THE MONSOONS OF THE CHILIAN LITTORAL. 139 



which flows along the west coast of South America, extending almost to Juan 

 Fernandez. 



The monsoonal effect varies greatly from year to year ; some years being character- 

 ised by weak monsoons, while in others the rain-bearing northerly air currents are 

 greatly intensified. There appears to be a very definite interrelation between the 

 position occupied by the Pacific and Atlantic " highs " and the Antarctic and sub- 

 Antarctic circulation which may help to throw light on the varying weather conditions 

 prevailing over the South American continent. To take merely a single instance, that 

 afforded by a comparison of the conditions from 20° to 65° S. for July of 1903 and 

 of 1904, based on returns from a large number of stations in South America and at 

 the Falklands, as well as the sub-Antarctic stations of the South Orkneys, Snow Hill, 

 and Wandel Island. In July 1903 the South Pacific " high," as shown by the winds and 

 pressure at Juan Fernandez, was well south of its normal position, and rainfall was 

 relatively small at all the Chilian coastal stations within the monsoonal area. In this 

 region southerly winds were in excess, and northerly winds, which bring the rain, in 

 defect of the average. Accompanying this excess of winds from higher latitudes, low 

 temperatures prevailed over Argentina and Chili, except in the extreme south of the 

 continent. Barometric pressure was below the normal at the South Orkneys and at 

 Snow Hill on the east side of Graham's Land, the Weddell Sea "low" being not only 

 deepened but lying farther west than usual. At Evangelists Island at the Pacific 

 entrance to the Straits of Magellan the weather was mild and precipitation high, the 

 same conditions extending to the Falklands and the South Orkneys, with westerly and 

 north-westerly winds predominating. 



In July 1904, on the other hand, conditions were exactly the reverse of the month 

 described. The South Pacific " high " was considerably to the north of the island of Juan 

 Fernandez, where barometric pressure was 0*38 inch lower than in the July previous, 

 while on the coast of Chili in the monsoon zone the fall of pressure averaged 0*20 inch 

 as compared with the July of 1903. A permanent low-pressure area lay off the coast 

 of Chili in lat. 42° S., as shown by the Daily Weather Maps of the Argentine Meteoro- 

 logical Office. To the north-west of this region of low pressure the prevailing winds, as 

 at Juan Fernandez, were from the west-south-west, while at coastal stations to the north 

 of it the winds blew from the north and north-west. All over this region deluges of rain 

 fell (see Table V.), the zone of heavy rainfall extending well into the centre of Argentina 

 between latitudes 38° and 45° S., and over to the Atlantic coast. With this excess of 

 equatorial winds, mean temperature was above the average. South of 45° S. the winds 

 were southerly, blowing in on the northern " low." Temperature in the southern provinces 

 of South America, at the Falklands, the South Orkneys, and Wandel Island was markedly 

 below the normal, the winds in general circulating round the Weddell Sea " low," which 

 was far to the east of its position in the July previous. Barometric pressure fell from 

 west to east south of 55° S., and was as high as 29*51 # inches at Wandel Island on the 



* At 32°, sea-level and standard gravity. 



