Nomenclature

Background (total) velocity

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Symbol	Description	Units
$u$	zonal or longitudinal component of velocity	$\mathrm{m}{\mathrm{s}}^{-1}$
$v$	meridional or transverse component of velocity	$\mathrm{m}{\mathrm{s}}^{-1}$
$w$	vertical component of velocity	$\mathrm{m}{\mathrm{s}}^{-1}$
$u_e$	error velocity	$\mathrm{m}{\mathrm{s}}^{-1}$
V	velocity perpendicular to mean flow	$\mathrm{m}{\mathrm{s}}^{-1}$
$W_d$	Profiler fall speed	$\mathrm{m}{\mathrm{s}}^{-1}$
$U_P$	Flow speed past sensor	$\mathrm{m}{\mathrm{s}}^{-1}$
b	Along-beam velocity from acoustic Doppler sensor	$\mathrm{m}{\mathrm{s}}^{-1}$
$b^{\prime }$	Along-beam velocity from acoustic Doppler sensor with background flow deducted	$\mathrm{m}{\mathrm{s}}^{-1}$
$\delta z$	Vertical size of measurement bin for acoustic Doppler sensor	$\mathrm{m}$
r	Along-beam distance from acoustic Doppler sensor	$\mathrm{m}$
$\delta r$	Along-beam bin size for acoustic Doppler sensor	$\mathrm{m}$
$\theta$	Beam transmit and receive angle relative to instrument axis for acoustic Doppler sensor	${}^{\circ }$

Turbulence properties

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Symbol	Description	Eqn	Units
$\epsilon$	The rate of dissipation of turbulent kinetic energy per unit mass by viscosity		$\mathrm{W}{\mathrm{kg}}^{-1}$
$R_i$	(Gradient) Richardson number; the ratio of buoyancy freqency squared to velocity shear squared	$R_i=\frac{N^2}{S^2}$
$P$	The production of turbulence kinetic energy, in a steady uniform stratified shear flow, equals the product of the Reynolds stress and the shear, for example $P=-\overline{u^{\prime }{w}^{\prime }}\frac{\partial U}{\partial z}$ . The production is balanced by the rate of dissipation turbulence kinetic energy through viscous friction, $\epsilon$ and the production of potential energy by the buoyancy flux, $B=-\frac{g}{\rho }\overline{{\rho }^{\prime }{w}^{\prime }}$.	$R_f=\frac{-B}{P}$		$R_f$	Flux Richardson number; the ratio of the buoyancy flux expended for the net change in potential energy (i.e., mixing) to the shear production of turbulent kinetic energy.	$R_f=\frac{-B}{P}$
$\mathrm{\Gamma }$	"Mixing coefficient"; in a stratified turbulent shear flow (where the production of turbulent kinetic energy by shear and the Reynolds stress, $P$, equals the rate of dissipation, $\epsilon$, plus the buoyancy production, $B$), it is the ratio of the rate of potential energy due to buoyancy production to the rate of loss of kinetic energy through viscous friction.	$\mathrm{\Gamma }=\frac{B}{\epsilon }=\frac{R_f}{1-R_f}$
${\kappa }_{\rho }$	Turbulent eddy diffusivity via the Osborn (1980) model	${\kappa }_{\rho }=\mathrm{\Gamma }\epsilon N^{-2}$	${\mathrm{m}}^2{\mathrm{s}}^{-1}$
$D_{LL}$	Second-order longitudinal structure function	$D_{LL}=⟨[b^{\prime }(r)-b^{\prime }(r+n\delta r){]}^2⟩$	${\mathrm{m}}^2{\mathrm{s}}^{-2}$

Fluid properties and background gradients for turbulence calculations

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Symbol	Description	Eqn	Units
$S_P$	Practical salinity		$-$
$T$	Temperature		${}^{\circ }\mathrm{C}$
$P$	Pressure		$\mathrm{dbar}$
$\rho$	Density of water	$\rho =\rho (T,S_a,P)$	$\mathrm{kg}{\mathrm{m}}^{-3}$
$\alpha$	Temperature coefficient of expansion	$\alpha =\frac{1}{\rho }\frac{\partial \rho }{\partial T}$	${\mathrm{K}}^{-1}$
$\beta$	Saline coefficient of contraction	$\beta =\frac{1}{\rho }\frac{\partial \rho }{\partial S_a}$
$S$	Background velocity shear	$S={({\left(\frac{\partial U}{\partial z}\right)}^2+{\left(\frac{\partial V}{\partial z}\right)}^2)}^{1/2}$	${\mathrm{s}}^{-1}$
${\nu }_{35}$	Temperature dependent kinematic viscosity of seawater at a practical salinity of 35	$\sim 1\times {10}^{-6}$	${\mathrm{m}}^2{\mathrm{s}}^{-1}$
${\nu }_{00}$	Temperature dependent kinematic viscosity of freshwater	$\sim 1\times {10}^{-6}$	${\mathrm{m}}^2{\mathrm{s}}^{-1}$
${\mathrm{\Gamma }}_a$	Adiabatic temperature gradient -- salinity, temperature and pressure dependent	$\sim 1\times {10}^{-4}$	$\mathrm{K}{\mathrm{dbar}}^{-1}$
$N$	Background stratification, i.e buoyancy frequency	$N^2=g[\alpha ({\mathrm{\Gamma }}_a+\frac{\partial T}{\partial z})-\beta \frac{\partial S_P}{\partial z}]$	$\mathrm{rad}{\mathrm{s}}^{-1}$

