Numerical simulations compared with measurements are used to investigate the effect of sea breezecirculation on the ozone accumulation over a highly industrialized peninsula in southern Italy, where high levels of ozoneconcentration are often registered. A frequent meteorological phenomenon in this region during weak summer synopticconditions is the development of complex sea breeze systems from the coastlines, with convergence areas within thepeninsula.A case study characterized by strong winds alternating with sea breeze circulations was selected.The simulations show that during weak synoptic conditions, sea breezes transport ozone and its precursors over landfrom the sea, as well as from the coastlines where the largest industrialized districts are localized. The overlapping breezeslead to ozone accumulation in the area where sea breeze convergence occurs. This may explain the high values of ozoneregistered close to the sea breeze convergence lines.The comparison between predictions and experimental data indicates that the numerical system successfully reproducesboth weather and ground level ozone concentration in different meteorological conditions, resulting in a fundamental toolfor both scientific comprehension of the evolution of air contaminants and interpretation of the monitoring data.

In this work a parametrization for the transport terms of the turbulent kinetic energy (TKE)budget equation, valid for a convective boundary layer (CBL) is presented. This is a hard taskto accomplish from experimental data, especially because of the difficulty associated to themeasurements of pressure turbulent fluctuations, which are necessary to determine thepressure correlation TKE transport term. Thus, employing a large eddy simulation (LES) afull diurnal planetary boundary layer (PBL) cycle was simulated. In this simulation a forcingobtained from experimental data is used, so that the numerical experiment represents amore realistic case than a stationary PBL. For this study all terms of the TKE budget equationwere determined for a CBL. From these data, polynomials that describe the TKE transportterms' vertical profiles were adjusted. The polynomials found are a good description ofthe LES data, and from them it is shown that a simple formulation that directly relatesthe transport terms to the TKE magnitude has advantages on other parameterizationscommonly used in CBL numerical models. Furthermore, the present study shows that theTKE turbulent transport term dominates over the TKE transport by pressure perturbationsand that for most of the CBL these two terms have opposite signs.

Aim of the present work is to investigate the potential effects of dust aerosols on the structure of some severe rainfall events in Liguria. These events are typically associated with intense southerly or southwesterly flows from Southern Mediterranean and Northern Africa and are often associated with mineral dust plumes originating from Northern Sahara. In particular the flooding event occurred in Vernazza (Cinque Terre) on October 25, 2011, is analyzed here.The specific research objective can be summarized in the so called "aerosol invigoration effect", that is how the increased aerosol concentration, caused by mineral dust plumes, may enhance convection and, consequently, ex- treme rainfall events. This is equivalent to investigating the influence that aerosols-clouds-radiation interactions may have on the physics and dynamics of the rainfall events, primarily by means of the so-called aerosols direct (including semi-direct) and indirect effects.The proposed research is primarily conducted on a numerical modeling basis. In this context, the Weather Research and Forecasting model with online coupled chemistry (WRF-Chem v. 3.8.1) is applied to simulate the formation of the convective storm and its feedback with dust aerosol. The employed simulation strategy concerns various model setups, obtained varying the sectional aerosol modules, starting from the "simple" GOCART mechanism to the more sophisticated MOSAIC.For this purpose, 3 sets of simulations are performed: (a) the control simulation (RAD0), in which the mineral dust does not interact with clouds and/or radiation, (b) the " radiation" (RAD) simulation, in which the dust transport is considered and aerosols direct effects are accounted for, and (c) the "total" simulation (TOT), in which aerosols direct and indirect effects are accounted for.

The Pampa-2016 experimental campaign have been performed in a typical Pampa lowland South American region, it consisted in both surface flux measurements (at 3 and 29 meters) and radiosonde launched every three hours. The resulting meteorological observations allowed the analysis of turbulent properties associated with both stable and convective boundary layer. The combined analysis of the surface data and vertical soundings have revealed some general characteristics of the atmospheric boundary layer for both the nocturnal stable conditions and the daytime convective environment. The continuous surface measurements, have shown that the Nocturnal Stable Inversion, occurring in calm wind situation, is generated basically by the radiative cooling mechanism that sets up after the late afternoon transition. The analysis of night-time surface data has showed also that under stable conditions in the case of vanishing wind speed, the friction velocity has unrealistic values that are very close to zero. This is an unwanted situation for numerical models that generally use this quantity as a lower boundary condition. The analysis of night-time temperature profiles has revealed two contrasting patterns in agreement with the classical classification of radiative night (very stable Boundary Layer) and a turbulent night (weakly stable Boundary layer). On the other side, the analysis of the daytime temperature profiles provided the estimation of the convective time scale, that is of the order of 10 minutes in agreement with experimental values. A spectral analysis and the consequent estimation of the spectral peaks under unstable and stable conditions are in agreement with literature values.

The Southern Brazilian region is specially affected by extreme weather events, very often intense wind gusts coming from deep convection may develop it self as a microburst producing winds higher than 100km/h. In order to understand the physical and dynamical process evolved in this phenomena, a static and isolated microburst is produced trough a Large Eddy Simulation. A quantitative analysis of propagation an maintenance of the microburst vortex ring is performed in order to understand its evolution.

The Southern Brazilian region is specially affected by extreme weather events, very often intense wind gusts coming from deep convection may develop it self as a microburst producing winds higher than 100km/h. In order to understand the physical and dynamical process evolved in this phenomena, a static and isolated microburst is produced trough a Large Eddy Simulation. A quantitative analysis of propagation an maintenance of the microburst vortex ring is performed in order to understand its evolution.

