INTERNAL METRICS
461
Another Class 2 diagnostic using the velocity fields is the EKE which can
be computed for instance along the 48°N zonal section in the various
systems and compared to EKE observations from Colin de Verdiere et al.
(1989). EKE distribution through the Gulf Stream at 55°W has also been
documented from current meter, drifter and float data by Richardson (1983;
1985). Abyssal eddy kinetic energy can also be referred to estimates given
by Schmitz (1984; 1996).
3.4. Class 3 metrics
Class 3 diagnostics are integrated quantities (integration done on the
original grid) such as:
x Volume transports (Sverdrup=10
6 m
3 /s) across chosen sections
(Figures 1 and 2). Depending on the section considered, one has to
provide the total volume transport or the volume transport per
defined potential temperature classes or density classes. For
example, the water flowing through the Florida Strait comes from
different Caribbean passages. The knowledge of the flow
distribution through these passages appears to be a significant test
for the North Atlantic model simulations (Böning et al. 1991;
Maltrud et al. 1998). Class 3 model volume transport across the
Florida Straits can be compared to real time Cable Voltage
measurements (Larsen, 1992). These measurements indicate an
annual mean mass transport of approximately 30 Sv, modulated by a
seasonal cycle in transport of roughly 6 to 10 Sv.
In the Mediterranean basin, the volume transport seasonal
variablility across several straits in the models can be compared to
observations gathered in Astraldi et al. (1999).
x The Overturning Streamfunction (OSF) (Sverdrup=10
6
m
3 /s) as a
function of latitude and depth (m) or potential temperature (°C) or
potential density (kg/m
3 ). The OSF characterizes the thermohaline
circulation established in response to external forcings (wind, heat
and freshwater fluxes) and to the water masses conservation taking
place in the buffer zones. The large scale overturning is not directly
observable, but an annual mean maximum OSF from 16 to 20 Sv
between 20°N and 40°N in the depth range 1000m to 1500m is
consistent with the estimates of the corresponding heat transport. At
24°N, repeated transoceanic sections contributed to get a remarkably
stable estimate of 17-18 Sv (Hall and Bryden, 1982; Roemmich and
Wunsch, 1985).
461
Another Class 2 diagnostic using the velocity fields is the EKE which can
be computed for instance along the 48°N zonal section in the various
systems and compared to EKE observations from Colin de Verdiere et al.
(1989). EKE distribution through the Gulf Stream at 55°W has also been
documented from current meter, drifter and float data by Richardson (1983;
1985). Abyssal eddy kinetic energy can also be referred to estimates given
by Schmitz (1984; 1996).
3.4. Class 3 metrics
Class 3 diagnostics are integrated quantities (integration done on the
original grid) such as:
x Volume transports (Sverdrup=10
6 m
3 /s) across chosen sections
(Figures 1 and 2). Depending on the section considered, one has to
provide the total volume transport or the volume transport per
defined potential temperature classes or density classes. For
example, the water flowing through the Florida Strait comes from
different Caribbean passages. The knowledge of the flow
distribution through these passages appears to be a significant test
for the North Atlantic model simulations (Böning et al. 1991;
Maltrud et al. 1998). Class 3 model volume transport across the
Florida Straits can be compared to real time Cable Voltage
measurements (Larsen, 1992). These measurements indicate an
annual mean mass transport of approximately 30 Sv, modulated by a
seasonal cycle in transport of roughly 6 to 10 Sv.
In the Mediterranean basin, the volume transport seasonal
variablility across several straits in the models can be compared to
observations gathered in Astraldi et al. (1999).
x The Overturning Streamfunction (OSF) (Sverdrup=10
6
m
3 /s) as a
function of latitude and depth (m) or potential temperature (°C) or
potential density (kg/m
3 ). The OSF characterizes the thermohaline
circulation established in response to external forcings (wind, heat
and freshwater fluxes) and to the water masses conservation taking
place in the buffer zones. The large scale overturning is not directly
observable, but an annual mean maximum OSF from 16 to 20 Sv
between 20°N and 40°N in the depth range 1000m to 1500m is
consistent with the estimates of the corresponding heat transport. At
24°N, repeated transoceanic sections contributed to get a remarkably
stable estimate of 17-18 Sv (Hall and Bryden, 1982; Roemmich and
Wunsch, 1985).