Antisymmetric wind stress fields and parity transformation of the correction streamfunctions in the western boundary layer of oceanic basins

Most models of the single-gyre, wind-driven oceanic circulation resort to wind stress fields that are strictly antisymmetric under a parity transformation with respect to a mid basin latitude. We show that, within the ambit of the weakly nonlinear quasi-geostrophic dynamics with a given frictional parametrization, this property of the wind stress implies a corresponding definite behaviour, under the same transform, of all the correction streamfunctions that constitute the perturbative expansion of the solution in the western boundary layer. The result generalizes what can be observed in some truncated expansions found in the literature and in the presence of an explicitly defined wind stress field

On the resting abyss of a two-layered ocean

In the framework of the theory of geostrophic contours, a sufficient condition is pointed out in order that the lower layer of a two-layered ocean be motionless

Time variability of atmospheric and marine parameters over the Adriatic region

The time evolution of atmospheric and marine parameters over the Adriatic region is studied for the period 1946-1996 on different time-scales. On the interannual and interdecadal time-scales evidence is found of the inverted barometer effect on sea level and the strong connection between air and sea temperatures. By contrast, opposite relationships are found on longer (secular) time-scales, which might be explained as different results of global climatic fluctuations on the atmospheric and marine parameters involved. On the interannual time-scale a correlation is found between sea-level pressure gradient along the basin and the water inflow/outflow through the Otranto Channel, in terms of sea level and sea temperature

Maximum downward propagation of the baroclinic wind-driven circulation into the ocean interior

In the framework of the Young and Rhines theory of the baroclinic, wind-driven circulation, we consider the problem of the determination of the maximum penetration depth, Dmax, of the motion into the ocean. On the basis of general results concerning the interface of no-motion D(x, y), we investigate the dependence of Dmax on a couple of parameters that select each buoyancy profile within a given class, having fixed a special family of vertical Ekman velocity fields. We also show some circulation patterns forced by a typical sinusoidal wind-stress and corresponding to different buoyancy profiles within the same class

Maximum downward propagation of the baroclinic wind-driven circulation into the ocean interior

In the framework of the Young and Rhines theory of the baroclinic, wind-driven circulation, we consider the problem of the determination of the maximum penetration depth, Dmax, of the motion into the ocean. On the basis of general results concerning the interface of no-motion D(x, y), we investigate the dependence of Dmax on a couple of parameters that select each buoyancy profile within a given class, having fixed a special family of vertical Ekman velocity fields. We also show some circulation patterns forced by a typical sinusoidal wind-stress and corresponding to different buoyancy profiles within the same class

The no-slip condition at the western boundary of a homogeneous ocean minimizes energy

It is not obvious, a priori, that the no-slip boundary condition is suitable for ocean circulation models based on quasi-geostrophic equations. But the no-slip condition is the one that minimizes the kinetic energy of the western boundary layer of a wind-driven ocean governed by fourth-order quasi-geostrophic equations. Moreover, the case of a very thin boundary layer is correctly described by the asymptotic solution when the no-slip condition is chosen. Then, it is physically sound to use the no-slip condition even in the western boundary of analytical or numerical ocean circulation models, be they linear or nonlinear

An inner additional condition for solving Munk-like ocean circulation models

The problem of determining the additional boundary conditions, in the framework of the wind-driven single-gyre ocean circulation with lateral diffusion of relative vorticity, is explored with reference to the western boundary and in the context of the classical linear Munk model. As, of necessity, each model solution satisfies a certain inner additional condition, the latter is used to select special kinds of partial-slip boundary conditions, one of which assures the dynamic stability of the linear solution. Moreover, as the boundary conditions are left unaffected by nonlinearity, the same condition can be applied also to the nonlinear model. In particular, an open question about the flow energetics, reported in the literature, is solved by using the present results

On the additional boundary condition of wind-driven ocean models on the eastern coast

In the homogeneous model of the wind-driven ocean circulation, the dynamics of the basin interior is basically governed by the Sverdrup balance and the related no mass-flux condition on the eastern boundary of the basin, which we assume to be square for conceptual simplicity. In the presence of lateral diffusion of relative vorticity, the additional condition on the eastern boundary (like the conditions on the other boundaries) is not demanded on physical grounds but it is arbitrary to a large extent. Hence, certain choices of such boundary condition can produce overall solutions which are “far” from that of Sverdrup in the eastern part of the domain, without any physical reason. In the present note we show that this discrepancy can be strongly reduced if the adopted additional boundary condition has the same form as that implicitly satisfied by the Sverdrup solution. Unlike the common approach, a criterion is thus derived which selects a suitable partial slip boundary condition according to the specific wind-stress field which is taken into account

On the dynamics of quasi-geostrophic intergyre gyres

An important aspect of the present climatic change concerns the wind-stress anomalies over the ocean. It is possible to associate to them a special current field, which appears between the subtropical and the subpolar gyres and is known as intergyre gyre. In the present paper we investigate its dynamics by including recent models of stochastic wind field into the classical model of ocean circulation at the basin scale of Rhines and Young. In the framework of an analytical approach, developed at the geostrophic level of approximation, we explore the circulation patterns of this recently discovered characteristic of double gyres

Symmetry defects in single-gyre, wind-driven oceanic systems

We explore some symmetry properties of the leading terms that constitute the solution describing the flow field structure in a wind-driven, bottom-dissipated ocean. Both the weakly non-linear and the highly non-linear regime are investigated. The main result is that the northward displacement and the westward intensification of the current system, which are typical of the subtropical gyres (for instance the North Atlantic Ocean), can be ascribed to an interplay between the symmetries of these terms. Moreover, a duality relationship allows us to relate the conclusions concerning one regime to the other