The objective of this work is to characterize the summer urban heat island (UHI) of Rome (Italy) through a dense weather station network, consisting of 17 units. Measurements were collected in summers 2019-2020. We used a recent approach for calculating the UHI intensity, which relates air temperature to imperviousness (IMP) satellite measurements. To asses the reliability of this method we made a comparison with a LCZ-based approach, finding compatible daily trends of UHI intensity with a fixed bias during night. The correlation coefficients between IMP and daily maximum, minimum and mean temperatures were 0.17, 0.81 and 0.82, respectively, reflecting the nighttime UHI peak observed in other cities. The UHI intensity diurnal cycle pattern showed, starting from its minimum of -0.1 °C at 10:00 (CET), a progressive increase which intensifies after sunset reaching a maximum of 3.4 °C at midnight, followed by a slight decrease which exacerbates after sunrise. We found no relevant correlation between UHI and heat waves.

Kelvin-Helmholtz billows (KHBs) within a rising turbulent layer during the transition period from stable to unstable stratification occurring in the morning hours in summertime at the interior of Antarctica (Dome C, Concordia station) are examined in this study. The wave pattern captured by high-resolution sodar echograms from November 2014-February 2015 exhibits regular braid-like structures, associated with Kelvin-Helmholtz shear instabilities. This phenomenon is observed in more than 70% of days in the selected period. Two main regimes of the morning evolution with KHBs are identified roughly, distinguished by the presence or absence of turbulence in the preceding night-time. The weather and turbulent conditions favouring the occurrence of these regimes are analyzed.Also, two distinct patterns of KHBs are identified: (i) quasi-periodical (with periods?8-15min) trains containing 5-10 braids, (ii) about continuous series lasting 20-90 min containing 20-80 braids. A composite shape of KHBs is determined. The periodicity of these waves is estimated to be between 20 and 70 s, and their wavelength is estimated roughly to be 100-400 m. The vertical thickness of individual braids at the wave crests ranges between 5 and 25 m. The total depth of a rising turbulent layer containing these waves varies between 15 and 120 m, and the ratio of the wavelength to the depth of the wave layer varies from 3 to 12 with a mean value ? 8.2. The morphology of the turbulence structure in the ABL is studied as a function of both temperature and wind field characteristics retrieved from an instrumented 45-m tower and an ultrasonic anemometer-thermometer at 3.5 m. The observational results highlight the necessity of considering the interaction between convective and wave processes when occurring simultaneously.

The RHAPS (Redox-Activity And Health-Effects Of Atmospheric Primary And Secondary Aerosol) project was launched in 2019 with the major objective of identifying specific properties of the fine atmospheric aerosol from combustion sources that are responsible for toxicological effects and can be used as new metrics for health-related outdoor pollution studies. In this paper, we present the overall methodology of RHAPS and introduce the phenomenology and the first data observed. A comprehensive physico-chemical aerosol characterization has been achieved by means of high-time resolution measurements (e.g., number size distributions, refractory chemical components, elemental composition) and low-time resolution analyses (e.g., oxidative potential, toxicological assays, chemical composition). Preliminary results indicate that, at the real atmospheric conditions observed (i.e., daily PM1 from less than 4 to more than 50 mu g m(-3)), high/low mass concentrations of PM1, as well as black carbon (BC) and water soluble Oxidative Potential (WSOP,) do not necessarily translate into high/low toxicity. Notably, these findings were observed during a variety of atmospheric conditions and aerosol properties and with different toxicological assessments. Findings suggest a higher complexity in the relations observed between atmospheric aerosol and toxicological endpoints that go beyond the currently used PM1 metrics. Finally, we provide an outlook to companion papers where data will be analyzed in more detail, with the focus on source apportionment of PM1 and the role of source emissions on aerosol toxicity, the OP as a predictive variable for PM1 toxicity, and the related role of SOA possessing redox-active capacity, exposure-response relationships for PM1, and air quality models to forecast PM1 toxicity.

