Seasonal to interannual variability from expendable bathythermograph and TOPEX/Poseidon altimeter data in the South Pacific subtropical gyre

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.