TM No. 377 



The vertically mounted ducted impeller provided the most accurate data 



because of stability in the suspension from the BBELS. By attaching a fast- 



response thermal sensor to the w impeller, one can measure the quantity - f>CpTw\ 

 where Cp is the thermal heat capacity of sea water, and T 1 is the temperature 

 fluctuation about the mean c This quantity, which has units of cal cm"^ sec" , 

 is a measure of net heat flux through a unit area brought about by the co variance 

 -Tty' . The BBELS, being located in an area having a shallow seasonal thermo- 

 cline to provide maximum temperature gradients, provides a suitable platform 

 from which to make such heat flux measurements. A small fast-response (0.1-0.2 

 sec) thermal sensor is under construction, and plans are being made to use it in 

 conjunction with the new low-velocity-threshold ducted impeller. 



2. There is little concrete evidence of the direct generation of a surface 

 current by wind stress. Recent results of open ocean current measurements (Day 

 and Webster, 1966) indicate fluctuations in near-surface currents which correlate 

 with wind fluctuations. However, obvious difficulties, both in precise current 

 measurements and in monitoring wind conditions, make the correlations somewhat 

 tenuous. What is needed is a precise monitoring of both wind and surface current 

 during a period of time when extreme wind variations occur, as with the passing 

 of a line squall. Such measurements of surface current and vertical gradient of 

 surface current, along with precise wind velocity monitoring, could be made from 

 the BBELS. This fixed platform would allow positioning of a number of vertically 

 spaced LBtDUM-type devices in the water column. By subtracting the effects of 

 tide current from the records, one might be able to determine the correlation 

 between wind intensity and wind-produced surface current. 



3. Plans are underway to mount rigidly a three -component (x, y, z) ducted 

 current meter (OMDUM IV") from the sea bottom to measure variances and covariances 

 associated with mean flow interaction with bottom roughness elements. This system 

 will contain a miniature battery-powered tape, recorder to store the raw output of 

 the u, v, and w velocity channels. It is hoped that a deep research vehicle can 

 be used to plant this system and to observe its response. 



4. The ducted meters, having both rapid response and directional charac- 

 teristics, could be used to assess the dynamics of strings of Richardson current 

 meter arrays placed in the deep ocean. These systems consist of several self- 

 contained Savonius rotor meters tethered in series between the sea surface and 

 the bottom, which may be deeper than 5000 meters. The dynamic motions, which 

 may be highly oscillatory and occur at different depths, can cause complex 

 perturbations of the suspended current meters, thus biasing the data. 



This dynamic system of moored current meters is so complex that an attempt 

 to analyze the three-dimensional motions of each tethered instrument from its own 

 data is prohibitive, since the driving forces are not known with any degree of 

 precision. It is, of course, these driving forces which we wish to determine in 

 the first place. 



By mounting orthogonal sets of ducted meters on the current meter system, one 

 could monitor the various translational and rotational motions occurring at various 

 points of the mooring system. In particular, the vertical surging motions could be 



167 



