Ice Phase Research Articles

The influence of stress anisotropy and stress shadow on frost cracking in rock

With growing research interest of liquefied natural gas storage in underground frozen host rock cavern, it is the key to have a comprehensive understanding of rock deformation and cracking under freezing and their impact on the stability of the underground storage caverns. In this work, a coupled thermo-hydro-mechanical model is developed in the framework of TOUGH-FEMM simulator to gain such understanding, where complex coupled processes involving water–ice phase transition as well as non-planar frost cracks are rigorously considered. In this model with the TOUGH-FEMM, heat transfer and fluid flow under freezing are simulated using TOUGH2, while mechanical deformation and cracking are simulated using the hybrid finite element-meshfree method (FEMM). The new modelling component for simulating temperature transfer and freezing-induced strain is validated against data from a previous laboratory experiment on sandstone by Neaupane et al. Finally, the influence of stress anisotropy and stress shadow on frost cracking are discussed using a set of experiments and TOUGH-FEMM modelling. The experimental and numerical results show that frost-induced cracks propagate towards to the direction of the maximum principal stress, while the stress shadow between multiple cracks has a significant impact on the damage pattern.

Dual‐permeability modeling of preferential flow and snowmelt partitioning in frozen soils

AbstractThe infiltrability of frozen soils modulates the partitioning of snowmelt between infiltration and runoff in cold regions. Preferential flow in macropores may enhance infiltration, but flow dynamics in frozen soil are complicated by soil heat transfer processes. We developed a dual‐permeability model that considers the interacting effects of freeze–thaw and preferential flow on infiltration and runoff generation in structured soils. This formulation was incorporated into the fully integrated groundwater–surface water model HydroGeoSphere, to represent water–ice phase change in macropores such that porewater freezing is governed by macropore–matrix heat exchange. Model performance was evaluated against laboratory experiments and synthetic test cases designed to examine the effects of preferential flow on snowmelt partitioning between infiltration, runoff, and drainage. Simulations were able to reproduce experimental observations of rapid infiltration and drainage behavior due to macropores very well, and approximated soil thaw to an acceptable degree. Simulation of measured data highlighted the importance of macropore hydraulic conductivity, as well as macropore–matrix heat and water transfer, on controlling preferential flow dynamics. Test cases replicated a range of snowmelt partitioning behavior commonly observed in frozen soils, including subsurface conditions that produce rapid infiltration and deeper drainage, the contrast between limited vs. unlimited infiltration responses to snowmelt, and the temporal evolution of runoff generation. This study demonstrates the important influence that water freezing along preferential flowpaths can have on infiltrability and runoff characteristics in frozen soils and provides a physically based description of this mechanism that links infiltration behavior to hydraulic and thermal properties of structured soils.

Influence of stabilizers on the microstructure of fresh sorbets: X-ray micro-computed tomography, cryo-SEM, and Focused Beam Reflectance Measurement analyses

Abstract X-ray micro-computed tomography was applied to determine the influence of stabilizers on the microstructure of fresh sorbets (i.e. at the outlet of a batch freezer), and more particularly on the air phase and the ice phase. Sucrose sorbets were tested with addition of one stabilizer: locust bean gum (LBG), hydroxypropylmethylcellulose (HPMC) or carboxymethylcellulose (CMC). It was shown that HPMC increased the quantity and decreased the size of air bubbles; it also decreased the ice crystals size unlike other stabilizers which had no effect on the size of ice crystals. Results were successfully compared with data from Cryo-Scanning Electron Microscopy (cryo-SEM) and completed with Focused Beam Reflectance Measurement (FBRM) analyses applied for dynamic studies during freezing process. The effect of HPMC on the ice phase would be linked to its surfactant properties; air bubbles could prevent crystal growth during the freezing process.

