General Theory of Ocean Currents in a Homogeneous Sea 



449 



extent of this type of inertia oscillation was examined in later current measurements in 

 the Baltic. Recordings from four anchored oceanographic research vessels between 

 the Latvian coast and Oland (along the 56° 20' parallel) in the Baltic all, except for 

 the vessel next to the Latvian coast, showed regular inertia oscillations at 15 m depth 

 (density transition layer) with amplitudes of up to 20 cm/sec. The inertia oscillations 

 (period 14-42 h = i pendulum day) had almost the same phase value but decreased 

 very rapidly towards the coast. The water masses along the parallel investigated thus 

 took part as a whole in the inertia oscillations (Kullenberg and Hela, 1942). 



Fig. 196. Velocity components of the currents pictured in Fig. 195 (according to Ekman). 



Specific inertia oscillations were found at the "Altair" anchor station in the area of 

 the Gulf Stream north of the Azores (44-6° N. 34-0° W., 16-20 June 1938). Analysis 

 of current measurements made at this station down to great depths (Defant, 1940 b) 

 showed that besides the semi-diurnal tide there was also a 17 h oscillation; this had a 

 large amplitude at all depths but the phases changed with depth. These phase changes 

 which are related to the oceanographic structure at this station indicate that these 

 inertia oscillations were coupled with internal waves which are the expression of a whole 

 system of inertia oscillations of the surrounding water masses (see Vol. II). The com- 

 bination of the 1 7 h wave with the semi-diurnal tide gives rise to beat phenomena with 

 a period of 14-3 h and a beat interval of 1-86 days. This shows in a typical way the 

 current values at all depths so that there can be no doubt that besides the tides, 

 inertia oscillations were present here. Harmonic analysis gave besides the tidal wave 

 also the value for the 17 h wave presented in Table 130. Division into different layers 

 follows from the similarity in the phase which between 15 and 30 m and between 

 500 and 800 m shows an abrupt change of about half a period. The 1 7 h wave shows 



Table 130. Inertia oscillations at the ''Altair' station 

 (16-20 Jime 1938; 44-6= N., 34-0° W.). Period 17 h 



2G 



