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By using Pielke and Mahrer 3D mesoscale model, the air-flow over Sardinia has been studied for three typical meteorological situations. North-westerly flow (Maestrale), characterized by dry cold wind, shows strong downdrought over the desertic part of the island. Southeasterly flow (Scirocco), in summer, shows little interaction between the large-scale flow and the lower atmospheric layer over land. Sea breezes are usually advected easterly by the prevailing winds. Comments on practical applications and on limitations in local weather forecasting follow.

In this paper we exhibit analytical solutions for the upwelling and the coastal currents induced by periodic wind stress. We present solutions for an infinite deep ocean and for a shallow ocean. There is upwelling only when the period of the forcing is longer than the inertial period,i.e. f>ω. When the period of the forcing is shorter than the inertial period,i.e. f

The velocity field, measured by Vercelli (1922-23) in the Strait of Messina hourly at six depths, is analysed to determine the size and the intensity of the energy-containing eddies. The analysis is performed by separating the turbulent component of the velocity field from the deterministic tidal component. The intensity of the turbulence is given by the averaged square of the aleatoric velocities. The size of the eddies is computed through correlation of the aleatoric velocities at different depths. Results show that the intensity of the turbulent field velocity is of the order of (50⤜60) cm s−1, while the size of the eddies is of the order of (20⤜45) m, reaching sometimes 70 m. These eddies are far beyond the inertial range predicted by the Kolmogorov theory. The eddies are due to Kelvin-Helmoltz shear instabilities between the surface and the deeper water.

Through numerical integration of the primitive equations, we study the summer circulation in the Po Valley, Italy. We investigate separately the mountain slope effect and the sea-breeze effect. The results show that, because of the mountain slope, there is convergence early in the morning and divergence during the day in the lower atmosphere. Further-more, the sea breeze generated by the Adriatic Sea is confined to the eastern side of the Valley. These two phenomena are expected. However, the model suggests that the convergence due to the slope is organized in an area as large as the valley and that, even if the sea breeze is a boundary layer circulation, the perturbation introduced triggers a train of gravity waves as deep as the troposphere. These effects might be very important for the distribution of the summer thunderstorms. Further specific investigations. Experimental and theoretical, are needed.

The cyclonic vortex of the Ligurian Sea is a very persistent feature of the Mediterranean Sea, even if its intensity varies seasonally. In this paper we examine the barotropic component of this vortex. In particular we study the influence of the bottom topography and of the coastlines in shaping the cyclonic flow. Furthermore we show that the barotropic part of the vortex is stable to finite perturbations, which may explain its persistency.

The barotropic atmospheric circulation in thef-plane andβ-plane middle-latitude channel has been studied with spectral low-order models in the quasi-geostrophic and the primitive-equation formulations. Results show that multiple equilibria and chaotic behaviour inf-plane may become nonchaotic (periodic) inβ-plane and that the chaoric behaviour inf-plane can appear only for a special choice of parameters. Furthermore, no significant difference appears inf-plane adding more spectral components.

We consider the perturbation of a stratified rotating fluid due to the crossing of a mountain ridge. The behaviour of the solutions is examined in the primitive Navier-Stokes equations in linear form studied by Queney. We produce the Green's functions of the problem at ground level at any distance from the perturbing ridge; in this sense it is an extension of the theory presented by Pierrehumbert. Furthermore, we discuss the relative contribution of the different terms and we examine the behaviour of small-scale waves with altitude. This work is also relevant for the parametrization of the subgrid physical effect in large numerical models, like the barrier effect of the Alps or the Rocky Mountains.

Results concerning the middle-latitude atmospheric flow in barotropic and quasi-geostrophic approximations are presented. With no dissipation, two semi-infinite regions of stability bound a finite region of instability, ensuring that the solutions are limited. In the presence of dissipation, above a critical value of forcing below which there is one stationary stable state, there are three stationary states, one unstable and two stable. Numerically we find that the two basins of attraction in phase space are strongly asymmetric, the one, corresponding to the solution resonant with the mountain, being much larger than the other. The model used for this study is the Charney-DeVore one.