Scale properties of sea ice deformation and fracturing

The sea ice cover, which insulates the ocean from the atmosphere, plays a fundamental role in the Earth's climate system. This cover deforms and fractures under the action of winds, ocean currents and thermal stresses. Along with thermodynamics, this deformation and fracturing largely controls the amount of open water within the ice cover and the distribution of ice thickness, two parameters of high climatic importance, especially during fall and winter (no melting). Here we present a scaling analysis of sea ice deformation and fracturing that allows us to characterize the heterogeneity of fracture patterns and of deformation fields, as well as the intermittency of stress records. We discuss the consequences of these scaling properties, particularly for sea ice modelling in global climate models. We show how multifractal scaling laws can be extrapolated to small scales to learn about the nature of the mechanisms that accommodate the deformation. We stress that these scaling properties preclude the use of homogenisation techniques (i.e. the use of mean values) to link different scales, and we discuss how these detailed observations should be used to constrain sea ice dynamics modelling. To cite this article: J. Weiss, D. Marsan, C. R. Physique 5 (2004).     

Optical properties of ice particles in young contrails

The single-scattering properties of four types of ice crystals (pure ice crystals, ice crystals with an internal mixture of ice and black carbon, ice crystals coated with black carbon, and soot coated with ice) in young contrails are investigated at wavelengths 0.65 and 2.13 μm using Mie codes for coated spheres. The four types of ice crystals show differences in their single-scattering properties because of the embedded black carbon whose volume ratio is assumed to be 5%. The bulk-scattering properties of young contrails consisting of the four types of ice crystals are further investigated by averaging their single-scattering properties over a typical ice particle size distribution found in young contrails. The effect of the radiative properties of the four types of ice particles on the Stokes parameters I, Q, U, and V is also investigated for different viewing zenith angles and relative azimuth angles with a solar zenith angle of 30° using a vector radiative transfer model based on the adding-doubling technique. The Stokes parameters at a wavelength of 0.65 μm show pronounced differences for the four types of ice crystals, whereas the counterparts at a wavelength of 2.13 μm show similar variations with the viewing zenith angle and relative azimuth angle. However, the values of the results for the two wavelengths are noticeably different.     

The conductivity properties of protons in ice and mechanism of magnetization of liquid water

From a study of electrical conductivity of protons in the hydrogen-bonded chains in ice we confirm that the magnetization of liquid water is caused by proton transfer in closed hydrogen-bonded chains occurring as a first order phase transition, through which the ice becomes liquid water. We first study the conductive properties of proton transfer along molecular chains in ice crystals in our model. Ice is a typical hydrogen-bonded molecular system, in which the interaction of localized fluctuation of hydrogen ions (H⁺) with deformation of a structure of hydroxyl group (OH) results in soliton motion of the protons along the molecular chains via ionic and bonded defects. We explain further the quantum conductive properties of proton transfer and determine its mobility and conductivity under constant electric-field using a new theory of proton transfer, which agree with experimental values. From features of first order phase-transition for ice, and some experimental data of pure and magnetized water we confirm further that there are not only free water molecules, but also many linear and closed hydrogen-bonded chains consisting of many polarized water-molecules in the liquid water. Thus a ring proton-current, which resembles to a “molecular current” or a “small magnet” in solids, can occur in the closed hydrogen-bond chains under action of an externally applied magnetic field. Then the water molecules in the closed chains can be orderly arrayed due to the magnetic interaction among these ring proton currents and the externally applied magnetic field. This is just the magnetized effect of the water. In such a case the optical and electronic properties of the water, including the dielectric constant, magnetoconductivity, refraction index, Raman and Infrared absorption spectra, are changed. We determine experimentally the properties of the magnetized water which agree with the theoretical results of our model. However, the magnetized effect of water is, in general, very small, and vanishes at temperatures above 100 ^○C.     

On the reflection and polarisation properties of ice cloud

A number of cirrus ice crystal scattering models are tested using measurements of total reflectance and polarised reflectance obtained from the space-based polarisation and directionality of Earth's reflectances (POLDER) instrument. In this paper, 1 day of global POLDER data is utilised taken from the 25 June 2003 to test the assumed ice crystal models. The POLDER instrument is able to test the validity of various ice crystal models since it can measure the total reflectance and polarised reflectance at up to 14 different viewing directions almost simultaneously between the scattering angles of about 60–180°. It is found that ice crystal models that are randomised (in this case the randomisation element is through distortion) from some pristine ice crystal geometry best fit simultaneous measurements of total and polarised reflectance. The optimal distortion parameter that best describes the POLDER measurements is found to be 0.40, which has been applied to a randomly oriented six-branched bullet-rosette and randomly oriented chain-like aggregate. Moreover, distorted ice crystals that have undergone significant distortions beyond 0.40 may fit the total reflectance measurements but not the polarisation measurements. Therefore, total reflectance measurements by themselves do not provide sufficient information to constrain assumed complex/distorted ice crystal models.     

