186 



SYNOPTIC RADIO METEOROLOGY 



Figure 4.1 shows contours of the mean value of A'^ at the surface, N s, 

 determined from eight years of data for August, 0200 local time. Minia- 

 ture circles indicate the 62 observing stations used to analyze this chart. 

 It is evident that coastal areas display high values of A'^s as compared with 

 inland locations. Low values of N s are apparent along the Appalachian 

 mountain chain and in the great mountain systems and inter-mountain 

 plateaus of the western United States. There is a marked similarity be- 

 tween the N s contours on figure 4.1 and the elevation contours of figure 

 5.8. As a sensitive indicator of changes in atmospheric density, A''^ dis- 

 plays a strong elevation dependence. To remove this effect the reduced- 

 to-sea-level expression, A^'o, was introduced in chapter 4 as: 



No = Ns exp 



H* 



(5.6) 



where z is height in kilometers and H* = 7.0 km is the scale height. 

 Scale height is the height at which the mean value of A^ has decreased to a 

 fraction 1/e of its initial value. A scale height of 7.0 km is in close agree- 

 ment with H* = 7.01 km for the NACA standard atmosphere with 80 

 percent relative humidity and H* = 6.95 km obtained from climatic 

 studies utilizing over two million observations of the variation in A^ over 

 the first kilometer above the surface of the earth [20]. The A^'o contours 



'00&500 



7000 a ovERjasa 



Figure 5.8. Ground elevation above sea level. 



