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The West African monsoon (WAM) originates in the Gulf of Guinea when the intertropical convergence zone (ITCZ) makes its landfall; whilst, the south Asian monsoon (SAM) originates in the Indian ocean when the ITCZ crosses the equator. The monsoonal dynamics are here studied after landfall using Gill’s tropospheric model with an implanted Ekman frictional layer (EFL). Ekman pumping increases low level convergence, making the lower monsoonal cyclone deeper and more compact that the upper anticyclone, by transferring tropospheric vorticity into the EFL. In the upper troposphere, air particles spiral-out anticyclonically away from the monsoons, subsiding over the Tropical Atlantic, the Tropical Indian ocean, or transiting into the southern hemisphere across the equator. Whilst marine air particles spiral-in cyclonically towards the WAM or the SAM, the latter appears to be a preferred ending destination in the absence of orography. The Himalayas introduced as a barrier to the monsoonal winds, strengthen the tropospheric winds by tightening the isobars. The Somali mountains (SMs), introduced as a barrier to the Ekman winds, separates the WAM and the SAM catch basins; thus, the Atlantic air particles converge towards the WAM and the Indian ocean particles converge towards the SAM. The Indian Ghats (IGs), introduced as a semi-impermeable barrier to the Ekman winds, deflect the marine air particles originated in the western Indian ocean towards the south-eastern flank of the SAM. In short, an upper single anticyclone encircles both monsoons; the Himalayas strengthen the upper-level winds by increasing the pressure gradients; the SMs split the EFL cyclone, keeping the marine air particles to the west of SMs in the WAM basin and the particles to the east of SMs in the SAM basin; the IGs guides transmit the air particles, deflecting them towards Bangladesh.

Although the effects of hailstorms usually interest limited areas, the damages can be severe. These, damages can be potentially reduced by a reliable hailstorm forecast. In Italy, only few regions have a network for monitoring hail events, the coverage of these networks is limited to small areas, and long-term and nationwide time series of hail events are not available, therefore the chances of improving the quality of the hail forecast are severely reduced. The aim of the present study is to collect data and information from different sources on hailstorms in order to evaluate the annual hailstorm frequency in Italy. In order to obtain more complete information about the hail distribution, different datasets have been used: i) daily information about hailstorm occurrence at fixed meteorological stations from the NCDC dataset; ii) events information (date, location, and hailstone size) obtained using hailstorm reports available from different agencies. In this study the hail events are classified according to the hailstone size, then a statistical approach is used in order to evaluate the mean annual frequency of the events at the municipality scale for each hailstone size class. The atmospheric parameters, known as hailstorm precursors, are estimated using the NCEP/NCAR daily reanalysis at 2.5 degree horizontal resolution. As a final result, this study presents a step forward towards a climatology of hail frequency in Italy at municipality scale for the period 1971–2009.

It is shown that landscape variability decreases the temperature in the surface layer when, through mesoscale flow, cool air intrudes over warm patches, lifting warm air and weakening the static stability of the upper part of the planetary boundary layer. This mechanism generates regions of upward vertical motion and a sizable amount of available potential energy and can make the environment of the lower troposphere more favorable to cloud formation. This process is enhanced by light ambient wind through the generation of trapped propagating waves, which penetrate into the midtropospheric levels, transporting upward the thermal perturbations and weakening the static stability around the top of the boundary layer. At moderate ambient wind speeds, the presence of surface roughness changes strengthens the wave activity, further favoring the vertical transport of the thermal perturbations. When the intensity of the ambient wind is larger than 5 m s−1, the vertical velocities induced by the surface roughness changes prevail over those induced by the diabatic flux changes. The analysis is performed using a linear theory in which the mesoscale dynamics are forced by the diurnal diabatic sensible heat flux and by the surface stress. Results are shown as a function of ambient flow intensity and of the wavelength of a sinusoidal landscape variability.

