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Reprinted with ■5ermi5sion from: NOAA TECHNICAL REPORT ERL 228-AOML 7-2, 



pp 25-1-25-55 1973. 



.THE ENERGY BALANCE OF WIND WAVES AND 

 THE REMOTE SENSING PROBLEM 



K. Hasselmann* 



Institute of Geophysics 

 University of Hamburg 



ABSTRACT 



Measurements of wave growth during the Joint North Sea 

 Wave Project (JONSWAP) indicate an energy balance of the 

 wave spectrum governed primarily by input from the atmos- 

 phere, nonlinear transfer to shorter and longer waves, and 

 advection. The pronounced spectral peak and sharp low 

 frequency cut-off characteristic of fetch-limited spectra 

 are explained as a self-stabilizing feature of the nonlinear 

 wave-wave interactions. The momentum transferred from the 

 atmosphere to the wind waves accounts for a large part of 

 the wind drag. Phillips' 'constant' is found to vary 

 appreciably with fetch and wind speed, the lo range of the 

 spectrum representing (for intermediate frequencies not too 

 far from the peak) an equilibrium between atmospheric input 

 and nonlinear transfer rather than a saturation spectrum 

 governed by wave breaking. These findings are relevant for 

 remote microwave sensing of the sea surface by backscatter 



*Presently at Woods Hole Oceanographic Institution 



Woods Hole, Massachusetts 02543 



W. H.O.I. Contribution No. 2843 



25-1 



