bluuebunny/crossref_metadata_2025 huggingface dataset:
Defining the Limits of Tubular-Handling Equipment at Extreme Tension Loadings
Authors: Bradford Dale W. , Payne Michael L. , Schultz Donald E. , Adams Burt A. , Vandervort Kurt D.
Published: March 2009

The purpose of this paper is to present the results of a comprehensive-test program conducted with five different sets of deepwater-landing string-handling equipment consisting of both conventional and unconventional technology. A thorough presentation will be made detailing initial testing at elastic loads approaching yield and final high-load testing beyond yield. All stages of the test program will be discussed including original testing protocol, test setup, testing performed, test results, and overall conclusions. This is one of the first standardized-test programs used across five different designs of handling equipment. This overall presentation of the test program is made to identify stress levels associated with the extreme loads that occur when landing very heavy casing strings in deepwater wells.
Delivering a Fully Qualified HP/HT Production Packer Following Field Failure
Authors: Humphreys Alan , Ross Robert
Published: March 2009

The failure of a primary barrier on a completed high-pressure/ high-temperature (HP/HT) well in the west Franklin field in the UK continental shelf in 2005 resulted in a significant pressure increase in the production annulus requiring a complex well-kill operation to resolve. Following this incident, an investigation program was undertaken to determine the root cause of the failure and, thereafter, to develop a solution. The failure investigation looked at all aspects of the well design and operations and found no clear cause. A "failure test" then was carried out that recreated the exact downhole conditions on surface. This test demonstrated that very small irregularities in the internal-casing profile would cause the packer casing seal to fail under severe bottomhole conditions. A program then was undertaken to develop a packer-seal system, suited to the severe well environment, that could withstand a specified degree of casing irregularity. A rigourous qualification program also was developed to verify the new systems capability in irregular casing.

The program was completely successful, and new packer-seal systems have been qualified to these enhanced standards and deployed in the field.
Sealing Capacity of API Connections—Theoretical and Experimental Results
Authors: Teodoriu Catalin , Badicioiu Marius
Published: March 2009

Hydraulic fracturing has become a state-of-the-art stimulation technique. It has been proved over the years that significant production increase can be obtained by applying the right fracturing technique. Now, the most advanced techniques of geothermal-energy-recovery systems widely use hydraulic fracturing.

The following paper presents the experimental results of the tests carried out on four different compounds using the improved "grooved-plate" method. The tests have shown a large variation of the tested-thread-compounds sealing capacity. Starting from the experimental results and the theoretical analysis of the American Petroleum Institute (API) connection, a useful chart was built to determine the real connection resistance, on the basis of its initial makeup torque. The chart offers to engineers involved in the design of a fracturing process the possibility to estimate the maximum pressure that may lead to a connection leak.
Adaptive Partial Drug Approval: A Health Policy Proposal
Authors: Manski Charles F
Published: March 2009

Charles Manski of Northwestern argues that the drug approval process should be more continuous, so that patients can have access to beneficial drugs earlier and at the same time there are incentives for longer term studies than the current system produces, which could limit problems like those caused by Vioxx.
Monoline Regulations to Control the Systemic Risk Created by Investment Banks and GSEs
Authors: Jaffee Dwight M.
Published: March 2009

The paper offers a framework and a specific proposal for the re-regulation of key components of the U.S. financial system in the aftermath of the subprime mortgage crisis. It begins with a review of those aspects of the subprime crisis that required the large, observed government interventions, namely the feared bankruptcy of individual banks, insurers, and government sponsored enterprises with the potential to create a meltdown of the entire financial system. The paper then develops legislative responses that would make future systemic failures and bailouts of this magnitude highly unlikely. The paper's key analytic device is to distinguish two financial firm activities: (1) risky investment activities (hedge fund" division) capable of causing firm bankruptcy, and (2) market-making and related activities (infrastructure" division), the failure of which would have systemic implications. The goal of the proposed regulatory change is to ensure that the infrastructure division is bankruptcy remote and can operate on a stand-alone basis if necessary even when losses from the hedge fund division threaten the holding company's solvency.
“But This Story of Mine Is Not Unique”: A Review of Research on African American Children’s Literature
Authors: Brooks Wanda , McNair Jonda C.
Published: March 2009

This article provides a review of research on African American children’s literature by synthesizing the growing body of textual and reader response research conducted across the past several decades. The literature presented in this article cuts across the disciplines of education as well as English and library science. Using the selective tradition as a theoretical underpinning, the authors review extant literature through a three-pronged thematic heuristic developed as a result of their analysis. These themes present research findings related to African American children’s literature as (1) contested terrain, (2) cultural artifact, and (3) literary art. The three themes generated to delineate the findings derived from a four-stage iterative process of analysis. By considering collective findings, a more careful and continued institutionalization of this literature can take place in schools, libraries, bookstores, popular media, and within families. The authors also address future implications for educational practice and research related to African American children’s literature.
The Role of Reader Characteristics in Processing and Learning From Informational Text
Authors: Fox Emily
Published: March 2009

