165 research outputs found
A numerical investigation of the sea breeze and slope flows around Rome
A three-dimensional non-hydrostatic prognostic mesoscale model is used to simulate the circulation around Rome, Italy, on a cloudless summer day with weak synoptic winds, with the aim of characterising the local circulation on
such days. The simulation shows that the sea breeze and slope flows play roles of comparable importance. At night the circulation is dominated by katabatic flow. During the late morning/early afternoon there is a sea breeze with a front curving pincer-like around Rome, and well-developed anabatic flows on all slopes. In the late afternoon, sea breeze and slope flows coalesce into a single circulation reaching hundreds of kilometers inland, with an offshore return flow aloft. Comparison with observations is favourable, particularly during the day
The upper-tropospheric forcing during the 10th-12th December 2003 storm over Calabria
In this study we revisit an intense and destructive storm that occurred over Calabria, southern Italy, on 10th-12th December 2003. This event was already analyzed by two of the authors at synoptic and planetary scales, however in this work we investigate the mesoscale of the storm by the RAMS (Regional Atmospheric Modeling System) model. Firstly it is shown that large-scale moisture source was mainly from the Mediterranean basin, then RAMS simulations are discussed to focus on the mesoscale of the storm. More precisely we evaluate the roles of Calabrian orography and the surface latent heat fluxes by the factor separation
technique. Results show that the role of Calabrian orography, even if important, decreased during the event whilst the role of surface latent heat fluxes was less affected through the entire event. A prominent mid tropospheric trough or cut-off low can be identified through this event prior and during the period of heavy rain. The upper-tropospheric level disturbance, associated with high potential vorticity (PV) values, consequence of a deep tropospheric intrusion of stratospheric air masses, coupled with the surface cyclone and reinforced the whole meteorological system which resulted in the heavy impact rainstorm over Calabria, mainly during 11th and 12th
December 2003
Tuning topological disorder in MgB
We carried out Raman measurements on neutron-irradiated and Al-doped MgB
samples. The irradiation-induced topological disorder causes an unexpected
appearance of high frequency spectral structures, similar to those observed in
lightly Al-doped samples. Our results show that disorder-induced violations of
the selection rules are responsible for the modification of the Raman spectrum
in both irradiated and Al-doped samples. Theoretical calculations of the phonon
density of states support this hypothesis, and demonstrate that the high
frequency structures arise mostly from contributions at of the
E phonon mode.Comment: 4 pages, 4 figure
A study of rainfall in the Roman area in the years 1951--2000
The daily rainfall data collected in the second half of the last century at 31 climatic stations in Lazio, Italy, have been subjected to statistical analysis in order to describe the pluviometric regime of the whole area on a multi-decadal time scale. The stations, for their geographical distribution within the region under study, are apt to represent different climatic zones, namely, a coastal, a rural, a suburban and an urban zone. The data have been treated both as time series and as geographicalstatisticalv
ariates with the double aim, first, to verify if in the area under study any changes in the yearly precipitation rate, frequency and its distribution over different classes of rain intensity, have occurred in the last 50 years; second, to evidence a possible correlation between the intensity of precipitation and any of some environmental variables such as altitude, distance from the coastline and
distance from the urban site. As for the first issue, it can be concluded that the precipitations over the Roman area in the period 1951–2000 show no significant trend; in particular, no trend is visible in any of the single classes of rain intensity, both absolute and percentile-based, considering either their frequency or their percent
contribution to the total. As for the second issue, significant correlations have been found in the spatial distribution of rainfall with any of the relevant environmental variables mentioned above. The results of the analysis also show that in the urban area a less amount of rain seem to fall than in the surroundings zones, a result that seems rather anomalous in consideration of the several known factors that favour the intensification of the rainfall in the city with respect to its surroundings. A detailed statistical characterization of all the single 31 stations over the whole period is also given via a separate study of the durations of droughts and of the statistics of rainy days, using best fits based on the Weibull probability distribution
Verification of precipitation forecasts from two limited-area models over Italy and comparison with ECMWF forecasts using a resampling technique
This paper presents the first systematic limited area model (LAM) precipitation verification work over
Italy. A resampling technique was used to provide skill score results along with confidence intervals. Two
years of data were used, starting in October 2000. Two operational LAMs have been considered, the
Limited Area Model Bologna (LAMBO) operating at the Agenzia Regionale Prevenzione e Ambiente-
Servizio Meteorologico Regionale (ARPA-SMR) of the Emilia–Romagna region, and the QUADRICS
Bologna Limited Area Model (QBOLAM) running at the Agenzia per la Protezione dell’Ambiente
e per i Servizi Tecnici (APAT). A 24-h forecast skill score comparison was first performed on the native 0.1°
high-resolution grids, using a Barnes scheme to produce the observed 24-h accumulated rainfall analysis.
