Statistical analysis and modelling of weather radar beam propagation conditions in the Po Valley (Italy)

Ground clutter caused by anomalous propagation (anaprop) can affect seriously radar rain rate estimates, particularly in fully automatic radar processing systems, and, if not filtered, can produce frequent false alarms. A statistical study of anomalous propagation detected from two operational C-band radars in the northern Italian region of Emilia Romagna is discussed, paying particular attention to its diurnal and seasonal variability. The analysis shows a high incidence of anaprop in summer, mainly in the morning and evening, due to the humid and hot summer climate of the Po Valley, particularly in the coastal zone. Thereafter, a comparison between different techniques and datasets to retrieve the vertical profile of the refractive index gradient in the boundary layer is also presented. In particular, their capability to detect anomalous propagation conditions is compared. Furthermore, beam path trajectories are simulated using a multilayer ray-tracing model and the influence of the propagation conditions on the beam trajectory and shape is examined. High resolution radiosounding data are identified as the best available dataset to reproduce accurately the local propagation conditions, while lower resolution standard TEMP data suffers from interpolation degradation and Numerical Weather Prediction model data (Lokal Model) are able to retrieve a tendency to superrefraction but not to detect ducting conditions. Observing the ray tracing of the centre, lower and upper limits of the radar antenna 3-dB half-power main beam lobe it is concluded that ducting layers produce a change in the measured volume and in the power distribution that can lead to an additional error in the reflectivity estimate and, subsequently, in the estimated rainfall rate

Reconstruction of reflectivity vertical profiles and data quality control for C-band radar rainfall estimation

International audienceMicrowave Doppler radars are considered a fairly established technique to retrieve rain rate fields from measured reflectivity volumes. However, in a complex orographic environment radar observations are affected by several impairments which should be carefully evaluated. Together with the enhancement of ground-clutter effects, the major limitation is represented by partial or total beam blocking caused by natural obstructions which very often impose to scan at high-elevation angles. These range-related limitations tend to reduce the potential role of operational weather radars in monitoring precipitation amount at ground within mountainous areas since, if either the nature or intensity of rainfall varies with height (e.g., melting effects during stratiform rain), radar returns at higher altitudes may be not representative of surface rain rate. Therefore, before to use the radar data, it is necessary to reduce, as much as possible, this evaluation errors and to estimate the reliability of the processed data. Near to the quality control, are needed quality indexes, taking into account each correction and elaboration step, that could be useful to retrieve a final quality value. In this work, we analyse the main factors that could be affect the efficiency of a reconstruction methodology of near-surface reflectivity fields from high-elevation reflectivity bins, in presence of complex orography. A climatologic schema is applied to infer near-surface reflectivity at a given range interval. The technique is developed in polar coordinates partially taking into account the antenna beam width degradation at longer ranges and overall computational efficiency for operational purposes. Thereafter, it is applied on a rainfall event observed by a C-band Doppler radar operating in S. Pietro Capofiume (Bologna, Italy) and the relation between the reconstruction error and possible quality indicators is analysed and discussed

The role of ceria-based nanostructured materials in energy applications

Ceria (CeO2) is enjoying increasing popularity in catalytic applications, and in some cases has established itself as an irreplaceable component. The reasons for such success stem from the intrinsic structural and redox properties of ceria. Reducing the ceria particles to the nanoscale has a profound impact on the catalytic behavior. The proliferation of improved synthetic methods that allow control over the final morphology and size of the nano-structures is opening new possibilities in terms of catalytic potential, particularly for energy-related applications