This article considers the role of reader characteristics in processing and learning from informational text, as revealed in think-aloud research. A theoretical framework for relevant aspects of readers’ processing and products was developed. These relevant aspects included three attentional foci for processing (comprehension, monitoring, and evaluation) and five types of processing behaviors (use of strategies, metacognition, monitoring, goal setting and pursuit, and use of prior knowledge). Relevant aspects of products included mental representations of text (textbase, situation model of text, situation model of phenomenon, and author model) and the quality of those representations. A body of 45 studies was identified, considering reader characteristics of ability, experience, knowledge, and interest. Overall, low levels of all these were associated with an emphasis on local-level processing and effortful construction of a textbase, whereas higher levels were associated with more globally directed, more effective, more flexible engagement, leading to better quality mental representations and greater learning.
School-Based Child Sexual Abuse Prevention Programs: A Review of Effectiveness
Authors: Topping Keith J. , Barron Ian G.
Published: March 2009

In this systematic and critical review of purely school based child sexual abuse prevention program efficacy studies, 22 studies meeting the inclusion criteria differed by target population, program implementation, and evaluation methodology. Measured outcomes for children included knowledge, skills, emotion, risk perception, touch discrimination, reported response to actual threat or abuse, disclosure, maintenance of gains, and negative effects. Many studies had methodological limitations (e.g., sampling problems, lack of adequate control groups, lack of reliable and valid measures). However, most investigators claimed that their results showed significant impact in primary prevention (increasing all children’s knowledge or awareness and/or abuse prevention skills). There was little evidence of change in disclosure. There was limited follow-up evidence of actual use and effectiveness of prevention skills, and the evidence for maintenance of gains was mixed. Several programs reported some negative effects. Very few studies reported implementation fidelity data, and no study reported cost-effectiveness. Implications for future research, policy, and practice are outlined.
Interpersonal Relationships, Motivation, Engagement, and Achievement: Yields for Theory, Current Issues, and Educational Practice
Authors: Martin Andrew J. , Dowson Martin
Published: March 2009

In this review, we scope the role of interpersonal relationships in students’ academic motivation, engagement, and achievement. We argue that achievement motivation theory, current issues, and educational practice can be conceptualized in relational terms. Influential theorizing, including attribution theory, expectancy-value theory, goal theory, self-determination theory, self-efficacy theory, and self-worth motivation theory, is reviewed in the context of the role of significant others in young people’s academic lives. Implications for educational practice are examined in the light of these theoretical perspectives and their component constructs and mechanisms. A trilevel framework is proposed as an integrative and relationally based response to enhance students’ motivation, engagement, and achievement. This framework encompasses student-level action (universal programs and intervention, targeted programs for at-risk populations, extracurricular activity, cooperative learning, and mentoring), teacher- and classroom-level action (connective instruction, professional development, teacher retention, teacher training, and classroom composition), and school-level action (school as community and effective leadership).
From Everyday to Scientific Observation: How Children Learn to Observe the Biologist’s World
Authors: Eberbach Catherine , Crowley Kevin
Published: March 2009

This article explores the development of observation in scientific and everyday contexts. Fundamental to all scientific activity, expert observation is a complex practice that requires the coordination of disciplinary knowledge, theory, and habits of attention. On the surface, observation appears to be a simple skill. Consequently, children may be directed to observe, compare, and describe phenomena without adequate disciplinary context or support, and so fail to gain deeper scientific understanding. Drawing upon a review of science education, developmental psychology, and the science studies literatures, this article examines what it means to observe within a disciplinary framework. In addition, everyday observers are characterized and a framework is proposed that hypothesizes how everyday observers could develop practices that are more like scientific observers.
Microstructure and mechanical properties of the AA6082 aluminium alloy with small additions of Sc and Zr
Authors: Vlach Martin , Smola Bohumil , Stulíková Ivana , Očenášek Vladivoj
Published: March 2009

The effect of Sc and Zr addition on microstructure and hardness development in a commercial as-cast and solution-treated (530 °C/45 min) AA6082 alloy was studied. The electrical resistivity decrease and hardness increase in the temperature range 180 – 300 °C are caused by precipitation of β′′ and/or β′ needles of the Mg – Si system. Precipitation and morphology changes of Al – Mn – Fe system phases in AA6082 and AA6082-ScZr alloys influence the resistivity significantly, but have a negligible effect on hardness. The initial hardness of Sc and Zr containing AA6082 alloys is higher mainly due to the presence of Al3(Sc, Zr) particles. This difference is less pronounced in the peak-hardening state. Natural ageing of solution-treated alloys influences microstructure development in both alloys when annealed subsequently up to 240 °C.
Mechanism and kinetics of the intermediary phase formation in Ti–Al and Ti–Al–Si systems during reactive sintering
Authors: Novák Pavel , Kubásek Jirí , Šerák Jan , Vojtěch Dalibor , Michalcová Alena
Published: March 2009

