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

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DIRECTIONAL RECORDING OF SWELL FROM DISTANT STORMS 541The background level consists of a flat valley near 10-2 cm2/(c/ks) for frequencies below40 c/ks rising steeply to 10 cm2/(c/ks) at 80 c/ks. Typically the ridges extend 10 to 100 timesabove the background level. Some ridges project into the low-frequency plain. The outstandingcase is the ridge associated with the hurricane on 22 October which projects to10 16 18 20 22 24 26 28 3001 \c/ks [0 -,EAST 90 ,120'2 aSOUTH 180 .2400 a4- 2 * Ia1 10 20 22 24 26 28 30 I* I I I OCOBER I 195 | |FIGURE20.Tetopcurveshowstheeergyensit fntoofimina20 Th ~ to cuv ~ shw th enrg dest as a fucino iei arwfeunybnaarwfeunybncentred at 37-5 ac/ks.~~~~~~ ahscrepnstoiznalctiaigrea7ah cetaldagagieis unity. *:1_ Fo exmpe on 27 Ocoe th enrg desty at 37* c/k is 01C2 a I a sad6 _offrom direction~~~~~~~al band af5 it areiniateenergyytehsora.UiUitgaon 27Otbrteeeg est t3 /si 5c2(/s, an 64%oftiseegycmsfom a dietoa inera .4 to 24.5 T.implythat all energ30'i aocnrte nti an a band ahumo al alcsfranis nit. Fo xml ,n aas low as ~~~~~30 ckahfrequencies(peio3 a)aorsodigde-wtraveeghi66. VOL 25.A
542 W. H. MUNK, G. R. MILLER, F. E. SNODGRASS AND N. F. BARBERsource of 22 October, due to a north Pacific hurricane, and three very distant events inAugust which have been traced to storms in the Indian Ocean (see ? 14).For the period May to September 1959 (figures 13 to 16), only the south-north pair ofinstruments was in operation. The directions of the major ridges have been determined bythe method discussed in ? 5, and the results are entered on the figures. During October all16 18 20 22 24 26 28 30cm2 I /c/kso:tEAST 0 ,,0' s : , , .,120' ' :*a**aia.*' :150 . .SOUTH18- * * ' *. ~ ~ ~~ , ~~ S , ~~~~~~ .a_.* . .~ ~a *210' ., . . , . . aIt . a240 -. :.. .. . a . . . _ .WEST 270 -'300 . . ..a. a.a330 . a a a a aaa.NORTH 0-. . . . a .60 . a,I 1 1 - t I t f I g s I I I16 18 20 22 24 26 28 30OCTOBER 1959FIGURE 21. The distribution of wave energy among various directions for a frequency bandcentred at 44 c/ks during 16 successive days (see legend to figure 20).three instruments were in operation, and it seemed worthwhile to present the completefield ofO(f, t) (figure 18). Figure 19 shows the fields ofE(f, t) for 16-17 October when spectrawere taken at 3 h intervals (rather than the customary daily interval). At these close timeintervals the energy and direction show the expected degree of continuity.The contour charts of energy and direction on the f-t diagrams contain most of theinformation obtained in our experiment. There are a number of interesting cuts . Verticalcuts (at a fixed time) reproduce the original spectra on which the contour charts are based.Horizontal cuts (at a fixed frequency) reveal a marked assymetry of the slopes on the twosides of the ridges and give some information about the arrival of scattered energy. Cuts
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Page 35 and 36: 538714Cld0,9~~~~~~~U0CldCIO.0a.)a.)
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Page 78 and 79: Munk et al. Phil. Trans A, volume 2

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