Parameterizations of the Planetary Boundary Layer (PBL) embedded in numerical weather prediction models are crucial in the simulation of local meteorology and require a special investigation. In this study we evaluate simulations at 1 km horizontal resolution using six PBL schemes of the Weather Research and Forecasting model (WRF) by comparison to observations performed in a coastal port-industrial area (Civitavecchia) on the Tyrrhenian coast of Central Italy. During the measurement campaign (April 2016) three types of atmospheric circulation regimes were identified: "breeze", "jet" and "synoptic". Some generalizations can be inferred from the results, despite the variety of settings analyzed (two sites, three regimes in both day and night conditions). Our results show that the temperature simulation is much more sensitive to the configuration at night than during the day, especially on breeze days, when the occurrence of stable boundary layer is favored. For wind speed, nonlocal schemes are very similar to each other, unlike the local closure schemes. The use of the urban Building Environment Parameterization (BEP) significantly improves the simulation of the 2 m temperature during the "jet" evenings and nights, while it entails a further overestimation of the temperature during the "breeze" days leading to a reduction of the bias.

A citizen science network to make cities weather ready

Numerical weather prediction models require an accurate parametrization of the energy budget at the air-ground interface, that can be obtained only through long-term atmospheric boundary layer measurements at different spatial and temporal scales. Despite their importance, such measurements are still scarce even in well-characterized areas. In this paper, a three-year dataset from four micrometeorological stations run by the Regional Agency for Environmental Protection of Lazio was analyzed to estimate albedo, zero-displacement height, roughness length and surface properties over Rome and its suburbs, characterizing differences and interconnections between urban, suburban and rural areas of the same municipality. The integral albedo coefficient at the zenith for the urban station was found to be almost twice that for suburban and rural stations. The zero-displacement height of the urban site was strongly dependent on wind direction, with values varying between 12.0 and 17.8 m, while the roughness length (approximate to 1.5 m) was almost independent of upwind direction, but it was significantly higher than the typical values calculated for rural stations (approximate to 0.4 m). The apparent thermal capacities and thermal conductivity at all the non-urban sites were in fair agreement with each other and typical of soils with relatively low water content, as expected for a relatively dry Mediterranean area like Rome, while the apparent thermal diffusivity reflected the presence of different soil types.

High-resolution large-eddy simulations of the Antarctic very stable boundary layer reveal a mechanism for systematic and periodic intermittent bursting. A nonbursting state with a boundary layer height of just 3m is alternated by a bursting state with a height of approximate to 5m. The bursts result from unstable wave growth triggered by a shear-generated Kelvin-Helmholtz instability, as confirmed by linear stability analysis. The shear at the top of the boundary layer is built up by two processes. The upper, quasi-laminar layer accelerates due to the combined effect of the pressure force and rotation by the Coriolis force, while the lower layer decelerates by turbulent friction. During the burst, this shear is eroded and the initial cause of the instability is removed. Subsequently, the interfacial shear builds up again, causing the entire sequence to repeat itself with a time scale of approximate to 10 min. Despite the clear intermittent bursting, the overall change of the mean wind profile is remarkably small during the cycle. This enables such a fast erosion and recovery of the shear. This mechanism for cyclic bursting is remarkably similar to the mechanism hypothesized by Businger in 1973, with one key difference. Whereas Businger proposes that the flow acceleration in the upper layer results from downward turbulent transfer of high-momentum flow, the current results indicate no turbulent activity in the upper layer, hence requiring another source of momentum. Finally, it would be interesting to construct a climatology of shear-generated intermittency in relation to large-scale conditions to assess the generality of this Businger mechanism.

