Showing papers by "ARPA-E published in 2001"

Wintertime variability of Mediterranean precipitation and its links with large-scale circulation anomalies

Abstract: A standard principal component analysis has been performed over the Mediterranean and over the larger European region on monthly precipitation anomalies for the winters between 1979 and 1995. The main centres of action of the associated EOFs are very similar for the two regions and the two sets of PCs are highly correlated with each other. Focusing on the Mediterranean region, the same analysis has been performed using 500 hPa geopotential height monthly anomalies taken from the operational NCEP analysis. Comparing the two sets of PCs associated with upper-air and surface data, a strong correlation has been found suggesting the presence of a two-way link between regional precipitation patterns and large-scale circulation anomalies. For both fields, the largest fraction of variance is explained by the North Atlantic Oscillation, while smaller but still substantial fractions are explained by other known patterns of large-scale variability such as the Eastern Atlantic pattern and the Euro-Atlantic blocking. No detectable connection has been found between Mediterranean precipitation patterns and El Nino SST anomalies during winter. With respect to temporal variability, significant trends have been found over most European areas during the winters considered. The associated pattern is characterised by a substantial increase of precipitation over western Scandinavia and a general decrease over southern Europe. This result is confirmed by analysing data from stations located in northern Italy.

The fractional Fick's law for non-local transport processes

Abstract: Fick's law is extensively adopted as a model for standard diffusion processes. However, requiring separation of scales, it is not suitable for describing non-local transport processes. We discuss a generalized non-local Fick's law derived from the space-fractional diffusion equation generating the Levy–Feller statistics. This means that the fundamental solutions can be interpreted as Levy stable probability densities (in the Feller parameterization) with index α (1<α⩽2) and skewness θ (|θ|⩽2−α). We explore the possibility of defining an equivalent local diffusivity by displaying a few numerical case studies concerning the relevant quantities (flux and gradient). It turns out that the presence of asymmetry (θ≠0) plays a fundamental role: it produces shift of the maximum location of the probability density function and gives raise to phenomena of counter-gradient transport.

A strategy for high-resolution ensemble prediction. I: Definition of representative members and global-model experiments

Abstract: In the last few years, tens of alternative weather forecasts have been made available to forecasters by operational ensemble prediction systems. In many forecasting applications, it is useful to identify (possibly in an objective way) a few representative ensemble members, deemed to represent the most interesting weather scenarios. In this paper, a strategy to select representative members (RMs hereafter) from an ensemble prediction is developed, and applied to four cases of medium-range ensemble forecasts performed with the European Centre for Medium-Range Weather Forecasts (ECMWF) Ensemble Prediction System (EPS). The four case-studies correspond to events of very intense rainfall (leading to localized floods) in the Alpine region, selected as benchmarks for numerical simulations in the Mesoscale Alpine Programme. The RM selection procedure uses a cluster analysis of the ensemble forecasts as its first step. For each cluster, an RM is defined to be the member with the smallest ratio between its average distance from the members of its own cluster and its average distance from the members of the other clusters. Distances are computed either using an L2-norm applied to 700 hPa geopotential height fields or an L1-norm to precipitation fields. RMs are compared with cluster centroids in the four case-studies of extreme rainfall. By definition, RMs are characterized by a synoptic-scale atmospheric flow similar to the flow of the corresponding cluster centroid, but they contain more small-scale features, especially in the prediction of weather parameters such as precipitation. RM initial conditions can be used to initiate higher-resolution global forecasts; alternatively, RMs may be used to define initial and boundary conditions for nested high-resolution forecasts with limited-area models. Integrations of RMs with the ECMWF global model at T1 319 horizontal resolution (compared with the T1 159 resolution used in the EPS) were performed. Results indicate that each higher-resolution forecast, started from RM initial conditions, remains closer to the low-resolution RM than to other ensemble members, but provides a more detailed forecast of weather parameters, especially in regions of complex topography. Experiments with a nested limited-area model, started from the same set of RMs, are described in a companion paper.

