Single Ice Research Articles

Charged Ice Particle Beams with Selected Narrow Mass and Kinetic Energy Distributions.

Small ice particles play an important role in atmospheric and extraterrestrial chemistry. Circumplanetary ice particles that are encountered by space probes at hypervelocities play a critical role in the determination of surface and subsurface properties of their source bodies. Here we present an apparatus for the generation of low-intensity beams of single mass-selected charged ice particles under vacuum. They are produced via electrospray ionization of water at atmospheric pressure and undergo evaporative cooling when transferred to vacuum through an atmospheric vacuum interface. m/z selection is achieved through two subsequent quadrupole mass filters operated in the variable-frequency mode within a range of m/z values between 8 × 104 and 3 × 107. Velocity and charge of the selected particles are measured using a nondestructive single-pass image charge detector. From the known electrostatic acceleration potentials and settings of the quadrupoles the particle masses could be obtained and be accurately controlled. It has been shown that the droplets are frozen within the transit time of the apparatus such that ice particles are present after the quadrupole stages and finally detected. The demonstrated correspondence between particle mass and specific quadrupole potentials in this device allows preparation of beams of single particles with a repetition rate between 0.1 and 1 Hz with various diameter distributions from 50 to 1000 nm at 30-250 eV of kinetic energy per charge. This corresponds to velocities and particle masses quickly available between 600 m/s (80 nm) and 50 m/s (900 nm) and particle charge numbers (positive) between 103 and 104[e], depending upon size.

High Molecular Weight Polyproline as a Potential Biosourced Ice Growth Inhibitor: Synthesis, Ice Recrystallization Inhibition, and Specific Ice Face Binding.

Ice-binding proteins (IBPs) from extremophile organisms can modulate ice formation and growth. There are many (bio)technological applications of IBPs, from cryopreservation to mitigating freeze-thaw damage in concrete to frozen food texture modifiers. Extraction or expression of IBPs can be challenging to scale up, and hence polymeric biomimetics have emerged. It is, however, desirable to use biosourced monomers and heteroatom-containing backbones in polymers for in vivo or environmental applications to allow degradation. Here we investigate high molecular weight polyproline as an ice recrystallization inhibitor (IRI). Low molecular weight polyproline is known to be a weak IRI. Its activity is hypothesized to be due to the unique PPI helix it adopts, but it has not been thoroughly investigated. Here an open-to-air aqueous N-carboxyanhydride polymerization is employed to obtain polyproline with molecular weights of up to 50000 g mol-1. These polymers were found to have IRI activity down to 5 mg mL-1, unlike a control peptide of polysarcosine, which did not inhibit all ice growth at up to 40 mg mL-1. The polyprolines exhibited lower critical solution temperature behavior and assembly/aggregation observed at room temperature, which may contribute to its activity. Single ice crystal assays with polyproline led to faceting, consistent with specific ice-face binding. This work shows that non-vinyl-based polymers can be designed to inhibit ice recrystallization and may offer a more sustainable or environmentally acceptable, while synthetically scalable, route to large-scale applications.

New metrics reveal the evolutionary continuum behind the morphological diversity of subglacial bedforms

Understanding the formation of subglacial bedforms is primordial to constrain ice-meltwater-bed interactions and the dynamics of past and present ice sheets. However, the difficulty to observe active subglacial bedforms below present-day ice sheets implies that their formation and evolution are essentially deduced from the inversion of morphological and sedimentological data from palaeo-subglacial bedforms. In this study, the morphological characteristics of subglacial bedforms are explored with a new approach based on the combination of three dimensionless morphometric indices i.e., circularity index, sinuosity index and elongation component ratio. We measure the spatial distribution of these indices on an unpublished database composed of ~13,500 digitized bedforms taken from two selected portions of the Irish Ice Sheet and Laurentide Ice Sheet beds considering that (1) all subglacial bedforms in each region were formed under a single ice flow configuration and (2) the bedforms may have developed either orthogonal, parallel, or oblique to ice displacement directions. Our results reveal a morphometric and spatial continuum along which ribbed bedforms of various lengths and shapes – ranging from circular to elongated flow-transverse forms – are incipient bedforms that can evolve into transitional sinuous ribbed bedforms, then into predominantly flow-parallel sinuous bedforms that progressively realign to form streamlined bedforms. Assuming the glaciological contexts of selected study areas, this continuum may provide a new geomorphic criterion to constrain spatial variations in subglacial conditions (e.g. ice flow velocity, bedrock characteristics, meltwater pressure).