Turbulent time scales and velocity variances for a convective boundary layer are derived from large eddy simulation spectral data. Spectral peak frequencies obtained from LES data are used directly in expressions that allow establishing such times scales and velocity variances. These turbulent parameters were compared with those provided by experimental turbulence data. The comparison employing a stochastic dispersion model and observed concentration data shows that both parameterizations reproduce adequately the contaminant dispersion process in a convective boundary layer.

The aim of this paper is to determine an accurate formulation for the sea-spray source function characteristic for the North-Western Mediterranean. To this end, the MACMod aerosol transport model was implemented in the study area using different sea-state dependent flux formulations. The simulations were compared to a large data set of aerosol size distributions acquired over the last ten years in the study area, yielding the evolution of the sea-spray concentrations with increasing fetch and hence, with the development of the wave field. This allowed for an improvement of the Demoisson et al. (2013) sea-spray source function (S3F) for the Mediterranean. The new formulation extends its validity to shorter fetch and larger radii and turned out to be most suitable for predicting the atmospheric concentrations of sea-spray aerosols in this region.

In this work it's derived a mathematical model to describe the meandering contaminants dispersion in the planetary boundary layer. The model employs a heuristic functional form for the velocity autocorrelation function which describes the negatives lobes observed in meandering data. Furthermore, the model is derived from the linearization of the Langevin equation. The mathematical equations, that represent the longitudinal and lateral wind components describe the bi-dimensional pattern of the meandering flow and can be utilized to calculate the contaminant concentrations occurring in situations in which the meandering phenomenon plays a decisive role.

Large Eddy simulation spectral data and Taylor statistical diffusion theory are used to obtain eddy diffusivities in a convective boundary layer. The derivation employs a fitting expression obtained from LES data for the vertical peak frequency. The vertical eddy diffusivities are well behaved and show similar patterns and magnitudes as those derived from experimental spectral peak frequency data. In addition, this new vertical eddy diffusivity was introduced into an advection diffusion equation which was solved by GILLT method and validated with observed contaminant concentration data of the Copenhagen experiment. The results of this new approach are shown to agree with the measurements of Copenhagen.

A turbulent subfilter viscosity for Large Eddy Simulation (LES) based on the Taylor statisticaldiffusion theory is proposed. This viscosity is described in terms of a velocity varianceand a time scale, both associated to the inertial subrange. This new subfilter viscositycontains a cutoff wavenumber kc , presenting an identical form (differing by a constant)to the Heisenberg subfilter viscosity. Therefore, both subfilter viscosities are describedin terms of a sharp division between large and small wavenumbers of a turbulent flowand, henceforth, Taylor and Heisenberg subfilter viscosities are in agreement with thesharp Fourier filtering operation, frequently employed in LES models. Turbulent statisticsof different orders, generated from atmospheric boundary layer simulations employingboth Taylor and Heisenberg subfilter viscosities have been compared with observations andresults provided by other simulations. The comparison shows that the LES model utilizingthe approaches of Taylor and Heisenberg reproduces these turbulent statistics correctly indifferent vertical regions of a planetary convective boundary layer (CBL).

The Lagrangian description of turbulence is very important in studies of mixing and dispersion. The following study focuses on the main aspects using data from high resolution Large Eddy Simulations and investigating basic results in Kolmogorov similarity giving an estimation of inertial subrange universal constants. It was possible to evaluate the velocity structure functions and the Lagrangian spectra in the inertial subrange, under different stability conditions, by tracking an ensemble of Lagrangian particles in the PBL simulated with a Large Eddy Simulation model. This allows a direct estimation of the inertial subrange constants and their dependence on the Planetary Boundary Layer stability conditions

In this study, the Weather Research and Forecasting model with online coupled chemistry (WRF-Chem) isapplied to simulate an intense Saharan dust outbreak event that took place over the Southern Italy in March 2016.The WRF model is found to reproduce well the synoptic meteorological conditions driving the dust outbreak: an omegalikepressure configuration associated with a weak cyclogenesis in the Iberian Peninsula. At the end of the simulatedperiod the merging of two minima produce a large depression in the Peninsular Italy.The model performances in reproducing the atmospheric desert dust load is evaluated using a multi-platformobservational dataset of aerosol and desert dust properties, including optical properties from satellite and ground-basedsun-photometers, plus in-situ particulate matter mass concentration (PM) data. This comparison allows us to investigatethe model ability in reproducing both the horizontal and the vertical displacement of the dust plume, and its evolutionin time. The preliminary comparison with satellite (MODIS-AQUA) and sunphotometers (AERONET) showed thatthe model is able to reproduce well the horizontal field of the aerosol optical depth (AOD) and its evolution in time.The routinely measurements of ARPA-Puglia revealed the intense dust outbreak with peak PM10 value larger than300 µg/m3 during march 23. On the other side, the model-measurements comparison for PM10 shows a good temporalmatching.The model-to-measurements comparisons allows the evaluation and the tuning of physics-based emission scheme thatis part of the WRF-Chem package release.

