Sample records for quasi-spherical ice crystals

  1. Cluster self-organization of intermetallic systems: Quasi-spherical nanocluster precursors with internal Friauf polyhedra (A-172) and icosahedra (B-137) in the Li19Na8Ba15 ( hP842) crystal structure

    NASA Astrophysics Data System (ADS)

    Ilyushin, G. D.; Blatov, V. A.

    2010-12-01

    A combinatorial and topological analysis of Li19Na8Ba15 ( hP842, a = 20 Å, c = 93 Å, V = 33552 Å3, P bar 3 ) has been performed using computer methods (the TOPOS program package). Two types of crystal-forming quasi-spherical nanoclusters about 20 Å in diameter with internal Friauf polyhedra (A-172) and icosahedra (B-137) have been established by the complete decomposition of the 3D factor graph of the structure into cluster substructures. Each type of nanoclusters forms close-packed 2D layers 36, which alternate along the c axis. The B-137 and A-172 nanoclusters are composed of three layers and have shell compositions (1 + 12 + 32 + 92) and (1 + 16 + 59 + 103) with local symmetries 3 and bar 3 , respectively; they were revealed for the first time in crystal structures as cluster precursors. The icosahedral B-137 nanocluster contains a 104-atom quasicrystal approximant (Samson cluster).

  2. Bacterial Ice Crystal Controlling Proteins

    PubMed Central

    Lorv, Janet S. H.; Rose, David R.; Glick, Bernard R.

    2014-01-01

    Across the world, many ice active bacteria utilize ice crystal controlling proteins for aid in freezing tolerance at subzero temperatures. Ice crystal controlling proteins include both antifreeze and ice nucleation proteins. Antifreeze proteins minimize freezing damage by inhibiting growth of large ice crystals, while ice nucleation proteins induce formation of embryonic ice crystals. Although both protein classes have differing functions, these proteins use the same ice binding mechanisms. Rather than direct binding, it is probable that these protein classes create an ice surface prior to ice crystal surface adsorption. Function is differentiated by molecular size of the protein. This paper reviews the similar and different aspects of bacterial antifreeze and ice nucleation proteins, the role of these proteins in freezing tolerance, prevalence of these proteins in psychrophiles, and current mechanisms of protein-ice interactions. PMID:24579057

  3. Cluster self-organization of intermetallic systems: Quasi-spherical nanocluster precursors with internal Friauf polyhedra (A-172) and icosahedra (B-137) in the Li{sub 19}Na{sub 8}Ba{sub 15} (hP842) crystal structure

    SciTech Connect

    Ilyushin, G. D., E-mail: ilyushin@ns.crys.ras.ru [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Blatov, V. A. [Samara State University (Russian Federation)

    2010-12-15

    A combinatorial and topological analysis of Li{sub 19}Na{sub 8}Ba{sub 15} (hP842, a = 20 A, c = 93 A, V = 33552 A{sup 3}, P3-bar) has been performed using computer methods (the TOPOS program package). Two types of crystal-forming quasi-spherical nanoclusters about 20 A in diameter with internal Friauf polyhedra (A-172) and icosahedra (B-137) have been established by the complete decomposition of the 3D factor graph of the structure into cluster substructures. Each type of nanoclusters forms close-packed 2D layers 3{sup 6}, which alternate along the c axis. The B-137 and A-172 nanoclusters are composed of three layers and have shell compositions (1 + 12 + 32 + 92) and (1 + 16 + 59 + 103) with local symmetries 3 and 3-bar, respectively; they were revealed for the first time in crystal structures as cluster precursors. The icosahedral B-137 nanocluster contains a 104-atom quasicrystal approximant (Samson cluster).

  4. Viewing Ice Crystals Using Polarized Light.

    ERIC Educational Resources Information Center

    Kinsman, E. M.

    1992-01-01

    Describes a method for identifying and examining single ice crystals by photographing a thin sheet of ice placed between two inexpensive polarizing filters. Suggests various natural and prepared sources for ice that promote students' insight into crystal structures, and yield colorful optical displays. Includes directions, precautions, and sample…

  5. Modeling Commercial Turbofan Engine Icing Risk With Ice Crystal Ingestion

    NASA Technical Reports Server (NTRS)

    Jorgenson, Philip C. E.; Veres, Joseph P.

    2013-01-01

    The occurrence of ice accretion within commercial high bypass aircraft turbine engines has been reported under certain atmospheric conditions. Engine anomalies have taken place at high altitudes that have been attributed to ice crystal ingestion, partially melting, and ice accretion on the compression system components. The result was degraded engine performance, and one or more of the following: loss of thrust control (roll back), compressor surge or stall, and flameout of the combustor. As ice crystals are ingested into the fan and low pressure compression system, the increase in air temperature causes a portion of the ice crystals to melt. It is hypothesized that this allows the ice-water mixture to cover the metal surfaces of the compressor stationary components which leads to ice accretion through evaporative cooling. Ice accretion causes a blockage which subsequently results in the deterioration in performance of the compressor and engine. The focus of this research is to apply an engine icing computational tool to simulate the flow through a turbofan engine and assess the risk of ice accretion. The tool is comprised of an engine system thermodynamic cycle code, a compressor flow analysis code, and an ice particle melt code that has the capability of determining the rate of sublimation, melting, and evaporation through the compressor flow path, without modeling the actual ice accretion. A commercial turbofan engine which has previously experienced icing events during operation in a high altitude ice crystal environment has been tested in the Propulsion Systems Laboratory (PSL) altitude test facility at NASA Glenn Research Center. The PSL has the capability to produce a continuous ice cloud which are ingested by the engine during operation over a range of altitude conditions. The PSL test results confirmed that there was ice accretion in the engine due to ice crystal ingestion, at the same simulated altitude operating conditions as experienced previously in flight. The computational tool was utilized to help guide a portion of the PSL testing, and was used to predict ice accretion could also occur at significantly lower altitudes. The predictions were qualitatively verified by subsequent testing of the engine in the PSL. The PSL test has helped to calibrate the engine icing computational tool to assess the risk of ice accretion. The results from the computer simulation identified prevalent trends in wet bulb temperature, ice particle melt ratio, and engine inlet temperature as a function of altitude for predicting engine icing risk due to ice crystal ingestion.

  6. Retardation of ice crystallization by short peptides

    Microsoft Academic Search

    Jun Soo Kim; Arun Yethiraj

    2009-01-01

    The effect of short peptides on the growth of ice crystals is studied using molecular dynamics simulations. The simulations focus on two sequences (Gly-Pro-Ala-Gly and Gly-Gly-Ala-Gly) that are found in collagen hydrolysate, a substance that is known to retard crystal growth. In the absence of peptides, the growth of ice crystal in the solution with the ice\\/water interface is observed

  7. An Overview of NASA Engine Ice-Crystal Icing Research

    NASA Technical Reports Server (NTRS)

    Addy, Harold E., Jr.; Veres, Joseph P.

    2011-01-01

    Ice accretions that have formed inside gas turbine engines as a result of flight in clouds of high concentrations of ice crystals in the atmosphere have recently been identified as an aviation safety hazard. NASA s Aviation Safety Program (AvSP) has made plans to conduct research in this area to address the hazard. This paper gives an overview of NASA s engine ice-crystal icing research project plans. Included are the rationale, approach, and details of various aspects of NASA s research.

  8. Retardation of ice crystallization by short peptides

    NASA Astrophysics Data System (ADS)

    Kim, Jun Soo; Yethiraj, Arun

    2009-03-01

    The effect of short peptides on the growth of ice crystals is studied using molecular dynamics simulations. The simulations focus on two sequences (Gly-Pro-Ala-Gly and Gly-Gly-Ala-Gly) that are found in collagen hydrolysate, a substance that is known to retard crystal growth. In the absence of peptides, the growth of ice crystal in the solution with the ice/water interface is observed in at a rate comparable to the experimental data. When peptides are present in the liquid phase, the crystal growth is retarded to a significant extent compared to the pure water. It is found that Gly-Pro-Ala-Gly is more effective (crystallization is up to 5 times slower than in its absence) than Gly-Gly-Ala-Gly (up to 3 times slower) implying that the role of the proline residue is important. The mechanism can be understood in the nature of binding of the peptides to the growing crystal.

  9. Evolution of crystal fabric: Ice-Age ice versus Holocene ice

    NASA Astrophysics Data System (ADS)

    Kennedy, J. H.; Pettit, E. C.

    2009-12-01

    Ice-Age ice has smaller crystals and higher concentrations of impurities than Holocene ice; these properties cause it to develop a more strongly-aligned crystal-orientation fabric. In many regions of the Antarctic and Greenland ice sheets, the Ice-Age ice is now at depth and its flow properties may dominate the ice flow patterns, particularly where sliding is minimal. We use a fabric evolution model, based on that developed by Thorsteinsson (2002), to explore the evolution of Ice-Age ice fabric along particle paths for ice within Taylor Glacier, a cold-based outlet glacier of the East Antarctic Ice Sheet. The bulk of the ice within Taylor Glacier consists of Ice-Age and older ice because the Holocene ice has ablated away (there is no Holocene ice remaining within 25km of the terminus, Aciego, 2007). We initialize the evolving fabric based on fabric measurements from Taylor Dome where available (DiPrinzio, 2003) and other ice core records. We compare model results with thin-section data from shallow cores taken near the terminus. As expected, crystal alignment strengthens along the ice particle path. Due to lateral shearing along valley walls and the ice cliffs (terminal ice cliffs are cold in winter and present a resistance to flow), a tilted single maximum is common near the terminus. The highly-aligned fabric of Ice-Age ice is significantly softer than Holocene ice in simple shear parallel to the bed, this softness not only results in faster flow rates for glaciers and ice sheets such as Taylor, but creates a climate-flow-fabric feedback loop through concentrating ice-sheet flow within the Ice-Age ice. Thorsteinsson, T. (2002), Fabric development with nearest-neighbor interaction and dynamic recrystallization, J. Geophys. Res., 107(B1), 2014, doi:10.1029/2001JB000244. S.M. Aciego, K.M. Cuffey, J.L. Kavanaugh, D.L. Morse, J.P. Severinghaus, Pleistocene ice and paleo-strain rates at Taylor Glacier, Antarctica, Quaternary Research, Volume 68, Issue 3, November 2007, Pages 303-313, ISSN 0033-5894, DOI: 10.1016/j.yqres.2007.07.013. DiPrinzio, Eos Trans. AGU, 84(46), Fall Meet. Suppl., Abstract C11C-0834, 2003

  10. Retardation of ice crystallization by short peptides.

    PubMed

    Kim, Jun Soo; Damodaran, Srinivasan; Yethiraj, Arun

    2009-04-23

    The effect of peptides on the growth of ice crystals are studied using molecular dynamics simulations. The growth of the ice crystal is simulated at a supercooling of 14 K, and the effect of a single tetrapeptide on the growth rate is calculated. For pure ice the simulated crystal grows at a rate comparable to experiment. When a peptide molecule is added near the interface, the growth rate is diminished significantly, by up to a factor of 5 for Gly-Pro-Ala-Gly and a factor of 3 for Gly-Gly-Ala-Gly. The retardation occurs via the binding of the peptide to the ice surface, suppression of ice growth near the binding site, and eventual growth of the crystal around the bound peptide. The peptide with a proline residue is more effective in retarding the crystal growth, and this can be understood from the conformation of the peptide within the frozen ice phase after overgrowth. The simulations suggest that short peptides can be effective antifreeze agents. PMID:19260668

  11. Scattering Phase Function of Bullet Rosette Ice Crystals

    Microsoft Academic Search

    Jean Iaquinta; Harumi Isaka; Pascal Personne

    1995-01-01

    Ice crystals in cirrus frequently exhibit the shape of a bullet rosette composed of multiple bullets that radiate from a junction center. The scattering phase function of these ice crystals, pertinent to the radiation budget of cirrus, may differ from the one obtained for ice crystals with a simple geometrical shape. In this paper, the authors studied the sensitivity of

  12. Proton order in the ice crystal surface

    PubMed Central

    Buch, V.; Groenzin, H.; Li, I.; Shultz, M. J.; Tosatti, E.

    2008-01-01

    The physics of the ice crystal surface and its interaction with adsorbates are not only of fundamental interest but also of considerable importance to terrestrial and planetary chemistry. Yet the atomic-level structure of even the pristine ice surface at low temperature is still far from well understood. This computational study focuses on the pattern of dangling H and dangling O (lone pairs) atoms at the basal ice surface. Dangling atoms serve as binding sites for adsorbates capable of hydrogen- and electrostatic bonding. Extension of the well known orientational disorder (“proton disorder”) of bulk crystal ice to the surface would naturally suggest a disordered dangling atom pattern; however, extensive computer simulations employing two different empirical potentials indicate significant free energy preference for a striped phase with alternating rows of dangling H and dangling O atoms, as suggested long ago by Fletcher [Fletcher NH (1992) Philos Mag 66:109–115]. The presence of striped phase domains within the basal surface is consistent with the hitherto unexplained minor fractional peaks in the helium diffraction pattern observed 10 years ago. Compared with the disordered model, the striped model yields improved agreement between computations and experimental ppp-polarized sum frequency generation spectra. PMID:18408162

  13. Volume of Ice Crystal Growing in Supercooled Water

    NASA Astrophysics Data System (ADS)

    Teraoka, Yoshikazu; Saito, Akio; Okawa, Seiji

    Recently, dynamic type of ice storage system has been high lightened, since it gives a solution to the problem of peak electrical load. The deferent types of the method of ice making produce the different types of ice, and the selection of the type of ice influence the coefficient of performance of ice storage system. Hence studying the shape of ice and its behavior such as stickiness are important. The shape of ice crystal depends on various factors such as concentration of solution, temperature, convection, time and so on. There are various types of ice exists, such as frazil ice, dendrite, needle ice, solid ice, slurry ice. However, there is no report measuring the volume of the crystal, yet, because the shape of the crystal is too complicated to measure. In this report, pure water was used and single crystal ice was formed in supercooled water. The shape of the crystal was measured in three-dimensions using Mach-Zehnder spectro-interferometer. Volume of the crystal was measured. It was found that the volume depends upon time and the degree of supercooling, and experimental equation was derived. Furthermore, projected area normal to c-axis was measured. It was found that the area depends not only on time but also the degree of supercooling.

