UPPER ATMOSPHERE — MASSET 



187 



This rules out solar electromagnetic radiation as the direct causative 

 agency. The alternative is a stream of corpuscles. This cannot con- 

 sist of charged particles of one sign, as their nnitual repulsion would 

 disperse the stream long before the earth was reached. It is supposed 

 that the stream is an ionized one containing protons and electrons in 

 equal concentration. Strong evidence for the presence of protons in 

 the incident stream has been afforded by the observations of Gartlein 

 [5] and of Meinel [6] of broad hydrogen lines in the auroral spectrum. 

 The broadening is due to a Dopj)ler effect which would be expected 

 if the lines were produced by fast incoming protons capturing elec- 

 trons from atmospheric atoms, and if some of these electrons were 

 captured into excited states. Radiation due to transitions from these 

 states would account for the observations. 



Altitude above sea level (km) 



Figure 4. — Observed decrease of magnetic field with height off the coast of Peru, using a 

 rocket-borne magnetometer. The sudden increase in the rate of fall of the field at 93 

 km. indicates the presence of a current layer at that altitude. 



There are a great number of problems still unsolved concerning 

 auroral phenomena. In some way the protons in the corpuscular 

 stream must be speeded up near the earth; if they had throughout 

 their journey the speed calculated from the time delay of auroral 

 onset they would not be energetic enough to penetrate to the levels at 

 which the auroral hydrogen lines are observed. The reason for the 

 concentration of auroral effects in a narrow belt of latitude in each 

 hemisphere is also far from clear. 



The night air-glow is a more or less steady emission of light from 

 the sky during the night, apart, of course, from starlight and any 

 moonlight. It is much weaker than the aurora and involves much less 

 energy. It is almost certainly due to transfer of some of the energy 

 stored up from sunlight during the day into radiation in the far 