Marche Region is a complex valley-coastal area in central Italy comprising valleys, hills, highly populated areas and industrial districts. During the past fifty years (namely from 1954 to 2010) the built-up area has almost tripled no way proportional to the increase of the resident population (+16%). In the same time span, airborne emissions have dramatically changed. Emissions from industrial facilities decreased due to the use of Best Available Techniques and the deindustrialization while small and/or mobile sources have become the most important players. This led to a significant deterioration of air quality in the cities of the Marche Region, especially due to road traffic and residential heating. For the new types of sources, emission estimate is the only way to assess local impact. The aim of this paper is to understand why the particulate matter concentrations in urban areas of the Marche Region are often above the legal limits, although several emission sources have decreased. To achieve reliable modelling, we applied two very different air quality models: CALPUFF and CAMx. CALPUFF is a non-steady-state puff dispersion modelling system while CAMx is an Eulerian photochemical model, able to estimate both primary and secondary particulate matter. CALPUFF results are useful to evaluate the concentration of primary particulate matter from the main industrial activities, and their contribution related to the total measured in the environmental monitoring unit. These values have been compared with the results of CAMx simulation which considers all the emissions allocated in a regular grid, so it is possible to assess the contribution of non-point sources such as urban traffic, residential heating and natural emissions.

Le particelle di aerosol influenzano il clima modificando sia il bilancio energetico globale attraverso l'assorbimento e la dispersione della radiazione solare (effetti diretti), sia le interazioni con le nuvole e lo sviluppo e il verificarsi di precipitazioni (effetti indiretti). Gli aerosol di origine naturale sono particolarmente importanti perché su scala globale rappresentano circa 70-85 % del totale delle polveri disperse in atmosfera. Le principali componenti dell'aerosol naturale sono lo spray marino, la polvere desertica, i solfati naturali, gli aerosol vulcanici e quelli generati dagli incendi boschivi naturali. Tra gli aerosol naturali il maggior contributo circa il 70% è dato dall'erosione della crosta terrestre, mentre lo spray marino e le polveri di origine vulcanica rappresentano rispettivamente il 15% e l'1,5%.Sebbene le misurazioni in situ e il telerilevamento satellitare e terrestre forniscano informazioni importanti sul carico, la distribuzione e le influenze dell'aerosol, tali misurazioni sono essenzialmente limitate nello spazio e nel tempo e, soprattutto, sono limitate nella loro capacità di distinguere tra le componenti naturali e antropogeniche degli aerosol. D'altra parte le simulazioni numeriche condotte con modelli di trasporto e chimica risentono fortemente delle parametrizzazioni utilizzate. In questo studio, sono state valutate le capacità del modello WRF-Chem nel simulare il trasporto e le caratteristiche spazio-temporali degli aerosol naturali nel bacino del Mediterraneo, considerando alcuni casi particolari. Ovvero, sono stati investigati e simulati separatamente i seguenti tre casi: (i) un episodio sahariano verificatosi nel giugno 2007; (ii) un evento di trasporto di spray marino nell'Italia sud-orientale nel periodo 1-7 luglio 2007 e (iii) l'emissione vulcanica dell'Etna nel periodo 1-7 dicembre 2015.Per ciascun caso è stata effettuata un'analisi di sensitività rispetto ad alcune parametrizzazione interne al modello, in particolare quelle legate agli schemi di emissione. Le simulazioni sono state confrontate con dati al suolo registrati nelle centraline di qualità dell'aria e in alcune campagne sperimentali, e con dati satellitari. I risultati evidenziano delle buone performance del modello nel caso di trasporto sahariano e trasporto di polvere vulcanica. Ulteriori approfondimenti sono invece necessari nel caso dello spray marino.

Occasionally, storms that share many features with tropical cyclones, including the presence of a quasi-circular eye a warm core and strong winds, are observed in the Mediterranean. Generally, they are known as Medicanes, or tropical-like cyclones (TLC). Due to the intense wind forcings and the consequent development of high wind waves, a large number of sea spray dropletsboth from bubble bursting and spume tearing processesare likely to be produced at the sea surface. In order to take into account this process, we implemented an additional Sea Spray Source Function (SSSF) in WRF-Chem, model version 3.6.1, using the GOCART (Goddard Chemistry Aerosol Radiation and Transport) aerosol sectional module. Traditionally, air-sea momentum fluxes are computed through the classical Charnock relation that does not consider the wave-state and sea spray effects on the sea surface roughness explicitly. In order to take into account these forcing, we implemented a more recent parameterization of the sea surface aerodynamic roughness within the WRF surface layer model, which may be applicable to both moderate and high wind conditions. The implemented SSSF and sea surface roughness parameterization have been tested using an operative model sequence based on COAWST (Coupled Ocean Atmosphere Wave Sediment Transport) and WRF-Chem. The third-generation wave model SWAN (Simulating Waves Nearshore), two-way coupled with the WRF atmospheric model in the COAWST framework, provided wave field parameters. Numerical simulations have been integrated with the WRF-Chem chemistry package, with the aim of calculating the sea spray generated by the waves and to include its effect in the Charnock roughness parametrization together with the sea state effect. A single case study is performed, considering the Medicane that affected south-eastern Italy on 26 September 2006. Since this Medicane is one of the most deeply analysed in literature, its investigation can easily shed some light on the feedbacks between sea spray and drag coefficients.

