Surface Melting Research Articles

Cold‐cap structure in a slurry‐fed electric melter

AbstractAs glass batch is charged into an electric melter, a cold cap forms on the glass melt surface. Heat transfer to the cold cap from the molten glass below and the melter atmosphere above determines the melting rate. A mathematical model of the cold cap and the experimental kinetic data of the feed‐to‐glass conversion that were collected for several simulated low‐activity and high‐level waste melter feeds allowed us to develop relationships between the internal structure of the cold cap, its properties, its thickness, and the internal heat transfer. This contribution shows the distribution of major crystalline phases and the cumulative evolution of gases within the cold cap. It also examines the temperature, conversion degree, and heating rate the melter feed is experiencing during the passage through the cold cap and their effects on the cold‐cap bottom temperature and morphology, which are important for the computational fluid dynamics simulations of melters.

SE‐Dome II Ice Core Dating With Half‐Year Precision: Increasing Melting Events From 1799 to 2020 in Southeastern Greenland

AbstractArctic 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.

The effect of Nd:YAG laser parameters on the microstructure, hot cracking susceptibility and elemental evaporation of surface melted AZ80 magnesium-based alloy

Laser surface melting (LSM) is an environmentally-safe technique in which melting and solidification occur in a very short reaction time, without affecting the bulk of the material. On the other hand, today, the use of magnesium as a very light metal, with excellent specific resistance, excellent sound damping and good casting ability, etc., has been expanded. Also, having low absorption of laser beams, strong tendency to oxidation, high thermal conductivity, etc are important drawbacks of these alloys. Today there is widespread agreement on the better resistance to hot cracking of magnesium alloys with Nd:YAG laser due to its shorter wavelength by comparison with CO2 laser. This research aims to investigate the effect of Nd:YAG laser surface melting parameters on the microstructural, phase changes and hot cracking susceptibility of the AZ80 magnesium base alloy. The results of current research showed that sample 5 with voltage, frequency, pulse duration and gas flow rate of 250V, 10 Hz, 4 ms, 5lit/min, respectively, and constant speed of 1 mms showed a remelted zone with minimum hot cracks and other defects. In conclusion by controlling the laser parameters such as pulse duration, shielding gas flow rate, laser frequency, scanning rate and the laser power, the susceptibility to hot cracking including both solidification and liquation cracking are significantly decreased.

Enhancement of cell attachment on Ti6Al4V via surface modifications using pulsed laser surface melting

The surface topography of biomedical implants made of Ti6Al4V significantly impacts cell attachment. This work aims to modify the surface topography of the Ti6Al4V surface using pulse laser surface melting (pLSM) to enhance fibroblast cell attachment. In pLSM, short laser pulses irradiate the surface resulting in localised melting and creating new features upon resolidification. Thus, surfaces are modified without the addition or removal of material. The effect of laser pulse duration and hatch spacing on the attachment of NIH3T3 fibroblast cells is examined in this study. The cells were cultured on the pLSM-textured surfaces and two control surfaces, viz., as-received and manually polished, and the results were studied after 24 h of cell culture using fluorescence microscopy. pLSM-textured surfaces showed improved cell attachment compared to the control surfaces. The surface textured with a 10 μs pulse duration and 75 % hatch spacing showed 395 % and 91 % improvement in attached cell density compared to the as-received surface and manually polished surface, respectively, because the induced feature size was comparable to the size of NIH3T3 fibroblast cells. Additionally, the periodic textures developed by pLSM resulted in a homogenous distribution of the cells across the area.