In this work, chemical reactions and phase transformations during reactive sintering of Ti – Al and Ti – Al – Si materials were investigated by differential thermal analysis. Kinetics and mechanism of the formation of intermediary phases are described on an experimental model system consisting of a bulk titanium sample exposed to molten aluminium or AlSi50 alloy. The results show that the reactive sintering is a reaction-controlled process in both systems. The reaction rate increases significantly with addition of silicon. According to the kinetics study, reactive sintering of TiAl36 and TiAl15Si15 alloys was carried out. TiAl15Si15 alloy was successfully sintered, while TiAl36 material showed extremely high porosity and presence of unreacted components.
Theoretical investigation of phase equilibria by the continuous displacement cluster variation method
Authors: Mohri Tetsuo
Published: March 2009

By employing the continuous displacement cluster variation method, order – disorder transition behavior of a two-dimensional square lattice is investigated. It is demonstrated that the distribution of displaced atoms around a Bravais lattice point continuously changes with temperature. The additional freedom of atomic displacement contributes to the entropy and thermal lattice expansion is confirmed. Finally, it is shown that the order – disorder transition temperature decreases as compared with the one by the conventional cluster variation method in which no local atomic displacements are allowed.
Vacancy–solute interaction in magnesium alloy WE54 during artificial ageing: a positron annihilation spectroscopy study
Authors: Moia Fabio , Calloni Alberto , Ferragut Rafael , Dupasquier Alfredo , Macchi Carlos Eugenio , Somoza Alberto , Nie Jian Feng
Published: March 2009

The vacancy – solute interaction during artificial ageing at 250 °C was studied in the commercial alloy WE54 by coincidence Doppler broadening of the positron annihilation radiation. The results show that in the initial state of ageing positron trapping is weak. Under these conditions, the faint signal comes predominantly from small Zr particles, with minor contributions from vacancy – Nd complexes. Positron trapping increases concomitantly with the formation of the ′- and 1-phases at the onset of precipitation hardening, and becomes very intense at later ageing stages when the 1-phase is formed. The chemical composition in contact with open-volume defects changes after 4 h of ageing with a progressive enrichment in Mg, concomitant with a hardness increase. There is evidence for a prevalence of Nd over Y up to 24 h of ageing and then a prevalence of Y over Nd for 96 h (Y/Nd 3) when the -phase is dominant.
Effects of prior homogenization treatments on microstructure development and mechanical properties of the extruded wrought magnesium alloy ZK60
Authors: Shahzad Muhammad , Janeček Miloš , Wagner Lothar
Published: March 2009

The wrought magnesium alloy ZK60 is extruded with and without prior homogenization treatments. Homogenization at 400 °C leads to effective dissolution of second phase particles whereas homogenization at 300 °C has little effect on them. These particles are broken down during the subsequent extrusion and play an important role in the dynamic recrystallization response of the alloy. Microstructure and mechanical properties after extruding with and without homogenization treatments are compared.
Recovery processes in magnesium alloy AX41 and AX41-12 vol.% C-fibre composite studied by dilatometry
Authors: Rudajevová Alexandra , Král Robert
Published: March 2009

The dilatation characteristics of pre-deformed AX41 magnesium alloy and AX41-12 vol.% C-fibre composite were determined in the temperature range 20 – 380 °C. Two fibre orientations for the composite were investigated: parallel and perpendicular to the axis sample. During the first thermal cycle after compression deformation, the recovery of the alloy and composite occurs in two steps. We observed the recovery of twins at low temperatures, and the recovery of dislocations at higher temperatures. The released plastic deformation is larger in composites with fibres perpendicular to the sample axis than in composites with fibres parallel to the sample axis. We analysed the deformation curves for the alloy and both composites.
Annealing effects after various thermo-mechanical treatments on microstructure and mechanical properties of the wrought magnesium alloy AZ80
Authors: Oo Min Zaw , Müller Julia , Janeček Miloš , Wagner Lothar
Published: March 2009

The magnesium alloy AZ80, received from Dead Sea magnesium in direct-chill cast condition was extruded at T = 350 °C using an extrusion ratio of ER = 12. The extruded bars were severe plastically deformed at 250 °C by utilizing thermo-mechanical treatments (TMT), either equal channel angular pressing (ECAP) or swaging.