The frequency, the location and the characteristics of convective rainfall events induced by the convergence of different sea breeze systems on a Mediterranean peninsula (Salento, in southeastern Italy) are analyzed. Such events have been studied considering satellite/radar images and output fields from two Limited Area Models in the summer period of 2011-2013. A total of 20 days have been detected in which the precipitation due to sea-breeze convergence was clearly observed in satellite and radar images. The synoptic conditions associated with these events have been identified considering the averages of some relevant meteorological parameters in the selected days and the anomaly with respect to the climate. The presence of a cold trough in the central Mediterranean basin appears as a fundamental ingredient for the occurrence of sea breeze convergence and associated precipitation. High-resolution simulations with two state-of-art numerical models have revealed that both of them are generally able to simulate a convergence pattern correctly, apart from a couple of cases for each model. The higher rainfall amounts occur with weak synoptic wind, and weak-to-moderate values of Convective Available Potential Energy (CAPE). When the synoptic wind is of moderate intensity, the region of convergence moves toward the Adriatic coast for a prevailing southerly component, and toward the Ionian coast for a prevailing northerly component. On the opposite, the skin sea surface temperature is relatively uniform and the difference between the Ionian and the Adriatic Seas, surrounding the peninsula on the east and west side, is generally smaller than 1 K, having only a marginal effect on the sea breeze patterns. Similarly, the value of CAPE before the occurrence of rainfall has low prognostic value. The results shows that limited area models with a grid spacing of few km appear as appropriate tools for the simulation for such relatively small scale phenomena. (C) 2015 Elsevier B.V. All rights reserved.

The three-dimensional structure and evolution ofan isolated and stationary microburst are simulated usinga time-dependent, high resolution Large-Eddy-Simulation(LES) model. The microburst is initiated by specifying asimplified cooling source at the top of the domain around2 km a.g.l. that leads to a strong downdraft. Surface windsof the order of 30ms-1 were obtained over a region of500m radius around the central point of the impinging downdraft,with the simulated microburst lasting for a few minutes.These characteristic length and time scales are consistentwith results obtained from numerical simulations of microburstsusing cloud-resolving models. The simulated flowreplicated some of the principal features of microbursts observedby Doppler radars: in particular, the horizontal spreadof strong surface winds and a ring vortex at the leadingedge of the cold outflow. In addition to the primary surfaceoutflow, the simulation also generated a secondary surge ofstrong winds that appears to represent a pulsation in the microburstevolution.These results highlight the capability of LES to reproducecomplex phenomena like microbursts, indicating the potentialusage of LES models to represent atmospheric phenomenaof time and space scales between the convective scaleand the microscale. These include short-lived convectivelygenerateddamaging winds.

The aim of this study is gaining further understanding of the structure of the marine atmospheric boundary layer (MABL) and its interaction with the synoptic scale forcing. A possible application of this study is to simulate mean and turbulent spatial and temporal structure of the marine boundary layer in order to optimise the structural design of offshore large wind turbines that now-a-days reach height up to 200 m. Large-Eddy Simulation (LES) have been performed and compared with offshore experimental data collected during the LASIE campaign performed in the Mediterranean in Summer 2007. Two simulations are performed: in the LES-NOFR run, the LES is left free to evolve without any external forcing, while in the LES-FR run a force-restore nudging technique has been implemented in LES, in order to force the model to the large-scale evolving situation. Model results have been compared against experimental soundings. Results show that the LES-FR outperforms the simulation without force-restore nudging for all the fields, demonstrating that incorporating changes in the large-scale features into the model is necessary in order to provide a realistic evolution of the meteorological fields at local scale.Thus, LES appears as a promising technique to be applied to the simulation of offshore cases, particularly suitable for wind energy applications.

The studies involving flow in offshore wind conditions increased in recent years. This interest is directly associated with the design conditions for wind turbines and wind farm aiming at optimizing the production of wind energy and the risk analysis during the lifetime a wind farm. In this context, the aim of this study is gaining additional understanding of the structure of the marine atmospheric boundary layer (MABL) and its interaction with the synoptic scale forcing. A potential application of this study is to simulate mean and turbulent spatial and temporal structure of the marine boundary layer in order to optimise the structural design of offshore modern wind turbines that may reach height up to 200 m. Large-Eddy Simulation (LES) have been performed and compared with offshore experimental data collected during the LASIE campaign performed in the Ligurian Sea during Summer 2007. Two simulations are performed under different synoptic conditions. Model results have been compared against experimental soundings. Results show that LES outperforms the mesoscale simulation, indicating that the inclusion of large-scale features into the model is necessary to provide a realistic evolution of the meteorological fields at local scale. In this context, LES appears as a promising technique, particularly suitable for offshore wind energy applications

A high-resolution Large-Eddy Simulation (LES) has been performed to simulate a sea-breeze circulation over an idealized peninsular domain. The simulation is forced with the surface latent/sensible heat fluxes and the large-scale horizontal pressure gradient that are obtained from a mesoscale simulation. This methodology allows the investigation of the physical phenomena that are peculiar for a sea-breeze circulation and that generally require spatial resolution approximately equal to one hundred metres or less. Here, small-scale dynamical effects associated to these phenomena, i.e. the interaction between the sea-breeze front with the convective turbulence generated over-land, the formation of the zero-velocity layer, and the development of the Kelvin-Helmholtz billows, are investigated. Results from the present numerical study have revealed the formation of a zero-velocity layer that is initially near the ground then it rises to define a well-marked sea-breeze depth. Scaling analysis applied to the LES output fields reveals that during the phase of inland penetration the scaling laws for sea-breeze strength and depth have both a proportionality coefficient equal to 0.15.

