THE NEAR-SURFACE LAYER OF THE OCEAN
The ADCP record from the 16 m bin shows a jump of the relative
velocity,
24
16
U
U
U
'
, of approximately 0.4 m s
-1 at the intersection of
the front (Figure 5-19). This is within the range of the preceding estimates
for the gravity current speed. (Note that the shipboard ADCP data start only
from 16 m.) The contour plot of the northward velocity component during
the subsequent meridional section of the R/V Kaiyo along 152
o
E (Figure
5-21) reveals signatures of a strong SSE near-surface current. The sharp
front visually observed in Figure 5-17 can be associated with the leading
edge of this near-surface current. According to the shipboard ADCP and
meteorological observations, an 8 m s
-1 SSE wind opposed the buoyant
spreading of the front (Figure 5-19).
There is a jump in the horizontal velocity component normal to the front
(Figure 5-19). The breaking of surface waves observed north of the front
(Figure 5-17) can be ascribed to the effect of surface wave–current
interactions.
Another observation of the sharp frontal interface is presented in Figure
5-22. This is an east-west section from the R/V Wecoma during TOGA
COARE. Visual observations of the ocean surface were not conducted for
this section, but evidence of convergence lines was seen in sections during
the preceding and following days. The data from the CTD sensor mounted
provided high-resolution data in the horizontal direction, and the data from a
towed undulating CTD (SEASOAR) provided information on the upper
ocean stratification during this case study. The 3 km horizontal grid of the
interpolated SEASOAR and ADCP data is, however, too coarse to resolve
small-scale horizontal features. In particular, the internal-wave train that
presumably can accompany the propagation of the gravity current cannot be
resolved with 3 km data since the theoretical wavelength of the wave train
(see Section 5.2.3) is only
2
0
10
~
6h
|
O
m.
A sharp front is clearly seen in the bow record of density at 45.6 km
(Figure 5-22a), associated with a rain-formed freshwater surface lens. Note
that only one boundary of this lens is sharp. The density and velocity contour
plots for the upper 100 m of the ocean from SEASOAR and ADCP
measurements (Figure 5-22b-d) reveal a density anomaly and signatures of
the near-surface current associated with this frontal structure. Between 25
and 50 km, this density anomaly has cyclonic vorticity, which appears to
have been caused by the inertial spin-down of an eastward equatorial jet
(Feng et al., 2001).
318
on the bow of the vessel at 2 m mean depth (Wijesekera et al., 1999a)
The ADCP record from the 16 m bin shows a jump of the relative
velocity,
24
16
U
U
U
'
, of approximately 0.4 m s
-1 at the intersection of
the front (Figure 5-19). This is within the range of the preceding estimates
for the gravity current speed. (Note that the shipboard ADCP data start only
from 16 m.) The contour plot of the northward velocity component during
the subsequent meridional section of the R/V Kaiyo along 152
o
E (Figure
5-21) reveals signatures of a strong SSE near-surface current. The sharp
front visually observed in Figure 5-17 can be associated with the leading
edge of this near-surface current. According to the shipboard ADCP and
meteorological observations, an 8 m s
-1 SSE wind opposed the buoyant
spreading of the front (Figure 5-19).
There is a jump in the horizontal velocity component normal to the front
(Figure 5-19). The breaking of surface waves observed north of the front
(Figure 5-17) can be ascribed to the effect of surface wave–current
interactions.
Another observation of the sharp frontal interface is presented in Figure
5-22. This is an east-west section from the R/V Wecoma during TOGA
COARE. Visual observations of the ocean surface were not conducted for
this section, but evidence of convergence lines was seen in sections during
the preceding and following days. The data from the CTD sensor mounted
provided high-resolution data in the horizontal direction, and the data from a
towed undulating CTD (SEASOAR) provided information on the upper
ocean stratification during this case study. The 3 km horizontal grid of the
interpolated SEASOAR and ADCP data is, however, too coarse to resolve
small-scale horizontal features. In particular, the internal-wave train that
presumably can accompany the propagation of the gravity current cannot be
resolved with 3 km data since the theoretical wavelength of the wave train
(see Section 5.2.3) is only
2
0
10
~
6h
|
O
m.
A sharp front is clearly seen in the bow record of density at 45.6 km
(Figure 5-22a), associated with a rain-formed freshwater surface lens. Note
that only one boundary of this lens is sharp. The density and velocity contour
plots for the upper 100 m of the ocean from SEASOAR and ADCP
measurements (Figure 5-22b-d) reveal a density anomaly and signatures of
the near-surface current associated with this frontal structure. Between 25
and 50 km, this density anomaly has cyclonic vorticity, which appears to
have been caused by the inertial spin-down of an eastward equatorial jet
(Feng et al., 2001).
318
on the bow of the vessel at 2 m mean depth (Wijesekera et al., 1999a)