While swaging led to similar grain refinements as observed after ECAP, yield stress and tensile strength values were by far superior in the swaged alloy. This result is explained by the unfavourable 45° texture component of the (0002) pole figure that develops during the massive shear deformation in ECAP. Unlike ECAP, the grain orientation after swaging is similar to the as-extruded condition. Annealing at elevated temperatures indicates very low thermal stability of microstructure and mechanical properties in the ECAP-ed alloy while both properties in the swaged microstructure are as stable as in the as-extruded reference.
FeAl-based alloys cast in an ultrasound field
Authors: Šíma Vladimír , Kratochvíl Petr , Kozelský Petr , Schindler Ivo , Hána Petr
Published: March 2009

An ultrasonic device was designed to fabricate relatively small (about 0.7 kg) vacuum chill castings of FeAl-based alloys with improved microstructure. The influence of ultrasound on the solidification microstructure of the Fe-40 at.% Al based castings was investigated. The subsequent hot-rolling of such an as-cast alloy was made using a special stainless steel bandage of the casting. This effectively prevents fraying and cracking caused by the thermal shock arising at the surface of the hot casting, when it comes in contact with a cold roller. The efficiency of ultrasonic vacuum casting, based on the influence of the acoustic cavitation on the solidification of the melt, is manifested by a refined microstructure of the prepared iron aluminides Fe-40 at.% Al with addition of C or Zr and B. First results of improved mechanical properties of these alloys are presented and discussed.
Strain-hardening behaviour of AZ31 magnesium alloys
Authors: Balík Jaroslav , Lukáč Pavel , Drozd Zdeněk , Kužel Radomír
Published: March 2009

The in-plane tensile behaviour of rolled sheets of the magnesium alloy AZ31 was investigated in both an H24 state and an aged state. Whereas the very high initial strain-hardening rate decreases monotonically with strain for the H24 samples, the annealed structure exhibits a striking increase in the strain-hardening rate. To explain this phenomenon, the occurrence of sessile dislocations associated with a secondary (pyramidal) slip is proposed. The absence of increasing hardening for the H24 state is supposed to be related to higher yield stresses (predeformations) within the grains of the polycrystalline aggregate.
Effect of annealing on microstructure and properties of twin-roll-cast Al–Mn alloys with different copper content
Authors: Slámová Margarita , Kubošová Andrea , Politello Julien , Cieslar Miroslav
Published: March 2009

Aluminium – manganese foils are used as fins in heat exchangers. Twin-roll casting reduces energy consumption, thus it is an environment-friendly casting procedure for these materials. Composition and processing variations affect foil properties and their optimization is a primary development goal. The results of a study of microstructure transformations occurring during the annealing of twin-roll-cast aluminium – manganese alloys with different copper content are reported and discussed. Microstructure and property evolution was monitored by resistometric measurements at – 196 °C during a slow stepwise heating up to 600 °C, microstructural analysis and hardness measurements. The copper content does not impact phase transformations but slightly modifies softening evolution with annealing temperature. Due to solid solution hardening, increasing copper content results in increased alloy hardness.
Hardening and softening in an Mg–Al–Ca matrix alloy reinforced with short graphite fibres
Authors: Trojanová Zuzanka , Lukáč Pavel
Published: March 2009

The mechanical properties of an AX41 magnesium alloy (4Al-1Ca-balance Mg; in wt.%) reinforced with Sigrafil C40 fibres were investigated. Compression tests were conducted at temperatures between 23 and 300 °C at a strain rate of 8.3 · 10– 5 s– 1. The yield stress and the maximum stress decrease with increasing testing temperature. The influence of the reinforcement on both characteristic stresses becomes weaker with increasing temperature. At higher temperatures, no significant work hardening was observed. The results indicate the occurrence of dynamic recovery. Possible hardening and softening mechanisms are discussed.
Austenite–martensite interfaces in strained foils of CuAlNi alloy
Authors: Ostapovets Andriy , Paidar Vaclav , Zarubova Niva
Published: March 2009

Geometrical analysis of austenite – martensite interfaces in foils of a CuAlNi alloy is performed on the basis of the phenomenological theory of martensite. The interfaces in the foils of the CuAlNi alloy are faceted. In order to assess possible facet planes, lattice invariant deformation in the form of a simple shear is included into the phenomenological theory. The orientation ranges where the normals to the facet planes can lie were obtained. They agree with the experimentally observed facet planes.
Thresholds in creep of magnesium alloy AX41 composites reinforced with short fibers
Authors: Milička Karel , Dobeš Ferdinand
Published: March 2009

Creep behavior of four magnesium Mg-4Al-1Ca alloy-based composites reinforced with short alumina or carbon fibers was investigated at temperatures 423, 473, 523, and 623 K. The threshold creep behavior was observed in all composites as well as in the matrix alloy AX41. Both types of fibers strongly increase creep resistance of the composites. A stronger strengthening effect was observed in composites with alumina fibers. The applied stress dependences of the minimum creep rate of all investigated materials were well described by Garofalo' sinh relationship modified for threshold concept. Threshold stresses and their temperature dependences were evaluated from the stress dependences and discussed in detail from the viewpoint of contemporary knowledge of mechanisms governing the creep behavior of metal-matrix composites.
Effect of crystallization on the deformation behavior of a Zr-based bulk metallic glass
Authors: Lendvai János , Gubicza Jenő: , Lábár János L. , Kuli Zoltán
Published: March 2009

