IM No, 37? 



This system had obvious shortcomings in that it did not indicate the 

 direction of horizontal flow and had relatively low time response (probably 



of the order of 1 or 2 seconds). Problems were encountered regarding the 

 best method of suspending the system from the vessel j i.e., by a rigid 

 vertical rod, a bottom mounting, or (as was finally decided) simply a 

 counter-weighted cable suspension. Since the tidal current in the estuary 

 attained 1>0 cm sec" 1 , it is probable (and was indeed inferred in the 

 report) that the dynamic interaction of the flow with the system may have 

 biased the records. 



Other measurements included mean current profiles, temperature, and 

 salinity fluctuations Computations were made of stability and of mixing 



attributes by using the methods of Jaeobson (1918) and Pritchard (1952). 



Of particular Interest are the estimated values of the Reynolds stress -pu-'u>' 

 (see equation 111-28). These were obtained from observations made on two 

 cruises by abstracting the horizontal and vertical velocity values at 3°second 

 intervals from the 2-minute records made at various stages of the tidal flow. 

 All records were obtained at low sea States because gross wave motions would 

 have disturbed the anchored vessel and, hence, perturbed the suspended meter 

 system. Twenty°eight estimates of the Reynolds stress were reported at 

 various depths from 0.2 meter down to 8.5 meters. Most of these estimates 

 fell below the 0.1 probability that the_ results were simply a result of 

 random correlation. The values of -paW" ranged from -1.7^ to -+62.2 dynes 

 cm" 2 , with a mean of about +lk and +23 dynes cm" 2 for the first and second 

 cruises, respectively. 



It is interesting, if not suggestive, that in both series of observa- 

 tions the largest estimated stresses often occurred near the surface, which 

 was well above the strong mean shear zone at the point of the pycnocline 

 caused by the salinity wedge present in the estuary e 



A series oi simultaneous measurements of the vertical and Horizontal 

 velocity components was ooxaired by Eowden and Fairfoaim (1956) and Bowden 

 (1962). These measurements were made utilizing a modification of an electro- 

 magnetic flow meter designed by Guelke and Schoute-Vanneek (l-9^7)» Ihe 

 sensing head of this meter is about 10 cm in diameter and contains an 

 external orthogonal array of electrodes and internal induction coils which 

 generate a constant magnetic field. The sea water, being an electrolyte, 

 produces an em£ proportional to the flux of the ions through the magnetic 

 field. This electric field is sensed by the two orthogonally mounted 

 electrode pairs „ Hence, from the voltage across the electrodes one can 

 infer the instantaneous vertical and horizontal fluid velocities. The 

 response time of this instrument is reported to be about 0.8 second* 

 These measurements are' significant in that they are the first recorded 

 attempt to directly measure the Reynolds stress within the ocean. The 

 authors report Reynolds stress values at distances from the bottom less 

 than 2 meters, ranging from +l.k to +4.1 dynes cm" 2 and directed downward 

 as indicated by a negative value of the co=>variance s These stresses are 



