124 DISCOVERY REPORTS 



force, and this region has received the name of the "roaring forties". Here the depressions almost 

 invariably pass to the southward and merely cause a variation of the wind from south-west to north- 

 west. South of 50° S barometric depressions travel in an eternal procession from west to east, with 

 their centres sometimes in about 50° S, sometimes near the Antarctic circle. On the northern sides 

 of these depressions the winds are westerly, and on their southern sides easterly, hence along the 

 trough of lowest pressure in 60° S, where the depressions are most frequent, the winds are very 

 variable. 



The departure of the coastal winds from directions more typically those of the trade 

 winds is a constant feature of the coast and was noted by Dampier as early as 1684. 

 It may be regarded as evidence of the fact that the surface air circulation of the Pacific, 

 which reaches a total height of little more than 5000-6000 ft., is cut off from that of the 

 Atlantic by the lofty barrier of the Andes. This has been suggested earlier by Mossman 

 (1909): 



There can be little doubt that the influence of the mountain chain of the Andes in modifying the 

 general circulation of the air is considerable, causing the coastal winds to conform to the shores of 

 the littoral, and to blow parallel with the main axis of the Andean Cordilleras. 



The suggestion made earlier, that the division between the areas of high and low 

 pressure lay at the time of our survey in 38° S, is no more than approximation. Moss- 

 man has been able to give figures to show that in normal conditions the division is 

 situated close to the 41° parallel. 



Bowman (1916) draws attention to a wind of local importance in the sea-breeze which 

 he describes as "without exception the most important meteorological feature of the 

 Peruvian coast " ; and the data he illustrates shows that this effect is conspicuous at least 

 as far south as Iquique on the Chilean coast. Off Callao, diurnal periodicity was de- 

 scribed at least as early as 1806 (Unanue). While the ship's movements prevented the 

 collection of data in sufficient detail to illustrate the significance of this sea-breeze, 

 our observations, and especially at Pisco (see Appendix IV, p. 259), are believed to lend 

 some support to its existence. Bowman gives the following description of it : 



Several graphic representations are appended to show the dominance of the sea-breeze (see wind 

 roses for Callao, Mollendo, Arica, and Iquique), but interest in the phenomenon is far from being 

 confined to the theoretical. Everywhere along the coast the virazon, as the sea-breeze is called in 

 contradistinction to the terral or land-breeze, enters deeply into the affairs of human life. According 

 to its strength it aids or hinders shipping; sailing boats may enter port on it or it may be so violent, 

 as, for example, it commonly is at Pisco, that cargo cannot be loaded or unloaded during the after- 

 noon. On the nitrate pampa of northern Chile (20-25° S) it not infrequently breaks with a roar that 

 heralds its coming an hour in advance. In the Majes Valley (12° S) it blows gustily for a half-hour 

 and about noon (often by eleven o'clock) it settles down to an uncomfortable gale. For an hour or 

 two before the sea-breeze begins the air is hot and stifling, and dust clouds hover about the traveller. 

 The maximum temperature is attained at this time and not around 2.00 p.m. as is normally the case. 

 Yet so boisterous is the noon wind that the labourers time their siesta by it, and not by the high tem- 

 peratures of earlier hours. In the afternoon it settles down to a steady, comfortable, and dustless 

 wind, and by nightfall the air is once more calm. 



The possible influence of this factor in relation to the hydrology of the coastal waters 

 is considered on pp. 210, 232 and 233. 



