ABSTRACT

Approximately two months of acoustic travel time data from a 5-transceiver acoustic tomography array covered an 1000 km-scale domain in the Kuroshio Extension and its southern recirculation gyre regions (28° -36° N, 143 ° --154° E) in summer 1997 are used for comparing with the TOPEX/POSIDON (T/P) altimeter measurements. The acoustic data show that the travel time variations are consistent well with contemporaneous variation of sea surface height anomalies (SSHA) from the T/P altimeter in the Kuroshio Extension region, but have significant different variations in the recirculation region. This difference is assumed due to that acoustic tomography is able to measure both of the signals associated with the seasonal thermocline (sea surface layer) and permanent thermocline (subsurface layer) changes, but the altimeter could mainly pick up the signal associated with the variation occurred above the seasonal thermocline in the recirculation region. A new approach is presented for the inversion of the acoustic travel times to separate and quantify the temperature variations between the seasonal and permanent thermocline. The inversions from the proposed approach provide that the temperature in the surface layer (0-100 m) had been warming up 1.2 ° C during the experimental period, while the temperature in subsurface layer (100-1500 m) had been cooling down about 0.2° C. This temperature up in surface layer derived from acoustic data is excellent consistent with the steric height change determined from the net heat flux data from NCEP. Zonal range-and-depth averaged (barotropic) westward-flowing current velocity determined from reciprocal acoustic travel times in the recirculation region is about 5 cm s^-1; it is comparable with the surface geostrophic current velocity determined from the SSHA of the T/P. The more northerly the Kuroshio Extension tends to correspond to the stronger recirculation surface and barotropic current.