PRESENTATION OF BASIC DATA 93 



the earth's surface from nearly 2 million radiosonde observations from 

 many diverse climates. 



At the time of analysis of the map series presented here, a value of 

 effective scale height, H* = 9.46 km, was in use. This form was 



Do = D, exp j^l 



(4.4) 



in which the value H* = 9.46 km was determined from the NACA dry 

 standard atmosphere. A Do chart is shown on figure 4.2, presenting a 

 gradient that is remarkably free of detail as compared to the N ^ chart of 

 figure 4.1, and is easily drawn for all areas of the country. 



An investigation of the elevation dependence of the surface wet term 



W. = ^^A^^ (4.5) 



revealed low correlations of log W s and height, indicating that W s is not 

 a marked exponential function of elevation. Contours of Ws for all 

 sections of the country are shown on figure 4.3. 



The maps that follow are completed in terms of a single reduced form 



A^o ^ {Ds + Ws) exp j^^l =^ Ns exp j^[, (4.6) 



where N s is reduced by the dry term effective scale height, H* = 9.46 km. 

 Figure 4.4 gives the A^o contours for the same time as the previous maps 

 of Do and W s- The A^o maps are no more difficult to prepare than the W s 

 maps and have effectively removed the station height dependence of N s. 

 One might wonder at the advisability of arbitrarily reducing the wet term 

 by the dry term correction. For the coastal areas of the country, where 

 the exponential height correction factor is nearly unity, this amounts 

 simply to adding the Do and W s maps for the mountain areas. Where the 

 height correction factor is large, the W s values are small with the result 

 that the gradient of the N isopleths obtained from the Do and W s maps is 

 essentially maintained on the Ao maps. As an example, for the series of 

 maps under discussion, the {Do -\- W s) difference between Reno, Nev. 

 (1,340 m elevation), and Oakland, Calif. (5.5 m elevation), is 21 N units, 

 while the Ao difference is 19 A^ units. 



The effects of this correction on the worldwide values can be seen from 

 figure 4.5, where As is plotted versus station elevation in kilometers. A 

 sample line illustrates the decay of As with height for Ao = 348. The 

 value of As for any other value of A^o would be obtained from a line parallel 

 \o the Ao = 348 line but having a zero intercept equal to the new value of 



