multiple decades into a qualitatively consistent picture. This distribution of properties was interpreted
in terms of a corresponding large-scale, steady,
flow pattern. Theories (wind-driven, thermocline,
etc.) were then constructed that produced flows
resembling the required circulation patterns.
It was inferred from this picture of very slow,
creeping or ‘spreading’ flows, that the relevant
time scales for serious change in the ocean circulation had to be of order 1000 years and longer,
with the abyssal ocean acting only as a passive
reservoir responding to the divergences of the
upper ocean.
Until about 1975, available computing power
permitted only coarse-resolution, extremely viscous numerical models of the ocean. These models
qualitatively mimicked the available analytical
solutions and this close agreement tended to confirm the historical paradigm. Almost all textbooks –
oceanographic, meteorological and climate – as
well as many current research papers, still reflect
this view of the ocean circulation.
2.1.2.2 The WOCE paradigm
At the time WOCE was conceived, in the late
1970s, use of the new technologies, especially
those able to produce time series, such as moored
current meters and drifting floats, had begun to
make it clear that the flow field in the ocean was
very different from the steady, large-scale simple
flow fields that had emerged out of the tongue
depiction by Wüst and others, and from the analytical and numerical models. Rather it showed a
flow field dominated by what has come to be
called ‘mesoscale eddies’, but which is actually
much more complex than any single, mesoscale
1
phenomenon. The kinetic energy of the variability
was seen to be roughly two orders of magnitude
larger than that associated with the quasi-steady
basin scales. Indeed, a major supposition behind
much of the WOCE design was that the ocean
changed on all space scales from the sub-Rossby
radius to the entire global circulation, and on all
time scales out to the oceanic lifetime.
The presence of an intense variability does not
necessarily mean that it has any dynamical or kinematical consequences: it could be a purely passive
‘noise’ phenomenon, causing sampling (aliasing)
difficulties, but of no further consequence. But it is
also true that it could be of enormous kinematical
and dynamical consequence with, for example, the
tongues being nothing but the integrated fields
obtained from an extremely complex small-scale
structure, rather than implying large-scale steady
mean flows (for an example, see Hogg and Owens,
1999, or any of the high-resolution model calculations, such as that of Smith et al., 2000).
Within the group that designed WOCE there
were two other overlapping, but nonetheless conflicting, views as to how best to understand the
oceanic role in climate. These two views were that
ultimate insight would be best obtained by:
1 regional and process-focused studies; or
2 observing where and how the ocean is changing
globally.
Finally, of course, WOCE followed both these
strategies to some degree. Regional programmes
such as the Subduction Experiment, Brazil Basin
Experiment and the Purposeful Tracer Experiment
were central to what came to be called WOCE
‘Core Project 3 – Gyre Dynamics’.
In the end, however, the major activities in
WOCE were on the global scale. Achieving this
global strategy was not so easy. The decade of
the 1970s, beginning with, among others, the
Mid-Ocean Dynamics Experiment (MODE Group,
1978), can be called the ‘decade of the mesoscale’.
Classical hydrographic work, which was often used
to depict the global-scale ocean of the steady paradigm, had come to many to seem less ‘scientific’
than did the study of physical processes. The latter
became accessible through powerful new technologies, including moored current meters, neutrally
buoyant floats, Current-Temperature-Depth probes
(CTDs), bottom pressure gauges, etc. In particular,
the occupation of long hydrographic lines had
almost ceased. Figure 2.1.1 shows most of the transoceanic hydrographic lines that had been obtained
following the last International Geophysical Year
(IGY) lines of 1959, and prior to the first WOCE
discussions of 1979. The Eltanin Survey (see
Gordon and Molinelli, 1982) was an exceptional
large-scale survey of the Southern Ocean. Furthermore, numerical models (e.g. Holland, 1978) were
beginning to show intense variability that seemed
to confirm an entire physical realm of oceanography previously completely unexplored. There was a
clear sense that the scientific future lay with regional
studies: much of the community was focused on
processes and the ‘physics’ of internal waves, the
mesoscale, upwelling, tropical waves and the like.
