N STRUCTURE IN I.C.A.O. ATMOSPHERE 



313 



50 



40 - 



MESO7PEAK 



OZONOPAUSE 

 H = 47gpkm 



400 800 1200 210 230 250 270 290 

 P(mbar) T(°K) 



100 200 300 



D = 77.6 Y 



Figure 8.1. The U.S. extension to the I.C.A.O. Standard Atmosphere. 



into 



\n y = — h/c + In ^, 



(8.5) 



which is the equation of a straight Hne on semilogarithmic paper. The 

 exponential distribution of W with height in this atmosphere follows 

 naturally from the definition of constant relative humidity, since the 

 saturation vapor pressure, e^, is itself, to a first approximation, an ex- 

 ponential function of temperature. It is evident that the value of W can 

 significantly affect the surface values of A^ but has no appreciable effect 

 upon the value of A'' at the tropopause. 



An examination of long term means from observations in the actual 

 atmosphere shows that this same general bi-exponential trend is observed 

 in practice, for temperate climates at least. Examples are given on 

 figures 8.3 and 8.4 for Bismarck, N.Dak., and Brownsville, Tex. 



Bismarck is typical of the high, dry great plains region of North 

 America which is frequently subjected to strong intrusions of arctic air, 

 while Brownsville represents the humid periphery of the Gulf of Mexico. 

 Even in these very dissimilar climates one finds a strong tendency towards 

 a bi-exponential distribution of A^, particularly when W is large. 



