196 



PRESSURE. 



Table 115. 



Actual and computed amplitude of surges. 



The agreement between the actual and calculated values on these simple assumptions 

 gives us good reason to believe that the amplitudes of the surges do decrease from 80° S., 

 120° W. in all directions, and therefore one is tempted to assign this position as the 

 centre of the pressure system in which the surges take place. 



The most simple physical explanation of the relationships we have found is the following : 

 We shall show in a future chapter that in the upper atmosphere over the whole Antarctic 

 the pressiire is cyclonic with the centre of lowest pressure over the low-lying region which 

 we have reason to believe exists in the Pacific quadrant of the Antarctic, and in which 

 the position mentioned above is situated (see figure 80). The surges are probably due to 

 increases and decreases in the intensity of this cyclone, and if so, then the surges should be 

 strongest near the centre of the cyclone and decrease roughly in proportion to the distance 

 from the centre. 



Pressure Correlation. 



Having shown that the pressure over the Antarctic increases and decreases as a whole, 

 we now proceed to investigate in how far the pressure outside the Antarctic is affected. For this 

 purpose the method used above of identifying simultaneous surges is no further available, 

 for the individual surges die out rapidly over the Southern Ocean. This can be seen by 

 comparing the surges at Kerguclen and Wellington shown on plate II with those for the 

 Gauss Station and Hut Point respectively. No relationship between the curves for these 

 pairs of stations similar to that existing between the curves for the Antarctic stations can 

 be recognised. We must now compare the mean pressure for longer periods if we are 

 to obtain useful results. We shall therefore take as our datimi the mean pressure for a 

 month and compare the mean monthly pressures at stations within and surrounding the 

 Antarctic. 



Before doing so, we must see whether the intimate relationship between the pressure at 

 different stations in the Antarctic found by means of the surges is still recognisable when we 

 use monthly means. 



Correlation of mean monthly pressure within the Antarctic. 



For this purpose data are available from McMurdo Sound, Snow Hill, the Gauss Station, 

 Kerguelen, South Orkneys and South Georgia. Unfortunately, however, the observations were not 



