A 4-DIMENSIONAL ANALYSIS OF THE THERMAL STRUCTURE IN THE GULF-OF-LION

The Theoretical and Experimental Tomography in the Sea Experiment (THE TIS 1) took place in the Gulf of Lion to observe the evolution of the temperature field and the process of deep convection during the 1991-1 992 winter. The temperature measurements consist, of moored sensors, c onductivity-temperature-depth and expendable bathythermograph surveys, ana acoustic tomography. Because of this diverse data set and since t he field evolves rather fast, the analysis uses a unified framework, b ased on estimation theory and implementing a Kalman filter. The resolu tion and the errors associated with the model are systematically estim ated. Temperature is a good tracer of water masses. The time-evolving three-dimensional view of the field resulting from the analysis shows the details of the three classical convection phases: preconditioning, vigourous convection, and relaxation. In all phases, there is strong spatial nonuniformity, with mesoscale activity, short timescales, and sporadic evidence of advective events (surface capping, intrusions of Levantine Intermediate Water (LIW)). Deep convection, reaching 1500 m, was observed in late February; by late April the field had not yet re turned to its initial conditions (strong deficit of LIW). Comparison w ith available atmospheric flux data shows that advection acts to delay the occurence of convection and confirms the essential role of buoyan cy fluxes. For this winter, the deep. mixing results in an injection o f anomalously warm water (Delta T similar or equal to 0.03 degrees) to a depth of 1500 m, compatible with the deep warming previously report ed.