Converting Combustion Engines to Electric Cars: Requirement, Perception, and Viability in Under-Developed Countries

Despite barely being a novel concept, EVs have been rising in popularity because of the development of the technology and infrastructure required to support EVs on a large scale, a growing concern for the climate, and a fight to lower carbon emissions. Even though the demand for EVs rising every year, there have been a few major roadblocks that are affecting the growth and development of EVs in developing countries and households with lower incomes, specifically the high initial cost of building the infrastructure of EVs, EVs being more expensive than regular Internal Combustion Engine cars, and a skeptical consumer market. However, making conversions of ICEs into EVs or Plug-in Hybrid EVs (PHEVs) might circumvent many of these issues, including combating the problem of replacing every single ICE with a brand-new EV in the span of a few decades. This paper discusses the cost, efficiency, and public perception of converting ICEs to EVs and what a viable business model can look like while paying particular attention to customer needs and public perception.

Anisotropy of the friction forces of rest and sliding frictionof single crystals of ice

The properties of the ice of natural reservoirs are due to its crystalline structure. The dependence of the mechanical and strength characteristics of single ice crystals on the angle between the direction of application of force to a single crystal and the direction of its C-axis is known. Basically, this dependence is due to the possibility of the base plates of a single crystal of ice sliding relative to each other. In physics, in addition to the mechanical and strength characteristics of a solid, the properties of the surfaces of a solid state, manifested in the process of friction, are of great importance. The friction of two single crystals of ice relative to each other has been investigated in experiments on rest friction and sliding friction. From an artificially grown plate of a single ice crystal, samples of single crystals of ice with a certain orientation of the C-axis were made for the experiment. The measurement of the rest friction coefficient of a single ice crystal was realized according to the classical scheme of recording the minimum angle at which the single crystal began to roll down an inclined surface. The dependence of the rest friction coefficient of ice single crystals on the mutual orientation of the C-axes of single crystals relative to each other was discovered. The coefficients of rest friction in the case that the C-axes of single ice crystals are parallel to each other significantly exceed those obtained when the C-axes of single ice crystals are perpendicular to each other. Measurements have shown that the anisotropy of sliding friction increases with increasing initial velocity of the single crystal on the surface of the second single crystal. This is explained by the fact that with the growth of the path traveled by the M2 crystal, the time of interaction of single crystals of ice also increases, during which the properties of the anisotropy of single crystals of ice relative to sliding friction are manifested. Studies have shown the presence of anisotropy of the friction forces of rest and friction of sliding of a pair of single crystals of ice.

Growth Mechanism of Ice Lens in Saturated Clay Considering Surface Charge

The main purpose of this study is to reveal the growth mechanism of ice lens in saturated clay. The deformation and fracturing of clay skeletons caused by ice crystal growth during the freezing process are gradually discussed, and a theoretical model for the whole process of ice lens growth considering the surface charge is proposed. Firstly, the electrical properties of clay surfaces and the pore structure characteristics of frozen clay are introduced, and the stress of pore walls during the growth of single pore ice crystals is calculated. Secondly, the values of parameters in the theoretical formula of separation pressure between adjacent clay particles are given when considering the linear elasticity of clay. Finally, the formation mechanism of the new lens is described, and the crack growth velocity equation is given. This paper shows that: there is a good consistency between the soil tensile strength of the macroscopic dimension and the intergranular separation pressure of the molecular dimension in judging the production conditions of the new lens; the formation of the new ice lens is the result of the destruction of the pore structure and the propagation of cracks caused by the growth of ice crystals, and more pore freezing can be caused only when the infiltration path of the ice crystals is formed in the pore structure. In order to verify the model, the ultimate compressive strength of soil calculated in this study was compared with the existing test results, and the rationality and correctness of the model are discussed. This study is of great significance to accurately understand the frost heave process.

