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MODELLAZIONE DISTRIBUITA DEL BILANCIO ENERGETICO E DELL¿ABLAZIONE DI UN GHIACCIAIO ALPINO:IL GHIACCIAIO DEI FORNI
Full text linkScopo di questo lavoro è stata la modellazione distribuita della fusione della neve e/o del ghiaccio sulla superficie di un ghiacciaio alpino (il Ghiacciaio dei Forni, Italia). A questo scopo sono stati applicati diversi metodi partendo dal più semplice (che dipende solo dalla temperatura dell’aria) a quelli più sofisticati (basati sul bilancio energetico). Sono stati applicati e testati, quindi, alcuni modelli per stimare e spazializzare i parametri meteorologici e i flussi energetici. Per ogni variabile analizzata, sono stati confrontati i valori modellizzati con quelli effettivamente misurati: in questo modo è stato possibile investigare l’affidabilità degli approcci scelti. Tutte le elaborazioni per la distribuzione dei parametri in ingresso che permettono la quantificazione del bilancio energetico superficiale sono state applicate a tutte le celle di un modello di elevazione digitale (DEM) con maglia 20 m x 20 m che descrive la superficie del Ghiacciaio dei Forni (Alpi Italiane).
In questo modo è stato possibile i) valutare le condizioni distribuite spazialmente e temporalmente di temperatura dell’aria e di pressione di vapore; ii) predire in determinati intervalli di tempo la distribuzione spaziale sia dell’ombreggiamento dovuto alla topografia circostante che della radiazione solare potenziale e globale; iii) modellare la radiazione infrarossa in arrivo dall’atmosfera; iv) definire i flussi turbolenti distribuiti; v) investigare le variazioni sia spaziali che temporali dei componenti del bilancio energetico; vi) quantificare i tassi di fusione anche nelle porzioni coperte da detrito; e vii) predisporre tutti i dati input necessari per calcolare le variazioni distribuite ad alta risoluzione temporale del bilancio energetico di tutta un’area glacializzata.
Il primo passaggio è consistito nel definire a livello puntuale il modello di bilancio energetico e, quindi, di massa a partire sia da dati misurati (attraverso una stazione meteorologica automatica supraglaciale installata sulla lingua del Ghiacciaio dei Forni, AWS1 Forni) sia da valori stimati. Una volta che sono stati ben definiti a livello puntuale i processi fisici coinvolti nella fusione, si è passati alla distribuzione degli stessi. Si è partiti dal modello di ablazione più semplice (T-index o degree-day) focalizzando lo studio sulla scelta della soglia di temperatura media giornaliera dell’aria che testimonia la presenza di fusione. Infatti tali condizioni possono verificarsi anche con temperature medie giornaliere inferiori a 273.15 K, in quanto è il bilancio energetico che governa i processi di fusione.
Successivamente sono stati testati diversi modelli di T-index che includono anche la componente radiativa (e non solo la temperatura dell’aria). In particolare è stato introdotto un nuovo approccio che considera anche la radiazione infrarossa netta. Inoltre sono stati applicati alcuni metodi per distribuire gli input meteorologici a questi modelli di T-index. In questo modo si è cercata una maggiore e più ampia applicazione di questi approcci anche su quei ghiacciai che non dispongono di stazioni meteorologiche o in particolare di un radiometro netto, necessario per le misure dirette della radiazione infrarossa.
Inoltre sono stati considerati i parametri che possono influenzare la variabilità dell’albedo superficiale: il detrito fine e sparso e l’acqua meteorica. In particolare si è proposto un metodo per investigare le caratteristiche del detrito fino e sparso che ricopre la superficie della lingua d’ablazione e le sue relazioni con l’albedo del ghiaccio. Infatti nonostante l’abbondante letteratura riguardante la deposizione delle polveri e del black carbon nelle zone di accumulo dei ghiacciai, sono disponibili pochi studi che descrivono questi fenomeni sulla superficie d’ablazione. Quindi è stato sviluppato un protocollo per i) campionare il detrito fine e sparso supraglaciale; ii) quantificare la sua copertura superficiale; iii) descrivere la sua composizione e le sue proprietà sedimentologiche; iv) misurare l’albedo; e v) identificare le relazioni tra l’albedo e la copertura detritica fine.
Si è passati poi ad analizzare la distribuzione dei flussi turbolenti. Lo scopo principale è stato quello di distribuire la pressione di vapore e di definire i coefficienti di scambio turbolento sia catabatico che di back-ground.