Climatic factors and weather type frequencies affecting Tuscany are examined to discriminate between vintages ranked into the upper- and lower-quartile years as a consensus from six rating sources of Chianti wine during the period 1980 to 2011. These rankings represent a considerable improvement on any individual publisher ranking, displaying an overall good consensus for the best and worst vintage years. Climate variables are calculated and weather type frequencies are matched between the eight highest and the eight lowest ranked vintages in the main phenological phases of Sangiovese grapevine. Results show that higher heat units; mean, maximum and minimum temperature; and more days with temperature above 35 °C were the most important discriminators between good- and poor-quality vintages in the spring and summer growth phases, with heat units important during ripening. Precipitation influences on vintage quality are significant only during veraison where low precipitation amounts and precipitation days are important for better quality vintages. In agreement with these findings, weather type analysis shows good vintages are favoured by weather type 4 (more anticyclones over central Mediterranean Europe (CME)), giving warm dry growing season conditions. Poor vintages all relate to higher frequencies of either weather type 3, which, by producing perturbation crossing CME, favours cooler and wetter conditions, and/or weather type 7 which favours cold dry continental air masses from the east and north east over CME. This approach shows there are important weather type frequency differences between good- and poor-quality vintages. Trend analysis shows that changes in weather type frequencies are more important than any due to global warming.

We analyse the anomalously warm summer months in the Mediterranean region using the 850 hPa temperature, T850, extracted from the ERA-40 reanalysis, in order to find how these anomalies are related to the anomaly of the jet stream over the Euro-Atlantic area. In this region, the westerly jet has two main branches: the Scandinavian jet and the Mediterranean jet, which, in summer, are at a meridional minimum distance. In addition, we analyse the heat waves in the Central Mediterranean in the last half century using the temperature observations collected at fifty surface stations distributed throughout the Italian peninsula and its two major islands, and we relate these events to the position of the Mediterranean jet. We find that, when these two jets are almost aligned, there is a streak of the Mediterranean jet over the Alps and, to the south of them, an anticyclonic vorticity aloft, which forces a strong subsidence and an adiabatic warming of the troposphere over the Mediterranean. This configuration is also a characteristic of anomalously warm spells over the basin. While, when the Mediterranean jet resides further south and along the northern rim of Africa, its meridional distance from the Scandinavian jet is relatively large, the vorticity over the Mediterranean is cyclonic and this region is relatively cool. The tropospheric temperature difference between these two configurations (Mediterranean jet over the Alps and jet over North Africa) is of the order of 3 °C. Since the correlation between the observed temperatures over Italy and the ERA-40 T850 in the Central Mediterranean is more than 90%, and more than 60% in the T850 of the entire Mediterranean basin, we conclude that the heat waves over Italy are representative of exceptionally warm episodes over the Central Mediterranean, and that a warm spell over Italy is a country-scale symptom of warm spells in the Mediterranean basin. Copyright  2006 Royal Meteorological Society.

China is the third largest Country (after Russia and Canada) extending from the West Pacific Ocean to the Tibet plateau, where the climate ranges from the monsoonal regime in the east to the extreme dryness in the west, and from tropical in the south to subarctic in the north. Traditionally, a large part of the population is dedicated to the agriculture, with a high percentage continuously migrating towards the industrial coastal areas. In this perspective, water represents a precious resource for living, industries and farming, and its scarcity, due to climate changes and variability, is an overwhelming problem for the entire community. Therefore it is fundamental to have a clear picture of the climate changes and trends undergoing in different regions of this vast and varied country. Moreover, understanding the climate variability in China will certainly give important hints on the trends of the vegetation, and, therefore, on the role of Chinese ecosystems in the global carbon cycle and global climate change, while the assessment of the impact of land-use changes on the local and regional climate will help in adaptation strategies. In this paper we present results on the climate analysis in selected regions, and on the climate variability affecting the water cycle and the land productivity.

A theory is presented for the evaluation of the different terms of the pressure gradient force, when mesoscale flow is driven by a sensible heat source in the planetary boundary layer (PBL), or by an elevated confined heat source, such as the release of the latent heat of condensation in a cloud. The nonlinear and linear, and the nonhydrostatic and the hydrostatic pressure gradient contributions are evaluated. The validity of the different approximations is discussed as a function of time and space scales. In addition, the validity of this approach is explored as a function of atmospheric environmental parameters, such as static stability, large-scale flow, and dissipation. By accessing the relative importance of each contribution, specific solution techniques for mesoscale atmospheric flows can be adopted. For example, when the linear contributions dominate, an exact analytic model could be used, rather than relying on numerical approximation solution techniques. When the hydrostatic contribution dominates, the spatial variation of the vertical temperature profile can be used to uniquely define the horizontal pressure gradient force.

