386
layer the constant value for the water density is taken to be equal to 1027 kg/m 3 • The
lower layer stands for the Mediterranean water pouring out from the eastern Mediterranean into the Atlantic. The constant density value taken in this layer was 1029 kg /m 3 .
The physical domain considered presents 4 different boundaries. Two 'natural'
boundaries, corresponding to the Spanish and Moroccan coast. Besides, two vertical
cuts as 'artificial' boundaries have to be considered to bound the domain: the western
one near Tarifa and the eastern by Punta de Banos.
As initial conditions, elevation and fluxes equal to zero have been imposed, i.e.,
start from a resting sea. The imposed boundary conditions are the following: at the
first layer, the input flux is imposed over the Strait of Gibraltar. A total flux of 1.24 Sv
is taken, which is the estimate corresponding to the annual mean of the Atlantic input
flux (see [3]). As tidal effects are not important in the Mediterranean, over the open sea
a no-elevation condition is imposed. At the second layer, equal input and output fluxes
over the two artificial boundaries are imposed, their magnitude has been chosen to be
approximately the 80% of the input Atlantic water, as deduce from observational data.
The meshes have been generated from digitalized cartographic data provided by
the I.E.O. (Instituto Espanol de Oceanografia), using HYPACK code. The bathymetry
function H was computed from digital cartographic data by means of an automatic
interpolation process over the mesh vertices. From this discrete function and the corresponding first layer mesh, the second, and subsequent, layer meshes are automatically
constructed suppressing the spare triangles, i.e., the elements, k in the first layer, with
H(k) > -100m are suppressed.
The first results were computed with no wind and the input/output boundary conditions described above. Figures 5, 6 correspond to the stationary state results which is
reached at time iteration 1000 (50 h, real time). They show the velocity fields for each
of the two layers.
The first layer simulated velocity field (fig 5) is in good agreement with observations,
the two gyres that appear in the Alboran Sea are well represented. In the second layer
we know about the existence of the outflowing intermediate Mediterranean water as
reflected in the numerical results (fig 5), where no aditional structure to the outpouring
flow can be found. For the elevation field (1]) (not shown) the general structure is
qualitatively well represented in the simulations: greater sinking in the Strait area than
in the eastern part. Nevertheless, the results do not show the great sinking of the
interface under the western Alboran gyre as has been observed to occur.
Numerical experiences corresponding to a 10 m/ s eastern wind were also carried out.
Only the velocity fields for the first layer at 400 and 1000 time iterations (20h and 50h
real time) have been displayed (figs. 7 and 8), where important differences from the
previous case can be observed. The wind influence on changes in mean position, shape
and size of the gyres is revealed.
Finally, the numerical results obtained with a 10m/s western wind (fig. 9 and 10)
at time iterations 400 and 1000 are presented. The results for the first layer velocity
field are shown. In this case, the western gyre fills nearly all the domain and the eastern
gyre disappears as have been observed through different campaigns to occur.
This wind sensitivity, observed in the numerical results, corresponds to observations,
but in a more pronounced way. However, the numerical results are computed with
layer the constant value for the water density is taken to be equal to 1027 kg/m 3 • The
lower layer stands for the Mediterranean water pouring out from the eastern Mediterranean into the Atlantic. The constant density value taken in this layer was 1029 kg /m 3 .
The physical domain considered presents 4 different boundaries. Two 'natural'
boundaries, corresponding to the Spanish and Moroccan coast. Besides, two vertical
cuts as 'artificial' boundaries have to be considered to bound the domain: the western
one near Tarifa and the eastern by Punta de Banos.
As initial conditions, elevation and fluxes equal to zero have been imposed, i.e.,
start from a resting sea. The imposed boundary conditions are the following: at the
first layer, the input flux is imposed over the Strait of Gibraltar. A total flux of 1.24 Sv
is taken, which is the estimate corresponding to the annual mean of the Atlantic input
flux (see [3]). As tidal effects are not important in the Mediterranean, over the open sea
a no-elevation condition is imposed. At the second layer, equal input and output fluxes
over the two artificial boundaries are imposed, their magnitude has been chosen to be
approximately the 80% of the input Atlantic water, as deduce from observational data.
The meshes have been generated from digitalized cartographic data provided by
the I.E.O. (Instituto Espanol de Oceanografia), using HYPACK code. The bathymetry
function H was computed from digital cartographic data by means of an automatic
interpolation process over the mesh vertices. From this discrete function and the corresponding first layer mesh, the second, and subsequent, layer meshes are automatically
constructed suppressing the spare triangles, i.e., the elements, k in the first layer, with
H(k) > -100m are suppressed.
The first results were computed with no wind and the input/output boundary conditions described above. Figures 5, 6 correspond to the stationary state results which is
reached at time iteration 1000 (50 h, real time). They show the velocity fields for each
of the two layers.
The first layer simulated velocity field (fig 5) is in good agreement with observations,
the two gyres that appear in the Alboran Sea are well represented. In the second layer
we know about the existence of the outflowing intermediate Mediterranean water as
reflected in the numerical results (fig 5), where no aditional structure to the outpouring
flow can be found. For the elevation field (1]) (not shown) the general structure is
qualitatively well represented in the simulations: greater sinking in the Strait area than
in the eastern part. Nevertheless, the results do not show the great sinking of the
interface under the western Alboran gyre as has been observed to occur.
Numerical experiences corresponding to a 10 m/ s eastern wind were also carried out.
Only the velocity fields for the first layer at 400 and 1000 time iterations (20h and 50h
real time) have been displayed (figs. 7 and 8), where important differences from the
previous case can be observed. The wind influence on changes in mean position, shape
and size of the gyres is revealed.
Finally, the numerical results obtained with a 10m/s western wind (fig. 9 and 10)
at time iterations 400 and 1000 are presented. The results for the first layer velocity
field are shown. In this case, the western gyre fills nearly all the domain and the eastern
gyre disappears as have been observed through different campaigns to occur.
This wind sensitivity, observed in the numerical results, corresponds to observations,
but in a more pronounced way. However, the numerical results are computed with