Infine sono state investigate le condizioni di fusione e il tasso di ablazione anche nelle porzioni del ghiacciaio coperte da detrito (ovvero le morene mediane nel caso del Ghiacciaio dei Forni). A questo scopo è stato applicato un modello semplice basato sul fatto che il flusso di calore conduttivo dipende dal gradiente di temperatura fra la superficie e il ghiaccio.This research deals with the estimation of the distributed snow and ice ablation amounts at an alpine glacier surface with a diurnal or sub-diurnal temporal resolution. Several methods were applied from the easiest one which depends only on the air temperature to the most exhaustive ones based on the energy budget. For this reason we applied and tested some models to estimate and distribute the meteorological parameters and the energy fluxes. For each analysed variable, the modelled values were compared to the ones measured at the surface of the Forni Glacier (Italian Alps) in order to investigate the reliability of the chosen approach. All the computations were aimed at obtaining the distribution of the factors driving the glacier energy budget on a digital elevation model (DEM) 20 x 20 m grid spaced which describes the surface of an Alpine debris free glacier (the Forni Glacier, Italian Alps).
In this way i) the spatial and temporal distribution of air temperature and vapour pressure conditions were evaluated; ii) the spatial distribution of topographic shading and of potential and global solar radiation for selected time intervals was predicted; iii) the distributed incoming infrared radiation was modelled; iv) the distributed turbulent fluxes were assessed; v) the spatial and temporal variations of the energy balance components were investigated; vi) the melt amount over the debris-covered areas was quantified as well; and vii) the short-term energy balance variations of a whole glacierized area can be easily computed.
Firstly the point energy and mass balance was modelled from measured (from a supraglacial automatic weather station set up on the tongue of the Forni Glacier, AWS1 Forni) and estimated values. Since the physical processes were assessed at the AWS1 Forni site, the distribution of the melting processes over the Forni Glacier surface was considered. In particular initially a simple degree-day model was applied with respect to the snow ablation focussing on the suitability of the chosen temperature threshold which witnesses melting conditions. In fact, melt does not necessarily occur at daily average air temperatures higher than 273.15 K, since it is determined by the surface energy budget which in turn is only indirectly affected by air temperature.
Several enhanced T-index models including solar radiation were considered as well. A new enhanced T-index model including infrared radiation was developed to evaluate distributed ice melt and compared with the other T-index methods. Different approaches were further tested to distribute the input meteorological and energy data driving the enhanced T-index methods (i.e. air temperature, solar and infrared radiation), which should allow a wider application of this approach upon glaciers not equipped with AWS, or without a net radiometer, necessary to directly measure infrared flux.
Moreover, the parameters affecting temporal and spatial albedo variability were considered: sparse and fine debris and dust, and rainfalls. In particular a method to investigate the characteristics of sparse and fine debris coverage at the glacier melting surface and its relation to ice albedo was proposed. In fact despite the abundant literature dealing with dust and black carbon deposition on glacier accumulation areas, few studies that describe the distribution and properties of fine and discontinuous debris and black carbon at the melting surface of glaciers are available. A protocol to i) sample fine and sparse supraglacial debris and dust, ii) quantify its surface coverage, iii) describe its composition and sedimentological properties, iv) measure ice albedo, and v) identify the relationship between albedo and fine debris coverage, was developed.
The distribution of the turbulent fluxes was also investigated. The main focuses were the distribution of the vapour pressure and the assessment of the katabatic and the back-ground turbulent exchange coefficients.
Finally the melting conditions and rate were also assessed over the glacier debris-covered area, which in the case of the Forni Glacier corresponds to the medial moraines. In this case a simple approach was applied based on the fact that the conductive heat flux depends on the temperature gradient from debris surface to ice
Preliminary results from antarctic albedo from remote sensing observations
Full text linkThe aim of the study is to analyse the surface albedo of the Ant-arctica and investigate eventual signals of variations in space and time between summer 2000/2001 and 2011/2012 by means of the GLASS albedo product. We followed a step-by-step procedure from micro- to macro-scale. At first, we analysed 95 glaciers around the continent, and we found limited temporal variability. Then, looking at spatial varia-tions, we divided Antarctica based on oceanic basins and by continen-tality. We found spatial signals, since mean albedo values range between 0.79 (Pacific and Atlantic basins) and 0.82 (Indian basin) and between 0.76 (along the shore) and 0.81 (inner continent). An increasing vari-ability was found from the inner continent to the shore, and heteroge-neous patterns among the basins, most likely due to meteorological and environmental conditions (mainly: temperature, precipitation, katabatic winds). Finally, the general patterns observed (considering the specific gla-ciers, the three basins and the three continentality sectors) were verified by the analysis of the whole continent and we did not find a significant change of summer averages over time, as they range between 0.79 and 0.80
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
Using daily air temperature thresholds to evaluate snow melting occurrence and amount on Alpine glaciers by <i>T</i>-index models: the case study of the Forni Glacier (Italy)
Full text linkGlacier melt conditions (i.e., null surface temperature and positive energy
budget) can be assessed by analyzing data acquired by a supraglacial
automatic weather station (AWS), such as the station installed on the
surface of Forni Glacier (Italian Alps). When an AWS is not present, the
assessment of actual melt conditions and the evaluation of the melt amount
is more difficult and simple methods based on T-index (or degree days)
models are generally applied. These models require the choice of a correct
temperature threshold. In fact, melt does not necessarily occur at daily air
temperatures higher than 0 °C. In this paper, we applied both
energy budget and T-index approaches with the aim of solving this issue.
