Journal of Oceanography, Vol. 59 (No. 6), pp. 751-763, 2003
Konstantin V. Lebedev1,3*, Max Yaremchuk1,3, Humio Mitsudera1,2, Iwao Nakano2 and Gang Yuan1
1International Pacific Research Center, University of Hawaii, Honolulu, HI 96822, U.S.A.
2Japan Marine Sciences and Technology Center, Natsushima, Yokosuka 237-0061, Japan
3P.P. Shirshov Institute of Oceanology, Moscow 117851, Russia
(Received 30 May 2002; in revised form 4 February 2003; accepted 14 March 2003)
Abstract: A finite-difference quasigeostrophic (QG) model of an open ocean region has been employed to produce a dynamically constrained synthesis of acoustic tomography and satellite altimetry data with in situ observations. The assimilation algorithm is based upon the 4D variational data interpolation scheme controlled by the model's initial and boundary conditions. The data sets analyzed include direct and differential travel times measured at the array of five acoustic transceivers deployed by JAMSTEC in the region of the Kuroshio Extension in 1997, Topex/Poseidon altimetry, CTD soundings, and ADCP velocity profiles. The region monitored is located within the area 27.5°-36.5°N, 143°-155°E. The results of assimilation show that mesoscale variability can be effectively reconstructed by five transceivers measuring direct and reciprocal travel times supported by relatively sparse in situ measurements. The misfits between model and data lie within the observational error bars for all the data types used in assimilation. We have compared the results of assimilation with the statistical inversion of travel time data and analyzed energy balances of the optimized model solution. Energy exchange between the depth-averaged and shear components of the observed currents reveals a weak decay of the barotropic mode at the rate of 0.2 ± 0.7·10-5 cm2/s3 due to topographic interaction. Mean currents in the region are unstable with an estimate of the available potential energy flux from the mean current to the eddies of 4.7 ± 2.3·10-5 cm2/s3. Kinetic energy transition has the same sign and is estimated as 2.8 ± 2.5·10-5 cm2/s3. Potential enstrophy is transferred to the mesoscale at a rate of 5.5 ± 2.7·10-18 s-3. These figures provide observational evidence of the properties of free geostrophic turbulence which were predicted by theory and observed in numerical experiments.