OCEAN WAVES AS A METEOROLOGICAL TOOL 
WAVE SPECTROGRAM 
15 
20 24 30 
aan, 
REZ “| 
<a 
FEBURARY 1945,GCT 
1097 
o 30° 20° 
SAAN EG WES 
Gy | 
= 
= 
0030 GCT 
17 FEB.1945 
LOCATION OF STORM FETCH 
Ye ETERMINED FROM WEATHER 
WUE 
MAPS. 
STORM POSITION COMPUTED 
FROM WAVE RECORDS 
FEBURARY 1945,GCT 
16™ w™ 
1200. ‘0000 
Fie. 13.—Application of storm-tracking method to wave records of 18-21 February 1945. The period spectrograms re- 
corded at Pendeen are shown to the left. Significant features on adjoining records are connected by dashed lines, marked 
,B,... 0. The corresponding foci are shown by the circles in the diagram at the lower right, where the shaded band gives 
ape of the storm determined from weather maps. One of these weather maps is shown at the upper right. (From Munk 
18 to 19 February, but focus O had its origin in the 
second storm system when it was still 3000 miles from 
the wave station. 
Discussion. A considerable number of meteorological 
sequences have been studied by means of the Pendeen 
wave records, and in all instances the agreement be- 
tween computations based on the wave records and the 
information on the weather maps was encouraging. In 
one instance, 26 June 1945, waves from a hurricane off 
the coast of Florida were faintly recognizable above the 
disturbance caused by a moderate local storm. To the 
author’s knowledge, attempts based on wave records 
taken along the coasts of the United States have not 
been equally successful. This can be attributed at least 
partly to instrumental difficulties. 
At one time the author had hoped that by shifting 
the range of maximum response of the instruments to- 
ward longer periods (by placing recording units of 
greater sensitivity in deeper water) it should be possible 
to record even longer forerunners, with periods, say, 
up to 60 sec, and correspondingly high velocities. Bx- 
perience in England [1] does not support this expecta- 
tion. Figure 14, based on thirteen well-substantiated 
storms, shows a correlation between maximum wind 
force of distant storms and the maximum recorded swell 
period. A possible explanation is contained in the fore- 
casting theory [16] according to which waves gain 
energy from the wind only if the wave age (wave 
velocity/wind velocity) is less than 1.37. The dashed 
line in Fig. 14 corresponds to values of the wave age 
ranging from 1.26 to 2.26. The preliminary conclusion 
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10 15 20 25 
MAXIMUM PERIOD OF SWELL IN SECONDS 
Fic. 14—Correlation between the maximum wind strength 
and the maximum period of swell generated for thirteen storms. 
(From Barber and Ursell [1].) 
is that fore-runners with periods longer than 25 sec, 
or perhaps 30 sec, are so low compared to other types of 
wave motion in that period range [10] that they would 
be associated with an unfavorable signal-to-noise ratio. 
Accordingly, the highest group velocities which one may 
