Mixing and diapycnal advection in the ocean
نویسندگان
چکیده
In the stratified ocean, vertical motions arise from both adiabatic and diabatic mechanisms. Diapycnal advection is the vertical component of flow across an isopycnal surface which occurs when mixing produces a divergent flux of buoyancy. Buoyancy forcing of the lateral flow by vortex stretching occurs when diapycnal advection rates vary with depth. Microstructure observations of enhanced turbulence above rough topography are presented. These data allow us to distinguish the influence of diabatic forcing on the circulation. Estimates of diapycnal advection are used to quantify the diabatic flow, and the role of diapycnal advection as a mechanism of vortex stretching on the circulation is assessed. The divergence of diapycnal mass flux is found to be a significant forcing mechanism for the circulation occurring above fracture zone topography. Moreover, both the direction and magnitude of diapycnal advection are dependent on the efficiency of turbulence at generating a buoyancy flux. Depth variations of diapycnal advection suggest the mixing efficiency is reduced in weakly stratified abyssal canyons.
منابع مشابه
Cautionary Tales of Persistent Accumulation of Numerical Error: Dispersive Centered Advection
In ocean modelling there is widespread appreciation for the severity of any error which involves spurious diapycnal mixing. Indeed, the extreme disparity between the timescales which characterize mixing in the isopycnal and diapycnal directions is a defining feature of oceanic fluid dynamics. Particular concern is therefore raised by any source of spurious diapycnal mixing which is persistent, ...
متن کاملSpurious Diapycnal Mixing Associated with Advection in a z-Coordinate Ocean Model
This paper discusses spurious diapycnal mixing associated with the transport of density in a z-coordinate ocean model. A general method, based on the work of Winters and collaborators, is employed for empirically diagnosing an effective diapycnal diffusivity corresponding to any numerical transport process. This method is then used to quantify the spurious mixing engendered by various numerical...
متن کاملInfluence of the Nonlinear Equation of State on Global Estimates of Dianeutral Advection and Diffusion
Recent work on the global overturning circulation and its energetics assumes that processes caused by nonlinearities of the equation of state of seawater are negligible. Nonlinear processes such as cabbeling and thermobaricity cause diapycnal motion as a consequence of isopycnal mixing. The nonlinear equation of state also causes the helical nature of neutral trajectories; as a consequence of t...
متن کاملComment on ‘‘Dynamical model of mesoscales in z-coordinates” and ‘‘The effect of mesoscales on the tracer equation in z-coordinates OGCMs” by V.M. Canuto and M.S. Dubovikov
Canuto and Dubovikov [Canuto, V.M., Dubovikov, M.S., 2006. Dynamical model of mesoscales in z-coordinates. Ocean Modelling, 11, 123–166; Canuto, V.M., Dubovikov, M.S., 2007. The effect of mesoscales on the tracer equation in z-coordinates OGCMs. Ocean Modelling 16, 17–27] claim that present oceanographic models ignore a leading-order diapycnal term in the mean buoyancy and tracer equations, whi...
متن کاملMulti-decadal trends in the advection and mixing of natural carbon in the Southern Ocean
[1] Multi-decadal trends in the advection, mixing, and airsea flux of natural carbon dioxide (CO2) in the Southern Ocean are investigated using output from a hindcast simulation of a non-eddy-resolving ocean model. Particular emphasis is placed on the model’s improved eddy-induced advection parameterization. From 1958 to 2007, the model predicts a significant increase in the outgassing of natur...
متن کامل