1,721,010 research outputs found
Analysis of polarization radar returns from ice clouds
No full textUsing a modified T-matrix code, some polarimetric single-scattering radar parameters (Zh,v, LDRh,v, ρhv, ZDR and δhv) from populations of ice crystals in ice phase at 94 GHz, modeled with axisymmetric prolate and oblate spheroidal shapes for a -size distribution with different α parameter (α = 0, 1, 2) and characteristic dimension Lm varying from 0.1 to 1.8 mm, have been computed. Some of the results for different radar elevation angles and different orientation distribution for fixed water content are shown. Deeper analysis has been carried out for pure extensive radar polarimetric variables; all of them are strongly dependent on the shapes (characterised by the aspect ratio), the canting angle and the radar elevation angle. Quantities like ZDR or δhv at side incidence or LDRh and ρhv at vertical incidence can be used to investigate the preferred orientation of the particles and, in some cases, their habits. We analyze scatterplots using couples of pure extensive variables. The scatterplots with the most evident clustering properties for the different habits seem to be those in the (ZDR [X = 0°], δhv [X = 0°]), in the (ZDR [X = 0°], LDRh [X = 90°]) and in the (ZDR [X = 0°], ρhv [X = 90°]) plane. Among these, the most appealing one seems to be that involving ZDR and ρhv variables. To avoid the problem of having simultaneous measurements with a side and a vertical-looking radar, we believe that measurements of these two extensive variables using a radar with an elevation angle around 45° can be an effective instrument to identify different habits. In particular, this general idea can be useful for future spaceborne polarimetric radars involved in the studies of high ice clouds. It is also believed that these results can be used in next challenge of developing probabilistic and expert methods for identifying hydrometeor types by W-band radars. © 2001 Elsevier Science B.V. All rights reserved
Atmospheric precipitation analysis in desert area using both disdrometers and satellite data
No full textCloud cover associated to cut-off low systems in the Mediterranean region
No full textCut-off low (COL) are middle and upper troposphere closed cyclonically circulating eddies isolated from the main
westerly stream; they are common features of Mediterranean meteorology in warm month and are often related to
sever weather. Ten years (1992-2001) of warm season ERA-40 reanalysis, available every six hours on 2.5°x2.5°
grid, are processed to extract a database of cut-off low occurrence in the Mediterranean basin and continental
Europe. The cloud structures related to the COL are analyzed using International Satellite Cloud Climatology
Project DX data available every 3 hours on a 30x30 km2 grid. For each COL occurrence, the size of the related
cloud shield is estimated, and the mean optical depth and cloud top height computed. Cloud patterns are studied
for different COL classes according to their vertical characteristics.
Out of a total of 273 COL selected episodes, for about the two thirds (184) the cloud analysis is possible. For
remaining third of the events the analysis is not carried out because it is not possible to automatically isolate the
cloud cover to be associated to a given COL. For 23 COL systems analyzed no cloudiness is associated at any
stage of the development, while for about 20 COL events the size of the cloud structure exceeds few millions of
square kilometres. The cloudiness size is related to the vertical structure of the COL: large size are found for those
systems that show a corresponding depression at the ground, small size or no cloudiness are found for systems
dynamically confined to upper tropospheric levels
Ballistic accretion on a point seed
Full text linkWe carefully discuss the two-dimensional ballistic aggregation process. Studying the microscopic discrete process, we theoretically derive the probability density function describing the single-particle accretion. Using this function, we describe the properties of the “fan”, obtained for ballistic aggregation on the single seed, and we predict its mean density and its opening angle. We discuss the shadowing effect on a microscopic scale, between the single particles and, on a larger scale, between grown structures, deriving the columnar microstructure direction law. Comparisons with numerical experiments are shown
Estimation of water vapor vertical distribution over the sea from Meteosat and SSM/I observations
No full textObject of this work is to explore the capabilities of multi-sensor water vapor (WV) observations for identification and classification of fronts and air masses in northern Atlantic and Mediterranean areas. We used data from the 6.3 micromete channel of the European geostationary satellite Meteosat: we retrieved the distribution of WV mean content in the layer between 600 and 300 hPa for cloudless areas. Multifrequency data from Special Sensor Microwave/Imager (SSM/I) are used to estimate: 1) the distribution of WV mean content in lowermost 500 m of the troposphere, and 2) the distribution of total WV content in the troposphere. The retrieval is performed over marine areas and outside heavy precipitation areas. We combined the three WV retrievals and we estimated the vertical WV profile at three tropospheric levels: the lowest one below 500 m (1000-960 hPa, from the SSM/I), the layer between 600 and 300 hPa (from the Meteosat) and the layer between 500 m and 600 hPa (as difference between these two fields and the total columnar content as from SSM/I). The performances of the three techniques are evaluated by comparison with European Center for Medium Range Weather Forecast (ECMWF) analysis: good agreement is found for both SSM/I retrievals (percentage of error between 15 and 25%) while for the 6.3 micrometer retrieval higher values are reported (about 45%). The combined approach is used to estimate vertical profiles of WV content with an accuracy suitable for semi-quantitative analysis of the moisture structure. Vertical cross sections of WV fields are obtained in proximity of frontal surfaces and discussed for one case study
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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