difference between the geostrophic velocity and
the ADCP velocity. In each case the measured
Ekman transport was in reasonable agreement
with the theoretical transport calculated from the
wind stress, and extended below the mixed layer
to the top of the pycnocline. As Chereskin et al.
(1997) note, ‘the Ekman contribution to the heat
and salt fluxes must be measured; it can not be
determined merely by inferring the volume transport from the wind and using the surface temperature and salinity.’
The ageostrophic part of LADCP profiles is also
turning out to be valuable. Using a parameterization based on the fine-scale internal wave shear
variance, Polzin and Firing (1997b) inferred a
factor of 10 elevation of turbulent kinetic energy
dissipation and diapycnal mixing rates in a region
of the Southern Ocean with strong near-bottom
currents relative to a nearby region with weaker
deep flow. A comparison between 18 simultaneous
eXpendable Current Profiler (XCP) and LADCP
profiles in the North Atlantic has shown that, after
spectral correction for their inherent high
wavenumber rolloff, LADCP profiles can yield
such parameterized estimates within a factor of
two of those based on the higher-resolution XCP
profiles (Polzin et al., 2000a).
3.1.4 Shipboard meteorology
In this section we will discuss underway meteorology measurements made during WHP cruises. The
Voluntary Observing Ship (VOS) programme is
beyond the scope of this chapter.
WOCE planners recognized that meteorological
data from research ships would have a number of
uses; these included: initialization of atmospheric
models (especially in data-sparse regions); provision of accurate estimates of basic meteorological
variables for comparison with ships of opportunity; comparison with model output; comparison
with satellite-derived quantities (Liu and Katsaros,
Chapter 3.4); validation of climatologies and
model-derived fluxes. The relevant chapter in the
WOCE operations and methods manual (Taylor
and Weller, 1991) gives further explanation.
The greatest requirement was for meteorological measurements that would enable the definition
of surface fluxes of heat, water and momentum
(Large and Nurser, Chapter 5.1). The objective
(WCRP, 1988b) was to obtain estimates (averaged
over monthly or longer time scales) of the four
components of heat flux to an uncertainty of
10 W m
92
, of evaporation and precipitation to
1 mm per day and wind stress to within 10%.
The basic observables are sea surface temperature, air temperature, wind velocity, barometric
pressure, incoming short- and long-wave radiation
and humidity. Ships in the WOCE programme
were valuable platforms from which to make
accurate in-situ measurements. The chief advantages of WOCE ships were: they travelled through
data-sparse areas; they were manned by crews
and scientists with an interest in obtaining good
meteorological data; and their operating schedules
permitted sensors and electronics to be returned to
laboratories periodically for calibration.
3.1.4.1 Developments for and during WOCE
Prior to WOCE, acquisition of meteorological
data was somewhat uneven, even on research
ships. Many, indeed most, of the research ships
that would take part in the WHP did not have
automated systems, so the only meteorological
data returned were the manual observations made
by the bridge officers and transmitted by radio or
in delayed mode from bridge Meteorological Logbooks. In the late 1980s, several countries were
developing automated systems to ensure that their
research ships routinely acquired and reported
high-quality meteorological data. In the UK, for
example, the Institute of Oceanographic Sciences
Deacon Laboratory (IOSDL) was developing a
system called MultiMet, and in the USA the IMET
(Improved Meteorological Measurements) system
was being developed at WHOI. Other countries
were undertaking similar developments. A careful
test of the ability of different systems and platforms to make the measurements was carried
out as part of the TOGA-COARE experiment in
November 1992–March 1993 (Bradley and Weller,
1995a,b, 1997).
The minimum suite of measurements required
on an automated system included wind velocity,
air temperature, air humidity, sea surface temperature, downward radiative fluxes and air pressure.
Other parameters of value included wind stress
measured using the dissipation technique, ocean
skin temperature (by downward-looking radiometer) and other radiative flux measurements. The
latter quantities are required specifically for satellite
data validation.