Quantum-mechanical exploration of the phase diagram of water

The set of known stable phases of water may not be complete, and some of the phase boundaries between them are fuzzy. Starting from liquid water and a comprehensive set of 50 ice structures, we compute the phase diagram at three hybrid density-functional-theory levels of approximation, accounting for thermal and nuclear fluctuations as well as proton disorder. Such calculations are only made tractable because we combine machine-learning methods and advanced free-energy techniques. The computed phase diagram is in qualitative agreement with experiment, particularly at pressures ≲ 8000 bar, and the discrepancy in chemical potential is comparable with the subtle uncertainties introduced by proton disorder and the spread between the three hybrid functionals. None of the hypothetical ice phases considered is thermodynamically stable in our calculations, suggesting the completeness of the experimental water phase diagram in the region considered. Our work demonstrates the feasibility of predicting the phase diagram of a polymorphic system from first principles and provides a thermodynamic way of testing the limits of quantum-mechanical calculations.

Mechanisms of salt rejection at the ice-liquid interface during the freezing of pore fluids in the seasonal frozen soil area

Seasonal frozen soil accounts for about 53.50% of the land area in China. Frozen soil is a complex multiphase system where ice, water, soil, and air coexist. The distribution and migration of salts in frozen soil during soil freezing are notably different from those in unfrozen soil areas. However, little knowledge is available about the process and mechanisms of salt migration in frozen soil. This study explores the mechanisms of salt migration at the ice-liquid interface during the freezing of pore fluids through batch experiments. The results are as follows. The solute concentrations of liquid and solid phases at the ice-liquid interface (CL*, CS*) gradually increased at the initial stage of freezing and remained approximately constant at the middle stage. As the ice-liquid interface advanced toward the system boundary, the diffusion of the liquid phase was blocked but the ice phase continued rejecting salts. As a result, CL* and CS* rapidly increased at the final stage of freezing. The distribution characteristics of solutes in ice and the liquid phases before CL* and CS* became steady were mainly affected by the freezing temperature, initial concentrations, and particle-size distribution of media (quartz sand and kaolin). In detail, the lower the freezing temperature and the better the particle-size distribution of media, the higher the solute proportion in the ice phase at the initial stage of freezing. Meanwhile, the increase in concentration first promoted but then inhibited the increase of solutes in the ice phase. These results have insights and scientific significance for the tackling of climate change, the environmental protection of groundwater and soil, and infrastructure protection such as roads, among other things.© 2021 China Geology Editorial Office.

Investigation of hydrogen bond vibrations of ice

Despite its simple molecular structure, water is still a mystery to scientists. For the atomic and molecular vibrational modes of ice, as is well known, there are two kinds of vibrations: intra-molecular O—H stretching vibration and H—O—H bending vibration within the molecules and three kinds of molecular spatial rotations. However, thirty years ago, a high flux inelastic neutron scattering experiment showed that there are two distinct characteristic peaks in the far-infrared molecular translational vibration region of many ice phases. The origins of these peaks have not been determined till now. In this work, based on the CASTEP code, a first-principles density functional theory plane wave programme, the vibrational spectra as well as the vibrational normal modes of a series of ice phases are investigated. Two kinds of intrinsic hydrogen bond vibrational modes are first found in hydrogen-ordered ice Ic. Then it is found to be a general rule among ice family. Based on the ideal model, we prove that the two vibrational modes can be classified as four-bond vibration and two-bond vibration. There are many coupling modes in-between due to tetrahedral structure deformation under high pressure. Besides, there are also some optical vibrational modes with lower energy in the translational region, such as cluster vibrations and inter-plane vibrations. In Ice VII/VIII and XV/VI, each of which consists of two sublattices, there exist non-hydrogen bond vibrations. These molecular translational vibrations can explain all the far-infrared vibrational spectrum of ice phase, which makes up the last piece of the jigsaw puzzle for the molecular vibration theory of ice. The two vibrational modes do not exist in liquid water due to the collapse of the rigid tetrahedral structure. Thus, a window remains for ice resonance absorption with minimum energy loss in water. This theory is expected to be applicable to industrial deicing, food thawing, gas hydrate mining, and biomolecule frozen molding, etc.

