CLIMATOLOGY OF THE PERUVIAN ANDES 



137 



border. It. also lies farther north, approximately in the latitude 

 of Lima, and this in part may help to explain the greater cloudi- 

 ness and rainfall. The rainfall for the year 1889-1890 was 6.14 

 inches, of which 3.94 fell in February. During the winter months 

 when the principal wind observations were taken, over 90 per cent 

 showed noon winds from a southerly direction while in the early 



6.30-7 a.m. 



11-12 a.m. 



6 p.m. 



Cloudiness 



Completely- 

 Overcast 



\ZZ\ Clear HM] 0-2.5 Eftl 2.5-7.5 IB 7.5-10 



Fig. 89 — Cloudiness at the desert station of Fig. 88 (near Caraveli), for the 

 summer (January to March) of 1913. 



morning northerly winds were frequent. It is also noteworthy 

 that the "directions of the upper currents of the atmosphere as 

 recorded by the motion of the clouds was generally between N. and 

 E." Plainly we are in the border region where climatic influences 

 are carried over from the plateau and combine their effects with 

 those from Pacific sources. Arequipa, farther south, and at an 

 altitude of 7,550 feet, resembles Chosica. For the years 1892 to 

 1895 its mean rainfall was 5.4 inches. 



Besides the seasonal variations of precipitation there are 

 longer periodic variations that are of critical importance on the 

 Coast Eange. At times of rather regular recurrence, rains that 

 are heavy and general fall there. Every six or eight years is said 

 to be a period of rain, but the rains are also said to occur some- 

 times at intervals of four years or ten years. The regularity is 

 only approximate. The years of heaviest rain are commonly as- 

 sociated with an unusual frequency of winds from the north, and 

 an abnormal development of the warm current, El Nino, from the 



