208 PRESSUEE, WINDS AND WEATHER. 



extremity touches or overlaps the ice barrier and its northern extremity reaches up to, or 

 near to, latitude 40° S., and eight of them encircle the earth. The rate of travel of the 

 cyclones is determined by the method described above to be 9-5° of longitude a day. 



This scheme deserves close attention, for it appears to explain satisfactorily many of the 

 characteristics of the weather in the southern hemisphere. 



(a) It accounts for the ' roaring forties,' for as the depressions move from west to 



east the regions between 40° S. and 60° S. being to the north of the centres 

 of the cyclones constantly come under the influence of strong westerly winds, 

 which change direction and intensity with variations of the barometer. It does 

 not, however, explain the easterly winds sometimes observed in the region of the 

 ' roaring forties.' 



(b) It also explains the easterly winds experienced in high southern latitudes, for they 



are complementary to the westerly winds on the other side of the centres of the 

 depressions. 



(c) The mean pressure in such a system would agree fairly well with the actual mean 



pressure observed, for the centres of the cyclones travelling along 60° would give 

 on the average a trough of low pressure in this region. 



The scheme, however, has several weak points. In the first place it is not based on 

 synoptic weather charts, no attempt apparently having been made to fit simultaneous observa- 

 tions together and show how they agree with such a system of high and low pressure areas. 

 It must also be remembered that it is based on two assumptions : (a) that the pressure 

 variations from day to day — especially in the Antarctic — are produced by travelling cyclones or 

 anticyclones ; and (b) that the cyclones have their centres all on or near 60° S. latitude. 

 This latter is very important, for the large area of the cyclones is a direct consequence of 

 the assumed positions of the centres of the cyclones. If the centres could be in any latitude, 

 the cyclones would of necessity be smaller and irregular, and the simplicity of the system 

 with many of the consequences drawn from it would be lost. Lockyer's system may then be 

 tested by these two criteria, and we shall have occasion later to apply both tests and to 

 find them both wanting. 



Meinardus in his discussion of the results of the Gauss Expedition also considers the 

 general pressure distribution over the Southern Ocean. His main conclusions on the point we 

 are now considering are summed up in the following quotations :— 



' When one reviews the weather conditions as a whole, which are associated with the 

 storms at the Gauss Station, there can be hardly a doubt that they are governed 

 by cyclonic pressure systems which, except in a few cases, pass from west to east 

 to the north of the winter station. The following may be mentioned in support 

 of this conclusion : the shape of the pressure curve (passage of wave crests and 

 troughs), the change of wind direction during storms from E. by N. or E. towards 

 the direction of the south-east quadrant, the changes of wind strength during storms, 

 as well as the precipitation and cloud conditions, particularly the direction of the 

 cloud motion before and after the storms.'* 



So far Meinardus and Lockyer are in agreement, but the former goes on to say : 



' During storms the winter station comes under the influence of the central area of 

 the cyclones and is not simply passed over by the outer regions. This is clearly 

 shown by the relationship between the strength of the wind and the depth of the 



* Deut3cli6 Sudpolar-Expedition, 1901-03, p. 294. 