Neural Networks Accelerate the Ab Initio Prediction of Solid–Solid Phase Transitions at High Pressures

High-level ab initio chemical calculations, such as second-order Møller-Plesset perturbation (MP2), are highly accurate but time-consuming, making it inefficient to apply to macromolecular systems. Here, we propose a newly efficient approach based on the neural network and fragment method to predict the Gibbs free energy, structural characteristics, and thus phase transition of solid crystal structures. The proposed approach has the same prediction accuracy as the MP2 calculation but is hundreds of times faster than the MP2. The predicted structures and phase transitions of two selected ice phases (IX and XV) under extreme conditions are in excellent agreement with the MP2 calculations and experimental results but with an extremely low computational cost. It not only predicts the high-pressure structures and phase diagrams of solid systems accurately and efficiently but also solves the problem of extreme calculation cost during a high-precision theoretical study on high-pressure molecular crystals with potentially essential applications.

In-cloud scavenging scheme for sectional aerosol modules – implementation in the framework of the Sectional Aerosol module for Large Scale Applications version 2.0 (SALSA2.0) global aerosol module

Abstract. In this study we introduce an in-cloud wet deposition scheme for liquid and ice phase clouds for global aerosol–climate models which use a size-segregated aerosol description. For in-cloud nucleation scavenging, the scheme uses cloud droplet activation and ice nucleation rates obtained from the host model. For in-cloud impaction scavenging, we used a method where the removal rate depends on the wet aerosol size and cloud droplet radii. We used the latest release version of ECHAM-HAMMOZ (ECHAM6.3-HAM2.3-MOZ1.0) with the Sectional Aerosol module for Large Scale Applications version 2.0 (SALSA) microphysics package to test and compare our scheme. The scheme was compared to a scheme that uses fixed scavenging coefficients. The comparison included vertical profiles and mass and number distributions of wet deposition fluxes of different aerosol compounds and for different latitude bands. Using the scheme presented here, mass concentrations for black carbon, organic carbon, sulfate, and the number concentration of particles with diameters larger than 100 nm are higher than using fixed scavenging coefficients, with the largest differences in the vertical profiles in the Arctic. On the other hand, the number concentrations of particles smaller than 100 nm in diameter show a decrease, especially in the Arctic region. These results could indicate that, compared to fixed scavenging coefficients, nucleation scavenging is less efficient, resulting in an increase in the number concentration of particles larger than 100 nm. In addition, changes in rates of impaction scavenging and new particle formation (NPF) can be the main cause of reduction in the number concentrations of particles smaller than 100 nm. Without further adjustments in the host model, our wet deposition scheme produced unrealistically high aerosol concentrations, especially at high altitudes. This also leads to a spuriously long lifetime of black carbon aerosol. To find a better setup for simulating aerosol vertical profiles and transport, sensitivity simulations were conducted where aerosol emission distribution and hygroscopicity were altered. Vertical profiles of aerosol species simulated with the scheme which uses fixed scavenging rates and the abovementioned sensitivity simulations were evaluated against vertical profiles from aircraft observations. The lifetimes of different aerosol compounds were also evaluated against the ensemble mean of models involved in the Aerosol Comparisons between Observations and Models (AEROCOM) project. The best comparison between the observations and the model was achieved with our wet deposition scheme when black carbon was emitted internally mixed with soluble compounds instead of keeping it externally mixed. This also produced atmospheric lifetimes for the other species which were comparable to the AEROCOM model means.

Superior Mechanical and Magnetic Performance of Highly Anisotropic Sendust‐Flake Composites Freeze Cast in a Uniform Magnetic Field

AbstractDespite extensive research, the manufacture in the bulk of high‐performance flake‐based magnetic composites with a highly aligned, nacre‐like structure remains challenging. Many challenges can be overcome by freeze casting in an externally applied, uniform magnetic field, which causes both the flakes and the composite walls of the cellular solid to align parallel to the B‐field lines. When appropriately sized, the flakes experience a second alignment parallel to the freezing direction because of a shear flow that occurs due to both the volumetric expansion of the ice phase and mold contraction during the directional solidification. The resulting orthotropic structure of the freeze‐cast magnetic composite is reflected in orthotropic mechanical and magnetic properties of the material. The magnetic composites manufactured by magnetic‐field assisted freeze casting outperform by a factor of 2–4 in terms of stiffness, strength, and toughness materials that are processed in the absence of a magnetic field and do not exhibit a monodomain architecture. Because of the highly aligned microstructure, it is possible to compact the initially lamellar composite with 90% porosity to at least 80% strain. The results presented in this study illustrate the tremendous potential for magnetic freeze casting of magnetic composites for use in power conversion.

