DEPARTURES-FROM-NORMAL METHOD 



79 



s 



WINTER 



CP MP MT cT 



WINTER WINTER SUMMER SUMMER 



\ ;; : 



320 340 



-2 0-2 2-4 -2 



T^l^-Tdnrad) 



Figure 3.16. A-unit profiles for typical air ynasses and refraction deviation from normal. 



where 



A.4(A^,) = ANih) + A[iV,|l-exp(-c,/i)!] 

 = AN{h) + N sCeexp{-Ceh)Ah, 



and TNs{h) is the value of r tabulated for various atmospheres in tables 

 9.10 to 9.17, dk and dk+i are in milliradians and must be from the N s ex- 

 ponential atmosphere used. The value of AA{N s) is obtained from sub- 

 traction of the A value at layer level, k, from the value of A at layer, A' + l. 

 The A value may be obtained by adding any given N{h) value, obtained 

 from RAOB or other similar data, to a value of A^s[l ~exp{ —ch]] for the 

 same height which may be obtained from figure 3.17. Since TNs{h) has 

 been calculated only for a few of the exponential atmospheres, these being 

 the A^, - 200.0, 252.9, 289.0, 313.0, 344.5, 377.2, 404.9, and 450.0 atmos- 

 pheres, one of these atmospheres must be used in the calculation of bend- 

 ing by the departures method. The selection of the particular atmos- 

 phere to be used is based on the value of the gradient of N, dN/dh, be- 

 tween the surface of the earth and the first layer considered. In table 3.2 

 are shown the ranges of the gradient for the choice of a particular ex- 

 ponential atmosphere. 



