| A finite-difference quasigeostrophic (QG) model of an open ocean region is employed for dynamically constrained synthesis of the 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 analyzed data sets include direct and differential travel times measured at the array of 5 acoustic transceivers deployed by JAMSTEC in the region of the Kuroshio Extension in 1997, Topex/Poseidon altimetry, CTD soundings, and ADCP velocity profiles. The monitored region is located within 27.5N-36.5N, 143E-155E. 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 model-data misfits lie within the observational error bars for all the data types used in assimilation. We compare the results of assimilation with the statistical inversion of travel time data and analyze energy balances of the optimized model solution. Energy exchange between the depth-averaged and shear components of the observed currents reveal 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 4.7±2.3*10-5 cm2/s3.Kinetic energy transition has the same sign and estimated as 2.8±2.5*10-5 cm2/s3. Potential enstrophy is transferred to mesoscale at a rate of 5.5±2.7*10-18 s-3. These figures provide an observational evidence of the properties of free geostrophic turbulence which were predicted by theory and observed in numerical experiments. |
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