Ice Habit Research Articles

Thermal hysteresis caused by non-equilibrium antifreeze activity of poly(vinyl alcohol)

Thermal hysteresis is often taken as the primary manifestation of antifreeze activity of biological non-equilibrium antifreezes, such as antifreeze proteins and antifreeze glycoproteins. Here we report evidence of the thermal hysteresis caused by poly(vinyl alcohol) (PVA). Similar to biological non-equilibrium antifreezes, PVA molecules stopped the growth of ice in the melt at temperatures even below the melting temperature of ice, although PVA exhibited very slight thermal hysteresis compared with most known biological antifreezes. The crystal habit of ice in the melt in the presence of PVA indicated that PVA molecules affected specific planes of the ice crystal.

Terminal fall velocity and the FASTEX cyclones

AbstractKnowledge of water‐drop and ice‐crystal terminal velocities is particularly important for an adequate representation of particle sedimentation in cloud‐resolving and large‐scale models. In this paper, a new method is proposed to retrieve terminal fall velocity from airborne‐Doppler‐radar observations. To extract the terminal fall velocity from the Doppler information, which mixes the three wind components and the terminal fall velocity, statistical considerations are introduced, stating that for a long sampling time span (a whole aircraft mission, for instance) and for moderate storms such as stratiform precipitation, the mean vertical air motions should vanish with respect to the mean terminal fall velocity. Statistical power‐law relationships between terminal fall speed and radar reflectivity are then developed, as well as profiles of mean terminal fall velocity. This underlying hypothesis of the method is validated with in situ measurements of the vertical wind component, averages of convective‐scale retrievals of the vertical wind component, and terminal fall speed–radar reflectivity (VT–Z) relationships derived from in situ measurements of the drop size distribution. These comparisons all indicate that the vertical air motion can indeed be neglected with respect to the terminal fall speed.A detailed analysis of the statistical relationships obtained in liquid and ice phases for six frontal cyclones at different stages of development shows that a ‘universal’ VT–Z rain relationship can be proposed for North Atlantic frontal cyclones at mature stage. This result and further arguments developed in the paper suggest that the drop size distributions are ‘equilibrium’ distributions. In the ice phase, such a ‘universal’ relationship is not found. It is nevertheless suggested in this study that such a general relationship might be derived if the frontal cyclones are split into categories depending on their stage of development. These VT–Z ‘universal’ relationships can be introduced in large‐scale model parametrization schemes in order to better describe the sedimentation of ice and water and dynamical–microphysical interactions occurring within North Atlantic frontal cyclones.Finally, a procedure is proposed to estimate the most representative type of ice particle from 2D‐P in situ sensor and airborne‐Doppler‐radar measurements. It consists of calculating the mean flight‐level Z and the VT–Z relationships in the ice phase for several theoretical ice habits, and to identify the ice habit that reasonably reproduces both the radar‐derived mean flight‐level Z and VT–Z ice relationship. Copyright © 2003 Royal Meteorological Society

Parameterization of shortwave cloud optical properties for a mixture of ice particle habits for use in atmospheric models

On the basis of single‐scattering optical properties precomputed with an improved geometric optics method, the bulk absorption coefficient, single‐scattering albedo, and asymmetry factor of ice particles have been parameterized as a function of the effective particle size of a mixture of ice habits, the ice water amount, and spectral band. The parameterization has been applied to computing fluxes for sample clouds with various particle size distributions and assumed mixtures of particle habits. It is found that flux calculations are not overly sensitive to the assumed particle habits if the definition of the effective particle size is consistent with the particle habits on which the parameterization is based. Otherwise, the error in the flux calculations could reach a magnitude unacceptable for climate studies. Different from many previous studies, the parameterization requires only an effective particle size representing all ice habits in a cloud layer but not the effective size of individual ice habits.

