CLOUD AND WIND. 



151 



Here we see a relationship similar to that found for Cape Evans with one important differ- 

 ence, namely, that class 1 is greater than 0. This brings out a difficulty which has been com- 

 mented on in previous discussions of cloud amount. It sometimes happens that cloud lingers 

 about some local geographical feature when it has disappeared from the sky as a whole. 

 Thus the following remark appeai-s in the discussion of the cloud observations made at the 

 Gauss Station : 



' Cloud amounts of 9 and 10 had practically the same significance, because the number 

 chosen depended on the presence or absence of a blue cloudless segment in the 

 south, which was probably connected with the anticyclone over the inland ice. 

 The same held for the classes and 1, which were governed by the appearance 

 of a bank of cloud (sometimes not seen because of dark nights) on the northern 

 horizon.' 



In the case of Cape Adare. which was surrounded by high mountains, cloud often lingered 

 about their summits when otherwise the sky was clear, thus accounting for the frequency 

 with which cloud 1 was reported. 



In order to remove as far as possible such disturbing factors as these, it is found advis. 

 able to consider only the three groups of cloud amounts : — 1, 2 — 8, 9 — 10 ; and this will be 

 done in the future discussion. Reduced to these three groups, the cloud observations at Cape 

 Evans and Cape Adare are shown in the following table, to which corresponding data for the 

 Gauss Station, Snow Hill and Lau)ie Island are added. 



Table 82. 

 Percantmje frequencij of three groups of Cloud Amount (yearly means). 



From this table the distribution of cloud over the Antarctic regions is obvious. The cloud 

 amount is high over the Southern Ocean and relatively low over the Ross Sea area. Also 

 the frequency of clear skies increases and of overcast skies decreases, as one pas.ses from the 

 centre of the Southern Ocean towards the south. This relationship is best explained by the 

 presence of an anticyclone over the Antarctic continent, which is bounded on the north by the 

 cyclones of the Southern Ocean. This result is important as it is an indication that, in spite 

 of the low pressure area over the Ross Sea, the weather conditions there are governed by 

 the Antarctic anticyclone. 



Clovd and Wind at Cape Evans. 



When discussing the cloud forms (page 148), it was stated that blizzards were generally 

 accompanied by overcast skies. The follo-i^ing table shows the relationship between cloud and 

 wind. 