We present an analytical evaluation and interpretation on how diabatic heating of the convective boundary layer (CBL) is transported upward into the midtroposphere by mesoscale flows, and how the air mixes with the environment and therefore weakens the atmospheric static stability. The thermodynamic imprint on the free atmosphere due to the irreversible processes such as mixing, dissipation, and diffusion, associated with the mesoscale flow, is more clearly shown when the forcing is periodic in time. Convective mixing in the CBL accounts for a thermodynamic perturbation of the order of a few degrees, while mixing associated with the mesoscale activity accounts for a perturbation of the order of half a degree. To isolate this last effect, we prescribe a periodic forcing with a 1 day period, so over 24 hours, the net diabatic input averages to zero, and the contribution due to the advection cancels out. In this formulation the perturbation is solely due to irreversible processes associated with the mesoscale. These perturbations are relevant, since they are smaller, but of the same order of magnitude as perturbations associated with mesoscale advection and the CBL mixing. A more complete evaluation of the relative contribution to the atmospheric perturbations due to the mesoscale activity was completed using an initial value problem approach. In this case, there is a net transport of the diabatic heat induced by the mesoscale flow. As a consequence, when the mesoscale flow persists for several days, the static stability of the atmosphere is eroded by the combined action of the diabatic heat, CBL mixing, and transport and mixing due to the mesoscale activity. In this paper we first evaluate the contribution of the irreversible processes using a periodic in time forcing. Then we examine the atmospheric impact due to a sequence of several sea breeze days, starting from rest at time zero and letting the flow evolve as an initial value problem. Results suggest that perturbations associated with mesoscale flows generated by landscape variability are of climatological importance and need to be introduced in a parametric form in coarser large-scale models, as presently is done with turbulent subgrid CBL processes.

We have developed a framework to parameterize mesoscale fluxes of heat, moisture, and momentum, in a cloud-free environment, which result from heterogeneous heating of flat land surfaces. The importance and parameterizability of these mesoscale fluxes is demonstrated using the mathematical concept of predictability. This methodology is used to estimate the relative importance of mesoscale, as contrasted with turbulent fluxes, in the Konza Prairie of Kansas during the FIFE field experiment.

Mediterranean climate change during the last 60 years is based on homogenized daily temperature and quality controlled precipitation observational data and gridded products. The estimated changes indicate statistically significant Mediterranean summer temperature increase and a reduction in winter precipitation in specific areas. Reconstructions of Mediterranean sea level suggest a rise of some 150 mm since the beginning of the nineteenth century. A 20 years long reanalysis (1985–2007) was produced, showing long term temperature variability and a positive salinity trend in the ocean layers from the surface to 1,500 m depth. A prominent increase in summer temperature extremes is found in the whole Mediterranean region, while warm bias in the mid twentieth century station data is removed by homogenization. No basin-wide trends in precipitation and droughts are found for the second half of the twentieth century, while trends in extreme winds are largely negative, as are those of the related cyclones and cut-off-lows. The role of large scale pressure patterns like the NAO for variabilities and trends is discussed for the different parameters considered.

The authors Present an analytical evaluation of the vertical heat and momentum fluxes associated with mesoscale flow generated by periodic and isolated thermal inhomogeneities within the convective boundary layer (CBL). The influence of larger-scale wind flow is also included. The results show that, with little or no synoptic wind, the vertical velocity is in phase with the diabatic temperature perturbations and that the mesoscale heat flux is positive and of the same order as the diabatic heat flux within the CBL. Above the CBL, the heat flux is negative and penetrates into the free atmosphere through a depth comparable to the depth of the CBL. In the presence of synoptic flow, the mesoscale perturbation is in the form of propagating waves that penetrate deeply into the free atmosphere. As a result, there is a net downward flux of momentum, which is dissipated within the CBL by turbulence. Furthermore, mixing with the environment of the air particles displaced by the waves results in a net negat...

