ii 



TEMPERATURE. 



gradient of 4°C. per 1,000 metres. It \vill be seen that with these assumptions the 

 temperatiue over the Barrier at 4,000 metres is only 2°0. lower than at the same height 



4000 



3000 



2000 



H 



m 

 en 



1000 



-40°c -30"c -20 c -io°c 



Temperature 



Fio. 14. Upper air temperatures over Ross Sea and Barrier. 



-0"c 



over the Ross Sea. Thus in 4,000 metres ascent the temperature difference between the 

 Barrier and the Ross Sea has been reduced from 14°C. to 2°C. 



An interesting and important consequence of this relationship is found when the tempera- 

 ture differences between the Barrier and the Ross Sea in July and January are compared. 

 On the right hand side of the diagram similar curves for January are shown. In this month 

 normal temperature gradients of about T'^C. per 1,000 metres probably exist always over both 

 the Barrier and the Sea. In consequence the full temperature flifference which exists near the 

 ground exists also at 4,000 metres. If the assumptions on which these curves are based 

 are true, the remarkable consequence results that the temperature difference between the 

 Barrier and the Ross Sea is less at 4,000 metres in July than in .January. In the next 

 section wo shall see that this conclusion is supported by the temperature observations during 

 \nnds. 



Temperature and Winds. 



The eifect of the wind on temperature is twofold — 



((«) the wind causes a mechanical mixing of the upper and lower strata which may 



appreciably affect the temperature near the ground ; 

 (b) the wind brings air from different geographical positions, which may be warmer 

 or colder according to the direction from which it comes. 

 With the vertical temperature distribution which we have seen exists over the Antarctic 

 during cold calm weather, the former of these two efiects nuist then play a large part. 