Many mesoscale thermally induced atmospheric motions may be regarded as gravity currents. Land/sea breezes and thunderstorm outflows are typical examples of gravity currents. A large number of laboratory have demonstrated that there are many dynamical similarities between laboratory density currents and atmospheric mesofronts such as thunderstorm outflows and land/sea breezes. The most important feature is the Kelvin-Helmotz instability (KHI) that occurs at the leading edge of the head of gravity current and are the responsible for the mixing between different density fluids. As the sea/land breeze forms near the coast, its head intrudes into the inland ambient air with a temperature stratification that changes with the same time scale as that of the sea/land breeze itself. This means that the structure and dynamics of the gravity current are influenced and modified by changing temperature stratification.In reality, the sea-breeze circulation is a complex phenomenon as it can be modified by many processes such as the synoptic forcing, the shape of coastline, orography, turbulence and cloud cover. A realistic simulation of the sea-breeze would require a model that can simulate the mesoscale sea-breeze circulation together with the small scale turbulent convective boundary layer that is developed over the heated land.A powerful tool for investigating the physics and dynamics of the changing gravity currents in the atmosphere is the large-Eddy Simulation (LES) numerical model. It defines three dimensional meteorological fields with high-enough resolution in the lowest few kilometers of the PBL and the it may be used to examine separately a whole range of atmospheric parameters.Our objective is to investigate the non linear interactions between the sea breeze and the convective turbulence overland. To achieve this purpose we need a model that is able to reproduce the required horizontal inhomogeneities in surface heat flux and drag coefficients as well as the turbulent eddies in the Planetary Boundary Layer.

A Large-Eddy Simulation study of the decay of the TKE during the evening transition in an urban boundary layer was performed. A realistic LES is employed to simulate an Urban Turbulence Project in the city of Turin (Italy). The LES simulation result have demonstrated that, during the last stage of decay the t-6 behavior persists after averaging the TKE over the entire boundary layer depth

This study investigates the Large-Eddy Simulation (LES) technique in the diurnally varying atmosphericboundary layer in conditions of realistic environmental forcing. The initial settings of meteorological fields are obtainedby 'ingesting' into the LES domain the vertical profiles of wind, temperature and specific humidity provided by themeteorological model WRF. The surface values of potential temperature and specific humidity from the WRF simulationare used as forcing parameters for the LES runs. These forcing parameters are updated during the runs every 1 h. Amethodology is developed to derive the components of the geostrophic wind profile that is used in LES to model the largescalehorizontal mean pressure gradient and treated as an external forcing. This methodology involves the meteorologicalmodel WRF. In this context, the WRF model has a dual task: (1) providing realistic atmospheric environmental forcings toLES and (2) providing a very large dataset to investigate possible improvements of the LES setting to make the numericalprediction more realistic.The principal results obtained by the present study is that the use of geostrophic wind shear profiles improves theprognostic capability of LES in reproducing the wind field pattern in the planetary boundary layer, this is an importantparameter for the proper description of the decay of the turbulent kinetic energy at sunset.

In the present work we use an Eulerian diffusion approach as the base for a micro-meteorologicaldispersion parametrisation for short range radioactive contamination modelling in the An-gra dos Reis nuclear power plant site. The closure of the diffusion equation is implementedby means of eddy diffusivity (K-theory). The parametrisations for the eddy diffusivity co-efficients are determined from micro-meteorological parameters that were extracted frommeso-scale Weather Research and Forecasting (WRF) simulations. The model is based onTaylors statistical theory together with a model for Eulerian turbulence spectra from a su-perposition of a buoyant and a shear contribution. We implement an interface between aLES model for the planetary boundary layer and orography related features of WRF andsimulate four days, from February, the 1st to the 4th of 2010, for the environment aroundthe nuclear power plant site at Angra dos Reis, Rio de Janeiro state, Brazil. After extractionof micro-meteorological data we determined the eddy diffusivities under the hypothesis ofhomogeneous turbulence. As the principal result we show the time dependence (for the timescale of a day) of the dimensionless vertical eddy diffusivity coefficients.

A major factor that influences the diurnal variation of turbulent kinetic energy (TKE) is the sensible heat flux at the surface. Here, the TKE variations are analysed during the morning transition phase because subsequent to the neutral or stable stratification during the night, peaks of concentration of scalars develop. The characteristics of the TKE during the growth phase of convection are analysed with the help of two analytical models. For this purpose, a three-dimensional spectral model of the growth of convection, starting from a neutral layer, and other formulations of micrometeorological parameters such as the convective and neutral spectra, velocity variance and dissipation rates are utilised. The peak values in the TKE spectra in the lower, middle and upper levels of the convective bound- ary layer showed a migration to higher wavelengths as the convection increased with time. The TKE evolutions generated by the analytical models agree fairly well with the results of large-eddy simulation for three vertical levels.

