Figure 1. Winter (Jan–Mar in the north and Jul–Sep in the south)
surface outcrops of 
n =
25.0 and 26.5 kg m
and the pycnocline
base (dashed lines) from seasonal climatologies of temperature (Levitus and Boyer 1994)
and salinity (Levitus et al. 1994).
Figure 2a. Maps of properties on n
= 25.0 kg m, within the tropical pycnocline.
Color palettes are consistent for Figs. 2–5 except for acceleration potential,
which has a varying offset. The locations of the mean hydrographic profiles
(black dots) are given by the average positions of the CTD stations within bins
mentioned in section 2. All panels are objectively mapped from values at these
locations. (a) Depth, contour intervals of 25 m. (b) Acceleration potential
relative to 900 dbar, contour intervals of 0.25 J kg
.
Figure 2b. (c) Salinity, contour intervals of 0.1 (PSS-78) . (d) Planetary
potential vorticity, contour intervals of 200 × 10
m s.
Figure 3a. Maps of properties on n
= 26.5 kg m, below the tropical pycnocline.
Details follow Fig. 2. (a) Depth, contour intervals of 25 m. (b) Acceleration
potential relative to 900 dbar, contour intervals varying from 0.1 to 0.25 J
kg.
Figure 3b. (c) Salinity, contour intervals of 0.1 (PSS-78). (d) Planetary
potential vorticity, contour intervals of 25 × 10
m s.
Figure 4. Mean meridional-vertical sections of salinity contoured at 0.1
intervals (PSS-78) with contours of n
at varying intervals (thick lines 25.0, 26.0, and 26.5 kg m)
overlaid in white. Color palettes follow Fig. 2. Nominal vertical exaggeration
is 5000:1. (a) 165°E. (b) 125°W.
Figure 5. Mean meridional-vertical sections of planetary potential vorticity
contoured at logarithmic intervals (10
m s)
with contours of n at varying
intervals (thick lines 25.0, 26.0, and 26.5 kg m)
overlaid in white. Color palettes follow Fig. 2. Nominal vertical exaggeration
is 5000:1. (a) 165°E. (b) 125°W.
Figure 6. Net meridional mass transport (10
kg s) excluding the mixed layer binned
in n every 0.2 kg m
from the South American coast to (a) 165°E at 8°S and (b) 135°E
at 8°N. In the south, equatorward flow is concentrated near the eastern
STMW density and poleward flow below n
= 26.1 kg m. In the north, equatorward
flow is at lighter densities and poleward flow below n
= 25.9 kg m. (c) Downward accumulated
integrals of (a) and (b) show the net interior transport within the pycnocline
(to n roughly 26 kg m)
in the northern hemisphere (6 × 10 kg
s) is much less than that in the southern
hemisphere (14 × 10 kg s).
Figure 7. Quasi-meridional interior pycnocline (mixed-layer base to pycnocline
base) mass transport (10 kg s)
zonally accumulated from the Americas westward. Symbols are individual integration
points and lines are objectively mapped assuming a Gaussian covariance with
a correlation length scale of 20° longitude and an error-to-signal energy
of 0.25. (a) Southern hemisphere transports at three latitudes (17°S solid
line, 12°S dashed, and 7°S dot-dashed) with a pycnocline base at n
= 26.2 kg m. (b) Northern hemisphere transport
between the NEC and NECC with a pycnocline base at n
= 25.9 kg m. (c) Northern hemisphere transport
between the NECC and SEC with a pycnocline base at n
= 25.9 kg m.
Table 1. Latitudinal range, maximum neutral density, and maximum pressure of the quasi-zonal tropical currents at 165°E and 125°W (see Fig. 4).
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