Hydrodynamic modelling of mesoscale eddies in the Black Sea

Abstract

A three dimensional structure of mesoscale circulation in the Black Sea is simulated using the Proudman Oceanographic Laboratory Coastal Ocean Modelling System. A number of sensitivity tests reveal the response of the model to changes in the horizontal resolution, time steps, and diffusion coefficients. Three numerical grids are examined with x-fine (3.2 km), fine (6.7 km) and coarse (25 km) resolution. It is found that the coarse grid significantly overestimates the energy of the currents and is not adequate even for the study of basin-scale circulation. The x-fine grid, on the other hand, does not give significant advantages compared to the fine grid, and the latter is used for the bulk of simulations. The most adequate parameters are chosen from the sensitivity study and used to model both the basin-scale circulation and day-to-day variability of mesoscale currents for the months of May and June of 2000. The model is forced with actual wind data every 6 h and monthly climatic data for evaporation, precipitation, heat fluxes and river run-off. The results of the fine grid model are compared favourably against the satellite imagery. The model adequately reproduces the general circulation and many mesoscale features including cyclonic and anticyclonic eddies, jets and filaments in different parts of the Black Sea. The model gives a realistic geographical distribution and parameters of mesoscale currents, such as size, shape and evolution of the eddies.

Small river plumes off the northeastern coast of the Black Sea under average climatic and flooding discharge conditions

“…7, which shows the modeled Black Sea current field at a depth of 10 m projected on a uniform grid with 10 km spatial resolution and averaged for June 2011. The model also reproduced seasonal variations of sea surface circulation, in particular winter-spring intensification of the Rim Current, meandering of the main flow of the Rim Current caused by baroclinic instability, and formation of multiple nearshore anticyclonic eddies during summer at the eastern part of the Black Sea (Oguz et al, 1992(Oguz et al, , 1993Titov, 2002;Zatsepin et al, 2003;Enriquez et al, 2005). The simulated main flow of the Rim Current shifts offshore (approximately 45 km) in June and its speed decreases to 20 cm s −1 (Fig.…”

Numerical simulations of dense water cascading on a steep slope

“…POLCOMS was designed as a regional ocean model for the study of coastal and shelf processes and has been extensively used and validated for the European continental shelf and the northeast Atlantic, most recently by Holt and James (2006) and Wakelin et al (2009), and other regions such as the Black Sea (Enriquez et al, 2005) and the Mediterranean Sea (Bolaños et al, 2007). The version of POLCOMS used in this study was modified to be used under the Windows operating system (Enriquez et al, 2005).…”

“…The version of POLCOMS used in this study was modified to be used under the Windows operating system (Enriquez et al, 2005).…”

The effect of various vertical discretization schemes and horizontal diffusion parameterization on the performance of a 3-D ocean model: the Black Sea case study

“…In order to suppress unnecessary curvature of terrain-following coordinates in the upper layer due to variations of bottom topography below 1550 m, the deepest numerical level (w level) was forced to be horizontal at this depth level to represent an "artificial bottom". It is a common view that the currents below 1000-1200 m are negligibly small (Demyshev et al, 2002;Enriquez et al, 2005); so the waters between 1550 m and the seabed were excluded from the simulation. The transition between the artificial and real bottom was slightly smoothed with a 9-point, 2-D filter.…”

“…Then short convective adjustment runs were invoked for a few time steps with very high vertical diffusivity (100 m 2 s −1 ) to eliminate small density inversions due to interpolation. Then the model was spun-up for about 7 months with no meteorological forcing and river discharges following the procedure detailed in Enriquez et al (2005), i.e. by freezing initial temperature and salinity distributions and allowing the currents to achieve an equilibrium with the density field.…”