THE UPPER ATMOSPHERE^ 



By G. M. B. DOBSON, D. Sc, F. R. S. 

 Reader in Meteorology in the University of Oxford 



Recent progress in the investigation of the upper regions of the 

 earth's atmosphere has been mainly along two different lines. The 

 first is connected with what may be called the meteorological state 

 of the atmosphere, namely, its temperature, density, etc., while the 

 second has to do with its electrical characteristics. Many balloons 

 carrying meteorological instruments have been sent up, but the great 

 majority of these have failed to reach a height of 25 kilometers. In 

 a few cases where specially large balloons were used a height of 30 

 kilometers has been reached and a balloon sent up in Russia has 

 recently been reported to have reached 40 kilometers. In order to 

 obtain information about the atmosphere at still greater heights it is 

 necessary to employ indirect methods of exploring the atmosphere. 

 Fortunately, several such indirect methods are available and it is 

 our present purpose to describe them and the results that have been 

 obtained from them. 



Meteorological conditions helow 20 kilometers. — From the large 

 number of sounding balloons which have been sent up in many 

 countries carrying recording instruments the general meteorolog- 

 ical conditions of the air up to 20 kilometers are now fairly well 

 known. In the lower part of the atmosphere the temperature falls 

 with increasing height at a rate of about 6° C. for every kilometer 

 rise. The exact rate at which the temperature falls differs from day 

 to day and may be different at one height from that at another 

 height. The fall of temperature with height does not, however, con- 

 tinue indefinitely, but at some fairly well-defined height it stops 

 and the temperature from this point upward is found to change 

 but little as the balloon ascends to its greatest height. The height 

 where the temperature ceases to fall — known as the Tropopause — 

 is usually between 8 and 14 kilometers in Europe. 



The results from recording balloons thus show that the atmos- 

 phere is divided into two parts by its thermal structure; the lower 



1 Reprinted by permission from Science Progress, vol. 30, no. 117, July 1935. 



183 



