164 



N CLIMATOLOGY 



20 40 60 80 100 120 140 160 180 200 

 ANGLE OF ARRIVAL OR DEPARTURE, ^o.lmrad) 



Figure 4.55. Comparison of total angular bending of radio rays within air masses. 



After Schulkin [1952]. 



the earth's atmosphere are given for extremes of air mass types and a 

 range of initial elevation angles, do, on figure 4.55 [43]. It is seen that 

 maritime tropical air produces 30 percent more bending than continental 

 polar air at initial angles or arrival or departures of about 10° (175 mrad) 

 and that this difference increases to about 70 percent at zero initial 

 elevation angle. Further, the magnitude of the total bending increases 

 rapidly with decreasing values of ^o- 



Figure 4.55 does not make it clear that differences in radio ray refrac- 

 tion arise from differences in the refractive index profiles of the two air 

 masses. It is the purpose of this section to show that various air masses 

 have characteristic refractive index profiles and that the radio ray refrac- 

 tion within each air mass is mirrored by the difference of the actual re- 

 fractive index structure from a standard atmosphere of exponential form. 



4.6.2. Refraction of Radio Rays 



The angular bending of a radio ray, ti,2 (see fig. 4.56) between two 

 points in the atmosphere of refractive indices rii and n2 is given by the 