Dynamic simulation of aircraft electro-impulse de-icing using bond-based peridynamics

Electro-impulse de-icing is a lightweight type of mechanical de-icing system that consumes little energy, provides high reliability, and offers wide application prospects. In this study, the bond-based peridynamics theory was used to simulate the dynamic damage process and evolution law of aircraft electro-impulse de-icing. The ice layer was simplified as a brittle material that satisfies the linear elastic constitutive relation. A numerical analysis model of the ice layer, aircraft skin substrate, and their interface was established to simulate the dynamic responses under a high strain rate. Considering the anisotropy of ice adhesion on the substrate, the interfacial bonds were described as shear bonds and tensile bonds, and the critical elongations of the two were derived. The tensile and shear capacities of the ice on the substrate were then simulated using these critical elongations, and the peeling rates of single ice particles and interfacial ice layers were taken as indexes describing the efficacy of electro-impulse de-icing. The process of electro-impulse de-icing was then analyzed for an aluminum substrate with two adjacent clamped edges. Finally, the results of the peridynamic simulation were compared with those of existing experiments and finite element models to verify the effectiveness of the peridynamic approach.

Key Parameters Controlling the Photodesorption Yield in Interstellar CO Ice Analogs: The Influence of Ice Deposition Temperature and Thickness

The overabundance of gas molecules in the coldest regions of space points to a nonthermal desorption process. Laboratory simulations show the efficient desorption of CO ice that is exposed to ultraviolet radiation, known as photodesorption, which decreases with increasing ice deposition temperature. However, our understanding of this abnormal phenomenon still remains elusive. In this work, we show that the same phenomenon—and, in particular, a dramatic drop in the photodesorption yield—is observed when the deposition temperature is 19 K and higher. Also, the minimum ice thickness that accounts for a constant photodesorption yield of CO ice is dependent on the deposition temperature, an observation that is reported here for the first time. We propose that the key parameters dominating the absorbed photon energy transfer in CO ice, and contributing to the measured photodesorption yields, are the energy transfer length, the desorption yield contributed by a single ice layer, and the relative effective surface area. These parameters should be incorporated into astrophysical models that simulate the photodesorption of the top CO-rich ice layer in icy dust populations, with a size distribution that is related to the ice thickness.

Improving aircraft aerodynamic performance with bionic wing obtained by ice shape modulation

For Unmanned Aerial Vehicles (UAVs) with limited electrical power to achieve effectively anti-/de-icing at the leading edge of the wing, a strategy of ice shape modulation was proposed. Isolated simulated ice shape pieces printed by 3D printing technology are mounted on a NACA0012 finite wing model, and its lift/drag coefficients and suction-side velocity fields are measured by the six-component force balance and the Particle Imaging Velocimetry (PIV), respectively. The ratio of the spanwise length of a single ice shape piece to chord length and the spanwise length of the non-icing area between the two adjacent single ice shape pieces are defined as dimensionless ice shape length (w/c) and dimensionless modulation ratio (w/λ), respectively. The results indicate that for a fixed w/λ, the wing lift coefficient first increases and then drops with increasing w/c, and a peak value exists when w/c is between 0.1 and 0.2. The lower the w/λ is, the higher the wing lift coefficient will be. The periodical variation of the flow separation area along the spanwise direction is attributed on the one hand to the acceleration effect of the flow field in the non-icing area which reduces the separation area, and on the other hand to the cross-flow caused by the streamwise vortices from the non-icing area to the icing area which promotes the mixing of the flow field (similar to vortex generators). The obtained modulation law is verified through flight tests and provides guidance for the use of ice shape modulation scheme for UAVs that cannot be completely anti-/de-icing under severe weather conditions.

