METEOROLOGY II3 



climate, by A. J. Brunt (1937). The fact that annual changes of 

 climate are more regular in tropical regions, especially over large 

 continents, renders Africa peculiarly favourable for the study of 

 cyclical variations, but unfortunately there are few records which 

 extend back to fifty years or over. The well-known Bruckner 

 cycles, with a periodicity of about thirty-five years, covering three 

 eleven-year cycles of sunspots, have been traced back in Europe 

 through several centuries. It appears, however, that 'generally 

 speaking the Briickner cycles characterize the higher latitudes 

 while the eleven-year cycle (i.e. one cycle of sunspots) is more 

 strongly expressed in equatorial regions.' Wayland (1935, p. 106). 



According to some authorities the sunspot cycle is felt with par- 

 ticular intensity in the East African region, where meteorology is 

 intimately bound up with hydrology. During the years of sunspot 

 minimum, solar radiation and hence evaporation are greatest and 

 rainfall is less than the average. This is reflected in the rise and fall 

 of the levels of the great lakes which offer enormous areas for 

 evaporation. The years of highest level have been roughly, 1895, 

 1906, 191 7, 1927-8, and the next is predicted for about 1939. 

 Dr. Brooks (1923) has shown that the levels of Lakes Victoria and 

 Albert rise and fall with a periodicity of about eleven years, the 

 lakes being high at sunspot maximum. He argues that, although the 

 rainfall over these basins is higher at sunspot maximum, the corre- 

 lation between lake levels and rainfall is much weaker than that 

 between lake levels and sunspot. Hence he concludes that the 

 physical explanation is to be sought in increased evaporation at 

 sunspot minimum, which is in keeping with the known fact that 

 the mean temperature in equatorial regions is about one degree F. 

 higher at sunspot minimum. 



A similar response to solar activity is disclosed by Dr. Dixey's 

 (1924 and 1927) researches into the level of Lake Nyasa, but the 

 relation here has been complicated by the blocking of the outlet 

 via the Shire river, which since 1920 led to a continuous rise in 

 lake level. The levels of Lake Tanganyika since 191 2 have been 

 made available by Gillman (1933), who shows that they too follow 

 the eleven-year cycle closely. His paper includes a series of graphs 

 bringing the data for Lakes Victoria, Albert, and Nyasa up to 

 1 93 1, but he adds a note of warning against premature generaliza- 



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