  14. Possible Mechanisms for Turbofan Engine Ice Crystal Icing at High Altitude

    NASA Technical Reports Server (NTRS)

    Tsao, Jen-Ching; Struk, Peter M.; Oliver, Michael

    2014-01-01

    A thermodynamic model is presented to describe possible mechanisms of ice formation on unheated surfaces inside a turbofan engine compression system from fully glaciated ice crystal clouds often formed at high altitude near deep convective weather systems. It is shown from the analysis that generally there could be two distinct types of ice formation: (1) when the "surface freezing fraction" is in the range of 0 to 1, dominated by the freezing of water melt from fully or partially melted ice crystals, the ice structure is formed from accretion with strong adhesion to the surface, and (2) when the "surface melting fraction" is the range of 0 to 1, dominated by the further melting of ice crystals, the ice structure is formed from accumulation of un-melted ice crystals with relatively weak bonding to the surface. The model captures important qualitative trends of the fundamental ice-crystal icing phenomenon reported earlier1,2 from the research collaboration work by NASA and the National Research Council (NRC) of Canada. Further, preliminary analysis of test data from the 2013 full scale turbofan engine ice crystal icing test3 conducted in the NASA Glenn Propulsion Systems Laboratory (PSL) has also suggested that (1) both types of ice formation occurred during the test, and (2) the model has captured some important qualitative trend of turning on (or off) the ice crystal ice formation process in the tested engine low pressure compressor (LPC) targeted area under different icing conditions that ultimately would lead to (or suppress) an engine core roll back (RB) event.

  15. A Quasi-Spherical Gravitational Wave Solution in Kaluza-Klein Theory

    E-print Network

    Malek Zareyan

    1996-06-07

    An exact solution of the source-free Kaluza-Klein field equations is presented. It is a 5D generalization of the Robinson-Trautman quasi-spherical gravitational wave with a cosmological constant. The properties of the 5D solution are briefly described.

  16. The structure of ice crystallized from supercooled water

    NASA Astrophysics Data System (ADS)

    Murray, Benjamin

    2013-03-01

    The freezing of water to ice is fundamentally important to fields as diverse as cloud formation to cryopreservation. Traditionally ice was thought to exist in two well-crystalline forms: stable hexagonal ice and metastable cubic ice. It has recently been shown, using X-ray diffraction data, that ice which crystallizes homogeneously and heterogeneously from supercooled water is neither of these phases. The resulting ice is disordered in one dimension and therefore possesses neither cubic nor hexagonal symmetry and is instead composed of randomly stacked layers of cubic and hexagonal sequences. We refer to this ice as stacking-disordered ice I (ice Isd) . This result is consistent with a number of computational studies of the crystallization of water. Review of the literature reveals that almost all ice that has been identified as cubic ice in previous diffraction studies and generated in a variety of ways was most likely stacking-disordered ice I with varying degrees of stacking disorder, which raises the question of whether cubic ice exists. New data will be presented which shows significant stacking disorder (or stacking faults on the order of 1 in every 100 layers of ice Ih) in droplets which froze heterogeneously as warm as 257 K. The identification of stacking-disordered ice from heterogeneous ice nucleation supports the hypothesis that the structure of ice that initially crystallises from supercooled water is stacking-disordered ice I, independent of nucleation mechanism, but this ice can relax to the stable hexagonal phase subject to the kinetics of recrystallization. The formation and persistence of stacking disordered ice in the Earth's atmosphere will also be discussed. The freezing of water to ice is fundamentally important to fields as diverse as cloud formation to cryopreservation. Traditionally ice was thought to exist in two well-crystalline forms: stable hexagonal ice and metastable cubic ice. It has recently been shown, using X-ray diffraction data, that ice which crystallizes homogeneously and heterogeneously from supercooled water is neither of these phases. The resulting ice is disordered in one dimension and therefore possesses neither cubic nor hexagonal symmetry and is instead composed of randomly stacked layers of cubic and hexagonal sequences. We refer to this ice as stacking-disordered ice I (ice Isd) . This result is consistent with a number of computational studies of the crystallization of water. Review of the literature reveals that almost all ice that has been identified as cubic ice in previous diffraction studies and generated in a variety of ways was most likely stacking-disordered ice I with varying degrees of stacking disorder, which raises the question of whether cubic ice exists. New data will be presented which shows significant stacking disorder (or stacking faults on the order of 1 in every 100 layers of ice Ih) in droplets which froze heterogeneously as warm as 257 K. The identification of stacking-disordered ice from heterogeneous ice nucleation supports the hypothesis that the structure of ice that initially crystallises from supercooled water is stacking-disordered ice I, independent of nucleation mechanism, but this ice can relax to the stable hexagonal phase subject to the kinetics of recrystallization. The formation and persistence of stacking disordered ice in the Earth's atmosphere will also be discussed. Funded by the European Research Council (FP7, 240449 ICE)

  17. Ice crystallization in water's ``no-man's land''

    Microsoft Academic Search

    Emily B. Moore; Valeria Molinero

    2010-01-01

    The crystallization of water at 180 K is studied through large-scale molecular dynamics simulations with the monatomic water model mW. This temperature is in the middle of water's ``no-man's land,'' where rapid ice crystallization prevents the elucidation of the structure of liquid water and its transformation into ice with state of the art experimental methods. We find that critical ice

  18. Modeling of ice crystal growth in laminar falling films for the production of pumpable ice slurries

    Microsoft Academic Search

    Kamal A. R. Ismail; Musa M. Radwan

    2003-01-01

    A generalized model has been developed to approximate the rate of ice crystal growth in a laminar developing falling film. In this model, the conservation equations of mass, momentum, energy and the transport equation governing ice crystal growth were solved numerically using finite differences based on the control volume method. The thermophysical properties of the mixture, such as density, specific

  19. A Critical Look at Ice Crystal Growth Data KENNETH G. LIBBRECHT1

    E-print Network

    Libbrecht, Kenneth G.

    , as is the structure of ice Ih, the normal form of ice. And yet, the growth of ice crystals from the vapor exhibitsA Critical Look at Ice Crystal Growth Data KENNETH G. LIBBRECHT1 Norman Bridge Laboratory. I review published data relating to the growth of ice crystals from water vapor under various

  20. Validation Ice Crystal Icing Engine Test in the Propulsion Systems Laboratory at NASA Glenn Research Center

    NASA Technical Reports Server (NTRS)

    Oliver, Michael J.

    2014-01-01

    The Propulsion Systems Laboratory (PSL) is an existing altitude simulation jet engine test facility located at NASA Glenn Research Center in Clevleand, OH. It was modified in 2012 with the integration of an ice crystal cloud generation system. This paper documents the inaugural ice crystal cloud test in PSLthe first ever full scale, high altitude ice crystal cloud turbofan engine test to be conducted in a ground based facility. The test article was a Lycoming ALF502-R5 high bypass turbofan engine, serial number LF01. The objectives of the test were to validate the PSL ice crystal cloud calibration and engine testing methodologies by demonstrating the capability to calibrate and duplicate known flight test events that occurred on the same LF01 engine and to generate engine data to support fundamental and computational research to investigate and better understand the physics of ice crystal icing in a turbofan engine environment while duplicating known revenue service events and conducting test points while varying facility and engine parameters. During PSL calibration testing it was discovered than heated probes installed through tunnel sidewalls experienced ice buildup aft of their location due to ice crystals impinging upon them, melting and running back. Filtered city water was used in the cloud generation nozzle system to provide ice crystal nucleation sites. This resulted in mineralization forming on flow path hardware that led to a chronic degradation of performance during the month long test. Lacking internal flow path cameras, the response of thermocouples along the flow path was interpreted as ice building up. Using this interpretation, a strong correlation between total water content (TWC) and a weaker correlation between median volumetric diameter (MVD) of the ice crystal cloud and the rate of ice buildup along the instrumented flow path was identified. For this test article the engine anti-ice system was required to be turned on before ice crystal icing would occur. The ice crystal icing event, an uncommanded reduction in thrust, was able to be turned on and off by manipulating cloud TWC. A flight test point where no ice crystal icing event occurred was also duplicated in PSL. Physics based computational tools were successfully used to predict tunnel settings to induce ice buildup along the low pressure compression system flow path for several test points at incrementally lower altitudes, demonstrating that development of ice crystal icing scaling laws is potentially feasible. Analysis of PSL test data showed that uncommanded reduction in thrust occurs during ice crystal cloud on operation prior to fan speed reduction. This supports previous findings that the reduction of thrust for this test article is due to ice buildup leading to a restricted airflow from either physical or aerodynamic blockage in the engine core flow path.

  1. Ice-Crystal Fallstreaks from Supercooled Liquid Water Parent Clouds

    NASA Technical Reports Server (NTRS)

    Campbell, James R.; O'C. Starr, David; Welton, Ellsworth J.; Spinhirne, James D.; Ferrare, Richard A.

    2003-01-01

    On 31 December 2001, ice-crystal fallstreaks (e.g., cirrus uncinus, or colloquially "Mare's Tails") from supercooled liquid water parent clouds were observed by ground-based lidars pointed vertically from the Atmospheric Radiation Measurement Southern Great Plains (SGP) facility near Lamont, Oklahoma. The incidence of liquid phase cloud with apparent ice-phase precipitation is investigated. Scenarios for mixed-phase particle nucleation, and fallstreak formation and sustenance are discussed. The observations are unique in the context of the historical reverence given to the commonly observed c h s uncinus fallstreak (wholly ice) versus this seemingly contradictory coincidence of liquid water begetting ice-crystal streaks.

  2. Non-adiabatic collapse of a quasi-spherical radiating star

    E-print Network

    Ujjal Debnath; Soma Nath; Subenoy Chakraborty

    2003-10-16

    A model is proposed of a collapsing quasi-spherical radiating star with matter content as shear-free isotropic fluid undergoing radial heat-flow with outgoing radiation. To describe the radiation of the system, we have considered both plane symmetric and spherical Vaidya solutions. Physical conditions and thermodynamical relations are studied using local conservation of momentum and surface red-shift. We have found that for existence of radiation on the boundary, pressure on the boundary is not necessary.

  3. The effect of ice crystal surface roughness on the retrieval of ice cloud microphysical and optical properties

    E-print Network

    Xie, Yu

    2007-09-17

    The effect of the surface roughness of ice crystals is not routinely accounted for in current cloud retrieval algorithms that are based on pre-computed lookup libraries. In this study, we investigate the effect of ice crystal surface roughness...

  4. Diagnosing the Ice Crystal Enhancement Factor in the Tropics

    NASA Technical Reports Server (NTRS)

    Zeng, Xiping; Tao, Wei-Kuo; Matsui, Toshihisa; Xie, Shaocheng; Lang, Stephen; Zhang, Minghua; Starr, David O'C; Li, Xiaowen; Simpson, Joanne

    2009-01-01

    Recent modeling studies have revealed that ice crystal number concentration is one of the dominant factors in the effect of clouds on radiation. Since the ice crystal enhancement factor and ice nuclei concentration determine the concentration, they are both important in quantifying the contribution of increased ice nuclei to global warming. In this study, long-term cloud-resolving model (CRM) simulations are compared with field observations to estimate the ice crystal enhancement factor in tropical and midlatitudinal clouds, respectively. It is found that the factor in tropical clouds is 10 3-104 times larger than that of mid-latitudinal ones, which makes physical sense because entrainment and detrainment in the Tropics are much stronger than in middle latitudes. The effect of entrainment/detrainment on the enhancement factor, especially in tropical clouds, suggests that cloud microphysical parameterizations should be coupled with subgrid turbulence parameterizations within CRMs to obtain a more accurate depiction of cloud-radiative forcing.

  5. Mixing of the immiscible: hydrocarbons in water-ice near the ice crystallization temperature.

    PubMed

    Lignell, Antti; Gudipati, Murthy S

    2015-03-19

    Structural changes in hydrocarbon-doped water-ice during amorphous to crystalline phase conversion are investigated using polycyclic aromatic hydrocarbons (PAHs) as probes. We show that aggregation of impurity molecules occurs due to the amorphous-crystalline transition in ice, especially when they are hydrophobic molecules such as PAHs. Using ultraviolet-visible (UV-vis), Fourier-transform Infrared (FTIR), and laser-induced-fluorescence (LIF) spectroscopic techniques, we show that, although ice infrared absorption features change from a broad structureless band corresponding to amorphous ice to a sharp structured crystalline ice bands, simultaneously, sharper isolated PAH UV absorption features measured in the amorphous ice host turn broad upon ice crystallization. A simultaneous decrease in the monomer fluorescence and increase in the excimer emission band is observed, a clear indication for the formation of PAH molecular aggregates when amorphous ice is converted to crystalline ice at higher temperatures. Similar to the irreversible amorphous-crystalline phase transitions, the UV, fluorescence, and excimer emissions indicate that PAHs undergo irreversible aggregation. Our studies suggest that organic impurities exist as aggregates rather than monomers trapped in crystalline water-ice when cycled through temperatures that convert amorphous ice to crystalline ice, rendering a better insight into phenomena such as the formation of cometary crust. This aggregate formation also may significantly change the secondary reaction pathways and rates in impurity-doped ices in the lab, on Earth, in the solar system, and in the interstellar medium. PMID:25302532

  6. Anisotropy in the crystal growth of hexagonal ice, Ih

    NASA Astrophysics Data System (ADS)

    Rozmanov, Dmitri; Kusalik, Peter G.

