TM No. 377 



CHAPTER I 



INTRODUCTION 



Over the past two decades ocean wave research has made notable advances fi 

 particularly in the study of storm generation and prediction, and the recording 

 of long surface gravity waves (e.g. , Snodgrass, Munk, and Tucker , 1958), 

 Most studies of wind driven waves have been involved with statistical analyses 

 of the inferred or measured kinetic properties of the free surface oscillations. 

 These properties are either determined by means of wave staff devices and 

 hobbling floats, or inferred by use of slope detectors , optical glitter patterns s 

 bottom-mounted pressure sensors , and other more esoteric devices. Much attention 

 has been given to the theoretical derivations of classical relationships and to 

 conjecturing empirical equations relating wave, spectra to frequency, wave length 

 and height, wind speed and duration, fetch and the like (see, for example;, Ocean 

 Wave Spectra, 1963, and Kinsman, 1965), 



A perusal of the published literature on ocean wave research, of which in- 

 deed there is no dearth, reveals a conspicuous absence of recorded observations 

 of actual particle motions associated with ocean waves. This situation can 

 probably be attributed to two factors; (1) the lack of sensing equipment to re- 

 cord faithfully the quasi-oscillatory and relatively high frequency motions of 

 waves, and (2) the difficulties involved in properly fixing the measuring instru- 

 ment in the ocean without altering or interfering seriously with the wave motions. 



Until the dynamic motions within the wind-generated waves can be accurately 

 described and hence modeled, at least in a statistical sense, there is little 

 hope of assessing the effects of wind stress in creating turbulent mixing of 

 momentum and heat in the ocean surface layers and in helping to produce major 

 ocean currents. In short, the motion beneath the sea surface holds the key to 

 the time and space variable distribution of the wind-imparted energy and momentum 

 flowing into and within the ocean, 



Welander (1961) emphasizes the need for knowledge about the free surface 

 and boundary processes and indicates that the basic laws of mechanics and thermo 

 dynamics can be applied to an ocean of given dimensions and chemical composition. 

 The distribution of temperature and salinity as well as the water motions in the 

 entire ocean are determined by a knowledge of; (1) the pressure and shear stresses 

 acting through the free surface; (2) the net heat flux through the surface layer; 

 and (3) the net mass flux through the surface layer (due to evaporation, precipi- 

 tation, freezing, melting, and estuary inflow). Further, the transport of heat 

 and momentum through the surface layers can only be effected by the proper turbu- 

 lent environment immediately beneath the ocean surface. This so-called "reactive 

 layer" is completely respondent to the turbulence generated by the wind itself and 

 by its dynamic counterpart, the driven surface waves. The flux of quantities such 

 as momentum, kinetic energy, and heat must be extremely sensitive to the time 

 variable climate of turbulence within the reactive surface layer. Hence, the need 

 is great for at least establishing a method or parameter to describe the turbulent 

 regime in the upper layer. 



