ARCTIC INFLUENCES ON AMERICAN CLIMATE 4 1 



as do form in the north are of course characterized by fairly low 

 temperature and, as these pass southward and eastward, furnish the 

 conditions necessary for the production of rain. 



Arctic Influences on Labrador 



As a concrete instance of the effect of the Arctic, operative the 

 year round, there is probably no better example than that evidenced 

 by the climate of northeastern America, including the major portion 

 of the Labrador Peninsula. Over all this region the prevailing winds 

 have a northerly component in summer as well as in winter, this owing 

 not to abnormally high pressure in the north but to the fact that in 

 all seasons the mean path of cyclonic areas lies to the southward of 

 this region. 



In the colder months the barometric gradient for north and north- 

 west winds is steep, owing to the very low pressure south and east of 

 Greenland. In summer the gradient slackens, but, with the ever- 

 present tendency for cyclonic areas to pass from the Gulf of St. Law- 

 rence towards the Gulf Stream to the eastward, northerly winds are 

 all too prevalent. 



In the northern portion of this northeastern territory there are 

 vast tracts of land where the climate is so completely dominated 

 by Arctic influences that the country is treeless and agriculture is 

 impossible. 



The Northern Limit of Tree Growth and 

 Agriculture in Canada 



The region north and west of Chesterfield Inlet probably has the 

 coldest and longest winter, and thence southward and westward 

 conditions improve. The northern limit of tree growth runs from near 

 Churchill northwestward to the head of Coronation Gulf and thence 

 near the coast line to the mouth of the Mackenzie. The whole country 

 to the north of this tree limit is tundra, called in the early days of 

 exploration the Barren Grounds, and to the southward there is a wide 

 zone where agriculture can never be successful. Perhaps a line from 

 Fort Simpson drawn southeastward to Fort Albany on James Bay 

 may roughly represent the northern limit of land where agriculture 

 may be moderately successful in a fair percentage of years. 



In the Mackenzie valley south of Fort Simpson the rigors of a 

 sub-Arctic climate are gradually mitigated, and westward to the 

 Rocky Mountains, especially in the region of the Peace River, the 

 climate is intermittently dominated by Pacific Ocean influences as 

 represented by the chinook effect. 