    2012-09-01

    Growth of ice crystals has attracted attention because ice and water are ubiquitous in the environment and play critical roles in natural processes. Hexagonal ice, Ih, is the most common form of ice among 15 known crystalline phases of ice. In this work we report the results of an extensive and systematic molecular dynamics study of the temperature dependence of the crystal growth on the three primary crystal faces of hexagonal ice, the basal {0001} face, the prism lbrace 10bar{1}0rbrace face, and the secondary prism lbrace 11bar{2}0rbrace face, utilizing the TIP4P-2005 water model. New insights into the nature of its anisotropic growth are uncovered. It is demonstrated that the ice growth is indeed anisotropic; the growth and melting of the basal face are the slowest of the three faces, its maximum growth rates being 31% and 43% slower, respectively, than those of the prism and the secondary prism faces. It is also shown that application of periodic boundary conditions can lead to varying size effect for different orientations of an ice crystal caused by the anisotropic physical properties of the crystal, and results in measurably different thermodynamic melting temperatures in three systems of similar, yet moderate, size. Evidence obtained here provides the grounds on which to clarify the current understanding of ice growth on the secondary prism face of ice. We also revisit the effect of the integration time step on the crystal growth of ice in a more thorough and systematic way. Careful evaluation demonstrates that increasing the integration time step size measurably affects the free energy of the bulk phases and shifts the temperature dependence of the growth rate curve to lower temperatures by approximately 1 K when the step is changed from 1 fs to 2 fs, and by 3 K when 3 fs steps are used. A thorough investigation of the numerical aspects of the simulations exposes important consequences of the simulation parameter choices upon the delicate dynamic balance that is involved in ice crystal growth.

  7. The Backscattering Linear Depolarization Ratio of Ice Clouds Composed of Small Ice Crystals

    NASA Astrophysics Data System (ADS)

    Schnaiter, M.; Abdelmonem, A.; Benz, S.; Leisner, T.; Möhler, O.; Wagner, R.

    2009-04-01

    The importance of small ice crystals (< 50 µm) for cirrus cloud radiative properties is a matter of controversial debate, mainly because some measurements seemed to clearly overestimate the number concentrations of small ice particles due to particle shattering on the instrument inlets. On the other hand, there is no doubt that small micrometer-sized ice crystals dominate the particle size distributions of contrails and cirrus clouds emerging from contrails. Polarisation LIDAR is frequently used to investigate the microphysics of contrails and contrail cirrus remotely. These investigations reveal unusually high maximum linear depolarization ratios of 0.5 - 0.7. The knowledge of the link between ice crystal depolarization and their size and shape is a prerequisite for the interpretation of these LIDAR data. Since young contrails consist of relatively small ice crystals with sizes typically less than 10 µm, the scattering matrix of these non-spherical particles can be calculated by the T-matrix method. In order to investigate the relation between the linear backscattering depolarization ratio and the microphysical properties of small ice particles that closely resemble those found in contrails and young cirrus, we started to run dedicated ice crystal nucleation and growth experiments at the large cloud simulation chamber AIDA of Forschungszentrum Karlsruhe. Such studies became feasible after the installation of the new in situ laser scattering and depolarization set up SIMONE at the chamber in 2006. The light scattering measurements are analyzed in the context of the microphysical properties of the ice clouds measured by optical cloud particle spectrometers, single particle imaging, and in situ infrared extinction spectroscopy. We compare our experimental results with theoretical results generated by the T-matrix method for finite cylinders. The results give new insight into the scattering depolarisation properties of small ice crystals grown under simulated contrail and cirrus formation conditions.

  8. Ground Based Remote Sensing Of Small Ice Crystals In Arctic Cirrus Clouds

    Microsoft Academic Search

    Subhashree Mishra; David Mitchell; Daniel DeSlover; Greg McFarquhar

    ABSTRACT Measurement of small ice crystals (D < 60 ?m) remains an unsolved and controversial issue in the cloud physics community. Concentrations of small ice crystals are hard to measure due to shattering of crystals at probe inlets. However, these small ice crystals alter cirrus cloud radiative properties and may affect the cirrus cloud feedback in global climate models. To

  9. Visual Simulation of Ice Crystal Growth

    Microsoft Academic Search

    Theodore Kim; Ming C. Lin

    2003-01-01

    The beautiful, branching structure of ice is one of the most striking visual phenomena of the winter landscape. Yet there is little study about modeling this effect in computer graphics. In this paper, we present a novel approach for visual simulation of ice growth. We use a numerical simulation technique from computational physics, the \\

  10. Dimensions and aspect ratios of natural ice crystals

    DOE PAGESBeta

    Um, J.; McFarquhar, G. M.; Hong, Y. P.; Lee, S.-S.; Jung, C. H.; Lawson, R. P.; Mo, Q.

    2014-01-01

    During the 2006 Tropical Warm Pool International Cloud Experiment (TWP-ICE) in the Tropics, the 2008 Indirect and Semi-Direct Aerosol Campaign (ISDAC) in the Arctic, and the 2010 Small PARTicles In CirrUS (SPARTICUS) campaign in mid-latitudes, high-resolution images of ice crystals were recorded by a Cloud Particle Imager at temperatures (T) between ?87 and 0 °C. The projected maximum dimension (D'), length (L'), and width (W') of pristine columns, plates, and component bullets of bullet rosettes were measured using newly developed software, the Ice Crystal Ruler. The number of bullets in each bullet rosette was also measured. Column crystals were furthermore »distinguished as either horizontally oriented columns or columns with other orientations to eliminate any orientation effect on the measured dimensions. Dimensions and aspect ratios (AR, dimension of major axis divided by dimension of minor axis) of crystals were determined as functions of temperature, geophysical location, and type of cirrus. Dimensions of crystals generally increased as temperature increased. Columns and bullets had larger dimensions (i.e., W') of the minor axis (i.e., a axis) for a given dimension (i.e., D' or L') of the major axis (i.e., c axis), and thus smaller AR, as T increased, whereas this trend did not occur for plate crystals. The average number of branches in bullet rosettes was 5.50±1.35 during three campaigns and 6.32±1.34 (5.46±1.34; 4.95±1.01) during TWP-ICE (SPARTICUS; ISDAC). The AR of bullets increased with the number of branches in bullet rosettes. Most dimensions of crystals and ARs of columnar crystals measured during SPARTICUS were larger than those measured during TWP-ICE and ISDAC at ?67 T T L–W relationships of columns derived using current data exhibited a strong dependence on temperature; similar relationship determined in previous studies were within the range of the current data.« less

  11. Crystallization of amorphous water ice in the solar system

    NASA Technical Reports Server (NTRS)

    Jenniskens, P.; Blake, D. F.

    1996-01-01

    Electron diffraction studies of vapor-deposited water ice have characterized the dynamical structural changes during crystallization that affect volatile retention in cometary materials. Crystallization is found to occur by nucleation of small domains, while leaving a significant part of the amorphous material in a slightly more relaxed amorphous state that coexists metastably with cubic crystalline ice. The onset of the amorphous relaxation is prior to crystallization and coincides with the glass transition. Above the glass transition temperature, the crystallization kinetics are consistent with the amorphous solid becoming a "strong" viscous liquid. The amorphous component can effectively retain volatiles during crystallization if the volatile concentration is approximately 10% or less. For higher initial impurity concentrations, a significant amount of impurities is released during crystallization, probably because the impurities are trapped on the surfaces of micropores. A model for crystallization over long timescales is described that can be applied to a wide range of impure water ices under typical astrophysical conditions if the fragility factor D, which describes the viscosity behavior, can be estimated.

  12. Ice Growth Measurements from Image Data to Support Ice Crystal and Mixed-Phase Accretion Testing

    NASA Technical Reports Server (NTRS)

    Struk, Peter M.; Lynch, Christopher J.

    2012-01-01

    This paper describes the imaging techniques as well as the analysis methods used to measure the ice thickness and growth rate in support of ice-crystal icing tests performed at the National Research Council of Canada (NRC) Research Altitude Test Facility (RATFac). A detailed description of the camera setup, which involves both still and video cameras, as well as the analysis methods using the NASA Spotlight software, are presented. Two cases, one from two different test entries, showing significant ice growth are analyzed in detail describing the ice thickness and growth rate which is generally linear. Estimates of the bias uncertainty are presented for all measurements. Finally some of the challenges related to the imaging and analysis methods are discussed as well as methods used to overcome them.

  13. Crystallization of CO2 ice and the absence of amorphous CO2 ice in space

    PubMed Central

    Escribano, Rafael M.; Muñoz Caro, Guillermo M.; Cruz-Diaz, Gustavo A.; Rodríguez-Lazcano, Yamilet; Maté, Belén

    2013-01-01

    Carbon dioxide (CO2) is one of the most relevant and abundant species in astrophysical and atmospheric media. In particular, CO2 ice is present in several solar system bodies, as well as in interstellar and circumstellar ice mantles. The amount of CO2 in ice mantles and the presence of pure CO2 ice are significant indicators of the temperature history of dust in protostars. It is therefore important to know if CO2 is mixed with other molecules in the ice matrix or segregated and whether it is present in an amorphous or crystalline form. We apply a multidisciplinary approach involving IR spectroscopy in the laboratory, theoretical modeling of solid structures, and comparison with astronomical observations. We generate an unprecedented highly amorphous CO2 ice and study its crystallization both by thermal annealing and by slow accumulation of monolayers from the gas phase under an ultrahigh vacuum. Structural changes are followed by IR spectroscopy. We also devise theoretical models to reproduce different CO2 ice structures. We detect a preferential in-plane orientation of some vibrational modes of crystalline CO2. We identify the IR features of amorphous CO2 ice, and, in particular, we provide a theoretical explanation for a band at 2,328 cm?1 that dominates the spectrum of the amorphous phase and disappears when the crystallization is complete. Our results allow us to rule out the presence of pure and amorphous CO2 ice in space based on the observations available so far, supporting our current view of the evolution of CO2 ice. PMID:23858474

  14. Light scattering by hexagonal ice crystals: solutions by a

    E-print Network

    Liou, K. N.

    Light scattering by hexagonal ice crystals: solutions by a ray-by-ray integration algorithm Ping for the solution of light scattering by nonspherical dielectric particles. The principles of geometric optics are applied to solve the internal electric field within the scattering particles (near field

  15. Ice nucleation: elemental identification of particles in snow crystals.

    PubMed

    Parungo, F P; Pueschel, R F

    1973-06-01

    A scanning field-emission electron microscope combined with an x-ray analyzer is used to locate the ice nucleus within a three-dimensional image of a snow crystal and determine the chemical composition of the nucleus. This makes it possible to better understand the effect of nuclei in cloud seeding. PMID:17806581

  16. The scavenging of high altitude aerosol by small ice crystals

    NASA Astrophysics Data System (ADS)

    Andrew Bell, D.; Saunders, Clive P. R.

    There have been several global models developed for the theoretical investigation of the removal of high altitude aerosol from the atmosphere, following concern about the injection of particulate material by nuclear explosions and volcanic events. These models lack a knowledge of the scavenging efficiencies of the small ice crystals associated with cirus clouds and storm ice anvils. These are the only hydrometers that could remove the injected particles. In the past there have been a number of practical studies into the scavenging efficiencies of large ice crystaks and snowflakes. A comparison of the extrapolated results of these findings and the theoretical models of Martin et al. (1980, Pure appl. Phys.188, 1109-1129, J. atmos. Sci.37, 1628-1638) for the small crystal situation has been made. It was found that in general the extrapolated results gave efficiencies that were significantly higher than the predicted value. This difference was found to be enhanced as the crystal diameter decreased. Experiments used small ice plates grown at ˜-18.5°C in a cloud chamber, which were then permitted to fall through a dense aerosol cloud, to provide the first direct measurements of the scavenging efficiencies of this small crystals under cloud conditions. Initial results are presented for mono-disperse NaCl aerosol particles of size 4-6 ?m.

  17. Investigations of electromagnetic scattering by columnar ice crystals

    NASA Technical Reports Server (NTRS)

    Weil, H.; Senior, T. B. A.

    1976-01-01

    An integral equation approach was developed to determine the scattering and absorption of electromagnetic radiation by thin walled cylinders of arbitrary cross-section and refractive index. Based on this method, extensive numerical data was presented at infrared wavelengths for hollow hexagonal cross section cylinders which simulate columnar sheath ice crystals.

  18. Light scattering by complex ice-analogue crystals

    NASA Astrophysics Data System (ADS)

    Ulanowski, Zbigniew; Hesse, Evelyn; Kaye, Paul H.; Baran, Anthony J.

    2006-07-01

    Angle-dependent light-scattering measurements on single ice analogues crystals are described. Phase functions and degree of linear polarization are measured for electrodynamically levitated crystals. A procedure for randomizing particle orientation during levitation is demonstrated. The dependence of scattering on the shape, complexity and surface roughness of the crystals is examined. The phase functions from complex crystals with smooth surfaces show little dependence on shape. There is close agreement between the measured functions and the analytic phase function for ice clouds. However, rosettes with rough surfaces have qualitatively different phase functions, with raised side and back scattering. The asymmetry parameter is typically about 0.8±0.04 and 0.63±0.05 for smooth and rough crystals, respectively. The 22° halo peak is present for smooth rosettes and aggregates but absent for rough rosettes. Two-dimensional scattering patterns from several crystals in fixed orientations are also shown. The results suggest that it may be possible to use such patterns to discriminate not only between crystals of different shape but also to obtain some information on surface properties.

