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Arctic warming has accelerated surface melting even in the highland areas of the Greenland ice sheet (GrIS). Understanding the relationship between climate and surface melting is essential for improving the estimates of ice‐sheet mass loss due to warming. Here we analyze a 250 m‐long ice core from the southeastern dome of GrIS (SE‐Dome site; 67°19′17″ N, 36°47′03″ W, 3,161 m a.s.l.), where the annual mean temperature is −20.9°C and the accumulation rate is high and there is a large discrepancy among climate models regarding snow accumulation estimates. A time scale was established for 1799–2020 with a half‐year uncertainty using annual counting of H2O2 concentration and five time horizons determined by electrical conductivity, melt events, and tritium concentration. The annual accumulation rate from the ice core shows no significant trend over 221 years and has an average of 1.04 ± 0.20 m w.e. year−1. In contrast, the frequency and thickness of refrozen melt layer (ML) have increased over 221 years, and are synchronized with temperature changes in the Arctic. The thickness of MLs correlates positively with the time‐integrated summer temperature anomaly using a reanalysis of air temperature. The in‐situ accumulation records in the southeastern GrIS provide an important basis for correcting reanalysis data such as ERA5, which in turn are valuable for improving regional climate models. Plain Language Summary: In recent years, Arctic temperatures have been increasing faster than global temperatures. In the inland Greenland ice sheet (GrIS), the surface snow melts on warm days, then the meltwater percolates in the snowpack and refreezes into melt layers (MLs). Here we describe an ice core, collected from the southeastern GrIS, which contains records of precipitation and MLs from 1799 to 2020. We then compare these results with the climatic data. The annual precipitation rate obtained from the ice core shows neither a decrease nor an increase over 221 years, suggesting no significant trend in the southeastern region. On the other hand, with Arctic warming, the ML thickness per year has increased through the 19th–21st centuries. In addition, there is a positive correlation between ML thickness and summer temperature. We conclude that the annual precipitation rate in southeastern GrIS is constant regardless of Arctic warming and the ice core is favorable for reconstructing environmental records from the pre‐industrial era to the present. Key Points: From an ice core in the southeastern Greenland ice sheet, we establish a time scale spanning 1799–2020 with a half‐year uncertaintyOver 221 years, the annual accumulation rate shows no significant trend, while the melt layer thickness has increased with Arctic warmingThe in‐situ accumulation records provide an important basis for correcting reanalysis data, which in turn are valuable for improving models [ABSTRACT FROM AUTHOR]

Establishing an accurate chronology is crucial for interpretation of ice core-based climatic records. While high snow accumulation rates characterise coastal Antarctica, thus enabling recovery of highly resolved climatic records, summertime melting at such low-elevation sites offers challenges in establishing a reliable chronological framework through traditional approaches using the seasonality of stable water isotope and ionic proxy records. Here, we assess visual stratigraphy (VS) obtained from line-scan images as a proxy for annual layer counting in firn section (top 50 m) of the IND-36/B9 ice core (dated 1919–2016 CE) from the Djupranen Ice Rise in central Dronning Maud Land, East Antarctica. We also used these images to obtain melt history for the site and found that traditional thickness-based quantification of melt proportion results in significant overestimations. Since density has dominant control on VS profile over the firn section, we first used circulant single-spectrum analysis to remove the secular trend and then we extracted the seasonal VS signals attributed to dust and sea-salt inclusions. We find that melt layers do not significantly alter the VS records if masked during pre-processing. The age–depth model based on the reconstructed VS profile revealed an excellent match with identified time-markers within an uncertainty of ±2 years.

Establishing an accurate chronology is crucial for interpretation of ice core-based climatic records. While high snow accumulation rates characterise coastal Antarctica, thus enabling recovery of highly resolved climatic records, summertime melting at such low-elevation sites offers challenges in establishing a reliable chronological framework through traditional approaches using the seasonality of stable water isotope and ionic proxy records. Here, we assess visual stratigraphy (VS) obtained from line-scan images as a proxy for annual layer counting in firn section (top 50 m) of the IND-36/B9 ice core (dated 1919–2016 CE) from the Djupranen Ice Rise in central Dronning Maud Land, East Antarctica. We also used these images to obtain melt history for the site and found that traditional thickness-based quantification of melt proportion results in significant overestimations. Since density has dominant control on VS profile over the firn section, we first used circulant single-spectrum analysis to remove the secular trend and then we extracted the seasonal VS signals attributed to dust and sea-salt inclusions. We find that melt layers do not significantly alter the VS records if masked during pre-processing. The age–depth model based on the reconstructed VS profile revealed an excellent match with identified time-markers within an uncertainty of ±2 years. [ABSTRACT FROM AUTHOR]

