Quasi-geostrophic equations revisited: The case of the ocean

Oceanic circulation on the beta-plane demands the presence of (at least) two scales of the motion to describe completely the flow structure and evolution both in the central-eastern area of the basin and in the western boundary layer. In each of the two regions of the basin, well-established quasi-geostrophic vorticity equations govern the flow. However, since these two regions are physically connected, a single and general vorticity equation is requested to hold in the Whole basin. In the present investigation, the inference of this last equation is analysed by comparing some methods found in the literature with another which is put forward by the authors

The Adriatic response to the bora forcing: a numerical study

Thispap er dealswith the bora wind effect on the Adriatic Sea circulation ass imulated by a 3-D numerical code (the DieCAST model). The main result of this forcing is the formation of intense upwellings along the eastern coast in agreement with previous theoretical studies and observations. Different numerical experiments are discussed for various boundary and initial conditions to evaluate their influence on both circulation and upwelling patterns

Frictional dissipation at the interface of a two-layer quasi-geostrophic flow

In two-layer ocean circulation models the possible dissipation mechanism arising at the interface between the layers is parameterised in terms of the difference between the horizontal velocities of the flow in each layer. We explain and derive such parameterisation by extending the classical Ekman theory, which originally refers to the surface and to the benthic boundary layers, to the interface of a quasi-geostrophic, two-layered flow

Dynamic boundary conditions and boundary layer approach to the wind-driven linear circulation problem

Boundary layer techniques are applied to a class of wind-driven, linear circulation models in which a wide set of dynamic boundary conditions are allowed. The results show that i) the eastern solution always exists and its O(1) component coincides with that of Sverdrup; ii) only a well-defined subset of boundary conditions are consistent with solutions representing, at least qualitatively, a typical subtropical gyre and, finally, iii) it is possible to employ infinite choices of boundary conditions which correspond to the same boundary layer solution

Shelf slope convection: A note for antarctic regions

Some basic processes associated with buoyancy-driven convection in the presence of coastal upwellingcurren ts were investigated in a 2.5D framework near the Adelie Coast of Antarctica. The surface buoyancy forcingw as derived from coolingand brine deposition due to ice formation, and was specified over a persistent off-shore polynya maintained by the off-shore katabatic winds. Rotational effects and the formation of a turbulent surface mixed layer were included in the model. The representation of topography was done via the VBM (virtual Boundary Method) that utilizes equivalent body forces in the momentum equation, thus enabling the use of very efficient Poisson solvers for the pressure, based on FFTs. The simulations were carried out near longitude 143E, between latitude 68S and 65S, over the nearshore shelf region. The hydrography was initialized with the 1/4 deg Levitus annual climatology. Two cases of idealized meteorological forcing were considered: constant winds blowingalong -shore and off-shore. The resultant motions in each case were characterized by interaction between the wind-driven upwellingmotions and the downward movingdense convection plumes, but with marked differences: a) the formation of a strongfron t under the open sea edge of the polynya only by off-shore winds; b) the periodic suppression of the surface off-shore currents and of the coastal upwelling only by the along-shore winds; c) the formation of deep upwelling currents along the slope between 400 and 200 meters only for along-shore winds, and d) the rapid filling of the surface layers (depths < 100m) with high salinities under the whole polynya by the off-shore forcing, vs. the delayed fillingof a narrow region near the downwellingplume with intermediate salinity values by the along-shore forcing

Dispersion of passive tracers in model flows: effects of the parametrization of small-scale processes

Abstract. A set of numerical experiments is presented, in which we study the dynamics of passive particles advected by given two-dimensional velocity fields and perturbed by a non-white noise with a characteristic time τ. Data and model results have shown that this kind of random perturbation is able to represent subgridscale processes for upper ocean mesoscale turbulence for regions of the world ocean where turbulence can be assumed to be homogeneous. Extensive computations in different fields characterized by cell-like structure, both stationary and time-dependent, representing very idealized geophysical flow situations, show that the presence of a finite correlation time scale does lead to enhanced or arrested dispersion, depending on the considered flow; however, it does not seem to affect the gross qualitative behaviour of the dispersion processes, which is primarily affected by the large-scale velocity field

Interaction of edge waves with swell on a beach

Excitation of edge waves on a beach by incoming swell is considered on the basis of shallow-water model. Subharmonic resonance mechanism of interaction is analyzed by multi-scaled expansion asymptotic techniques. The generation of edge waves between wave breakers is found to have a dynamic threshold. It is defined by intensity and frequency of incoming swell, geometry of a shore zone. Nonlinear no stationary wave solutions for the envelope of interacting edge waves are described by generalized Sine-Gordon model. An infinite set of exact solutions are received by the Lamb method for the phase synchronism regime of wave’s interaction

On the dynamical conditions concomitant with the bottom anoxia in the Northern Adriatic Sea: A numerical case study for the 1977 event

The aim of the present investigation is to explain the dramatic phenomenon of anoxia/hypoxia waters observed in the Northern Adriatic Sea during August 1977 by using the data collected in the DINAS 2 oceanographic campaign and modelling them by means of a three-dimensional numerical model for the Whole basin. The model has been forced with ECMWF surface reanalysis data—wind stress, heat fluxes and river discharges. The main result lies in the high temporal and spatial correlation between the observed anoxia areas and the centres of anticyclonic circulation produced by the model. Further investigations seem to be necessary for a better matching between observed and simulated thermohaline fields

Climate variations in the Northern Hemisphere based on the use of an atmosphere-ocean IPCC model

Forced and natural variability of modelled and observed Atlantic Ocean temperature and Atlantic Meridional Overturning Circulation (AMOC) is studied. In the observations and in a forced climate model run, we find increasing temperature at 1000m in the Atlantic (20N). SVD analysis shows that, for both model data and observations, a high index of North Atlantic Oscillation (NAO) corresponds to negative temperature anomaly at 1000m to the north of 55N, although geographical details of temperature anomaly distribution are different for the model and observations. Particular attention has been paid to the influence of the fresh water flux due to the present global warning on the slowing down of the AMOC. It is shown that fresh water flux change is only a secondary cause of reduced AMOC in global warming conditions, while heat flux change is probably the main reason. Finally, it is shown that internal model AMOC variability is positively correlated with the near-surface air temperature in Atlantic-European Arctic sector on a 10-year time scale

Intersecting Architectural Surfaces Between Graphic and Analytic Representations

Representing an architectural shape, mediating design/formal/semantic needs, means respecting its specificity according to the purposes with which one operates; therefore, teaching how to represent an architectural shape is a complex operation, especially if this happens in the first year of the degree course in Architecture where the heterogeneity of students' background requires a preliminary definition of a common language. Students are firstly introduced to theoretical geometries which underlie architectural shapes. So, they have to know the basis of Geometry (both Descriptive and Analytical) in order to proceed within these issues. This process requires to underline the two `souls' of architectural shapes: the theoretical and the build one. Moreover, it also leads to investigate two different types of theoretical shapes: the one that lies behind the design idea and the other one which underlies the built. We propose teaching examples focused on reading architectural shapes as a result of intersections of surfaces