In order to obtain a very accurate power spectrum analysis of waves 

 of periods from 10 to 30 hours, which include the tidal periods, the time 

 interval would have to be 3 to 5 hours and the length of the period, therefore, 

 at least 3 to 5 times as long as the present records, i.e.,ifrom 75 to 125 days. 

 Such a record could be obtained at a fixed weather ship location if regular 

 bathythermograph readings were taken there. 



The presence of aliasing in the record may be important. Pierson (1952) 

 defines aliasing by saying that if the observational interval is too large, 

 the power per band width can have other values of power from other frequencies 

 aliased into (or added into) the true values for the particular band desired. 

 If there is any large amount of pbwer associated with periods of less than 

 one hour in the present case, the spectral analysis is in error by that amount. 

 Schule (1952) has discussed the existence of internal waves with periods of 

 minutes. In order to show that internal waves with such periods have ap- 

 preciable power, it would be necessary to have records taken every minute, 

 comprising a large number of observations with lags of 200 to 500 taken into 

 account. However, if the power associated with internal waves of periods 

 less than one hour is low, i.e., in the noise level, it then becomes possible 

 to consider that the spectrum is white below about 20 hours and that the 

 conclusions of the preceding paragraphs apply. 



The mean depth of the 66° F. isotherm was 32h feet and its standard 

 deviation 87 feet. The mechanism which caused approximately diurnal periods 

 in the isothermal depth could not have been vertical heating, for two reasons: 

 the depth is too great, and the isotherm was located below the thermocline, 

 which was fairly sharp. A horizontal pulsation of water of different tempera- 

 tures could have caused* the observed change. The average diurnal change in 

 the depth of the isotherm was about 150 feet. It remains therefore to find 

 the mechanism which caused diurnal advection of heat into the area of Operation 

 STANDSTILL. 



V. EDDY MOTION IN THE AREA OF 0FERATI0N STANDSTILL 



A. Eddies Resulting From Instability 



As a result of a survey of the Gulf Stream made almost simultaneously 

 with Operation STANDSTILL, it has been suggested that regular pulses in the 

 Gulf Stream may be initiated by the diurnal tide of the Gulf of Mexico (Von 

 Arx, Bumpus, and Richardson, 195M. At intervals of 2h hours the tidal motion 

 may set into action jets of fast-moving water and produce noticeable fluctua- 

 tions in the structure of the Gulf Stream. On the south side of the stream, 

 it may be postulated that eddies, set up in phase with the inertial period, 

 influenced the area of Operation STANDSTILL. Each eddy contained a jet of 

 warmer water in swift motion followed by a slower moving current of cooler 

 water. As this alternately warm and cool water passed through the area of 

 the operation, the isotherms moved upward and downward in response to the 

 water movement. 



The regular pulses in the G u lf Stream may be compared mathematically to 

 perturbations in a geostrophic flow. If a geos trophic flow is perturbed, 

 the flow vector will show an acceleration which will cause a particle to 

 deviate from geostrophic flow. This deviation may be represented as 