Results show that the year-to-year quality variation of wines produced in North and Central Italy depends on the large-scale climate variability, and that the wine quality improvement in the last four decades is partially due to an increase of temperature and to a decrease of precipitation in West and Central Mediterranean Europe (WME; CME). In addition, wine quality is positively correlated with air temperature throughout the entire active period of the grapevine, weakly negatively correlated with precipitation in spring, and well negatively correlated in summer and fall. The month-to-month composites of the NAO anomaly show that, in years of good quality wine, this anomaly is negative in late spring, oscillates around zero in summer, and is positive in early fall; while, in years of bad quality wine, it is positive in late spring and summer, and negative in early fall, i.e. its polarity has an opposite sign in spring and fall in good versus bad years. The composite seasonal maps show that good wines are produced when the spring jet stream over the Atlantic diverts most of the weather perturbations towards North Europe, still providing a sufficient amount of rainwater to CME; when summer warming induced by southerly winds is balanced by the cooling induced by westerly winds; and when a positive geopotential anomaly over WME shelters CME from fall Atlantic storms. Bad quality wines are produced when the jet stream favors the intrusion of the Atlantic weather perturbations into the Mediterranean. Results suggest that atmospheric pattern persistencies can be used as precursors for wine quality forecast.

Sixty-four southwest Pacific island meteorological stations were used to develop ENSO-related austral warm season (November–April) rainfall climatologies for 1961–90. Historical data for the same station set were then examined for 1955/56, one of the strongest La Niñas of the twentieth century. The pattern for that event was typical of a well-coupled protracted La Niña, with above-normal rainfall (>150%) observed for 17 stations in the case study. Tropical cyclone tracks were also used to illustrate the proximal effects of historical storms on station rainfall. Several stations that were located along the northern edge of the tropical cyclone swarm, but south of a region of anomalously low rainfall, were selected as possible candidates having been close to the mean South Pacific convergence zone (SPCZ) location. Linear interpolations between those stations highlighted a likely SPCZ position for the 1955/56 event. The reconstructed SPCZ location indicated a position southwest of normal, consistent with many La Niñas observed during the satellite era. The 1955/56 SPCZ reconstruction compared favorably with NOAA Cooperative Institute for Research in Environmental Sciences (CIRES) twentieth-century reanalysis (20CR) positions of maximum atmospheric water content and omega (time derivative of pressure that illustrates vertical velocity, and a proxy for convection and SPCZ location) at 500 hPa. Comparisons between Global Precipitation Climatology Project (GPCP) warm season rainfall composite plots for several satellite era La Niñas and one well-coupled La Niña event that occurred during 2010/11 to omega at 500 hPa and maximum rainfall amounts suggest that the 1955/56 reconstruction from in situ rainfall measurements captured the SPCZ location. These findings suggest that use of the 20CR could help to identify hemispheric-scale atmospheric circulation features like the SPCZ and improve understanding of ENSO dynamics prior to the satellite era.

This is a study on the impact of the jetstream in the Euro-Atlantic region on the rainfall distribution in the Mediterranean region; the study, based on data analysis, is restricted to the Mediterranean rainy season, which lasts from September to May. During this season, most of the weather systems originate over the Atlantic, and are carried towards the Mediterranean region by the westerly flow. In the upper troposphere of the Euro-Atlantic region this flow is characterized by two jets: the Atlantic jet, which crosses the ocean with a northeasterly tilt, and the African jet, which flows above the coast of North Africa. This study shows that the cross-jet circulation of the Atlantic jet favors storm activity in its exit region, while the cross-jet circulation of the African jet suppresses this kind of activity in its entrance region, with the 1st jet-stormtrack covariance mode explaining nearly 50% of the variability. It follows that the rainfall distribution downstream to these cross-jet circulations is strongly influenced by their relative positions. Specifically, in fall, rainfall is abundant in the western Mediterranean basin (WM), when the Atlantic jet is relatively strong but its northeasterly tilt is small, and the African jet is in its easternmost position. In winter, rainfall is abundant in the eastern Mediterranean basin (EM); this is when the Atlantic jet reaches the Scandinavian peninsula and the African jet is in its westernmost position. In spring, when the two jets weaken, the Atlantic jet retreats over the ocean, but the African jet stays in its winter position, rainfall is abundant in the Alpine region and in the Balkans. In addition, the covariance between precipitation and the jetstream has been evaluated. In fall, the latitudinal displacement of the Atlantic jet and the longitudinal displacement of the African jet modulate rainfall anomalies in the WM, with 38% explained covariance. In winter, the latitudinal displacement of the Atlantic jet produces rainfall anomalies in the western and central Mediterranean, with 45% explained covariance. In spring, the latitudinal displacement of the African jet produces rainfall anomalies, with 38% explained covariance.