  19. Ice crystal growth in a dynamic thermal diffusion chamber

    NASA Technical Reports Server (NTRS)

    Keller, V. W.

    1980-01-01

    Ice crystals were grown in a supersaturated environment produced by a dynamic thermal diffusion chamber, which employed two horizontal plates separated by a distance of 2.5 cm. Air was circulated between and along the 1.2 m length of the plates past ice crystals which nucleated and grew from a fiber suspended vertically between the two plates. A zoom stereo microscope with a magnification which ranged from 3X to 80X and both 35 mm still photographs and 16 mm time lapse cine films taken through the microscope were used to study the variation of the shape and linear growth rate of ice crystals as a function of the ambient temperature, the ambient supersaturation, and the forced ventilation velocity. The ambient growth conditions were varied over the range of temperature 0 to -40 C, over the range of supersaturation 4% to 50% with respect to ice, and over the range of forced ventilation velocities 0 cm/s to 20 cm/s.

  20. Laboratory Investigation of Direct Measurement of Ice Water Content, Ice Surface Area, and Effective Radius of Ice Crystals Using a Laser-Diffraction Instrument

    NASA Technical Reports Server (NTRS)

    Gerber, H.; DeMott, P. J.; Rogers, D. C.

    1995-01-01

    The aircraft microphysics probe, PVM-100A, was tested in the Colorado State University dynamic cloud chamber to establish its ability to measure ice water content (IWC), PSA, and Re in ice clouds. Its response was compared to other means of measuring those ice-cloud parameters that included using FSSP-100 and 230-X 1-D optical probes for ice-crystal concentrations, a film-loop microscope for ice-crystal habits and dimensions, and an in-situ microscope for determining ice-crystal orientation. Intercomparisons were made in ice clouds containing ice crystals ranging in size from about 10 microns to 150 microns diameter, and ice crystals with plate, columnar, dendritic, and spherical shapes. It was not possible to determine conclusively that the PVM accurately measures IWC, PSA, and Re of ice crystals, because heat from the PVM evaporated in part the crystals in its vicinity in the chamber thus affecting its measurements. Similarities in the operating principle of the FSSP and PVM, and a comparison between Re measured by both instruments, suggest, however, that the PVM can make those measurements. The resolution limit of the PVM for IWC measurements was found to be on the order of 0.001 g/cubic m. Algorithms for correcting IWC measured by FSSP and PVM were developed.

  1. Dimensions and aspect ratios of natural ice crystals

    DOE PAGESBeta

    Um, J.; McFarquhar, G. M.; Hong, Y. P.; Lee, S.-S.; Jung, C. H.; Lawson, R. P.; Mo, Q.

    2015-01-01

    During the 2006 Tropical Warm Pool International Cloud Experiment (TWP-ICE) in the tropics, the 2008 Indirect and Semi-Direct Aerosol Campaign (ISDAC) in the Arctic, and the 2010 Small PARTicles In CirrUS (SPARTICUS) campaign at mid-latitudes, high-resolution images of ice crystals were recorded by a Cloud Particle Imager at temperatures (T) between ?87 and 0 °C. The projected maximum dimension (D'), length (L'), and width (W') of pristine columns, plates, and component bullets of bullet rosettes were measured using newly developed software, the Ice Crystal Ruler. The number of bullets in each bullet rosette was also measured. Column crystals were furthermore »distinguished as either horizontally oriented columns or columns with other orientations to eliminate any orientation effect on the measured dimensions. The dimensions and aspect ratios (AR, the dimension of the major axis divided by the dimension of the minor axis) of crystals were determined as functions of temperature, geophysical location, and type of cirrus. Dimensions of crystals generally increased with temperature. Columns and bullets had larger dimensions (i.e., W') of the minor axis (i.e., a axis) for a given dimension (i.e., D' orL') of the major axis (i.e., c axis), and thus smaller AR, as T increased, whereas this trend did not occur for plate crystals. The average number of branches in bullet rosettes was 5.50 ± 1.35 during three campaigns and 6.32 ± 1.34 (5.46 ± 1.34; 4.95 ± 1.01) during TWP-ICE (SPARTICUS; ISDAC). The AR of bullets increased with the number of branches in bullet rosettes. Most dimensions of crystals and ARs of columnar crystals measured during SPARTICUS were larger than those measured during TWP-ICE and ISDAC at ?67 L–W relationships of columns derived using current data exhibited a strong dependence on temperature; similar relationships determined in previous studies were within the range of the current data.« less

  2. Quasi-liquid layers on ice crystal surfaces are made up of two different phases

    PubMed Central

    Sazaki, Gen; Zepeda, Salvador; Nakatsubo, Shunichi; Yokomine, Makoto; Furukawa, Yoshinori

    2012-01-01

    Ice plays crucially important roles in various phenomena because of its abundance on Earth. However, revealing the dynamic behavior of quasi-liquid layers (QLLs), which governs the surface properties of ice crystals at temperatures near the melting point, remains an experimental challenge. Here we show that two types of QLL phases appear that exhibit different morphologies and dynamics. We directly visualized the two types of QLLs on ice crystal surfaces by advanced optical microscopy, which can visualize the individual 0.37-nm-thick elementary steps on ice crystal surfaces. We found that they had different stabilities and different interactions with ice crystal surfaces. The two immiscible QLL phases appeared heterogeneously, moved around, and coalesced dynamically on ice crystal surfaces. This picture of surface melting is quite different from the conventional picture in which one QLL phase appears uniformly on ice crystal surfaces. PMID:22232653

  3. Determination of the Boltzmann constant using a quasi-spherical acoustic resonator.

    PubMed

    Pitre, Laurent; Sparasci, Fernando; Truong, Daniel; Guillou, Arnaud; Risegari, Lara; Himbert, Marc E

    2011-10-28

    The paper reports a new experiment to determine the value of the Boltzmann constant, k(B)=1.3806477(17)×10(-23) J K(-1), with a relative standard uncertainty of 1.2 parts in 10(6). k(B) was deduced from measurements of the velocity of sound in argon, inside a closed quasi-spherical cavity at a temperature of the triple point of water. The shape of the cavity was achieved using an extremely accurate diamond turning process. The traceability of temperature measurements was ensured at the highest level of accuracy. The volume of the resonator was calculated from measurements of the resonance frequencies of microwave modes. The molar mass of the gas was determined by chemical and isotopic composition measurements with a mass spectrometer. Within combined uncertainties, our new value of k(B) is consistent with the 2006 Committee on Data for Science and Technology (CODATA) value: (k(B)(new)/k(B_CODATA)-1)=-1.96×10(-6), where the relative uncertainties are u(r)(k(B)(new))=1.2×10(-6) and u(r)(k(B_CODATA))=1.7×10(-6). The new relative uncertainty approaches the target value of 1×10(-6) set by the Consultative Committee on Thermometry as a precondition for redefining the unit of the thermodynamic temperature, the kelvin. PMID:21930563

  4. Observations of an Impurity-driven Hysteresis Behavior in Ice Crystal Growth at Low Pressure

    E-print Network

    Libbrecht, Kenneth G.

    Observations of an Impurity-driven Hysteresis Behavior in Ice Crystal Growth at Low Pressure Abstract. We describe observations of a novel hysteresis behavior in the growth of ice crystals under near the growth velocity vn normal to the surface of a crystal facet in terms of the Hertz-Knudsen formula vn

  5. Precision Measurements of Ice Crystal Growth Rates Kenneth G. Libbrecht1

    E-print Network

    Libbrecht, Kenneth G.

    Precision Measurements of Ice Crystal Growth Rates Kenneth G. Libbrecht1 Department of Physics precise measurements of the growth rates of the principal facets of ice crystals. Particular attention Introduction The growth of snow crystals from water vapor in air is governed by a number of factors, with vapor

  6. Effects of ice crystal habit on thermal infrared radiative properties and forcing of cirrus

    Microsoft Academic Search

    Manfred Wendisch; Ping Yang; Peter Pilewskie

    2007-01-01

    The impact of assumed ice crystal morphology on thermal infrared (IR) radiative properties of subtropical cirrus is quantified. In particular, the crystal-shape-dependent profiles of downwelling and upwelling thermal IR (broadband and spectral) irradiances and the radiative forcing of cirrus (at the top and bottom of the atmosphere) are investigated. For this purpose, airborne measurements of ice crystal size distribution (in

  7. Synthesis of monodisperse, quasi-spherical silver nanoparticles with sizes defined by the nature of silver precursors.

    PubMed

    Li, Houshen; Xia, Haibing; Ding, Wenchao; Li, Yijing; Shi, Qiurong; Wang, Dayang; Tao, Xutang

    2014-03-11

    Monodisperse, quasi-spherical silver nanoparticles (Ag NPs) with controlled sizes have been produced directly in water via adding the aqueous solutions of the mixtures of AgNO3 and sodium citrate to boiling aqueous solutions of ascorbic acid (AA). Different compounds, including NaCl, NaBr, KI, Na2SO4, Na2CO3, Na2S, and Na3PO4, are added to the AgNO3/citrate mixture solutions to form new silver compounds with fairly low solubility in water, which are used as precursors instead of soluble Ag(+) ions to synthesize Ag NPs via AA/citrate reduction. This enables us not only to produce monodisperse, quasi-spherical Ag NPs but also to tune the sizes of the resulting NPs from 16 to 30 nm according to the potential of new silver precursors as well as the concentrations of anions. PMID:24528373

  8. Junction Conditions and Consequences of Quasi-Spherical Space-Time with Electro-Magnetic Field and Vaidya Matric

    E-print Network

    Soma Nath; Ujjal Debnath; Subenoy Chakraborty

    2007-11-07

    In this work the junction conditions between the exterior Reissner-Nordstrom-Vaidya space-time with the interior quasi-spherical Szekeres space-time have been studied for analyzing gravitational collapse in the presence of a magneto-hydrodynamic fluid undergoing dissipation in the form of heat flow. We have discussed about the apparent horizon and have evaluated the time difference between the formation of apparent horizon and central singularity.

  9. Ice-Crystallization Kinetics during Fuel-Cell Cold-Start

    NASA Astrophysics Data System (ADS)

    Dursch, Thomas James, Jr.

    Proton-exchange-membrane fuel cells (PEMFCs) show promise in automotive applications because of their high efficiency, high power density, and potentially low emissions. To be successful in automobiles, PEMFCs must permit rapid startup with minimal energy from subfreezing temperatures, known as cold-start. In a PEMFC, reduction of oxygen to water occurs in the cathode catalyst layer (CL). Under subfreezing conditions, water generated during startup solidifies and hinders access of gaseous oxygen to the catalytic sites in the cathode CL, severely inhibiting cell performance and potentially causing cell failure. Achieving cold-start is difficult in practice, due to potential flooding, sluggish reaction kinetics, durability loss, and rapid ice crystallization. Currently, however, few studies focus on the fundamentals of ice crystallization during cold-start. Elucidation of the mechanisms and kinetics of ice formation within PEMFC porous media is, therefore, critical to successful cell startup and high performance at low temperatures. First, an experimental method is presented for obtaining isothermal ice-crystallization kinetics in water-saturated gas-diffusion layers (GDLs). Ice formation is initially studied in the GDL because this layer retains a significant amount of product water during cold-start. Isothermal ice-crystallization and ice-nucleation rates are obtained in commercial Toray GDLs as functions of subcooling using differential scanning calorimetry (DSC). A nonlinear ice-crystallization rate expression is developed using Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory, in which the heat-transfer-limited growth rate is determined from the moving-boundary Stefan problem. Predicted ice-crystallization rates are in excellent agreement with experiment. A validated rate expression is thus available for predicting ice-crystallization kinetics in GDLs. Ice-crystallization kinetics is also considered under experimental settings similar to real PEMFC operating conditions where ice invariably forms non-isothermally. Non-isothermal ice-crystallization rates and ice-crystallization temperatures are obtained in water-saturated GDLs as a function of cooling rate. Our previously developed ice-crystallization rate expression is extended to non-isothermal crystallization to predict ice-crystallization kinetics at various cooling rates. For non-isothermal ice formation, we find that cooling rate has a negligible effect on the crystallization rate when crystallization times are much faster than the time to decrease the sample temperature by the subcooling. Therefore, a pseudo-isothermal method is proposed for non-isothermal crystallization kinetics using isothermal crystallization kinetics evaluated at the non-isothermal crystallization temperature. Catalyst layers also retain a significant amount of product water during cold-start. Accordingly, ice nucleation and growth in PEMFC CLs are investigated using isothermal DSC and compared to isothermal galvanostatic membrane-electrode assembly (MEA) cold-starts. Measured ice-crystallization and ice-nucleation rates follow expected trends from classical nucleation theory. Following our previous approach, a quantitative nonlinear ice-crystallization rate expression is developed from the JMAK framework. To validate ice-crystallization kinetics within PEMFCs, we further measure and predict MEA cell-failure time during isothermal galvanostatic cold-start. Using a simplified PEMFC isothermal cold-start continuum model, MEA cell-failure times predicted using the newly obtained rate expression are compared to that predicted using a traditional thermodynamics-based approach. From this comparison, conditions are identified under which including ice-crystallization kinetics is critical and to elucidate the impact of freezing kinetics on low-temperature PEMFC operation. During cold-start, the time for recovering cell performance strongly depends on the rate of melting residual ice by reactive heat generation. Non-isothermal ice melting in water-saturated GDLs is investigated using DSC with various he

  10. The Influence of Radiation on Ice Crystal Spectrum in the Upper Troposphere

    NASA Technical Reports Server (NTRS)

    Zeng, Xiping

    2008-01-01

    This theoretical study is carried out to investigate the effect of radiation on ice crystal spectrum in the upper troposphere. First, an explicit expression is obtained for the ice crystal growth rate that takes account of radiative and kinetic effects. Second, the expression is used to quantitatively analyze how radiation broadens the ice crystal spectrum and then reveal a new precipitation mechanism in the upper troposphere and the stratosphere. Third, the radiative effect is used to explain the subvisual clouds near the tropopause.

