Lab. de Phys. des Oceans, IFREMER, BP 70, 29280 Plouzane, France
IFM, 2300 Kiel, Germany
Acoustic tomography has been applied to observation of winter convection in the Gulf of Lion during the THETIS-1 experiment conducted during the 1991--92 winter by a European group (IFM Kiel, IFREMER Brest, and IACM Heraklion). A global analysis of all types of temperature measurements collected during THETIS 1 will be presented. Data issued from temperature sensors, thermistor chains, and CTD have been merged with the tomographic measurements in order to recover the time evolution of the full 3-D temperature field. The method relies on inversion and Kalman filtering methods. It can be considered as a new step toward ``observation systems.'' Monitoring of the whole area during the ``preconditioning'' phase shows the influence of surface cooling on the vertical stratification. This effect is inhomogeneous and the situation evolves with time, influenced by horizontal advection. The relative importance of surface forcing and advection is responsible for the intermittent nature of convection which happens with different intensity from year to year. After convection, the behavior of the mixed water chimney and the evolution of the vertical profile toward the initial state is documented.