Abstract Previous reconstructions of summer temperatures from ice cores have relied on a statistical relationship between a melt layer and temperature observed at nearby stations. This study presents a novel method for reconstructing summer temperatures from melt layers in ice cores using an energy balance model that incorporates heat conduction and meltwater refreezing in the firn. We use the seasonal patterns in the ERA‐Interim reanalysis data set for an ice core site to calculate the amounts of refreezing water within the firn under various summer mean temperature (SMT) and annual precipitation conditions, and prepared calibration tables containing these three variables. We then estimate the SMTs from the refreezing amount and annual accumulation, both of which can be obtained from an ice core. We apply this method to four ice cores that were recovered from sites with different climates: two sites on the Greenland Ice Sheet, one in Alaska, and one in Russian Altai. The reconstructed SMTs show comparable variations with those of observed temperatures at nearby stations. The nonlinear relationship between SMT and melt layer thickness differs between sites, indicating that a single linear approximation cannot be employed to estimate SMT. Sensitivity analyses suggest that the annual temperature range, amount of annual precipitation, and firn albedo (which is a time‐invariant value in the model) significantly affect the relationship between SMT and melt layer thickness. This new method provides an alternative to existing approaches and yields an independent estimate of SMT from ice cores that have been affected by melting.

Previous reconstructions of summer temperatures from ice cores have relied on a statistical relationship between a melt layer and temperature observed at nearby stations. This study presents a novel method for reconstructing summer temperatures from melt layers in ice cores using an energy balance model that incorporates heat conduction and meltwater refreezing in the firn. We use the seasonal patterns in the ERA‐Interim reanalysis data set for an ice core site to calculate the amounts of refreezing water within the firn under various summer mean temperature (SMT) and annual precipitation conditions, and prepared calibration tables containing these three variables. We then estimate the SMTs from the refreezing amount and annual accumulation, both of which can be obtained from an ice core. We apply this method to four ice cores that were recovered from sites with different climates: two sites on the Greenland Ice Sheet, one in Alaska, and one in Russian Altai. The reconstructed SMTs show comparable variations with those of observed temperatures at nearby stations. The nonlinear relationship between SMT and melt layer thickness differs between sites, indicating that a single linear approximation cannot be employed to estimate SMT. Sensitivity analyses suggest that the annual temperature range, amount of annual precipitation, and firn albedo (which is a time‐invariant value in the model) significantly affect the relationship between SMT and melt layer thickness. This new method provides an alternative to existing approaches and yields an independent estimate of SMT from ice cores that have been affected by melting. Plain Language Summary: Melt layers in ice cores have been widely used as a proxy for summer temperatures. Previous studies established a statistical relationship between melt layer thickness and temperature observed at nearby stations and then applied it to the deeper part of the ice core. This study presents a novel method for reconstructing summer temperatures from the melt layer thickness in an ice core using an energy balance model that incorporates heat conduction and meltwater refreezing in the firn. We calculate the refreezing amounts within the firn under various summer mean temperature (SMT) and annual precipitation conditions, for which a reanalysis data set is systematically changed. We then estimate the SMTs from the refreezing amount (estimated from melt layer thickness) and annual accumulation, both of which can be obtained from an ice core. We apply this method to four ice cores recovered from different climatic sites. The reconstructed SMTs show comparable variations with those of observed temperatures at nearby stations. The relationship between SMT and melt layer thickness differs between sites, indicating that a single approximation cannot be employed to estimate SMT. This new method provides an alternative independent estimate of SMT from ice cores affected by melting. Key Points: A novel method to reconstruct summer temperatures from melt layers by a numerical model is developed and applied to four ice coresNonlinear relations between summer temperature and melt layer thickness suggest that a traditional linear approximation is not applicableRelation between summer temperature and melt layer thickness is affected by annual temperature range, annual precipitation and firn albedo [ABSTRACT FROM AUTHOR]

This study delves into the dynamic behavior of reactive grains within metalized propellants during surface deflagration. Our grain-scale simulations account for both fast and slow deflagration processes involving two distinct metal fuels, namely zirconium and magnesium, with potassium perchlorate (KClO 4) as the common oxidizer. Our primary goal is to develop a model and numerical technique capable of replicating the surface reactions observed in experiments. To achieve this, we utilize the compressible Navier–Stokes equations, incorporating the Arrhenius rate law and Johnson-Cook stress model. We pay particular attention to the melt layer, where surface burning occurs in an open atmosphere, and we develop a mechanism to describe the interaction between reactive grains and exhaust gases. We differentiate between two limiting scenarios: convective burning, where unreacted particles experience high-speed compression waves leading to reduced thermal diffusion within the cold reactant, and diffusive burning, characterized by insufficient pressure from particles undergoing both reaction and deformation to erode the burning surface. This results in pronounced agglomeration and the formation of gaseous metal oxides above the melt layer. The results shed light on critical factors influencing surface combustion, including the thermal softening of reactive particles, the time required for particle agglomerations, and tangential forces at multi-element interfaces within the grain-scale simulation domain. [ABSTRACT FROM AUTHOR]