  11. A Flexible Parameterization for Shortwave Optical Properties of Ice Crystals

    NASA Technical Reports Server (NTRS)

    VanDiedenhoven, Bastiaan; Ackerman, Andrew S.; Cairns, Brian; Fridlind, Ann M.

    2014-01-01

    A parameterization is presented that provides extinction cross section sigma (sub e), single-scattering albedo omega, and asymmetry parameter (g) of ice crystals for any combination of volume, projected area, aspect ratio, and crystal distortion at any wavelength in the shortwave. Similar to previous parameterizations, the scheme makes use of geometric optics approximations and the observation that optical properties of complex, aggregated ice crystals can be well approximated by those of single hexagonal crystals with varying size, aspect ratio, and distortion levels. In the standard geometric optics implementation used here, sigma (sub e) is always twice the particle projected area. It is shown that omega is largely determined by the newly defined absorption size parameter and the particle aspect ratio. These dependences are parameterized using a combination of exponential, lognormal, and polynomial functions. The variation of (g) with aspect ratio and crystal distortion is parameterized for one reference wavelength using a combination of several polynomials. The dependences of g on refractive index and omega are investigated and factors are determined to scale the parameterized (g) to provide values appropriate for other wavelengths. The parameterization scheme consists of only 88 coefficients. The scheme is tested for a large variety of hexagonal crystals in several wavelength bands from 0.2 to 4 micron, revealing absolute differences with reference calculations of omega and (g) that are both generally below 0.015. Over a large variety of cloud conditions, the resulting root-mean-squared differences with reference calculations of cloud reflectance, transmittance, and absorptance are 1.4%, 1.1%, and 3.4%, respectively. Some practical applications of the parameterization in atmospheric models are highlighted.

  12. Microphysical Ice Crystal Properties in Mid-Latitude Frontal Cirrus

    NASA Astrophysics Data System (ADS)

    Schlage, Romy; Jurkat, Tina; Voigt, Christiane; Minikin, Andreas; Weigel, Ralf; Molleker, Sergej; Klingebiel, Marcus; Borrmann, Stephan; Luebke, Anna; Krämer, Martina; Kaufmann, Stefan; Schäfler, Andreas

    2015-04-01

    Cirrus clouds modulate the climate by reflection of shortwave solar radiation and trapping of longwave terrestrial radiation. Their net radiative effect can be positive or negative depending on atmospheric and cloud parameters including ice crystal number density, size and shape. Latter microphysical ice crystal properties have been measured during the mid-latitude cirrus mission ML-CIRRUS with a set of cloud instruments on the new research aircraft HALO. The mission took place in March/April 2014 with 16 flights in cirrus formed above Europe and the Atlantic. The ice clouds were encountered at altitudes from 7 to 14 km in the typical mid-latitude temperature range. A focus of the mission was the detection of frontal cirrus linked to warm conveyor belts (WCBs). Within WCBs, water vapor is transported in the warm sector of an extra-tropical cyclone from the humid boundary layer to the upper troposphere. Cirrus cloud formation can be triggered in the WCB outflow region at moderate updraft velocities and additionally at low updrafts within the high pressure system linked to the WCB. Due to their frequent occurrence, WCBs represent a major source for regions of ice supersaturation and cirrus formation in the mid-latitudes. Here, we use data from the Cloud and Aerosol Spectrometer with detection for POLarization (CAS-POL) and the Cloud Combination Probe (CCP), combining a Cloud Droplet Probe (CDP) and a greyscale Cloud Imaging Probe (CIPgs) to investigate the ice crystal distribution in the size range from 0.5 µm to 1 mm. We derive microphysical cirrus properties in mid-latitude warm front cirrus. Further, we investigate their variability and their dependence on temperature and relative humidity. Finally, we compare the microphysical properties of these frontal cirrus to cirrus clouds that formed at low updrafts within high pressure systems or at high updraft velocities in lee waves. We quantify statistically significant differences in cirrus properties formed in these various meteorological regimes. Our studies of mid-latitude cirrus clouds help to better understand their radiative properties in order to assess their impact on climate.

  13. Fluidized bed heat exchangers to prevent fouling in ice slurry systems and industrial crystallizers

    Microsoft Academic Search

    P. Pronk

    2006-01-01

    Ozon layer depletion and global warming by synthetic refrigerants forces refrigeration industries to switch over to natural but hazardous refrigerants like ammonia and hydrocarbons. A promising technology to safely use the latter refrigerants is the application of indirect refrigeration systems with ice slurry as heat transfer fluid. Ice slurry, a suspension of aqueous solution and small ice crystals, has a

  14. Molecular surface structure of a low-temperature ice Ih(0001) crystal

    Microsoft Academic Search

    N. Materer; U. Starke; A. Barbieri; M. A. Van Hove; G. A. Somorjai; G. J. Kroes; C. Minot

    1995-01-01

    An ice film with thickness greater than 10 A was crystallized on a clean Pt(111) surface. Its external surface structure was investigated at 90 K by dynamical low-energy electron diffraction (LEED), followed by molecular dynamics simulations and ab initio quantum chemical calculations. The results favor the common hexagonal ice 1h structure over other forms of ice, with (0001) termination. A

  15. Laboratory studies on the uptake of aromatic hydrocarbons by ice crystals during vapor depositional crystal growth

    NASA Astrophysics Data System (ADS)

    Fries, Elke; Starokozhev, Elena; Haunold, Werner; Jaeschke, Wolfgang; Mitra, Subir K.; Borrmann, Stephan; Schmidt, Martin U.

    Uptake of aromatic hydrocarbons (AH) by ice crystals during vapor deposit growth was investigated in a walk-in cold chamber at temperatures of 242, 251, and 260 K, respectively. Ice crystals were grown from ambient air in the presence of gaseous AH namely: benzene (C 6H 6), toluene (methylbenzene, C 7H 8), the C 8H 10 isomers ethylbenzene, o-, m-, p-xylene (dimethylbenzenes), the C 9H 12 isomers n-propylbenzene, 4-ethyltoluene, 1,3,5-trimethylbenzene (1,3,5-TMB), 1,2,4-trimethylbenzene (1,2,4-TMB), 1,2,3-trimethylbenzene (1,2,3-TMB), and the C 10H 14 compound tert.-butylbenzene. Gas-phase concentrations calculated at 295 K were 10.3-20.8 ?g m -3. Uptake of AH was detected by analyzing vapor deposited ice with a very sensitive method composed of solid-phase micro-extraction (SPME), followed by gas chromatography/mass spectrometry (GC/MS). Ice crystal size was lower than 1 cm. At water vapor extents of 5.8, 6.0 and 8.1 g m -3, ice crystal shape changed with decreasing temperatures from a column at a temperature of 260 K, to a plate at 251 K, and to a dendrite at 242 K. Experimentally observed ice growth rates were between 3.3 and 13.3×10 -3 g s -1 m -2 and decreased at lower temperatures and lower value of water vapor concentration. Predicted growth rates were mostly slightly higher. Benzene, toluene, ethylbenzene, and xylenes (BTEX) were not detected in ice above their detection limits (DLs) of 25 pg g ice-1 (toluene, ethylbenzene, xylenes) and 125 pg g ice-1 (benzene) over the entire temperature range. Median concentrations of n-propylbenzene, 4-ethyltoluene, 1,3,5-TMB, tert.-butylbenzene, 1,2,4-TMB, and 1,2,3-TMB were between 4 and 176 pg g ice-1 at gas concentrations of 10.3-10.7 ?g m -3 calculated at 295 K. Uptake coefficients ( K) defined as the product of concentration of AH in ice and density of ice related to the product of their concentration in the gas phase and ice mass varied between 0.40 and 10.23. K increased with decreasing temperatures. Values of Gibbs energy (? G) were between -4.5 and 2.4 kJ mol -1 and decreased as temperatures were lowered. From the uptake experiments, the uptake enthalpy (? H) could be determined between -70.6 and -33.9 kJ mol -1. The uptake entropy (? S) was between -281.3 and -126.8 J mol -1 K -1. Values of ? H and ? S were rather similar for 4-ethlytoluene, 1,3,5-TMB and tert.-butylbenzene, whereas 1,2,3-TMB showed much higher values.

  16. Atomically Resolved Images of Ih Ice Single Crystals in the Solid Phase

    NASA Astrophysics Data System (ADS)

    Kobayashi, Keita; Koshino, Masanori; Suenaga, Kazu

    2011-05-01

    The morphology and crystal structure of nanoparticles of ice were examined by high-resolution transmission electron microscopy. Two different crystal structures were found and unambiguously assigned to hexagonal (Ih) and cubic (Ic) ice crystals. Direct observation of oxygen columns clearly revealed the hexagonal packing of water molecules. Electron energy-loss spectroscopy was used to monitor the electronic excitation in ice, suggesting possible dissociation of water molecules. Dynamic process of phase transition between Ih and Ic phases of individual ice nanoparticles under electron beam irradiation was also monitored by in situ transmission electron diffractometry.

  17. An uncoupled multiphase approach towards modeling ice crystals in jet engines

    Microsoft Academic Search

    Mohamed Shezad Nilamdeen

    2010-01-01

    A recent series of high altitude turbofan engine malfunctions, characterized by flameout and sudden power losses have been reported in recent years. The source of these incidents has been hypothesized to be due to the presence of ice crystals at high altitudes. Ice crystals have been shown to have ballistic trajectories and consequently enter the core engine flow, without getting

  18. Polarized light scattering by hexagonal ice crystals: theory Qiming Cai and Kuo-Nan Liou

    E-print Network

    Liou, K. N.

    Polarized light scattering by hexagonal ice crystals: theory Qiming Cai and Kuo-Nan Liou on light scattering by nonspherical ice crystals have been limited to unpolarized cases1-3 or cases A scattering model involving complete polarization information for arbitrarily oriented hexagonal columns

  19. Quantifying sensitivities of ice crystal number and sources of ice crystal number variability in CAM 5.1 using the adjoint of a physically based cirrus formation parameterization

    NASA Astrophysics Data System (ADS)

    Sheyko, B. A.; Sullivan, S. C.; Morales, R.; Capps, S. L.; Barahona, D.; Shi, X.; Liu, X.; Nenes, A.

    2015-04-01

    We present the adjoint of a cirrus formation parameterization that computes the sensitivity of ice crystal number concentration to updraft velocity, aerosol, and ice deposition coefficient. The adjoint is driven by simulations from the National Center for Atmospheric Research Community Atmosphere Model version 5.1 CAM 5.1 to understand the sensitivity of formed ice crystal number concentration to 13 variables and quantify which contribute to its variability. Sensitivities of formed ice crystal number concentration to updraft velocity, sulfate number, and is sufficient but sulfate number concentration is low, indicating a sulfate-limited regime. Outside of the tropics, competition between homogeneous and heterogeneous nucleation may shift annually averaged sensitivities to higher magnitudes, when infrequent strong updrafts shift crystal production away from purely heterogeneous nucleation. Outside the tropics, updraft velocity is responsible for approximately 52.70% of the ice crystal number variability. In the tropics, sulfate number concentration and updraft jointly control variability in formed crystal number concentration. Insoluble aerosol species play a secondary, but still important, role in influencing the variability in crystal concentrations, with coarse-mode dust being the largest contributor at nearly 50% in certain regions. On a global scale, more than 95% of the temporal variability in crystal number concentration can be described by temperature, updraft velocity, sulfate number, and coarse-mode dust number concentration.

  20. Microfluidic experiments reveal that antifreeze proteins bound to ice crystals suffice to prevent their growth

    PubMed Central

    Celik, Yeliz; Drori, Ran; Pertaya-Braun, Natalya; Altan, Aysun; Barton, Tyler; Bar-Dolev, Maya; Groisman, Alex; Davies, Peter L.; Braslavsky, Ido

    2013-01-01

    Antifreeze proteins (AFPs) are a subset of ice-binding proteins that control ice crystal growth. They have potential for the cryopreservation of cells, tissues, and organs, as well as for production and storage of food and protection of crops from frost. However, the detailed mechanism of action of AFPs is still unclear. Specifically, there is controversy regarding reversibility of binding of AFPs to crystal surfaces. The experimentally observed dependence of activity of AFPs on their concentration in solution appears to indicate that the binding is reversible. Here, by a series of experiments in temperature-controlled microfluidic devices, where the medium surrounding ice crystals can be exchanged, we show that the binding of hyperactive Tenebrio molitor AFP to ice crystals is practically irreversible and that surface-bound AFPs are sufficient to inhibit ice crystal growth even in solutions depleted of AFPs. These findings rule out theories of AFP activity relying on the presence of unbound protein molecules. PMID:23300286

  1. Bioprospecting for microbial products that affect ice crystal formation and growth

    Microsoft Academic Search

    Brent C. Christner

    2010-01-01

    At low temperatures, some organisms produce proteins that affect ice nucleation, ice crystal structure, and\\/or the process\\u000a of recrystallization. Based on their ice-interacting properties, these proteins provide an advantage to species that commonly\\u000a experience the phase change from water to ice or rarely experience temperatures above the melting point. Substances that bind,\\u000a inhibit or enhance, and control the size, shape,

  2. Numerical Comparison of Two Ice Crystal Formation Mechanisms on Snowfall Enhancement from Ground-Based Aerosol Generators

