1,721,193 research outputs found
Katabatic wind and Terra Nova Bay polynya: a study using two different versions of the Eta model
No full textEta model is an international model, used for research or development in a lot of countries. Moreover, it is one of the mesoscale numerical weather prediction model operational at National Center for Environmental Prediction (NCEP) and at Center for Weather Prediction and Climate Studies (CPTEC).In the late nineties came out a problem about strong downslope winds, that tend to be underestimated in Eta model simulations; in recent publications of Mesinger and Jovic [1], and Mesinger, Jovic et al. [2] is suggested that the problem could be due to step-mountain eta discretization, and is proposed a simple scheme to address it (eta ‘sloping steps’). An updated version of Eta model that contains in particular this modification (available at CPTEC web site www.cptec.inpe.br/etaweb) was used in this work. Strong interactions take place between katabatic winds and coastal polynyas, like Terra Nova Bay (TNB) polynya [3]. Because of the almost impossible access to TNB in winter, model simulations are an important tool for the study of polynya’s events, besides the Eta model has been used with good results for studying Antarctic conditions [4]. This study is focused on a TNB polynya case happened in period September 15-16-17/2003; the presence of coastal polynya of about 3100 Km2 in that days over TNB is displayed in ASAR satellite images [3]. 72-h simulations of the meteorological conditions in that period were carried on with Eta model in old (NCEP) and new (CPTEC) version, both coupled with a land surface model derived from the Oregon State University (OSU). The simulations were performed with 50 layers from sea surface to 25 hPa, with higher resolution near the bottom of the domain. Horizontal resolution was 0.05x0.05 transformed degrees (about 8Kmx8Km).Using the NCEP and CPTEC versions of the Eta model, descriptions of the event, in particular the representation of the katabatic wind, are presented and discussed
Low level wind and coastal Terra Nova Bay polynya:A study by Eta model simulations.
No full textThe study focuses on a real event of katabatic wind and polynya at Terra Nova Bay (TNB). The katabatic winds and the impact of an open polynya on their intensity are simulated by a numerical atmospheric model. The event was selected as satellite images of September 2003 displaying a fluctuating TNB polynya, in particular on 16 September, the area of open water was of about 3100 km2. Simulations of the meteorological conditions of 15-16-17 September were carried on with the limited area Eta model, which is a three-dimensional, primitive equation, grid-point model. It is one of the mesoscale numerical weather prediction models operational at the National Centers for Environmental Prediction of the U.S. National Weather Service. The Eta model is coupled with a land surface model derived from the Oregon State University model and it is able to perform hydrostatic and non-hydrostatic runs. Further, terrain following or quasi-horizontal coordinates can be selected. Eta has been used for applications at mid-latitudes and, in an older version, for the study of Antarctic summer conditions. Eta runs were performed, both including the sea ice cover in the TNB area and a polynya of realistic extension, as shown from the satellite images in order to get an insight into the sensitivity of the katabatic wind to the presence of a polynya of realistic extension. The results show the strong effect of the polynya, included in the initialization of model simulations: the low level katabatic wind is intensified from the presence of the sea ice free area.The simulations were carried on using terrain following coordinates with 45 layers from sea surface to 25 hPa, with higher resolution near the bottom of the domain. Horizontal resolution was 0.05×0.05 transformed degrees (about 8 Km × 8 Km as approximate distance between two mass points on the semi-staggered Arakawa E grid). ECMWF and NCEP data provided initial and boundary conditions.Numerical simulations and results are presented and discussed
Antarctic katabatic winds and their interaction with a coastal polynya in Terra Nova Bay, studied by Eta Model simulations and satellite images
No full textCoastal polynyas are areas of partially or totally ice free water which form in coastal regions during the wintertime in spite of the low air temperatures. Coastal polynyas are often referred to as ‘latent heat polynyas’ .They are thought to be opened and maintained by strong offshore winds blowing over the area, and by the curvature of the coastline. Sea ice is removed by the wind and new ice is constantly formed and exported (Smith et al, 1990) with a consequent release of latent heat . Atmospheric numerical modelling and satellite observations are fundamental tools for the analysis of winter polynya events occurring over remote and often data sparse polar regions.This study concerns the region of Terra Nova Bay (TNB) in Antarctica, where a recurring coastal polynya occurs offshore the Italian Antarctic Base ‘Mario Zucchelli Station’ (MZS). The aim is the study of a real event of TNB polynya and the two way interaction between strong katabatic winds, blowing from the coast, and development of the polynya. The atmospheric circulation of the area is studied by simulations performed with ETA model in its last version (Mesinger et al., 2006), also with a piecewise linear advection for the wind field. A previous version of the model was yet successfully used for simulations in the Antarctic area (De Carolis et al, 2006, Casini e Morelli, 2007). Satellite images from AMSR-E (Morelli et al, 2007) and AVHRR and observational data integrate the analysis. The presented case study is a polynya event happened during the period 12-17 July 2006. AMSR-E images displayed the presence of a sea ice free area, that reached an extension of 4000 km2 on 16 July 2006. 72 hours simulations were carried on in order to study the atmospheric circulation of the period over a large area; ECMWF analyses provided the initial and boundary conditions. Furthermore, ETA simulations, nested in the previous domain, were performed with a finer resolution. To gain some insight on atmospheric response to open water within a sea ice field, simulations were carried on both with and without a prescribed open polynya (derived by AMSR-E images) forced in the initial conditions . Simulations were performed with 50 layers in the vertical from sea surface to 25 hPa, with higher resolution near the bottom of the domain. Horizontal resolution was 0,125x0,125 transformed degrees (about 15kmx15km) for the coarser grid, and 0,05x0,05 transformed degrees for the finer grid (about 8kmx8km), respectively. Numerical simulations show that cyclonic structures were moving over the Ross Sea, and that the polynya development, displayed by satellite images, was related to the katabatic wind field blowing from the Reeves glacier. ETA simulations performed with an realistic open water region in the initial conditions show a strengthening of the surface wind field over the ice free area
Default-assumption consequence relations in a preferential setting: Reasoning about normality.