An analytical evaluation of the vertical heat fluxes associated with the mesoscale flow generated by thermal inhomogeneities in the PBL in the absence of a synoptic wind is presented. Results show that the mesoscale fluxes are of the same order as the diabatic heat fluxes. In the sea-breeze case results show that in the lower layer of the atmosphere the heat flux is positive over the land and negative over the sea with an overall positive horizontal average. In the free atmosphere above the PBL the mesoscale vertical heat flux is negative over the land and over the sea; that is, the lower atmosphere becomes warmer while the free atmosphere above becomes cooler. As a result the mesoscale flow contributes to the weakening of the atmospheric stability within a region that extends a Rossby radius distance from the coastline, and up to an altitude larger than twice the depth of the convective PBL. The average momentum flux equals zero because the momentum removed over the sea is fed back into the atmo...

We consider further the Differential Daisyworld model of Watson and Lovelock that we have analyzed in a previous paper (De Gregorio et al., 1992). In this work we introduce a delay in the birthrate of the species. We consider three different models: the constant time lag model and the strong and the weak delay models. In the weak delay case no value of the delay changes the asymptotic stability of the stationary solutions. In the constant time lag and in the strong delay models, however, there exists a critical value of the delay, above which periodic solutions appear. These periodic solutions are numerically found to be globally attracting even for large delay when the linear approximation analysis is no longer valid. For both models, very regular behavior is obtained if the percentage coverage of the fertile ground of the Earth is much less than 1. As the percentage of the fertile ground increases, however, chaotic behavior is possible.

We have developed a hydrological prognostic index, HOWI (hydrological onset and withdrawal index), for the onset and the withdrawal of the West African monsoon (WAM), based on the vertically integrated moisture transport (VIMT). The regions of West Africa with the same climatological onset (withdrawal) date are characterized by a large change of the VIMT around the onset (withdrawal) date. By analyzing the variability of the VIMT, we determine the extension and the geographical position of these regions, which we take sufficiently large to filter out the fast weather variability. It turns out that the regions with the same climatological onset date do not usually coincide with the regions with the same climatological withdrawal date, the areas with the maximum variability of the VIMT during the onset phase are usually a fraction of the area where the variability of the VIMT is large during the withdrawal phase. This is because the onset has active phases and pauses in time and it is fragmented in space, while the withdrawal is rather rapid and almost uniformly distributed through the entire monsoonal region. When the monsoon moves inland, the rainfall slightly trails behind the arrival of the moisture, and, when the monsoon moves back towards the gulf of Guinea, the moisture slightly precedes the retreating rainfall. In a specific region, we say that the onset (withdrawal) of the monsoon occurs when the moisture reaches (declines to) half of its climatological value. The level of the moisture relatively to its climatological value is evaluated through the HOWI, i.e., at the onset (withdrawal) the HOWI is zero with a positive (negative) tendency. We find that the dates of the onset of the monsoon determined using the HOWI, computed in the region where the VIMT has its maximum variability during the onset phase of WAM, well agree with the dates of the sudden transition of the ITCZ (Intertropical Convergence Zone) from 5 to 10A degrees N. The uncertainty on the onset date is of the order of 2 pentads, which is comparable to the uncertainty on the date of the sudden transition of the ITCZ. We, then, use the HOWI to determine the onset and the withdrawal dates of the monsoon for the period 1979-2004, finding that an early (late) onset usually preludes to a longer (shorter) monsoonal season with more (less) cumulated rain. Finally, we compare the onset dates in the Sahelian region, for the period 1979-2004, with those determined using methods based on rainfall.