Abstract: In the current paradigm, magma primarily exists in the crust as a crystalline mush containing distributed melt lenses. If a melt‐rich (or fluid) lens is less dense than the overlying mush, then Rayleigh‐Taylor (RT) instabilities will develop and could evolve into spheroids of ascending melt. Due to contrasting melt‐mush rheologies, the theoretical RT instability wavelength can be orders of magnitude larger than the magmatic system. We explored how this confinement affects the gravitational stability of melt lenses through laboratory experiments with pairs of liquids with one layer much thinner and up to 2.2·105 times less viscous than the other; we extended the viscosity ratio to 106 with linear stability analysis. We found the growth rate of a bounded RT instability is approximately ΔρgD 6 π μ 2, where Δρ is the difference in density between the fluids, g is gravity, D is the container diameter, and μ2 is the viscosity of the thicker viscous layer. This differs from the unbounded case, where the growth rate also depends on the thickness and viscosity of the thin, low‐viscosity layer. Applying the results to melt lenses in magmatic mushes, we find that for the ranges of expected rheologies, the timescales for development of the instability, and the volumes of packets of rising melt generated span very wide ranges. They are comparable with the frequencies and sizes of volcanic eruptions and episodes of unrest and so suggest that RT instabilities in mush systems can cause episodic volcanism. [ABSTRACT FROM AUTHOR]

Abstract: Warming in high‐elevation regions has societally important impacts on glacier mass balance, water resources, and sensitive alpine ecosystems, yet very few high‐elevation temperature records exist from the middle or high latitudes. While a variety of paleoproxy records provide critical temperature records from low elevations over recent centuries, melt layers preserved in alpine glaciers present an opportunity to develop calibrated, annually resolved temperature records from high elevations. Here we present a 400‐year temperature proxy record based on the melt layer stratigraphy of two ice cores collected from Mt. Hunter in Denali National Park in the central Alaska Range. The ice core record shows a sixtyfold increase in water equivalent total annual melt between the preindustrial period (before 1850 Common Era) and present day. We calibrate the melt record to summer temperatures based on weather station data from the ice core drill site and find that the increase in melt production represents a summer warming rate of at least 1.92 ± 0.31°C per century during the last 100 years, exceeding rates of temperature increase at most low‐elevation sites in Alaska. The Mt. Hunter melt layer record is significantly (p < 0.05) correlated with surface temperatures in the central tropical Pacific through a Rossby wave‐like pattern that enhances high temperatures over Alaska. Our results show that rapid alpine warming has taken place in the Alaska Range for at least a century and that conditions in the tropical oceans contribute to this warming. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate the anode erosion pattern caused by the blowing effect in constricted vacuum arcs under an axial magnetic field (AMF). The blowing effect was reflected from the microstructure of the melt layer on the anode. A pair of 42-mm-diameter AMF contacts were installed inside a detachable vacuum chamber. The contact material was CuCr25 (25% Cr). The arc modes were observed with a high-speed charge-coupled device video camera. The anode surface temperature after current zero was measured with a two-color pyrometer. The microstructure of the cross section of the anode surface melt layer was observed by scanning electron microscopy. The experimental arc currents increased from 10.5 to 17.8 kA (rms) with an interval of 2 kA. The results show that the anode erosion pattern in constricted arcs is caused by an interactive process of thermal and mechanical effects. The constricted arc columns melted the anode surface material and blew the molten material from the center to the peripheral region. The redistribution of the anode molten layer caused by this blowing effect formed two erosion regions on the anode surface. The depth of the melt layer in the central region was less than 100 \mu \textm , but in the peripheral region it was in the range of 100–400 \mu \textm . In these different erosion regions of the anode melt layer, there was considerable variation in both size and shape of the Cr sphere. Moreover, the thermal and mechanical effects of the constricted arc redistributed the Cr content of the molten layer on the anode surface. The Cr content in the central region (Erosion Region I) increased to 31% and in the periphery region (Erosion Region II) it decreased to 18%, respectively, from 25% before the experiments. [ABSTRACT FROM PUBLISHER]

Abstract: Seismic and mineral physics structures suggest melt can be generated at the top of the transition zone. Because the melt phase is significantly more compressible than the solid phase, it is expected that a density crossover occurs with increasing pressure. Experimental studies suggest this crossover lies towards the base of the upper mantle. If the density crossover lies above the 410 km discontinuity, melt will collect and form a layer until such time as it reaches the crossover when part of it may become unstable. We investigate the stability of a compressible melt layer which intersects the density crossover. Analytic models of instabilities are used to determine the effects of compressibility and crossover location on instability growth rates. We find that increasing the compressibility increases growth rates due to the fact that rising perturbations expand and become more unstable as they rise. If the density crossover lies above a melt layer at the transition zone, perturbations must be large before becoming unstable, making it likely that the layer would remain. However, when the density crossover lies within the melt layer, all perturbations are unstable and they drain the melt layer completely unless diapiric separation occurs. [Copyright &y& Elsevier]

