METEOROLOGY I I I 



north-west. In winter the cold of the high veld raises the pressure 

 sufficiently to cause something of an outflowing monsoon, weaken- 

 ing the south-east trade. Dr. Brooks and Mr. Mirrlees relate the 

 distribution of rainfall in tropical Africa in each month of the year 

 to the main stream-lines of the circulation. Rain falls: (i) along the 

 line of separation or 'front' between currents of different physical 

 quality, as between the humid south-west monsoon and the dry 

 harmattan of the Guinea Coast; (2) where two or more stream- 

 lines converge, as in the case of northerly and southerly trade 

 winds meeting in the equatorial rain-belt; (3) where humid winds 

 meet or converge upon mountains, as in the Cameroons and 

 Abyssinia. 



A great contrast exists between West and East Africa in the 

 equatorial belt. In West Africa the equatorial rains are enormously 

 enhanced in their northern summer migration by the moist south- 

 west monsoon which interacts with dry winds from the north. In 

 East Africa, on the other hand, the local circulation is entirely 

 dominated by the centre of low pressure on the Persian Gulf. This 

 prevents the indraught of any moisture-laden monsoon, or any 

 convergence of air-currents over Italian Somaliland, where the 

 equatorial rains are almost entirely suppressed. 



The encircling equatorial rain-belt, which moves northward and 

 southward with the vertical sun, may be regarded as the main- 

 spring of the atmospheric circulation in the sense that its position 

 and intensity help to actuate the other wind and pressure belts of 

 the earth's surface. It is likely to be specially sensitive to any 

 periodic fluctuations in the output of solar energy. In view of the 

 probability that Abyssinia receives the whole of its summer rain, 

 which supplies the autumn Nile flood, from winds blowing ulti- 

 mately from the Gulf of Guinea, there is great need for meteoro- 

 logical stations capable of taking pilot balloon observations, in the 

 north part of the Belgian Congo and the south-west part of the 

 Anglo-Egyptian Sudan. 



CHANGES OF CLIMATE 



It is now well established that a pluvial epoch occurred in Africa 

 at about the same time as the glacial epoch in Europe, and that 