Adsorption of ice-binding proteins onto whole ice crystal surfaces does not necessarily confer a high thermal hysteresis activity

Many psychrophilic microorganisms synthesize ice-binding proteins (IBPs) to survive the cold. The functions of IBPs are evaluated by the effect of the proteins on the nonequilibrium water freezing-point depression, which is called “thermal hysteresis (TH)”, and the inhibitory effect of the proteins on the growth of larger ice crystals, which is called “ice recrystallization inhibition (IRI)”. To obtain mechanical insight into the two activities, we developed a modified method of ice affinity purification and extracted two new IBP isoforms from Psychromyces glacialis, an Arctic glacier fungus. One isoform was found to be an approximately 25 kDa protein (PsgIBP_S), while the other is a 28 kDa larger protein (PsgIBP_L) that forms an intermolecular dimer. Their TH activities were less than 1 °C at millimolar concentrations, implying that both isoforms are moderately active but not hyperactive IBP species. It further appeared that both isoforms exhibit high IRI activity even at submicromolar concentrations. Furthermore, the isoforms can bind to the whole surface of a hemispherical single ice crystal, although such ice-binding was generally observed for hyperactive IBP species. These results suggest that the binding ability of IBPs to whole ice crystal surfaces is deficient for hyperactivity but is crucial for significant IRI activity.

Evaluation of bulk microphysics parameterizations for simulating the vertical structure of heavy rainfall between Korea and the United States

The Korean Peninsula and the United States (US) have many contrasting precipitation characteristics that are part of the oceanic monsoon and continental convection. This study evaluated 11 microphysics schemes in the Weather Research and Forecasting model in terms of vertical reflectivity structure for heavy rainfall during the summer in Korea and the US. Compared to satellite radar observation, the correlation coefficients for the reflectivity structure for 11 microphysics schemes were 0.581–0.906 and 0.745–0.918 for the Korean and US domains, respectively. We observed that a simple scheme (such as the use of single moment and limited ice categories) does not always fail, and complex methods do not always succeed. The relatively low correlation over Korea versus the US was assumed because many microphysics parameterizations were developed and tuned over the US. Consequently, some microphysics schemes exhibited a severe overestimation of reflectivity in both the upper and lower levels over the Korean Peninsula. In contrast, a microphysics scheme that was evaluated and improved for both continental and maritime convection regions, showed the best performance on the Korean Peninsula too. This highlights the importance of evaluation for various regions with different precipitation characteristics to improve parameterization of cloud microphysics. Because Korean and US domains are representative areas of oceanic monsoon and continental convection, we expect that this study can serve as a conceptual guide to suggest which microphysics parameterizations should be used for a realistic simulation in continental and oceanic monsoon precipitation regimes.

Numerical Modelling of Droplets and Beads Behavior over Super-Hydrophobic and Hydrophilic Coatings under in-Flight Icing Conditions

Current technology has produced a wide range of advanced micro-structured surfaces, designed for achieving the best wettability and adhesion performances for each specific application. In the context of in-flight icing simulations, this opens new challenges since the current most popular and successful ice accretion prediction tools neglect the details of the droplet behavior opting for a continuous film model. Here, a phenomenological model, following, in a Lagrangian approach, the evolution of the single droplets from the impinging to the onset of rivulets, is developed to simulate the performances of super-hydrophobic surfaces in icing application. Possible rebound and droplet spread on the impact, coalescence, single ice bead formation and droplet to rivulet transition are taken into account. The first validation shows how the models are able to predict the anti-icing capability of a super-hydrophobic surface coupled with a heating system.

P-220 Ice crystals propagation velocity is related to the type and concentration of cryoprotectants and impacts cells and tissue vitrification success

