Chapter Six 



THE WIND SYSTEM OVER THE 

 NORTH ATLANTIC 



It is important to describe briefly the winds over the North Atlantic 

 Ocean, because it is generally supposed that the surface circulation of the 

 ocean is caused by them. Many of the older textbooks of meteorology 

 emphasize the mean wind distribution so heavily that one is Hkely to over- 

 look the considerable fluctuations which occur in wind distribution from 

 day to day. At present, theories such as those described in Chapter VII 

 take into account only the mean wind distribution. Just what the efi'ects 

 of the widespread interruptions and irregularities of atmospheric flow on 

 the ocean circulation are, is still to be told. 



NORMAL CIRCULATION 



Chase (MS, 1951) has made an extensive study of the surface pressures in 

 the last half-century on the North Atlantic, using the historical weather 

 maps for the Northern Hemisphere (U. S. Weather Bureau, for the period 

 beginning in 1899), and has since incorporated information from the normal 

 weather maps. Northern Hemisphere (U. S. Weather Bureau, 1952). The 

 normal sea-level pressure (yearly average) is shown in fig. 46. By far the 

 largest area of the ocean is covered by a single high-pressure cell with winds 

 traveling in a clockwise direction about its center. The normal sea-level 

 pressures at two different seasons of the year are shown in figs, 47 and 48. 

 The center of the high is at its most northeasterly position in January ; 

 by March it has moved almost 1200 miles to the southwest and is at its 