Occasionally, cyclones with tropical-like characteristics, sometimes called as Medicanes, are observed in theMediterranean. Due to the intense wind forcing and the consequent development of high wind waves, a largenumber of sea spray droplets are likely to be produced at the sea surface. On the other side, it is known thatMedicane intensity is sensitive to fluxes of momentum and enthalpy between the ocean and atmosphere in thehigh wind core of the storm. It has been recognized that much of this exchange between ocean and atmosphere islikely mediated by sea spray. In particular, the enhancement of sea-air enthalpy flux under severe wind speed issupplied by sea spray that produces the large amount of heat necessary to generate and maintain the hurricane core.Laboratory studies, numerical spray droplets models and observations have proved that sea spray can redistributeenthalpy between the temperature and humidity fields in the marine boundary layer. In particular, the role ofre-entrant spray particles, the portion of spray that fall back into the sea, have the important effect of cooling theocean thus representing a net enthalpy flux to the atmosphere.This work represents an integrated numerical study utilising the third-generation wave model (SWAN) two-waycoupled with the Weather Research and Forecasting Model, running in both stand-alone configuration (WRF) andintegrated with the chemistry package (WRF-Chem). The latter is configured using GOCART aerosol module,which explicitly consider the emission and transport of sea spray aerosol. An additional sea spray source functionfor severe wind conditions has been implemented in the WRF-Chem model under the GOCART aerosol module.The operative sequence is performed considering the offline coupling sequence: first SWAN with WRF, andthen SWAN with WRF-Chem. With this sequence, there is a full consistency between the wind field and wavegeometry.A test is performed considering the Medicane occurred in South-Eastern Italy on September 26, 2006. ThisMedicane is one of the most deeply analyzed in literature, so that an intensive investigation of the feedbacksbetween sea-spray, drag coefficients and latent heat flux may be made considering our integrated approach incomparison with its known features.

Occasionally, storm that shares many features with tropical cyclones, including the presence of a warm core, are observed in the Mediterranean. Sometimes, they are called Medicanes. Due to the intense wind forcing and the consequent development of high wind waves, a large number of sea spray droplets are likely to be produced at the sea surface. In this work, sea spray droplets refer to film, jet and spume droplets. The typical radii at formation of bubble-mediated film and jet droplets are typically less than 5 and 20 ?m, respectively. Spume droplets, which torn off from the crest of breaking waves, are larger, with minimum radius at formation generally about 20 ?m, and a maximum one around 500 ?m. The spray droplets with radii between 10 and 300 ?m (Zhao et al., 2006) contribute most to the air-sea exchange processes of momentum and heat. At this purpose we implemented the Sea Spray Source Function (SSSF) of Wan et al. (2017) in WRF-Chem model version 3.6.1 using the GOCART aerosol sectional module. This SSSF simulates the emission of spume droplets in addition to film and jet droplets, only these last ones are taken into account by still commonly used SSSFs.Traditionally, air-sea momentum flux is computed through the classical Charnock relation (1955) that does not explicitly consider the wave-state and sea spray effects on sea surface roughness. In order to take into account both effects, we implemented the Liu et al. (2011) parameterization of sea surface aerodynamic roughness within the WRF surface layer model (sf_sfclay_physics). It is based on the Volkov (2001) and Makin (2005) parametrizations and may be applicable to both moderate and high wind conditions. This work represents an integrated numerical study utilising the third-generation wave model (SWAN) two-way coupled with the Weather Research and Forecasting Model, running in both stand-alone configuration (WRF) and integrated with the chemistry package (WRF-Chem, modified as described above). The latter is configured using GOCART aerosol module, which explicitly consider the emission and transport of sea spray aerosol. The operative sequence is performed considering first the offline coupling SWAN with WRF, and then the two-way coupling SWAN with WRF-Chem. With this sequence, there is a full consistency between the wind field and wave geometry.A test is performed considering the Medicane occurred in South-Eastern Italy on September 26, 2006. This Medicane is one of the most deeply analyzed in literature, so that an intensive investigation of the feedbacks between sea-spray, drag coefficients and latent heat flux may be made considering our integrated approach in comparison with its known features.

Mediterranean coastal regions are regularly affected by localized heavy precipitation events, resulting in very dangerous flash floods, often of limited predictability. Due to its position, exposed to southerly moist flows from the Mediterranean Sea, and the steep orography near the coasts, one of the most affected areas is Liguria region in northwestern Italy. Extreme precipitation is usually observed between late summer and midautumn, when heat and moisture fluxes from the Mediterranean Sea are the highest. The typical synoptic situation responsible for such events are also associated with desert dust transport towards the Mediterranean and occasionally the Alpine region and Central Europe. Four different case studies corresponding to severe rainfall events occurred over Liguria between October 2010 and October 2014 have been considered and numerical experiments have been performed with the Weather Research and Forecasting (WRF) model to investigate the sensitivity of predicted precipitation to horizontal resolution, microphysics schemes and SST initialization. In particular, two different SST initializations are considered: a coarse field provided by a global atmospheric model and a high-resolution multisatellite analysis. The response of heavy precipitation to SST is a complex one, which involves the modification of PBL and low-level flow characteristics and its interaction with topography. The impact of satellite-derived SST on total predicted precipitation appears beneficial especially for simulations initialized the day before the event, due to the relatively slow adjustment of atmospheric fields to the higher-resolution initial condition. Conversely, such an impact is generally neutral or even negative for 24 h forecasts. The analysis of the most recent episode (October 2014) suggests that a satellite-retrieved SST initial field can improve the quantitative precipitation forecast only when the large-scale forcing is accurate enough. Finally, some preliminary simulations have been performed with the online-coupled meteorology-chemistry model WRF-Chem to investigate the possible role of natural aerosols (dust and sea salt) in the modulation of severe precipitation events in Liguria.

