Tables 753 and 754 599 



TABLE 753. — Ionization in the Upper Atmosphere of the Earth 



(Hulburt, Phys. Rev., 34, 1167, 1929; 35, 24, 1930; 37, i, 1931.) 



Each cm 3 of the upper atmosphere is assumed approximately electrically neutral. Above 

 60 km the ionization is assumed to be caused by solar ultra-violet light ; below, by cosmic 

 radiation. At any height s km above sea-level, let the numbers per cm 3 of singly-charged 

 positive ions, negative ions and electrons be y+, y- and ye. Then y+ = y- + ye, and since ye 

 is in general small compared to y-, the values of y + and y- are nearly equal. Above 60 km 

 the positive ion densities y + are given in Table 754- The electron density ye increases with 

 rtoa max. value ye at a height : m ; y e max. and cm are given in Table 754a. Above and 

 below the max. y e can not yet be estimated with certainty. The values for y + and ye max. 

 may be correct within a factor of 2 ; a zero value means a small value. The tables are for 

 average equinoctial conditions and solar quiescence, halfway between the periods of max. 

 and min. solar activity. The values should be increased and reduced by roughly 2570 to 

 refer to epochs of max. and min. solar activity. During magnetic storms the ionization 

 increases, being perhaps double the tabular values for a severe storm. In polar regions it is 

 probably not greatly different from that for latitude 6o°. The seasonal changes are small 

 at the equator. In temperate latitudes for winter and summer use the values for latitudes 

 about 20 higher and lower. Below 60 km the ionization due to cosmic radiation is mde^- 

 pendent of the latitude, hour of the day, solar activity, etc., and y + is 8X 10, 1.0 X 10, 

 1.9 X io 3 , 2.2 X io 3 , 2.9 X io 3 , and 3.5 X io 8 at 0, 10, 20, 30, 40, and 50 km. 



TABLE 754. — Ion Density y f in the Upper Atmosphere 



Noon 



3 p. m. or 9 a. m. 



6 p. m. or 6 a. m. 



Smithsonian Tables 