Climate-induced stresses, more than in the past, expose trees to hazards possibly compromising their stability, with serious risk for people, objects, structures and infrastructures. In order to prevent trees falling phenomena, a constant improvement of the knowledge of relations between trees and meteorological events (trees-wind in particular) is crucial. Any new technology able to support research and monitoring in this direction must therefore be studied, tested, and finally adopted in order to create an infrastructure that would bring indisputable advantages from a social, economic and environmental point of view. The aim of this study is to test the applicability of GNSS receivers for monitoring wind-associated tree movements. The case study reported here refers to an experimental analysis carried out on an Italian stone pine (Pinus pinea L.). The analysis was carried out by applying a single-frequency GNSS receiver (an u-blox M6 evaluation kit available on the market at 300$) at the top of the tree and evaluating the results obtained in term of velocities and positions. Then, values obtained were correlated with wind characteristics by a sonic anemometer installed very close to the pine tree (within 15 meters), in order to independently record the impacting wind fields (velocity, direction). This allowed us to study the correlation between the wind velocity (cause) and tree movements (effect). Statistic outputs evaluation provides very promising results, showing the capability of this instrumental solution in the analysis of movement patterns. The study, indeed evidenced that accuracy of measurements and their relative errors are enough for the research purposes.

The characteristics of the vertical and temporal structure of the coastal atmospheric boundary layer are variable for different sites and are often not well known. Continuous monitoring of the atmospheric boundary layer was carried out close to the Tyrrhenian Sea, near Tarquinia (Italy), in 2015-2017. A ground-based remote sensing instrument (triaxial Doppler sodar) and in-situ sensors (meteorological station, ultrasonic anemometer/thermometer, and net radiometer) were used to measure vertical wind velocity profiles, the thermal structure of the atmosphere, the height of the turbulent layer, turbulent heat and momentum fluxes in the surface layer, atmospheric radiation, and precipitation. Diurnal alternation of the atmospheric stability types governed by the solar cycle coupled with local sea/land breeze circulation processes is found to be variable and is classified into several main regimes. Low-level jets (LLJ) at heights of 100-300 m above the surface with maximum wind speed in the range of 5-18 ms-1 occur in land breezes, both during the night and early in the morning. Empirical relationships between the LLJ core wind speed characteristics and those near the surface are obtained. Two separated turbulent sub-layers, both below and above the LLJ core, are often observed, with the upper layer extending up to 400-600 m. Kelvin-Helmholtz billows associated with internal gravity-shear waves occurring in these layers present opposite slopes, in correspondence with wind speed gradients. Our observational results provide a basis for the further development of theoretical and modelling approaches, taking into account the wave processes occurring in the atmospheric boundary layer at the land-sea interface.

The three-axes Doppler sodar Latan-3 operated on an oceanographic stationary platform in the coastal zone of the Black Sea in June 2015. The platform is located 450 meters offshore from the southern coast of the Crimea Peninsula in the region of Katsiveli (44.39°N, 33.99°E). The water depth at the site is about 30 meters. The atmospheric boundary layer (ABL) typical for the mediterranean seas was observed when the wind is from the sea. The physical processes typical for the coastal mountain terrain was observed when the wind was from the shore. Complex measurements of the ABL parameters were performed using a sodar. Auxiliary measurements of the ABL parameters were performed using a temperature profiler and an ultrasonic thermometer-anemometer. Observations were made mostly during a fair weather with a pronounced diurnal course of meteorological parameters. Sodar data analysis revealed a strong wave activity in the ABL. Internal gravity waves with amplitudes of up to one hundred meters were regularly observed in a layered turbulence structure under stable conditions. Various forms of Kelvin-Helmholtz billows were observed at the interface between the sea breeze and the return flow aloft and in the low level jets.

Urban expansion takes massive proportions in recent years, and population is expected to reach 60% by 2030. The combined effect of global climate change and rapid urbanization makes the residents of urban areas more vulnerable to a range of urban environmental problems, including high air pollution levels, inability to manage energy consumption, overburdened thermal bioclimate and heat-related deaths. These problems are strongly connected with the Urban Heat Island (UHI) effect, that is considered to be one of the most representative and well-documented manifestation of climate modifications due to urbanization. The 3-year long EU LIFE ASTI project (Implementation of a forecAsting System for urban heaT Island effect for the development of urban adaptation strategies) started at the end of 2018 to design, implement, and validate a forecasting system combined with a heat health warning tool for the short-term prediction of the UHI, especially during heat wave events, in two Mediterranean cities - Thessaloniki and Rome. The expected results will also be used to further investigate the UHI climate change impact over the two cities, as well as to perform sensitivity studies for quantifying, assessing and promoting mitigation plans to reduce UHI risks.

