Some Aspects of Turbulence Role in Oceanic Currents - Selected Topics of Computational and Experimental Fluid Mechanics - page 178

(a) (b)

Fig. 2 Detailed maps of the survey regions for the two different projects: a LADDER, Larval
dispersal on the deep east Pacific rise and b DIMES, Diapycnal and Isopycnal mixing experiment
in the southern ocean

2.1 Fine-Structure Parameterization

The particular “fine-structure parametrization” described in this manuscript is used to
estimate the vertical diffusivity parameters based on hydrographic profiles
(temperature, salinity and pressure) and velocity profiles (zonal and meridional
velocities). These variables are some of the most vastly measured quantities in
the ocean using LADCP/CTD casts (Lowered Acoustic Doppler Current Pro-
filer/Conductivity Depth Temperature). From those profiles, the internal wave field
shear, V Z ,(Eq. 2 ) and strain,

− N 2

N 2

N 2 , can be estimated. This internal wave field
undergoes non-linear interactions and departs from a wave field of reference com-
monly called “Garrett-Munk spectrum”. Themore it departs from this semi-empirical
background spectrum the more/less turbulent mixing results. The scalings of turbu-
lence in the ocean interior resulting fromwave-wave interactions have been validated
since 1989 (Gregg 1989 ). Those methods have been improved from the shear-based
parametrization (Gregg 1989 ), to the strain-based parametrization with a prescribed
shear/strain variance ratio (Polzin et al. 1995 ), and finally the combination of both:
shear-and-strain-based parametrization (Gregg et al. 2003 ).
These “fine-structure” approaches have been used to estimate diffusivities as part
of a very large ongoing project, CLIVAR (Climate Variability and Predictability),
which among many other measurements performs LADCP/CTD measurements on
routinely basis. Kunze et al. ( 2006 ) performed one of the most exhaustive estimates
of diapycnal mixing using the databases from that particular experiment. He kindly
provided the code used in Kunze et al. ( 2006 ) and after validating it, it was possible to
observe for the LADDER project large values of dissipation near the seamount chain.

ʾ z =

2.2 Microstructure Direct Measurements

The microstructure measurements are performed with an autonomous device, which
contains several probes with high resolution: shear probes ( ∂ u /∂ z and ∂ v /∂ z ),