THE THUNDERSTORM— EVANS AND McEACHRON 



183 



Watt ^^ has pointed out, the difficulties involved in obtaining accurate 

 information on the processes going on in thunderclouds are tremen- 

 dous, and it is probable that it will be a long time before sufficient 

 knowledge can be obtained to solve the problem. 



BANERJI'S THUNDERSTORM MODEL 



Banerji ^* ^^ has proposed a thunderstorm model, shown in figure 2, 

 in which a region of high negative charge concentration precedes a 



10 



COOL 

 MOIST 

 SEA 

 AIR 



warm 

 moist a- 

 hiqhiu 

 unstable 

 inland air. 



60 



50 



40 30 20 



Distance in Kilometres 



10 



^(y 







Colabaf 

 Observatoni 



Royal Meteorological Society 



Figure 2.— Distribution of electrical charge in a thunderstorm. 

 (After Banerji.) 



region of high positive charge concentration, at the front of the 

 cloud. Jensen has photographed lightning discharges while recording 

 the instantaneous field changes caused by them. His results appear 

 to favor Banerji's storm model. Plate 1, figure 2, is a composite 

 picture, taken by Jensen,^^ showing two discharges half a minute 

 apart at t^e front of a storm. The cloud is moving from left to right. 

 The discharge to the right was from a negatively charged region in 

 the cloud, while the one to the left was from a positively charged 

 region. This is in agreement with Banerji's prediction. 



" Watt, R. A. Watson, The present position of theories of the electricity of thunderstorms. Quart. Journ. 

 Roy. Meteorol. Soc, vol. 57, pp. 133-142, 1931. 



i« Banerji, S. K., The electrical field of overhead thunderclouds. Quart. Journ. Roy. Meteorol. Soc, vol. 

 56, pp. 305-331, 1930. 



'» Banerji, S. K., The electrical field of overhead thunderclouds, Phil. Trans. Roy. Soc, ser. A, vol. 231, 

 pp. 1-27, 1932. 



" Jensen, J. C, The branching of lightning and the polarity of thunderclouds, Journ. Franklin Inst., 

 vol. 216, pp. 707-748, Dec. 1933. 



