Simulations of quasigeostrophic currents derived from satellite altimetry and acoustic tomography of an open ocean region

Abstract

Acoustic tomography (AT) and satellite altimetry (SA) measure properties of the ocean state with high temporal resolution. That makes these data suitable for long-term monitoring of mesoscale features in the open ocean regions, where the open boundaries are the major sources of model forecast uncertainties on timescales larger than 1 week. In this paper, a finite-difference quasigeostrophic model of an open ocean region is considered as a possible tool for interpolating AT-SA data in space and time. The assimilation algorithm is based upon the 4D variational data assimilation scheme controlled by the initial and boundary conditions of the model. The model configuration used in the simulations corresponds to the AT array deployed by the Japan Marine Science and Technology Center (JAMSTEC) in the region of the Kuroshio Extension in 1997. Twin data experiments show that mesoscale features in an area of 1000 km × 1000 km can be effectively monitored by five acoustic transceivers, measuring reciprocal travel times. The quality of assimilation is studied as a function of the position of the transceivers in the vertical and the effective number of monitored rays. It is shown that reciprocal travel time observations (differential tomography) in combination with SA provide a significant improvement of the quality of assimilation.