The electrifying effects of carbon-CeO2 interfaces in (electro)catalysis

Abstract The exceptional and unique properties of cerium dioxide have encouraged scientists to exploit this material beyond its traditional role as a promoter in automotive engines. Electrochemical processes relevant to fuel cells, electrolyzers, and sensors can be facilitated or even directly catalyzed by the CeO2, whose redox properties are ideal for electrochemistry. However, given the insulating nature of pure ceria, the inclusion of conductive materials at the boundary with the metal oxide is necessary to boost the catalytic activity. Carbon in its various forms and morphologies is a dominant component in ceria-based electrocatalysts, significantly facilitating electron transfers and providing high surface area and improved stability. Moreover, given the improved electronic conductivity of reduced CeO2 in the wake of the decreased grain boundary impedance, the combination with a conductive component, such as carbon, can facilitate a reduction of the ceria

Carbon nanotubes and catalysis: the many facets of a successful marriage

Carbon nanotubes have emerged as unique carbon allotropes that bear very interesting prospects in catalysis. Their use is mostly related to that of supports for inorganic metal catalysts, including molecular catalysts, metal nanoparticles, metal oxides or even more complex hierarchical hybrids. However, several reports have shown that they can intriguingly act as metal-free catalysts, with performance often superior to that of other carbon materials, in particular when ad hoc organic functional groups are attached prior to catalytic screening. The range of catalytic reactions is quite wide, and it includes standard organic synthesis, electrocatalysis, photocatalysis as well as other important industrial processes. In the last few years, the energy sector has acquired a dominant role as one of the most sought-after fields of application, given its ever-increasing importance in society

Electrocatalytic CO2 reduction: role of the cross-talk at nano-carbon interfaces

The electrocatalytic CO2 reduction reaction (CO2RR) is an interfacial process, involving a minimum of three phases at the contact point of gaseous CO2 with the electrodic surface and the liquid electrolyte. As a consequence, surface chemistry at composite interfaces plays a central role for CO2RR selectivity and catalysis. Each interface defines a functional boundary, where active sites are exposed to a unique environment, with respect to distal sites in the bulk of organic and inorganic domains. While the individual role of each component-type is hardly predictable "a-solo", the interface ensemble works via a strategic interplay of individual effects, including: (i) enhanced electrical conductivity, (ii) high surface area and exposure of the interfacial catalytic sites, (iii) favorable diffusion and feeding of reactants, (iv) complementary interactions for the "on/off" stabilization of cascade intermediates, (v) a secondary sphere assistance to lower the activation energy of bottleneck steps, (vi) a reinforced robustness and long-term operation stability. Selected CO2RR case studies are compared and contrasted to highlight how the organic domains of carbon nanostructures merge with metal and metal-oxide active sites to separate tasks but also to turn them into a cooperative asset of mutual interactions, thus going beyond the classic "Divide et Impera" rule

The Role of Structured Carbon in Downsized Transition Metal-Based Electrocatalysts toward a Green Nitrogen Fixation

Electrocatalytic Nitrogen Reduction Reaction (NRR) to ammonia is one of the most recent trends of research in heterogeneous catalysis for sustainability. The stark challenges posed by the NRR arise from many factors, beyond the strongly unfavored thermodynamics. The design of efficient heterogeneous electrocatalysts must rely on a suitable interplay of different components, so that the majority of research is focusing on development of nanohybrids or nanocomposites that synergistically harness the NRR sequence. Nanostructured carbon is one of the most versatile and powerful conductive supports that can be combined with metal species in an opportune manner, so as to guide the correct proceeding of the reaction and boost the catalytic activity

Clutter and rainfall discrimination by means of doppler-polarimetric measurements and vertical reflectivity profile analysis

The estimation of rainfall rate and other parameters from radar scattering volume is heavily affected by the presence of intense sea and ground clutter and echoes which appears in anomalous propagation condition. To deal with these non meteorological echoes we present a new clutter removal algorithm which combines the results of previous works. The algorithm fully exploits both the Doppler and polarimetric capabilities of the radar used and the analysis of vertical reflectivity profile in order to achieve the better identification of the meteorological and non-meteorological targets. The algorithm has been applied to the C-band radar of Monte Settepani (Savona, Italy), which runs in a high-topography environment. Preliminary results are presented