(Invited) Corrosion Process of Metals below the Freezing Point

Atmospheric corrosion has been intensively investigated using an acceleration test using a temperature/humidity cycling in a laboratory to investigate the corrosion mechanism and the outdoor exposure test to evaluate the actual corrosion progress in a real environment. Corrosion of metals in a cold district is recently paid attention because a considerable amount of anti-freezing agents are sparged to the driveway in the winter season and cause severer corrosion of vehicles and structures. Repetition of freezing/melting of water also induces physical stress to the material and influences, for example, the mass-transportation process related to the corrosion reaction. In this study, therefore, the corrosion behavior of metals in the freezing condition was investigated both the outdoor exposure test and the laboratory test. In the laboratory test, low-temperature cycling was applied to the galvanic couples of Zn-steel plate cold commercial (SPCC) pair. A pair was set in a sample holder with a gap distance of ca. 0.1 mm between two metal plates and placed in a small box to avoid the direct blowing in a temperature-controlled chamber. Basic temperature cycling was composed of 4-stages as (i) low temperature (T L = –20°C, 1 h), (ii) transition from T Lto T H (1 h) (iii) high temperature (e.g., T H = 0, 1 h), and (iv) transition from T H to T L (1 h),. Relative humidity (RH) in a chamber was not actively controlled. The T and RH presented in this paper were measured by using a T & RH sensor close to the sample. At T L, 0.1% NaCl solution of ca. 1 cm3 was dropped at the gap that was immediately frozen. Fig. 1(a) shows the typical galvanic current i g in a single T-cycle observed at the gap covered with ice. In this condition, the ice was not almost melted at T H. The i g increased with T but not dependent on RH because the current flowed mainly under or around the ice. The considerably large i g observed under the ice proposed that the ionic conductivity was maintained even at the freezing temperature as –20 °C. Probably a thin liquid layer of concentrated NaCl solution was formed at the interface between the metals and ice due to the exclusion of salt from the solid ice phase during the freezing process. The presence of the liquid phase was also investigated by the different experiments of the impedance measurement between two Pt electrodes in the freezing condition. After many T-cycles, T H was raised to 2 °C to accelerate the melting of ice and, thus, the evaporation of melted water. After the many cycling, the surface was almost dried and covered with a mixture of corrosion products and salt. Fig. 1(b) shows the i g in this condition. The i g flowed at T L where the RH was rather high at stage i, increased with increasing T at stage iv, and dropped with lowering RH at T H in stage iii. This behavior was similar to that observed in the ordinal wet, and dry test conducted higher than the melting point. From these results, the atmospheric corrosion process in the cold district includes the ordinal atmospheric corrosion on the dry area and wet-corrosion in the quasi-solution under the ice. Figure 1