A computational model is developed to study the effects of alumina layer formation on an ablative surface, when exposed to high temperature particle laden gas flow. The one-dimensional model is developed taking into consideration the thermal loading, particle loading and the temperature dependence of the thermo-physical properties of alumina. A fully implicit finite volume method is used to solve the coupled set of non-linear heat conduction equations. The solidification interface is tracked using the Lagrangian interpolation technique. The particle mass flux was found to be the major factor affecting the solid layer growth rate and the heat transferred to the ablative layer. The gas heat flux also has a major effect on the solid growth rate and the heat transferred to the ablative surface, but only for the lower particle mass fluxes. On the other hand the particle temperature has a linear effect on the solidification dynamics and the heat transferred to the ablative surface for all particle mass fluxes. The heat transferred to the ablative surface is reduced by approximately 40–90%, depending on the mass fluxes, due to the formation of the alumina layer. [Copyright &y& Elsevier]

A new form of material removal in laser ablation is explained. Long (up to 1 mm) nanofibers with a radius approximately 150–200 nm are obtained when a polymethylmethacrylate (PMMA) target is irradiated with a single pulse of a KrF excimer laser. The model suggests an expulsion of energetic droplets by an intense pressure of the plume to the exterior of the spot. For the transient melt of a polymeric viscous liquid resulting from UV laser excitation, such droplets provide the heads of the jets pulled from the melt bath, giving rise, after re-solidification, to nanofibers. The initial speed of fiber spinning is extremely high (840 m/s, maximum velocity) and unusual properties of the laser-produced nanofibers may be expected. [Copyright &y& Elsevier]

The paper is focused on the results of the experimental study of the influence of target inclination on metal (Al, Ti, W, SS) response, such as visible radiation flux on the target surface and melt layer behaviour, during high heat ( P irr ∼ 100 GW/m 2 ) plasma impacting relevant to plasma disruptions in ITER. The direct measurements of the visible (Δλ ≈ 400-700 nm) radiation flux on graphite and tungsten targets had shown that specific energy can be characterised by the level Q R ∼ 0.25 MJ/m 2 for ∼100 GW/m 2 plasma irradiation in the presence of 2-3 T magnetic field for both materials. The influence of target inclination on radiation characteristics is discussed. The inclination of the target also results in the appearance of a shift of the erosion imprint in two perpendicular directions. The possible mechanisms of it are discussed. Some results of the study of the melt layer structure for oblique irradiation are given and discussed. [ABSTRACT FROM AUTHOR]

Optimization of welding for thermoplastic parts strongly depends on the material properties, part design, as well as the welding operating technology conditions. Laser transmission welding requires preferential deposition of energy and subsequent melting of the material in the interfacial zone. This is optimized when the laser beam is transmitted through the transparent part and absorbed by the adjoining part to be welded. Energy deposition can be controlled to some extent by adjusting laser parameters (power, choice of beam focussing optics, sweep rate etc.).The thermoplastic material properties may have the greater influence and need to be characterized for optimum material selection. Commercial nylon type materials cover a large array of compositions, which may affect the welding process. To guide selection of nylon based plastics for a range of applications we have measured the influence of specific factors such as fiber-glass, mineral filler, impact modifier content, additives, and color versions on the Near InfraRed (NIR) transmission properties.In a following paper (Part II)a1 we have related these findings to the mechanical performance of shear and butt joints produced under various laser welding technology conditions (laser beam power, welding speed, laser beam/spot diameter, clamp pressure, plastic color, etc.). Comprehensive results of this evaluation will assist designers and technologists in thermoplastics selection for laser welding applications. The purpose of this report is to increase the understanding of the plastics engineering community regarding the usefulness and possible applicability of laser transmission welding (LTW) technology for nylon made components. [ABSTRACT FROM PUBLISHER]

An important parameter controlling the mobility of melt layer in laser ablation of polymers is the viscosity. We report the first experiments to measure it at the extreme conditions of ultraviolet (UV) KrF laser ablation for poly(ethylene terephthalate) (PET). The volume of laser-induced bumps (re-solidified molten material expelled from the irradiated area to its periphery) is measured with AFM microscopy. The comparison of this value with an analytical modelling (based on the solution of Navier–Stokes equations for viscous melt flow induced by the gradient of ablation plume pressure with the use of experimentally measured melt depth) allows to calculate the kinematic viscosity of laser melt layer on the polymer surface. It appears to be about an order of magnitude greater than the kinematic viscosity of water at room temperature. [Copyright &y& Elsevier]