The crystallization process in a Zr-based bulk metallic glass with the composition Zr44Ti11Cu10Ni10Be25 was studied during isothermal annealing above the glass transition temperature at 682 K. Indentation creep tests were applied to study the effect of crystallization on the viscosity. It was found that the increase in viscosity during crystallization is primarily caused by the hard crystalline grains and secondarily by the change of the chemical composition of the remaining liquid phase. The deformation behavior at room temperature is studied by three-point bending tests. The strength of the specimens decreases significantly in the first step of the crystallization process.
Physical aspects of plastic deformation in Mg–Al alloys with Sr and Ca
Authors: Trojanová Zuzanka , Lukáč Pavel
Published: March 2009

Magnesium alloys of AJ (Mg – Al – Sr) and AX (Mg – Al – Ca) series were deformed at temperatures between room temperature and 300 °C. Stress relaxation tests were performed in order to reveal features of the thermally activated dislocation motion. The work hardening rate = d/d decreases with increasing stress and temperature. Analysis of the – plots revealed the hardening and softening mechanisms operating during the deformation. Internal and effective components of the applied stress have been estimated. Very high values of the internal stress estimated at lower temperatures decrease rapidly with increasing deformation temperature. The apparent activation volume decreases with increasing effective stress. The values of the activation volume as well as the activation enthalpy indicate that the main thermally activated process is most probably the glide of dislocations in non-compact planes.
Core structure of screw dislocations in hcp Ti: an ab initio DFT study
Authors: Tarrat Nathalie , Benoit Magali , Morillo Joseph
Published: March 2009

The core structure of screw dislocations in -Ti was studied in the cluster approach with ab initio DFT-GGA, and in both the cluster and quadrupole approaches with a recently highly optimized EAM central force potential. With the EAM potential we have shown that finite-size effects, in the cluster approach, are negligible down to the size studied in the ab initio DFT calculations that have shown unambiguously a preferential prismatic core spreading for the dislocation. Our results are in agreement with previously published approximated calculations using empirical or semi-empirical interaction models: only approximated interaction models, taking explicitly into account the covalent directional bonding of the d electrons, can properly account for the preferential prismatic core spreading against the basal one; and empirical interaction models without angular force components are inadequate. Interestingly, at first sight, the relaxed core structures (basal or prismatic) obtained with empirical or semi-empirical interaction models are almost identical to the ones obtained with the ab initio DFT calculations.
Experimental study of particle concentration fluctuations in a turbulent steady flow
Authors: Cierco François-Xavier , Naaim Mohamed , Naaim-Bouvet Florence
Published: March 2009

Specific features of the physics of blown sand and PVC particles were investigated in wind-tunnel experiments. The fluctuations in particle concentration over time were derived from image processing of high-speed films (500 Hz). Spectral analysis of these time series showed a slowly decreasing slope within a frequency range that could be larger than the inertial sub-range of the free stream. A specific transport regime also appears in the lower part of the flow for frequencies less than 10 Hz. The role of turbulence in the generation of this regime is discussed using a simple theoretical model able to describe the aerodynamic behavior of a particle.
Spatial variability of new snow amounts derived from a dense network of Alpine automatic stations
Authors: Egli Luca
Published: March 2009

Since 1996, a dense network of Alpine automatic weather and snow-measurement (Interkantonales Mess- und Informationssystem (IMIS)) stations has been in operational use for local and regional avalanche warning. The measurements of the IMIS stations are assumed to be representative for spatially extended regions around the measuring sites for applications in avalanche risk management. In this study, the regional representativeness of these stations with regard to the daily amount of new snow is investigated. The results show that the amount of daily new snow is spatially correlated in a range of ∼5–55 km. Regarding simultaneous observations of daily new snow measurements, which are ∼5–10 km apart, the probability of detection (POD) is given as 0.5±0.03. In this paper, the POD of an automatic warning network is introduced as an indicator of the representativeness of point measurement information for avalanche warning applications. The results of this study may mark a reference value for verification of spatially distributed Alpine meteorological models which evaluate the amount of daily new snow in the Swiss Alps.
Glacier thickening and decay analysis from 50 years of glaciological observations performed on Glacier d’Argentière, Mont Blanc area, France
Authors: Vincent C. , Soruco A. , Six D. , Le Meur E.
Published: March 2009

