219 



DISCUSSION: A.H. Woodcock 



John Isaacs has reminded us of the fundamental fact that oceanographic 

 instruments are, in effect, extensions of our sense organs, and that these in- 

 struments aid us in constructing and testing our mental models of the ocean. 

 The trend in this process of model building and testing is toward more complex 

 devices for making measurements. I would like to point out, however, that 

 the air- sea boundary region is one area of ocean study in which the sense or- 

 gans can be used directly to obtain a qualitative "mental model" of some of the 

 sma,ll scale motions which occur. These motions are revealed by living and 

 non - living "instruments" found immersed in the air and sea: birds, fog, 

 smoke, seaweed, plankton. 



Qualitative studies of the nature of some of the motions in the sea and air, 

 as revealed by the naturally occurring "instruments", have already been made 

 and published. There is a real need, however, for instruments designed to 

 test quantitatively the indicated motions, and to aid us thereby in judging their 

 probable significance in the transfer of properties between air and sea. A few 

 brief remarks about the apparent nature of the air and water motions are given 

 below. 



WATER MOTIONS NEAR THE SEA SURFACE 



Over much of the Western North Atlantic Ocean and during most of the 

 year surface waters contain the floating algae Sargassum. This plant indicates 

 that during winds of force 3 or more surface waters converge in lines lying 

 parallel to the wind direction. During strong winds, descending currents under 

 these convergence lines draw the positively buoyant plants beneath the surface. 

 During winds less than about force 3 the plants converge in "patches" or "is- 

 lands", suggesting a columnar region of descent of surface waters. Tests of 

 the rates of rise of Sargassum plants indicate that descending motions in excess 

 of 4 to 7 centimeters per second must on occasion exist under the lines of con- 

 vergence. 



The existence of the columnar or linear regions of convergence can be 

 readily tested with simple drift bottles, provided a small boat is used which will 

 not seriously disturb the natural small-scale motions of the surface waters. 

 My drift bottle studies in the Gulf of Mexico were made from a twelve foot 

 dinghy. Drift bottle tests in a force 3 wind among lines of convergence showed 

 an average descent of surface water beneath the lines of one cubic meter per 

 meter length of line for each three minute time interval. 



AIR MOTIONS NEAR THE SEA SURFACE 



Over a large part of the Western North Atlantic there is a flow of sensible 

 heat from the sea to the atmosphere. The lower air, thus heated, tends on oc- 

 casion to rise in a patterned fashion. The form of this ascent varies with wind 

 speed, being columnar during lower speeds and linear with higher speeds. The 

 pattern of this air motion and its change of form with wind speed has been indi- 

 cated by the soaring flight performance of sea birds, by smoke, and by steam 

 fog in cold air overlying warm seas. 



DISCUSSION AND CONCLUSIONS 



Thus there is some evidence that the exchange of properties across the 

 sea- air interface occurs in the presence of a continuous patterned removal of 

 the bounding fluid surfaces, to unknown heights or depths. It has been suggest- 