Theoretical Length and Time Scales

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Symbol	Description	Eqn	Units
${\tau }_N$	Buoyancy timescale	${\tau }_N=\frac{1}{N}$	$\mathrm{s}$
$T_N$	Buoyancy period	$T_N=\frac{2\pi }{N}$	$\mathrm{s}$
$L_E$	Ellison length scale (limit of vertical displacement without irreversible mixing)	$L_E=\frac{⟨{\rho }^{\prime 2}{⟩}^{1/2}}{\partial \bar{\rho }/\partial z}$	$\mathrm{m}$
$L_Z$	Boundary (law of the wall) length scale	$L_Z=0.39z_w$ with 0.39 being von Kármán's constant	$\mathrm{m}$
$L_S$	Corssin length scale	$L_S=\sqrt{\epsilon /S^3}$	$\mathrm{m}$
$L_K$	Kolmogorov length scale (smallest overturns)	$L_K={\left(\frac{{\nu }^3}{\epsilon }\right)}^{1/4}$	$\mathrm{m}$
$L_o$	Ozmidov length scale, measure of largest overturns in a stratified fluid	$L_o={\left(\frac{\epsilon }{N^3}\right)}^{1/2}$	$\mathrm{m}$
$L_T$	Thorpe length scale	$L_T$	$\mathrm{m}$
$z_w$	Distance from a boundary	$z_w$	$\mathrm{m}$

Turbulence Spectrum

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These variables are used to express the Turbulence spectrum expected shapes.

Symbol	Description	Eqn	Units
$\mathrm{\Delta }t$	Sampling interval	$\frac{1}{f_s}$	$\mathrm{s}$
$f_s$	Sampling rate	$f_s=\frac{1}{\mathrm{\Delta }t}$	${\mathrm{s}}^{-1}$
$\mathrm{\Delta }s$	Sample spacing	$\mathrm{\Delta }s=U_P\mathrm{\Delta }t$	$\mathrm{m}$
$\mathrm{\Delta }l$	Linear dimension of sampling volume (instrument dependent)		$\mathrm{m}$
$f$	Cyclic frequency	$f=\frac{\omega }{2\pi }$	$\mathrm{Hz}$
$\omega$	Angular frequency	$\omega =2\pi f$	$\mathrm{rad}{\mathrm{s}}^{-1}$
$f_N$	Nyquist frequency	$f_N=0.5f_s$	$\mathrm{Hz}$
$k$	Cyclic wavenumber	$k=\frac{f}{U_P}$	$\mathrm{cpm}$
$\hat{k}$	Angular wavenumber	$\hat{k}=\frac{\omega }{U_P}=2\pi k$	$\mathrm{rad}{\mathrm{m}}^{-1}$
$\tilde{k}$	Normalized wavenumber	e.g., $\tilde{k}=k{L}_K,L_K={\left({\nu }^3/\epsilon \right)}^{1/4}$	-
$\tilde{\mathrm{\Phi }}$	Normalized velocity spectrum	e.g., ${\tilde{\mathrm{\Phi }}}_u(\tilde{k})={\left(ϵ{\nu }^5\right)}^{-1/4}{\mathrm{\Phi }}_u(k)$	-
$\tilde{\mathrm{\Psi }}$	Normalized shear spectrum	e.g., $\tilde{\mathrm{\Psi }}(\tilde{k})=L_K^2{\left(ϵ{\nu }^5\right)}^{-1/4}\mathrm{\Psi }(k)$	-
$k_{\mathrm{\Delta }}$	Nyquist wavenumber, based on sampling volume size $\mathrm{\Delta }l$	$k_{\mathrm{\Delta }}=\frac{0.5}{\mathrm{\Delta }l}$	$\mathrm{cpm}$
$k_N$	Nyquist wavenumber, via Taylor's hypothesis	$k_N=\frac{f_N}{U_P}$	$\mathrm{cpm}$
$\mathrm{\Psi }(k)$	Shear spectrum. Use ${\mathrm{\Psi }}_1$, ${\mathrm{\Psi }}_2$ to distinguish the orthogonal components of the shear. Use ${\mathrm{\Psi }}_N$ for the Nasmyth spectrum, ${\mathrm{\Psi }}_{PK}$ for the Panchev-Kesich spectrum and ${\mathrm{\Psi }}_L$ for the Lueck spectrum.		${\mathrm{s}}^{-2}{\mathrm{cpm}}^{-1}$
$\mathrm{\Phi }(k)$	Velocity spectrum. Use ${\mathrm{\Phi }}_u$, ${\mathrm{\Phi }}_v$, ${\mathrm{\Phi }}_v$, or ${\mathrm{\Phi }}_1$, ${\mathrm{\Phi }}_2$ , ${\mathrm{\Phi }}_3$ for the different orthogonal components of the velocity. Use ${\mathrm{\Phi }}_K$ for the Kolmogorov spectrum.		${\mathrm{m}}^2{\mathrm{s}}^{-2}{\mathrm{cpm}}^{-1}$