Alexey Androsov

Cell-vertex discretization of shallow water equations on mixed unstructured meshes

Finite-volume discretizations can be formulated on unstructured meshes composed of different polygons. A staggered cell-vertex finite-volume discretization of shallow water equations is analyzed on mixed meshes composed of triangles and quads. Although triangular meshes are most flexible geometrically, quads are more efficient numerically and do not support spurious inertial modes of triangular cell-vertex discretization. Mixed meshes composed of triangles and quads combine benefits of both. In particular, triangular transitional zones can be used to join quadrilateral meshes of differing resolution. Based on a set of examples involving shallow water equations, it is shown that mixed meshes offer a viable approach provided some background biharmonic viscosity (or the biharmonic filter) is added to stabilize the triangular part of the mesh.

Open-ocean convection in the Greenland Sea: preconditioning through a mesoscale chimney and detectability in SAR imagery studied with a hierarchy of nested numerical models.

Aspects of the hydrodynamics of the Greenland Sea were investigated through a hierarchy of nested numerical models. The simulations were particularly conceived to study, under realistic conditions, the hydrodynamics induced by the presence of a convectively generated oceanic mesoscale chimney as well as its long-term influence on the local convective activity. To this purpose, a very high resolution, fully non-hydrostatic 3D model capable of simulating submesoscale convective vertical plumes was nested into an ocean-ice, regional hydrostatic 3D model which was initialised and forced through the global, coupled atmosphere ocean 3D REMO/MPI-OM model. In the central part of the Greenland Sea, the hydrological structure of an observed, convectively generated oceanic mesoscale chimney and a corresponding reconstructed velocity field were imposed as a part of the forcing for the non-hydrostatic numerical model. Two different, short-term realistic scenarios were simulated corresponding, respectively, to episodes characterized by a strong mean oceanic heat loss and by a weak mean oceanic heat gain in the central Greenland Sea. In order to evaluate the role played by mesoscale convective chimneys in promoting preconditioning to open-ocean deep-penetrating convection, two long-term simulations of the hydrodynamics of the Greenland Sea were performed using the same model hierarchy and the forcing as described above. The two runs differed merely in that only in one of them the hydrological and velocity structure of a convective chimney were inserted in the central Greenland Sea as a part of the forcing. The dependence of simulated surface convergence patterns on grid step in the central Greenland Sea was also investigated in order to assess the capability of numerical models of predicting the detectability of convective events in synthetic aperture radar imagery.

Tidal Records as Liquid Climate Archives for Large-Scale Interior Mediterranean Variability

Characterization of interior ocean variability is necessary for understanding climate. Water mass evolution shapes ocean-atmosphere interactions and contributes to determine timescales for global and regional climate variability. However, a robust assessment of past state and variability of the ocean interior is prevented by sparseness/shortness of historical subsurface observations and uncertainties affecting proxy-based reconstructions. Here, we propose a novel approach to infer past large-scale interior ocean variability with unprecedented accuracy and temporal resolution. It exploits links between stratification determined by “large-scale” water mass distributions and local dynamics. We characterize interannual interior ocean variability in the Mediterranean Sea in the early 20th century contained in tidal measurements in the Strait of Messina, and demonstrate the general applicability of our method, paving the way to a new approach to analyze historical oceanographic records: Regions where different water masses are known to collide can thus act as magnifying glasses for basin-scale interior ocean variability, hence providing “liquid archives” for climatology.

Non-Hydrostatic Dynamics of a Region with an Underwater Mountain

Non-hydrostatic boundary–value problem is considered in the 3-D domain representing a strait with an underwater sill. The equations are integrated in the boundary–fitted coordinates on irregular grid. For detection of non-hydrostatic effects the grid has increased resolution at sill slopes. The method is applied for simulation non-hydrostatic dynamics in the Strait of Messina.