26 JVIETEOROI-OGY 



ice-fields in the first case, but after that the position of the surface divide would 

 depend in part on the relative waste and supply effected by the prevalent winds. 



Near the Magnetic Polar area the great size of the sastrugi indicate winds of great 

 violence. These probably blow most strongly in the winter time, or in late autumn 

 and early spring, when the atmospheric gradient between the extra cold land and the 

 still open sea would be steepest. 



Reference has already been made to the prevalence of the plateau wind, which is 

 a land breeze on a large scale at night-time. When marching along the coast in 

 October, November, and December of 1908, we found that the plateau wind reached 

 the coast between about 8 p.m. and 10 p.m. and would go on blowing until about 

 between 9 a.m. and 10 a.m. the following morning. It would usually freshen a little 

 after midnight. Its usual speed appeared to be 12 to 15 miles an hour, scarcely 

 sufficient to raise any drift snow, but with just sufficient speed to "sweep 

 the carpet," that is, drive the snow before it in a thin moving layer an inch or two 

 deep over the surface of the sea ice. The immense sastrugi at the Drygalski Glacier 

 show that towards winter the winds must blow from off the plateau with great fury, 

 as already stated. 



It would seem as though the Ross Sea was the chief centre of Ioav pressure. This 

 would be due, of course, to its relatively warm water surface which is lightening the 

 air above it, partly by warming, partly by supplying aqueous vapour to it. The cold 

 airs to the south of Ross Sea rush into it from the south or south-east. The cold 

 airs of the plateau stream into it from the west. It will thus be seen that the 

 surface winds on the Magnetic Pole Plateau tend to blow radially outwards from the 

 highest part of the plateau towards the sea, and at first sight do not seem likely to 

 be bringers of snow. 



Whence then come the snows which feed the plateau ? On December 27, from our 

 position on the inland side of Mount Larsen, cumulus and alto-cumulus could be seen 

 drifting inland from N.N.E. off the Ross Sea towards the S.S.W., and at a still higher 

 level the clouds were drifting inland from the N.E. 



Later on the same day, great rolls of alto-stratus could be seen drifting N. W. to 

 about S.E. The rolls were strongly bent with their convexities directed towards the 

 S.E. to E.S.E., as though they were being pushed over in this direction by a strong 

 N.W. upper current. At Erebus, the normal downward limit of this current, which 

 appeared very steady and constant there, was about 15,000 feet above sea level. 



Some additional light may be thrown on the snow supply of the Magnetic 

 Pole Plateau, if we consider the conditions on the plateau west of the Ferrar 

 Glacier. Here most of the snow which fell in November, according to Scott, 

 came from a general S.W. by W. direction. On December 9, 1903, on the 

 same plateau Scott records that there was evidence of a recent snowfall earlier that 

 December, and that this December snowfall is far heavier on the edge than in the 

 interior of the continent. He also states that the wind there in its most southerly 