Bayesian analysis of Juno/JIRAM's NIR observations of Europa

Decades of observations of Europa's surface in the near-infrared (NIR), spanning spacecrafts like Galileo, Cassini and New Horizons, along with ground based observations, have revealed a rich mixture of species on Europa's surface. Adding to the NIR data of Europa, Juno spacecraft's spectrometer JIRAM has observed it in the 2–5 μm wavelength region. Here we present analysis of select spectra from this dataset, focusing on the two forms of water-ice - amorphous and crystalline. We were limited in our ability to include other dominant Europan species, like acid hydrate, due to unavailability of their optical constants over the entire JIRAM wavelength range. We also take this as an opportunity to present a novel Bayesian spectral inversion framework. Traditional spectral fitting methods, for example a grid-based search of parameter space, lack a systematic way to quantify detection significances of the species included in the model, statistically constrain surface properties and explore degenerecies of solution. Our Bayesian inference framework overcomes these shortcomings by confidently detecting amorphous and crystalline ice in the JIRAM data and permits probabilistic constraints on their compositions and average grain sizes to be obtained. We first validate our analysis framework using simulated spectra of amorphous and crystalline ice mixtures and a laboratory spectrum of crystalline ice. We next analyze the JIRAM data and, through Bayesian model comparisons, find that a two-component, intimately mixed model of amorphous and crystalline ice, henceforth referred to as TC-IM, is strongly preferred (at 26σ confidence) over a two-component model of the same materials but where their spectra are areally/linearly mixed. We also find that the TC-IM model is strongly preferred (at > 30σ confidence) over single-component models with only amorphous or crystalline ice, indicating the presence of both these phases of water ice in the data. Given the high SNR of the JIRAM data, abundances and grain sizes of amorphous and crystalline ice are very tightly constrained for the analysis with the TC-IM model. The solution corresponds to a mixture with a very large number density fraction (99.952−0.001+0.001 %) of small (23.12−1.01+1.01 microns) amorphous ice grains, and a very small fraction (0.048−0.001+0.001 %) of large (565.34−1.01+1.01 microns) crystalline ice grains. The overabundance of small amorphous ice grains we find is consistent with previous studies. The maximum-likelihood spectrum of the TC-IM model, however, is in tension with the data in the regions around 2.5 and 3.6 μm, and indicates the presence of non-ice components not currently included in our model. Our new technique therefore holds the promise of being able to identify these minor species hiding in Europan reflectance data in future work and constrain their abundances and physical properties.

Liquid water contains the building blocks of diverse ice phases

Water molecules can arrange into a liquid with complex hydrogen-bond networks and at least 17 experimentally confirmed ice phases with enormous structural diversity. It remains a puzzle how or whether this multitude of arrangements in different phases of water are related. Here we investigate the structural similarities between liquid water and a comprehensive set of 54 ice phases in simulations, by directly comparing their local environments using general atomic descriptors, and also by demonstrating that a machine-learning potential trained on liquid water alone can predict the densities, lattice energies, and vibrational properties of the ices. The finding that the local environments characterising the different ice phases are found in water sheds light on the phase behavior of water, and rationalizes the transferability of water models between different phases.

Optimisation of freezing efficiency of hole-bottom freezing technique for gas hydrate sampling: Study on factors influencing dry ice phase transition

Natural gas hydrate sampling technology is an important means to study in situ properties. Currently, there are certain limitations in the application of pressure preservation technology, such as poor sealing and low success rates. Hole-bottom freezing sampling technology has the advantages of a simple structure, large sample size, and high fidelity. To solve the problem of low freezing efficiency, the quality of the cold source was controlled by changing the specific surface area of dry ice, ambient pressure, and temperature difference. The experimental results show that the improvement of heat transfer efficiency by the specific surface area and the temperature difference is mainly reflected in the cold source injection process. At the same time, it changes the viscosity of the cold source to make it easier to adhere, which will cause a large amount of dry ice loss and reduce freezing efficiency. The increase in ambient pressure will inhibit the sublimation of dry ice, reduce the heat transfer rate of phase change, and affect the freezing efficiency. Meanwhile, a solid layer will be formed and the cold source cannot be injected. According to the results, granular dry ice was selected to prepare a cold source with a temperature difference of 105K and ambient pressure of 0.1 MPa.

Promote anti- /de- frosting by suppressing directional ice bridging

Condensation frost is one of the most common types of icing encountered in nature and industrial applications, while its accretion induces multiple non-negligible negative impacts. Many passive anti-/de- frosting approaches by tailoring surface topology and chemistry have been reported recently. To date, however, reliable engineered surfaced that can be compatible with heat exchangers from both mechanical and economic perspectives are limited. In this paper, we present a hierarchically structured surface that can profoundly reduce the frost coverage, and meanwhile promote the rapid removal of frost melts. This surface consists of microgroove pattern and nanoblade structure, where the former provides preferential sites for the growth of condensed droplets, and the latter promises a robust water repellent nature. During frosting, the ice phase spreads only among droplets on groove edges while condensed droplets in valleys are completely evaporated off, yielding a typical pattern that ice stripes distribute discretely in the dry background. During defrosting, frost melts coalesce into large droplets that spontaneously depart the substrate surface. Our results open up a new avenue for surface engineering, particularly on the design of economic and scalable anti-/de- frosting surfaces.

