Some past and future applications of acoustic tomography
Uwe Send
Institut fuer Meereskunde
Duesternbrooker Weg 20, 24159 Kiel, Germany
Tel.: (+49) (431) 5973827
Fax : 5973821
email: usend@ifm.uni-kiel.de
Abstract:
In this presentation, four applications of large-scale acoustic techniques to topics in physical oceanography are presented. These include a study of deep convection in the northwestern Mediterranean on 70-200km scale, cross-basin monitoring of heat content evolution in much of the western Mediterranean basin, a pilot study to monitor the transport through the Strait of Gibraltar with cross-strait transmissions, and multi-year ongoing observations of water mass formation and export in the Atlantic subpolar gyre.
1. Convection in the Gulf of Lions ("THETIS").
In the winter of 1991/92, an experiment took place in the northwestern Mediterranean convection regime, in cooperation with Ifremer/Brest and Forth/IACM Heraklion. It consisted of various observational components, and a 400HZ tomography array (70-200km scale) was deployed to observe the large-scale evolution of the system. In spite of severe technical problems, the tomography observations along various sections through the convection regime could document the large-scale evolution of the vertical temperature distribution, as the surface forcing caused successively deeper mixing. Through a quantitative comparison with surface heat fluxes it was possible to quantify the contribution of horizontal eddy advection to the heat budget to be approximately 20%, i.e. to within about 80% the heat budget is simply a 1-dimensional local mixed-layer behaviour. This is a topic of intense current interest, e.g. for parameterizing eddy fluxes in numerical models. The volume of convected water could be estimated from the tomography data to correspond to an area of 60km radius, which yields an estimate for the annual-mean water mass formation rate of 0.3Sv. Further, the restratification process and its time scales were observed on the large scale, and the value of 40days for the latter now serves to test theories which try to explain this process.