Sensitivity of the MAR regional climate model snowpack to the parameterization of the assimilation of satellite-derived wet-snow masks on the Antarctic Peninsula

Abstract. Both regional climate models (RCMs) and remote sensing (RS) data are essential tools in understanding the response of polar regions to climate change. RCMs can simulate how certain climate variables, such as surface melt, runoff and snowfall, are likely to change in response to different climate scenarios but are subject to biases and errors. RS data can assist in reducing and quantifying model uncertainties by providing indirect observations of the modeled variables on the present climate. In this work, we improve on an existing scheme to assimilate RS wet snow occurrence data with the “Modèle Atmosphérique Régional” (MAR) RCM and investigate the sensitivity of the RCM to the parameters of the scheme. The assimilation is performed by nudging the MAR snowpack temperature to match the presence of liquid water observed by satellites. The sensitivity of the assimilation method is tested by modifying parameters such as the depth to which the MAR snowpack is warmed or cooled, the quantity of water required to qualify a MAR pixel as “wet” (0.1 % or 0.2 % of the snowpack mass being water), and assimilating different RS datasets. Data assimilation is carried out on the Antarctic Peninsula for the 2019–2021 period. The results show an increase in meltwater production (+66.7 % on average, or +95 Gt), along with a small decrease in surface mass balance (SMB) (−4.5 % on average, or −20 Gt) for the 2019–2020 melt season after assimilation. The model is sensitive to the tested parameters, albeit with varying orders of magnitude. The prescribed warming depth has a larger impact on the resulting surface melt production than the liquid water content (LWC) threshold due to strong refreezing occurring within the top layers of the snowpack. The values tested for the LWC threshold are lower than the LWC for typical melt days (approximately 1.2 %) and impact results mainly at the beginning and end of the melting period. The assimilation method will allow for the estimation of uncertainty in MAR meltwater production and will enable the identification of potential issues in modeling near-surface snowpack processes, paving the way for more accurate simulations of snow processes in model projections.

Preparation of Rechargeable Antibacterial Polypropylene/N-Halamine Materials Based on Melt Blending and Surface Segregation.

Polypropylene (PP) has been widely used in health care and food packaging fields, however, it lacks antibacterial properties. Herein, we prepared the polymeric antibacterial agents (MPP-NDAM) by an in situ amidation reaction between 2,4-diamino-6-dialkylamino-1,3,5-triazine (NDAM) and maleic anhydride grafted polypropylene (MPP) using the melt grafting method. The effects of reaction time and monomer content on the grafting degree of N-halamine were investigated, and a grafting degree of 4.86 wt % was achieved under the optimal reaction conditions. PP/MPP-NDAM composites were further obtained by a melt blending process between PP and MPP-NDAM. With the adoption of surface segregation technology, the content of N-halamine structure on the surface of PP/MPP-NDAM composites was significantly increased. The antibacterial tests showed that the PP/MPP-NDAM composite could achieve 99.9% bactericidal activity against 1.0 × 107 CFU/mL of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) within 10 and 5 min of contact, respectively. The antibacterial effect became more pronounced with the prolongation of chlorinated time, and it could achieve 99.9% bactericidal activity against E. coli within merely 1 min of contact.

Role of 26Al and impact-generated atmosphere in the early thermal evolution, differentiation, and volatile-rich core of Mars

The InSight mission's high-quality seismic data and cosmochemical models have demonstrated that Mars has a volatile-rich core. It is proposed that Mars formed early, before the solar nebular gas dispersed, and/or it accreted volatile-rich material to account for its volatile-rich interior. The early accreted Mars must have gravitationally attracted proto-atmosphere from the surrounding solar nebula. If its building blocks were rich in volatiles, it might have acquired impact-generated atmosphere during accretion. By considering the decay energy of the short-lived radionuclide (SLR) 26Al and the blanketing effect of the primordial and impact-generated atmosphere during the initial 10 Ma of the formation of the solar system, we present the results of numerical simulations carried out for the early thermal evolution and core formation of Mars. To explain the formation of a large iron core of Mars as suggested by the seismometer of InSight mission, we considered the 60% EH- and 40% CI-chondrite composition for the building blocks of Mars. The blanketing effect of impact generated H2O + CO2+CO + H2 atmosphere caused the melting of surface silicates to form magma ocean at surface. We thoroughly examined the effects of several variables on the timing of complete core formation, including the initial water content in the accreted material, timescale of onset of accretion after the formation of CAIs, duration of accretion, absorption coefficient of CO2, efficiency of degassing of volatiles, and melting temperature. The results of present study show that the decay energy of SLR 26Al caused the widespread heating and melting of interior of Mars. For complete core formation, Mars must accrete within the first ∼2 Ma in order to explain the volatile-rich core. Further, the timescales of core formation were found to be strongly dependent on the assumed melting curve. For longer timescales of accretion, the interior of Mars experienced incomplete differentiation even by assuming high water content in the accreted material and larger absorption coefficient for CO2. However, Mars does not have to accrete within 2 Ma for the core to fully develop if the Rayleigh- Taylor (RT) instability is present in the dense metallic layer on top of the undifferentiated interior. A short accretion time is only valid if RT-instability is neglected. Hence, we expect that the volatiles in the magma ocean could also be transferred to core by Rayleigh-Taylor instability. We also parameterized the thermal influence of gravitational heat produced during the differentiation of Mars to study its influence on the thermal evolution of the planet. The outcomes of the present work have implications to explain the timing of partition of volatiles in the Martian interior and formation of an early atmosphere on Mars.

