U.S. Dept. of Commerce / NOAA / OAR / PMEL / Publications

The Pacific Subsurface Countercurrents and an Inertial Model

Gregory C. Johnson and Dennis W. Moore

National Oceanic and Atmospheric Administration/Pacific Marine Environmental Laboratory, Seattle, Washington

Journal of Physical Oceanography, 27, 2448-2459
Not subject to U.S. copyright. Published in 1997 by the American Meterological Society.

Gallery of Figures and Tables

Figure 1

Fig. 1. Mean meridional eq01.gif (1119 bytes) and S sections in the top 500 m of the ocean from 10S to 10N along 165E, 155W, and 110W. Contour intervals are 1C (thick lines 5C) for eq01.gif (1119 bytes) and 0.1 PSS-78 (thick lines 0.5 PSS-78) for S. Vertical exaggeration is 4000:1.


fig02sm.gif (19479 bytes)

Fig. 2. As in Fig. 1 but for eq01.gif (1119 bytes)n and N2. Contour intervals vary for both quantities, but thick lines are at 1.0 kg m-3 intervals for eq01.gif (1119 bytes)n and 200  10-6 s-2 intervals for N2.

Figure 3

Fig. 3. Salinity on eq01.gif (1119 bytes)n = 26.5 kg m-3, with contour intervals of 0.05 PSS-78 and saltier values increasingly shaded (top panel). Depth of eq01.gif (1119 bytes)n = 26.0 kg m-3, with contour intervals of 25 m and deeper values increasingly shaded (second panel from top). Depth of eq01.gif (1119 bytes)n = 26.8 kg m-3, with contour intervals of 25 m and deeper values increasingly shaded (third panel from top). Thickness between eq01.gif (1119 bytes)n = 26.0 and 26.8 kg m-3, with contour intervals of 25 m and thicker values increasingly shaded (bottom panel). All panels are objectively mapped from the values at each mean hydrographic profile location as described in the text. The mapping uses the Peters projection.

Figure 4

Fig. 4. Perspective view of the model jet from 30W of south at 30 elevation (solid lines for visible jet boundaries, dashed lines for hidden boundaries). The surface layer is not discussed. The pycnocline depth, D, is the interface between layer 0 and layer 1. This interface is constant in latitude but slopes linearly up to the east (upper plane of dotted lines). Since layer 0 is ignored, D can be thought of as inverted topography at the top of layer 1. The interface depth between the active layer 1 and the quiescent abyssal layer 2 is eq01.gif (1119 bytes). This deeper interface is constant on either side of the jet (lower sets of dotted lines), but slopes up within it, where the velocity, u, is finite. The interface depths D and eq01.gif (1119 bytes) are both negative values referenced to the surface, but their difference, the layer 1 thickness, h, is a positive quantity. The reduced gravity, g', at eq01.gif (1119 bytes) is related to the neutral density anomalies, eq01.gif (1119 bytes)n, as discussed in section 5. As the pycnocline shoals to the east, the jet edges ye and yp shift poleward as the jet thickens, conserving Bernoulli function and potential vorticity on streamlines. Vertical-meridional exaggeration is 167,000:1 and meridional-zonal exaggeration is 124:1.


Figure 5
Fig. 5. Active layer thickness within the model jet plotted against latitude from 140E to 80W at 20 intervals (top left panel) and velocity plotted against latitude from 140E to 80W at 20 intervals (top right panel). Jet edges (thick dashed lines in bottom panel) are plotted over thickness between eq01.gif (1119 bytes)n = 26.0 and 26.8 kg m-3 as in the bottom panel of Fig. 3. The jet shifts poleward, narrows in the meridional, thickens in the vertical, and accelerates to the east as a consequence of conservation of potential vorticity and Bernoulli function under the shoaling pycnocline.

 

If your browser cannot view the following table correctly, click this link for a GIF image of Table 1

Table 1. Geostrophic volume transport and velocity calculations made for the Pacific SSCCs using the mean meridional sections at each longitude, referenced to 700-dbar pressure. Only eastward flow between eq01.gif (1119 bytes)n = 25.5 and 27.3 kg m-3 within the latitude bounds given is used in the transport calculations. Volume transport and transport-weighted eq01.gif (1119 bytes)n remain roughly constant from west to east. Peak velocity latitudes, depths, and magnitudes show the Tsuchiya jet cores shifting poleward, shoaling, and maintaining speed from west to east.


Transport calculations Peak velocities


Section
(long)
Latitude
bounds
Volume
Transport
(106 m3 s-1)
Transport
weighted
eq01.gif (1119 bytes)n
(kg m-3)
Peak
latitude
Peak depth
(m)
Peak magnitude
(m s-1)

South SSCC
165E 5-2S 6.6 26.62 2.5S 250 0.17
155W 8-3S 4.1 26.67 3.5S 250 0.07
110W 6-3S 6.2 26.57 5.5S 160 0.16
North SSCC
165E 2-5N 10.3 26.58 2.5N 240 0.26
155W 2-5N 7.0 26.63 3.5N 220 0.21
110W 3-6N 7.4 26.45 4.5N 130 0.21


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