Papers by Carlo Pellacani
Il Nuovo Cimento B, 1976
ABSTRACT Summary The problem of internal waves in a stratified Boussinesq fluid at rest is consid... more ABSTRACT Summary The problem of internal waves in a stratified Boussinesq fluid at rest is considered. In particular, the local behaviour of internal waves at levels where their frequency equals the local value of the Brunt-Väisälä frequency is analysed. To do that, particular continuous profiles of the BV frequency are studied. It is shown how the local behaviour of disturbances at those levels can be analysed and predicted by making use of a particular, quite simple, mathematical technique. The results obtained are in good agreement with those that could be predicted by an intuitive analysis of the problems. Some particulars of the solutions are discussed and a comparison with previous theoretical approaches is carried out.
Il Nuovo Cimento C, 1983
ABSTRACT Summary Solutions of the anelastic pressure equation are studied, with a perturbative sc... more ABSTRACT Summary Solutions of the anelastic pressure equation are studied, with a perturbative scheme, for certain assumed and idealized forcing distributions. Previous results, obtained in the Boussinesq approximation and the new ones are compared for the case of deep cumulus convection. Meaningful differences are found in the upper and lower parts of the cloud between the new and the previous estimate of vertical pressure gradient force induced by buoyancy forcing and by drag forcing in the case of a nonprecipitating cloud.
ABSTRACT Summary The dispersion law of internal gravity waves in a stratified fluid at rest is in... more ABSTRACT Summary The dispersion law of internal gravity waves in a stratified fluid at rest is investigated: it is shown that the introduction of an oscillating component of the stratification parameter along the vertical direction introduces an infinite number of branches of the dispersion relation. The importance of this effect for the estimate of the triadic nonlinear interaction between internal waves is suggested as one of the most relevant consequences of the results reported.
Summary It has been known for many years that waves of different kind propagating in a fluid and... more Summary It has been known for many years that waves of different kind propagating in a fluid and incident on a mean flow localized shear layer can exhibit, in the linear theory, a reflection coefficient larger than unity. When this phenomenon takes place the wave is said to be over-reflected at the shear layer. In this paper the over-reflection of inertial-gravity
Physics of Fluids, 1979
ABSTRACT The destabilizing effect of the over-reflection mechanism in stratified fluids in horizo... more ABSTRACT The destabilizing effect of the over-reflection mechanism in stratified fluids in horizontal sheared motion is considered. It is shown that the behavior of unstable modes, induced by the contemporary presence of jumps in both the mean horizontal velocity and the Brunt-Vaisala frequency located at different heights, can be interpreted in terms of successive reflections and over-reflections at the Brunt-Vaisala frequency jump and at the vortex sheet, respectively. A very good accord is obtained with the predictions of the linear theory of unstable modes with small associated growth rates.
Il Nuovo Cimento B, 1977
Summary A numerical analysis of the instability range of stratified sheared flows is carried out... more Summary A numerical analysis of the instability range of stratified sheared flows is carried out. Attention is devoted to cases in which a variation of the Brunt-Väisälä frequency exists far from a localized shear layer. It is shown that such BV jumps significantly affect the spectrum of turbulence induced by a localized shear layer.
Tellus A, 1989
The statistical effect of a time-changing zonal forcing on the large scale, barotropic components... more The statistical effect of a time-changing zonal forcing on the large scale, barotropic components of the atmospheric circulation is considered. It is suggested that maxima of the statistical distribution of the zonal wind and traveling planetary wave intensity are the results of transitions between different, locally in time, dominating regimes. This interpretation is substantially different from that commonly adopted, which identifies the statistical maxima with the attractors of the theoretical models. To clarify this point, results from a numerical simulation, clearly showing the effects of transitions on distributions, are discussed. It is shown in particular how the properties of the basin of attraction of different regimes can deeply affect the resulting distributions of the relevant physical quantities. It is also shown how maxima of distributions have no simple connections with equilibria computed under the assumption of constant zonal forcing. These results suggest new interpretations of the statistics.
Il Nuovo Cimento B, 1989
Summary The problem of determining the magnetic lines in a confined plasma near a reverse field ... more Summary The problem of determining the magnetic lines in a confined plasma near a reverse field pinch equilibrium is considered. The Poincar� map in a poloidal plane is analytically determined up to quadratic terms and a systematic approximation with standard maps is considered. The transport coefficient in the quasi-linear approximation is analytically determined and the corresponding confinement time agrees with the
Il Nuovo Cimento B, 1976
Summary A mathematical analysis of the stability problem of stratified fluids in horizontal shea... more Summary A mathematical analysis of the stability problem of stratified fluids in horizontal sheared motion is given as an initial-value problem in order to avoid the difficulties encountered in applying classical hydrodynamic stability methods. Good agreement is obtained with results given by other authors in the two-dimensional case. An extension of the stability analysis to the three-dimensional case is given. Such extension is discussed and it is shown how the results obtained are in quite good agreement with the well-known Squire theorem.
Il Nuovo Cimento B, 1975
Summary A mathematical analysis is given of the linearized equations of motion of an inviscid Bo... more Summary A mathematical analysis is given of the linearized equations of motion of an inviscid Boussinesq fluid in the neighbourhood of an «irregular» critical layer in order to understand the nature of the interaction between gravity waves and mean flow at heights where a jet has been developed in the velocity profile. Infinities in both amplitude and wave number of the inviscid solution show that diffusion and transition to turbulence are directly involved at irregular critical layers. Diffusion terms must then be taken into account for a proper representation of the interaction between gravity waves and mean flow at a critical level.
La Rivista del Nuovo Cimento, 1983
Pure and Applied Geophysics PAGEOPH, 1983
The effect of variations in time of the zonal flow is investigated by the study of a simplified t... more The effect of variations in time of the zonal flow is investigated by the study of a simplified truncated model of a barotropic atmosphere in the presence of an oscillating zonal forcing.
Pure and Applied Geophysics PAGEOPH, 1985
We discuss the form-drag instability for a quasi-geostrophic channel flow. We first study the cha... more We discuss the form-drag instability for a quasi-geostrophic channel flow. We first study the characteristics of this instability in a barotropic flow, considering in detail the influence of the meridional scale and discussing which structure of the perturbation zonal flow must be chosen in order to describe properly this instability.
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Papers by Carlo Pellacani