A Surface Radiation Balance Dataset from Siple Dome in West Antarctica for Atmospheric and Climate Model Evaluation

Abstract A field campaign at Siple Dome in West Antarctica during the austral summer 2019/20 offers an opportunity to evaluate climate model performance, particularly cloud microphysical simulation. Over Antarctic ice sheets and ice shelves, clouds are a major regulator of the surface energy balance, and in the warm season their presence occasionally induces surface melt that can gradually weaken an ice shelf structure. This dataset from Siple Dome, obtained using transportable and solar-powered equipment, includes surface energy balance measurements, meteorology, and cloud remote sensing. To demonstrate how these data can be used to evaluate model performance, comparisons are made with meteorological reanalysis known to give generally good performance over Antarctica (ERA5). Surface albedo measurements show expected variability with observed cloud amount, and can be used to evaluate a model’s snowpack parameterization. One case study discussed involves a squall with northerly winds, during which ERA5 fails to produce cloud cover throughout one of the days. A second case study illustrates how shortwave spectroradiometer measurements that encompass the 1.6-μm atmospheric window reveal cloud phase transitions associated with cloud life cycle. Here, continuously precipitating mixed-phase clouds become mainly liquid water clouds from local morning through the afternoon, not reproduced by ERA5. We challenge researchers to run their various regional or global models in a manner that has the large-scale meteorology follow the conditions of this field campaign, compare cloud and radiation simulations with this Siple Dome dataset, and potentially investigate why cloud microphysical simulations or other model components might produce discrepancies with these observations. significance statement Antarctica is a critical region for understanding climate change and sea level rise, as the great ice sheets and the ice shelves are subject to increasing risk as global climate warms. Climate models have difficulties over Antarctica, particularly with simulation of cloud properties that regulate snow surface melting or refreezing. Atmospheric and climate-related field work has significant challenges in the Antarctic, due to the small number of research stations that can support state-of-the-art equipment. Here we present new data from a suite of transportable and solar-powered instruments that can be deployed to remote Antarctic sites, including regions where ice shelves are most at risk, and we demonstrate how key components of climate model simulations can be evaluated against these data.

The June 2022 extreme warm event in central West Antarctica

AbstractThe Antarctic surface mass balance has been shown to be sensitive to the impacts of atmospheric rivers (ARs), which bring anomalous amounts of both moisture and heat from lower latitudes poleward. Therefore, describing the characteristics of ARs and their intensity and frequency in the Antarctic regions by applying detection algorithms became a key method to evaluating their impacts on the surface mass balance and melting events. Several intense AR events have influenced Antarctica during the year 2022, and here we report an event with a peak on 10 June 2022 that was detected at 84°S, having a potential impact on West Antarctica. The extreme warm event originated in the Southern Pacific subtropical region and evolved towards the Southern Ocean, crossing the northern Antarctic Peninsula, before reaching as far as most inland regions in Antarctica, different from other typical ARs that are mostly restricted to the continental coast.

