Measurements of a Barotropic Planetary Vorticity Mode in an Eddy-Resolving Quasi-geostrophic Model Using Acoustic Tomography

Abstract

Abstract An acoustic source and receiver are placed at 800 m depth and are separated by 4000 km in a two-layer, steady-wind driven, flat bottom eddy-resolving quasi-geostrophic circulation model. Time series of sea surface elevation and upper and lower layer meridional currents are generated for comparison against a series of acoustic travel time. The spectra of the time series exhibit a broad mesoscale peak neat a period of 40 days. The spectrum of the acoustic travel time contains a significant peak which is not present in the spectra of the point measurements, due to a resonant barotropic osci11ation with a period of 29.0 days. In this numerical model, basin-scale tomographic measurements are a useful method of sensing the large-scale resonant barotropic oscillations because the tomographic system attenuates the “noise” from the mesoscale.