REFRACTIVE INDEX PARAMETERS 



193 



8- 



LEGEND 



WARM FRONT 

 A=N + NoCl-exp(-I)j 

 WHERE No=3l3 

 H=70 km 



300 400 500 



DISTANCE, km 



600 



Figure 5.16. Idealized warm front in A units. 



from it, requiring only a knowledge of the altitude of the observed refrac- 

 tive index measurement and the local elevation angle of the radio ray. 

 The potential refractive modulus of I. Katz [27], 



<P 



Po + b 



eo 



(5.12) 



where 6 is the potential temperature and eo the potential vapor pressure, 

 is also in current use. The constants b and c of (5.12) are given in the 

 development of modification to A'' data in chapter 1 (1.39). The potential 

 refractive modulus has been employed by Jehn [25] to study polar waves 

 over North America. Refractivity, A'', cannot accurately be recovered 

 from (p for bending calculations unless additional information is available; 

 namely, observed temperature and vapor pressure. The concept of the 

 potential refractive modulus arose out of the earlier refractive modulus, 

 M (see ch. 1), which may be defined by 



M 



4 



1 + 



a_ 



X 10' = N(z) + 



z 

 Laj 



X 10'= 



(5.13) 



where z = height above the earth's surface and a — earth's radius. 