A strategy for high‐resolution ensemble prediction. II: Limited‐area experiments in four Alpine flood events

Abstract: A high-resolution ensemble system, based on five runs of a limited-area model (LAM), is described. The initial and boundary conditions for the LAM integrations are provided by the representative members (RMs) selected from the European Centre for Medium-Range Weather Forecasts Ensemble Prediction System (EPS). EPS members are grouped in five clusters; then, from each cluster, an RM is selected, according to the methodology described in the companion paper. The ability of the high-resolution ensemble system to predict the occurrence of heavy rainfall events (either five or six days ahead) is tested for four cases of floods over the Alpine region. Results show that, in two case-studies, the LAM integration corresponding to the RM of the highly populated cluster predicts the observed rainfall with a very good degree of time and spatial accuracy. In the other two cases, the extreme events are captured by at least one of the runs nested on the members of the less populated clusters. Probability maps constructed from LAM integrations provide great detail on the location of the regions affected by heavy precipitation and the information gained with respect to EPS probability maps and LAM deterministic forecasts is highlighted. The probabilistic estimates based on the LAM ensembles are also shown to be of valuable assistance to forecasters in issuing early flood alerts, contributing to the definition of a flood-risk alarm system.

Precipitation estimations from geostationary orbit and prospects for METEOSAT Second Generation

Abstract: For over two decades operational rainfall estimations from geostationary satellites have represented an ambitious aspiration of scientists and an identified need of operational meteorologists. A wide variety of infrared and combined visible and infrared methods have been proposed for the identification of suitable relationships between satellite-observed cloud top radiative features and rainfall at the ground. Microwave-based retrievals, however, correlate rainfall and internal cloud microphysical features more successfully. The most significant limitation, however, is the indirect character of the retrieval that correlates microphysical and dynamical cloud characteristics with rain amounts at ground level. METEOSAT Second Generation signals a new era for geostationary satellites with its new 12 channel imager SEVIRI and 15 minute full-disk image repeat cycle. SEVIRI is expected to contribute significantly to a better characterisation of clouds and atmospheric stability by means of improved infrared calibration, radiometric performances, imaging frequency and multispectral image analysis. The significant increase of multispectral cloud observations is expected to provide new data for the improvement of rainfall estimations from geostationary orbit. The anticipated progress from enhanced imaging frequency and multispectral data for the definition of new techniques is discussed. Considerations for operational applications, chiefly for nowcasting, are also provided as they are the main goal of the satellite. Future developments and synergies with other geostationary and polar orbiting instruments, passive and active, are finally considered as the ultimate strategy for more accurate instantaneous rainfall estimations at all latitudes. Copyright © 2001 Royal Meteorological Society

Use of the vertical reflectivity profile for identification of anomalous propagation

Abstract: Anomalous propagation (anaprop), analogous to the upper mirage in the visual wavelengths, is still a major problem in radar meteorology. This phenomenon assumes particular importance in automatic recognition and estimation of rainfall. Anaprop echoes from terrain features such as hills and coasts often give echoes up to 50‐60 dBZ, equivalent to heavy rain or hail in severe thunderstorms. Anaprop echoes from sea waves may be comparable in strength to those from moderate precipitation and also form similar patterns. Based on the evidence that the vertical reflectivity profile of precipitation is quite different from the anaprop profile, two methods for anaprop identification are presented. The method proposed by the Servizio Meteorologico Regionale (SMR, Italy) simply uses the operational scan procedure to discriminate between precipitation and anaprop. At the Swedish Meteorological and Hydrological Institute an ‘ad hoc’ scan strategy has been developed in order to obtain much more detail of the lowest reflectivity profile. A number of statistical parameters have been used to achieve a better discrimination between precipitation, land and sea clutter. A number of case studies, representing different echo intensities and patterns, and including a case of anaprop with embedded precipitation, are presented to assess the impact of these methods.