Improvement of the wear resistance of 20CrMnTi steel gear by discrete laser surface melting

This paper studied the effect of discrete laser surface melting on the wear resistance of gears. The radial ribs on the surface of intertidal shellfish had the function of anti-abrasion. The discrete laser surface melted (DLSMed) units were processed on the gear surface, and they looked like radial ribs.The microstructure and wear morphology of the DLSMed unit were observed under a scanning electron microscope. The phase composition and residual stress of the DLSMed unit were analyzed through a X-ray diffractometer. The hardness of the DLSMed unit was measured with a microhardness tester. The roughness of the DLSMed unit was measured with a surface topography meter. The wear test of gear was carried out with a Forschungsstelle für Zahnräder und Getriebebau (FZG) testing machine. The lubricating oil analysis technology was used as the evaluation basis of gear wear performance. The experimental results showed that discrete laser surface melting could refine the grain on the gear surface, improve the hardness of the gear, and form residual compressive stress on the gear surface. The cross-sectional area of the DLSMed unit gradually decreased as the laser scanning speed increased. As the cross-sectional area of the DLSMed unit decreased, the wear resistance of the gear also deteriorated. Finally, the wear mechanism of the DLSMed gear was discussed from many aspects.

Streamflow Composition and Water “Imbalance” in the Northern Himalayas

AbstractThe Yarlung Zangbo River (YZR) is the largest river in the northern Himalayas, providing crucial water resources for downstream. A full understanding of the streamflow dynamics and regional water budget is critical to secure water security of the Himalayan water tower. Here we establish a comprehensive hydrological model to simulate the precipitation‐runoff‐evapotranspiration‐groundwater‐streamflow complex in the YZR basin. We decipher contributions of different water sources (e.g., precipitation, meltwater, groundwater) to YZR's streamflow and estimate that groundwater sustains ∼36% of annual streamflow in the YZR, while precipitation and melt surface runoff contribute 40% and 24%, respectively. Combining modeling, observation and reanalysis data, our results reveal a water “imbalance” that ∼31% of annual precipitation and meltwater (∼333 mm yr−1 or ∼85 km3 yr−1) is unaccounted for in the YZR basin. We propose that the “excess water” discharges to deep fractured bedrock aquifers, which is promoted by widespread permeable active structures (e.g., faults, fractures). This hypothesis is supported by groundwater storage (GWS) estimates where inclusion of the deep groundwater bridges the discrepancy between baseflow‐derived (shallow) GWS and those derived from the Gravity Recovery and Climate Experiment satellite data. The deep groundwater most likely flows across basins, bypasses streams, and finally discharges to downstream aquifers in the Indo‐Gangetic Plain as mountain block recharge. This study not only provides a comprehensive analysis of the streamflow composition in the YZR, but also contributes to shaping a more complete picture of the functionality of the Himalayan water tower, highlighting the importance of groundwater in regional water transfers.

Glacier melt detection at different sites of Greenland ice sheet using dual-polarized Sentinel-1 images

ABSTRACT Synectic Aperture Radar (SAR) backscatter coefficient is sensitive to glacier surface physical characteristic changes, including the states of melting and refreezing, but it is also sensitive to incidence angle variation. This study explores the capability of monitoring Greenland Ice Sheet (GrIS) melting status with Sentinel-1 dual-polarized images by referring to Automatic Weather Station (AWS) records. Sentinel-1 SAR images at five coastal regions of the GrIS are obtained from 2017 to 2021. The backscatter coefficients are normalized to an incidence angle of 30° with an empirical model. Time series of five backscatter coefficients profiles covering AWS illustrates different patterns of the ice surface dielectric constant dynamics in different elevations. The wet snow radar zone shows clear backscatter coefficients decreasing during the melting seasons, but the bare ice radar zone behaves more complexly during the melting seasons. The numbers of melting days at different elevations are also derived for each profile based on −3 dB backscatter coefficient decrease of HH and/or HV polarization, showing the heterogeneous ablation processes over the GrIS. The daily maximum 2 m air temperature on two consecutive days (before and on the SAR acquisition day) exceeds 0°C, and the daily average 2 m air temperature exceeds −0.5°C on the SAR acquisition day that was recorded by the AWS finds good agreements with the −3 dB decrease of the backscatter coefficients, suggesting the GrIS surface melting can be well captured by dual-polarized Sentinel-1 C-band SAR images. The overall agreement and Kappa coefficients are mostly better than 0.85 and 0.70, respectively, for HH images and 0.80 and 0.60, respectively, for HV images, suggesting a better performance of the co-polarized image. High temporal resolution and wide-swath SAR sequence imagery provide suitable data sources for monitoring glacier surface melting-refreezing stats; further analysis is requested to quantitatively link the volume of melting with backscatter coefficient and other SAR data sources.