The mechanical properties of ice X with particular emphasis on its auxetic potential

H2O ice is known to exist as a number of different polymorphs. One such polymorph is ice X, a symmetrical phase of ice which is known to be stable at high pressures and low temperatures. In this work, the mechanical properties of ice X have been studied through DFT simulations, and it has been shown that ice X has the potential to exhibit auxetic behaviour (negative Poisson's ratio) at 45° off-axis in the (100), (010) and (001) planes. Studying the deformation of two orthogonally interconnected rhombi has shown that this predicted negative Poisson's ratio can be attributed to the interplay between distortion and hinging of these rhombi. Moreover, it has been shown that the auxetic potential of ice X increases with an increase in hydrostatic pressure, which behaviour is explained by the rhombi approaching quasi-perfect behaviour resulting in a decrease in the distortion of the rhombi and an increase in hinging mechanism.

Effects of structural attributes on the rheological properties of ice cream and melted ice cream.

Although the ice phase greatly influences the properties of ice cream, other structural components also affect its rheological behavior, particularly after melting. In this study, mix viscosity (serum phase viscosity), extent of fat destabilization (FD), and overrun were manipulated to produce different microstructures. The effects of these structural components were evaluated on the rheological properties of the ice creams and melted ice creams. In oscillatory thermorheometry, mix viscosity and then overrun, influenced G' and tanδ below -10 °C. When ice phase decreased (between -10 and -2.7 °C), mix viscosity had reduced effects, but continued to strongly affect G' and tanδ, followed by FD, and with lower effects from overrun. When the ice phase was completely melted at 0 °C, FD had most influence on G' and tanδ, followed by overrun, and with lower effects from mix viscosity. In creep/recovery test, six-element model described well creep behavior of melted ice cream at 0 °C. Viscous behavior at lower shear rate (η0 0 °C) was most influenced by mix viscosity, followed by FD, and lower overrun effects. In stress growth measurement, transient behavior, represented by σY 0 °C, of melted matrix at 0 °C was most influenced by FD, followed by mix viscosity, with lower overrun effects. In flow ramp measurement, Hysteresis Area was most affected by mix viscosity, followed by overrun, and with lower FD effects. Moreover, correlation between Hyst 0 °C and tanδ Peak suggested that structure formation affected the magnitude of tanδ Peak. These results document the importance of microstructure on properties of melted ice cream. PRACTICAL APPLICATION: The understanding of how structural components, such as mix viscosity, fat destabilization, and overrun, affect the ice cream matrix can help manufacturers to control its rheological behavior. The influence of these structural components on the G', tanδ, η0 0 °C , σY 0 °C , and Hyst 0 °C can be also used to understand the structural rearrangements that occur in meltdown tests and sensory analyses for future studies. Therefore, elucidation of these mechanisms on the rheological properties can directly assist in quality control and new product development in the ice cream industry.

Experimental Study on Displacement of Water by Sub-Zero N-Hexanol in a Straight Channel

Series of displacement tests of water by cold n-hexanol (below 0 °C) in a straight tube were conducted to investigate the freezing-accompanied displacement process, which occurs during the cryogenic fracturing process. The interrelationship between water freezing and displacement flow was studied. It was found that the displacement flow could significantly affect the water distribution in the flow channel. Along with the displacement proceeding, the n-hexanol overtook the water in the flow direction gradually, and the water in the center of the channel was driven to the edge area. Moreover, the initially integrated water phase split into several parts during the displacement process. Once the water freezing occurred, two typical ice blockage patterns, i.e., complete ice blockage and incomplete ice blockage, were observed. In incomplete ice blockage pattern, the channel cross-section was partly occupied by the ice phase, which mainly affected the rate of subsequent fluid flow. In complete ice blockage pattern, the channel cross-section was fully occupied by the ice phase, which cut off the fluid flow in the original direction. Based on the test results, the influences of the initial water temperature, initial water column length and flow rate of n-hexanol on the formation of different ice blockage patterns are discussed. The decrease of the initial water temperature and the increase of the initial water column length are preferred to induce the occurrence of complete ice blockage. However, changing n-hexanol flow rate could lead to the occurrence of both incomplete ice blockage and complete ice blockage, which depends on the actual situations.