Numerous glaciological data have been obtained from measurements carried out on Glacier d’Argentière, Mont Blanc area, France, since the beginning of the 20th century. Moreover, data on annual mass balance, ice-flow velocity, thickness variation and length fluctuation have been obtained from yearly measurements performed since 1975. This dataset provides an excellent opportunity to analyze the relationships between surface mass balance and dynamic response over time periods during which net mass balance changed from positive to negative. Following a positive specific-net-balance period between 1960 and 1981, the ablation zone experienced a large increase in thickness and ice-flow velocities. Conversely, the highly negative specific-net-balance period since 1982 has led to strong thinning, deceleration and retreat of the tongue. The response of these observed dynamics to surface mass balance is analyzed from ice-flux calculations performed on three transverse cross-sections. Our results reveal that the ice fluxes are largely accommodated by ice-flow velocities. Velocity fluctuations are synchronous over the entire area studied. In the largest part of the glacier, no compressing/extending flow change has been observed over the last 30 years and thickness changes are solely driven by surface mass-balance changes. However, on the tongue of the glacier, thickness changes do not depend on surface mass balance but are mainly driven by changes in the longitudinal strain rate.
Meteorological controls on snow and ice ablation for two contrasting months on Glacier de Saint-Sorlin, France
Authors: Six D. , Wagnon P. , Sicart J.E. , Vincent C.
Published: March 2009

The influence of meteorological variables on snow/ice melting has been analyzed for two very contrasting months, in summer 2006, on Glacier de Saint-Sorlin, French Alps. July 2006 was the warmest July since 1950, and August 2006 was the coldest August since 1979. The total energy available for melting was just over half as much in August as in July, due to a sharp decrease in net shortwave radiation and in turbulent flux. This decrease of net shortwave radiation was mainly controlled by a strong increase in albedo responsible for an increase of reflected shortwave radiation, as well as by a reduction in incident shortwave radiation. During the two months, net longwave radiation remained almost unchanged. The mass balance computed from energy-balance modelling or with a degree-day approach was in good agreement with measured mass balance. Differences were attributed to space and time surface aspect variations which mainly controlled the observed mass balance.
Best possible estimation of mass balance combining glaciological and geodetic methods
Authors: Thibert E. , Vincent C.
Published: March 2009

Variance analysis of the long time series of mass balances recorded on Glacier de Sarennes (45°07’ N, 6°07’ E) France, since 1949 shows that the variability can be separated linearly in two spatial and temporal terms. Annual balances deviate from their mean values over the period of record by an annual amount that is uniform over the glacier. Annual balances at each stake are therefore highly correlated, and sampling at a single site would be acceptable to record the annual deviation. A result of the linear character of the variance is the possibility of obtaining a systematic error-free estimate of the annual glacier-total budget by combining the mean annual balance obtained from photogrammetry and the annual deviation obtained from the variance analysis, rather than using the traditional area integration of balances at each stake.
On the role of subsurface heat conduction in glacier energy-balance modelling
Authors: Pellicciotti Francesca , Carenzo Marco , Helbing Jakob , Rimkus Stefan , Burlando Paolo
Published: March 2009

We discuss the inclusion of the subsurface heat-conduction flux into the calculation of the energy balance and ablation at the glacier–atmosphere interface. Data from automatic weather stations are used to force an energy-balance model at several locations on alpine glaciers and at one site in the dry Andes of central Chile. The heat-conduction flux is computed using a two-layer scheme, assuming that 36% of the net shortwave radiation is absorbed by the surface layer and that the rest penetrates into the snowpack. We compare simulations conducted with and without subsurface heat flux. Results show that assuming a surface temperature of zero degrees leads to a larger overestimation of melt at the sites in the accumulation area (10.4–13.3%) than in the ablation area (0.5–2.8%), due to lower air temperatures and the presence of snow. The difference between simulations with and without heat conduction is also high at the beginning and end of the ablation season (up to 29% for the first 15 days of the season), when air temperatures are lower and snow covers the glacier surface, while they are of little importance during periods of sustained melt at all the locations investigated.
Climatic implications of reconstructed early–mid Pliocene equilibrium-line altitudes in the McMurdo Dry Valleys, Antarctica
Authors: Krusic A.G. , Prentice M.L. , Licciardi J.M.
Published: March 2009

Early–mid Pliocene moraines in the McMurdo Dry Valleys, Antarctica, are more extensive than the present alpine glaciers in this region, indicating substantial climatic differences between the early–mid Pliocene and the present. To quantify this difference in the glacier–climate regime, we estimated the equilibrium-line altitude (ELA) change since the early–mid Pliocene by calculating the modern ELA and reconstructing the ELAs of four alpine glaciers in Wright and Taylor Valleys at their early–mid Pliocene maxima. The area–altitude balance ratio method was used on modern and reconstructed early–mid Pliocene hypsometry. In Wright and Victoria Valleys, mass-balance data identify present-day ELAs of 800–1600ma.s.l. and an average balance ratio of 1.1. The estimated ELAs of the much larger early–mid Pliocene glaciers in Wright and Taylor Valleys range from 600 to 950±170ma.s.l., and thus are 250–600±170m lower than modern ELAs in these valleys. The depressed ELAs during the early–mid-Pliocene most likely indicate a wetter and therefore warmer climate in the Dry Valleys during this period than previous studies have recognized.
Comparison of mass balances for Vernagtferner, Oetzal Alps, as obtained from direct measurements and distributed modeling
Authors: Paul Frank , Escher-Vetter Heidi , Machguth Horst
Published: March 2009

