Sensitivity of a Greenland ice sheet model to atmospheric forcing fields

in Cryosphere (The) (2012), 6

Predicting the climate for the future and how it will impact ice sheet evolution requires coupling ice sheet models with climate models. However, before we attempt to develop a realistic coupled setup, we ... [more ▼]

Predicting the climate for the future and how it will impact ice sheet evolution requires coupling ice sheet models with climate models. However, before we attempt to develop a realistic coupled setup, we propose, in this study, to first analyse the impact of a model simulated climate on an ice sheet. We undertake this exercise for a set of regional and global climate models. Modelled near surface air temperature and precipitation are provided as upper boundary conditions to the GRISLI (GRenoble Ice Shelf and Land Ice model) hybrid ice sheet model (ISM) in its Greenland configuration. After 20 kyrs of simulation, the resulting ice sheets highlight the differences between the climate models. While modelled ice sheet sizes are generally comparable to the observed one, there are considerable deviations among the ice sheets on regional scales. These deviations can be explained by biases in temperature and precipitation near the coast. This is especially true in the case of global models. But the deviations between the climate models are also due to the differences in the atmospheric general circulation. To account for these differences in the context of coupling ice sheet models with climate models, we conclude that appropriate downscaling methods will be needed. In some cases, systematic corrections of the climatic variables at the interface may be required to obtain realistic results for the Greenland ice sheet (GIS). [less ▲]

Sensitivity of Greenland Ice Sheet surface mass balance to surface albedo parameterization: a study with a regional climate model

in Cryosphere (The) (2012), 6

We present a sensitivity study of the surface mass balance (SMB) of the Greenland Ice Sheet, as modeled using a regional atmospheric climate model, to various parameter settings in the albedo scheme. The ... [more ▼]

We present a sensitivity study of the surface mass balance (SMB) of the Greenland Ice Sheet, as modeled using a regional atmospheric climate model, to various parameter settings in the albedo scheme. The snow albedo scheme uses grain size as a prognostic variable and further depends on cloud cover, solar zenith angle and black carbon concentration. For the control experiment the overestimation of absorbed shortwave radiation (+6%) at the K-transect (west Greenland) for the period 2004–2009 is considerably reduced compared to the previous density-dependent albedo scheme (+22%). To simulate realistic snow albedo values, a small concentration of black carbon is needed, which has strongest impact on melt in the accumulation area. A background ice albedo field derived from MODIS imagery improves the agreement between the modeled and observed SMB gradient along the K-transect. The effect of enhanced meltwater retention and refreezing is a decrease of the albedo due to an increase in snow grain size. As a secondary effect of refreezing the snowpack is heated, enhancing melt and further lowering the albedo. Especially in a warmer climate this process is important, since it reduces the refreezing potential of the firn layer that covers the Greenland Ice Sheet. [less ▲]

The sensitivity of optimal rail‐road terminal locations to intermodal freight costs variations

Conference (2012, September 05)

In the last decades, the market of goods became globalized, increasing international trade relations and the demand for long distance transportation. As a consequence of the larger distances traveled and ... [more ▼]

In the last decades, the market of goods became globalized, increasing international trade relations and the demand for long distance transportation. As a consequence of the larger distances traveled and of the containerization of goods, maritime transportation became more efficient and reliable. In the hinterland, intermodal (rail-road) freight transportation emerged as a competitive alternative to truck-only transportation. In one of its possible meanings, intermodal freight transportation is the multimodal chain of container-transportation services [1] that, e.g., brings containers from (or to) the seaport by barge or rail to (or from) an intermodal terminal in the hinterland from where they are shipped by truck to their final destination (or origin). This study focus on inland intermodal freight transport, in particular, on the rail–truck transport of cargo containers in Belgium. This European country has a long rail system and in the last years has readapted this system in order to handle with containerized cargo. Since 2004, some rail-road terminals have been built and new intermodal services between the seaports of Belgium have been established. In addition, with the aim of promoting the modal share of intermodal rail-road transport, the federal government of Belgium started subsidizing part of the rail transport cost and of the transshipments costs at the rail-road terminals. With these investments the intermodal freight flows in Belgium have increased. [less ▲]

Sensitivity of simulated surface wetness duration to meteorological variations in three different regions of Grand-Duchy of Luxembourg

Poster (2010, November 23)

Surface wetness duration (SWD) is an important factor influencing the occurrence of winter wheat diseases. For this reason, SWD is extremely important for the management of crop protection activities. In ... [more ▼]