Temperature dependence of ice optical constants: Implications for simulating the single-scattering properties of cold ice clouds

For a spectrum from ultraviolet to microwave and a temperature range from 160 to 270 K, the optical constants of water ice are compiled on the basis of the Kramers-Kronig relation in conjunction with existing datasets reported in literature. Significant temperature dependence is observed in both the mid-infrared and longer wavelengths. A sensitivity study at wavelengths in the infrared split window region indicates that the temperature dependence of the single-scattering properties of ice crystals is not negligible. Thus, it is necessary to take into account the temperature dependence of ice optical constants when simulating the radiative properties of cirrus clouds for various applications to remote sensing under cirrus cloud conditions.     

IR spectroscopic study of surface properties of amorphous water ice

The state of the surface of amorphous ice with a specific surface area of about 160 m²/g obtained by the condensation of water vapor at 77 K is studied by IR spectroscopy. As the temperature increases to 130–160 K, absorption bands of surface hydroxyl groups vanish, whereas changes in bands characteristic of hydroxyl groups in the bulk of ice are indicative of a phase transition of ice from amorphous to the polycrystalline structure. The surface sites of amorphous ice are characterized with low-temperature adsorption of carbon monoxide. It is shown that there are two types of CO adsorption sites, free hydroxyl groups and oxygen atoms of surface coordinately unsaturated water molecules. Upon adsorption of nitrogen, methane, and carbon monoxide, in addition to the perturbation of surface OH groups, reversible changes in the spectrum are observed in the region of vibrations of bulk hydroxyls, which indicate that the strength of hydrogen bonds between water molecules in the surface layer of icy particles increases approaching the strength of these bonds in the crystal and that the ice surface becomes less amorphous. These results indicate that the properties of the ice surface layer substantially depend on the presence of adsorbed molecules.     

Electromagnetic properties of ice near the water-ice phase transition temperature

Freshwater ice in a cavity was studied under heating to 0°C followed by cooling at a frequency of 6.3 GHz. Splitting of a resonant transmission line at 60–70 MHz was detected. This effect may be associated with the existence of two vibrational modes in ice, with the coupling between them increasing near 0°C. In such a medium, two waves with identical polarizations and similar wavenumbers can exist. This assumption was confirmed experimentally by measuring the 13-GHz radiation transmission through a natural freshwater ice cover. These measurements detected signal oscillations caused by the interference of two waves, with alternation of maxima and minima with a period of 4.6 m, which corresponds to a beat frequency of ～37 MHz.     

Dependence of ice crystal optical properties on particle aspect ratio

The single-scattering properties of randomly oriented hexagonal ice crystals have been extensively used to study the bulk radiative properties of ice clouds. It has been reported in the literature that the asymmetry factors of these particles vary with their aspect ratios in a “V-pattern” with the minimum at a unit aspect ratio. However, this phenomenon was not explained in the previous studies. The present paper reports on an in-depth analysis of the optical properties of hexagonal ice crystals. It is shown that the delta-transmission is primarily responsible for the aforementioned “V-pattern” variation of the asymmetry factor as a function of the aspect ratio. Additionally, the term (1?f_δ)g is also partially responsible for the large values of the total asymmetry factor in the case of small aspect ratios, where f_δ indicates the ratio of the amount of the energy associated with the delta-transmission rays to the total amount of the scattered energy and g is the asymmetry factor associated with the geometric optics rays.     

Dielectric properties of ice and liquid water from first-principles calculations

We present a first-principles study of the static dielectric properties of ice and liquid water. The eigenmodes of the dielectric matrix E are analyzed in terms of maximally localized dielectric functions similar, in their definition, to maximally localized Wannier orbitals obtained from Bloch eigenstates of the electronic Hamiltonian. We show that the lowest eigenmodes of E (-1) are localized in real space and can be separated into groups related to the screening of lone pairs, intra-, and intermolecular bonds, respectively. The local properties of the dielectric matrix can be conveniently exploited to build approximate dielectric matrices for efficient, yet accurate calculations of quasiparticle energies.     

Evolution with time of the dielectric properties of dispersed ice microcrystals

Summary The evolution with time of the characteristics of the dielectric relaxation of water molecules in dispersions of ice microcrystals has been studied by means of the thermally stimulated depolarization current (TSDC) method. With advancing stage of evolution,i.e. with increasing preservation time at constant preservation temperature and with increasing preservation temperature at constant preservation time, the mean values of relaxation time and activation energy have been found to decrease. The extent and the rate of the evolution have been compared to those in other forms of ice: ice samples with high content of disturbance, polycrystalline ice samples and single ice crystals. The observed similarities and differences in the behaviour of the different ice forms have been discussed in terms of the influence of extrinsic physical and chemical defects on the generation and motion of orientational Bjerrum defects.     