Nucleation effects on the habit of vapour grown ice crystals from −18 to −42°C

AbstractIce crystals have been nucleated and grown by a new method where supersaturation is controlled by combining static diffusion chamber and expansion chamber techniques. Crystals were nucleated and grown on $50\ \mu \hbox{m}$ diameter glass filaments at pressures of 500 to 300 hPa, typical of clouds with temperatures from −18 to −42°C, respectively. Crystals were also nucleated on particles of finely powdered silver iodide and kaolinite adhering to glass filaments, in order to investigate effects on habit due to different nucleating materials. Critical supersaturations for nucleation were measured for each case and were in good agreement with previous nucleation studies. Crystals were grown at ice supersaturations which ranged from less than 1% to just above water saturation. For ice growth below a critical supersaturation, nucleation was achieved by applying a brief adiabatic expansion to the static diffusion chamber with a filament in place and the chamber evacuated to the target pressure for the temperature of interest. Nucleation occurred at a critical supersaturation, followed by growth at a lower value. A review of past laboratory experiments and recent in situ observations reveals good agreement between laboratory and field observations when the effects of nucleating methods and growth times are taken into account. Contrary to studies which report the habit of ice as ‘prism’‐like or columnar below approximately −22°C, the habit is found to be plate‐like for temperatures ranging from −18°C to −40°C at ice supersaturations relevant to the atmosphere. Additionally, the plate‐like‐habit distribution is dominated by polycrystalline forms, which is consistent with aspects of past laboratory studies and recent observations obtained with improved aircraft instrumentation. The habits and habit distributions obtained from glass and kaolinite most closely resemble those observed in the atmosphere, while the results from silver iodide show large differences. Below −40°C, the habit becomes columnar except at low supersaturation, and is still dominated by polycrystals which appear as rosettes for ice supersaturations greater than about 20%. ‘Bullet rosettes’ were observed to nucleate and grow on clean glass threads below −40°C but not on kaolinite which predominantly grew single columns and irregular polycrystals with columnar components; silver iodide produced single columns with few polycrystals. This behaviour indicates that rosettes result from ice nuclei which share few or no crystallographic similarities with ice, and is consistent with that expected from homogeneous nucleation. Critical supersaturation measurements for nucleation were extended down to −70°C, and revealed that below −40°C ice crystals can nucleate on glass at ice supersaturations of 25%, and at values of approximately 15% on kaolinite or silver iodide. Copyright © 2002 Royal Meteorological Society

A method for the parameterization of cloud optical properties in bulk and bin microphysical models. Implications for arctic cloudy boundary layers

Computationally efficient and numerically accurate methods for computing band-averaged cloud optical properties for radiative transfer interactions with various microphysical parameterizations are described. Parameterizations for bulk microphysical models employing generalized gamma distribution representations of the size spectra and binned representations, in which the size spectra fluctuate with time, are discussed. It is shown that simple exponential fits and look-up tables may be used with minimal computational cost and high accuracy for bulk microphysical models. Binned microphysical representations may be parameterized using mean properties for each bin, if averaged appropriately. The implications for the radiative scheme are discussed in comparison with the computed radiative budget of fall/spring season mixed-phase Arctic stratus clouds (ASC). Compared to liquid clouds of the same water path, mixed-phase ASC absorb and reflect less radiation, and transmit more radiation to the surface. This results in greater cooling (warming) of the surface, by up to 60 W m −2, in the infrared (solar) by mixed-phase clouds. The radiative properties of mixed-phase clouds show a significant sensitivity to crystal habit for clouds with ice water paths ≳25 g m −2. Surface net fluxes and cloud absorption may vary by up to 15 W m −2, depending on the ice habit. It is also shown that mixed-phase clouds are more sensitive to the choice of ice effective radius ( r e,i) than liquid clouds are to r e. Using values of from the literature, it is shown that the surface net fluxes can vary by as much as 50 W m −2 depending on the value of r e,i. Furthermore, it is shown that the sign of the surface net flux (i.e. warming or cooling) may be dependent on the value of r e,i selected.

Thermal analysis of the tertiary butyl alcohol-water system and its implications on freeze-drying.

Utilizing differential scanning calorimetry (DSC) for tertiary butyl alcohol (TBA) solutions a phase diagram was constructed for the TBA-water system. By utilizing thermal treatment during the DSC measurements the metastable states were eliminated. The phase diagram fit that for a congruently melting compound in which compound formation occurred with a maximum at 70% TBA representing pure TBA hydrate. Two eutectics occurred at 20% (Eutectic A) and 90% (Eutectic B). A freeze-drying microscope revealed that TBA altered the crystal habit of ice. A concentration of 3% TBA was required before large needle-shaped ice crystals became evident. The addition of 10% TBA to the system resulted in even finer needle-shaped ice crystals. At the eutectic compositions (20% and 90% TBA), the frozen eutectic mixture could not be resolved with the microscope because eutectic crystals are very small. The 70% TBA solution, which corresponds to the melting of pure TBA hydrate, formed very large hydrate crystals. The rate of sublimation of the TBA and water molecules was found to be concentration dependent. At concentrations below 20% TBA (water rich portion of the phase diagram) water molecules sublimed faster while at concentrations above 20% TBA (TBA rich portion of the phase diagram) TBA molecules sublimed faster. At the eutectic A composition, both TBA and water molecules sublimed at the same rate. This may be because all of the TBA molecules are strongly associated with each other in the form of a clathrate hydrate.