Accurate measurement of turbulent parameters under weak turbulence at low temperatures in the atmospheric stable boundary layer still remains a challenge, especially in polar regions. The main instruments to measure atmospheric turbulence parameters are three-dimensional ultrasonic anemometer-thermometers (hereinafter, sonics). Many studies evidence that in some cases the behaviour of spectra of wind speed and temperature looks unreliable. We compared devices of two renowned manufacturers: Gill Instruments Ltd and Metek Scientific HmbH; one model of Gill HS50, and two models of Metek USA-1 and uSonic-3. Measurements were carried out at Concordia station (Dome C, Antarctica), during the summer period, and in a suburban area of Rome (Italy) in all seasons. The behaviour of turbulence spectra at the higher frequency range (in the inertial subrange) under stable stratification was carefully analysed with different approaches and compared with previous results. Relationships between thermal and mechanical turbulence intensities under different stability conditions were considered. The comparison showed both advantages and disadvantages of different sonics depending on weather conditions and a field of application. 1) USA-1 and uSonic-3 by Metek generate elevated electronic quasi-white noise signal in the frequency range > 1 Hz that distorts spectrum slopes and structure parameter estimates (especially for temperature) under weak turbulence conditions. So, it is not possible to measure accurately spectra at frequencies within the inertial subrange, and, accordingly, the wind and temperature structure parameters CV2 and CT2 for weak turbulence. However, it has essential advantage since keeps stable correct functioning under low temperatures up to -40°C and resistance to extremely low temperatures up to -80°C. A built-in heater allows measurements of the mean wind components up to -50°C, however, increases the intensity of turbulent fluctuations. 2) As for HS50 Gill, it is capable to provide accurate measurements of weak-turbulence parameters in the inertial sub-range even under neutral and very stable stratification conditions. However, it has some inherent limitations, as follows: (i) measured sonic temperature is not correct (overestimation of 2-6°C) at all conditions; (ii) sometimes non-stable measurements of the sonic temperature (jumps, non-regular low-frequency trends, spikes in a random way) occur at low temperatures (less than -30°C), that can distort flux estimates and create ambiguities when studying sub-mesoscale phenomena; (iii) the manufacture prohibits its operation at temperatures lower than -40°C; (iv) the absence of correct measurements when the flow direction is around 180 °in reference to the head direction. Also, different calculation methods of turbulent parameters (eddy-covariance and spectral approaches) were verified and compared for different stability conditions. Summarizing, the proper choice of the instrument and calculation approach depends on what variables and characteristics of turbulence we want to determine.

Characteristics of atmospheric turbulence in the stable boundary layer are not well understandable so far. A long-term experiment was performed at Concordia station (Dome C, Antarctica) in 2012, 2014 and 2015 to study the spatial and temporal structure of turbulence in very strong static stability in extremely low temperatures as those observed in winter. Significant thermal turbulence often occurs and extends up to several tens of metres in spite of: (i) the large static stability due to strong temperature inversions extending up to 100-600 m, with a total inversion strength reaching 20-40C at very low temperatures; (ii) the absence of orographic features; (iii) the absence of the diurnal cycle of solar heating. The thermal turbulence pattern was examined using an advanced high-resolution sodar starting from the lowest few metres with a vertical resolution better than 2 m. Sodar observations were complemented by in situ measurements: a weather station and radiometers near the surface, temperature and wind-speed sensors at six levels on a 45-m tower, and radiosondes. The depth of the surface-based turbulent layer (SBTL) at Dome C during the whole winter was directly measured experimentally for the first time. It has an average depth of 25 m, varying from a few to several tens of metres, against an inversion-layer depth of 350 m. Relationships between the depth of the SBTL and atmospheric parameters such as temperature, wind speed, longwave radiation, Brunt-Väisälä frequency and Richardson number are shown. The SBTL under steady weather conditions was analyzed and classified into three prevailing types: 1) a very shallow layer with a depth < 15 m; 2) a shallow layer of depth 15-70 m with uniform internal structure; 3) a shallow layer of depth 20-70 m with waves. Meteorological conditions (including the shape of temperature and wind speed profiles) accompanying the considered SBTL types are determined and described. Wind speed was found to be a relevant meteorological variable influencing the formation and development of the STL. Wave activity in the SBTL is observed during a significant portion of the time, with sometimes regular (with periodicity of 8-15 min) trains of Kelvin-Helmholtz billow-like waves occurring at periods of 20-60 s, and lasting several hours. The main characteristics of the wavelike structures (shape, spatial and temporal scales) were determined. Our observational data provide an experimental basis necessary for improvement, developing and verification of advanced modelling and theoretical approaches to deep understanding of the features of turbulence under stable stratification conditions.

