79 research outputs found
L'invettiva contro Gildone.Motivi di propaganda politica e prassi letteraria.(Per un commento a Claud.carm.15)
2006/2007L’indagine ha permesso di mettere in luce la complessità di un poema che è prima di tutto un’opera a sostegno della politica di Stilicone e contiene un messaggio, duplice (di rimprovero e parenetico), inviato all’Oriente dell’Impero relativo alla necessaria concordia fra le due parti e fra i fratelli reggenti, Onorio e Arcadio. Claudiano eleva a dignità epica un episodio politico-militare la cui conclusione, più che da una vera e propria battaglia (che nella realtà non avvenne mai), era stato determinato dall’abile strategia di Stilicone.
La specificità dell’opera consiste in una elevata cifra retorica dell’elemento panegiristico di cui si è fornita documentazione. La condanna di Stilicone come hostis publicus, da parte della corte orientale, obbliga il poeta ad assegnare al generale vandalo un ruolo di secondo piano e determina l’impossibilità di attribuirgli una responsabilità diretta nella risoluzione della vicenda gildonica. Tale condizionamento storico-politico si traduce in una strategia narrativa in cui il soggetto centrale del racconto diventa Gildone, il nemico o piuttosto l’anti-eroe, a cui si contrappone in modo implicito (esplicito raramente) proprio Stilicone.
Stilicone incarna così l’eroe della tradizione romana, rispettoso della fides verso i familiari (in qualità di suocero di Onorio) e la patria. Le azioni del generale vandalo sono exempla di pietas e in netta antitesi con quelle di Gildone che però non compare mai come attore nella vicenda. L’opposizione tra i due si traduce in definitiva nella vittoria morale di Stilicone. Il generale vandalo, compie il suo ingresso nel finale del poema (352), preparato dall’encomio ad opera di Teodosio il Grande. Nel poema dunque la vittoria su Gildone non viene descritta mediante il racconto dei fatti, ma è sancita sul piano etico per mezzo della contrapposizione fra i due antagonisti.
Il presente lavoro cerca di mettere in luce le ragioni che nell’In Gildonem hanno determinato il silenzio di Claudiano sugli antefatti e sulle operazioni in rapporto al più dettagliato resoconto della vicenda e al vero e proprio panegirico di Stilicone nella successiva Laus. Il confronto fra le due opere indurrebbe infatti a individuare nella prima una sorta di anticipazione dei motivi enfatizzati, senza reticenze, nella Laus. In questa prospettiva di lettura le due opere risultano complementari e ciò permetterebbe di superare la posizione della critica (Döpp 1980, Hajdu 1996-1997, Charlet 2000) che ritiene l’In Gildonem incompiuto tanto da ipotizzare la mancata pubblicazione di un secondo libro.XX Ciclo198
The impact of model resolution on the simulated Holocene retreat of the southwestern Greenland ice sheet using the Ice Sheet System Model (ISSM)
Geologic archives constraining the variability of the Greenland
ice sheet (GrIS) during the Holocene provide targets for ice sheet models to
test sensitivities to variations in past climate and model formulation. Even
as data–model comparisons are becoming more common, many models simulating
the behavior of the GrIS during the past rely on meshes with coarse
horizontal resolutions (≥10 km). In this study, we explore the impact of
model resolution on the simulated nature of retreat across southwestern
Greenland during the Holocene. Four simulations are performed using the Ice
Sheet System Model (ISSM): three that use a uniform mesh and horizontal mesh
resolutions of 20, 10, and 5 km, and one that uses a nonuniform mesh with
a resolution ranging from 2 to 15 km. We find that the simulated retreat can
vary significantly between models with different horizontal resolutions based
on how well the bed topography is resolved. In areas of low topographic
relief, the horizontal resolution plays a negligible role in simulated
differences in retreat, with each model instead responding similarly to
retreat driven by surface mass balance (SMB). Conversely, in areas where the bed
topography is complex and high in relief, such as fjords, the lower-resolution models (10 and 20 km) simulate unrealistic retreat that occurs as
ice surface lowering intersects bumps in the bed topography that would
otherwise be resolved as troughs using the higher-resolution grids. Our
results highlight the important role that high-resolution grids play in
simulating retreat in areas of complex bed topography, but also suggest that
models using nonuniform grids can save computational resources through
coarsening the mesh in areas of noncomplex bed topography where the SMB
predominantly drives retreat. Additionally, these results emphasize that care
must be taken with ice sheet models when tuning model parameters to match
reconstructed margins, particularly for lower-resolution models in regions
where complex bed topography is poorly resolved.</p
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The future sea-level contribution of the Greenland ice sheet: A multi-model ensemble study of ISMIP6
The Greenland ice sheet is one of the largest contributors to global mean sea-level rise today and is expected to continue to lose mass as the Arctic continues to warm. The two predominant mass loss mechanisms are increased surface meltwater run-off and mass loss associated with the retreat of marine-terminating outlet glaciers. In this paper we use a large ensemble of Greenland ice sheet models forced by output from a representative subset of the Coupled Model Intercomparison Project (CMIP5) global climate models to project ice sheet changes and sea-level rise contributions over the 21st century. The simulations are part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6).We estimate the sea-level contribution together with uncertainties due to future climate forcing, ice sheet model formulations and ocean forcing for the two greenhouse gas concentration scenarios RCP8.5 and RCP2.6. The results indicate that the Greenland ice sheet will continue to lose mass in both scenarios until 2100, with contributions of 90-50 and 32-17mm to sea-level rise for RCP8.5 and RCP2.6, respectively. The largest mass loss is expected from the south-west of Greenland, which is governed by surface mass balance changes, continuing what is already observed today. Because the contributions are calculated against an unforced control experiment, these numbers do not include any committed mass loss, i.e. mass loss that would occur over the coming century if the climate forcing remained constant. Under RCP8.5 forcing, ice sheet model uncertainty explains an ensemble spread of 40 mm, while climate model uncertainty and ocean forcing uncertainty account for a spread of 36 and 19 mm, respectively. Apart from those formally derived uncertainty ranges, the largest gap in our knowledge is about the physical understanding and implementation of the calving process, i.e. the interaction of the ice sheet with the ocean. © Author(s) 2020