It is well known that aerosols modify the Earth's radiative budget by scattering and absorbing solar and terrestrial radiation. In addition, they affect cloud development and precipitation formation by acting as cloud condensation nuclei (CCN) and ice nuclei (IN), thus indirectly changing the energy budget. Dust aerosols, in particular, have been recently shown to play an important role in the development and evolution of Atlantic tropical cyclones. Considering this, the present study aims to examine the potential effects of dust on the genesis and evolution of tropical-like Mediterranean cyclones (Medicanes). To this end, a Medicane event that took place between 13 and 16 December 2005 is selected for a case study. Analysis of satellite imagery shows clearly that a significant amount of mineral dust was advected into the Medicane, thus making it an ideal case study. In the context of a multi-model inter-comparison, four (4) different regional climate models are employed for simulating the event. The effects of dust (both direct and indirect) on the Medicane genesis and development will be quantified and compared among the four models.

In the frame of the project EDOC@WORK3.0, Education and Work on Cloud, a monitoring plan has been carried out in the highly industrialized town of Taranto (one of the most polluted sites of Italy) in order to investigate contemporary indoor and outdoor concentrations of NO2 and SO2 by passive sampling devises (Radiello). Simultaneously indoor and outdoor samplings of NO2 and SO2 were performed from 2nd November 2015 to 2nd December 2015 in nine sites scattered in the investigated area at different quotes and distances from the industrial complex. Our findings show substantial differences between the spatial distributions of the two pollutants and support the hypothesis of two different prevalent sources for NO2 and SO2. In particular, we find diffusive sources of NO2 linked mainly to the vehicular traffic and secondarily to industrial sources. In contrast, SO2 was mainly associated to industrial sources present in the area, representing also a proxy of the mixture of air contaminants associated to industrial processes. Our hypothesis is also confirmed by analysis of data measured by ARPA air quality monitoring stations. Comparison between indoor and outdoor concentrations confirms that outdoor pollutants infiltrate to indoor environments, moreover it highlights potential NO2 indoor sources basically linked to cooking activities, representing adverse health effects for population risk categories such as children or cooks. Considering that urban people spend a lot of their time in indoors, attention should be paid both to outdoor pollutant sources and to indoor sources. © 2018 Elsevier B.V.

The Pampa-2016 experimental campaign have been performed in a typical Pampa lowland South American region, it consisted in both surface flux measurements (at 3 and 29 meters) and radiosonde launched every three hours. The resulting meteorological observations allowed the analysis of turbulent properties associated with both stable and convective boundary layer. The combined analysis of the surface data and vertical soundings have revealed some general characteristics of the atmospheric boundary layer for both the nocturnal stable conditions and the daytime convective environment. The continuous surface measurements, have shown that the Nocturnal Stable Inversion, occurring in calm wind situation, is generated basically by the radiative cooling mechanism that sets up after the late afternoon transition. The analysis of night-time surface data has showed also that under stable conditions in the case of vanishing wind speed, the friction velocity has unrealistic values that are very close to zero. This is an unwanted situation for numerical models that generally use this quantity as a lower boundary condition. The analysis of night-time temperature profiles has revealed two contrasting patterns in agreement with the classical classification of radiative night (very stable Boundary Layer) and a turbulent night (weakly stable Boundary layer). On the other side, the analysis of the daytime temperature profiles provided the estimation of the convective time scale, that is of the order of 10 minutes in agreement with experimental values. A spectral analysis and the consequent estimation of the spectral peaks under unstable and stable conditions are in agreement with literature values.

Cyclones with characteristics similar to tropical cyclones, although smaller in size,are sometimes observed in the Mediterranean Sea. Several studies have analyzedtheir genesis, evolution, and decay, shedding some light on the mechanismsresponsible for their development. However, some of these cyclones were notproperly reproduced in terms of track and intensity by neither real-time simulationsnor hindcasts, emphasizing the delicate role of small-scale upper level features inthe development of these cyclones.Also, the cyclone intensity is very sensitive to the intense fluxes between the oceanand atmosphere in the high-wind core. The importance to reproduce properly theair-sea interaction has been recently investigated by means of a coupledatmosphere-wave-ocean model (COAWST), which exchanges consistently the seasurface fluxes between the atmospheric model (WRF) and the ocean circulationmodel (ROMS), including also the effect of waves (SWAN).Finally, considering the importance of sea spray droplets in the air-sea exchange,an integrated numerical study has been undertaken, using the wave model SWANtwo-way coupled with WRF-CHEM (the WRF model integrated with the chemistrypackage). A new sea spray generation function under severe wind condition isproposed in WRF-CHEM, in particular in the GOCART aerosol module, whichexplicitly considers the emission and transport of sea spray aerosol.

The Weather Research and Forecasting model with online coupled chemistry (WRF-Chem) is applied to simulate a severe Saharan dust outbreak event that took place over Southern Italy in March 2016. Numerical experiments have been performed applying a physics-based dust emission model, with soil properties generated from three different Land Surface Models, namely Noah, RUC and Noah-MP. The model performance in reproducing the severe desert dust outbreak is analysed using an observational dataset of aerosol and desert dust features that includes optical properties from satellite and ground-based sun-photometers, and in-situ particulate matter mass concentration (PM) data. The results reveal that the combination of the dust emission model with the RUC Land Surface Model significantly over-predicts the emitted mineral dust; on the other side, the combination with Noah or Noah-MP Land Surface Model (LSM) gives better results, especially for the daily averaged PM10.

