REPORT ON OCEANOGRAPHY 61 



Adventional variation of temperature and salinity due to tidal cur- 

 rents was discussed by T. Ichiye (OM, 4, 1952). He also treated the 

 modification of wave form when a long wave propagates through a 

 channel of varying sections. He applied his theory to the Akashi Seto, 

 a channel connecting Osaka Bay to another basin situated to the west, 

 and computed the permeability of the waves when two eave trains meet 

 in this channel (KMOM, 9, 1951). 



A new development in the discussion of the tidal currents in the 

 Straits of Shimonoseki separating Honshu and Kyushu, two major is- 

 lands of Japan, was made by Mashito, Nakano. He also pointed out 

 a comment about its prediction (GJ, 58, 1949, 213-216). 



Seiches and Secondary Undulations of Tides 



On the occasion of cyclonic storms attacking our islands we fre- 

 quently notice oscillations of period 1-3 minutes accompanying the 

 tidal oscillations on mareograms. This phenomenon, now called "surf 

 beats," has been long known in Japan. M. Nakano reports a remark- 

 able series of such undulations which accompanied the storm of 1-5 

 April 1936, and observed on the mareograms of tidal stations along the 

 Japanese coasts. Nakano gives a very intensive examination of this phe- 

 nomenon (OM, 1, 1949, 13-32). 



T. Ichiye treated theoretically the oscillations which will be caused 

 by a sudden impulse of wind exerted on the sea surface and obtained 

 the relation between the shape of the bay, time variation of the stress 

 and the amplitude. He pointed out that an impulsive stress is more 

 effective on producing seiches (JOSJ, 6, 1950), 



Sea Level 



In 1951 S. Yamaguti showed that the monthly mean sea-level cor- 

 rected for astronomical, meteorological, and oceanographical effects, can 

 be fairly used for discussion of the vertical displacement of the earth's 

 crust and sometimes may be used in place of precise levelling (GSB, 2, 

 1950). 



Waves 



Studies of waves have been made partly in connection with some 

 practical applications. Forecasting of waves and swells has been needed 

 for the safety of ships, for protection of coasts and harbors, and in 

 connection with various problems of coastal engineering. These fore- 

 casting and practical studies have mainly been carried out by the staff of 

 the Hydrographic Office, Central Meteorological Observatory, and a 

 number of branch organizations (M. Nakano, S. Unoki, and K. Yuge, 

 OM, 5, 1953; H. Arakawa and K. Suda, MWR, 81, 1953; M. Uda, GM, 