Abstract Study question How different cryoprotectants at various concentrations affect ice crystals formation and propagation during vitrification? Summary answer The velocity of ice crystal propagation is inversely related to concentration and type of cryoprotectants and is responsible for downstream cell damage during vitrification. What is known already Vitrification has replaced slow freezing for oocyte and embryo cryopreservation and is now being considered also for gonadal tissue. However, the results in terms of both vitrification and rewarming survival rates are still not uniform. Understanding the complex physical events controlling ice crystals formation, propagation and expansion are key for improving cryoprotectant solutions and overcoming challenges. Study design, size, duration Basic science research. Ice crystal propagation velocity was measured in solutions of four cryoprotectants: dimethyl sulfoxide (DMSO), propylene glycol (PG), ethylene glycol (EG) and glycerol (Gly), at various concentrations in supercooled temperatures. Each experiment used five 0.25ml and five 2ml straws (volume 0.1 ml and 1 ml) containing different cryoprotectant combinations (DMSO:EG, EG:PG, DSMO:PG, DMSO:Gly, EG:Gly, PG:Gly and EG+PG vs EG+DMSO), immersed in alcohol baths prepared at 8-10 °C below the freezing points of each solution. Participants/materials, setting, methods Alcohol baths were set as follows: (1) between -10 °C and -12 °C for straws with 0% and 10% (v/v) DMSO, EG, PG and Gly; (2) -15 °C to -19 °C for the 20%; (3) -19.5 to -24 °C for the 30%, and for the mixture of 15% EG and 15% PG and 15% EG and 15% DMSO (most used vitrification solutions); and (4) -25 to -36 °C for the 40%. A 50µm thermocouple measured supercooling. Student’s T-test analyzed differences. Main results and the role of chance Seeding was done by touching the straw end with LN- precooled forceps until visualizing a small ice crystal. Following 10 to 60s the distance to which the ice crystals grew inside the straws was evaluated using a fine caliber. Ice crystal propagation was inversely correlated to type and cryoprotectant concentrations. Propylene glycol showed statistically significant lower ice crystals growth velocity up to concentrations of 30% (v/v), compared to DMSO and EG at the same concentrations (p < 0.05). Moreover, the ice crystal velocity of PG was also lower than Gly at these same concentrations. The combination of EG with PG decreased ice crystal propagation better than EG with DMSO. At concentrations of 40%, there were no differences. These results suggest that current cryopreservation vitrification solutions are not optimized and combining PG with other CPs has advantages. Using a vitrification solution of 40% DMSO or EG, the velocity of crystal growth was in the range of 0.1mm/sec (6mm/min). This means that to vitrify large tissues, a cooling rate of over 1000 °C/min from RT to a temperature of -196 °C (ΔT of 220 °C in 13 seconds) is necessary to avoid a single ice nucleus to grow to a size of 1.3mm during cooling or warming. Limitations, reasons for caution Assessing the velocity of ice propagation is a novel concept to perfect vitrification/warming solutions. Wider implications of the findings These results pave the way to develop protocols and platforms able to minimize the deleterious impact of cryoprotectant concentrations on both cells and tissues survival after vitrification. Trial registration number not applicable

Diverse cloud radiative effects and global surface temperature simulations induced by different ice cloud optical property parameterizations

The representation of ice cloud optical properties in climate models has long been a difficult problem. Very different ice cloud optical property parameterization schemes developed based on very different assumptions of ice particle shape habits, particle size distributions, and surface roughness conditions, are used in various models. It is not clear as to how simulated climate variables are affected by the ice cloud optical property parameterizations. A total of five ice cloud optical property parameterization schemes, including three based on the ice habit mixtures suitable for general ice clouds, mid-latitude synoptic ice clouds, and tropical deep convective ice clouds, and the other two based on single ice habits (smooth hexagonal column and severely roughened column aggregate), are developed under a same framework and are implemented in the National Center for Atmospheric Research Community Atmospheric Model version 5. A series of atmosphere-only climate simulations are carried out for each of the five cases with different ice parameterizations. The differences in the simulated top of the atmosphere shortwave and longwave cloud radiative effects (CREs) are evaluated, and the global averaged net CRE differences among different cases range from − 1.93 to 1.03 Wm−2. The corresponding changes in simulated surface temperature are found to be most prominent on continental regions which amount to several degrees in Kelvin. Our results indicate the importance of choosing a reasonable ice cloud optical property parameterization in climate simulations.

