THE UPPER ATMOSPHERE DOBSON 



191 



If all the oxygen were separated from the other gases and formed 

 into a simihir layer by itself, it would make a layer about 1,700 

 meters deep. If the same were done for the ozone in the atmos- 

 phere, we should find a layer only about 3 millimeters deep on the 

 average. In other words the ratio of ozone to oxygen is as 3 milli- 

 meters to 1,700 meters. This small amount of ozone is not dis- 

 tributed uniformly through the atmosphere but is chiefly found at 

 great heights. There is a little present in the surface air and the 

 proportion of ozone to the other gases increases with height until 

 the maximum proportion is found at a height of about 35 kilometers. 



Besides varying with 

 the weather conditions, 

 the amount of ozone 

 in the atmosphere has a 

 well-marked seasonal va- 

 riation and also varies 

 from one part of the 

 earth to another in a reg- 

 ular manner according to 

 the latitude. Both these 

 effects are shown in fig- 

 ures 3 and 4, from which 

 it will be seen that the 

 amount of ozone is gen- 

 erally large in the spring 

 and small in the autumn. 

 This annual variation in- 

 creases from almost 

 nothing near the Equator 

 to a large range in high 

 altitudes. Moreover, the 

 total amount of ozone 

 is, in general, least at the Equator and greatest in high latitudes. 



It is however, the changes in the ozone content of the atmosphere 

 with weather conditions that is of the greatest interest. Figures 

 5 and 6 show a typical depression and anticyclone, the thin con- 

 tinuous lines being isobars. The thick broken lines indicate the 

 ozone distribution in these two pressure systems. The figures do 

 not relate to any one particular case, but are the result of measure- 

 ments on a large number of occasions. Any one particular depres- 

 sion or anticyclone may show minor differences, but the same gen- 

 eral features are found in nearly every case. 



The amount of ozone in the atmosphere is measured by spectro- 

 scopic observations of sunlight, in which the amount of the absorp- 



H lOH 



— - — Ozone 

 Presiure 



Figure 5. — Ozone in cyclonic areas. Tlie continuous 

 lines are drawn to represent a typical cyclonic 

 depression of middle latitudes. The thick broken 

 lines show the distribution of ozone : plus values 

 show that the ozone is above the normal, wkile 

 minus values show that it is below the normal. 

 Tslote the marked concentration of ozone to the west 

 and southwest of the center of the depression. 