    Microsoft Academic Search

    Zhidong Li; R. L. Pitter

    1997-01-01

    Two mechanisms of ice crystal formation, contact freezing and very rapid condensation freezing, were applied to numerical simulations of ground-based seeding with the Guide Model, an orographic cloud model, to study whether different mechanisms of ice crystal formation substantially affect precipitation patterns and intensities. Although the numerical model has limitations, it was expected to indicate how different ice crystal formation

  3. Modeling of Commercial Turbofan Engine With Ice Crystal Ingestion: Follow-On

    NASA Technical Reports Server (NTRS)

    Jorgenson, Philip C. E.; Veres, Joseph P.; Coennen, Ryan

    2014-01-01

    The occurrence of ice accretion within commercial high bypass aircraft turbine engines has been reported under certain atmospheric conditions. Engine anomalies have taken place at high altitudes that have been attributed to ice crystal ingestion, partially melting, and ice accretion on the compression system components. The result was degraded engine performance, and one or more of the following: loss of thrust control (roll back), compressor surge or stall, and flameout of the combustor. As ice crystals are ingested into the fan and low pressure compression system, the increase in air temperature causes a portion of the ice crystals to melt. It is hypothesized that this allows the ice-water mixture to cover the metal surfaces of the compressor stationary components which leads to ice accretion through evaporative cooling. Ice accretion causes a blockage which subsequently results in the deterioration in performance of the compressor and engine. The focus of this research is to apply an engine icing computational tool to simulate the flow through a turbofan engine and assess the risk of ice accretion. The tool is comprised of an engine system thermodynamic cycle code, a compressor flow analysis code, and an ice particle melt code that has the capability of determining the rate of sublimation, melting, and evaporation through the compressor flow path, without modeling the actual ice accretion. A commercial turbofan engine which has previously experienced icing events during operation in a high altitude ice crystal environment has been tested in the Propulsion Systems Laboratory (PSL) altitude test facility at NASA Glenn Research Center. The PSL has the capability to produce a continuous ice cloud which is ingested by the engine during operation over a range of altitude conditions. The PSL test results confirmed that there was ice accretion in the engine due to ice crystal ingestion, at the same simulated altitude operating conditions as experienced previously in flight. The computational tool was utilized to help guide a portion of the PSL testing, and was used to predict ice accretion could also occur at significantly lower altitudes. The predictions were qualitatively verified by subsequent testing of the engine in the PSL. In a previous study, analysis of select PSL test data points helped to calibrate the engine icing computational tool to assess the risk of ice accretion. This current study is a continuation of that data analysis effort. The study focused on tracking the variations in wet bulb temperature and ice particle melt ratio through the engine core flow path. The results from this study have identified trends, while also identifying gaps in understanding as to how the local wet bulb temperature and melt ratio affects the risk of ice accretion and subsequent engine behavior.

  4. Structural Changes and Energy Cumulation in an Iron-Nickel Alloy upon Quasi-Spherical Explosive Loading

    SciTech Connect

    Zel'dovich, V. I.; Khomskaya, I. V.; Frolova, N. Yu.; Kheifets, A. E.; Gundyrev, V. M. [Institute of Metal Physics, Ural Division, Russian Academy of Sciences, ul. S. Kovalevskoi 18, Ekaterinburg, 620041 (Russian Federation); Litvinov, B. V.; Purygin, N. P. [All-Russia Research Institute of Technical Physics, Russian Federal Nuclear Center, Snezhinsk, Chelyabinsk oblast, 456770 (Russian Federation)

    2006-08-03

    Ball samples of the Fe-31.8 wt % Ni-0.05 wt % C iron-nickel alloy one of which was in an austenitic state and the other was in a martensitic-austenitic state were subjected to quasi-spherical shock-wave loading under identical conditions. A comparison of the results obtained under the same loading conditions on the samples of the same alloy in two different initial states made it possible to establish the influence of the initial phase composition on the structural changes and on the effect of energy cumulation.

  5. Microscopic pattern of ice crystal growth in the presence of thermal hysteresis proteins

    SciTech Connect

    Coger, R.; Rubinsky, B. (Univ. of California, Berkeley, CA (United States). Dept. of Mechanical Engineering); Fletcher, G. (Memorial Univ. of Newfoundland, St. John's, Newfoundland (Canada))

    1994-08-01

    This study examines the effect of thermal hysteresis proteins (THPs) from the winter flounder (Psuedopleuronectes americanus) on the ice-water interface morphology during freezing of aqueous solutions. Experiments were performed using a directional solidification stage, and the development of the two-phase interface was observed through a microscope and recorded by a video system. Unusual ice crystal morphologies were observed, including faceted ice crystal growth along the (1100) crystal plane; spicular or needlelike growth in the (1010) direction; and growth parallel to the c-axis, (0001), consisting of incorporated liquid inclusions bounded by hexagonal prism faces. The observed crystallographic structures can be explained as an effect of the interaction between the THPs and the primary prism faces of ice crystals. This results in an increase in the Gibbs free energy of these planes, followed by ice growth into the supercooled liquid adjacent to these faces.

  6. New metastable form of ice and its role in the homogeneous crystallization of water.

    PubMed

    Russo, John; Romano, Flavio; Tanaka, Hajime

    2014-07-01

    The homogeneous crystallization of water at low temperature is believed to occur through the direct nucleation of cubic (Ic) and hexagonal (Ih) ices. Here, we provide evidence from molecular simulations that the nucleation of ice proceeds through the formation of a new metastable phase, which we name Ice 0. We find that Ice 0 is structurally similar to the supercooled liquid, and that on growth it gradually converts into a stacking of Ice Ic and Ih. We suggest that this mechanism provides a thermodynamic explanation for the location and pressure dependence of the homogeneous nucleation temperature, and that Ice 0 controls the homogeneous nucleation of low-pressure ices, acting as a precursor to crystallization in accordance with Ostwald's step rule of phases. Our findings show that metastable crystalline phases of water may play roles that have been largely overlooked. PMID:24836734

  7. New metastable form of ice and its role in the homogeneous crystallization of water

    NASA Astrophysics Data System (ADS)

    Russo, John; Romano, Flavio; Tanaka, Hajime

    2014-07-01

    The homogeneous crystallization of water at low temperature is believed to occur through the direct nucleation of cubic (Ic) and hexagonal (Ih) ices. Here, we provide evidence from molecular simulations that the nucleation of ice proceeds through the formation of a new metastable phase, which we name Ice 0. We find that Ice 0 is structurally similar to the supercooled liquid, and that on growth it gradually converts into a stacking of Ice Ic and Ih. We suggest that this mechanism provides a thermodynamic explanation for the location and pressure dependence of the homogeneous nucleation temperature, and that Ice 0 controls the homogeneous nucleation of low-pressure ices, acting as a precursor to crystallization in accordance with Ostwald’s step rule of phases. Our findings show that metastable crystalline phases of water may play roles that have been largely overlooked.

  8. Ikaite crystal distribution in Arctic winter sea ice and implications for CO2 system dynamics

    NASA Astrophysics Data System (ADS)

    Rysgaard, S.; Søgaard, D. H.; Cooper, M.; Pu?ko, M.; Lennert, K.; Papakyriakou, T. N.; Wang, F.; Geilfus, N. X.; Glud, R. N.; Ehn, J.; McGinnnis, D. F.; Attard, K.; Sievers, J.; Deming, J. W.; Barber, D.

    2012-12-01

    The precipitation of ikaite (CaCO3·6H2O) in polar sea ice is critical to the efficiency of the sea ice-driven carbon pump and potentially important to the global carbon cycle, yet the spatial and temporal occurrence of ikaite within the ice is poorly known. We report unique observations of ikaite in unmelted ice and vertical profiles of ikaite abundance and concentration in sea ice for the crucial season of winter. Ice was examined from two locations: a 1 m thick land-fast ice site and a 0.3 m thick polynya site, both in the Young Sound area (74° N, 20° W) of NE Greenland. Ikaite crystals, ranging in size from a few µm to 700 µm were observed to concentrate in the interstices between the ice platelets in both granular and columnar sea ice. In vertical sea-ice profiles from both locations, ikaite concentration determined from image analysis, decreased with depth from surfaceice values of 700-900 µmol kg-1 ice (~ 25 × 106 crystals kg-1) to bottom-layer values of 100-200 µmol kg-1 ice (1-7 × 106 kg-1), all of which are much higher (4-10 times) than those reported in the few previous studies. Direct measurements of total alkalinity (TA) in surface layers fell within the same range as ikaite concentration whereas TA concentrations in bottom layers were twice as high. This depth-related discrepancy suggests interior ice processes where ikaite crystals form in surface sea ice layers and partly dissolved in bottom layers. From these findings and model calculations we relate sea ice formation and melt to observed pCO2 conditions in polar surface waters, and hence, the air-sea CO2 flux.

  9. Cloud Ice Crystal Orientation Inferred from Global Precipitation Measurement (GPM) Microwave Imager

    NASA Astrophysics Data System (ADS)

    Gong, J.; Wu, D. L.; Evans, K. F.; Kim, K. M.

    2014-12-01

    Ice crystal orientation can produce significantly different scattering in vertically (V) and horizontally (H) polarized microwave radiances and affect the accuracy of cloud ice measurement. Designed to observe the precipitable-sized particles, GPM Microwave Imager (GMI) is used in this study to infer ice crystal orientation inside ice clouds. By identifying ice cloud scenes using the 183.3±3 GHz channel, we compare the 89 and 166 GHz radiances for their V-H differences. Ice cloud crystals are found highly polarized with V-H > 0 throughout the tropics and the mid-latitude jet regions. The V-H difference can be as large as 10% (5%) of the mean radiance at 166 GHz (89 GHz). The largest values generally occur over convective outflows, but decreasing in the vicinity of deep convective cores and remote thin cirrus regions. The negative V-H values prominently happen in the equator side of the winter hemisphere storm track regions. A polarized radiative transfer model is employed to interpret the observed polarization. Simulations with systematically oriented non-spherical ice particles can reproduce the observed V-H differences, while spherical or randomly oriented non-spherical particles cannot. This finding suggests that accurate cloud ice retrievals must take into account ice crystal orientation. The observed V-H relationship with cloud regimes may relate with vertical velocity, in-cloud turbulence, lightning, and other physical processes, which will be briefly discussed in this presentation.

  10. Study of the implosion characteristics of quasi-spherical wire arrays on the Angara-5-1 facility at currents of up to 4 MA

    SciTech Connect

    Aleksandrov, V. V.; Volkov, G. S.; Grabovski, E. V.; Gribov, A. N.; Gritsuk, A. N.; Laukhin, Ya. N.; Mitrofanov, K. N.; Oleinik, G. M.; Sasorov, P. V.; Frolov, I. N. [Troitsk Institute for Innovation and Fusion Research (Russian Federation)

    2012-04-15

    Results are presented from experimental studies of the spatial distribution of the density of matter in the central part of the discharge gap and the formation of the temporal profile of the X-ray power in the course of implosion of quasi-spherical wire arrays at discharge currents of up to 4 MA. The spatial distribution of the X-ray intensity in the central part of the discharge gap and the temporal profile of the X-ray power are used as implosion characteristics of quasi-spherical wire arrays. The quasi-spherical arrays were formed by the radial stretching of unstrained wires of initially cylindrical and conical wire arrays under the action of the electrostatic field. The temporal profile of the output X-ray pulse in the photon energy range of 0.1-1 keV is shown to depend on both the geometrical parameters of the quasi-spherical array and the longitudinal distribution of its mass. It is found that a 40% increase in the wire mass due to deposition of an additional mass in the equatorial region of a quasi-spherical array leads to a 15% increase in the average current radius of the pinch and a 30% decrease in the X-ray yield. Experiments with quasi-spherical arrays made of kapron fibers with deposited Al and Bi conducting layers were also carried out. It is demonstrated that application of such arrays makes it possible to control the profile and duration of the generated X-ray pulse by varying the mass, material, and location of the deposited layer. It is found that deposition of an additional mass in the form of a thin Bi stripe on tungsten wires near the cathode end of the array allows one to mitigate the influence of the cathode zipper effect on the pinch compression and formation of the X-ray pulse in tungsten arrays.

  11. Effects of pre-existing ice crystals on cirrus clouds and comparison between different ice nucleation parameterizations with the Community Atmosphere Model (CAM5)

    NASA Astrophysics Data System (ADS)

    Shi, X.; Liu, X.; Zhang, K.

    2015-02-01

    In order to improve the treatment of ice nucleation in a more realistic manner in the Community Atmosphere Model version 5.3 (CAM5.3), the effects of pre-existing ice crystals on ice nucleation in cirrus clouds are considered. In addition, by considering the in-cloud variability in ice saturation ratio, homogeneous nucleation takes place spatially only in a portion of the cirrus cloud rather than in the whole area of the cirrus cloud. Compared to observations, the ice number concentrations and the probability distributions of ice number concentration are both improved with the updated treatment. The pre-existing ice crystals significantly reduce ice number concentrations in cirrus clouds, especially at mid- to high latitudes in the upper troposphere (by a factor of ~10). Furthermore, the contribution of heterogeneous ice nucleation to cirrus ice crystal number increases considerably. Besides the default ice nucleation parameterization of Liu and Penner (2005, hereafter LP) in CAM5.3, two other ice nucleation parameterizations of Barahona and Nenes (2009, hereafter BN) and Kärcher et al. (2006, hereafter KL) are implemented in CAM5.3 for the comparison. In-cloud ice crystal number concentration, percentage contribution from heterogeneous ice nucleation to total ice crystal number, and pre-existing ice effects simulated by the three ice nucleation parameterizations have similar patterns in the simulations with present-day aerosol emissions. However, the change (present-day minus pre-industrial times) in global annual mean column ice number concentration from the KL parameterization (3.24 × 106 m-2) is less than that from the LP (8.46 × 106 m-2) and BN (5.62 × 106 m-2) parameterizations. As a result, the experiment using the KL parameterization predicts a much smaller anthropogenic aerosol long-wave indirect forcing (0.24 W m-2) than that using the LP (0.46 W m-2) and BN (0.39 W m-2) parameterizations.

