Table 860 653 



OCEANOGRAPHY 



(See Nat. Res. Council Bull. 85, 1932) 

 TABLE 860. — Waves of the Sea (Patton, Marmer) 



Wave forms. — Progression of wave form across a stretch of water ; actual cyclic move- 

 ment (circular in deep water; elliptical, long axis horizontal, in shallow) of particle; there 

 also may be a forward propagation of particles. Form of ocean wave, trochoid or prolate 

 cycloid. If a = height of crest, b = depth of trough, both from undisturbed water level, 

 h and I, the height and length of wave, then a = (h/l) + 0.7854 (h'/l) ; b=(h/2) 

 — o.7854(/i70 (Gaillard, 1904). 



Wind -waves in deep water are surface waves. Particle motions decrease rapidly with 

 depth; halved for each 1/9 I of depth. If height of wave— vertical distance between crest 

 and trough, /, distance between consecutive same phases, v, velocity, p, period, v = l/p\ 

 v= (g/2ir)tl; gr = gravity; p = (2w/g)hl= (2ir/g)v; l — (g/2w)p 2 = (2w/g)v 2 . 



Principal factors: Strength and duration of wind, fetch exposed to wind. Highest 

 (hurricane) waves in open sea, about 15 m; may be higher through interference, etc., over 

 30 m. No fixed relation between / and h. Some observed ratios (Gaillard) : h, 0.6 to 

 1.5 m, 30; 3 to 6 m, 20; > 9 m, 14. 150 m long not uncommon; some up to 300 m. 



Swell. — As waves pass from disturbed area they degenerate to a gentle swell ; not im- 

 portant in mid-ocean but may be dangerous to exposed coasts and harbors. Periods 

 (Morocco coasts) 7 to 20 sec, height 0.45 to 4.5 m. 



Waves in shallow water are considerably different. If depth of water greater than length 

 of wave, water deep; less, shallow. Wave of translation (Russell, Rep. British Assoc, 

 8, 417, 1838; 14, 311, 1845).— All the water is .above the undisturbed level; there is actual 

 translation of the water particles ; due to sudden addition of water, as with breaking of a 

 wave. 



Wave pressure may be as great as 3.3 X 10" dyne/cm 2 . 



Seismic waves: Lisbon tidal wave, 1755, 18,3 m; Krakatoa, 1883, 21 m at Telok Betong. 



Smithsonian Tables 



