SECT. 5] SITRCiES 643 



either direction with the same phase velocity. With rotation of the earth, the 

 two frequencies differ in magnitude by /, and hence the phase velocities for 

 waves (of the same wavelength) moving to right or left along the coast differ 

 by //A* for the zero order. The effect of the earth's rotation becomes important, 

 as we would expect, only for waves whose period becomes appreciable as 

 compared to that of half a pendulum day. 



If the resurgences observed along the east coast of the United States are 

 related to a "wake" of edge waves trailing a hurricane according to the hypo- 

 thesis of Munk et al. (1956), edge waves would be formed whose phase velocity 

 would equal that of the speed of propagation of the hurricane along the coast. 

 Hurricanes in this region frequently progress northward, parallel to shore, over 

 the shelf. This direction corresponds to the positive y direction, and so cti, 

 which has the negative value, gives the appropriate frequency. The frequency 

 can be obtained from the first equation of (59) as a function of the phase 

 velocity, c = — aijk : 



1-1=7+/- 



Let us consider as an example the surge at Atlantic City, shown in Fig. 6 of 

 section 2, caused by the hurricane of 14-15 September, 1944. The velocity of 

 propagation of the storm northward along the coast was about 16 m/sec. 

 Setting this equal to c and putting s — 5.0 x 10~^ and /= 0.94 x 10"^ sec~i gives 

 7^ = 4.4 h and L = 250 km, as compared to the observed period of about 5.6 h. 



The most severe handicap of this theory, as applied to surges on a gently 

 sloping shelf, may be the omittance of the bottom stress. The method of taking 

 the bottom stress into account described in section 3-A would give a substantial 

 improvement. 



Freeman et al. (1957) have successfully reproduced some observed storm 

 tides along regular coastlines from wind observations by making some rather 

 surprising assumptions : they neglect shoreward transport, longshore surface 

 slope, field acceleration and divergence of transport (allowing the continuity 

 condition to be violated). 



References 



Bowden, K. F., 19.53. Note on wind drift in a channel in tlie presence of tidal currents. 



Proc. Roy. Soc. London, A219, 426-446. 

 Bowden, K. F., 1956. The flow of water through the Straits of Dover related to wind and 



differences in sea level. Phil. Trans. Roy. Soc. London, A248, 517-551. 

 Corkan, R. H., 1948. Storm surges in the North Sea, Vols. 1 and 2. U.S. Hydrographic 



Office, Misc. 15702, Washington, D.C. 

 Corkan, R. H., 1950. The levels in the North Sea associated with the storm disturbance of 



8 January 1949. Phil. Trans. Roy. Soc. London, A242, 493-525. 

 Crease, J., 1956. Long waves on a rotating earth in the presence of a semi-infinite barrier. 



J. Fluid Mech., 1, 86-96. 

 Dantzig, D. van, 1958. Free oscillation of a fluid in a rectangular basin. Math. Cent. 



Amsterdam, Rep. TW 49. 

 Dantzig, D. van, 1959. Einige analytische Ergebnisse iiber die Wasserbewegung in einem 



untiefen Meere. Z. angew. Math. Mech., 39, 169-179. 