It is long been recognized that land and sea contrasts produce sea breezes. More recently, it has become evident that landscape variations which result in spatial gradients in surface heat flux can produce mesoscale circulations as strong as sea breezes. However, it remains to determine how small a horizontal variation in surface heating can still produce a significant mesoscale circulation. It order to address this question, in this paper we present results for one Fourier component. While only the linear response can be evaluated using this tool, such models have been shown to be effective at identifying dominant physical processes associated with sea breezes (Rotunno, 1983; Dalu and Pielke, 1989, 93). This approach can also be used to assist in the development of a parameterization of mesoscale effects generated by spatial surface sensible heat variability for use in larger scale models. The primitive equations can be reduced to an equation for the streamfunction: $$\left[ {{{\left({\frac{\partial }{{\partial x}} + {k_p}} \right)}^2} + k_o^2} \right]\frac{{{\partial ^2}\varphi }}{{\partial {z^2}}} + \left[ {{{\left( {\frac{\partial }{{\partial x}} + {k_p}} \right)}^2} + {l^2}} \right]\frac{{{\partial ^2}\varphi }}{{\partial {x^2}}} = - \frac{1}{{{U^2}}}\frac{{\partial Q}}{{\partial x}}$$ (1) $$\begin{gathered}\frac{{\partial \varphi }}{{\partial z}} = u {\text{and}} \frac{{\partial \varphi }}{{\partial x}} = - w; {l^2} = \frac{{N_o^2}}{{{U^2}}} - \frac{{{U_{zz}}}}{U}; p = s + \lambda ; {k_p} = \frac{p}{U} + \frac{{K{k^2}}}{U} {\text{and}} {k_o} = \frac{f}{U} \hfill \\h = {h_o}\frac{1}{2}\left[ {1 + {a_1}\sin \left( {kx} \right) + {a_2}\cos \left( {kx} \right)} \right] = {h_o}\frac{1}{2}\left[ {1 + a\sin \left( {kx + b} \right)} \right] \hfill \\\end{gathered}$$ (2) $${a_1} = \frac{{\lambda \left( {\lambda + K{k^2}} \right)}}{{{{\left( {\lambda + K{k^2}} \right)}^2} + {k^2}{U^2}}}; {a_2} = - \frac{{\lambda kU}}{{{{\left( {\lambda + K{k^2}} \right)}^2} + {k^2}{U^2}}}; \mathop {\lim }\limits_{k,U \to \infty } {a_1},{a_2} = 0$$ (3) $${h_a} = \frac{1}{2}{h_o}\left( {1 + a} \right) Q = \frac{{{Q_o}q\left( s \right)}}{2}\left[ {1 + a\sin \left( {kx + b} \right)} \right]He\left( {{h_a} - z} \right)$$ (4)

We present an analytical evaluation of the perturbations to mesoscale atmospheric flows induced by surface thermal inhomogeneities., We apply the theory to a sea breeze case in the presence or in the absence of an inland lake. We show also some particles trajectories for these two cases. Furthermore we show that at least to the extend of the linear response of the atmosphere terrain thermal inhomogeneities which have a separation of the order of the depth of the boundary layer need not be resolved in a numerical model, because these inhomogeneities are spatially averaged by the atmospheric response.

We review the relevance of predictability theory to flows in local domains that are modified by boundary conditions produced by topography, surface physical forcing, or imposition of numerical lateral boundary constraints. There is an apparent inconsistency between the results of classical predictability theory and limited domain experiments. We attempt to reconcile the discrepancy by analysis of error growth and chaos. The analysis suggests that boundary conditions provide the dominant flow contribution for many limited domain predictions, and this motivates review of error spread from uncertain boundary specification. Case summaries include free flows of the troposphere, moist convection, topographically bounded local flows, and flows above other complex surfaces. A tentative conclusion is that boundary uncertainty does not provoke chaotic responses so easily as do small imperfections of initial data, even for dynamical systems that are chaotic in global or periodic domains. One exception to this appears to be the case that the boundary uncertainty possesses a spatial scale that is not much shorter than the perimeter bounding the simulation domain.