The effect of tertiary butyl alcohol on the resistance of the dry product layer during primary drying.

The addition of low concentrations of tertiary butyl alcohol (TBA) (3-10% w/v) was shown to influence the crystal habit of ice by causing the formation of needle-shaped ice crystals. The sublimation of these needle-shaped ice crystals resulted in a dry product layer with little resistance. Using a microbalance technique it was shown that the primary drying stage for 5% w/v sucrose solution was considerably shorter when 5% w/v TBA was added due to a lower resistance of the dried cake above the frozen solution. In the absence of TBA the frozen solution had an initially high resistance of approximately 60 cm2 torr hr/gm due to the formation of a skin; once the skin cracked the resistance reached a constant value of 10 cm2 torr hr/gm. The solution containing TBA had a dried product resistance in the range of 0.5-3 cm2 torr hr/gm. The total time required to dry the product in the absence of TBA in the microbalance was 100 hours as compared to 10 hours for the solution containing 5% w/v TBA. The specific surface area of the freeze-dried cake produced from a 5% w/v sucrose solution containing 5% w/v TBA was 8.57 m2/gm as compared to 0.67 m2/gm for solutions not containing TBA. The addition of TBA to the sucrose solution did not change the collapse temperature, but the rapid rate of sublimation prevented the product from ever reaching the collapse temperature.

Characterization of different ice habits according to nucleation processes in the electrolyte LiCl · RH 2O (6 < R < 9)

The ability to observe different ice nucleation processes in LiCl · RH 2O electrolytes is demonstrated by light scattering experiments. The homogeneous ice nucleation mechanism is analyzed on the basis of Turnbull's theory. This nucleation operates in supercooled water, as deduced from the volumic dependence of the samples on R(5 < R < 9), and is compatible with the definition of the electrolyte as a heterogeneous submicroscopic LiCl·6H 2O medium composed of H 2O and LiCl·6H 2O.

Noctilucent clouds: Simulation studies of their genesis, properties and global influences

The formation, evolution and properties of noctilucent clouds are studied using a timedependent one-dimensional model of ice particles at mesospheric altitudes. The model treats ice crystals, meteoric dust, water vapor and air ionization as fully interactive cloud elements. For ice particles, the microphysical processes of nucleation, condensation, coagulation and sedimentation are included; the crystal habits of ice are also accounted for. Meteoric dust is analyzed in the manner of Hunten et al. (1980). The simulated particle sizes range from 10 Å to 2.6μm. The chemistry of water vapor and the charge balance of the mesosphere are also analyzed in detail. Based on model calculations, including numerous sensitivity tests, several conclusions are reached. Extremely cold mesopause temperatures (<140K) are necessary to form noctilucent clouds; such temperatures only exist at high latitudes in summer. A water vapor concentration of 4–5 ppmv is sufficient to form a visible cloud. However, a subvisible cloud can exist in the presence of only 1 ppmv of H 2O. Ample cloud condensation nuclei are always present in the mesosphere; at very low temperatures, either meteoric dust or hydrated ions can act as cloud nuclei. To be effective, meteoric dust particles must be larger than 10–15 Å in radius. When dust is present, water vapor supersaturations may be held to such low values that ion nucleation is not possible. Ion nucleation can occur, however, in the absence of dust or at extremely low temperatures (<130K). While dust nucleation leads to a small number (<10cm −3) of large ice particles (>0.05 μm radius) and cloud optical depths (at 550 nm) ∼10 −4, ion nucleation generally leads to a large number (∼10 3cm −3) of smaller particles and optical depths ∼10 −5). However, because calculated nucleation rates in noctilucent clouds are highly uncertain, the predominant nucleus for the clouds (i.e., dust or ions) cannot be unambiguously established. Noctilucent clouds require several hours-up to a day-to materialize. Once formed, they may persist for several days, depending on local meteorological conditions. However, the clouds can disappear suddenly if the air warms by 10–20 K. The environmental conditions which exist at the high-latitude summer mesopause, together with the microphysics of small ice crystals, dictate that particle sizes will be ≲ 0.1 μm radius. The ice crystals are probably cubic in structure. It is demonstrated that particles of this size and shape can explain the manifestations of noctilucent clouds. Denser clouds are favored by higher water vapor concentrations, more rapid vertical diffusion and persistent upward convection (which can occur at the summer pole). Noctilucent clouds may also condense in the cold “troughs” of gravity wave trains. Such clouds are bright when the particles remain in the troughs for several hours or more; otherwise they are weak or subvisible. Model simulations are compared with a wide variety of noctilucent cloud data. It is shown that the present physical model is consistent with most of the measurements, as well as many previous theoretical results. Ambient noctilucent clouds are found to have a negligible influence on the climate of Earth. Anthropogenic perturbations of the clouds that are forecast for the next few decades are also shown to have insignificant climatological implications.