  12. Stability relationship for water droplet crystallization with the NASA Lewis icing spray

    NASA Technical Reports Server (NTRS)

    Marek, C. John; Bartlett, C. Scott

    1987-01-01

    In order to produce small droplets for icing cloud simulation, high pressure air atomizing nozzles are used. For certain icing testing applications, median drop sizes as small as 5 mm are needed, which require air atomizing pressures greater than 3000 kPa. Isentropic expansion of the ambient temperature atomizing air to atmospheric pressure can result in air stream temperatures of -160 C which results in ice crystals forming in the cloud. To avoid such low temperatures, it is necessary to heat the air and water to high initial temperatures. An icing spray research program was conducted to map the temperatures below which ice crystals form. A soot slide technique was used to determine the presence of crystals in the spray.

  13. Stability relationship for water droplet crystallization with the NASA Lewis icing spray nozzle

    NASA Technical Reports Server (NTRS)

    Marek, C. John; Bartlett, C. Scott

    1988-01-01

    In order to produce small droplets for icing cloud simulation, high pressure air atomizing nozzles are used. For certain icing testing applications, median drop sizes as small as 5 mm are needed, which require air atomizing pressures greater than 3000 kPa. Isentropic expansion of the ambient temperature atomizing air to atmospheric pressure can result in air stream temperatures of -160 C which results in ice crystals forming in the cloud. To avoid such low temperatures, it is necessary to heat the air and water to high initial temperatures. An icing spray research program was conducted to map the temperatures below which ice crystals form. A soot slide technique was used to determine the presence of crystals in the spray.

  14. Identification of a Novel "Fishbone" Structure in the Dendritic Growth of Columnar Ice Crystals

    E-print Network

    Libbrecht, Kenneth G.

    Identification of a Novel "Fishbone" Structure in the Dendritic Growth of Columnar Ice Crystals was sufficiently high ­ typically greater than 100-200 percent [6]. We have come to refer to them as "fishbones

  15. An Investigation of Light Scattering by Irregular Ice Crystals via PSTD 

    E-print Network

    Zhang, Jianing

    2014-07-28

    to determine the validity PSTD with CPML. We propose a random field model for surface irregularities of ice crystals with roughened surfaces. Results using this model show that reflection probability decreases exponentially as the roughness is increased...

  16. Preferred Ice Crystal Orientation Fabric Measurements within the Greenland Ice Sheet Using Multi-Polarization Radar Data

    NASA Astrophysics Data System (ADS)

    Velez-Gonzalez, J. A.; JiLu, L.; Leuschen, C.; Gogineni, P.; Van der Veen, C. J.; Tsoflias, G. P.; Drews, R.; Harish, A. R.

    2013-12-01

    Discharge of ice from the Greenland Ice Sheet to the ocean has increased significantly over the last 25 years due to the acceleration of important outlet glaciers. It was reported that the Greenland Ice Sheet contributed about 2.5 m out of about 6 m of sea-level rise during the Eemian interglacial period. The temperatures during Eemian were reported to be about 8o×4o C higher than the mean of the past millennium. Laboratory measurements have shown that glacial ice, characterized by preferred crystal orientation fabric (COF), is three times more deformable than ice with randomly oriented crystalline structures. Layers characterized by preferred ice COF can influence the flow behavior of a glacier or ice sheet. However, COF measurements are typically obtained from ice cores, and thus are very spatially limited and mostly constrained to areas with little ice flow. A more efficient technique to map the extent of ice fabric over larger regions of ice sheets is needed to better understand the effects on large scale ice flow processes. Radar measurements are capable of discriminating between reflections caused by changes in density, electrical permittivity and COF by exploiting the anisotropic and birefringent properties of ice crystals. For this investigation two radar datasets were collected during the survey of the Greenland Eemian Ice Drilling Site (77.45°N 51.06°W) in August 2008, using a ground-based and chirped-pulse Multi-Channel Radar Depth Sounder (MCRDS) developed by the Center for Remote Sensing of Ice Sheets (CReSIS). The radar used two transmit and eight receive antennas at the center frequency of 150 MHz with a bandwidth of 30 MHz. The first data set consisted of polarimatric measurements acquired in a circular pattern (radius: 35 m) with two co-polarized antenna orientations (one transmitter and four receivers oriented with 90° offsets in the directions of the incident H-Field and E-Field, respectively). Analysis of the circular data shows a periodic power variation with four distinct extinction patterns occurring at 90 degree intervals starting at approximately 700 m depth. Furthermore a 20 degree phase change is observed between the E- and H-field data. Both observations suggest that approximately 72% of the 2542m ice column exhibits birefringent anisotropy caused by preferred ice crystal orientation. The second dataset was acquired in a grid pattern consisting of twenty 10-Km 2D lines (NW to SE) spaced at 0.5-Km and three 10-Km lines (NE to SW) spaced at 2.5-Km. Both transmit and eight receive antenna were oriented parallel to the vehicle track, resulting in E-Field co-polarized data. We will determine the dominant COF relative to the ice divide for a 100 square Km region around the NEEM camp using the results from both datasets. The results of this investigation will be compared to the NEEM ice core observations to determine the accuracy of the analysis. In this investigation we will provide a brief overview of the system and experiments and present the results of data analysis.

  17. Characterisation of ice and THF hydrate slurry crystal size distribution by microscopic observation method

    Microsoft Academic Search

    Anthony Delahaye; Laurence Fournaison; Jacques Guilpart

    2010-01-01

    The objective of the present work is to characterise, using an experimental microscopic observation device, the crystal size distribution (CSD) of ice and tetrahydrofuran (THF) hydrate slurries, which can be used as two-phase refrigerant fluids for cold transportation and storage in the field of secondary refrigeration. Three different solutes (ethanol, propylene glycol and sodium chloride) were used to form ice

  18. Crystal ice formation of solution and its removal phenomena at cooled horizontal solid surface

    Microsoft Academic Search

    Tetsuo Hirata; Mitsutoshi Kato; Koji Nagasaka; Masaaki Ishikawa

    2000-01-01

    Experimental studies for crystal ice formation and its removal phenomena of ethylene glycol solution on a cooled horizontal plate have been performed. Onset condition for ice removal phenomenon is examined experimentally as well as analytically. As a cooled plate, a glass, an acrylic resin, a polyvinyl chloride, a silicone resin and the copper plates are used. It is found that

  19. Enhanced lidar backscattering by quasi-horizontally oriented ice crystal plates in cirrus clouds

    Microsoft Academic Search

    Ping Yang; Yong X. Hu; David M. Winker; Jun Zhao; Chris A. Hostetler; Lamont Poole; Bryan A. Baum; Michael I. Mishchenko; Jens Reichardt

    2003-01-01

    The backscattering of light by quasi-horizontally oriented hexagonal ice plates is investigated because of its pertinence to lidar measurements of cirrus clouds. For oriented ice crystals, the commonly used geometric optics ray-tracing method is not applicable to the computation of the scattered field in certain scattering directions, in particular, the backscattering direction, because of the singularity problem inherent to the

  20. Radiative Transfer in Cirrus Clouds. Part III: Light Scattering by Irregular Ice Crystals

    Microsoft Academic Search

    Y. Takano; K. N. Liou

    1995-01-01

    A new Monte Carlo\\/geometric ray-tracing method has been developed for the computation of the scattering, absorption, and polarization properties of ice crystals with various irregular structure, including hollow columns, bullet rosettes, dendrites, and capped columns. The shapes of these ice crystals are defined by appropriate geometric models and incident coordinate systems. The incident photons are traced with a hit-and-miss Monte

  1. Geometric-optics integral-equation method for light scattering by nonspherical ice crystals

    Microsoft Academic Search

    Ping Yang; K. N. Liou

    1996-01-01

    A new geometric-optics model has been developed for the calculation of the single-scattering and polar- ization properties for arbitrarily oriented hexagonal ice crystals. The model uses the ray-tracing tech- nique to solve the near field on the ice crystal surface, which is then transformed to the far field on the basis of the electromagnetic equivalence theorem. From comparisons with the

  2. A Theoretical Determination of the Capture Efficiency of Small Columnar Ice Crystals by Large Cloud Drops

    Microsoft Academic Search

    Jeffrey K. Lew; Hans R. Pruppacher

    1983-01-01

    A theoretical model has been formulated to study by numerical techniques the efficiency E with which columnar ice crystals grown at temperatures between 3 and 8°C are captured in a cloud by relatively large, supercooled cloud drops. The ice crystals studied had lengths L of 15 L 240 m and diameters D of 1.5 D 240 m. and L\\/D values

  3. Realization of quasi-spherical implosion using pre-shaped prolate wire arrays with a compression foam target inside

    NASA Astrophysics Data System (ADS)

    Zhang, Yang; Ding, Ning; Li, Zhenghong; Xu, Rongkun; Chen, Dingyang; Ye, Fan; Zhou, Xiuwen; Chen, Faxin; Chen, Jinchuan; Li, Linbo; Xiao, Delong; Sun, Shunkai; Xue, Chuang; Shu, Xiaojian; Wang, Jianguo

    2015-02-01

    Quasi-spherical (QS) implosion of wire arrays and its impact on the foam target have been studied on the 100 ns 1.5 MA Qiangguang-I facility, which suggests that a high quality impact between the QS implosion and foam target can be achieved by adjusting load's initial shape carefully to match the external magnetic pressure. Implosions of loads with H/d ˜ 1.2 were studied with a self-emission x-ray pinhole image system and a dark field schlieren system. The radially developed spike-like instabilities indicate the spherical convergence of plasma. The observed radiation on the foam target surface suggests satisfying implosion symmetry and wire-foam impact simultaneity. An average implosion speed of 10.5 × 106 cm/s was obtained with an optical streak image system. The derived peak kinetic energy density ˜2.1 kJ/cm is remarkably higher than cylindrical cases, which agree with the expectations.

  4. High energy signatures of quasi-spherical accretion onto rotating, magnetized neutron star in the ejector-accretor intermediate state

    E-print Network

    Bednarek, W

    2015-01-01

    We consider a simple scenario for the accretion of matter onto a neutron star in order to understand processes in the inner pulsar magnetosphere during the transition stage between different accretion modes. A simple quasi-spherical accretion process onto rotating, magnetized compact object is analyzed in order to search for the radiative signatures which could appear during transition between ejecting and accreting modes. It is argued that different accretion modes can be present in a single neutron star along different magnetic field lines for specific range of parameters characterising the pulsar (rotational period, surface magnetic field strength) and the density of surrounding medium. The radiation processes characteristic for the ejecting pulsar, i.e. curvature and synchrotron radiation produced by primary electrons in the pulsar outer gap, are expected to be modified by the presence of additional thermal radiation from the neutron star surface. We predict that during the transition from the pure ejecto...

  5. Tropical tropopause ice clouds: A new approach to answer the mystery of low crystal numbers

    NASA Astrophysics Data System (ADS)

    Spichtinger, Peter; Krämer, Martina

    2013-04-01

    Water vapour is the most important natural green house gas. However, in the stratosphere an increase in water vapour would possibly result in a net cooling of the earth-atmosphere system. The major entrance pathway of trace substances into the stratosphere is the tropical tropopause layer (TTL). The TTL water vapor budget, and thus the exchange between troposphere and stratosphere, depends crucially on the occurrence and properties of ice clouds in this cold region (T < 200 K). New observations indicate that very low ice crystal numbers frequently occur in the TTL. This phenomenon is not yet understood and is not compatible with the idea that homogeneous freezing of solution droplets is the major pathway of ice formation. These low ice number concentrations are consistent with observed persistent high ice supersaturations inside cold TTL cirrus clouds, which in turn control the exchange of water vapor with the stratosphere. Here, we reproduce in-situ measurements of frequencies of occurrence of ice crystal concentrations by extensive model simulations, driven by the special dynamical conditions in the TTL, namely the superposition of slow large-scale updrafts with high-frequency short waves. The simulations show that about 80% of the observed incidences of low ice crystal concentrations can be explained by 'classical' homogeneous ice nucleation in the very slow updrafts (< 1cm/s), about 19% stem from heterogeneous freezing, while the remaining of about 1% originates from homogeneous freezing in slightly faster updrafts (> 1cm/s). The mechanism limiting the ice crystal production from homogeneous freezing in an environment full of gravity waves is that freezing events are stalled -due to the shortness of the gravity waves- before a higher number concentration of ice crystals can be formed.

