J. Gilson et al., RELATIONSHIP OF TOPEX POSEIDON ALTIMETRIC HEIGHT TO STERIC HEIGHT ANDCIRCULATION IN THE NORTH PACIFIC/, J GEO RES-O, 103(C12), 1998, pp. 27947-27965
TOPEX/Poseidon altimetric height is compared with 20 transpacific eddy
-resolving realizations of steric height. The latter are calculated fr
om temperature (expendable bathythermograph (XBT)) and salinity (expen
dable conductivity and temperature profiler (XCTD)) profiles along a p
recisely repeating ship track over a period of 5 years. The overall di
fference between steric height and altimetric height is 5.2 cm RMS. On
long wavelengths (lambda < 500 km), the 3.5 cm RMS difference is due
mainly to altimetric measurement errors but also has a component from
steric variability deeper than the 800 m limit of the XBT. The data se
ts are very coherent in the long wavelength band, with coherence ampli
tude of 0.89. This band contains 65% of the total variance in steric h
eight. On short wavelengths (lambda > 500 km), containing 17% of the s
teric height variance, the 3.0 cm RMS difference and lowered coherence
are due to the sparse distribution of altimeter ground tracks along t
he XBT section. The 2.4 cm RMS difference in the basin-wide spatial me
an appears to be due to fluctuations in bottom pressure. Differences b
etween steric height and altimetric height increase near the western b
oundary, but data variance increases even more, and so the signal-to-n
oise ratio is highest in the western quarter of the transect. Basin-wi
de integrals of surface geostrophic transport from steric height and a
ltimetric height are in reasonable agreement. The 1.9 x 10(4) m(2) s(-
1) RMS difference is mainly because the interpolated altimetric height
lacks spatial resolution across the narrow western boundary current.
A linear regression is used to demonstrate the estimation of subsurfac
e temperature from altimetric data. Errors diminish from 0.8 degrees C
at 200 m to 0.3 degrees C at 400 m. Geostrophic volume transport, 0-8
00 m, shows agreement that is similar to surface transport, with 4.8 S
verdrup (Sv) (10(6) m(3) s(-1)) RMS difference. The combination of alt
imetric height with subsurface temperature and salinity profiling is a
powerful tool for observing variability in circulation and transport
of the upper ocean. The continuing need for appropriate subsurface dat
a for verification and for statistical estimation is emphasized. This
includes salinity measurements, which significantly reduce errors in s
pecific volume and steric height.