No full textWe attempt at a logical characterization of reasoning about normality based on the intuition that a normal situation is represented by a stable set of default assumptions. Within the context of preferential consequence relations we shall define a normality operator \$\backslash lhr\$ and study its logical properties. Finally we shall focus on the AGM-like postulates for the normality expansion, contraction and revision
Atmospheric response to a realistic coastal polynya in Terra Nova Bay (Antarctica) simulated by ETA model
No full textCoastal polynyas are areas of open water (and/or very thin ice) which form adjacent to coasts or blocking feature in polar regions during the wintertime, when the sea water is expected to be ice covered. They are thought to be maintained by strong offshore winds blowing over these area and/or by ocean currents. Sea ice is removed as it forms and drifted offshore. In polynya areas a direct contact is established between the relatively warm sea water and the cold, dry atmosphere. As a consequence, the physical characteristics of the atmospheric boundary layer change. The work presented here concerns a real polynya event in the region of Terra Nova Bay (TNB), Antarctica, where a recurring coastal polynya occurs nearby the Italian Antarctic Base. The aim is the study of atmospheric response to the presence of a open water area of realistic size by three-dimensional numerical simulations. Atmospheric numerical modelling is a fundamental tool for the study of air - polynya interactions in the remote polar regions, where observational data are difficult. The numerical model used for the simulations is a recent version of ETA model (Mesinger et al., 2006), with the addition of a piecewise linear advection for the wind field. ECMWF and NCEP data provided the initial and boundary conditions. A previous version of the model had already been successfully used in the Antarctic area (De Carolis et al, 2006, Casini and Morelli, 2007). As a first step to analyze the polynya event, numerical simulation was performed for the period from 12 to 17 July 2006 in order to study the development of the katabatic wind (Morelli and Casini, 2008; Morelli, 2008). Daily satellite images, concerning the period, display that a sea ice free area formed on 15 and 16 July, reaching its maximum extension of about 4000 km2 on 16 July (Morelli et al.,2007). In order to gain insight on the atmospheric response to open water area within a sea ice field, ETA model runs were carried out from 15 to 17 July 2006 both with and without the polynya (as derived by satellite image) included in the initial conditions. Results from these experiments will be presented. Simulations were performed with 50 layers in the vertical from sea surface to 25 hPa, with higher resolution near the bottom of the domain. Horizontal resolution was 0,125x0,125 transformed degrees (about 20kmx20km). Numerical simulations show that the polynya had significant effects on temperature, specific humidity, vertical velocity and horizontal wind speed throughout the boundary layer. The effects are found over and downwind the sea ice free area. The presence of polynya produced significant thermal modifications in atmosphere. Turbulent kinetic energy also responded to its presence and the low level wind speed changed over the open water area. References: Casini, G., Morelli, S. (2007) ‘Katabatic wind and Terra Nova Bay polynya: a study using two different versions of ETA model’, Geophysical Research Abstract, vol. 9, 02656.De Carolis G., Morelli, S., Parmiggiani, F., and Casini G. (2006) ‘Terra Nova Bay polynya: a study by satellite microwave observations and Eta model simulations’,Geophysical Research Abstract, vol. 8, 08433Mesinger F., Jovic D., Sin Chan Chou, Gomes J.L., Bustamante J.F. (2006) ‘Wind forecast around the andes using the sloping discretization of the Eta coordinate’, Proceedings of 8 ICSHMO, Foz do Iguacu, Brazil, 24-28 April 2006, INPE.Morelli S., Casini G., Parmiggiani F. (2007) ‘Wintertime katabatic event and polynya at Terra Nova Bay: a study by ETA simulations and AMSR-E images’, Extended Abstract of 2nd Antarctic Meteorological Observation, Modeling and Forecasting (AMOMF) Workshop, June 2007.Morelli S., Casini G. (2008) ‘Antarctic katabatic winds and their interaction with a coastal polynya in Terra Nova Bay, studied by ETA model simulations and satellite images’, Geophysical Research Abstract, vol. 10.Morelli S. (2008) ‘ETA Model simulation of winter katabatic events over the Terra Nova Bay area, Antarctica’. Third ICTP conference on "Current Efforts Toward Advancing the Skill of Regional Weather Prediction. Challenges and Outlook", 8-10 October 2008
A Note on Cumulative Stereotypical Reasoning
No full textWe address the problem of providing a logical characterization of reasoning based on stereotypes. Following cite\Leh98\ we take a semantic perspective and we base our model on a notion of semantic distance. While still leading to cumulative reasoning, our notion of distance does, unlike Lehmann's, allow reasoning under inconsistent information. Key words: Stereotypes, prototypes, cumulative reasoning, nonmonotonic logic, default-assumption logic
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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