PART I — THE SOLAR-TERRESTRIAL ENVIRONMENT 



Figure 1-5 — ATMOSPHERIC TEMPERATURE DISTRIBUTION 



This chart shows the average distribution of temperature with height (lapse rate) of 

 the mid-latitude atmosphere. Lines ending with the word "pause" indicates the 

 boundary between two spheres. These boundaries are not always well established. 



can attain escape velocity and leave 

 the earth entirely. The region in 

 which an atom can proceed outward 

 without colliding with other atoms is 



known as the exosphere, the true 

 outer limit of the neutral atmosphere. 

 The exosphere's presence can be de- 

 tected from the ground because hy- 



drogen scatters sunlight at night, but 

 its properties have been little ex- 

 plored. 



The Mesosphere — This region, 

 which overlaps the D region of the 

 ionosphere, is the object of much 

 current interest. It is a region of 

 extreme complexity, in which mete- 

 orological phenomena, mixing, and 

 photochemistry all play a part. It 

 is made up mostly of molecular ni- 

 trogen and oxygen, just like the lower 

 atmosphere, but it contains many 

 minor constituents which, because of 

 their chemical reactivity or ready 

 ionizability, dominate the energies of 

 the region. Among these are ozone, 

 atomic oxygen, nitric oxide, water 

 vapor, and many others. The region 

 has proved extremely difficult to ex- 

 plore directly, since the atmosphere 

 is too dense to allow satellites to 

 remain long in orbit and too high 

 for the balloon techniques that are 

 used at lower altitudes. Most existing 

 information has come from rocket 

 soundings, but even here the prob- 

 lems are severe because of the com- 

 paratively high density and the fact 

 that rockets generally travel through 

 the region at supersonic speeds, cre- 

 ating shock waves that disturb con- 

 ditions locally. 



The photochemistry of the region 

 has recently been under intensive 

 study, both through rocket experi- 

 ments and by way of laboratory 

 measurements of the rates of the 

 various key chemical reactions. A 

 broad picture of the important mech- 

 anisms is beginning to emerge, but 

 the roles played by transport and 

 movements in carrying constituents 

 from one point to another are still 

 largely unexplored. Of special im- 

 portance is the question of turbulence 

 in the mesosphere and its influence 

 on mixing of the various constituents. 

 Many of the problems of dispersing 

 pollutants in the lower atmosphere 

 arise from mechanisms similar to 

 those of distributing minor constitu- 

 ents in the mesosphere; many of the 

 photochemical reactions responsible 

 for smog formation are also the same. 

 Thus, the work presently being car- 



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