyr Strait and suggest
that it is due to an intense upwelling taking place in the "Siberian half' of the Anadyr Strait.
Throughout the summer period the Anadyr upwelling is likely to bring nutrients from the lower
layer to the euphotic zone - where photosynthesis can take place -, continuously fuelling the
primary production (Walsh et al., 1989).
No device is able to directly measure vertical fluxes at reasonable cost. Moreover, indirect
methods for estimating the magnitude of the vertical motions are known to be rather inaccurate.
It is worth pointing out that the pathological behaviour of the standard closure does not seem
to be directly related to the mesh size. For instance, with /',.z = 2 m and /',.z = 0.5 m, the level
2.5 model still exhibits unacceptable oscillations, whereas the quasi-equilibrium version
produces results free of unphysical noise (Deleersnijder and Luyten, 1994). With non zero
Coriolis factor if -:t:: 0), the rate of deepening of the turbulent layer is considerably slower
(Mellor and Strub, 1980), but the level 2.5 model's results are still significantly less acceptable
than those of the quasi-equilibrium model (Deleersnijder and Luyten, 1994).
Conclusion. The numerical experiments described above clearly show that ensuring the
physical well-foundedness of a given parameterization is not sufficient. The stability functions
tested, which seemingly are a small detail in the governing equations, may be deemed equally
valid from a physical point of view, but lead to significantly different model results. One should
always investigate the influence of every parameterization on the behaviour of the whole model.
In general, this is not an easy task, which is no excuse for disregarding it...
5. Interpretation of the results of a three-dimensional marine model
In this Section, we address the problem of interpreting the large amount of information
generated by a marine model. The study concentrates on the understanding of the vertical
velocity field of a three-dimesional model of the region of the Berig Strait.
The Pacific and Arctic Oceans exchange mass, momentum and energy through the Bering
Strait only (Fig. 6). The region of the Bering Strait exhibits some of the most intense biological
productivity ever measured in the sea (Sambrotto et aI., 1984), with peak values that can be of
the order of 10- 2 kg C m- 2 day-I. From a physical and biological point of view, this region is
thus of great importance.
The monthly flow through the Bering Strait, which is of order 1 Sverdrup (= 10 6 m 3 s-I), is
directed to the North, i.e., from the Pacific to the Arctic. Since Coachman and Aagaard (1966),
it seems clear that this northward flow is primarily induced by the water level difference
between the Pacific and the Arctic. It is also believed that the variability of the flow mainly
results from the wind forcing (Coachman and Aagaard, 1988). On average, two thirds of the
flow pass through the Anadyr Strait.
In the domain of interest the salinity variations are predominantly horizontal, whereas the
temperature contrasts are mostly observed in the vertical direction, with a marked thermocline
(Coachman et al., 1975). Satellite infra-red pictures show that a plume of cold water originates
in the Anadyr Strait, near the Siberian coast. Although its extent depends on meso-scale
phenomena, the cold water plume seems to be a permanent hydrodynamic feature (Fig. 7).
All in situ data analysed by Brasseur (1991) and Brasseur and Haus (1991) confirm the
existence and persistence of a plume of cold water downstream of the Anadyr Strait and suggest
that it is due to an intense upwelling taking place in the "Siberian half' of the Anadyr Strait.
Throughout the summer period the Anadyr upwelling is likely to bring nutrients from the lower
layer to the euphotic zone - where photosynthesis can take place -, continuously fuelling the
primary production (Walsh et al., 1989).
No device is able to directly measure vertical fluxes at reasonable cost. Moreover, indirect
methods for estimating the magnitude of the vertical motions are known to be rather inaccurate.