THE NEAR-SURFACE LAYER OF THE OCEAN
Ferrari and Rudnick (2000) found the horizontal density ratio R in the
subtropical Pacific mixed layer is close to 1 for horizontal scales > 100 m.
Statistics for one month of low-latitude observations acquired during TOGA
COARE (see Figure 5-30) indicate that there are numerous cases of noncompensated density fronts (i.e.,
1
R z ). These statistics, however, relate to
the sharp interfaces only (i.e., those less than ~100 m width) and are
therefore not contradictory to the results of Ferrari and Rudnick (2000).
5.4.7 Observations of sharp frontal interfaces in mid- and highlatitudes
The substantial observational statistics of the sharp frontal interfaces
reported here are from tropical latitudes only. Sharp fronts have been
observed in mid-latitudes as well. To our knowledge there are only a few
case shipboard observations (Zenk and Katz, 1975; Soloviev and Zatsepin,
1992); no representative statistics have been obtained in mid-latitudes.
In high latitudes, sharp frontal interfaces are expected to be present in
the marginal ice zone during periods of ice meting. To our best knowledge
there have been no horizontal microstructure measurements in the nearsurface layer of the ocean in polar seas.
At this point, we do not know exactly how the sharp frontal interfaces
are affected by Earth’s rotation. From general considerations, the rotation
should not directly affect the internal structure of sharp fronts because their
width is so small. Fronts, nevertheless, are associated with larger scale
anomalies; these anomalies may depend on Earth’s rotation even near the
equator. In particular, the sharp front shown in Figure 5-22a was found at
the edge of a density anomaly with cyclonic vorticity, that appears to be
caused by the inertial spin-down of an eastward equatorial jet (Feng et al.,
2001). In mid-latitudes, mesoscale eddies wind the sharp fronts into spirals
(Munk and Armi, 2001).
5.5 Internal Waves in the Near-Surface Pycnocline
As described in Section 4.1.3, the shallow diurnal thermocline and rainformed halocline are subject to perturbations in the form of internal waves.
In some instances, these internal waves become large, transform into billows
or rolls, and can produce signatures in SST and on SAR images.
5.5.1 Large amplitude internal waves
The terminology “large amplitude” internal wave in this context means
that the amplitude of the internal wave is of the order of the distance to the
346
Ferrari and Rudnick (2000) found the horizontal density ratio R in the
subtropical Pacific mixed layer is close to 1 for horizontal scales > 100 m.
Statistics for one month of low-latitude observations acquired during TOGA
COARE (see Figure 5-30) indicate that there are numerous cases of noncompensated density fronts (i.e.,
1
R z ). These statistics, however, relate to
the sharp interfaces only (i.e., those less than ~100 m width) and are
therefore not contradictory to the results of Ferrari and Rudnick (2000).
5.4.7 Observations of sharp frontal interfaces in mid- and highlatitudes
The substantial observational statistics of the sharp frontal interfaces
reported here are from tropical latitudes only. Sharp fronts have been
observed in mid-latitudes as well. To our knowledge there are only a few
case shipboard observations (Zenk and Katz, 1975; Soloviev and Zatsepin,
1992); no representative statistics have been obtained in mid-latitudes.
In high latitudes, sharp frontal interfaces are expected to be present in
the marginal ice zone during periods of ice meting. To our best knowledge
there have been no horizontal microstructure measurements in the nearsurface layer of the ocean in polar seas.
At this point, we do not know exactly how the sharp frontal interfaces
are affected by Earth’s rotation. From general considerations, the rotation
should not directly affect the internal structure of sharp fronts because their
width is so small. Fronts, nevertheless, are associated with larger scale
anomalies; these anomalies may depend on Earth’s rotation even near the
equator. In particular, the sharp front shown in Figure 5-22a was found at
the edge of a density anomaly with cyclonic vorticity, that appears to be
caused by the inertial spin-down of an eastward equatorial jet (Feng et al.,
2001). In mid-latitudes, mesoscale eddies wind the sharp fronts into spirals
(Munk and Armi, 2001).
5.5 Internal Waves in the Near-Surface Pycnocline
As described in Section 4.1.3, the shallow diurnal thermocline and rainformed halocline are subject to perturbations in the form of internal waves.
In some instances, these internal waves become large, transform into billows
or rolls, and can produce signatures in SST and on SAR images.
5.5.1 Large amplitude internal waves
The terminology “large amplitude” internal wave in this context means
that the amplitude of the internal wave is of the order of the distance to the
346