Jonas Nycander

Lagrangian decomposition of the Deacon Cell

The meridional overturning cells in the Southern Ocean are decomposed by Lagrangian tracing using velocity and density fields simulated with an ocean general circulation model. Particular emphasis is given to the Deacon Cell. The flow is divided into four major components: (1) water circling around Antarctica in the Antarctic Circumpolar Current (ACC), (2) water leaving the ACC toward the north into the three world oceans, (3) water coming from the north and joining the ACC, mainly consisting of North Atlantic Deep Water (NADW), and (4) interocean exchange between the three world oceans without circling around Antarctica. The Deacon Cell has an amplitude of 20 Sv, of which 6 Sv can be explained by the the east-west tilt of the ACC, 5 Sv by the east-west tilt of the subtropical gyre, and the remaining 9 Sv by the differences of the slope and depth of the southward transport of NADW and its return flow as less dense water. The diabatic or cross-isopycnal Deacon Cell is only 2 Sv.

Thermodynamic analysis of ocean circulation

Abstract Calculating a streamfunction as function of depth and density is proposed as a new way of analyzing the thermodynamic character of the overturning circulation in the global ocean. The sign of an overturning cell in this streamfunction directly shows whether it is driven mechanically by large-scale wind stress or thermally by heat conduction and small-scale mixing. It is also shown that the integral of this streamfunction gives the thermodynamic work performed by the fluid. The analysis is also valid for the Boussinesq equations, although formally there is no thermodynamic work in an incompressible fluid. The proposed method is applied both to an idealized coarse-resolution three-dimensional numerical ocean model, and to the realistic high-resolution Ocean Circulation and Climate Advanced Model (OCCAM). It is shown that the overturning circulation in OCCAM between the 200- and 1000-m depth is dominated by a thermally indirect cell of 24 Sverdrups (1 Sv ≡ 106 m3 s−1), forced by Ekman pumping. In th...

A Comparison of Tidal Conversion Parameterizations for Tidal Models

AbstractThe conversion of barotropic to baroclinic tidal energy in the global abyssal ocean is calculated using three different formulations. The calculations are done both “offline,” that is, using externally given tidal currents to estimate the energy conversion, and “online,” that is, by using the formulations to parameterize linear wave drag in a prognostic tidal model. All three schemes produce globally integrated offline dissipation rates beneath 500-m depth of ~0.6–0.8 TW for the M2 constituent, but the spatial structures vary significantly between the parameterizations. Detailed investigations of the energy transfer in local areas confirm the global results: there are large differences between the schemes, although the horizontally integrated conversion rates are similar. The online simulations are evaluated by comparing the sea surface elevation with data from the TOPEX/Poseidon database, and the error is then significantly lower when using the parameterization provided by Nycander than with the ...

Tidal generation of internal waves from a periodic array of steep ridges

The generation of internal gravity waves by an oscillatory tidal flow over a periodic array of thin vertical walls is calculated analytically. For small values of the non-dimensional height

The World Ocean Thermohaline Circulation

B=2\pi H\!N/L\omega

Stable and unstable vortices attached to seamounts

, the radiated power per wall is the same as for a single thin wall, and proportional to

Internal tide generation by abyssal hills using analytical theory

B^2

Standing waves in the Gulf of Finland and their relationship to the basin‐wide Baltic seiches

, in agreement with the linear scaling. (Here

Energy Conversion, Mixing Energy, and Neutral Surfaces with a Nonlinear Equation of State

H

Flow-dependent versus flow-independent initial perturbations for ensemble prediction

is the wall height,