Aircraft measurements collected on the Spanish Mediterrenean coast during BEMA (Biogenic Emissions in a Mediterranean Area) are used to study the spatial distribution of the thermal internal boundary layer (TIBL) height. The BEMA experiment, aimed to determine the contribution of biogenic emissions on tropospheric ozone production, took place around the coast of Valencia in June 1997. Turbulent fluxes, trace gases, thermodynamical and dynamical parameters, measured by the French aircraft ARAT are used to study the TIBL. In particular, the TIBL height is determined from the spatial distribution of several of these parameters (for example the humidity, ozone or the turbulent kinetic energy). The values obtained from the data for different observation periods are compared with the results of an analytical model, based on the conservation of heat. The detailed measurements allow the determination of the different contributions to the evolution of the TIBL depth