A comparison of acoustic and TOPEX/POSEIDON altimetric data in the Kuroshio Extension region during summer 1997

Abstract

Approximately two months of data from a five-transceiver acoustic tomography array in the Kuroshio Extension (KE) in the summer of 1997 are used for comparing with the TOPEX/POSEIDON (T/P) altimeter measurements. The acoustic data show that travel time (TT) variations are very consistent with contemporaneous variations of sea surface height anomalies (SSHA) as in the T/P in the KE front region, but have significant differences in the KE recirculation region. This difference is assumed to be due to the fact that the altimeter might not pick up the signal associated with the variations occurring below the seasonal thermocline. The inversions from a new approach show that the temperature in the surface layer (0–100 m) had been warming up 1.0 °C during the experimental period, but cooling down about 0.2 °C in the subsurface layer (100–1500 m). This temperature warming up in the surface layer derived from acoustic data is excellent, consistent with the steric height change determined from net heat flux data of the NCEP/NCAR. Zonal range and depth averaged (barotropic) westward-flowing current velocity determined from reciprocal acoustic TTs in the recirculation region is about 5 cm/s; it is comparable with the surface geostrophic current velocity determined from the SSHA of the T/P. Acoustic tomography complements the altimetry.