20 METEOROLOGY 



45° F. (23'3° C. to 25° C.) the temperature in one case rising, at Cape Boyds from 

 — 30° F. to 15° F. (— 34° C. to — 8° C). While there are obvious reasons for 

 beheving that some of this rise of temperature is due to Fohn effect, and caused by 

 the compression of air diving from a height on to the South Pole Plateau, and thence 

 diving again on to the Ross Barrier, we consider that the Fohn effect is not by any 

 means responsible for it all, but that the rise of temperature, as Commander 

 Hepworth has suggested,* is due in a great measure to the rapid transfer of warm 

 air at a high level in the Antarctic cyclone to replace the air that is lost during a 

 blizzard originating near the Temperature Pole. 



Finally in regard to the temperature of the Antarctic Regions as compared with 

 the Arctic, the following explanations of well-known facts, though obvious, have not, 

 as far as we are aware, found their way into text-books, so that we may venture to 

 quote them here. 



Antarctica differs from the Arctic chiefly in the lowness of the Antarctic summer 

 temperature, and the lesser cold of Antarctica as compared with the Arctic in their 

 respective winters. According to Hann's figures the mean winter temperature at 

 the North Pole in January is — 4r8° F., whereas in the corresponding winter month, 

 July, in the Southern Hemisphere the mean temperature is about — 28° F.f This 

 greater winter cold in the Arctic as compared with the Antarctic is surely due 

 chiefly to the geographical differences between the North and South Poles 

 respectively. In winter not only is the whole of the Arctic Ocean frozen over, but 

 the isotherm of freezing is down to a mean position in January of about 48° N. lat. 

 In the month of July in the Southern Hemisphere the mean isotherm of freezing is 

 situated in about 55° S. lat. This gives an area below freezing in the month of 

 January in the Northern Hemisphere half as much again as that at a similar 

 temperature during the winter of the Southern Hemisphere. Thus there is a mass 

 action tending to increase cold in the Northern as compared with the Southern 

 Hemisphere winter. The cold is further increased in the Northern Hemisphere 

 by the surface relief, which is the very opposite in the two hemispheres. In the 

 Southern Hemisphere the normal curve of the earth spheroid is bulged outwards into 

 a huge dome which acts at once as a gigantic starter of convection currents, and so 

 leads to a rapid interchange of air between the Temperature Pole and warmer 

 regions ; on the other hand, the Arctic Ocean is encircled by land much of which 

 being fairly high acts as a wall of circumvallation to retain the cold air at the North 

 Pole during winter, and by keeping it from moving checks convection currents, and 

 stops access of warmer air from the south. On the other hand, in Antarctica, even 

 in the depth of winter, no part of the continent is more than 1000 miles distant from 



* " National Antarctic Expedition," 1901-4. " Meteorology," part i. p. 449. 



t We have now the information that Amundsen found the mean temperature, for August 1911, at 

 the edge of the Ross Birrier, in the Bay of Whales, at Framheim no less th.in -IS-loF. (-44-5° C). 

 Thi'» may modify the above argument in so far as relates to winter temperatures in Antarctica. 



