76 DEACON AND WEBB [CHAP. 3 



For convenient conversion of F values at different reference heights, the 

 following ratios to 7^(8 m) are given. They are calculated from the logarithmic 

 profile form for the case 7^(4 m) = 0.1, but for other 7^(4 m) values, differing by 

 up to 30%, they remain correct to within a few per cent. They are, of course, 

 equally applicable to Fm, Fh or Fe. 



If further values are required they may be calculated from 



F{b)IF{a) - [ln(6/a)r(a)+l]-i. 



G. Further DisciLssion of the Effects of Thermal Stratification 



The effects of thermal stratification on the profiles, as illustrated by the 

 curvature in Fig. lib, are qualitatively the same as are observed over land. It 

 is indeed most likely that the effects are virtually identical over land and sea, 

 though this awaits confirmation by a sufficient number of high-quality measure- 

 ments over the sea. 



We now proceed to outline the information available from observations over 

 land. Even here the subject is still under investigation, and, although a fairly 

 detailed picture of the behaviour of the profiles has been formed, there are still 

 gaps to be filled in and further effort is needed in the improvement of observa- 

 tional methods and site selection. Accounts of the subject up to recent years 

 are to be found in Sutton (1953), Sheppard (1958), Charnock (1958) and 

 Priestley (1959). 



H. Lajpse Conditions 



In unstable (lapse) conditions, the transfer coefficients are greater than in 

 inversions, and the unstable case is, therefore, the more important from the 

 point of view of vertical transfer. 



The case of free convection, with wind-shear effects negligible in comparison 

 with thermal effects, has been considered in the similarity theory of Priestley 

 (1954), which indicates the form of the temperature profile as 



dejdz oc s-4/3. (35) 



In a further study Priestley (1955) has examined experimental data in terms 



» 



of the corresponding dimensionless heat flux, H, defined by 



H = HlpCp{glTy/2z^ddiez\^'^, (36) 



