148 



DISCOVERY REPORTS 



STATION NUM6ER5_W5E36 

 MILES FROM COAST _ ' 50 



WSG43 



WS64I 

 W5642 |W56C 



18-12° S: SAN JUAN AND CALLAO 



The meteorological and hydrological conditions off San Juan and Callao present an 

 interesting contrast with one another and with those off Arica (compare Figs. 4 and 16 

 and also 31-33). At Arica in calm wind-free conditions, surface isotherms were bunched 

 close to the coast, yet upwelling and northerly current were strong inshore. Off San 

 Juan a strong south-east wind blew and upwelling was such that the surface isotherms 

 spread out from the coast. Off Callao the wind lay towards the shore, with a slackening 

 of upwelling and with the surface isotherms again bunched close to the shore. ^ 



Off San Juan the volume of cool water was greater than at any region hitherto 

 examined. Upwelling phenomena were evidently at their height, and the temperature 

 rose from 13-79 to I9'25° C. at 95 miles offshore. Beyond this the ship crossed a patch 

 of water, warmer than the sea on either side, and which appeared to differ from the 

 surrounding water in its movement (see p. 

 129). It was some 50 miles wide and had 

 a maximum temperature of about i9'48^ C. 

 A warm wedge of very similar water was 

 met later off Callao where it was also about 

 the same width but closer to the coast; 

 here its direction of movement was not 

 noted. Northwards of Callao the wedge 

 was traced to the Guanape Islands and 

 possibly beyond, and later in the season it 

 was again identified off Callao (see p. 171). 

 Its appearance in section is seen in Figs. 

 32, 33 and 52. 



The absence of current at Callao, the on- 

 shore wind and the closing of surface iso- 

 therms with the coast, indicate that the 

 temperature section illustrated in Fig. 32 

 may be a record of subsidence and not of 

 an upwelling of cool water. This conclusion 

 receives further support from observations 

 of a seasonal character given on pp. 169- 



171 Fip CT F'g- 3'- Distribution of temperature (° C). Section 



rp, „ .,, , . off Arica, June 19-20. The position of this section is 



Ihese features are illustrated m the ^hown in Figs. 3 and 1 1 ; the corresponding saUnity 



curves of surface temperature along the section, in Fig. 43. 



path of the current (Fig. 34). Curves illus- 



1 It should be understood that in this account the observations are presented in chronological order and 

 that the hydrological conditions are therefore traced from south to north. To avoid inconsistency in treating 

 the subject as a whole, it is necessary, also, to trace counter-currents against their direction of flow. The 

 reader is asked to bear this in mind, particularly in the description of the warm wedge ; conclusions on its 

 nature will be drawn after the evidence of salinity and of other data has been considered. 



200- 



SOUNDING IN METRES_a277 