Seasonal forecasting of landfast ice in Foggy Island Bay, Alaska in support of ice road operations

Landfast ice along the Arctic coasts plays an important role in supporting ecosystem services, local communities and offshore activities by industry. Seasonal predictions of landfast ice conditions are generally lacking in current seasonal forecasting products but are needed especially for planning of on-ice activities such as the construction of ice roads. This study focuses on the planned offshore development of Liberty Island where there is a need to generate seasonal forecasts for the construction of ice roads in Foggy Island Bay along the Beaufort Sea coast in northern Alaska. Due to the lack of prior in-situ observations of ice thickness in the region, a combination of newly obtained field measurements, remote sensing data analysis and modeling were employed to produce prototype seasonal forecasts of ice thickness in the landfast ice around Liberty Island. Seasonal forecasts initialized in September and March were built using Climate Forecast System seasonal forecast model data coupled with a single column ice model to forecast ice thickness that capture the start and end of the operational season, respectively. The results showed that the model forecasts had modest skill in capturing the timing of key ice thickness thresholds needed to support vehicle traffic during the start of the season in November–December but very limited skill with end of season and ice breakup forecasts. Much of the forecast skill was improved through bias correction but such improvement was hampered by the lack of long-term observational data in the region. Integration of the observational data and modeling is necessary to begin development of seasonal forecasts in this data sparse region.

A New Structure for the Sea Ice Essential Climate Variables of the Global Climate Observing System

Abstract Climate observations inform about the past and present state of the climate system. They underpin climate science, feed into policies for adaptation and mitigation, and increase awareness of the impacts of climate change. The Global Climate Observing System (GCOS), a body of the World Meteorological Organization (WMO), assesses the maturity of the required observing system and gives guidance for its development. The Essential Climate Variables (ECVs) are central to GCOS, and the global community must monitor them with the highest standards in the form of Climate Data Records (CDR). Today, a single ECV—the sea ice ECV—encapsulates all aspects of the sea ice environment. In the early 1990s it was a single variable (sea ice concentration) but is today an umbrella for four variables (adding thickness, edge/extent, and drift). In this contribution, we argue that GCOS should from now on consider a set of seven ECVs (sea ice concentration, thickness, snow depth, surface temperature, surface albedo, age, and drift). These seven ECVs are critical and cost effective to monitor with existing satellite Earth observation capability. We advise against placing these new variables under the umbrella of the single sea ice ECV. To start a set of distinct ECVs is indeed critical to avoid adding to the suboptimal situation we experience today and to reconcile the sea ice variables with the practice in other ECV domains.

The Ice Particle and Aggregate Simulator (IPAS). Part II: Analysis of a Database of Theoretical Aggregates for Microphysical Parameterization

Abstract Bulk ice-microphysical models parameterize the dynamic evolution of ice particles from advection, collection, and sedimentation through a cloud layer to the surface. Frozen hydrometeors can grow to acquire a multitude of shapes and sizes, which influence the distribution of mass within cloud systems. Aggregates, defined herein as the collection of ice particles, have a variety of formations based on initial ice particle size, shape, falling orientation, and the number of particles that collect. This work focuses on using the Ice Particle and Aggregate Simulator (IPAS) as a statistical tool to repetitively collect ice crystals of identical properties to derive bulk aggregate characteristics. A database of 9 744 000 aggregates is generated with resulting properties analyzed. After 150 single ice crystals (monomers) collect, the most extreme aggregate aspect ratio calculations asymptote toward and ϕca ≈ 0.50 for aggregates composed of quasi-horizontally oriented and randomly oriented monomers, respectively. The results presented are largely consistent with both a previous theoretical study and estimates derived from ground-based observations from two different geographic locations. Particle falling orientation highly influences newly formed aggregate aspect ratios from the collection of particles with extreme aspect ratios; quasi-horizontally oriented particles can produce aggregate aspect ratios an order of magnitude more extreme than randomly oriented particles but can also produce near-spherical aggregates as the number of monomers comprising the aggregate reach approximately 100. Finally, a majority of collections result in aggregates that are closer to prolate than oblate spheroids.

