EVAPORATION IN THE SURFACE ENERGY BALANCE 35 



Apart from the special difficulties of working over tall, flexible crops, it is 

 thought that acceptable results can now be obtained (albeit with highly 

 complex apparatus) over 'ideal' sites in the absence of 'oasis' or advection 

 situations. This can be done by using knowledge (which is already avail- 

 able) of the stabihty dependence of the aerodynamic parameters described 

 above. With the energy balance checks and data-processing apparatus now 

 available, it should soon be possible to provide a standard against which the 

 more promising of the simpler field techniques can be compared. 



ACKNOWLEDGMENTS 



The writer has only recently taken over the work of the Meteorological 

 Office Research Unit at Cambridge and is indebted to his immediate 

 predecessor, Mr. J. B. Tyldesley, and to his colleague, Mr. C. P. Tugwell, 

 for many stimulating discussions and for access to unpubhshed results on 

 the 1959 and i960 seasons' work. However, the responsibility for presenta- 

 tion and criticism is my own. This paper is pubhshed with the permission 

 of the Director-General of the Meteorological Office. 



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