Comparing elevation and backscatter retrievals from CryoSat-2 and ICESat-2 over Arctic summer sea ice

Abstract. The CryoSat-2 radar altimeter and ICESat-2 laser altimeter can provide complementary measurements of the freeboard and thickness of Arctic sea ice. However, both sensors face significant challenges for accurately measuring the ice freeboard when the sea ice is melting in summer months. Here, we used crossover points between CryoSat-2 and ICESat-2 to compare elevation retrievals over summer sea ice between 2018–2021. We focused on the electromagnetic (EM) bias documented in CryoSat-2 measurements, associated with surface melt ponds over summer sea ice which cause the radar altimeter to underestimate elevation. The laser altimeter of ICESat-2 is not susceptible to this bias but has other biases associated with melt ponds. So, we compared the elevation difference and reflectance statistics between the two satellites. We found that CryoSat-2 underestimated elevation compared to ICESat-2 by a median difference of 2.4 cm and by a median absolute deviation of 5.3 cm, while the differences between individual ICESat-2 beams and CryoSat-2 ranged between 1–3.5 cm. Spatial and temporal patterns of the bias were compared to surface roughness information derived from the ICESat-2 elevation data, the ICESat-2 photon rate (surface reflectivity), the CryoSat-2 backscatter, and the melt pond fraction derived from Sentinel-3 Ocean and Land Color Instrument (OLCI) data. We found good agreement between theoretical predictions of the CryoSat-2 EM melt pond bias and our new observations; however, at typical roughness <0.1 m the experimentally measured bias was larger (5–10 cm) compared to biases resulting from the theoretical simulations (0–5 cm). This intercomparison will be valuable for interpreting and improving the summer sea ice freeboard retrievals from both altimeters.

Laser fusion cutting: The missing link between gas dynamics and cut edge topography

In laser cutting, the fundamental role of the gas flow for melt removal and kerf formation is generally accepted. Beyond this vague understanding, however, the underlying physical mechanisms are not yet fully understood. In particular, detailed data concerning the momentum and heat transfer between the gas and melt have seldom been reported. This study addresses the local interactions between the cutting gas and kerf surface (melt film surface) in a fundamental way based on a combined experimental, theoretical, and numerical approach. Typical solid-state laser cut edges are analyzed considering the characteristic surface structures and the basic influences of the gas flow on the global and local melt movement. Here, apparent structures in the micrometer range indicate the effect of vortical gas structures close to the wall. Theoretical investigation of the gas boundary layer is conducted by semiempirical equations and the transfer of basic results from the boundary layer theory. It is shown that the boundary layer is in transition between the laminar and turbulent flow, and local flow separations and shock-boundary layer interactions primarily induce spatially periodic and quasistationary instability modes. An improved numerical model of the cutting gas flow confirms the theoretical results and exhibits good agreement with experimental cut edges, reproducing relevant instability modes and quantifying the local momentum and heat transfer distributions between the gas and melt. With the knowledge gained about the underlying physical mechanisms, promising approaches for improvements of the fusion cutting performance are proposed.

