Air-Sea Interactions ; Program at IMST 



layers obtained at the interface between an airflow and a water mass. 

 The three basic processes of momentum, heat and mass transfer will 

 be effectively realized by controlling air velocity, temperature and 

 humidity, and water velocity and temperature. Furthermore, 

 appropriate heating or cooling will provide an approximate repre- 

 sentation of the most important radiation effects. 



However, such experiments will be really useful in modelling 

 the atmospheric-oceanic phenomenon, only if the three aforementioned 

 specific features: turbulent atmospheric structure, stratification 

 effects, and interface motion, are at least partially reproduced. 

 This seems feasible, provided that a sufficiently large facility can 

 be realized. 



2. Simulation of the Atmospheric Dynamical Structure 



It is well known that the atmospheric surface layer motions 

 can be simulated in the laboratory, in so-called "micrometeorologi- 

 cal wind-tunnels" (see e.g. Pocock [ I960] , Cermak et al. [ 1966] , 

 McVehil et al. [ 1967] , Mery [ 1968]). In short, these~rnotions are 

 characterized, on one hand by extremely high values of Reynolds 

 number, and on the other hand, by stratification effects corresponding 

 to appreciable values of Richardson number. For a good modelling, 

 these dimensionless numbers have to keep significant values in the 

 laboratory flow. For the latter, this implies rather large tempera- 

 ture differences, and low wind velocities. In consequence, to pre- 

 serve sufficiently high Reynolds numbers while observing cumulative 

 stratification effects, it is necessary to build large facilities. Simi- 

 lar conclusions are reached if one considers the problem of main- 

 taining the ratio between the roughness height at the surface and the 

 boundary layer thickness or the Monin-Obukhov length, or if one 

 requires the reproduction of an appreciable Kolmogorov inertial 

 range. 



For these reasons, the test section length of micrometeoro- 

 logical wind tunnels reaches several tens of meters and the velocity 

 range is of the order of a few meters per second, while provision 

 is made for creating temperature differences of several tens of 

 degrees centigrade. The main characteristics of our project are as 

 follows: 



- Length of the water surface forming the interface in the test 

 section: 40 meters. 



- Air velocity range: 0.5 to 14 meters per second. 



- Maximum temperature and specific humidity differences: 30 C, 

 and 25. 10' Kg water by Kg air. 



The estimated performance of the facility is sketched by Fig. 5, 

 which shows the rather wide range of dimensionless parameters that 

 should be covered. The general scheme of the tunnel is given in 

 Fig. 6. It is a closed-circuit wind-tunnel, with several rather 



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