Continental Winds. 567 



the rainfall heaviest at just the season when crops need 

 most water. 



722. The World Winds of January. The prevailing 

 winds of the world, as they are observed during the month 

 of January, are represented in Fig. 263, the lines of black 

 circles showing where the modified tropical high pressure 

 calm belts are situated, and the light circles showing where 

 the equatorial calm belt and other low pressure areas are. 



In the southern hemisphere, where it is summer, and 

 where the amount of land is small compared with the 

 water, the tropical high pressure calm belt is crowded to- 

 ward the pole on the land and the air is heaped up on the 

 water, and the arrows show that the wind blows toward 

 ,the land ; but in the northern hemisphere, where it is win- 

 ter, and where the amount of land is much larger, it is 

 also drawn toward the poles by the extreme cold of the 

 land, while a low area is formed over each of the northern 

 oceans. The wind blows off both continents onto the two 

 oceans and there are upper currents tending toward the 

 land from the low areas. 



The equatorial calm belt is farther south everywhere, 

 but especially so over South America and over Africa and 

 Australia, where the land becomes warmest. 



723. World Winds in July. At this time of the year, 

 when the northern hemisphere has the vertical rays of the 

 sun and the longest days, the large masses of land have be- 

 come over-heated, the equatorial calm belt has been drawn 

 northward and expanded into wide continental low areas, 

 crowding the high pressure belt of the Tropic of Cancer 

 upon the Atlantic and Pacific oceans, as represented in 

 Fig. 264. The warm air rising over the continents and 

 flowing over upon the oceans makes high pressure there 

 and low pressure over the land, and this brings surface 

 winds and moisture from the sea, giving rains to the land 

 in the summer season. 



