CHAPTER VII. 



THE GENERAL AIR CIRCULATION OVER THE ANTARCTIC. 



As stated at the commencement of the last chapter it was originally thought that atmos- 

 pheric pressure decreases from the belt of high pressure near latitude 35° S. right up to the 

 South Pole. The discovery of the high easterly winds south of latitude 40°, however, shows 

 that this is impossible. 



In 1893 * the significance of these easterly winds was clearly recognised and the existence 

 of an anticyclone over the Antarctic was postulated to account for them. Later expeditions 

 confirmed an increase of pressure with increasing latitude south of about latitude 6()° S. and 

 the idea of an anticyclone over the region within the Antarctic Circle was confirmed. The 

 Antarctic anticyclone now became as firmly fixed in the minds of meteorologists as the idea 

 of the Polar cyclone had been previously. 



We have already seen that it occupies a very prominent part in Lockyer's scheme of the 

 air circulation over the southern hemisphere, and Hepworth and others speak of it as if 

 it were an undoubted feature of the Antarctic. Hobbs goes still further and contends that 

 an anticyclone exists over every extensive snow-covered land, and takes the Antarctic and 

 Greenland as the two most pronounced examples. To the anticyclones which owe their origin 

 to a snow-covered land Hobbs has given the name ' glacial anticyclone ' and he has worked 

 out at considerable length the meteorological featiu-es of such anticyclones. His conclusions 

 as to the conditions over the Antarctic are so important that they must be considered in 

 detail here. 



Hnhhs' Theory of the Glacial Anticyclone.^ — Hobbs summarizes the evidence for fixed glacial 

 anticyclones under the following eight headsj : — • 



(1) Centrifugal flow of surface air currents above inland-ice masses. 



(2) Outward (centrifugal) sweeping of surface snow largely derived from the central 



areas, and its deposition and accumulation as a marginal fringe about the inland- 

 ice. 



(3) Snow in large part wind-driven above the sloping portions of the ice mass. 



(4) Sudden warming of the air at the end of the blizzard — fohn effect in descending 



currents. 



(5) Behaviour of upper air currents and movements of the cirri. 



(6) The evolution of the Antarctic blizzard and its termination. 



(7) Areas of relative calm corresponding to the flat central bosses of the ice domes. 



* Frioker. Journal of the Royal Geographical Society, Volume II, page 254, 1893. 

 Murray. Journal of the Royal Geographical Society, Volume III, pa^e 17, 1894. 

 ■]• Tho Rolo of the Glacial Anticyclone in the Air Circulation of ths Globe, by W. H. Hobbs. Proo. American 

 Pliilosophical Society, Volume LIV, No. 218, August 1915. 

 ^ J Ibid; page 689. 