The direct comparison of modeled glacier mass-balance distribution with field measurements could be problematic, as the methodology of determination and the processes considered at the point or catchment scale could differ strongly. Moreover, direct measurements cover only small parts of a glacier, and model performance is thus difficult to assess outside these regions. Remaining opportunities for model validation include comparison of snowlines, as derived from remote-sensing data, and maps of the mass-balance distribution, as interpreted by observers with local knowledge. This study compares such hand-drawn maps of the Vernagtferner (Oetzal Alps) mass balance with the modeled pattern as obtained from a distributed energy-/mass-balance model of intermediate complexity. The model is driven by measured daily values of temperature, global radiation and precipitation from a nearby climate station and grids of mean daily potential global radiation and climatologic annual precipitation sums. Compared with the direct measurements, the calculated mean mass balance and equilibrium-line altitude agreed very well in both balance years, although the spatial pattern of the mass-balance distribution displayed larger deviations in regions influenced by snowdrift or local topographic undulations. However, compared with the remaining snow as visible on a satellite image from 1999, the modeled snowline pattern for a larger sample of glaciers is in very good agreement.
Reconstruction of the annual balance of Vadret da Morteratsch, Switzerland, since 1865
Authors: Nemec Johanna , Huybrechts Philippe , Rybak Oleg , Oerlemans Johannes
Published: March 2009

We have reconstructed the annual balance of Vadret da Morteratsch, Engadine, Switzerland, with a two-dimensional energy-balance model for the period 1865–2005. The model takes into account a parameterization of the surface energy fluxes, an albedo that decreases exponentially with snow depth as well as the shading effect of the surrounding mountains. The model was first calibrated with a 5 year record of annual balance measurements made at 20 different sites on the glacier between 2001 and 2006 using meteorological data from surrounding weather stations as input. To force the model for the period starting in 1865, we employed monthly temperature and precipitation records from nearby valley stations. The model reproduces the observed annual balance reasonably well, except for the lower part during the warmest years. Most crucial to the results is the altitudinal precipitation gradient, but this factor is hard to quantify from the limited precipitation data at high elevations. The simulation shows an almost continuous mass loss since 1865, with short interruptions around 1920, 1935 and 1980. A trend towards a more negative annual balance can be observed since the beginning of the 1980s. The simulated cumulative mass balance for the entire period 1865–2005 was found to be –46mw.e.
20th-century climate change inferred from four long-term point observations of seasonal mass balance
Authors: Huss Matthias , Bauder Andreas
Published: March 2009

Four long-term time series of seasonal mass-balance observations, all starting in 1914, have been compiled for two stakes on Claridenfirn and one stake on Grosser Aletschgletscher and Silvrettagletscher, Switzerland. These data represent the longest records of mass balance worldwide. A mass-balance model based on the temperature-index approach is used to correct field data for varying observation dates and data gaps and to separate accumulation and ablation. The homogenized continuous 93 year time series cover most of the 20th century and enable us to investigate temporal, regional and altitudinal variability in mass balance and changes in the climatic forcing on glaciers. A high-altitude site shows summer balance trends opposite to those at three stakes located near the equilibrium line. Since 1975, melt rates have increased by 10%(10 a)−1 periods of enhanced climatic forcing are detected: 1943–53 and 1987–2007. The energy consumed for melt was higher in the 1940s despite lower air temperatures compared to the years since 1987. We find evidence for a change in the glacier surface heat budget, which has important implications for the long-term stability of degree-day factors in empirical temperature-index modelling.
Sensitivity of net mass-balance estimates to near-surface temperature lapse rates when employing the degree-day method to estimate glacier melt
Authors: Gardner Alex S. , Sharp Martin
Published: March 2009

Glacier mass-balance models that employ the degree-day method of melt modeling are most commonly driven by surface air temperatures that have been downscaled over the area of interest, using digital elevation models and assuming a constant free air lapse rate that is often taken to be the moist adiabatic lapse rate (MALR: –6.5°Ckm–1). Air-temperature lapse rates measured over melting glacier surface are, however, consistently less steep than free air values and have been shown to vary systematically with lower-tropospheric temperatures. In this study, the implications of including a variable near-surface lapse rate in a 26 year (1980–2006) degree-day model simulation of the surface mass balance of Devon Ice Cap, Nunavut, Canada, are examined and compared with estimates derived from surface air temperatures downscaled using a constant near-surface lapse rate equal to the measured summer mean (–4.9°Ckm–1) and the MALR. Our results show that degree-day models are highly sensitive to the choice of lapse rate. When compared with 23 years of surface mass-balance measurements from the northwest sector of the ice cap, model estimates are significantly better when surface air temperatures are downscaled using a modeled daily lapse rate rather than a constant lapse equal to either the summer mean or the MALR.
Four decades of winter mass balance of Vernagtferner and Hintereisferner, Austria: methodology and results
Authors: Escher-Vetter Heidi , Kuhn Michael , Weber Markus
Published: March 2009