Surface wetness duration (SWD) is an important factor influencing the occurrence of winter wheat diseases. For this reason, SWD is extremely important for the management of crop protection activities. In order to understand the SWD variability and its influence on winter wheat disease, the objective of this study was to (i) determine the sensitivity of our model on varying input plant parameters and (ii) to evaluate the influence of simulated SWD to meteorological variations in three different climatic regions of the Grand-Duchy of Luxembourg (EVERLANGE, OBERCORN and SCHIMPACH). In this work, an agrometeorological model known as the Surface Wetness Energy Balance (SWEB) was applied for the simulation of SWD. The model was previously applied in another study for winter wheat cultivars and was adapted for use with agrometeorological data easily available from standard meteorological monitoring stations. Based on weather data and simulated SWD data, sensitivity analyses were performed to compare the effects of relative humidity, air temperature, wind speed and net radiation on wetness duration over one growing season (March-July) at three test sites. The results indicated that the sensitivities were very similar at three sites and there was no spatial trend (i.e. difference between locations) in the sensitivities. However, the model is most sensitive to relative humidity and differences between 0.5 and 25 h (per month) SWD were found when increasing/decreasing relative humidity by 10%. The model was least sensitive to changes in air temperature, showing differences of only 0.5–2 h (per month) in SWD. Intermediate sensitivity is found for rainfall, net radiation and wind speed. Among the input plant parameters values, SWD was most sensitive to the maximum fraction of canopy allowed as wet surface area, leaf area index, maximum water storage per unit area and least sensitive to crop height. The sensitivity to parameter values was less important compared to the sensitivity to the meteorological variable relative humidity. [less ▲]

Sensitivity of steel building frames to joint properties.

in Proceedings of the International Colloquium on Stability of Steel Structures (1995)

Sensitivity of the black sea's ecosystem to physical processes: first results of a high resolution 3D interdisciplinary model

in Balopoulos, E.; Chronis, G.; Lipiatou, E. (Eds.) et al International conference. Oceanography of the eastern Mediterranean and Black Sea. Similarities and differences of two interconnected basins (2000)

A hydrodynamical model of the general circulation in the Black Sea has been build up, using the GHER (GeoHydrodynamics and Environment Research) three-dimensional, non-linear, baroclinic, turbulent ... [more ▼]

A hydrodynamical model of the general circulation in the Black Sea has been build up, using the GHER (GeoHydrodynamics and Environment Research) three-dimensional, non-linear, baroclinic, turbulent closure model. A model with 5 km horizontal resolution and 25 vertical levels is used to compute the typical seasonal cycle by forcing the model with climatological monthly mean fields of temperature, salinity and wind stress at the air-sea interface. Furthermore, the river discharges of the Danube, the Dnestr and the Dnepr are taken into account. This high resolulion model resolves the baroclinic instabilities generated by the interactions of the boundary current with the coastline geometry or with the continental shelf/slope topography. A simple ecosystem model defined by a nitrogen cycle is coupled with Ihe hydrodynamical model. The state variables of this model are defined as those which are necessary and sufficient to assess the effects of the physical processes, and in particular of the boundary current instability , on the space time distribution of the primary and secondary productions. The results of the 3D ecohydrodynamic model are compared with CZCS data of surface chlorophyll fields collected during the period from 1978 to 1986. [less ▲]

A SENSITIVITY STUDY OF THE EFFECTS OF SOLAR LUMINOSITY CHANGES ON THE EARTHS GLOBAL TEMPERATURE

in Annales Geophysicae [= ANGEO] (1988), 6(1), 101-112

Sensitivity to ampicillin and cephalothin of enzymes involved in wall peptide crosslinking in Escherichia coli K12, strain 44

in European Journal of Biochemistry (1974), 41(3), 457-463

After extraction of the membranes of Escherichia coli K12 strain 44 by Brij-36T, each of the four enzyme activities (natural transpeptidase, unnatural transpeptidase, carboxypeptidase and endopeptidase ... [more ▼]

After extraction of the membranes of Escherichia coli K12 strain 44 by Brij-36T, each of the four enzyme activities (natural transpeptidase, unnatural transpeptidase, carboxypeptidase and endopeptidase) of the wall peptide crosslinking system, occurs in two forms characterized by large differences in their sensitivity to ampicillin (but much smaller differences in their sensitivity to cephalothin). The fractionation of the enzyme activities into two groups of low and high sensitivity to ampicillin is achieved essentially by chromatography of the membrane extract on DEAE-cellulose. [less ▲]

Sensitivity-based approaches for handling discrete variables in optimal power flow computations

in IEEE Transactions on Power Systems (2010), 25(4), 1780-1789

This paper proposes and compares three iterative approaches for handling discrete variables in optimal power flow (OPF) computations. The first two approaches rely on the sensitivities of the objective ... [more ▼]

This paper proposes and compares three iterative approaches for handling discrete variables in optimal power flow (OPF) computations. The first two approaches rely on the sensitivities of the objective and inequality constraints with respect to discrete variables. They set the discrete variables values either by solving a mixed-integer linear programming (MILP) problem or by using a simple procedure based on a merit function. The third approach relies on the use of Lagrange multipliers corresponding to the discrete variables bound constraints at the OPF solution. The classical round-off technique and a progressive round-off approach have been also used as a basis of comparison. We provide extensive numerical results with these approaches on four test systems with up to 1203 buses, and for two OPF problems: loss minimization and generation cost minimization, respectively. These results show that the sensitivity-based approach combined with the merit function clearly outperforms the other approaches in terms of: objective function quality, reliability, and computational times. Furthermore, the objective value obtained with this approach has been very close to that provided by the continuous relaxation OPF. This approach constitutes therefore a viable alternative to other methods dealing with discrete variables in an OPF. [less ▲]

The sensitization to airborne allergens in Czech patients with allergic disorders is dramatically higher than sensitization of Ukrainian patients

Poster (2003, May 14)