instrument meters. The box together with 

 storage batteries is then installed in a skiff 

 and anchored at sea. The instrument meters 

 are 0-1 microammeters calibrated in degrees 

 Centigrade, wind velocity, etc. Thermistors 

 are used as sensing elements in the instru- 

 ment string. Electronic damping is utilized 

 to minimize any tendency of the instrument 

 needles to swing due to the rolling and pitch- 

 ing of the skiff. The camera is a 16 mm., 

 nnagazine-loaded type, operated by a timing 

 motor, and takes an exposure at half-hour 

 intervals. The timing motor also operates a 

 microswitch which turns on a bank of incan- 

 descent lights for a period of a few seconds 

 every half hour. A simple transistorized 

 flasher circuit is used to operate a beacon 

 light mounted on the mast of the skiff. 



At the present time the lead-acid storage 

 battery is being used to power the anchored 

 instrument stations. Research and develop- 

 ment is being conducted on means of utilizing 

 a thermoelectric generator for the purpose 

 of charging batteries, the heat to be supplied 

 by butane gas. Some work has also been 

 conducted on a device that makes use of the 

 rolling motion of the skiff in which it is 

 installed, to produce sufficient electric current 

 to keep a storage battery charged. 



The hulls have been camouflaged to reduce 

 the likelihood of interference with them. A 

 radio-signalling device has been developed to 

 aid location. 



Moored station type C, for study of internal 

 waves (C. S. Cox)--- From January 1959 through 

 June 1960 the following work was undertaken 

 to develop methods of recording internal waves 

 from unattended moored instrument stations 

 and to analyze the measurements in order 

 to find the mechanisms of generation, propa- 

 gation, and decay of the waves.* 



Internal waves in the sea exist because 

 sea water is stratified. Displacement of in- 

 ternal layers from their equilibrium position 

 results in the formation of waves within the 

 body of the water which can propagate away 

 from the generator. The internal waves are 

 important to the economy of the sea for a 

 variety of reasons: 



1. Internal waves by their oscillatory na- 

 ture introduce uncertainty into discrete meas- 

 urements of dynamic heights. 



' Peripheral to the main investigation, this study received about 25 

 percent of Its support from the STOR program because of the need to 

 encourage the design of other types of moored stations after the fail- 

 ure of type A. It was also seen that the study of internal waves per se 

 could have some significance for the tuna oceanography program, 

 e,g., as a mechanism for distributing biota. The bulk of the support, 

 about 75 percent of the total, came from the Office of Naval Research. 



2. Turbulence in the sea is intimately con- 

 nected with internal waves: weak turbulent 

 eddies in a vertical plane form internal waves, 

 and conversely, breaking internal waves form 

 vertical turbulence. Thus internal waves are 

 connected with mixing processes in the sea. 



3. Internal waves carry off energy from 

 one place in the sea and distribute it else- 

 where. For example, it has been calculated that 

 tidal streams in the deep sea lose energy to 

 internal waves when they pass over sea 

 mountains of a suitable shape. The average 

 energy transferred in this way probably is 

 larger than the energy supplied by wind- 

 induced stirring to water below 500 m. depth. 

 It is part of the aim of this investigation to 

 find the amount of energy made available to 

 internal waves in this way, how far it can 

 be transported and by what mechanism it 

 becomes degraded to random motions. 



4. Internal waves may influence sea life 

 directly by subjecting organisms to vertical 

 and horizontal motions of considerable extent. 

 It is not uncommon to find internal tidal 

 oscillations with a vertical amplitude of 70 m., 

 somewhat below the euphotic zone. It seems 

 likely that the associated vertical velocities 

 of 1 cm. sec."l will have a profound effect on 

 slow moving animals which migrate below the 

 euphotic zone. 



In spite of their importance few observa- 

 tions have been made of internal waves in 

 the deep sea. Recent observations by Reid 

 (1956) show the existence of large internal 

 tides off the California coast. Records of 

 sea bottom temperatures at depths of 50 m. 

 and 500 m. off Castle Harbor, Bermuda 

 (Haurwitz, Stommel, and Munk, 1959) show 

 the existence of irregular changes of re- 

 markably large amplitude (about 1° C. at 

 500 m.) which these authors attribute to a 

 continuous spectrum of internal waves. An 

 alternate explanation in terms of the con- 

 vection of turbulent eddies past the ther- 

 mometers is possible, however. Many papers 

 have dealt with observations and interpreta- 

 tion of internal tides (e.g., Defant, 1932, 1950) 

 but Haurwitz (1954) pointed out that most of 

 the periods of observation have been too short 

 to give statistically reliable results. There 

 is no question, however, that large amplitude 

 oscillations of low frequency do occur in the 

 ocean. 



To measure internal waves in the deep sea 

 and to resolve them into their component 

 frequencies require observations of vertical 

 motion (or, equally well, of temperature at 

 fixed depths) for a sufficient time duration, 

 preferably a few weeks. To separate the os- 

 cillations into normal modes in the vertical, 

 one must observe from surface to bottom. 



11 



