Directional Recording of Swell from Distant Storms - Department of ...

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DIRECTIONAL RECORDING OF SWELL FROM DISTANT STORMS 545similar refraction diagrams were prepared for other frequencies. Figure 27 is a plot ofrecorded direction against off-shore direction, beyond the shoal areas. At high frequenciesthe refraction is negligible throughout and the two directions are equal, as indicated. Forvery low frequencies the recorded directions lie in a narrow interval about the normal to theshore line.120 km I-HS4* N,014San Clemente I.FIGURE 25. The continental borderland off San Clemente Island. Depth contours are drawn for0, 50, 100, 150, 200 and 250 fm. Areas shallower than 100 fm are shaded. Incoming waves arelimited by San Nicolas Island to the north and Point Eugenia on Baja California to the south.To help visualize the expected dependence of wave direction on frequency, we haveplotted the solution to the ray-optics problem for two idealized cases. Figure 28 shows therefraction by a cylindrical shoal (depth 200 m) for a recorder located in deep water (800 m)at a distance of two shoal diameters. For comparison with observations we wish to displaythe result on a diagram with frequency and recorded direction as co-ordinates, drawinglines of equal off-shore direction (figure 29 right). Rays exceeding a critical angle
546 W. H. MUNK, G. R. MILLER, F. E. SNODGRASS AND N. F. BARBERj931 /~~~~~~~~~~~~~~~~~~~FIGURE 26. The refraction of waves of frequency 37-5 c/ks in the region shown in figure 25. Dashedcurves give the 100 fm contours. The solid lines correspond to rays intersecting at the positionof the wavre recorders. These are drawn for recorded directions of 185, 190, ... 2700. The offshoredirections are indicated.arcsin (ji) =14?*5 at the recorder are not refracted and appear as vertical lines. For any offshoredirection exceeding the critical value there are two recorded directions, the direct rayand the refracted ray. Suppose OO ? 200. For the direct ray qr ? 200; for the refracted rayat 20 c/ks ?r = -8? (in the half of the diagram not shown) . Figure 29 left shows the correspondingpattern associated with straight parallel contours. The actual situation is in a sensea combination of the two examples, and the relations are complex.
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Page 25 and 26: 528 W. H-. MUNK, G. R. MILLER, F. E
Page 33 and 34: 00207'-0.C-0-01~~~~~~~~~~~~~~~~~~~~
Page 35 and 36: 538714Cld0,9~~~~~~~U0CldCIO.0a.)a.)
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Page 49 and 50: 140? 1300 1200 1100 1000 900 80016t
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Page 78 and 79: Munk et al. Phil. Trans A, volume 2

Directional Recording of Swell from Distant Storms - Department of ...

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