In this study, long-term series of winter mass balances from two neighbouring glaciers in the southern Oetztal Alps, Austria, i.e. Hintereisferner and Vernagtferner, are analyzed with respect to the methods used in their determination. For this purpose, (1) some basic data of field surveys are presented, (2) the influence of different temporal systems is discussed, and (3) the profile, contour and a ‘model’ method based on energy-balance ablation modelling and measured net mass balance are discussed with respect to the reliability of the resulting series. The main findings of the investigations are: (1) The winter mass-balance series for Hintereisferner and Vernagtferner as determined with all applied methods result in a reliable climatologic average of 1000±100mmw.e. (2) When using the profile method, different spatial integration approaches are quite sensitive to the altitudinal coverage and the spatial pattern of observations. (3) The error of the model method occurs randomly, whereas contour as well as profile-method errors are more systematic. (4) Filtered time series from the two glaciers show similar tendencies for the last three decades.
The ‘benchmark glacier’ concept – does it work? Lessons from the North Cascade Range, USA
Authors: Fountain Andrew G. , Hoffman Matthew J. , Granshaw Frank , Riedel Jon
Published: March 2009

Benchmark glaciers were established in many alpine areas during the 1960s as part of the International Hydrological Decade to represent ‘typical’ mass and energy processes on glaciers in different climatic regions around the world. These glaciers have received new interest in the past decade because they are used to infer the contribution of alpine glacier wastage to global sea-level rise. We compare South Cascade Glacier, the benchmark glacier for the northwest contiguous USA, and four other secondary glaciers, against the topographic, area and mass changes of 321 glaciers in the surrounding region. Results show that South Cascade Glacier is unusually large, of lower slope and much larger area and had mass losses greater than most other glaciers in the region. Three of the four secondary glaciers were much more typical. Year-to-year variations in mass balance were highly correlated between all five glaciers, and any of these glaciers, including the benchmark glacier, could be used to infer temporal mass variations in the region. However, the use of South Cascade Glacier to estimate area/mass losses for the region would result in overestimating the area/mass changes by a factor of three. Local differences in the magnitude of annual glacier mass balance control cumulative mass changes and area changes. There appears to be no way to select a representative glacier a priori, and knowledge of changes over the region is required. Therefore, there may be great uncertainty in estimates of sea-level rise from the wastage of alpine glaciers based on the benchmark approach. We recommend re-evaluation of regional glacier mass changes inferred from benchmark glaciers in critical regions.
Calculation of sensible-heat flux over a melting ice surface using simple climate data and daily measurements of ablation
Authors: Braithwaite Roger J.
Published: March 2009

Sensible-heat flux is obviously important for glacier ablation but is difficult to measure routinely. Sensible-heat flux can be estimated from wind-speed and temperature data using a dimensionless heat-transfer coefficient. Values of the heat-transfer coefficient are evaluated for six sites by correlating measured melt energy with a wind–temperature variable (product of daily mean wind speed, temperature and mean atmospheric pressure for the altitude in question). Data are available for short periods from two sites in Arctic Canada and two sites in North Greenland, and for hundreds of days of record at Nordbogletscher and Qamanârssûp sermia in South and West Greenland, respectively. Average transfer coefficients for four out of the six sites are close to 0.003, which is in reasonable agreement with values reported elsewhere, while larger values of 0.0047 and 0.0057 are found at the other two sites. Heat-transfer coefficients are also estimated on a monthly basis for the two long records, and substantial variations are found, suggesting that the method should not be used for <20–30 days of data. The present study is based on manually observed ablation and climate data, but the approach could be updated to use data from automatic recording stations using modern sensors.
Geodetic and direct mass-balance measurements: comparison and joint analysis
Authors: Graham Cogley J.
Published: March 2009

This paper describes a new compilation of both direct and geodetic mass-balance measurements, develops a procedure to reduce diverse balance measurements over different time-spans to common time-spans, and presents updated estimates of global average balance of small glaciers based on the enlarged compilation. Although geodetic measurements are fewer than direct measurements, they cover four times as many balance years. Direct and geodetic measurements are unbiased with respect to one another, but differences are often substantial. The statistical procedure can be understood by imagining that an n-year balance measurement is an average of a series of 1 year measurements. The series is hypothetical but we can calculate the uncertainty of each of its elements if, in addition to its measured average, we can also estimate its standard deviation. For this claim to be valid, the annual series must be stationary and normally distributed with independent (roughly, uncorrelated) elements, for which there is reasonable evidence. The need to know the standard deviation means that annual direct measurements from a nearby glacier, or equally reliable information about variability, are indispensable. Given this information, the new methodology results in moderately more negative balances. This is probably because tidewater glaciers are better represented in the geodetic data. In any case, the most recent published estimate of global average balance, 0.8–1.0mma–1 of sea-level equivalent for 2001–04, is now increased substantially to 1.1–1.4 mma–1 for 2001–05.