Growth kinetics of ice from the vapour phase and its growth forms

A new interpretation of the habits of ice growing from vapour is proposed. The basic habits of ice alternate three times: plates (A) → -4°C → columns (B) → -10°C → plates (C) → between -20°C and -35°C → columns (D). The theory is based on a view- that the surface of ice just below 0°C is covered with a quasi-liquid layer, whose thickness ϑ or coverage δ decreases with falling temperature, and therefore the growth mechanism of a crystal face changes also as follows: (I) Vapour—Quasi-Liquid— Solid mechanism (δ > 1), (II) Adhesive Growth on a surface strongly adsorbed by H 2O molecules (0.02 < δ < 1) and (III) Two- Dimensional Nucleation Growth on a surface with low eigen adsorption (δ < 0.02). The type of surface structure and consequently the growth mechanism depends on the surface orientation and the temperature. The complicated habit change is caused mainly by the combination of surface kinetics of the {0001} and {101̄10} face. The first and second conversion temperature ( T AB, T BC) are expected to be independent of the absolute supersaturation δ P as found in experiments. On the other hand, the third ( T CD) is the temperature where the usual two-dimensional nucleation growth rate of the {0001} face reaches the one of the {10 1 0} face, and exceeds it by the effect of diffusion field, so that the third conversion temperature falls with decreasing δ P. The marked columnar crystals observed at -7°C can be explained only by taking into account the spherical volume diffusion field near the {0001} face and a cylindrical one near the {101̄10} face. For plate-like crystals between -10°C and -20°C to -35°C the surface diffusion from {0001} to {1010} and volume diffision with cylindrical symmetry near {101̄10} faces is very important.

雪結晶の成長カイネティクスおよび晶癖変化

A new interpretation on habits of ice growing from vapour is proposed. The primary habits of ice alternate three times (plates → -4°C→columns →-10°C plates →from -20°C to -35°C→columns) with decreasing temperature.The theory is based on a viewpoint that the surface of ice just below 0°C is covered with a quasi liquid layer, whose depth or coverage ϑ decreases with decrearing temperature, and then the growth mechanism of a surface changes also as followings : a) Vapour-Quasi Liquid-Solid-Mechanism (ϑ>1), b) Adhesive Growth on the surface with strong eigen adsorption by water molecules (0.01<ϑ< 1), and c) Two-Dimensional Nucleation Growth on the surface with little eigen adsorption (ϑ<0.01) . As the change in surface structure as well as growth mechanism depend on surface orientation, the complicated habits change is caused mainly by the combination of growth mechanism of each surface, i. e. basal {0001} -and prism {1010} -surface.

Adsorption inhibition as a mechanism of freezing resistance in polar fishes.

Polar fishes are known to have serum proteins and glycoproteins that protect them from freezing, by a noncolligative process. Measurements of antifreeze concentrations in ice and scanning electron micrographs of freeze-dried antifreeze solutions indicate that the antifreezes are incorporated in ice during freezing. The antifreezes also have a pronounced effect on the crystal habit of ice grown in their presence. Each of four antifreezes investigated caused ice to grow in long needles whose axes were parallel to the ice c axis. Together these results indicate the antifreezes adsorb to ice surfaces and inhibit their growth. A model in which adsorbed antifreezes raise the curvature of growth steps on the ice surface is proposed to account for the observed depression of the temperature at which freezing occurs and agrees well with experimental observations. The model is similar to one previously proposed for other cases of crystal growth inhibition.

Habits of ice grown in supercooled water and aqueous solutions

Abstract At small supercoolings the direction of growth of ice in pure water and aqueous solutions is parallel to the basal plane. As the supercooling is increased the growth direction of the dendrites become inclined at an angle to the basal plane, the angle increasing with supercooling. The most general habit of growth now has the form of two symmetrically situated hollow hexagonal pyramids joined at their apices. At still larger supercoolings further growth ensues from the initial dendrites comprising the pyramidal segments and complex three-dimensional structures are produced which are nevertheless single crystals. It is noted that the pyramidal growth habit occurs also in ice crystals formed from the vapour phase at high supersaturations and in Tyndall figures produced in the melting of ice. The non-rational growth of the dendrites is explained in terms of deposition predominantly on basal surfaces on one side of the dendrite tip and on prism faces on the other, the direction of growth being determin...