12 INTRODUCTION. 



half is occupied by winds of a greater velocity than 30 miles an hour. The majority of 

 winds from the &o\ith are typical blizzards. As in every section of this work reference will 

 be made to the blizzard, it is desirable that a short account of this phenomenon should 

 be given here. 



The origin of the word blizzard is unknown, but it is now used in meteorological 

 literature for any high wind accompanied by unui^ual cold and snowfall. In the Antarctic 

 the members of our expedition used the term rather loosely and any high -wind was called 

 a blizzard almost independently of its direction and of the weather conditions accompanjing 

 it. There is, however, no doubt about the description of a typical blizzard which would be 

 given by anyone who has spent a year in McMurdo Sound. 



In the most typical case light cirrus cloud first spreads over the sky and gradually 

 gets thicker and lower, until finally the whole sky is covered with a uniform dark gray 

 layer of cloud. For a longer or shorter period there may be a complete calm and then 

 the wind lises. We shall see later that over the Barrier the blizzard wind blows from the 

 south parallel to the Western Mountains, but Ross Island stands up as a great obstruction 

 in its path and the southerly wind is deflected into two streams, one of which passes the 

 Island on the east, and the other passes into and blows through McMurdo Sound on the 

 west. The actual direction of the air motion in a blizzarxl at different parts of the Sound 

 depends on the surrounding land masses. At Cape Evans the blizzards are deflected by the 

 shoulder of Mount Erebus into easterly to south-easterly winds. The arrival of the wind is 

 frequently very sudden and within a few mijiutes, a calm may be replaced by a wind of 

 30 or 40 miles an hour. Figure 46, page 128, shows three typical examples of the sudden 

 setting in of a blizzard. This however is by no means a general rule, and on many occasions 

 a gentle southerly wind will got stronger and stronger until it develops into full blizzard 

 force. 



In a true blizzard the wind is accompanied by clouds of driven snow. The snow is 

 in the form of exceedingly fine grains which penetrate through the smallest chink or hole 

 in a house or tent. The whole air appears to be full of drift, so that it is impossible to 

 see any great distance, and when it is at its worst even a tent cannot be seen for more 

 than a few yards. Not only does the drift make it difficult to see, but anyone exposed 

 to it seems to become bewildered and to lose all power of thinking clearly. For these 

 reasons it is sheer folly to attempt to travel in a blizzard even when the tempsrature is 

 relatively high and the wind at one's back. 



There can be no doubt that the large amount of drift in a blizzard is due to the high 

 wind sweeping along with it all the snow which has been precipitated, for none can settle 

 out of the air except in a few sheltered places where large snow-drifts accumulate. Thus 

 with only a moderate rate of precipitation the lower atmosphere in time contains a great 

 deal of snow. Opinions differed as to the relative importance of old snow blown up from 

 the surface and new snow which is falling. M)' own experience led to the conclusion that 

 thne can never be really bad drift unless new snow is actually falling. I have certainly 

 seen a high wind convert newly-fallen snow from the surface into drift, but this drift was 

 never so thick and bewildering as the drift which accompanies heavily overcast skies from 

 which new snow is falling. If no new snow has fallen for several days the highest wind 

 produces only a low surface drift, for the surface of the snow becomes compact in a 

 comparatively short time. For a really bad blizzard both high wind velocity and actual 

 precipitation are necessary. The wind during blizzards is often squally and generally gusty, and 

 on some occasions the gustiness is very marked, see figure 38A. There is a tendency for a 

 blizzard to become more gusty towards its end ; but this is by no means a general rule. 



