232 



PRESSURE, WINDS AND WEATHER. 



We now see that both theoretically and actually the pressure waves themselves give 

 little information as to the winds to be expected while the diSerence curve is of primary 

 importance. 



We will now pass on to study in detail the theoretical pressure distributions shown 

 in the b diagrams on figures 66 to 73. 



It must, however, be pointed out that for purposes of calculations we have had to use 

 a pure harmonic pressure curve which ends with the same pressure at each station that it 

 started with. In reality the waves were far from being harmonic, they were nearly always 

 very unsymmetrical, the crest and the trough being of unequal size. They changed their form 

 and also their relative phases as they travelled from Framheim to Cape Adare. 



We must not therefore expect to find the whole sequence of changes carried through 

 in the same order for each individual wave. For any given position of an actual wave we 

 must choose the position of the theoretical wave which most nearly represents the actual 

 conditions, and compare the actual and theoretical pressure distribution at those epochs. 



It will be seen at once that the eight diagrams may be divided into two main tvpes, 

 which are associated with southerly and northerly winds at Cape Evans respectively. We 

 shall call these the blizzard type and the northerly wind type. The former of these includes 

 the four diagrams 69 to 72. In each of these the highest pressure is over the Barrier and 

 the lowest over the Ross Sea. The most typical distribution is that in which the blizzard 

 is the strongest, figure 71. In all these diagrams the wind at Framheim is from the east 

 or slightly from the north of east. The northerly tj'pe includes the two diagrams 66 and 67, 

 in each of these the wind at Framheim is southerly. Diagrams 68 and 73 are intermediate. 

 It will be noticed that the theoretical pressure distribution gives at Framheim only winds 

 between N.E., through S. to S.W. ; and these are closely related to the winds at Cape 

 Evans, for during southerly winds at Cape Evans the winds at Framheim are strong and 

 between N.E. and E., while with northerly winds at Cape Evans the winds at Framheim 

 are light and between south-east and south-west. 



To investigate whether these relationships hold in the actual observations the following 

 table has been prepared :^ 



Table 126. 

 Winds at Framheim. 



The first line shows the preponderance of winds from the direction between N.E. through 

 S. to S.W. The remaining directions from W.S.W. to N.N.E. have only 8 per cent, of the 

 wind between them. 



