Chapter 4: FINE STRUCTURE AND MICROSTRUCTURE
is observed in the upper 9 m of the ocean. Judging from the salinity profile
the amount of precipitation was approximately 60 mm.
There is a 3.3-m deep quasi-homogeneous layer in the salinity profile. It
presumably results from the nighttime convective mixing that worked
against stable salinity stratification (X Figure 4-11). The temperature inversion
observed between 3.3 and 4.2 m is consistent with this interpretation.
In the upper right corner of X Figure 4-11, the near-surface temperature and
salinity profiles are shown with higher resolution. There is a 0.4 m thick
diurnal mixed layer and the diurnal thermocline is found in the depth range
from 0.4 m to 0.8 m. The diurnal mixed layer and diurnal thermocline are
found close to the ocean surface due to low wind speed conditions.
The layer between 3.3-m and 4.2-m depth, with unstable temperature
stratification, is expanded in the upper right corner of X Figure 4-11X . This
temperarture inversion is overcompensated by the stable salinity
stratification; thus the density profile is stable. The combination of unstable
temperature stratification and stable salinity stratification provides favorable
conditions for the development of layering convection due to double
diffusion of heat and salt. It is remarkable that a step-like structure, typical
for layering convection, is evident within the depth range from 3.3 to 4.2 m.
Freshwater input often results in forming a barrier layer in the upper
ocean mixed layer (see Sections 1.7.4 and 7.6.3). The barrier layer has been
recognized as a crucial element of tropical warm pool dynamics (Lukas and
Lindstrom, 1991). The barrier layer isolates the warm water of the upper
ocean layer by reducing the entrainment cooling from below the mixed layer
and by providing slippery conditions within the mixed layer. The existence
of the barrier layer plays a key role in the onset of El Niño, through a
complex process that involves ocean vertical mixing, sea surface
temperature, wind stress, freshwater flux, and large-scale ocean-atmosphere
dynamics.
4.2 Surface-Intensified Jets
4.2.1 Slippery Near-Surface Layer of the Ocean Arising Due to
Diurnal Warming
Woods (1968) hypothesized that the water above a strong thermocline can
slide over the underlying water with a minimum of friction. Houghton
(1969) called this phenomenon the slippery seas. He observed the slippery
seas in the coastal region of Acapulco; the stratification was associated with
lateral advection of warm water.
Montgomery and Stroup (1962) reported near-surface currents in the
equatorial ocean intensify during daytime but obtained only fragmentary
235
is observed in the upper 9 m of the ocean. Judging from the salinity profile
the amount of precipitation was approximately 60 mm.
There is a 3.3-m deep quasi-homogeneous layer in the salinity profile. It
presumably results from the nighttime convective mixing that worked
against stable salinity stratification (X Figure 4-11). The temperature inversion
observed between 3.3 and 4.2 m is consistent with this interpretation.
In the upper right corner of X Figure 4-11, the near-surface temperature and
salinity profiles are shown with higher resolution. There is a 0.4 m thick
diurnal mixed layer and the diurnal thermocline is found in the depth range
from 0.4 m to 0.8 m. The diurnal mixed layer and diurnal thermocline are
found close to the ocean surface due to low wind speed conditions.
The layer between 3.3-m and 4.2-m depth, with unstable temperature
stratification, is expanded in the upper right corner of X Figure 4-11X . This
temperarture inversion is overcompensated by the stable salinity
stratification; thus the density profile is stable. The combination of unstable
temperature stratification and stable salinity stratification provides favorable
conditions for the development of layering convection due to double
diffusion of heat and salt. It is remarkable that a step-like structure, typical
for layering convection, is evident within the depth range from 3.3 to 4.2 m.
Freshwater input often results in forming a barrier layer in the upper
ocean mixed layer (see Sections 1.7.4 and 7.6.3). The barrier layer has been
recognized as a crucial element of tropical warm pool dynamics (Lukas and
Lindstrom, 1991). The barrier layer isolates the warm water of the upper
ocean layer by reducing the entrainment cooling from below the mixed layer
and by providing slippery conditions within the mixed layer. The existence
of the barrier layer plays a key role in the onset of El Niño, through a
complex process that involves ocean vertical mixing, sea surface
temperature, wind stress, freshwater flux, and large-scale ocean-atmosphere
dynamics.
4.2 Surface-Intensified Jets
4.2.1 Slippery Near-Surface Layer of the Ocean Arising Due to
Diurnal Warming
Woods (1968) hypothesized that the water above a strong thermocline can
slide over the underlying water with a minimum of friction. Houghton
(1969) called this phenomenon the slippery seas. He observed the slippery
seas in the coastal region of Acapulco; the stratification was associated with
lateral advection of warm water.
Montgomery and Stroup (1962) reported near-surface currents in the
equatorial ocean intensify during daytime but obtained only fragmentary
235