Is the coefficient of eddy potential vorticity diffusion positive? Part1: barotropic zonal channel.

The question of whether the coefficient of diffusivity of potential vorticity by mesoscale eddies is positive is studied for a zonally reentrant barotropic channel using the quasi-geostrophic approach. The topography is limited to the first mode in the meridional direction but is unlimited in the zonal direction. We derive an analytic solution for the stationary (time-independent) solution. New terms associated with parameterized eddy fluxes of po-tential vorticity appear both in the equations for the mean zonal momentum balance, and the kinetic energy balance. These terms are linked with the topographic form stress exerted by parameterized eddies. It is demonstrated that in regimes with zonal flow (analogous to the Antarctic Circumpolar Current), the coefficient of eddy potential vorticity diffusivity must be positive

NEMO-ICB (v1.0): interactive icebergs in the NEMO ocean model globally configured at eddy-permitting resolution

An established iceberg module, ICB, is used interactively with the Nucleus for European Modelling of the Ocean (NEMO) ocean model in a new implementation, NEMO–ICB (v1.0). A 30-year hindcast (1976–2005) simulation with an eddy-permitting (0.25°) global configuration of NEMO–ICB is undertaken to evaluate the influence of icebergs on sea ice, hydrography, mixed layer depths (MLDs), and ocean currents, through comparison with a control simulation in which the equivalent iceberg mass flux is applied as coastal runoff, a common forcing in ocean models. In the Southern Hemisphere (SH), drift and melting of icebergs are in balance after around 5 years, whereas the equilibration timescale for the Northern Hemisphere (NH) is 15–20 years. Iceberg drift patterns, and Southern Ocean iceberg mass, compare favourably with available observations. Freshwater forcing due to iceberg melting is most pronounced very locally, in the coastal zone around much of Antarctica, where it often exceeds in magnitude and opposes the negative freshwater fluxes associated with sea ice freezing. However, at most locations in the polar Southern Ocean, the annual-mean freshwater flux due to icebergs, if present, is typically an order of magnitude smaller than the contribution of sea ice melting and precipitation. A notable exception is the southwest Atlantic sector of the Southern Ocean, where iceberg melting reaches around 50% of net precipitation over a large area. Including icebergs in place of coastal runoff, sea ice concentration and thickness are notably decreased at most locations around Antarctica, by up to ~ 20% in the eastern Weddell Sea, with more limited increases, of up to ~ 10% in the Bellingshausen Sea. Antarctic sea ice mass decreases by 2.9%, overall. As a consequence of changes in net freshwater forcing and sea ice, salinity and temperature distributions are also substantially altered. Surface salinity increases by ~ 0.1 psu around much of Antarctica, due to suppressed coastal runoff, with extensive freshening at depth, extending to the greatest depths in the polar Southern Ocean where discernible effects on both salinity and temperature reach 2500 m in the Weddell Sea by the last pentad of the simulation. Substantial physical and dynamical responses to icebergs, throughout the global ocean, are explained by rapid propagation of density anomalies from high-to-low latitudes. Complementary to the baseline model used here, three prototype modifications to NEMO–ICB are also introduced and discussed

Modeling the global circulation response and the regional response of the Arctic Ocean to the external forcing anomalies

The problem of numerical modeling and analysis of the large-scale World Ocean circulation variability under variations of the external forcing is considered. A numerical model was developed in the INM RAS and is based on the primitive equations of the ocean circulation written in a spherical generalized ?-coordinate system. The model's equations are approximated on a grid with resolution of 2.5° × 2° × 33, and the North Pole is displaced to the continental point (60°E, 60.5°N). There are two stages for the numerical experiments. The quasi-equilibrium circulation of the World Ocean under the climatological atmospheric forcing is simulated at the first stage. The run is carried out over a period of 3000 years during which a quasi-equilibrium model regime is formed. At the second stage, the sensitivity of the model ocean circulation to the atmospheric forcing perturbations in the Southern Hemisphere is studied. According to the results, the strongest regional changes in the hydrography take place in the Arctic Ocean. Substantial changes of sea's surface height and local anomalies of the temperature and salinity are formed there

Numerical model of the Baltic Sea circulation

The problem of numerical simulation of the Baltic Sea large-scale circulation is considered. The Baltic Sea numerical model is based on the two previous models: the model of ocean dynamics developed at the Institute of Numerical Mathematics of the RAS and the FRESCO model of marine hydroecosystem developed at the Estonian Marine Institute, University of Tartu. The model is based on primitive equations written in spherical ? coordinates with a free surface in the hydrostatic and Boussinesq approximations. The structure of numerical algorithm is described. The algorithm is based on the method of multicomponent splitting and includes splitting by physical processes and spatial coordinates. The equations of sea dynamics are written in a symmetrized form. The problem is split into several energetically balanced subsystems (splitting by physical processes). Each subsystem can be additionally split into subsystems of a simpler structure (splitting by spatial coordinates). The numerical experiment consists in the calculation of the Baltic Sea hydrodynamic fields with the spatial horizontal resolution of ~3.5 km and 25 vertical ?-levels nonuniformly distributed over the depth. The atmospheric forcing is calculated according to the Era-Interim data, the calculation period is 2 years: 2007 and 2008. The results of numerical simulation demonstrate good resemblance to observation data, as well as the results of the Baltic Sea dynamics computation obtained from other models