Two nonparametric skill scores were used: the equitable threat score (ETS) and the Hanssen and Kuipers
score (HK). Frequency biases (BIA) were also calculated. LAM forecasts were also remapped on a lowerresolution
grid (0.5°), using a nearest-neighbor average method; this remapping allowed for comparison
with ECMWF model forecasts, and for LAM intercomparisons at lower resolution, with the advantage of
reducing the skill score sensitivity to small displacements errors. LAM skill scores depend on the resolution
of the verification grid, with an increase when they are verified on a lower-resolution grid. The selected
LAMs have a higher BIA compared to ECMWF, showing a tendency to overforecast precipitation, especially
along mountain ranges, possibly due to undesired effects from the large-scale and/or convective
precipitation parameterizations. Lower ECMWF BIA accounts for skill score differences. LAMBO precipitation
forecasts during winter (adjusted for BIA differences) have less misses than ECMWF over the
islands of Sardinia and Sicily. Higher-resolution orography definitely adds value to LAM forecasts
A detailed study of rainfall in the Roman area in the decade 1992–2001
A study of the rainfall regime in the Roman area over the decade 1992-2001 has been undertaken on using tipping pluviometers data, coming from 23 climatic stations located in Rome and in its surroundings. The time response of the
instruments and the automatic acquisition system ensure a resolution of less than 1 minute, thus offering the possibility of an accurate evaluation of intense and extreme
events. The mean yearly rainfall over the whole decade has been determined for each station, obtaining values between 682 and 870mm/year, with a geographical average of 771 and a standard deviation of 47. A study of the rainfall distribution within the 48 half-hours of the day has been carried out in order to ascertain whether preferred times for rain events exist. The analysis has evidenced that this is the case, with high rainfall rates mostly occurring in the late morning and low rates in the late night. Typical values of the maximum 30-min rainfall ever recorded at any given station oscillate between 25 and almost 60 mm. A separate analysis of rainy and dry days has been carried out on studying the statistics of the time delays between two successive tips of the pluviometer. This allowed a characterization of the intense rains as well as of the droughts: the resulting histograms show the existence of a bimodal distribution explained in terms of two kinds of rain events, intense summer showers and drizzles distributed over the rest of the year. As for the droughts, the longest durations appear to range from one to about seven months. On confining the analysis to the rainy days only, the rain intensity data for each station has been plotted and fitted with a Weibull distribution. The corresponding Weibull parameters, while gathering around common mean values, do not show any recognizable pattern when regressed, for instance, versus the altitude of the station or the distance from the coastline. Last, the likelihood that a day of the year, taken at random, be a rainy day or not has been computed for each station yielding probability values ranging from 0.18 to 0.22
Predictability of intense rain storms in the Central Mediterraneanbasin: sensitivity to upper-level forcing
International audienceThis study investigates the sensitivity of a moderate-intense storm that occurred over Calabria, southern Italy, to upper-tropospheric forcing from a Potential Vorticity (PV) perspective. A prominent mid-troposheric trough can be identified for this event, which occurred between 22?24 May 2002, and serves as the precursor agent for the moderate-intense precipitation recorded. The working hypothesis is that the uncertainty in the representation of the upper-level disturbance has a major impact on the precipitation forecast and we test the hypothesis in a two-step approach. First, we examine the degree of uncertainty by comparing five different scenarios in a Limited area model Ensemble Prediction System (LEPS) framework which utilizes the height of the dynamical tropopause as the discriminating variable. Pseudo water vapour images of different scenarios are compared to the corresponding METEOSAT 7 water vapour image at a specific time, antecedent to the rain occurrence over Calabria, in order to evaluate the reliability of the different precipitation scenarios simulated by the LEPS. Second, we examine the impact of upper tropospheric PV variations on precipitation by comparing model simulations with slightly different initial PV fields. Initial velocity and mass fields in each case are balanced with the chosen PV perturbation using a PV inversion technique. The results of this study support the working hypothesis
Optical properties of the Ce and La di-telluride charge density wave compounds
The La and Ce di-tellurides LaTe and CeTe are deep in the
charge-density-wave (CDW) ground state even at 300 K. We have collected their
electrodynamic response over a broad spectral range from the far infrared up to
the ultraviolet. We establish the energy scale of the single particle
excitation across the CDW gap. Moreover, we find that the CDW collective state
gaps a very large portion of the Fermi surface. Similarly to the related rare
earth tri-tellurides, we envisage that interactions and Umklapp processes play
a role in the onset of the CDW broken symmetry ground state
Pressure dependence of the single particle excitation in the charge-density-wave CeTe system
We present new data on the pressure dependence at 300 K of the optical
reflectivity of CeTe, which undergoes a charge-density-wave (CDW) phase
transition well above room temperature. The collected data cover an
unprecedented broad spectral range from the infrared up to the ultraviolet,
which allows a robust determination of the gap as well as of the fraction of
the Fermi surface affected by the formation of the CDW condensate. Upon
compressing the lattice there is a progressive closing of the gap inducing a
transfer of spectral weight from the gap feature into the Drude component. At
frequencies above the CDW gap we also identify a power-law behavior, consistent
with findings along the Te series (i.e., chemical pressure) and
suggestive of a Tomonaga-Luttinger liquid scenario at high energy scales. This
newest set of data is placed in the context of our previous investigations of
this class of materials and allows us to revisit important concepts for the
physics of CDW state in layered-like two-dimensional systems
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A Surface Site Interaction Point Method for Dissipative Particle Dynamics Parametrization: Application to Alkyl Ethoxylate Surfactant Self-Assembly.
Dissipative particle dynamics (DPD) is a coarse-grained approach to the simulation of large supramolecular systems, but one limitation has been that the parameters required to describe the noncovalent interactions between beads are not readily accessible. A first-principles computational method has been developed so that bead interaction parameters can be calculated directly from ab initio gas-phase molecular electrostatic potential surfaces of the molecular fragments that represent the beads. A footprinting algorithm converts the molecular electrostatic potential surfaces into a discrete set of surface site interaction points (SSIPs), and these SSIPs are used in the SSIMPLE (surface site interaction model for the properties of liquids at equilibrium) algorithm to calculate the free energies of transfer of one bead into a solution of any other bead. The bead transfer free energies are then converted into the required DPD interaction parameters for all pairwise combinations of different beads. The reliability of the parameters was demonstrated using DPD simulations of a range of alkyl ethoxylate surfactants. The simulations reproduce the experimentally determined values of the critical micelle concentration and mean aggregation number well for all 22 surfactants studied.Engineering and Physical Sciences Research Counci
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