30 



SCIENCE 



[N. S. Vol. XL. No. 1018 



recent publication is a thorough treatment of 

 the complex rainfall conditions of California. 

 The chief factors controlling rainfall • there 

 are centers of action (" hyperbars and infra- 

 bars"), prevailing surface drift, ocean effect, 

 topography and ocean currents (including up- 

 welling cold water^). The influence of the 

 positions of the centers of action may be 

 summed up in this general law : " Typical wet 

 winters on the California coast occur when the 

 North Pacific low overlies the continent west 

 of a line drawn from Calgary to San Francisco. 

 Typical dry winters are associated with a west- 

 ward extension of the continental high to the 

 coast line and a retreat of the Aleutian low to 

 the northwest." The prevailing surface drift 

 of the atmosphere is northwest in summer but 

 southerly and westerly in winter. In winter, 

 these winds from the Pacific Ocean supply 

 ample moisture for rainfall where topography 

 causes them to rise. The complexity of ocean 

 currents and ocean temperatures on this coast 

 may locally affect rainfall. 



The rainfall resulting from the combination 

 of these factors is moderate to heavy (more 

 than 2,000 mm.) on the west slopes of the 

 coast ranges and Sierra Nevadas, but light on 

 the east side. On the wfist slopes of the Sierras 

 from the floor of the Great Valley to an alti- 

 tude of 1,500 meters, the rainfall increases on 

 the average about 75 mm. per 100 meters of 

 ascent. Above 1,500 meters, the rainfall seems 

 to decrease slightly with altitude. The rate 

 of decrease of rainfall with decreasing altitude 

 down the east slope is variable, depending on 

 the height and the rainfall of the mountain 

 crest. On the line of the Central Pacific Eail- 

 road, the rainfall decreases 14Y mm. per 100 

 meters of descent. In southern California, the 

 zone of maximum rainfall is much higher, and 

 the rate of increase with altitude is about 50 

 mm. per 100 meters up to 2,500 m. The de- 



1 This upwelling is most marked in summer and 

 is caused by the strong northwest winds of the 

 great North Pacific high: G. F. MeEwen, "Pecu- 

 liarities of the California Climate," M. W. B., 

 January, 1914, pp. 14-23. See also, W. G. Reed, 

 "The Japan Current and the Climate of Cali- 

 fornia," M. W. S., February, 1914, pp. 100-101. 



tails of California rainfall are shown in com- 

 prehensive tables. 



Parts of . California are subject to excessive 

 rains. These rains are of the cloudburst tjrpe 

 in the drier areas. In the wetter portions, the 

 excessive rains are less intense but of greater 

 duration. A large table of excessive precipi- 

 tation is given. In the high mountains, snow- 

 fall, so important for irrigation and water- 

 power, is very heavy. Special attention is 

 paid to the snowfall and melting of snow on 

 the ground at Summit (alt. 2,138 m.). The 

 average annual snowfall there is more than 

 1,000 cm. Tamarack, a station at 2,438 m. 

 altitude, has an even heavier snowfall. In 

 the table, a snowfall of 2,260 cm. is indicated 

 in the winter of 1906-07. The record maxi- 

 mum for any month was 998 cm. in January, 

 1911. The rainfall of San Francisco is treated 

 in detail at the end of the memoir.^ 



THE MONTHLY WEATHER REVIEW 



The Monthly Weather Review with the 

 January, 1914, issue has reverted to the more 

 or less popular form it had until July, 1909. 

 The material is classified under the heads (1) 

 Aerology, (2) General Meteorology, (3) Fore- 

 casts and General Conditions of the Atmos- 

 phere, (4) Eivers and Floods, (5) Bibliography, 

 (6) Weather of the Month. Some of the 

 articles' in the January and February num- 

 bers are briefly considered below. 



Lorin Blodget's " Climatology of the United 

 States " : An Appreciation. By Robert DeC. 

 Ward. (Pp. 23-27.) This great work, a pio- 

 neer in its field, receives deserved praise and 

 attention in this article. Professor Ward 

 quotes many of the happy and vivid descrip- 

 tions of the climate of the United States and 

 its human effects which are as valuable to-day 

 as ever. Evidently little has been added to 

 our knowledge of the general conditions and 

 controls of the climates of the United States 

 in the last fifty years. The advance has been 

 chiefly in the study of the details. 



" The Meteorological Aspect of the Smoke 



2 Cf. also W. G. Heed, ' ' Variations in Eainf all 

 in California," M. W. S., November, 1913, pp. 

 1785-1790. 