The annual and diurnal behavior of the temperature differences in urban areas is important to predict the possible impacts of the future land-use development on climate change and air pollution in heavily populated areas. The behavior of the temperature as well as wind spatio-temporal differences in turn is strongly interconnected with the turbulent and radiative fluxes variability. A 3-year dataset from three automated micrometeorological stations run by the Regional Agency for Environment Protection of Lazio and located in and around the city of Rome is used. The distribution of the urban heat island intensity for the whole period of measurements peaks at 1 °C, but higher values are frequently registered especially referring to differences with the coastal site also due to the sea-breeze cooling effects. The city is generally drier and characterized by winds of lower intensity reaching their maximum 1 h later with the respect to the sub-urban/coastal sites during the afternoon. The micrometeorological data are also analyzed to estimate some key parameter characteristic of the terrain, which represents the main forcing in the numerical models for UHI estimates, such as the albedo, aerodynamics and atmospheric turbulence parameters.

Observations of two typical contrasting weakly stable and very stable boundary layers from the winter at Dome C station, Antarctica, are used as a benchmark for two centimetre-scale-resolution large-eddy simulations. By taking the Antarctic winter, the effects of the diurnal cycle are eliminated, enabling the study of the long-lived steady stable boundary layer. With its homogeneous, flat snow surface, and extreme stabilities, the location is a natural laboratory for studies on the long-lived stable boundary layer. The two simulations differ only in the imposed geostrophic wind speed, which is identified as the main deciding factor for the resulting regime. In general, a good correspondence is found between the observed and simulated profiles of mean wind speed and temperature. Discrepancies in the temperature profiles are likely due to the exclusion of radiative transfer in the current simulations. The extreme stabilities result in a considerable contrast between the stable boundary layer at the Dome C site and that found at typical mid-latitudes. The boundary-layer height is found to range from approximately 50m to just 5m in the most extreme case. Remarkably, heating of the boundary layer by subsidence may result in thermal equilibrium of the boundary layer in which the associated heating is balanced by the turbulent cooling towards the surface. Using centimetre-scale resolutions, accurate large-eddy simulations of the extreme stabilities encountered in Antarctica appear to be possible. However, future simulations should aim to include radiative transfer and sub-surface heat transport to increase the degree of realism of these types of simulations.

Wavelike motions (similar to Kelvin-Helmholtz billows, KHBs) within the rising inversion layers during the morning transition of the atmospheric boundary layer (ABL) are investigated. The KHBs were depicted in sodar echograms obtained in a rural terrain near Moscow (Russia) in 2011. Power spectra of the intensity of the sodar return signal were calculated from inversion layers and from convective areas underneath. Comparison of the dominant spectral maximums for the inversion and convective parts of the ABL show connection between convective plumes and KHBs.

