REFRACTIVE INDEX PARAMETERS 



189 



LEGEND 

 WARM FRONT 

 N ISOPLETH 



300 400 500 



DISTANCE, km 



Figure 5.12. Idealized warm front in N units. 



Early attempts to compensate for the decrease of A^ with height used 

 the constant gradient of the effective earth's radius theory, l/4a, where a 

 is the radius of the earth. As an illustration, the strong elevated layer 

 found during the summer in southern California was studied in terms of a 

 form of (1.32) for B, given by 



B = N{z) + (39.2)2, 



(5.7) 



where N{z) is the value of A^ at height z in kilometers [38]. Since A^ tends 

 to be an exponential function of height rather than the linear function 

 assumed by the effective earth's radius theory, the B unit approach over- 

 corrects when z is greater than about 1 km. 



This point is illustrated by figures 5.13 and 5.14 where the A'^ data of 

 figures 5.11 and 5.12 are plotted in terms of B units. Note that the over- 

 correction produces a cross section in which A'^ increases with height from 

 a value of 310 at the surface to 360 at 5 km. A function of exponential 

 form was designed to account for the systematic decay of density with 

 height that characterizes the terrestrial atmosphere, as given by 



A = A^(z)+313[l - jexp {- f^\'] 



(5.8) 



