256 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 13 



been necessary to construct a ten-foot stockade about the ranch house, 

 but even with this protection shutters must be provided for the window^s 

 so that the w^indow glass will not be abraded by the sand-blasting. On 

 Santa Barbara the intensity of the wind reaches an unknown maximum. 

 Twice the instrument station of the north peak was wrecked, the rain 

 gauge recording c^dinder blown out, the wire screen protecting the 

 instruments torn loose and blown over onto the east terrace. Twice the 

 anemometer on the ridge station was wrecked when the anemometer 

 cups were blown off. 



At Wilson Cove on San Clemente Island the average wind velocity 

 for the period from April 1, to June 30, 1940, was 11.8 miles per hour. 

 On the terrace south of the ranch house on Santa Rosa the average 

 wind velocity for a period of 193 days, from October 10, 1921, to May 

 13, 1922 was 12.0 miles per hour. It is interesting that the average 

 for the night hours was almost identical with that for daylight hours. 

 On the eastern bluff of Santa Barbara near the cabin the wind velocity 

 for the two years from March 26, 1940, to April 1, 1942, averaged 7.8 

 miles per hour. It should be noted that the anemometer here was only 

 7.5 feet from the ground, whereas the Weather Bureau anemometers 

 are usually placed thirty feet from the ground. On each of the three 

 islands referred to, the recording station was on the lee side of the island 

 and was operating for different periods of time. The observation that 

 the prevailing winds show less force on the south and east tends to be 

 confirmed. 



Observation of the more exposed sections of the islands indicates 

 that the winds there are much stronger, but reliable records are almost 

 wholly lacking. On Santa Barbara the anemometer which was twice 

 wrecked, situated 7.5 feet above the ground, gave a reading from Sep- 

 tember 11, 1940, to December 6, 1941, of 16.8 miles per hour for the 

 average wind velocity. The wind is the most powerful factor in the 

 environment of the island plant communities. Its variation is so great 

 from one topographical location to another that it appears to be the 

 most effective agent in the distribution and limitation of the communities. 

 This will be treated in more detail later. 



The maritime climate of the islands shows also the following char- 

 acteristics: (1) a mean noon relative humidity of over 60 per cent, (2) 

 a mean July temperature of less than 22°C. (71.6° F.), (3) an aridity 

 coefficient of 12 per cent or less (Gorczynski, 1940, p. 5), and (4) night 

 or morning low stratus or fog for the greater part of the year. 



The designation "foggy desert," as defined by Russell (1926, p. 

 79), might appear to be applicable to some of the southern islands. 



