METEOROLOGICAL RECORDS 



159 



Direction of wind 



N. W. 

 W. ... 

 S. W. 



s 



S. E. . 



E 



N. E. . 

 CALM 



Percentages of Total Observations 2 



Aug. 20 



— 



Sept. 30 



7 a. m. 



1 p. m. 



7 p. m. 



15.6 



8.0 



14.2 



28.1 



40.0 



40.0 





4.0 



5.7 

 2.8 



2.8 









12.5 



8.0 



2.8 



18.8 



12.0 



8.6 



25.0 



28.0 



17.1 

 5.7 



Oct. 1 



— 



Nov. 6 



7 a. m. 



1 p. m. 



7 p. m. 



6.7 











13.3 



35.3 



30.7 



6.7 



11.8 



11.1 



3.3 



5.9 



16.7 

 5.5 



S 3 







40.0 

 13.3 

 16.7 



23.5 



5.9 



17.6 



11.1 

 8.3 

 8.3 



The high percentage of northwest winds during afternoon 

 hours is due to the up-valley movement of the air common to almost 

 all mountain borders. The air over a mountain slope is heated 

 more than the free air at the same elevation over the plains (or 



N N _ N 



7 a.m 



1 p.m. 



7 p.m. 



Fig. 100 — Wind roses for Maehu Piceliu, August 20 to November 6, 1912. 



lower valley) ; hence a barometric gradient towards the mountain 

 becomes established. At Machu Picchu the Canyon of Torontoy 

 trends northwest, making there a sharp turn from an equally 

 sharp northeast bend directly upstream. The easterly components 

 are unrelated to the topography. They represent the trades. If 

 a wind rose were made for still earlier morning hours these winds 

 would be more faithfully represented. That an easterly and 

 northeasterly rather than a southeasterly direction should be as- 

 sumed by the trades is not difficult to believe when we consider 

 the trend of the Cordillera — southeast to northwest. The observa- 



* Percentages given because the number of observations varies. 