An experiment to investigate atmospheric turbulence was performed at Concordia station (Dome C, Antarctica) during winter 2012, finding significant turbulence in a near-surface layer extending to heights of a few tens of metres, despite the strong stable stratification. The spatial and temporal behaviour of thermal turbulence is examined using a high-resolution sodar, starting from the lowest few metres with a vertical resolution better than 2 m. Sodar observations are complemented by in situ measurements using a weather station and radiometers near the surface, temperature and wind-speed sensors at six levels on a 45-m tower, and radiosondes. The depth of the surface-based turbulent layer (SBTL) at Dome C during the whole winter is directly measured experimentally for the first time, and has an average depth of ? 23 m, varying from a few to several tens of metres, while the inversion-layer depth ? 380 m. Relationships between the depth of the SBTL and atmospheric parameters such as the temperature, wind speed, longwave radiation, Brunt-Väisälä frequency and Richardson number are shown. The SBTL under steady weather conditions is analyzed and classified into three prevailing types: 1) a very shallow layer with a depth < 15 m, 2) a shallow layer of depth 15-70 m with uniform internal structure, 3) a shallow layer of depth 20-70 m with waves. Wave activity in the SBTL is observed during a significant portion of the time, with sometimes regular (with periodicity of 8-15 min) trains of Kelvin-Helmholtz billow-like waves occurring at periods of 20-60 s, and lasting several hours.

In order to prevent trees falling phenomena, a constant improvement of the knowledge of relations between trees and meteorological events (trees-wind in particular) is crucial. The case study reported here refers to an experimental analysis carried out on an individual of Italian stone pine (Pinus pinea L.). The analysis was carried out by applying a low-cost GNSS receiver at the top of the tree and evaluating the results obtained in term of velocities, positions and frequencies; the next step was to correlate the values obtained with those measured by a sonic anemometer.

Consumer drones have recently become a threat in many real scenarios, since they are difficult to detect and track, and can be easily used to perform criminal activities such as smuggling of illicit materials, surveillance operations or network hacking, and stealing data. Existing technologies are either not suitable to detect an object that can be as small as 10 cm, or quite expensive and complicated to deploy. We carried out a field experiment to explore the possibility of tuning a well-known, low-cost acoustic radar (sodar), commonly used in atmospheric physics, to detect and track consumer drones. The vertical position of a small drone retrieved by a single-sodar antenna turned out to be in good agreement with that measured by its onboard GPS (correlation coefficient 0.93), and no significant bias was observed. Despite being preliminary, these results support the use of such a technique to retrieve reliably the position of small unmanned aerial vehicles.

Climate-induced stresses, more than in the past, exposes trees to hazards possibly compromising their stability, with serious risk for people, structures and infrastructures. In order to prevent trees falling phenomena, a constant improvement of the knowledge of relations between trees and meteorological events (trees-wind in particular) is crucial. Any new technology that can support the research and the monitoring in this direction has hence to be investigated, tested and eventually adopted if able to give a support. The case study reported here refers to an experimental analysis carried out on an individual of Italian stone pine (Pinus pinea L.) vegetating in the CNR-RM 1 Research Area of Montelibretti (Italy). The boundary conditions have been studied with the help of different survey instruments, including an anemome- ter, in order to define as accurately as possible the relation between the gusts of wind and the pattern of movement of the trees. The experimentation has been carried out through the use of a single frequency GNSS receiver; its autonomy and low cost make it, indeed, very competitive compared to other instruments that can be used for similar purposes. The data were collected over approximately two months at 1 second rate, and they were processed both by RTKLIB and VADASE software, in order to preliminary investigate on the average data quality, considering the non optimal installation of the GNSS antenna partially surrounded by pine canopy, and then to analyse positions and velocity time series and vibration frequencies during the wind storms. A sonic anemometer was installed very close to the pine tree (within 20 meters), in order to independently record the impacting wind fields (velocity, direction) and to enable correlation analysis between them and the tree response. The aim of this analysis is to define a new stability index on the basis of the kinematic behaviour of the tree, and to identify a specific alarm threshold to be used for timely safety intervention. The medium-term objective of the proposed methodology is to demonstrate the feasibility to realize a low-cost GNSS-based device (possibly complemented with other sensors as MEMS accelerometers), enabling the instal- lation of a network to monitor permanently and in real time the mechanical responses of different tree species, on different soil types, to wind storms. The collected data will allow a larger comprehension of the trees-wind relations and the definition of new indexes that will support the studies related to tree stability. This infrastructure will be clearly beneficial from a social, economic and environmental point of view.