1,721,016 research outputs found
Cloud Classification Using METEOSAT VIS-IR Imagery
No full textA new method is proposed which allows for reasonably accurate cloud classification based upon Gaussian approximation of cloud emission and using a pair of visible-infrared, high resolution METEOSAT images. Its most important characteristic is the very low amount of CPU time required for a single classification. It becomes then suitable for application in very short range weather forecasting (nowcasting) by ensuring the adequate time coverage and necessary rapidity of use for the operational environment. Two classifications of summer and winter meteorological situations are presented
Operational rainfall estimation using METEOSAT infrared imagery: its potential and drawbacks
No full textThe performances of two rainfall-estimation methods based upon the infrared channels of geostationary satellites are examined for very-short-range weather forecasting. A flood-hazard monitoring application in the Arno River Basin in Central Italy in November 1987 is presented. Results demonstrate that the rain-estimation techniques applied in the nowcasting environment are a powerful aid to the forecaster. Evidence is also provided that rain estimates must be correctly interpreted in terms of the structure of precipitation systems to avoid the considerable errors that can stem from routine, purely numerical applications. -Author
A method to derive satellite-based extreme precipitation return levels in poorly gauged areas
Full text linkPrecipitation frequency analysis based on satellite products is still limited by estimation errors and by the use of statistical methods inadequate for these products. However, when it comes to poorly gauged areas of the world, satellite products can be a vital source of information. We present here a new method to derive satellite-based estimates of extreme precipitation quantiles with long return period in poorly gauged areas. The method relies on the identification of relations between statistics of the satellite estimation error and errors in the parameters of a non-asymptotic extreme value distribution. We show an application of the method in three areas with diverse climatic conditions in Austria and in the South-eastern Mediterranean, showcasing results for different scenarios of rain gauge density. We find that simple linear relations can explain 35-90% of the variance in the error of the parameters of the non-asymptotic extreme value distribution. Using these relations, we derive estimates of extreme return levels with drastically reduced bias and dispersion with respect to the ones directly obtained from the satellite estimates
Satellite rainfall estimates: new perspectives for meteorology and climate from the EURAINSAT project
No full textSatellite meteorology is facing a crucial period of its history since recent missions have revealed instrumental for
quantitative rainfall measurements from space and newly conceived missions are at hand. International partnership
is rapidly developing and research projects keep the community focused on rapidly developing research and
operational issues. A perspective is given through the structure of EURAINSAT, a project of the 5th Framework
Programme of the European Commission. Its key objective is the development of algorithms for rapidly-updated
satellite rainfall estimations at the geostationary scale. The project is fostering international research on satellite
rainfall estimations building a bridge between Europe and the U.S. for present and future missions.PublishedJCR Journalope
The effect of complex orography on the development of a tornadic outbreak in the Po Valley
No full textHow can tornadic supercells be influenced by complex orography? In this study the authors address this issue by studying a tornado outbreak that affected the Po Valley in northern Italy on 19 September 2021. During the event seven tornadoes (four of them ranked as F2 according to the Fujita scale) developed between Lombardia and Emilia-Romagna regions in a few hours. Although tornadoes are not rare in Italy, so many tornadoes in such a short time is an unusual event. The event was studied exploiting observations and numerical simulations obtained with the convection permitting MOLOCH model. Observations showed that during the event there were two low-level boundaries in the Po Valley: a cold front coming from the Alps and a dry line generated by the downslope winds from the Apennines. These two boundaries created a triple point, like those observed during tornado outbreaks in the US Midwest, but on a smaller scale. Numerical simulations with 500 m grid spacing showed that a warm and moist air tongue from the Adriatic Sea played a fundamental role in generating the supercells. Moreover, by means of numerical experiments, it has been proved that the structure and location of the moist air tongue was sensitive to the Froude number of the south-westerly flow from the Apennines: the greater the Froude number, the further north and narrower was the tongue of air, with impacts on the development of supercells. Finally, the dry line played a key role in the generation of tornadoes. In fact, kinematic and windshear parameters were comparable to typical values observed in the US-tornado events only along a narrow path ahead the dry line
A Conceptual Model for the Development of Tornadoes in the Complex Orography of the Po Valley
No full textThe Po Valley in northern Italy is a hotspot for tornadoes in Europe in spite of being surrounded by two mountain ridges: the Alps in the north and the Apennines in the southwest. The research focuses on the case study of 19 September 2021, when seven tornadoes (four of them rated as F2) developed in the Po Valley in a few hours. The event was analyzed using observations and numerical simulations with the convection-permitting Modello Locale in Hybrid Coordinates (MOLOCH) model. Observations show that during the event in the Po Valley, there were two surface boundaries that created a triple point: an out fl ow boundary generated by convection triggered in the Alpine foothills and a dryline generated by downslope winds from the Apennines, while warm and moist air advected westward from the Adriatic Sea east (ahead) of the boundaries. Tornadoes developed about 20 km northeast of the triple point. Numerical simulations with 500-m grid spacing suggest that the development of supercells and drylines in the Po Valley was sensitive to the elevation of the Apennines. Simulated vertical pro f iles show that the best combination of instability and wind shear for the development of tornadoes was attained within a narrow area located ahead of the dryline. A conceptual model for the development of tornadoes in the Po Valley is proposed, and the differences between tornado environments over a fl at terrain and over a region with complex terrain are discussed
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
- …