2.1 Global Problems and Global Observations
49
1 ‘Synoptic’ scale to a meteorologist.
in terms of a corresponding large-scale, steady,
flow pattern. Theories (wind-driven, thermocline,
etc.) were then constructed that produced flows
resembling the required circulation patterns.
It was inferred from this picture of very slow,
creeping or ‘spreading’ flows, that the relevant
time scales for serious change in the ocean circulation had to be of order 1000 years and longer,
with the abyssal ocean acting only as a passive
reservoir responding to the divergences of the
upper ocean.
Until about 1975, available computing power
permitted only coarse-resolution, extremely viscous numerical models of the ocean. These models
qualitatively mimicked the available analytical
solutions and this close agreement tended to confirm the historical paradigm. Almost all textbooks –
oceanographic, meteorological and climate – as
well as many current research papers, still reflect
this view of the ocean circulation.
2.1.2.2 The WOCE paradigm
At the time WOCE was conceived, in the late
1970s, use of the new technologies, especially
those able to produce time series, such as moored
current meters and drifting floats, had begun to
make it clear that the flow field in the ocean was
very different from the steady, large-scale simple
flow fields that had emerged out of the tongue
depiction by Wüst and others, and from the analytical and numerical models. Rather it showed a
flow field dominated by what has come to be
called ‘mesoscale eddies’, but which is actually
much more complex than any single, mesoscale
1
phenomenon. The kinetic energy of the variability
was seen to be roughly two orders of magnitude
larger than that associated with the quasi-steady
basin scales. Indeed, a major supposition behind
much of the WOCE design was that the ocean
changed on all space scales from the sub-Rossby
radius to the entire global circulation, and on all
time scales out to the oceanic lifetime.
The presence of an intense variability does not
necessarily mean that it has any dynamical or kinematical consequences: it could be a purely passive
‘noise’ phenomenon, causing sampling (aliasing)
difficulties, but of no further consequence. But it is
also true that it could be of enormous kinematical
and dynamical consequence with, for example, the
tongues being nothing but the integrated fields
obtained from an extremely complex small-scale
structure, rather than implying large-scale steady
mean flows (for an example, see Hogg and Owens,
1999, or any of the high-resolution model calculations, such as that of Smith et al., 2000).
Within the group that designed WOCE there
were two other overlapping, but nonetheless conflicting, views as to how best to understand the
oceanic role in climate. These two views were that
ultimate insight would be best obtained by:
1 regional and process-focused studies; or
2 observing where and how the ocean is changing
globally.
Finally, of course, WOCE followed both these
strategies to some degree. Regional programmes
such as the Subduction Experiment, Brazil Basin
Experiment and the Purposeful Tracer Experiment
were central to what came to be called WOCE
‘Core Project 3 – Gyre Dynamics’.
In the end, however, the major activities in
WOCE were on the global scale. Achieving this
global strategy was not so easy. The decade of
the 1970s, beginning with, among others, the
Mid-Ocean Dynamics Experiment (MODE Group,
1978), can be called the ‘decade of the mesoscale’.
Classical hydrographic work, which was often used
to depict the global-scale ocean of the steady paradigm, had come to many to seem less ‘scientific’
than did the study of physical processes. The latter
became accessible through powerful new technologies, including moored current meters, neutrally
buoyant floats, Current-Temperature-Depth probes
(CTDs), bottom pressure gauges, etc. In particular,
the occupation of long hydrographic lines had
almost ceased. Figure 2.1.1 shows most of the transoceanic hydrographic lines that had been obtained
following the last International Geophysical Year
(IGY) lines of 1959, and prior to the first WOCE
discussions of 1979. The Eltanin Survey (see
Gordon and Molinelli, 1982) was an exceptional
large-scale survey of the Southern Ocean. Furthermore, numerical models (e.g. Holland, 1978) were
beginning to show intense variability that seemed
to confirm an entire physical realm of oceanography previously completely unexplored. There was a
clear sense that the scientific future lay with regional
studies: much of the community was focused on
processes and the ‘physics’ of internal waves, the
mesoscale, upwelling, tropical waves and the like.
2.1 Global Problems and Global Observations
49
1 ‘Synoptic’ scale to a meteorologist.