Coagulation studies on photodegraded and photocatalytically degraded polystyrene microplastics using polyaluminium chloride

Microplastics are ubiquitous persistent emerging contaminants, and its presence has been detected even in the most pristine and fragile ecosystems. Advanced oxidation processes are one of the novel degradation technologies used for the elimination of microplastics from the environment. In this study, the effect of ultraviolet C (UV-C, 253.7 nm) and ultraviolet A (UV-A, 365 nm) irradiations on polystyrene (PS) microplastic properties in the presence and absence of titanium dioxide were studied along with their coagulation performances using polyaluminium chloride (PAC). The effects of solar irradiation on the chemical properties of microplastics in aqueous and dry conditions were also investigated. PS microplastics (1.5 g) in three size ranges, 300–150 μm, 150–75 μm, and <75 μm were used during this experiment. After 45 days of irradiation, samples showed discolouration, brittleness, and loss of hydrophobicity. Images obtained from scanning electron microscope revealed smoothening and melting of PS surfaces upon UV exposure. Attenuated total reflectance- Fourier transform infrared spectroscopy and X-ray photon spectroscopy of photoaged samples revealed chemical alterations, bond cleavage and formation of oxygenated functional groups on microplastic surfaces. PAC coagulation of samples before and after UV irradiation showed drastic differences in removal efficiencies, with UV-C irradiated microplastics exhibiting maximum efficiency. Large sized and photocatalytically degraded microplastics showed better removal efficiencies than small sized particles. The 300–150 μm sized PS microplastic, degraded photo catalytically under UV-C irradiation showed approximately 99 % removal efficiency, while PS < 75 μm photodegraded under UV-A irradiation showed only 74.2 % removal efficiency.

A Comprehensive Review of Ultrahigh Molecular Weight Polyethylene Fibers for Applications Based on Their Different Preparation Techniques

Ultrahigh molecular weight polyethylene (UHMWPE) fiber is widely recognized for its exceptional properties, including high strength-to-weight ratio, toughness, and chemical resistance, making it a preferred material for reinforcement in various applications. However, its low melting point, surface inertness, and weak adhesion to polymer matrices have limited its potential use in some fields. Researchers have addressed these shortcomings by focusing on surface modifications through physical treatment or chemical coating, thereby enhancing the versatility of materials in numerous UHMWPE fiber composites. By improving the tribological and interfacial properties of UHMWPE, various applications can be explored, including prosthetic joints, energy-absorbing road safety systems, microelectromechanical system devices, and protective materials for defense and personal thermal management. This review provides a comprehensive overview of the remarkable performance of UHMWPE and its composites, providing insights into its wide array of applications.

Understanding the formation of “false friends” (hidden lack of fusion defects) in laser beam welding by means of high-speed synchrotron X-ray imaging

This paper provides a fundamental understanding of “false friend” formation, i.e., hidden defects associated with lack of fusion, using an experimental setup that allowed an insight into the processing zone based on high-speed synchrotron X-ray imaging. The setup enabled the welding of a lap joint of AISI 304 high-alloy steel sheets (X5CrNi18-10/1.4301), with the ability to adjust different gap heights between top and bottom sheet (up to 0.20 mm) and to acquire high-speed X-ray images at 100 kHz simultaneously with the welding process. On this basis, a time-resolved description of the “false friend” formation can be provided by visualizing the interaction between keyhole and melt pool during laser welding and solidification processes within the gap area. The bridgeability of the gap was limited due to the gap height and insufficient melt supply leading to the solidification of the bridge. The distance between the solidified bridge and the keyhole increased with time, while the keyhole and melt pool dynamics initiated the formation of new melt bridges whose stability was defined by melt flow conditions, surface tension, and gap heights. The alternating formation and solidification of melt bridges resulted in entrapped areas of lacking fusion within the weld, i.e., “false friends.” Finally, based on the results of this study, a model concept is presented that concludes the main mechanisms of “false friend” formation.