We start by distinguishing between the occurrence of snowmelt and the
reduction in snow depth due to actual ablation (from snow depth data
recorded by a sonic ranger). Then we find the daily average temperature
thresholds (by analyzing temperature data acquired by an AWS on Forni
Glacier) which, on the one hand, best capture the occurrence of significant
snowmelt conditions and, on the other, make it possible, using the T-index,
to quantify the actual snow ablation amount. Finally we investigated the
applicability of the mean tropospheric lapse rate to reproduce air
temperature conditions at the glacier surface starting from data acquired by
weather stations located outside the glacier area.
We found that the mean tropospheric lapse rate allows for a good and reliable
reconstruction of glacier air temperatures and that the choice of an
appropriate temperature threshold in T-index models is a very important
issue. From our study, the application of the +0.5 °C
temperature threshold allows for a consistent quantification of snow ablation
while, instead, for detecting the beginning of the snow melting processes
a suitable threshold has proven to be at least −4.6 °C
Distribution of the surface energy budget: Preliminary analysis on the incoming solar radiation. the case study of the Forni Glacier (Italy)
Full text linkThis study represents a contribution to distribution of the surface energy budget of the Forni Glacier (Ortles-Cevedale Group, Upper Valtellina, Italy). The analyses are based on data acquired at S. Caterina Valfurva (a village in the glacier valley at 1768 m ellipsoidal elevation WGS84) by an Automatic Weather Station (AWS) installed and managed by the Lombardy Agency for the Environment ("ARPA Lombardia"). We focus on the two most important meteorological parameters affecting surface energy budget: air temperature (T) and incoming shortwave radiation (SWin). Data collected from the ARPA AWS are used to evaluate these parameters at the glacier surface during the meteorological summer 2009 (from 1st June to 31st August 2009) and then the computations are validated through comparison with data recorded by an AWS installed at the surface of Forni Glacier tongue ("AWS1 Forni", 2669 m ellipsoidal elevation WGS84). The analysis of the distributed air temperature data enabled identification of the lowest value (-11.9 degrees C), found at the Mount S. Matteo peak (3669 m) on 22nd June at 8: 00 pm, and the highest value (+16.1 degrees C), recorded at the glacier terminus (2497 m) on 23 rd July at 2: 00 pm. The seasonal temperature amplitude (Tmax-Tmin) was 28 degrees C. The hottest week was 20th-26th July 2009 and the coldest was 1st-7th June 2009. Regarding daily SWin distribution, the maximum value (406.9 Wm(-2)) was recorded on 13th June and the minimum (28.5 Wm(-2)) on 6th June. From the analysis of hourly SWin values we could distinguish between days with clear sky conditions and days with intense cloud cover. Weekly mean SWin data showed the greatest value (327.1 Wm(-2)) from 20th-26th July 2009 and the lowest (207.8 Wm(-2)) from 22nd-28th June 2009. Furthermore, in analysing SWin it is critical to take into account the problem of shading. Using the Hillshade tool of ArcGIS, which takes into account only the slope and the aspect of each grid cell neglecting the surrounding topography effect, we compiled 66 shadow maps. Finally this study represents a first approach in modelling the distributed incoming solar radiation. In fact the considered driving factors are the elevation, the slope and the aspect of each grid cell. The next step will consist in taking into account the surrounding topography and the actual atmosphere conditions as well
Decisione/indecisione di voto come moderatore della relazione tra atteggiamenti impliciti ed espliciti
No full textSURFACE ENERGY BUDGET AND MELT AMOUNT FOR THE YEARS 2009 AND 2010 AT THE FORNI GLACIER (ITALIAN ALPS, LOMBARDY)
No full textThis paper reports the surface energy budget and the melt amount
evaluated at one location at the Forni Glacier (Italian Alps, Lombardy)
during the years 2009 and 2010. The analysis was supported by high resolution
meteorology and energy data collected by an Automatic Weather
Station (named AWS1 Forni) which has been running at the glacier surface
(2669 m, ellipsoidal elevation) since 26 September 2005. The AWS is
also equipped with a sonic ranger to measure snow depth and its variability.
It resulted that in the years 2009 and 2010 the glacier melt at about
2700 m of altitude was equal to –11.32 m w.e.; these results were confirmed
by comparisons with field ablation data collected nearby the AWS
during the summer season 2009 and 2010
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
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