On the electric properties of ice doped with NH4F

Measurements of the dielectric constant and the electric conductivity of ice doped with about 10^?2N NH₄F led to an activation energy of the relaxation time of 0.10 eV=2.4 kcal/Mol. Despite the fact that the relaxation times of pure and doped ice are about the same at temperatures close to ?10°C, the statement ofDengel et al. [1], that NH₄F doping does not affect the dielectric relaxation, cannot be maintained in view of the large difference in activation energies.     

The O-H distance in ice

The thermodynamic properties of normal and para-hydrogen are computed from multiple time-step path integral hybrid Monte Carlo (PIHMC) simulations. Four different isotropic pair potentials are evaluated by comparing simulation results with experimental data. The Silvera–Goldman potential is found to be the most accurate of the potentials tested for computing the density and internal energy of fluid hydrogen. Using the Silvera–Goldman potential, simulation and experimental data are compared on isobars ranging from 0.1 to 100 MPa and for temperatures from 18 to 300 K. The Gibbs free energy is calculated from the PIHMC simulations by an adaptation of Widom's particle insertion technique to a path integral fluid. A new method is developed for computing phase equilibria for quantum fluids directly by combining PIHMC with the Gibbs ensemble technique. This Gibbs–PIHMC method is used to calculate the vapour–liquid phase diagram of hydrogen from simulations. Agreement with experimental data is good.     

Effect of weak magnetic fields on the properties of water and ice

We establish that a number of physical properties of water and ice are significantly changed by an alternating magnetic field of a certain frequency. The changes in the physical parameters of ice are several times stronger than the changes in the corresponding parameters of water. Heating water to 50°C destroys the magnetic effects. When the field is much weaker than the geomagnetic field, a change in water purity (bidistilled instead of distilled water) only broadens the extrema observed in the state dependences of water and ice on the frequency of the alternating magnetic field of constant amplitude. The magnitude and intensity of these extrema are unaffected by water purity. The effects of the geomagnetic field on the properties of ice and water are also discussed.Translated form Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 13–17, May, 1988.     

Ab initio study of the structure and dynamical properties of crystalline ice

We investigated the structural and dynamical properties of a tetrahedrally coordinated crystalline ice from first principles based on density functional theory within the generalized gradient approximation with the projected augmented wave method. First, we report the structural behaviour of ice at finite temperatures based on the analysis of radial distribution functions obtained by molecular dynamics simulations. The results show how the ordering of the hydrogen bonding breaks down in the tetrahedral network of ice with entropy increase, in agreement with the neutron diffraction data. We also calculated the phonon spectra of ice in a 3× 1× 1 supercell using the direct method. So far, due to the direct method used in this calculation, the phonon spectra are obtained without taking into account the effect of polarization arising from dipole–dipole interactions of water molecules, which is expected to yield the splitting of longitudinal and transverse optic modes at the Γ point. The calculated longitudinal acoustic velocities from the initial slopes of the acoustic mode are in reasonable agreement with the neutron scattering data. Analysis of the vibrational density of states shows the existence of a boson peak at low energy of the translational region, a characteristic common to amorphous systems.     

The viscoplastic behaviour of ice in polar ice sheets: experimental results and modelling

The slow motion of polar ice sheets is governed by the viscous deformation of anisotropic ices. Physical mechanisms controlling the deformation of ice crystal and polycrystal are reviewed. For the low stress conditions prevailing in ice sheets, the stress exponent of the flow law is lower than 2 and the deformation is dominated by the glide of dislocations on the basal plane. The mismatch of slip at grain boundaries induces large strain inhomogeneities partially relieved in ice sheets by grain growth and recrystallisation. The hard X-ray diffraction technique can be used to describe the orientation gradients within grains. The structure of ice along deep ice cores in Antarctica and Greenland exhibits significant changes in the shape, size and orientation of grains. A large variation of ice viscosity with depth is therefore expected. Polycrystal deformation models accounting for the changing rheological properties of polar ice are discussed. These models must predict and take into account the intracrystalline field heterogeneity. To cite this article: M. Montagnat, P. Duval, C. R. Physique 5 (2004).     

北极冰下双轴声道传播特性研究

本文利用第六次北极科学考察的所得的楚科奇海温盐深数据,开展了北极海域声传播特性研究。通过引入Diachok海冰散射模型,将海冰界面模拟为无限椭圆形半圆柱体在自由界面的随机分布,利用Twersky散射理论计算了海冰的反射系数。使用简正波中的KRAKENC模型,结合海冰参数,进行了传播损失仿真分析。研究表明,北极的双声道波导中表面声道的传播特性与声源频率和收发深度紧密相关。深海声道与北极典型声速结构的传播特性一致,具有频率选择特性,在20 Hz左右时传播特性较为理想。此外,在远程传播时,深海声道的传播特性要优于表面声道。