METEOROLOGY 



rose to an altitude of over 20,000 ft. above sea-level. 

 Under these circumstances it penetrated far above the 

 level of a current of air from the pole northwards, so that 

 its summit came well within the sweep of the higher wind 

 blowing in a southerly direction, the result being that the 

 steem-cloud in this region was dragged over powerfully 

 towards the south-east. On such occasions one usually 

 saw evidence of two high-level currents, the one coming 

 from a northerly direction, its under limit being about 

 15,000 ft. above sea-level; and the other, or middle cur- 

 rent from a southerly quarter, usually blowing towards 

 the east-north-east, meeting its upper limit at 15,000 ft. 

 normally while its lower limit was between 6000 and 7000 

 ft. above sea-level. While these two currents were blow- 

 ing strongly, there would frequently be a surface current 

 blowing gently from the north. This would bring up 

 very dense masses of cumulus cloud from off Ross Sea. 

 The cumulus would drift up to the 6000 or 7000 ft. level 

 on the north-west slopes of Erebus, and then the tops 

 of the cumulus would be cut off by the lower edge of the 

 northward flowing middle current. Wisps of fleecy cloud 

 would be swept along to the east-north-east torn from the 

 tops of these cumulus clouds by the middle current. The 

 whole appearance is illustrated in the accompanying 

 diagram. 



It is of especial interest to note the eff ects of blizzards 

 on the direction of movement of the high-level currents, as 

 well as on their altitude. As the result of our ascent of 

 Erebus we ascertained that the whole of the snowfall 

 lying within the rim of the second great crater, at an 

 altitude of from 11,500 to over 12,000 ft., is strongly 

 ridged with sastrugi, which trend from about west-south- 

 west to east-north-east in the direction of the prevalent 

 middle-air current. The sharp points of these sastrugi 



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