72 FREQUENCY OF WAVE CONDITIONS 



reasons, the category '"low," as used below and on the charts, includes 

 "calm'' unless otherwise noted. 



The value of presentations of this sort depends chiefly on how far 

 the data on which they are based can be regarded as representative. 

 The percentages have been taken into account only for such of the 5° 

 squares as were the subject of at least 10 reports for the time in 

 question; this minimal number is so small that the contours as laid 

 down on the charts are offered only as the roughest of approximations, 

 except perhaps along the chief steamer lanes, where the picture is 

 more dependable. Where fewer than 10 reports were available for a 

 5° square, the area has been left untinted. 



The features of seas and swells of primary and secondary import- 

 ance to the mariner are the frequencies with which these run high and 

 low, respectively, in one part of the ocean or another at different times 

 of the year. It has seemed sufficient to limit the comparison to 

 winter and summer, these being the seasons when the weather is 

 either at its stormiest or the reverse over most parts of the oceans. 

 In the following discussion, "summer" and "winter" refer to those 

 seasons in the Northern Hemisphere. 



Paucity of data has made it necessary to base each of the seasonal 

 charts for the Indian Ocean, for the South Pacific, and for the South 

 Atlantic on percentages derived from the total observations for two 

 months (July and August representing summer conditions and Janu- 

 ary and February, winter) . Winter conditions in the North Atlantic 

 are also shown by combining the data for January and February, 

 since the percentages derived in this way appear to yield a more 

 representative winter picture for that area. Winter conditions in 

 the North Pacific are based on data for February alone, and summer 

 conditions for both the North Pacific and the North Atlantic are 

 drawn up from August reports only. 



NORTH ATLANTIC 



Summer. — The northern part of the North Atlantic is least often 

 rough in July and August for the very obvious reason that winds of 

 gale force (force 6 to 8 Beaufort or stronger) are least frequent then, 

 even in high latitudes. It is only to the northward of the general 

 latitudes of southern Newfoundland, for example, and of southern 

 Britain — locally, too, off the coast of northwest Africa — that seas 

 higher than 8 feet have been reported as often, even, as 10 percent of 

 the time for August; while seas of even that moderate height, in 

 frequency greater than 20 percent, have been reported only for the 

 waters between southern Greenland and Scotland. 



Elsewhere throughout the North Atlantic the seas of late summer 

 may be characterized as the least often high and as the most often low 



