MODIFIED EFFECTIVE EARTH'S RADIUS 



63 



This last relationship comes from the observed relationship between 

 6 to 8 year averages of daily observations of A'^s and AA^, the difference 

 between N s and the value of A'' at 1 km above the earth's surface: 



-AA^ = A^,, - A^(l km). 



It is evident from figure 3.4 that for average conditions, a relationship 

 exists between AA'' and A^'^. The least squares determination given by 

 (3.40) was based upon 888 sets of monthly mean values of AA'^ and N s 

 from 45 United States weather stations representing many diverse cli- 

 mates. This relationship between AA'^ and N s is expected to represent 

 the best estimate of a majority of individual profiles and certainly will 

 closely agree with average conditions for the United States with one 

 notable exception, southern California in the summer. These data, al- 

 though shown on figure 3.4, were excluded from the least squares deter- 

 mination due to their singular large range of AA'' compared to their small 

 range of A''^ which resulted in a marked "finger" of points rising from the 

 main body of the data. This obvious departure of data points (24 points 

 out of a total of 912) plus the well-known unique nature of the southern 

 California summer climate were taken as sufficient justification for ignor- 

 ing these points, although, as shall be seen, the ray bendings based upon 



-AN 



230 240 250 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400 



Figure 3.4. Eighl-year average N, versus 6-year average AN at 0300 and 1500 GMT 



