Measurements of a Barotropic Planetary Vorticity Mode in an Eddy- Resolving Quasi-Geostrophic Model Using Acoustic Tomography
Abstract
The resonant barotropic oscillations (modes) predicted by the quasi- geostrophic(QG) theory are difficult to observe in the ocean. Large-scale measurements over lengthy durations may be required in order to observe these waves. The capability of receiving long-range sound transmissions in the ocean implies that acoustic methods may be well-suited for study of large-scale motions. In particular, basin-scale tomographic arrays may provide the coverage over sufficient time periods as well as the sensitivity needed to resolve the modes. In this study we investigate whether the analysis of the travel time fluctuations of tomographic transmissions can detect large-scale barotropic planetary oscillations in a QG model. A tomographic array is placed in a 2- layer, flat bottom, steady-wind driven QG circulation model to investigate whether analysis of acoustic travel time changes can detect large-scale barotropic oscillations. Time series of sea surface elevation and upper and lower layer meridional currents are generated for comparison against a series of acoustic travel times. The spectra of these time series exhibit a broad mesoscale peak near a period of 40 days. The spectrum of the acoustic travel time contains a significant peak due to a resonant barotropic oscillation with a period of 28.6 days which is not present in the spectra of the point measurements. In the numerical model, basin-scale tomographic measurements are a better method of sensing the large-scale resonant barotropic oscillations than are conventional point measurements because the tomographic system attenuates the 'noise' from the mesoscale. Theses.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 1988
- Accession Number
- ADA205409
Entities
People
- Wendy B. Lawrence
Organizations
- Woods Hole Oceanographic Institution