THE NEAR-SURFACE LAYER OF THE OCEAN
c
T
' and
R
T
' , as a function of u . The main effect of solar radiation on the
cool skin is observed at low wind speeds. Figure 2-17 shows the diurnal
evolution of the temperature difference across the aqueous thermal
molecular sublayer and the direct (interfacial) air-sea gas transfer velocity
under idealized insolation conditions. For low wind speeds, suppression of
free convection due to the absorption of solar radiation has a strong effect on
the gas transfer at the ocean-air interface. This is because the surface renewal
time “jumps” at some threshold level of insolation. For the temperature
difference across the aqueous thermal molecular sublayer, this effect is not
as big as for the gas exchange because of the partial compensation of surface
cooling by solar heating.
2.4.5 Comparison with cool-skin field data
Sea surface temperature measurements in the western equatorial Pacific
made by Hartmut Grassl from the R/V Vickers during TOGA COARE from
30 January to 26 February 1993 near 156
o E, 2
o S have provided the data set
that is particularly useful in validating parameterizations for the temperature
difference across the cool skin. The sea surface temperature data were taken
with infrared radiometer. The bulk water temperature was measured with a
standard shipboard thermosalinograph pumping water from 3 m depth. At
night, the temperature differences in the upper 3 m were usually very small
(a few hundredths of a degree at most). During daytime the difference
between sea surface temperature and water temperature taken at 3 m depth
could be affected by the presence of shallow diurnal thermocline as
schematically shown in Figure 2-18. In addition, precipitation effects result
in a stable salinity stratification (the near-surface rain-formed halocline),
which is usually accompanied by temperature gradients. The likely presence
of fine thermohaline structure in the upper few meters of the ocean under
low wind speed conditions is one of the limitations of the cool-skin model
validation. (More details about the fine thermohaline structure of the nearsurface layer of the ocean can be found in Chapter 4.)
As a first approximation, the temperature difference across the diurnal
thermocline ('T d ) can be accounted for with a model of the diurnal mixed
layer and thermocline. We make use of two types of models for the diurnal
mixed layer and thermocline. The first model is that of Price et al. (1986),
hereafter referred to as PWP. The second model is that of Stull and Kraus
(1987), hereafter referred as SK. The SK model is the so-called transilient
(nonlocal) model, which represents the turbulent transport by a cascade of
eddies. The absorption of solar radiation is simulated with 9 spectral
components for water type IB (see Chapter 1, Table 1.2), which prevails in
the TOGA COARE domain.
116
c
T
' and
R
T
' , as a function of u . The main effect of solar radiation on the
cool skin is observed at low wind speeds. Figure 2-17 shows the diurnal
evolution of the temperature difference across the aqueous thermal
molecular sublayer and the direct (interfacial) air-sea gas transfer velocity
under idealized insolation conditions. For low wind speeds, suppression of
free convection due to the absorption of solar radiation has a strong effect on
the gas transfer at the ocean-air interface. This is because the surface renewal
time “jumps” at some threshold level of insolation. For the temperature
difference across the aqueous thermal molecular sublayer, this effect is not
as big as for the gas exchange because of the partial compensation of surface
cooling by solar heating.
2.4.5 Comparison with cool-skin field data
Sea surface temperature measurements in the western equatorial Pacific
made by Hartmut Grassl from the R/V Vickers during TOGA COARE from
30 January to 26 February 1993 near 156
o E, 2
o S have provided the data set
that is particularly useful in validating parameterizations for the temperature
difference across the cool skin. The sea surface temperature data were taken
with infrared radiometer. The bulk water temperature was measured with a
standard shipboard thermosalinograph pumping water from 3 m depth. At
night, the temperature differences in the upper 3 m were usually very small
(a few hundredths of a degree at most). During daytime the difference
between sea surface temperature and water temperature taken at 3 m depth
could be affected by the presence of shallow diurnal thermocline as
schematically shown in Figure 2-18. In addition, precipitation effects result
in a stable salinity stratification (the near-surface rain-formed halocline),
which is usually accompanied by temperature gradients. The likely presence
of fine thermohaline structure in the upper few meters of the ocean under
low wind speed conditions is one of the limitations of the cool-skin model
validation. (More details about the fine thermohaline structure of the nearsurface layer of the ocean can be found in Chapter 4.)
As a first approximation, the temperature difference across the diurnal
thermocline ('T d ) can be accounted for with a model of the diurnal mixed
layer and thermocline. We make use of two types of models for the diurnal
mixed layer and thermocline. The first model is that of Price et al. (1986),
hereafter referred to as PWP. The second model is that of Stull and Kraus
(1987), hereafter referred as SK. The SK model is the so-called transilient
(nonlocal) model, which represents the turbulent transport by a cascade of
eddies. The absorption of solar radiation is simulated with 9 spectral
components for water type IB (see Chapter 1, Table 1.2), which prevails in
the TOGA COARE domain.
116