CLIMATOLOGY 



(frost snow) ; (5) drainage of this chilled and relatively 

 dense air to lower levels; (6) drifting of the snow with 

 the winds, and the consequent extension so far as tempera- 

 ture and other conditions will permit of the ice-covered 

 area.^ 



Hobbs believes that sufficient snow supply is obtained 

 in the interior of the plateau from ice crystals in the 

 cirrus clouds which descend in the interior of the anti- 

 cyclone and are first melted and then vaporized by the 

 adiabatic elevation of the temperature. The snowfall 

 resulting from these cirrus crystals in Hobbs' opinion 

 consists of those minute spicules and plates described 

 by sledgers near the Pole, which differ greatly from 

 the snowfall near sea level. (The present writer would 

 expect to find the cirrus layer at the Pole considerably 

 lower than the five miles indicated in Hobbs' figures.) 



G. C. Simpson in 1923 offered another solution which 

 in part combines the theories of Meinardus and Hobbs. 

 He writes : 



Over the snow-covered surface of the Antarctic, whether 

 at sea level or at the height of the plateau, radiation is so 

 strong that the air is abnormally cooled, especially in the 

 layers immediately above the surface. This cooled air is 

 heavier than the surrounding air, and therefore the pres- 

 sure increases from the exterior to the interior of the polar 

 area; in other words the pressure distribution is anti- 

 cyclonic and the air movement in general outwards. Above 

 each anticyclone a cyclone forms on account of the rela- 



3 Quoted by Hobbs, Glacial Anticyclones (New York, Mac- 

 millan, 1926), p. 182, as a good summary of his theory by 

 Humphreys. 



