CAPE AD ARE. 239 



when there were few and small pressure waves and no cold layer, the blizzards commenced 

 with light winds which slowly developed into storms. 



Summary. — On account of its geographical position and temperature conditions the pressure 

 over the Barrier tends to be higher than the pressure over the Ross &'ea immediately to its 

 north. The air moving under the pressure distribution is deflected to the left by the rotation 

 of the earth and moves towards the west. Its westerly motion is arrested by the range of 

 mountains which runs approximately north and south along the western edge of the BaiTier 

 and Ross Sea. The deflected air current flows northwards as a concentrated stream over the 

 north-western corner of the Barrier near to Ross Island on which Cape Evans is situated. 



A system of parallel pressure waves has been shown to travel over the whole area in 

 an approximately north-westerly direction. These waves modify the normal pressure distribu- 

 tion, sometimes intensifying it, when the normal air current over the west of the Barrier 

 develops into a blizzard, and sometimes completely reversing it when northerly winds are 

 experienced at Cape Evans. 



Pressure, winds and weather at Cape Adare. 



We are now able to consider the conditions at Cape Adare which have not entered 

 into our previous discussion. If one turns over the plates of pressure curves it is quite 

 clear that Cape Adare comes under the influence of the pressure waves which we have 

 found to be the governing factor of the wind and weather over the Barrier. On examining 

 the pressure curve for Cape Adare in detail, however, we shall find an important difference 

 between it and the curves for Cape Evans and Framheim. The pressure waves at Cape Adare 

 will be seen frequently to have irregularities which are not shown on the curves for the 

 other two stations. To take a concrete example the curve for June 19th on plate 7 should 

 be examined. It is quite obvious that here we have at Cape Adare a sudden dip imposed 

 on what would otherwise have been the crest of the pressure wave which passed over Fram- 

 heim twelve hours previously. Several similar dips in the Cape Adare curve will be seen and 

 as the majority of them are connected with hurricane winds it is natural to associate them 

 with passing cyclones. Luckily just as the Terra Nova approached Cape Adare at the end of 

 December 1911 to remove the party, one of these depressions passed, and the simultaneous 

 observations made on the ship and at the Cape give us valuable information which we shall 

 be able to use in our discussion. We will therefore unfold plate 23 and examine the pressure 

 curves and maps for the period December 29th to January 2nd. It will be noticed that on 

 plate 23 a curve has been added giving the pressure and winds as observed on the ship. 

 The position of the ship was constantly changing, therefore its latitude and longitude at noon 

 each day have been entered below the pressure curve. The maps for this period show the 

 passage eastwards of a depression, the centre of which passed at a short distance to the north 

 of Cape Adare. These maps teach several important lessons. 



(a) The local conditions in the south of the Ross Sea are not appreciably affected by 

 the relatively deep depression passing near Cape Adare. Also the high south-east winds at 

 Cape Adare are not the continuation of Barrier blizzard winds. Although we have no actual 

 observations between Cape Evans and Cape Adare to prove this statement yet it is quite 

 impossible to draw isobars to fit the pressure and wind observations without the ridge 

 of high pressure over the north-west of the Ross Sea which makes such a continuation im- 

 possible (see maps for December 31st). 



(b) It will be noticed that the winds at the ship change from northerly to southerly 

 directions as the depression passes, while at Cape Adare the wind, as soon as it comes 

 under the influence of the depression, remains practically constant in direction varying 

 little from south-east. There is not the slightest doubt that this is the result of the land 

 masses surrounding the meteorological station on Cape Adare. The northern coast of 