SECTION 3 NEW WAYS OF OBSERVING THE OCEAN
120
the ADCP velocity. In each case the measured
Ekman transport was in reasonable agreement
with the theoretical transport calculated from the
wind stress, and extended below the mixed layer
to the top of the pycnocline. As Chereskin et al.
(1997) note, ‘the Ekman contribution to the heat
and salt fluxes must be measured; it can not be
determined merely by inferring the volume transport from the wind and using the surface temperature and salinity.’
The ageostrophic part of LADCP profiles is also
turning out to be valuable. Using a parameterization based on the fine-scale internal wave shear
variance, Polzin and Firing (1997b) inferred a
factor of 10 elevation of turbulent kinetic energy
dissipation and diapycnal mixing rates in a region
of the Southern Ocean with strong near-bottom
currents relative to a nearby region with weaker
deep flow. A comparison between 18 simultaneous
eXpendable Current Profiler (XCP) and LADCP
profiles in the North Atlantic has shown that, after
spectral correction for their inherent high
wavenumber rolloff, LADCP profiles can yield
such parameterized estimates within a factor of
two of those based on the higher-resolution XCP
profiles (Polzin et al., 2000a).
3.1.4 Shipboard meteorology
In this section we will discuss underway meteorology measurements made during WHP cruises. The
Voluntary Observing Ship (VOS) programme is
beyond the scope of this chapter.
WOCE planners recognized that meteorological
data from research ships would have a number of
uses; these included: initialization of atmospheric
models (especially in data-sparse regions); provision of accurate estimates of basic meteorological
variables for comparison with ships of opportunity; comparison with model output; comparison
with satellite-derived quantities (Liu and Katsaros,
Chapter 3.4); validation of climatologies and
model-derived fluxes. The relevant chapter in the
WOCE operations and methods manual (Taylor
and Weller, 1991) gives further explanation.
The greatest requirement was for meteorological measurements that would enable the definition
of surface fluxes of heat, water and momentum
(Large and Nurser, Chapter 5.1). The objective
(WCRP, 1988b) was to obtain estimates (averaged
over monthly or longer time scales) of the four
components of heat flux to an uncertainty of
10 W m
92
, of evaporation and precipitation to
1 mm per day and wind stress to within 10%.
The basic observables are sea surface temperature, air temperature, wind velocity, barometric
pressure, incoming short- and long-wave radiation
and humidity. Ships in the WOCE programme
were valuable platforms from which to make
accurate in-situ measurements. The chief advantages of WOCE ships were: they travelled through
data-sparse areas; they were manned by crews
and scientists with an interest in obtaining good
meteorological data; and their operating schedules
permitted sensors and electronics to be returned to
laboratories periodically for calibration.
3.1.4.1 Developments for and during WOCE
Prior to WOCE, acquisition of meteorological
data was somewhat uneven, even on research
ships. Many, indeed most, of the research ships
that would take part in the WHP did not have
automated systems, so the only meteorological
data returned were the manual observations made
by the bridge officers and transmitted by radio or
in delayed mode from bridge Meteorological Logbooks. In the late 1980s, several countries were
developing automated systems to ensure that their
research ships routinely acquired and reported
high-quality meteorological data. In the UK, for
example, the Institute of Oceanographic Sciences
Deacon Laboratory (IOSDL) was developing a
system called MultiMet, and in the USA the IMET
(Improved Meteorological Measurements) system
was being developed at WHOI. Other countries
were undertaking similar developments. A careful
test of the ability of different systems and platforms to make the measurements was carried
out as part of the TOGA-COARE experiment in
November 1992–March 1993 (Bradley and Weller,
1995a,b, 1997).
The minimum suite of measurements required
on an automated system included wind velocity,
air temperature, air humidity, sea surface temperature, downward radiative fluxes and air pressure.
Other parameters of value included wind stress
measured using the dissipation technique, ocean
skin temperature (by downward-looking radiometer) and other radiative flux measurements. The
latter quantities are required specifically for satellite
data validation.
SECTION 3 NEW WAYS OF OBSERVING THE OCEAN
120