COUPLING BETWEEN SEA AND AIR 



409 



make direct measurements of the feedback links in the atmosphere- 

 ocean system. Under laboratory conditions experimental studies 

 of feedback systems can be made by a frequency response tech- 

 nique. Certain periodic forces are applied, and the response 

 characteristics of the system are studied as dependent on the 

 frequency. 



In nature one has few opportunities to arrange experiments 

 of this kind. It seems, however, not impossible that even a feed- 

 back link such as the one seen in Fig. 2 may be subjected to 



Fig. 2. Schematic representation of the feedback circuit relating the atmos- 

 pheric circulation with the wind-dri\en ocean circulation. 



direct experimental study. It was stated earlier that the effect 

 needed to drive the ocean currents in the North Atlantic would be 

 of the order 10^ kw. If an additional effect of, say, 100.000 kw to 

 1 Mekw is applied, one would thus expect effects of the order of 

 0.1% to 1% in the circulation. Such effects normally drown in the 

 general ocean "noise," but by keeping a fixed frequency for a 

 sufficiently long time, it may be possible to separate out even such 

 small signals. In this connection it may be of interest to mention 

 that some studies are in progress as to the feasibility of attaining 

 observable changes in the barotropic ocean circulation with a 

 period of the order of a few days by bubbling air periodically 

 through the water below swift surface currents, thereby changing 

 the momentum exchange between the deep and the surface waters. 

 Even small changes in the barotropic mode will be reflected in 

 sea-level changes that can be measured by an appropriate pressure 

 gage on the sea bottom. Whether or not any such experiments are 



