Mc. Mccarthy et al., Seasonal to interannual variability from expendable bathythermograph and TOPEX/Poseidon altimeter data in the South Pacific subtropical gyre, J GEO RES-O, 105(C8), 2000, pp. 19535-19550
Estimates of dynamic height anomalies from expendable bathythermograph (XBT
) and TOPEX/Poseidon (T/P) sea surface height (SSH) measurements were compa
red along a, transect at similar to 30 degrees S in the South Pacific. T/P
SSH anomalies were calculated relative to a 5 year time mean. XBT dynamic h
eight was calculated relative to 750 m using measured temperature and an ob
jectively mapped climatological temperature-salinity relationship. The anom
aly was obtained by subtracting out an objectively-mapped climatological dy
namic height relative to 750 m. XBT temperature sections show evidence of a
double-gyre structure, related to changes in shallow isopycnals near the g
yre's center. XBT dynamic height and T/P SSH anomalies compare well with an
RMS difference of 3.8 cm and a coherence above 0.7 for scales larger than
300 km. The differences between the two measures of dynamic height yield sy
stematic patterns. Time-varying spatial averages of the differences are fou
nd to be related to changes in Sverdrup transport, zonal surface slope diff
erences, and the 6 degrees C isotherm depth. Higher zonally averaged altime
try SSH than zonally averaged XBT height and larger northward transport fro
m altimetry SSH than from XBT height correspond to gyre spinup determined f
rom Sverdrup transport changes. This implies mass storage during gyre spinu
p due to the phase lag between the Ekman pumping and the full baroclinic Sv
erdrup response. Increases in the spatially averaged differences and zonal
slope differences, associated with gyre spinup, correspond to shoaling in t
he 6 degrees C isotherm depth, requiring deep baroclinic changes out of pha
se with the 6 degrees C isotherm depth changes.