Modeling of surface energy balance for Icelandic glaciers using remote-sensing albedo

Abstract. During the melt season, absorbed solar energy, modulated at the surface by albedo, is one of the main governing factors controlling surface melt variability for glaciers in Iceland. An energy balance model was applied with the possibility of utilizing spatiotemporal Moderate Resolution Imaging Spectroradiometer (MODIS) satellite-derived daily surface albedo driven by high-resolution climate forcing data to reconstruct the surface energy balance (SEB) for all Icelandic glaciers for the period 2000–2021. The SEB was reconstructed from April through September for 2000–2021 at a daily time step with a 500 m spatial resolution. Validation was performed using observations from various glaciers spanning distinct locations and elevations with good visual and statistical agreement. The results show that spatiotemporal patterns for the melt season have high annual and interannual variability for Icelandic glaciers. The variability was influenced by high climate variability, deposition of light-absorbing particles (LAPs) from volcanic eruptions and dust hotspots in pro-glacial areas close to the glaciers. Impacts of LAPs can lead to significant melt enhancement due to lowering of albedo and increased short-wave radiative energy forced at the surface. Large impacts on the SEB were observed for years with high LAP deposits, such as the volcanic eruption years of 2004, 2010 and 2011 and the sand- and dust-rich year of 2019. The impacts of volcanic eruptions and other LAP events were estimated using historical mean albedo under the same climatology forcing to provide estimations of melt energy enhancements. The impact of LAPs was often significant even though the glaciers were far away from the eruption location. On average, the melt enhancements due to LAPs were ∼27 % in 2010, ∼16 % in 2011 and ∼14 % in 2019 for Vatnajökull, Hofsjökull and Langjökull.

Atmospheric drivers of melt-related ice speed-up events on the Russell Glacier in southwest Greenland

Abstract. The Greenland Ice Sheet is a major contributor to current and projected sea level rise in the warming climate. However, uncertainties in Greenland's contribution to future sea level rise remain, partly due to challenges in constraining the role of ice dynamics. Transient ice accelerations, or ice speed-up events, lasting from 1 d to 1 week, have the potential to indirectly affect the mass budget of the ice sheet. They are triggered by an overload of the subglacial drainage system due to an increase in water supply. In this study, we identify melt-induced ice speed-up events at the Russell Glacier, southwest Greenland, in order to analyse synoptic patterns driving these events. The short-term speed-up events are identified from daily ice velocity time series collected from six GPS stations along the glacier for each summer (May–October) from 2009 to 2012. In total, 45 ice speed-up events are identified, of which we focus on the 36 melt-induced events, where melt is derived from two in situ observational datasets and one regional climate model forced by ERA5 reanalysis. We identify two additional potential water sources, namely lake drainages and extreme rainfall, which occur during 14 and 4 out of the 36 melt-induced events, respectively. The 36 melt-induced speed-up events occur during synoptic patterns that can be grouped into three main clusters: (1) patterns that resemble atmospheric rivers with a landfall in southwest Greenland, (2) patterns with anticyclonic blocking centred over southwest Greenland, and (3) patterns that show low-pressure systems centred either south or southeast of Greenland. Out of these clusters, the one resembling atmospheric river patterns is linked to the strongest speed-up events induced by 2 to 3 d continuously increasing surface melt driven by anomalously high sensible heat flux and incoming longwave radiation. In the other two clusters, the net shortwave radiation dominates the contribution to the melt energy. As the frequency and intensity of these weather patterns may change in the warming climate, so may the frequency and intensity of ice speed-up events, ultimately altering the mass loss of the ice sheet.

Entropy analysis of Cu-Al2O3 based hybrid and Cu based mono nanofluid flows through porous medium: A comparative study

The motive of this research article, is to present a comparative study of entropy generation for a system of MHD mixed convection non-Darcy porous medium flow of mono and hybrid nanofluids over a melting surface. Darcy–Forchheimer model for the flow through porous medium is employed to formulate the problem under consideration. The dimensional momentum and heat equations governing the flow are transformed into a non-dimensional ODEs with the help of similarity variables. The similarity solution of the dimensionless differential equation is computed with the MATLAB’s bvp4c package. The influence of various embedded parameters on the flow fields and entropy generation are examined. The study reveals that the entropy generation in Cu−Al2O3 water based hybrid nanofluid is smaller compared to that of Cu-water based mono nanofluid. The findings of the study have bearing in the fields involving oil flow filtration, crude oil production, electronic cooling equipment etc.