72 



DEACON AND WEBB 



[chap. 3 



the true surface temperature is lower than that measured just below the 

 surface, and estimated values of Fe will appear low as a result. 



iii. Radiative heat exchange. In addition to the transfer of heat between sea 

 and air by the processes already considered, there is some radiative transfer 

 giving rise to a source or sink of heat between surface and measurement level. 

 This effect, pointed out by Sverdrup (1943), is only likely to be of significant 

 magnitude when the other transfers are small, i.e. under stable conditions with 

 light wind. 



Either of the first two effects would cause a displacement of measured 

 temperatures in the sense actually found in Fig. 12, with the line of best fit 



7"2 - Ts , deg. F 



Fig. 13. Potential temperatvire difference between 4 and 12.6 m, plotted against tempera- 

 ture difference between sea and air — observations in Port Phillip Bay and Bass 

 Strait, October, 1955 (reproduced from Deacon, Sheppard and Webb, 1956, Fig. 10). 

 The straight line is that fitted in Fig. 12 carried over with the appropriate scale con- 

 version. Symbols indicate wind speed at 10 m: 



X > 5.5 m/sec o 4.5 to 5.5 m/sec ▲ 2.5 to 4.5 m/sec 



passing to the left of the origin (in the case of spray, this would be the effect of 

 a flux of heat towards the region where evaporation of spray is consuming 

 latent heat). However, it is not yet certain, though it appears probable, that 

 the displacement from the origin is real : in the investigation plotted in Fig. 12, 

 the corresponding displacement is in fact exhibited by the simultaneous 

 measurements at greater heights up to 1 3 m ; and a similar displacement is 

 clearly evident in the measurements of ^22 — ^5 by Johnson and Meredith 

 reproduced by Deacon, Sheppard and Webb (1956). On the other hand, the 

 displacement is not clearly apparent in all investigations, for example that 

 reproduced in Fig. 13. It is clear that examination of extensive temperature 