The future sea-level contribution of the Greenland ice sheet: a multi-model ensemble study of ISMIP6
The Greenland ice sheet is one of the largest contributors to global mean sea-level rise today and is expected to continue to lose mass as the Arctic continues to warm. The two predominant mass loss mechanisms are increased surface meltwater run-off and mass loss associated with the retreat of marine-terminating outlet glaciers. In this paper we use a large ensemble of Greenland ice sheet models forced by output from a representative subset of the Coupled Model Intercomparison Project (CMIP5) global climate models to project ice sheet changes and sea-level rise contributions over the 21st century. The simulations are part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). We estimate the sea-level contribution together with uncertainties due to future climate forcing, ice sheet model formulations and ocean forcing for the two greenhouse gas concentration scenarios RCP8.5 and RCP2.6. The results indicate that the Greenland ice sheet will continue to lose mass in both scenarios until 2100, with contributions of 90±50 and 32±17 mm to sea-level rise for RCP8.5 and RCP2.6, respectively. The largest mass loss is expected from the south-west of Greenland, which is governed by surface mass balance changes, continuing what is already observed today. Because the contributions are calculated against an unforced control experiment, these numbers do not include any committed mass loss, i.e. mass loss that would occur over the coming century if the climate forcing remained constant. Under RCP8.5 forcing, ice sheet model uncertainty explains an ensemble spread of 40 mm, while climate model uncertainty and ocean forcing uncertainty account for a spread of 36 and 19 mm, respectively. Apart from those formally derived uncertainty ranges, the largest gap in our knowledge is about the physical understanding and implementation of the calving process, i.e. the interaction of the ice sheet with the ocean
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Future Sea Level Change Under Coupled Model Intercomparison Project Phase 5 and Phase 6 Scenarios From the Greenland and Antarctic Ice Sheets
Projections of the sea level contribution from the Greenland and Antarctic ice sheets (GrIS and AIS) rely on atmospheric and oceanic drivers obtained from climate models. The Earth System Models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6) generally project greater future warming compared with the previous Coupled Model Intercomparison Project phase 5 (CMIP5) effort. Here we use four CMIP6 models and a selection of CMIP5 models to force multiple ice sheet models as part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). We find that the projected sea level contribution at 2100 from the ice sheet model ensemble under the CMIP6 scenarios falls within the CMIP5 range for the Antarctic ice sheet but is significantly increased for Greenland. Warmer atmosphere in CMIP6 models results in higher Greenland mass loss due to surface melt. For Antarctica, CMIP6 forcing is similar to CMIP5 and mass gain from increased snowfall counteracts increased loss due to ocean warming
Strategies for preventing group B streptococcal infections in newborns: A nation-wide survey of Italian policies
Implementation of higher-order vertical finite elements in ISSM v4.13 for improved ice sheet flow modeling over paleoclimate timescales
Paleoclimate proxies are being used in conjunction with ice sheet modeling
experiments to determine how the Greenland ice sheet responded to past
changes, particularly during the last deglaciation. Although these
comparisons have been a critical component in our understanding of the
Greenland ice sheet sensitivity to past warming, they often rely on modeling
experiments that favor minimizing computational expense over increased model
physics. Over Paleoclimate timescales, simulating the thermal structure of
the ice sheet has large implications on the modeled ice viscosity, which can
feedback onto the basal sliding and ice flow. To accurately capture the
thermal field, models often require a high number of vertical layers. This is
not the case for the stress balance computation, however, where a high
vertical resolution is not necessary. Consequently, since stress balance and
thermal equations are generally performed on the same mesh, more time is
spent on the stress balance computation than is otherwise necessary. For
these reasons, running a higher-order ice sheet model (e.g., Blatter-Pattyn)
over timescales equivalent to the paleoclimate record has not been possible
without incurring a large computational expense. To mitigate this issue, we
propose a method that can be implemented within ice sheet models, whereby the
vertical interpolation along the z axis relies on higher-order polynomials,
rather than the traditional linear interpolation. This method is tested
within the Ice Sheet System Model (ISSM) using quadratic and cubic finite
elements for the vertical interpolation on an idealized case and a realistic
Greenland configuration. A transient experiment for the ice thickness
evolution of a single-dome ice sheet demonstrates improved accuracy using the
higher-order vertical interpolation compared to models using the linear
vertical interpolation, despite having fewer degrees of freedom. This method
is also shown to improve a model's ability to capture sharp thermal gradients
in an ice sheet particularly close to the bed, when compared to models using
a linear vertical interpolation. This is corroborated in a thermal
steady-state simulation of the Greenland ice sheet using a higher-order
model. In general, we find that using a higher-order vertical interpolation
decreases the need for a high number of vertical layers, while dramatically
reducing model runtime for transient simulations. Results indicate that when
using a higher-order vertical interpolation, runtimes for a transient ice
sheet relaxation are upwards of 5 to 7 times faster than using a model which
has a linear vertical interpolation, and this thus requires a higher number of
vertical layers to achieve a similar result in simulated ice volume, basal
temperature, and ice divide thickness. The findings suggest that this method
will allow higher-order models to be used in studies investigating ice sheet
behavior over paleoclimate timescales at a fraction of the computational cost
than would otherwise be needed for a model using a linear vertical
interpolation
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