126 



THE ANDES OF SOUTHERN PERU 



JUNE 



JULY 



AUG. 



SEPT. 



sized, a condition clearly shown on the Pilot Charts of the South 

 Pacific Ocean, issued by the U. S. Hydrographic Office. 



The hydrographic feature of greatest importance is the Hum- 

 boldt Current. To its cold waters is largely due the remarkably 

 low temperatures of the coast. 1 In the latitude of Lima its mean 



surface temperature is about 

 10° below normal. Lima itself 

 has a mean annual tempera- 

 ture 4.6° P. below the theo- 

 retical value for that latitude, 

 (12° S.). An accompanying 

 curve shows the low tem- 

 perature of Callao during the 

 winter months. From mid- 

 June to mid-September the 

 mean was 61° P., and the 

 annual mean is only 65.6° P. 

 (18° C). The reduction in 

 temperature is accompanied by 

 a reduction in the vapor capac- 

 ity of the super-incumbent air, 

 an effect of which much has 

 been made in explanation of 



Fig. 76— Temperatures at Callao, June- 

 September, 1912, from observations taken 

 by Captain A. Taylor, of Callao. Air tem- 

 peratures are shown by heavy lines; sea 

 temperatures by light lines. In view of 

 the scant record for comparative land and 

 water temperatures along the Peruvian 

 coast this record, short as it is, has special 

 interest. 



the west-coast desert. That it is a contributing though not ex- 

 clusive factor is demonstrated in Fig. 77. Curve A represents 

 the hypothetical change of temperature on a mountainous coast 

 with temporary afternoon onshore winds from a warm sea. 

 Curve B represents the change of temperature if the sea be 

 cold (actual case of Peru). The more rapid rise of curve B 

 to the right of X-X', the line of transition, and its higher eleva- 

 tion above its former saturation level, as contrasted with A, 

 indicates greater dryness (lower relative humidity). There has 

 been precipitation in case A, but at a higher temperature, hence 



'Hann (Handbook of Climatology, translated by R. De C. Ward, New York, 1903) 

 indicates a contributory cause in the upwelling of cold water along the coast caused 

 by the steady westerly drift of the equatorial current. 