Using Gauss's divergence theorem, we examine the role of the net radiative cooling and of the entrainment of potentially warm air from the free atmosphere into the surface layer in determining the intensity of the cold-air outflow at the rim of the Antarctic continent. The result shows that a large amount of cold air, significant at even a global climatological scale, is exported through this process from high- to low-latitude regions. The theory gives also the average intensity of the wind at the coast. In the coastal regions of Antarctica the wind exhibits a complex behavior. Observations show that katabatic winds in the near-coastal region can be periodic or continuous, or can stay a long time in a quiescent near-critical state, then burst in short and strong gusts. We examine some aspects of these katabatic winds in terms of the mesoscale energy theory developed by Dalu and Green (1983). This complex behavior is described by a nonlinear system, where the relevant parameter is the Froude number of the inflow at a Rossby radius distance from the coast. The analytical theory developed agrees well with qualitative features observed.

In this paper we present several theoretical results concerning currents forced by the wind in coastal regions, for a shallow sea and for a very deep sea. We investigate the time behavior and the spatial structure of the stream function and the momentum components, i.e., the onset, the transient, the asymptotic, and the periodic behavior of the currents and of the upwelling, forced by winds of different spatial and time structures. Results show that the intensity of the along coast jet initially grows linearly under a δ in time wind impulse, quadratically under a Heaviside in time wind impulse, and cubically under a linearly growing wind impulse. The asymptotic state is such that the intensity of the current vanishes if the wind impulse has a finite duration, while the intensity of the sea current has a final finite amplitude if the wind intensity goes to some finite value. If the wind stress is periodic in time, there is upwelling only when the period of the forcing is longer than a characteristic time scale, which is the sum of the inertial period and the friction e-folding time. Otherwise there are waves which propagate away from the region where the wind stress is acting. The spatial structure is such that the upwelling occurs in a horizontal region of the order of the Rossby deformation radius, corrected by the effect of friction (and by the effect of periodicity, when the wind stress is periodic in time). However, the horizontal gradient of the wind stress can be more important than the Rossby deformation radius in determining the horizontal extent of the upwelling region.

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

We examine the kinetic energy that may be generated from surface heating. Cumulonimbus, cumulus, mesoscale and large-scale conversion of potential into kinetic energy can be identified in an idealized way, as distinct processes. Each has a characteristic thermodynamic efficiency.

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.

Mesoscale circulations, induced by mesoscale available potential energy diabatically generated in the boundary layer are studied through the numerical integration of primitive equations. The energetics of a sea-breeze simulation is studied in some detail. After 12 hours of simulation the kinetic energy is about a quarter of the mesoscale available potential energy diabatically produced. We comment on the energy lost by the upstream difference scheme, and on some aspects of the unavailability of available potential energy in such a system that together describe this level of inefficiency.

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.

In this paper we present theoretical results concerning the sea breeze intensity and its inland penetration as a function of latitude and friction. We produce solutions for the spatial structure of the streamfunction and momentum components and for their Line behavior in the case of a step function forcing of finite duration, and in the case of periodic forcing. Results show that the sea breeze initially has an aspect ratio equal to unity and that earth rotation and friction aged its intensity but they are unimportant in determining its early geometry. The sea breeze has a characteristic time scale which is a combination of the inertial period and the e-folding time due to friction. For a time larger than this characteristic time scale, the inland penetration of the sea breeze is confined by a Rossby deformation radius, which includes a frictional effect. In fact, friction and inertia reduce, not only the intensity, but also the horizontal scale of motion; at the equator the controlling parameter...

After a short description of the soundings carried out during an oceanographical survey in the Sicilian and Sardinian channels in May and June 1970, the results of the nuclei condensation measurements in the sea are here reported. The data presented are the first about condensation nuclei countings in the Mediterranean. The values found are very similar to those ones found by other researchers, during surveys carried out in the Atlantic and Pacific Oceans, even if there is no direct reference to them.

The problem of the propagation of a gravity (density) current, with initial configuration: density p2 in the region \(0 < X < + \infty \),\( - \infty < y < + \infty \), 0 < z < H and density \({p_1} = {p_2} + \delta p\) in the region \( - \infty < X < 0\), \( - \infty < y < + \infty \), 0 < z < H and rigidly bounded at z=0, H (Fig. 1(a)) is approached using Green and Dalu mesoscale energetics theory (4).