ix Climates of the World 139 



from the west. The same action is seen on the west coast 

 of South America, but there the uniform face of the Andes 

 deflects the wind back again. On the eastern shores of 

 the southern continents the monsoon effects strengthen the 

 prevailing trade winds. 



194. Winds of the Northern Hemisphere in January. 

 The north tropical zone of high pressure forms a con- 

 tinuous belt round the world, narrow over the oceans, but 

 extending right up to the polar regions over the two 

 northern continents. Over these continents, air is continu- 

 ally descending from the upper atmosphere, where its place 

 is being taken by the air driven up from over the northern 

 oceans and southern continents. The Arctic low-pressure 

 area is cut up into two comparatively small depressions, 

 one with its centre between Iceland and Greenland, the 

 other in the North Pacific Ocean. In consequence of this 

 arrangement the north-east trade winds of the Atlantic blow 

 into the Carribean Sea and against the coast of South 

 America beyond the equator, and under the influence of the 

 South American low-pressure area, unite with the south- 

 east trades, blowing up the valley of the Amazon, and 

 obliterate the belt of calms along the coast. The North 

 Atlantic low-pressure area, while maintaining the south-west 

 winds of western Europe, draws in cold north-east winds 

 on the east coast of North America. The high pressure 

 over North America gives rise to monsoon winds which 

 attain considerable force as north-westers along the west 

 coast of Central America, and also sets up prevailing 

 northerly winds down the Mississippi valley. 



195. Winter Monsoon of Indian Ocean. About the 

 month of October, when the pressure over the great Asiatic 

 continent becomes higher than that over the ocean, light 

 northerly winds set in in the Bay of Bengal and the 

 Arabian Sea, gradually changing to north-east winds at 

 sea, where they represent the trade winds, but rarely 

 attaining great force, and often broken by calms. Along 

 the base of the Himalayas in the plain of the Ganges the 

 wind is north-westerly. This state of matters lasts for 

 several months, coming to a climax in January. Over 