The diurnal evolution of a cloud free, marine boundary layer is studied by means of experimental measurements and numerical simulations. Experimental data belong to an investigation of the mixing height over inner Danish waters. The mixed-layer height measured over the sea is generally nearly constant, and does not exhibit the diurnal cycle characteristic of boundary layers over land. A case study, during summer, showing an anomalous development of the mixed layer under unstable and nearly neutral atmospheric conditions, is selected in the campaign. Subsidence is identified as the main physical mechanism causing the sudden decrease in the mixing layer height. This is quantified by comparing radiosounding profiles with data from numerical simulations of a mesoscale model, and a large-eddy simulation model. Subsidence not only affects the mixing layer height, but also the turbulent fluctuations within it. By analyzing wind and scalar spectra, the role of subsidence is further investigated and a more complete interpretation of the experimental results emerges. © 2014 Author(s).

Large-Eddy Simulation is performed for a single day from the Cooperative Atmosphere-Surface Exchange Study (CASES-99) field program. This study investigates an observed case of evening transition boundary layer over land. Parameters of the ambient atmosphere in the LES-decay studies conducted so far were typically prescribed in an idealized form. To provide suitable data under the wide range of the PBL weather conditions, the LES should be able to adequately reproduce the PBL turbulence dynamics including - if possible - baroclinicity, radiation, large scale advection and not only be related to a decreasing surface heating. In addition LES-decay studies usually assume that the sensible heat flux decreases instantaneously or with a very short time scale. The main purpose of this investigation is to study the decay of boundary-layer average turbulent kinetic energy at sunset with large-eddy simulation that is forced with realistic environment conditions. This allows investigating the Turbulent Kinetic Energy decay over the realistic time scale that is observed in the atmosphere. During the intermediate and last stage of decay of the boundary-layer average Turbulent Kinetic Energy the exponents of the decay power law t-n go from 2 to 6, as evidenced by experimental results and recent analytical modelling in the surface layer.

The Large-eddy simulation (LES) model is used to investigate the influence of the Tropical Urban Heat Island (UHI) in the vertical structure of the Planetary Boundary Layer (PBL) under adiabatic and non-saturated conditions. An idealized UHI is represented by two-dimensional patches of heat fluxes at the surface defining variable Bowen ratio along the horizontal domain. The results indicated that the heterogeneities are able to induce the formation of intense updraft over the center of warm patch. This buoyant thermal transports the moisture from the lower to the upper part of the PBL and penetrate the entrainment zone. Consequently, the urban-breeze circulation can contribute to the clouds development at the top of the PBL over the UHI.

The aim of this study is to derive a new expression for the vertical turbulent velocityvariance using LES data in a convective boundary layer.

A fully coupled meteorology-chemistry-aerosol model (WRF-Chem) is applied to simulate the Saharan dust outbreak over the Mediterranean regions. Two dust emission schemes, namely, those of Jones et al., (2010), and Shao (2001) are evaluated using the the GOCART aerosol model. To investigate the performance of each dust emission scheme, a case study was carried out for a Mediterranean dust event that took place between 21 and 23 May 2014. Considering the time average Aerosol Optical Depth, simulation results reproduced satisfactorily the outbreak and transport pattern of dust plumes. However, the estimated dust emission amounts in each scheme differ greatly due to the presence of several tuning parameters, that must be adjusted considering satellite and ground based experimental data.

In this study, the Weather Research and Forecasting model with online coupled chemistry (WRF-Chem) is applied to simulate an intense Saharan dust outbreak event that took place over the Mediterranean in May 2014. Comparison of a simulation using a physics-based desert-dust emission scheme with a numerical experiment using a simplified (minimal) emission scheme is included to highlight the advantages of the former. The model was found to reproduce well the synoptic meteorological conditions driving the dust outbreak: an omega-like pressure configuration associated with a cyclogenesis in the Atlantic coasts of Spain. The model performances in reproducing the atmospheric desert dust load were evaluated using a multi-platform observational dataset of aerosol and desert dust properties, including optical properties from satellite and ground-based sun-photometers and lidars, plus in-situ particulate matter mass concentration (PM) data. This comparison allowed us to investigate the model ability in reproducing both the horizontal and the vertical displacement of the dust plume, and its evolution in time. The comparison with satellite (MODIS-TERRA) and sunphotometers (AERONET) showed that the model is able to reproduce well the horizontal field of the aerosol optical depth (AOD) and its evolution in time (temporal correlation coefficient with AERONET of 0.85). On the vertical scale, the comparison with lidar data at a single site (Rome, Italy) confirms that the desert dust advection occurs in several, superimposed 'pulses' as simulated by the model. Cross-analysis of the modeled AOD and desert-dust emission fluxes further allowed to infer the source regions of the observed plumes. The vertical displacement of the modeled dust plume was in rather good agreement with the lidar soundings, with correlation coefficients among aerosol extinction profiles up to 1 and mean discrepancy of about 50%. The model-measurements comparison for PM10 and PM2.5 showed a good temporal matching, although it revealed a marked overestimation of PM10 and PM2.5 (of the order of 70% during the dust peak). For PM10, it was also possible to investigate the accordance between the model- and the measurements-based dust-PM10, this confirming the model PM10 overestimation to be related to over-predicted dust mass up to a factor of 140%. In all the model-to-measurements comparisons performed, the enhanced capabilities of the physics-based emission scheme with respect to its simplified, minimal version were evident and are documented.