CLIMATOLOGY OF THE NORTH ATLANTIC 



BY J. M. AUSTIN 



1. Introduction. 



The principal features of the weather over the North Atlantic Ocean have 

 been treated by various investigators. In general we find that the weather charac- 

 teristics of a particular region have been based either upon a long period of ship 

 and land station observations or upon specific ship expeditions. Unfortunately, .^^^y^^ 

 however, the various climatological reports are not readily available to every synop- ^ 



tic meteorologist, and it is the purpose of this report to present this climatological 

 material in an abbreviated form. 



Because the climatological data is intended to give the weather forecaster a 

 general background of the weather over the North Atlantic, an attempt has been 

 made to accumulate and condense the available information for various regions 

 into a series of simple ocean charts. Furthermore, since aerological information is 

 of vital importance, it was considered desirable to include upper air data wherever 

 possible. The charts, which will be discussed later, have been drawn for four months 

 of the year — ■ February, May, August and November. These months correspond 

 to winter, spring, summer and fall weather conditions over the Atlantic. In many 

 cases, where the change from winter to summer is obvious, only two maps have been 

 included. Likewise, charts were not drawn for every season when it was considered 

 that the information was of only minor importance. 



2. Mean Sea-Level Pressure and Wind Charts. 



Figures 1 and 2 show the mean sea-level pressure and wind distribution for 

 the months of February and August respectively. These maps were constructed 

 on the basis of data published by Schott.-^ The persistency of winds in excess of 

 Beaufort Force 3 is indicated approximately by the length of the wind arrows. 



Both maps show that, in the mean, there is an anticyclone in the south and 

 a cyclone between Greenland and Iceland with a low pressure trough extending 

 from Davis Strait to northern Scandinavia. North of this trough we find the general 

 easterlies of high latitudes. The significant differences between summer and winter 

 may be summarized briefly as follows: 



(i) The Icelandic low is considerably deeper in winter and there is a cor- 

 respondingly more intense circulation in winter than in summer. This is illustrated 

 by the large region which is covered by winds in excess of Beaufort Force 6 in winter. -;- 



It will be observed that^tlie strongest surface winds in winter shift from 35° N in L^m--'' 

 the western Atlantic to near 65° N in the eastern Atlantic. In summer the strongest 

 winds are found in the middle Atlantic about 55 °N and near the coast of Africa 

 in low latitudes. 



(^) The subtropical anticyclone is more developed and more extensive in 

 summer. In comparison to the cyclonic circulation as far south as 30° N in winter, 

 Figure 2 shows that there is, in general, anticyclonic control to 45° N in summer. 



(5) The latitudinal displacement of the subtropical anticyclone results in^^^j^^^^^. 

 a northward shift of the trades in summer. 



{^]^) As a result of the intensification of the subtropical high in summer, the 



