156 MR JOHN AITKEN ON DYNAMICS OF CYCLONES AND ANTICYCLONES. 



The movements of the southern storm track seem to be governed by the same law. 

 In winter it attains its most south erly position, drawn southwards apparently by the 

 hot moist air of the Mediterranean, over which area the storms move at this season, 

 but when summer comes the continental area to the north becomes warmer than the 

 Mediterranean, and the track of the storms moves northwards, and in summer is across 

 continental Europe. It will be noticed that these two storm tracks move in opposite 

 directions at the same season, the northern track moving south in summer and north in 

 winter, while the southern one moves north in summer and south in winter. 



It thus appears that storms tend to form and move over areas in which there is a 

 supply of hot moist air, and to change their tracks so as always to follow the changes 

 in the position of the best supply, and it is difficult to understand why this should be 

 so, unless the hot moist air is the cause and source of energy in the cyclone. 



Another consideration which leads us to suppose that convection currents play an 

 important part in cyclones is the greater violence of the winds over cyclonic than 

 anticyclonic areas, a result we would not expect to find unless some source of energy 

 came into action in the cyclonic area. All these considerations point to the conclusion 

 that however important the action of anticyclones may be in the formation of cyclones, 

 yet cyclones are, to a very large extent, convectionally driven. 



The general circulation over our area, as pointed out, is more from the south during 

 winter than during the summer months. This change is partly brought about by the 

 weakening during the latter season of the anticyclone to the south-west of Europe, but 

 Apparently much more to the disappearance of the anticyclone over Siberia and 

 Northern Asia. In winter, Eastern Europe and Northern Asia are covered by a large 

 -and well-marked high-pressure area, and it would appear that it is this high-pressure 

 area to the north-east which causes the anticyclonic circulation to turn more to the 

 northwards in winter than in summer, so that the high winter air temperature and hot 

 Gulf Stream water which carry the high winter temperature to Iceland and Scandinavia 

 would appear to be greatly due to the high-pressure area over Siberia and Northern 

 Asia. I fear I must apologise for adding one more theory to the many explaining the 

 high winter temperature of the north-west of Europe. It seems strange that the cold 

 over the northern parts of Europe and Asia should play any part in the abnormally 

 high winter temperature of the sea and the lands surrounding the north-western parts 

 of the Atlantic. 



