140
V. Commodari, S. Pierini
the wind-driven circulation inside the Ross Sea (here the velocity vectors, with a
scale different from that of Fig. 3a, are reported in every grid point). A cyclonic circulation can be observed ail along both the Ross Ice shelf and the western Coast of
the Ross Sea. The transport appears intensified along the ice shelf; sub-basin scale
features are also présent, such as a nearly closed cyclonic gyre in the eastern part of
the basin. Along Victoria Land the flow intensifies and, more to the north, converges
with the EWD outside of the Ross Sea.
We now pass to consider the effect of the boundary forcing of Fig. 2b which, as
stated in Section 2, is supposed to be almost équivalent to the wind forcing of Fig.
2a outside the Ross Sea (now the Ross Sea dynamics is therefore purely driven by
the external circulation through topographie coupling). Figure 4a,b show the
asymptotic circulation thus induced. It is interesting to note that, indeed, the Ross
Sea gyre is very similar to that of Fig. 3a, apart from the area adjacent to the eastern boundary where different boundary conditions hâve been imposed in the two
cases. It is immediately apparent that the internai circulation of the Ross Sea is
much weaker than that of the wind-driven case, as shown in more detail in Fig. 4b
(note that the scaling is ten times smaller than in Fig. 3b). The steep continental
shelf acts as a dynamic barrier, strongly limiting the intrusion of the EWD into the
Ross Sea so as to conserve potential vorticity. The weak residual circulation
induced by the external EWD is seen to be concentrated in the north-eastern part
of the basin in the form of a cyclonic gyre, while in the north-western part the circulation is fairly similar to that of Fig. 3b.
In conclusion, two main results can be drawn from our numerical experiments.
Firstly, the barotropic transport inside the Ross Sea has a cyclonic structure intensified along the Southern boundaries and with sub-basin cyclonic features. Secondly,
the internai circulation is basically driven by the local winds and only very weakly
by the external circulation.
3.2 Comparison with Observations
Let us now analyze available experimental data in connection with our numerical
results. The circulation in the Ross Sea has been the subject of several experimental investigations and the prevailing idea is that a mainly cyclonic circulation
is présent (e.g. [9]) with strong transports along the Ross Ice shelf, in agreement
with our results. Lagrangian data obtained by surface drifters confirm the
cyclonic character of the upper océan circulation as mainly driven by the wind
[10]. Pillsbury and Jacobs [11] used current meter measurements to show that
between 170 and 180°W, in the vicinity of the ice shelf front, the flow présents a
U-shaped cyclonic structure, again in substantial agreement with Figs. 3b and 4b.
More recently, in the framework of the Italian PNRA, six current meter moorings
were deployed in the Ross Sea [12, 13]. The data (courtesy of P. Picco) averaged
over the summer 1994-1995 are presented in Fig. 5: the black arrows represent the
velocities measured by intermediate depth current meters (at 150- to 280-m
depth) while the gray ones give bottom currents (see [13] for details).
The most notable feature is the strong barotropic character of the circulation,
which suggests that the wind is probably the main forcing of the climatological cir-
V. Commodari, S. Pierini
the wind-driven circulation inside the Ross Sea (here the velocity vectors, with a
scale different from that of Fig. 3a, are reported in every grid point). A cyclonic circulation can be observed ail along both the Ross Ice shelf and the western Coast of
the Ross Sea. The transport appears intensified along the ice shelf; sub-basin scale
features are also présent, such as a nearly closed cyclonic gyre in the eastern part of
the basin. Along Victoria Land the flow intensifies and, more to the north, converges
with the EWD outside of the Ross Sea.
We now pass to consider the effect of the boundary forcing of Fig. 2b which, as
stated in Section 2, is supposed to be almost équivalent to the wind forcing of Fig.
2a outside the Ross Sea (now the Ross Sea dynamics is therefore purely driven by
the external circulation through topographie coupling). Figure 4a,b show the
asymptotic circulation thus induced. It is interesting to note that, indeed, the Ross
Sea gyre is very similar to that of Fig. 3a, apart from the area adjacent to the eastern boundary where different boundary conditions hâve been imposed in the two
cases. It is immediately apparent that the internai circulation of the Ross Sea is
much weaker than that of the wind-driven case, as shown in more detail in Fig. 4b
(note that the scaling is ten times smaller than in Fig. 3b). The steep continental
shelf acts as a dynamic barrier, strongly limiting the intrusion of the EWD into the
Ross Sea so as to conserve potential vorticity. The weak residual circulation
induced by the external EWD is seen to be concentrated in the north-eastern part
of the basin in the form of a cyclonic gyre, while in the north-western part the circulation is fairly similar to that of Fig. 3b.
In conclusion, two main results can be drawn from our numerical experiments.
Firstly, the barotropic transport inside the Ross Sea has a cyclonic structure intensified along the Southern boundaries and with sub-basin cyclonic features. Secondly,
the internai circulation is basically driven by the local winds and only very weakly
by the external circulation.
3.2 Comparison with Observations
Let us now analyze available experimental data in connection with our numerical
results. The circulation in the Ross Sea has been the subject of several experimental investigations and the prevailing idea is that a mainly cyclonic circulation
is présent (e.g. [9]) with strong transports along the Ross Ice shelf, in agreement
with our results. Lagrangian data obtained by surface drifters confirm the
cyclonic character of the upper océan circulation as mainly driven by the wind
[10]. Pillsbury and Jacobs [11] used current meter measurements to show that
between 170 and 180°W, in the vicinity of the ice shelf front, the flow présents a
U-shaped cyclonic structure, again in substantial agreement with Figs. 3b and 4b.
More recently, in the framework of the Italian PNRA, six current meter moorings
were deployed in the Ross Sea [12, 13]. The data (courtesy of P. Picco) averaged
over the summer 1994-1995 are presented in Fig. 5: the black arrows represent the
velocities measured by intermediate depth current meters (at 150- to 280-m
depth) while the gray ones give bottom currents (see [13] for details).
The most notable feature is the strong barotropic character of the circulation,
which suggests that the wind is probably the main forcing of the climatological cir-