implementation of an internationally agreed plan,
internationally agreed standards and the international management and sharing of data. Significant technical developments achieved during
WOCE have now opened the door for an ongoing
global ocean observing system. Two of the most
significant technical developments are:
¥ accurate ocean surface topography measurements by satellite sensors, first of all by TOPEX/
POSEIDON, but also by ERS-1 and -2 altimeters (Fu, Chapter 3.3);
¥ development of profiling autonomous Lagrangian
floats determining upper ocean structure and
mean current on a prescribed pressure surface
about every 2 weeks and with typical survival times of about 4 years (Davis and Zenk,
Chapter 3.2).
Developing the new technologies and demonstrating the feasibility of a global observing system are
only the first steps to building a truly global
observing system. Applications like ocean weather
forecasting, global seasonal climate variability predictions, better guidance for fisheries, etc., require
the operational implementation of a global array
of such floats and the continuation of altimeter
measurements beyond the endorsed experimental
phase. Sustained observations of the ocean interior
and its surface have not only been recognized as
prerequisites for progress in prediction of climate
variability on seasonal time scales, but also for
the understanding of decadal to century time-scale
climate variability, a major challenge for climate
science.
Now that a near-real-time ocean observing
system has been shown to be feasible and costeffective, both CLIVAR (Climate Variability and
Predictability study of WCRP) and GODAE
(Global Ocean Data Assimilation Experiment)
are implementing within the Integrated Global
Observing Strategy (IGOS) a pilot project to
demonstrate the value of a global float array in
combination with satellite altimetry. Besides operational ocean observations for climate research
and predictions, we still lack certain types of
observations in the atmosphere, namely, the threedimensional distribution of liquid water and ice,
vertical profiles of minor constituents like ozone,
and wind profiles in the lower troposphere. Since
cloud–radiation interaction is a source of major
uncertainty in the response of the climate system
to an external forcing (by the sun or by human
activities), I wrote, in 1996, on behalf of the Joint
Scientific Committee for WCRP, to the major
space agencies, asking for the development of an
active sensor combination for the measurement of
cloud water and ice. At the same time, I also
pointed to the need for a better geoid determination in order to be able to exploit fully ongoing
altimeter measurements for oceanography and
climate research.
To implement operational observing systems, it
is necessary to start first with a research network
and to demonstrate the benefit of the network for
society as a whole. Only then will the resources for
an ongoing operational commitment be provided.
Scientists within WCRP are working to repeat
these steps for as yet unobserved parts of the climate system, such as the deep ocean, sea-ice thickness, and the isotopic composition of precipitation,
river water and snow. However, operational
implementation will only follow if it is demonstrated to be a prerequisite for further progress
and if cost-effective observational strategies are
available or can be developed.
1.1.3 Ocean–atmosphere interaction and
climate
The ocean and atmosphere transport on average
roughly the same amount of heat from low to high
latitudes. However, this is achieved in remarkably different manners. The atmosphere does it
mainly by transient eddies in the middle and high
latitudes; the ocean does it mainly by boundary
currents, large gyres (wind-driven to a large
extent) and the vertical overturning of the ocean.
Although the sun delivers more energy to the
southern hemisphere since we are at present nearest to the sun in January, the northern hemisphere
nevertheless contains the thermal equator at all
seasons over the Atlantic and the Pacific. In the
Atlantic, this is due to the shape of South America
and Africa and to the Atlantic transporting – as
WOCE studies have made clearer – about 10
15 W
of heat across the equator into the northern hemisphere (Bryden and Imawaki, Chapter 6.1). While
the ocean is influenced by the atmosphere through
fluxes of momentum, fresh water, incoming solar
irradiance (Fig. 1.1.1, see Plate 1.1.1, p. 44) and
atmospheric thermal radiation, sea surface temperature is the main parameter influencing the heat
1.1 Climate and Oceans
5
Grassl
internationally agreed standards and the international management and sharing of data. Significant technical developments achieved during
WOCE have now opened the door for an ongoing
global ocean observing system. Two of the most
significant technical developments are:
¥ accurate ocean surface topography measurements by satellite sensors, first of all by TOPEX/
POSEIDON, but also by ERS-1 and -2 altimeters (Fu, Chapter 3.3);
¥ development of profiling autonomous Lagrangian
floats determining upper ocean structure and
mean current on a prescribed pressure surface
about every 2 weeks and with typical survival times of about 4 years (Davis and Zenk,
Chapter 3.2).
Developing the new technologies and demonstrating the feasibility of a global observing system are
only the first steps to building a truly global
observing system. Applications like ocean weather
forecasting, global seasonal climate variability predictions, better guidance for fisheries, etc., require
the operational implementation of a global array
of such floats and the continuation of altimeter
measurements beyond the endorsed experimental
phase. Sustained observations of the ocean interior
and its surface have not only been recognized as
prerequisites for progress in prediction of climate
variability on seasonal time scales, but also for
the understanding of decadal to century time-scale
climate variability, a major challenge for climate
science.
Now that a near-real-time ocean observing
system has been shown to be feasible and costeffective, both CLIVAR (Climate Variability and
Predictability study of WCRP) and GODAE
(Global Ocean Data Assimilation Experiment)
are implementing within the Integrated Global
Observing Strategy (IGOS) a pilot project to
demonstrate the value of a global float array in
combination with satellite altimetry. Besides operational ocean observations for climate research
and predictions, we still lack certain types of
observations in the atmosphere, namely, the threedimensional distribution of liquid water and ice,
vertical profiles of minor constituents like ozone,
and wind profiles in the lower troposphere. Since
cloud–radiation interaction is a source of major
uncertainty in the response of the climate system
to an external forcing (by the sun or by human
activities), I wrote, in 1996, on behalf of the Joint
Scientific Committee for WCRP, to the major
space agencies, asking for the development of an
active sensor combination for the measurement of
cloud water and ice. At the same time, I also
pointed to the need for a better geoid determination in order to be able to exploit fully ongoing
altimeter measurements for oceanography and
climate research.
To implement operational observing systems, it
is necessary to start first with a research network
and to demonstrate the benefit of the network for
society as a whole. Only then will the resources for
an ongoing operational commitment be provided.
Scientists within WCRP are working to repeat
these steps for as yet unobserved parts of the climate system, such as the deep ocean, sea-ice thickness, and the isotopic composition of precipitation,
river water and snow. However, operational
implementation will only follow if it is demonstrated to be a prerequisite for further progress
and if cost-effective observational strategies are
available or can be developed.
1.1.3 Ocean–atmosphere interaction and
climate
The ocean and atmosphere transport on average
roughly the same amount of heat from low to high
latitudes. However, this is achieved in remarkably different manners. The atmosphere does it
mainly by transient eddies in the middle and high
latitudes; the ocean does it mainly by boundary
currents, large gyres (wind-driven to a large
extent) and the vertical overturning of the ocean.
Although the sun delivers more energy to the
southern hemisphere since we are at present nearest to the sun in January, the northern hemisphere
nevertheless contains the thermal equator at all
seasons over the Atlantic and the Pacific. In the
Atlantic, this is due to the shape of South America
and Africa and to the Atlantic transporting – as
WOCE studies have made clearer – about 10
15 W
of heat across the equator into the northern hemisphere (Bryden and Imawaki, Chapter 6.1). While
the ocean is influenced by the atmosphere through
fluxes of momentum, fresh water, incoming solar
irradiance (Fig. 1.1.1, see Plate 1.1.1, p. 44) and
atmospheric thermal radiation, sea surface temperature is the main parameter influencing the heat
1.1 Climate and Oceans
5
Grassl