A generalized Fick's law to describe non-local transport effects

Abstract: Fick's law is extensively used as a model for turbulent diffusion processes. It requires separation of scales between those of the process driving the diffusion mechanism and the scale of variation of the mean quantity being diffused. This makes the model unsuitable for the description of non-local transport processes like those occurring in some turbulent flows. A generalized Fick's law is proposed using a fractional derivative operator which accounts for non-local phenomena in virtue of its integral nature. This generalization is suggested as a model for two typical phenomena, like those observed in the convective boundary layer (CBL), which cannot be reduced to a local formulation: the inadequacy in the flux-gradient relationship when considering bottom-up dispersion (in particular, the counter-gradient transport) and the vertical drift of the location of the maximum concentration even in the absence of the mean velocity field. The solution of the generalized diffusion equation qualitatively reproduces the above described features, supporting the fractional derivative description of turbulent transport in complex flows. A quantitative approach requires extensive investigation in order to deal with the details of real cases.

Determination of uranium isotopes in food and environmental samples by different techniques: a comparison.

Abstract: The uranium concentration in 59 samples of bottled and tap water, mainly from northern Italy, was measured by different techniques. Results obtained by inductively coupled plasma mass spectrometry (ICP-MS), semiconductor alpha spectrometry and low level liquid scintillation counting with alpha/beta discrimination (LSC) have been compared. High resolution gamma spectrometry and semiconductor alpha spectrometry have been used to analyse uranium in a variety of organic and inorganic samples. Isotopic secular equilibrium in the 238U series may be lacking or hidden by auto-absorption phenomena, so caution should be used in evaluating gamma spectrometry data. Alpha spectrometry has also been used to ascertain the possible pollution from depleted uranium in the environment.

Radon survey in schools in north-east Italy.

Abstract: During the year 2000 the Regional Agency for Environmental Protection (ARPA) of Friuli Venezia Giulia together with the Pordenone Province carried out a survey to determine the radon concentration in the schools. About 900 measurements have been carried out in 300 schools located both in the mountainous and in the flat territory. Moreover, geological information was gathered, both on a regional scale and, where possible, on a small detailed scale. The purpose of this study is to consider the possibility of using all the data collected to discover some radon prone areas. The first results of this study seem to locate some radon prone areas where the cover consists of very permeable gravelly deposits.

Comparison of different methods for the assessment of the environmental gamma dose

Abstract: Four different techniques for the assessment of environmental gamma dose are discussed and compared: high pressure ionisation chamber (Reuter-Stokes type), TLD dosemeters (GR-200), in situ gamma ray spectrometry and dose evaluation from the activity concentration of radionuclides in the soil. Soil samples gathered from a field near Turin (North-West Italy) have been analysed with a p-type HPGe, and their radionuclide concentrations have been used to evaluate the dose at 1 m above the soil surface. At the same location the dose rate was evaluated with the in situ gamma ray spectrometry (with a portable n-type HPGe) and with the ionisation chamber and the TLD dosemeters. The contribution of cosmic rays was added to the dose rate calculated from the soil samples and the in situ gamma spectrometry. The results obtained with these four techniques agree well within 20%.

Performance of the ARPA-SMR limited-area ensemble prediction system: two flood cases

Abstract: . The performance of the ARPA-SMR Limited-area Ensemble Prediction System (LEPS), generated by nesting a limited-area model on selected members of the ECMWF targeted ensemble, is evaluated for two flood events that occurred during September 1992. The predictability of the events is studied for forecast times ranging from 2 to 4 days. The extent to which floods localised in time and space can be forecast at high resolution in probabilistic terms was investigated. Rainfall probability maps generated by both LEPS and ECMWF targeted ensembles are compared for different precipitation thresholds in order to assess the impact of enhanced resolution. At all considered forecast ranges, LEPS performs better, providing a more accurate description of the event with respect to the spatio-temporal location, as well as its intensity. In both flood cases, LEPS probability maps turn out to be a very valuable tool to assist forecasters to issue flood alerts at different forecast ranges. It is also shown that at the shortest forecast range, the deterministic prediction provided by the limited area model, when run in a higher-resolution configuration, provides a very accurate rainfall pattern and a good quantitative estimate of the total rainfall deployed in the flooded regions.

