UPWELLING AND LOCAL WIND 209 



Salaverry), the wind blew predominantly from the east to east-south-east and the 

 isotherms of 20, 19, 18 and 17° C. were at 55, 46, 42 and 14-5 miles from the shore 

 (pp. 152-3). Then the wind changed to south-west and south-south-west, and on the run 

 seawards from the Guahape Islands on a line not far from the first, it was discovered 

 that all isotherms had moved closer inshore : the same isotherms were found at 46, 34, 

 29 and 8-5 miles respectively. As at Antofagasta, divergence and convergence of the 

 surface water with the coast — of which upwelling and changes of surface temperature 

 are indices — appear to show some dependence on local wind. Off this coast the south- 

 east wind is approximately parallel to the shore, and the deflection westwards of surface 

 waters is again to be interpreted as showing the influence of the earth's rotation. The 

 closing of surface isotherms with the coast during the south-westerly onshore wind 

 shows that the forces leading to divergence had relaxed, and it is possible that sub- 

 sidence of the heavier inshore water was in progress. 



At the same time it is also possible that the cool inshore water was carried away by 

 current towards the north (Table I), and that the warm off'shore water was brought 

 nearer to the coast through a modification of the anticyclonic swirl described on p. 192. 

 Reference to Fig. 63 will show that a shift of surface isotherms towards the coast would 

 follow if — and in fact might be evidence that — the southern end of the swirl and par- 

 ticularly the convergence of the warm wedge with the coast had travelled northwards. 

 Movement of the kind might take place with or without simultaneous subsidence of the 

 inshore water. 



Callao 



The third illustration is provided by a series of observations outside Callao, off the 

 island of Palominos, which was visited on eight occasions between June 26 and August 

 20. The graph in Fig. 51 shows that the observations fall into three periods. During 

 the first the water at all depths experienced a rise of temperature amounting at the 

 surface to a mean daily rise of 0-04^ C. ; during the second period a fall of 0-082° C. per 

 day; and during the third a rise of 0-065° C. P^"" "^^Y- Corresponding with these 

 changes of temperature the wind direction and force changed too. During the period of 

 strong upwelling the wind had the greatest easterly component and blew with a mean 

 velocity of 7 m.p.h. During the periods of weak upwelling or of subsidence the wind 

 blew less vigorously and with a smaller easterly component. Although this, in principle, 

 tallies with other observations, the change in hydrological conditions seems excessive 

 when set against the wind alteration. 



These changes, together with other data, have been cited on p. 194 as evidence of the 

 possibility that on or before June 26 the warm wedge was converging with the coast 

 southwards of Callao. Between July 8 and 1 1, on the other hand, temperature observa- 

 tions suggest convergence of the wedge northwards of Callao {vide supra, withdrawal of 

 cool water from the Guanape Islands). These data, considered in relation to the 

 observations off Palominos Island (Fig. 51), suggest that the temperature off Palominos 

 rose with the approach of the warm wedge from the south and sank with its withdrawal 

 to the north. Observations after these dates are too scanty to show whether the further 



