346 research outputs found
Observed crustal uplift near the Southern Patagonian Icefield constrains improved viscoelastic Earth model
Thirtyâone GPS geodetic measurements of crustal uplift in southernmost South America determined extraordinarily high trend rates (> 35 mm/yr) in the northâcentral part of the Southern Patagonian Icefield. These trends have a coherent pattern, motivating a refined viscoelastic glacial isostatic adjustment model to explain the observations. Two endâmember models provide good fits: both require a lithospheric thickness of 36.5â±â5.3 km. However, one endâmember has a mantle viscosity near η =1.6 Ă1018âPaâs and an ice collapse rate from the Little Ice Age (LIA) maximum comparable to a lowest recent estimate of 1995â2012 ice loss at about â11 Gt/yr. In contrast, the other endâmember has much larger viscosity: η = 8.0 Ă1018âPaâs, half the postâLIA collapse rate, and a steadily rising loss rate in the twentiethâcentury after AD 1943, reaching â25.9 Gt/yr during 1995â2012.Fil: Lange, H.. Technische Universitaet Dresden; AlemaniaFil: Casassa, G.. Centro de Estudios Cientificos; Chile. Universidad de Magallanes; ChileFil: Ivins, E. R.. Institute of Technology. Jet propulsion Laboratory; Estados UnidosFil: Schroeder, L.. Technische Universitaet Dresden; AlemaniaFil: Fritsche, M.. Technische Universitaet Dresden; AlemaniaFil: Richter, Andreas Jorg. Technische Universitaet Dresden; Alemania. Universidad Nacional de la Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas. Departamento de AstrometrĂa; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata; ArgentinaFil: Groh, A.. Technische Universitaet Dresden; AlemaniaFil: Dietrich, R.. Technische Universitaet Dresden; Alemani
Quantifying mass balance processes on the Southern Patagonia Icefield
ArtĂculo de publicaciĂłn ISIWe present surface mass balance simulations of
the Southern Patagonia Icefield (SPI) driven by downscaled
reanalysis data. The simulations were evaluated and interpreted
using geodetic mass balances, measured point balances
and a complete velocity field of the icefield for spring
2004. The high measured accumulation of snow of up to
15.4 m w.e. yrâ1
(meters water equivalent per year) as well
as the high measured ablation of up to 11 m w.e. yrâ1
is reproduced
by the model. The overall modeled surface mass
balance was positive and increasing during 1975â2011. Subtracting
the surface mass balance from geodetic balances,
calving fluxes were inferred. Mass losses of the SPI due to
calving were strongly increasing from 1975â2000 to 2000â
2011 and higher than losses due to surface melt. Calving
fluxes were inferred for the individual glacier catchments and
compared to fluxes estimated from velocity data. Measurements
of ice thickness and flow velocities at the glaciersâ
front and spatially distributed accumulation measurements
can help to reduce the uncertainties of the different terms in
the mass balance of the Southern Patagonia Icefield.FONDECYT
3140135
European Union
22637
Stochastic control applied to the ISWEC Wave Energy System
ISWEC (Inertial Sea Wave Energy Converter) is a fl oating marine device able to harvest sea waves energy by the interaction between the pitching motion of a fl oater and a spinning fl ywheel which can drive an electric PTO. In the ISWEC the hull dynamics is governed and controlled by the gyroscopic torque. The optimal control logic results in tuning the fl oater dynamics to the incoming waves in order to maximize the power transfer from the waves to the fl oater. In this paper the control problems of the ISWEC are stated and a control scheme based on the sub-optimal stochastic control logic is presented. The control scheme here presented has been tested using real wave records acquired at the deployment location in Pantelleria Island, which is one of the most energetic sites of the Mediterranean Sea
On the Limits of Analogy Between Self-Avoidance and Topology-Driven Swelling of Polymer Loops
The work addresses the analogy between trivial knotting and excluded volume
in looped polymer chains of moderate length, , where the effects of
knotting are small. A simple expression for the swelling seen in trivially
knotted loops is described and shown to agree with simulation data. Contrast
between this expression and the well known expression for excluded volume
polymers leads to a graphical mapping of excluded volume to trivial knots,
which may be useful for understanding where the analogy between the two
physical forms is valid. The work also includes description of a new method for
the computational generation of polymer loops via conditional probability.
Although computationally intensive, this method generates loops without
statistical bias, and thus is preferable to other loop generation routines in
the region .Comment: 10 pages, 5 figures, supplementary tex file and datafil
Modeling past and future surface mass balance of the Northern Patagonia Icefield
Glaciers are strongly retreating and thinning in Patagonia. We present new inferences about the climatic situation and the surface mass balance on the Northern Patagonia Icefield in the past and the future using a combined modeling approach. The simulations are driven by NCAR/NCEP Reanalysis and ECHAM5 data, which were physically downscaled using the Weather Research and Forecasting regional climate model and simple sub-grid parameterizations. The surface mass balance model was calibrated with geodetic mass balance data of three large non-calving glaciers and with point mass balance measurements. An increase of accumulation on the Northern Patagonia Icefield was detected from 1990â2011 as compared to 1975â1990. Using geodetic mass balance data, calving losses from the Northern Patagonia Icefield could be inferred, which doubled in 2000â2009 as compared to 1975â2000. The 21st century projection of future mass balance of the Northern Patagonia Icefield shows a strong increase in ablation from 2050 and a reduction of solid precipitation from 2080, both due to higher temperatures. The total mass loss in the 21st century is estimated to be 592±50 Gt with strongly increasing rates towards the end of the century. The prediction of the future mass balance of the Northern Patagonia Icefield includes several additional sources of errors due to uncertainties in the prediction of future climate and due to possible variations in ice dynamics, which might modify the geometry of the icefield and change the rate of mass losses due to calving
Observed crustal uplift near the Southern Patagonian Icefield constrains improved viscoelastic Earth model
Thirtyâone GPS geodetic measurements of crustal uplift in southernmost South America determined extraordinarily high trend rates (> 35 mm/yr) in the northâcentral part of the Southern Patagonian Icefield. These trends have a coherent pattern, motivating a refined viscoelastic glacial isostatic adjustment model to explain the observations. Two endâmember models provide good fits: both require a lithospheric thickness of 36.5â±â5.3 km. However, one endâmember has a mantle viscosity near η =1.6 Ă1018âPaâs and an ice collapse rate from the Little Ice Age (LIA) maximum comparable to a lowest recent estimate of 1995â2012 ice loss at about â11 Gt/yr. In contrast, the other endâmember has much larger viscosity: η = 8.0 Ă1018âPaâs, half the postâLIA collapse rate, and a steadily rising loss rate in the twentiethâcentury after AD 1943, reaching â25.9 Gt/yr during 1995â2012.Facultad de Ciencias AstronĂłmicas y GeofĂsica
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