52 



WEATHER AND CLIMATE 



general climate of a region averages about the same 

 year after year and changes only slightly over long 

 periods. 



It is perfectly natural that people should think that 

 climate changes frequently, for we are continually ex- 

 periencing changes in the weather from hour to hour 

 and day to day. Temperature changes, winds change, 

 pressure changes, and relative humidity changes, and 

 yet when each of these factors is averaged, year after 

 year, about the same result for a given locality is ob- 

 tained. This average of all the weather conditions is 

 spoken of as the climate of that region. 



There are many types of climate on the earth. The 

 polar regions, both Arctic and Antarctic, are ice-: 

 bound wastes where the temperature stays most of 

 the time below the freezing point of water. There is a 



International News Photos, Inc. 



FIG. 83. THE CLIMATE OF THE POLAR REGIONS 



band about 1500 miles wide on either side of the 

 equator encircling the globe where one may encounter 

 the highest temperatures, luxuriant growth, freezing- 

 temperatures and no growth, the most arid parts of 

 the world, and the regions of greatest moisture or 

 relative humidity. This is due principally to variations 

 in rainfall and altitude. England is farther north than 

 New York, and yet its climate is much milder. The 

 climate of regions near bodies of water is much more 

 moderate than regions in the same latitude but away 

 from water. A city that has a high altitude may ex- 

 perience a much different climate from that of one 

 nearby but at a lower altitude. Study the pictures of 

 this topic and learn all you can from them about the 

 varied climates of the world. 



The earth is divided into climatic zones. Figure 84 

 shows these zones and their boundaries. The Torrid 

 Zone is the largest, extending 23 l / 2 degrees on either 

 side of the equator. In the Northern Hemisphere the 

 Torrid Zone is separated from the North Temperate 

 Zone by an imaginary line known as the Tropic of 



Cancer and in the Southern Hemisphere from the 

 South Temperate Zone by a similar line, the Tropic 

 of Capricorn. The North and South Temperate Zones 

 are 43 degrees in width. The North Temperate Zone 

 extends from the Tropic of Cancer to the Arctic Circle 

 and the South Temperate Zone from the Tropic of 

 Capricorn to the Antarctic Circle. The North Frigid 

 or Arctic Zone lies between the Arctic Circle and the 

 North Pole, while the South Frigid, or Antarctic Zone 

 is between the Antarctic Circle and the South Pole. 

 Each of the two frigid zones extends 23^ degrees 

 from the pole. 



The boundaries of the zones of the earth are estab- 

 lished by astronomy. The boundaries are based upon 

 the following facts : that the earth is inclined on its 

 axis 2Zy 2 degrees to the plane of its orbit, that it ro- 

 tates on its axis, and that it revolves about the sun. 

 When the earth is in such a position in its orbit that 

 the North Pole is toward the sun, the sun's rays just 

 cover the North Frigid Zone. In other words, they 

 extend as far as the Arctic Circle. This occurs about 

 June 21 of each year. Six months later when the earth 

 has moved half way around its orbit, or about De- 



J_RO_PK: o\ CANCER 



FIG. 84. CLIMATIC ZONES 



cember 21, the South Pole is toward the sun and the 

 rays extend 23^ degrees from this pole, or as far as 

 the Antarctic Circle. In other words, they cover the 

 South Frigid Zone. 



The Tropics of Cancer and Capricorn represent the 

 farthest points north and south of the equator that 

 the vertical rays of the sun strike. 