UAV-based geomorphological evolution of the Terminus Area of the Hailuogou Glacier, Southeastern Tibetan Plateau between 2017 and 2020

Hailuogou (HLG) Glacier, a rapidly receding temperate glacier in the southeastern Tibetan Plateau, has been observed to lose mass partly through ice frontal mechanical ablation (i.e., ice collapse). These events are difficult to monitor and quantify due to their small scale and frequent nature. However, recent developments in Uncrewed Aerial Vehicles (UAV) have provided a possible approach to track their spatiotemporal variation and their impact on the geomorphological evolution of the glacier terminus area. Here, we present analysis from UAV surveys conducted over eight field campaigns to the HLG Glacier, providing evidence of glacier change between October 2017 and November 2020. Structure from Motion with Multi-View Stereo (SfM-MVS) was applied to produce multi-temporal Digital Surface Models (DSMs) and orthophoto mosaics, from which geomorphological maps and DEMs of Difference (DoDs) were derived to quantify glacier changes. These analyses reveal that at the margins of the glacier terminus retreated 132.1 m over the period of analysis, and that in the area specifically affected by collapsing (i.e., the glacier collapsed terminus), it retreated 236.4 m. Overall the volume lost in the terminal area was of the order of 184.61 ± 10.32 × 104 m3, within which the volume change due to observed collapsing events comprises approximately 28%. We show that ice volume changes at the terminus due to a single ice collapse event may exceed the interannual level of volume change, and the daily volume of ice loss due to ice calving exceeds the seasonal and interannual level by a factor of ~2.5 and 4. Our results suggest that the evolution of the HLG Glacier terminus is dominantly controlled by the frontal ice-water interactions. If the future evolution of glaciers such as HLG Glacier is to be robustly predicted, the contribution of mechanical ablation should be accounted for by numerical models.

Comparison of ice dynamics using full-Stokes and Blatter–Pattyn approximation: application to the Northeast Greenland Ice Stream

Abstract. Full-Stokes (FS) ice sheet models provide the most sophisticated formulation of ice sheet flow. However, their applicability is often limited due to the high computational demand and numerical challenges. To balance computational demand and accuracy, the so-called Blatter–Pattyn (BP) stress regime is frequently used. Here, we explore the dynamic consequences of using simplified approaches by solving FS and the BP stress regime applied to the Northeast Greenland Ice Stream. To ensure a consistent comparison, we use one single ice sheet model to run the simulations under identical numerical conditions. A sensitivity study to the horizontal grid resolution (from 12.8 to a resolution of 0.1 km) reveals that velocity differences between the FS and BP solution emerge below ∼ 1 km horizontal resolution and continuously increase with resolution. Over the majority of the modelling domain both models reveal similar surface velocity patterns. At the grounding line of the 79∘ North Glacier the simulations show considerable differences whereby the BP model overestimates ice discharge of up to 50 % compared to FS. A sensitivity study to the friction type reveals that differences are stronger for a power-law friction than a linear friction law. Model differences are attributed to topographic variability and the basal drag, in which neglected stress terms in BP become important.

Drift of elastic floating ice sheets by waves and current: Multiple sheets

A nonlinear theoretical model for deformations, oscillations, and drift motions of multiple elastic ice sheets in shallow waters due to combined nonlinear waves and uniform current is presented. The model is based on the Green–Naghdi theory for the fluid motion and the thin plate theory for the deformation of the ice sheets. In principle, there are N number of the floating sheets with arbitrary lengths, drafts, and rigidities, which may be located at arbitrary distances from each other. Nonlinear waves of solitary and cnoidal types are considered, and there are no restrictions on the wave properties (wave height or wave period). The sheets, located at different positions, are shown to drift with different speeds, but surge in most of the wave conditions with equal amplitudes. It is shown systematically that wavelength and spacing between the sheets are the critical parameters determining the drift response of a set of freely floating ice sheets. When wavelength is equal to the distance between the centers of the sheets, they bend and drift in resonance, causing the largest wave reflection. The ambient current is found to affect the drift motion of the sheets nonlinearly. This work complements the part I paper of the same title, where drift motion of a single ice sheet was investigated.