Chapter 4: FINE STRUCTURE AND MICROSTRUCTURE
The dashed line S in the
t
V depth contour plot (X Figure 4-8X d)
corresponds to the R.M.S. uncertainty of pressure-to-depth conversion (the
hydrostatic pressure bias has already been removed) at occasional
intersections of the water-air interface as detected by the conductivity cell. It
illustrates the uncertainty of pressure-to-depth conversion due to the
dynamic pressure component and the ~0.6 m horizontal spacing between the
C, T and P sensors. The R.M.S. uncertainty in the pressure-to-depth
conversion is estimated as being between 0.02 dbar and 0.1 dbar (Soloviev
and Lukas, 1996).
The contour plot of salinity in density coordinates (X Figure 4-8X e) shows
practically no anomalies. This supports the wavelike nature of the
disturbances observed on the t
V depth contour plot on the horizontal scales
resolved by this contour plot (l >100 m).
4.1.6 Combined effect of diurnal and freshwater cycles on the upper
ocean structure
The schematics of the diurnal thermocline in X Figure 4-1X do not include
cases with precipitation effects. Rainfalls produce near-surface salinity
stratification, which helps to trap the net solar heating during daytime and
cooling during nighttime in the near surface layer of the ocean, thus
enhancing the diurnal SST amplitude.
The freshwater cycle may thus modify diurnal heating of the near-surface
layer of the ocean. Buoyancy fluxes due to precipitation increase the static
stability of the upper ocean, suppressing turbulent exchange with deeper
waters. The rainfall influences the diurnal cycle by trapping heat near the
surface (Anderson et al., 1996). An example is given in X Figure 4-9. The
salinity profile shows a salinity depression within the upper 5 m due to a
previous rain. Turbulent mixing is mainly localized within this stably
stratified near-surface layer (note larger velocity strain fluctuations
'/
dw dz
in the upper 5 m). Subsequent diurnal warming develops within this
freshwater lens.
X Figure 4-10 gives additional experimental evidence of a strong
modification of the near-surface layer due to rain. It helps to understand how
the combined effect of daytime solar heating and previous freshwater influx
due to rain results in the strong density stratification of the upper ocean. In
the case shown in X Figure 4-10X , the diurnal mixed layer and diurnal
thermocline evolve on the background of the temperature structure within
the rain-formed mixed layer. According to X Figure 4-10X the temperature of
the rain-formed mixed layer is lower than that of the underlying water mass.
This is typical for a rain-formed mixed layer after previous nighttime surface
cooling (Fedorov and Ginzburg, 1988; Lukas, 1990b). The profiles shown in
231
The dashed line S in the
t
V depth contour plot (X Figure 4-8X d)
corresponds to the R.M.S. uncertainty of pressure-to-depth conversion (the
hydrostatic pressure bias has already been removed) at occasional
intersections of the water-air interface as detected by the conductivity cell. It
illustrates the uncertainty of pressure-to-depth conversion due to the
dynamic pressure component and the ~0.6 m horizontal spacing between the
C, T and P sensors. The R.M.S. uncertainty in the pressure-to-depth
conversion is estimated as being between 0.02 dbar and 0.1 dbar (Soloviev
and Lukas, 1996).
The contour plot of salinity in density coordinates (X Figure 4-8X e) shows
practically no anomalies. This supports the wavelike nature of the
disturbances observed on the t
V depth contour plot on the horizontal scales
resolved by this contour plot (l >100 m).
4.1.6 Combined effect of diurnal and freshwater cycles on the upper
ocean structure
The schematics of the diurnal thermocline in X Figure 4-1X do not include
cases with precipitation effects. Rainfalls produce near-surface salinity
stratification, which helps to trap the net solar heating during daytime and
cooling during nighttime in the near surface layer of the ocean, thus
enhancing the diurnal SST amplitude.
The freshwater cycle may thus modify diurnal heating of the near-surface
layer of the ocean. Buoyancy fluxes due to precipitation increase the static
stability of the upper ocean, suppressing turbulent exchange with deeper
waters. The rainfall influences the diurnal cycle by trapping heat near the
surface (Anderson et al., 1996). An example is given in X Figure 4-9. The
salinity profile shows a salinity depression within the upper 5 m due to a
previous rain. Turbulent mixing is mainly localized within this stably
stratified near-surface layer (note larger velocity strain fluctuations
'/
dw dz
in the upper 5 m). Subsequent diurnal warming develops within this
freshwater lens.
X Figure 4-10 gives additional experimental evidence of a strong
modification of the near-surface layer due to rain. It helps to understand how
the combined effect of daytime solar heating and previous freshwater influx
due to rain results in the strong density stratification of the upper ocean. In
the case shown in X Figure 4-10X , the diurnal mixed layer and diurnal
thermocline evolve on the background of the temperature structure within
the rain-formed mixed layer. According to X Figure 4-10X the temperature of
the rain-formed mixed layer is lower than that of the underlying water mass.
This is typical for a rain-formed mixed layer after previous nighttime surface
cooling (Fedorov and Ginzburg, 1988; Lukas, 1990b). The profiles shown in
231