Variations of the Isotopic Ratios of Uranium in Environmental Samples Containing Traces of Depleted Uranium: Theoretical and Experimental Aspects

Abstract: The possibility of using conventional analysis, such as γ spectrometry and α spectrometry, for the detection of traces of depleted uranium (DU) in environmental samples has been investigated. The expected values have been compared with the experimental results obtained by using mollusc samples gathered in the Adriatic Sea. The analysis has shown that it is possible to detect DU, if the percentage composition is about 20% depleted uranium and 80% natural uranium, for a sample containing 10 Bq.kg -1 of 238 U. The possibility of extending this approach to samples with any given uranium concentration is investigated.

Electromagnetic Field Monitoring and Control Systems: State-of-the-Art and Work-in-Progress

Abstract: The development of EMF monitoring and control systems unquestionably represents one of the major innovations in the range of methodologies for evaluating, through measurement, the so-called environmental electromagnetic pollution. The interest recently shown by ARPA and municipal and provincial councils for setting up electromagnetic field monitoring and control systems has created significant developments in the field under examination. This paper attempts to provide a complete overview of the technical possibilities provided by electromagnetic field monitoring and control systems in the environment and their possible applications. Equipment currently available and under development is described, as well as the most significant work-in-progress in this sector. In the near future, several monitoring systems will be proposed and set up by municipalities and provinces, or directly by telecommunications companies. For this reason, it is more than ever necessary that agreement be reached at a national level to define a unified methodological and operating approach to enable monitoring data from different sources to be compared.

Trace benzene monitoring in the outdoor air: comparative results between measurements carried out with an innovative approach and a std. GC tool

Abstract: The monitoring of benzene, toluene and xylene traces in the outdoor air using a metal oxide semiconductor thin film gas sensor as detectors has been proved in a recent paper [1] where the system was assembled in a gas chromatographic-like configuration. The final goal was to realize a reliable analytical system suitable to separate and quantitatively measure the BTX compounds at ppb level. The World Health Organization pointed out the risks for the health due to these pollutants, evidencing a demand for a systematic control dangerous species achieved with low cost detection units, such as the prototype presented here following. In this paper the first attempt to monitor traces of benzene under real operating conditions is reported and the results of 2 months comparative test carried out with BTX unit installed in a remote monitoring station and working in parallel with a std. GC system are presented and discussed.

Application of a Photochemical Model in Alpine Forest Sites

Abstract: Mountain rural sites can be subject to high ozone concentrations (Puxbaum et al., 1991; Gay, 1991; Sandroni,1994) that can lead to plant injuries. Very often, unfortunately,such sites do not have a sufficient number of monitoring stations to accurately capture the spatial patterns and temporal evolution of ozone concentrations. The present studyaims at the reproduction of ozone patterns in a forest site onthe southern slopes of the Alps. The calculation of ozone concentrations has been carried out for a three days episode,by using the CALGRID model. Meteorological fields have been obtained by the application of the CALMET model. Emissions have been calculated for the main sources categories in the area (biogenic and road transport), with a bottom up techniqueand derived from a regional inventory for minor sources. Finally, boundary conditions have been derived from a simulation performed over a larger area (240 × 232 km2). The CALGRID model application has provided realistic ground-level concentrations. However, some differences have been spotted between estimated and observedconcentrations, particularly at nighttime, when concentrationsare more influenced by local effects. The methodology used andresults obtained are presented, the comparison with measurements and the temporal evolution of ozone vertical profile in different locations of the domain is discussed.