TEMPERATURE AND WIND. 51 



wind brought with tbem comparatively high temperatures, while, when the southerly wind 

 set in, the temperature dropped rapidly and remained low so long as the wind continued. 



The examples given above have had to be restricted in number, and therefore only 

 typical cases have been chosen from the large number available. It goes \vithout saying that 

 the direct relationship between wind and temperature was not always so clearly shown as 

 in the cases illustrated ; but the relationship is more or less discernible throughout. The 

 raising of the temperature by all winds in the winter and the dependence of the temperature 

 on the wind direction in the summer are the two outstanding features of the relationship 

 between wind and temperature at Cape Evans. 



The large rise in temperature caused by southerly blizzards during the winter was first 

 observed on the Discovery Expedition. The true cause was not realised, and the explanations 

 then given have led to two very erroneous ideas becoming firmly fixed in meteorological 

 literature. They are both included in the following paragraph taken from page 424 of the 

 discussion of the meteorological results of the Discovery Expedition. 



' The rise of temperature in these gales from south-east and east-south-east, doubtless, 

 is in some measure due to the fohn effect produced dynamically by the descent 

 of air from the mountain tops, and also to the check given, by wind in motion, 

 to cooling by radiation. But may it not, to some extent at least, be attributed 

 to the conveyance of warmer air drawn from lower latitudes, circulating about a 

 low pressure system and conveying to the locality the higher temperatur-es of the 

 region whence it originated ? ' 



These explanations have been generally accepted and quoted in nearly every paper dealing 

 with the meteorology of the Ross Sea area ; it is important, therefore, that they shordd be 

 criticised in the light of our fuller knowledge. 



Fohn. — The fohn effect has been introduced to account for the high temperature of the 

 winds. Air is supposed to start from the plateau surrounding the Barrier and to be dynami- 

 cally warmed by its forced descent to sea-level. If such forced descent does take place, 

 for which however there is no evidence, the air might be warmed, but at the same time there 

 would be a corresponding fall in the relative humidity of the air. Now one of the chief 

 characteristics of an Antarctic blizzard is the heavily overcast sky and large precipitation, 

 which would be qiute impossible with descending air. Even if a satisfactory explanation had 

 not been already given this consideration alone would be sufficient to .show that the high 

 temperatures in blizzards are not due to a fohn effect. 



Air Circulation about a Low Pressure System.- — It has been usually assumed that blizzards 

 are due to the passage eastwards of low pressure systems having their centres over the 

 southern ocean. It will be shown later that such cyclones do not affect the Ross Sea area 

 and that blizzards are due to entirely different causes. Even if this were not the case it 

 is easy to show that the high temperatures in blizzards are not due to ' the conveyance 

 of warmer air drawn from lower latitudes, circulating about a low pressure system and con- 

 veying to the locality the higher temperature of the region whence it originated.' In such 

 a circulation air which reached McMurdo Sound as a south-easterly wind, would have previously 

 passed over Framheim as a northerly wind when it was nearer its place of origin. It would 

 therefore be warmer at Framheim than when it reached McMurdo Sound after passing over 

 the cold Barrier. To test this hypothesis the temperature at Cape Evans and Framheim 

 during blizzards at the former station have been compared, with the result shown in the 

 followinji; table : — 