Numerical Simulation Study on the Microphysical Processes of Typhoon Wipha Using a New Moisture Conditioning Method

Yang, W.X.; Hu, Z.X.; Lei, H.C., and Li, B.D., 2020. Numerical simulation study on the microphysical processes of Typhoon Wipha using a new moisture conditioning method. In: Guido Aldana, P.A. and Kantamaneni, K. (eds.), Advances in Water Resources, Coastal Management, and Marine Science Technology. Journal of Coastal Research, Special Issue No. 104, pp. 156–159. Coconut Creek (Florida), ISSN 0749-0208.With the non-static mesoscale model ARPS (Advanced Regional Prediction System), by using the NCEP/ NCAR global final analysis data, and the global surface and sounding data under MICAPS (Meteorological Information Comprehensive Analysis and Process System) assimilated in 4 dimensions as the initial field and lateral boundary conditions, the initial moisture field is adjusted according to the surface accumulated rain of each 6 h, and the triple nested simulation is conducted to produce 3 dimensional high time -spatial (Wipha) are analysed. The results are significant for understanding the cloud structure and the precipitation forming mechanisms of the Typhoon storm. It is found that the ice phase microphysical processes are the key storm mechanisms in different periods. The melting graupel confirms that the rain is the most important mechanism. The intensity of the production of graupel varies in accordance with the Typhoon.

Poro-mechanical model of strain hysteresis due to cyclic water freezing in partially saturated porous media

The paper presents a novel mathematical model of coupled hygro-thermo-mechanical processes in a porous material, partially saturated with liquid water and exposed to temperatures below the freezing point of pore water. Water – ice phase change is modelled by means of a non-equilibrium approach considering both water supercooling and a hysteresis of ice content during freezing and thawing of moist porous materials. The hysteresis results in different crystallization pressure and material strains during freezing and thawing processes at a given temperature. The latter effect is modelled by means of the effective stress principle, considering crystallization pressure of ice in the material pores. Methods used for discretization of the model equations and their numerical solution are described.The model is applied for solving the numerical example dealing with laboratory Dynamic Mechanical Analysis test of two different cement mortars saturated with water and exposed to temperatures below the freezing point of water (down to −15 °C) where hysteresis of strains was observed. The results are used for experimental validation of the proposed model. Then, for a 1-D case concerning water freezing-thawing of a wall, the effects on the simulation results of the phase-change model parameters, of the material hygro-thermal state, of the supercooling phenomenon and finally of the rate of temperature variation, are analyzed and discussed.

Extremes become routine in an emerging new Arctic

The Arctic is rapidly warming and experiencing tremendous changes in sea ice, ocean and terrestrial regions. Lack of long-term scientific observations makes it difficult to assess whether Arctic changes statistically represent a ‘new Arctic’ climate. Here we use five Coupled Model Intercomparison Project 5 class Earth system model large ensembles to show how the Arctic is transitioning from a dominantly frozen state and to quantify the nature and timing of an emerging new Arctic climate in sea ice, air temperatures and precipitation phase (rain versus snow). Our results suggest that Arctic climate has already emerged in sea ice. Air temperatures will emerge under the representative concentration pathway 8.5 scenario in the early- to mid-twenty-first century, followed by precipitation-phase changes. Despite differences in mean state and forced response, these models show striking similarities in their anthropogenically forced emergence from internal variability in Arctic sea ice, surface temperatures and precipitation-phase changes. The short observational record makes it difficult to gauge how unprecedented recent Arctic warming is. A multi-model large ensemble estimates a new Arctic climate has emerged for sea-ice extent. As the Arctic shifts from a primarily frozen state, temperature and precipitation follow within decades.