2.4. Sourct~s of Occciri T irrhulmct.
Turbulcnce may be generated in the ocean by a wide variety of mechanisms such as shear flow, breaking surface and internal wives, and buoyant
instahility due to surface cooling or internal . . inversions ” in the iiormally
stably stratified water column. Less obvious mechanisms such as nonlinear
wave -wave. wave-shear, and wave- stratification interactions may also
occur, as well as phenomena resulting from the difference in molecular
diffusivities of momentum, temperature. and salinity. One of the most challenging problems of physical oceanography will be to isolate the wide variety
of such turbulence-related phenomena which no doubt exist in some parts of
the diverse oceans and which will be revealed by increasingly smsitive and
detailed measurements.
3. Rtsi i 1 . n
2.1. C r o m w l l Cirrrlvit
The instrumented **fish” described previously was lowed at the equator
and at I ’ N at depths just above the point of maximum velocity of the Pacific
Equatorial undercurrent. Dissipation rates c,. cq, x , , and x3 were estimated
from ducted current meter and cold film temperature spectra as described in
Williams and Gibson (1974) and Gibson and Williams (1973). Mean velocity. temperature, and salinity profiles were determined by Taft et 01. (1974)
and were used to calculate the vnlues of Vaisailla frequency N, Richardson
number Ri, eddy viscosity vT. and eddy diffusivity of sensible heat D., shown
in Table 11.
Detailed description of the measurements leading to Table I1 are given in
Williams and Gibson (1974). Substantial agreement was found between the
various estimate of x and G, which ranged between 10- ’ and lo-* C2/sec
for x and were constant at 0.08 cma/sec3 Tor E. From these values and from
the mean temperature profile it was possible to calculatc vT values of 12 -25
cm2/sec compared to 0.5-27 cm2/sc for D,, which are quite reasonable
compared to other diffusivity estimates determined by previous oceanographic observations of mean quantities (see Table I11 for definition of v I
and DT).
Attempts were made to increase the bridge voltage until the probe became
velocity sensitive in a constant current mode, but these were unsuccessful
because of high noise. By adjusting bridge voltage and frequency, and by
expcrimenting with combinations of filters and differentiation of the signal
before recording, taking on-line fast Fourier transform power spectra with
the IIIM 18(X) computer on hoard the Thomcrs Wasliirigron it was possible to
extract the rather noisy temperature spectra in Williams and Gibson (1974)
Turbulcnce may be generated in the ocean by a wide variety of mechanisms such as shear flow, breaking surface and internal wives, and buoyant
instahility due to surface cooling or internal . . inversions ” in the iiormally
stably stratified water column. Less obvious mechanisms such as nonlinear
wave -wave. wave-shear, and wave- stratification interactions may also
occur, as well as phenomena resulting from the difference in molecular
diffusivities of momentum, temperature. and salinity. One of the most challenging problems of physical oceanography will be to isolate the wide variety
of such turbulence-related phenomena which no doubt exist in some parts of
the diverse oceans and which will be revealed by increasingly smsitive and
detailed measurements.
3. Rtsi i 1 . n
2.1. C r o m w l l Cirrrlvit
The instrumented **fish” described previously was lowed at the equator
and at I ’ N at depths just above the point of maximum velocity of the Pacific
Equatorial undercurrent. Dissipation rates c,. cq, x , , and x3 were estimated
from ducted current meter and cold film temperature spectra as described in
Williams and Gibson (1974) and Gibson and Williams (1973). Mean velocity. temperature, and salinity profiles were determined by Taft et 01. (1974)
and were used to calculate the vnlues of Vaisailla frequency N, Richardson
number Ri, eddy viscosity vT. and eddy diffusivity of sensible heat D., shown
in Table 11.
Detailed description of the measurements leading to Table I1 are given in
Williams and Gibson (1974). Substantial agreement was found between the
various estimate of x and G, which ranged between 10- ’ and lo-* C2/sec
for x and were constant at 0.08 cma/sec3 Tor E. From these values and from
the mean temperature profile it was possible to calculatc vT values of 12 -25
cm2/sec compared to 0.5-27 cm2/sc for D,, which are quite reasonable
compared to other diffusivity estimates determined by previous oceanographic observations of mean quantities (see Table I11 for definition of v I
and DT).
Attempts were made to increase the bridge voltage until the probe became
velocity sensitive in a constant current mode, but these were unsuccessful
because of high noise. By adjusting bridge voltage and frequency, and by
expcrimenting with combinations of filters and differentiation of the signal
before recording, taking on-line fast Fourier transform power spectra with
the IIIM 18(X) computer on hoard the Thomcrs Wasliirigron it was possible to
extract the rather noisy temperature spectra in Williams and Gibson (1974)