Chapter 4: FINE STRUCTURE AND MICROSTRUCTURE
The above estimates imply that the entrainment at the lower boundary of
the diurnal mixed layer is negligible. The entrainment conditions are
X
X
parameterizations and numerical models. In particular, this leads to a
2
u
rather than
3
u
dependence for the diurnal temperature amplitude (as well as
a
0
u rather than
1
u
dependence for the diurnal jet amplitude).
From the above analysis it is also obvious that large diurnal warming
events are exclusively associated with the buoyant regime in the near-surface
layer of the ocean. Inequality X (4.37)X is thus a necessary condition for the
development of large diurnal warming events. X Figure 4-28X shows results of
calculations of the equilibrium mixed layer depths for low and high latitudes
at a low wind speed. Interestingly, during intense diurnal warming,
inequality X (4.37)X can be satisfied for both low and high latitudes. This
suggests that large diurnal events can be observed not only in mid- and low
latitudes but also at relatively high latitudes (during the boreal or austral
summer, respectively), which is consistent with the satellite-derived diurnal
amplitudes shown in X Figure 4-25X .
Rotation effects nevertheless can indirectly influence the diurnal cycle
even under low wind speed conditions by affecting dynamics of the diurnal
jet (see Section X 4.2X ). The Coriolis force deflects the diurnal jet to the right
(left) of the wind in the northern (southern) hemisphere. Under the same
environmental conditions, the magnitude of the diurnal jet is maximal in
equatorial regions, where the direction of diurnal jet coincides with the wind
stress direction.
It should be noted that similar relationships hold for the rain-induced
mixed layer. The buoyancy flux due to rain can play a similar, stabilizing
role as the buoyancy flux due to solar heating. This can explain substantial
drops of salinity observed in the rain patches in low wind speed zones.
In the polar seas where SST can drop to 0P
o
PC
(or even below it), the
thermal expansion coefficient is small. The buoyancy contribution due to the
absorption of solar radiation diminishes, and the buoyancy effects can no
longer dominate over rotation effects. An exception is the marginal ice zone
with melting ice where the freshwater supply leads to restratification of the
upper ocean mixed layer. Fine structure of the near-surface layer of the polar
seas is considered in Section X 4.6X .
4.5 Modeling Large Diurnal Warming Events
4.5.1 Radiative-convective mixed layer
Raschke (1975) calculated vertical profiles of temperature in the upper
ocean during equinoxes under the assumption of no turbulent mixing and no
265
incorporated into the analysis in Section 4.2.2, in the framework of
The above estimates imply that the entrainment at the lower boundary of
the diurnal mixed layer is negligible. The entrainment conditions are
X
X
parameterizations and numerical models. In particular, this leads to a
2
u
rather than
3
u
dependence for the diurnal temperature amplitude (as well as
a
0
u rather than
1
u
dependence for the diurnal jet amplitude).
From the above analysis it is also obvious that large diurnal warming
events are exclusively associated with the buoyant regime in the near-surface
layer of the ocean. Inequality X (4.37)X is thus a necessary condition for the
development of large diurnal warming events. X Figure 4-28X shows results of
calculations of the equilibrium mixed layer depths for low and high latitudes
at a low wind speed. Interestingly, during intense diurnal warming,
inequality X (4.37)X can be satisfied for both low and high latitudes. This
suggests that large diurnal events can be observed not only in mid- and low
latitudes but also at relatively high latitudes (during the boreal or austral
summer, respectively), which is consistent with the satellite-derived diurnal
amplitudes shown in X Figure 4-25X .
Rotation effects nevertheless can indirectly influence the diurnal cycle
even under low wind speed conditions by affecting dynamics of the diurnal
jet (see Section X 4.2X ). The Coriolis force deflects the diurnal jet to the right
(left) of the wind in the northern (southern) hemisphere. Under the same
environmental conditions, the magnitude of the diurnal jet is maximal in
equatorial regions, where the direction of diurnal jet coincides with the wind
stress direction.
It should be noted that similar relationships hold for the rain-induced
mixed layer. The buoyancy flux due to rain can play a similar, stabilizing
role as the buoyancy flux due to solar heating. This can explain substantial
drops of salinity observed in the rain patches in low wind speed zones.
In the polar seas where SST can drop to 0P
o
PC
(or even below it), the
thermal expansion coefficient is small. The buoyancy contribution due to the
absorption of solar radiation diminishes, and the buoyancy effects can no
longer dominate over rotation effects. An exception is the marginal ice zone
with melting ice where the freshwater supply leads to restratification of the
upper ocean mixed layer. Fine structure of the near-surface layer of the polar
seas is considered in Section X 4.6X .
4.5 Modeling Large Diurnal Warming Events
4.5.1 Radiative-convective mixed layer
Raschke (1975) calculated vertical profiles of temperature in the upper
ocean during equinoxes under the assumption of no turbulent mixing and no
265
incorporated into the analysis in Section 4.2.2, in the framework of