  6. A new experimental setup to investigate nucleation, dynamic growth and surface properties of single ice crystals

    NASA Astrophysics Data System (ADS)

    Voigtlaender, Jens; Bieligk, Henner; Niedermeier, Dennis; Clauss, Tina; Chou, Cédric; Ulanowski, Zbigniew; Stratmann, Frank

    2013-04-01

    The nucleation and growth of atmospheric ice particles is of importance for both, weather and climate. However, knowledge is still sparse, e.g. when considering the influences of ice particle surface properties on the radiative properties of clouds. Therefore, based on the experiences with our laminar flow tube chamber LACIS (Leipzig Aerosol Cloud Interaction Simulator, Stratmann et al., 2004), we developed a new device to characterize nucleation, dynamic growth and light scattering properties of a fixed single ice crystal in dependence on the prevailing thermodynamic conditions. Main part of the new setup is a thermodynamically controlled laminar flow tube with a diameter of 15 mm and a length of 1.0 m. Connected to the flow tube is a SID3-type (Small Ice Detector, Kaye et al., 2008) instrument called LISA (Leipzig Ice Scattering Apparatus), equipped with an additional optical microscope. For the investigations, a single ice nucleus (IN) with a dry size of 2-5 micrometer is attached to a thin glass fiber and positioned within the optical measuring volume of LISA. The fixed particle is exposed to the thermodynamically controlled air flow, exiting the flow tube. Two mass flow controllers adjusting a dry and a humidified gas flow are applied to control both, the temperature and the saturation ratio over a wide range. The thermodynamic conditions in the experiments were characterized using a) temperature and dew-point measurements, and b) computational fluid dynamics (CFD) calculations. Dependent on temperature and saturation ratio in the measuring volume, ice nucleation and ice crystal growth/shrinkage can occur. The optical microscope allows a time dependent visualization of the particle/ice crystal, and the LISA instrument is used to obtain 2-D light scattering patterns. Both devices together can be applied to investigate the influence of thermodynamic conditions on ice crystal growth, in particular its shape and surface properties. We successfully performed deposition nucleation experiments considering kaolinite and SnowmaxTM (Johnson Controls Snow, Colorado, USA) particles. Different temperatures and saturation ratios were considered resulting in different growth rates and ice crystal shapes. We have proven the feasibility of the setup for investigating ice particle nucleation and growth. Further investigations and data evaluation concerning the quantification of the ice particle's surface properties are ongoing. Kaye, P., Hirst, E., Greenaway, R., Ulanowski, Z., Hesse, E., DeMott, P., Saunders, C., Conolly, P.: Classifying atmospheric ice crystals by spatial light scattering, Optics Letters, 33, 1545-1547, 2008. Stratmann, F., Kiselev, A., Wurzler, S., Wendisch, M., Heintzenberg, J., Charlson, R. J., Diehl, K., Wex, H., Schmidt, S.: Laboratory studies and numerical simulations of cloud droplet formation under realistic supersaturation conditions., J. Atmos. Ocean. Tech., 21, 876-887, 2004

  7. Laboratory Investigation of Contact Freezing and the Aerosol to Ice Crystal Transformation Process

    SciTech Connect

    Shaw, Raymond A. [Michigan Technological University

    2014-10-28

    This project has been focused on the following objectives: 1. Investigations of the physical processes governing immersion versus contact nucleation, specifically surface-induced crystallization; 2. Development of a quadrupole particle trap with full thermodynamic control over the temperature range 0 to –40 °C and precisely controlled water vapor saturation ratios for continuous, single-particle measurement of the aerosol to ice crystal transformation process for realistic ice nuclei; 3. Understanding the role of ice nucleation in determining the microphysical properties of mixed-phase clouds, within a framework that allows bridging between laboratory and field measurements.

  8. Polarimetric radar observations of the growth of highly-aligned ice crystals in the presence of supercooled water

    E-print Network

    Hogan, Robin

    Polarimetric radar observations of the growth of highly-aligned ice crystals in the presence aligned, which suggeststhat the normal growth mechanism (for the larger crystals at least) is aggrega to the radar signal themselves, the indication is that ice crystals in a highly supersaturated envir- onment

  9. Textural and crystal-fabric anisotropies and the flow of ice masses.

    PubMed

    Baker, R W

    1981-03-01

    Accurate modeling and prediction of glacier response requires a better understanding of the influence of physical anisotropies on creep. To investigate the effects of variations in the degree of preferred crystallographic orientation and ice crystal size on creep, 19 samples of anisotropic glacier ice were deformed in simple shear. Results indicate that the time required for ice samples to reach the minimum strain rate decreases as crystal size increases; an increase in crystal-fabric development from an isotropic fabric to one with a strong single maximum results in an enhancement of the minimum strain rate by a factor of 4; and a doubling of the crystal size results in about a ninefold increase in the minimum strain rate. PMID:17744932

  10. Measurements of high number densities of ice crystals in the tops of tropical cumulonimbus

    NASA Astrophysics Data System (ADS)

    Knollenberg, R. G.; Kelly, K.; Wilson, J. C.

    1993-05-01

    Imaging and light scattering instruments were used during the January/February 1987 STEP Tropical Experiment at Darwin, Australia, to measure ice crystal size distributions in the tops of tropical cumulonimbus anvils associated with tropical cyclones and related cloud systems. Two light scattering instruments covered particles from 0.1-?m to 78-?m diameter. Particles larger than 50-?m diameter were imaged with a two-dimensional Grey optical array imaging probe. The measurements were made at altitudes ranging from 13 to 18 km at temperatures ranging from -60° to -90°C. Additional measurements made in continental cumulonimbus anvils in the western United States offer a comparative data set. The tropical anvil penetrations revealed surprisingly high concentrations of ice crystals. Number densities were typically greater than 10 cm-3 with up to 100 cm-3 if one includes all particles larger than 0.1 ?m and can approach condensation nuclei in total concentration. In order to explain the high number densities, ice crystal nucleation at altitude is proposed with the freezing of fairly concentrated solution droplets in equilibrium at low relative humidities. Any dilute liquid phase is hypothesized to be transitory with a vanishingly short lifetime and limited to cloud levels nearer -40°C. Homogeneous nucleation of ice involving H2SO4 nuclei is attractive in explaining the high number densities of small ice crystals observed near cloud top at temperatures below -60°C. The tropical size distributions were converted to mass using a spherical equivalent size, while the continental anvil data were treated as crystalline plates. Comparisons of the ice water contents integrated from the mass distributions with total water contents measured with NOAA Lyman-alpha instruments require bulk densities equivalent to solid ice for best agreement. Correlation between the two data sets for a number of flight passes was quite good and was further improved by subtraction of water vapor density values ranging between ice and water saturation. Ice water contents up to 0.07 g m-3 were observed in the tropical anvils with over 0.1 g m-3 in continental anvils. The size distributions in tropical anvils generally reveal mass modes at sizes of 20-40 ?m. With rare exceptions, particles larger than 100 ?m were not observed near the cloud tops. In continental cumulonimbus anvils, much larger plate crystals approaching 1 mm in size account for the majority of the ice water. Most of the ice crystal mass lofted to anvil altitudes falls to lower levels prior to evaporating. The anvils can experience strong radiational heating as well as cooling depending upon lower cloud cover, particle size distribution, and time of day.

  11. Effects of Pre-Existing Ice Crystals on Cirrus Clouds and Comparison between Different Ice Nucleation Parameterizations with the Community Atmosphere Model (CAM5)

    SciTech Connect

    Shi, Xiangjun; Liu, Xiaohong; Zhang, Kai

    2015-01-01

    In order to improve the treatment of ice nucleation in a more realistic manner in the Community Atmospheric Model version 5.3 (CAM5.3), the effects of preexisting ice crystals on ice nucleation in cirrus clouds are considered. In addition, by considering the in-cloud variability in ice saturation ratio, homogeneous nucleation takes place spatially only in a portion of cirrus cloud rather than in the whole area of cirrus cloud. With these improvements, the two unphysical limiters used in the representation of ice nucleation are removed. Compared to observations, the ice number concentrations and the probability distributions of ice number concentration are both improved with the updated treatment. The preexisting ice crystals significantly reduce ice number concentrations in cirrus clouds, especially at mid- to high latitudes in the upper troposphere (by a factor of ~10). Furthermore, the contribution of heterogeneous ice nucleation to cirrus ice crystal number increases considerably.Besides the default ice nucleation parameterization of Liu and Penner (2005, hereafter LP) in CAM5.3, two other ice nucleation parameterizations of Barahona and Nenes (2009, hereafter BN) and Kärcher et al. (2006, hereafter KL) are implemented in CAM5.3 for the comparison. In-cloud ice crystal number concentration, percentage contribution from heterogeneous ice nucleation to total ice crystal number, and preexisting ice effects simulated by the three ice nucleation parameterizations have similar patterns in the simulations with present-day aerosol emissions. However, the change (present-day minus pre-industrial times) in global annual mean column ice number concentration from the KL parameterization (3.24×106 m-2) is obviously less than that from the LP (8.46×106 m-2) and BN (5.62×106 m-2) parameterizations. As a result, experiment using the KL parameterization predicts a much smaller anthropogenic aerosol longwave indirect forcing (0.24 W m-2) than that using the LP (0.46 W m-2) and BN (0.39 W m-2) parameterizations.

  12. The enhancement of lidar backscattering by horizontally oriented ice crystal plates in cirrus clouds

    Microsoft Academic Search

    P. Yang; Y. X. Hu; J. Zhao; D. M. Winker; C. A. Hostetler; B. A. Baum; S.-C. Tsay; B.-C. Gao; M. I. Mishchenko

    2002-01-01

    The backscattering of radiation at 0.532 and 1.064 ?m wavelengths by quasi-horizontally oriented hexagonal ice plates is investigated. The geometric optics ray tracing method is not applicable to the scattering problem associated with oriented ice crystals (in particular, in backscattering direction) because of the singularity of the ray-tracing technique. In the present study, we solve the scattered field of quasi-horizontally

  13. Surface melting of ice Ih single crystals revealed by glancing angle x-ray scattering

    Microsoft Academic Search

    A. Lied; H. Dosch; J. H. Bilgram

    1994-01-01

    We present glancing angle x-ray scattering experiments at [00.1], [10.0], and [11.0] surfaces of ice Ih single crystals. The temperature dependence of the evanescent Bragg scattering upon heating reveals a quasiliquid surface layer well below the melting point of each investigated ice surface. At [10.0] and [11.0] surfaces, thermal faceting is observed, which is briefly discussed. The ``oxygen-forbidden'' (00.4) Bragg

  14. Uptake of gaseous aromatic hydrocarbons by non-growing ice crystals

    NASA Astrophysics Data System (ADS)

    Fries, Elke; Haunold, Werner; Jaeschke, Wolfgang; Hoog, Ines; Mitra, Subir K.; Borrmann, Stephan

    Laboratory studies were performed in a walk-in cold chamber to investigate the uptake of aromatic hydrocarbons by non-growing ice crystals at -20 °C. Dendritic ice crystals were grown by vapor deposition and exposed to organic gases (benzene, toluene, ethylbenzene, m/ p-xylene, o-xylene, n-propylbenzene, 4-ethyltoluene, 1,3,5-trimethylbenzene, tert-butylbenzene, 1,2,4-trimethylbenzene, and 1,2,3-trimethylbenzene) at gas-phase concentrations between 2.8 and 33.1 ?g m -3. During all exposure experiments, the gas/air stream was maintained at ice saturation to avoid ice crystal growth or evaporation. An analytical method comprising of solid-phase-micro-extraction followed by gas chromatography/mass spectrometry (SPME/GC-MS) was applied, which allows detection of organic compounds in melted ice at 0.025 ng g ice-1. The SPME/GC-MS method was an appropriate tool to determine the uptake of organic compounds by ice crystals at the applied gas-phase concentrations. However, it was not possible to detect any of the test substances in ice samples after exposure. No adsorption could be detected by increasing gas-phase concentrations. Neither increasing exposure time nor lowering flow rate of the carrier gas caused detectable adsorption effects of aromatic compounds on ice. Our results indicate that adsorption of aromatic hydrocarbons is either insignificant or highly reversible at -20 °C. These findings are consistent with reversible adsorption processes reported already for many oxygenated organic compounds like alcohols, acids, and aldehydes. Although the specific surface area of dendritic ice crystals is large, the results of our study demonstrate that gas uptake by ice surfaces is negligible for the removal of aromatic hydrocarbons in the atmosphere. This is an indication that the occurrence of aromatic hydrocarbons in precipitation cannot be explained by surface adsorption. There must be another accumulation process leading to concentrations of aromatic hydrocarbons found in field studies which is still unknown.

  15. Molecular surface structure of a low-temperature ice Ih(0001) crystal

    SciTech Connect

    Materer, N.; Starke, U.; Barbieri, A.; Van Hove, M.A.; Somorjai, G.A. [Lawrence Berkeley Lab., CA (United States)]|[Univ. of California, Berkeley, CA (United States); Kroes, G.J. [Vrije Universiteit, Amsterdam (Netherlands); Minot, C. [Universite Pierre et Marie Curie, Paris (France)

    1995-04-27

    An ice film with thickness greater than 10 A was crystallized on a clean Pt(111) surface. Its external surface structure was investigated at 90 K by dynamical low-energy electron diffraction (LEED), followed by molecular dynamics simulations and ab initio quantum chemical calculations. The results favor the common hexagonal ice 1h structure over other forms of ice, with (0001) termination. A full-bilayer termination is found, but with much enhanced amplitudes of motion of the O atoms in the outermost layer of H{sub 2}O molecules, even at 90 K, so that these molecules were undetected experimentally by LEED. 14 refs., 2 figs.

  16. Structural transformation in supercooled water controls the crystallization rate of ice.

    PubMed

    Moore, Emily B; Molinero, Valeria

    2011-11-24

    One of water's unsolved puzzles is the question of what determines the lowest temperature to which it can be cooled before freezing to ice. The supercooled liquid has been probed experimentally to near the homogeneous nucleation temperature, T(H) ? 232 K, yet the mechanism of ice crystallization-including the size and structure of critical nuclei-has not yet been resolved. The heat capacity and compressibility of liquid water anomalously increase on moving into the supercooled region, according to power laws that would diverge (that is, approach infinity) at ~225 K (refs 1, 2), so there may be a link between water's thermodynamic anomalies and the crystallization rate of ice. But probing this link is challenging because fast crystallization prevents experimental studies of the liquid below T(H). And although atomistic studies have captured water crystallization, high computational costs have so far prevented an assessment of the rates and mechanism involved. Here we report coarse-grained molecular simulations with the mW water model in the supercooled regime around T(H) which reveal that a sharp increase in the fraction of four-coordinated molecules in supercooled liquid water explains its anomalous thermodynamics and also controls the rate and mechanisms of ice formation. The results of the simulations and classical nucleation theory using experimental data suggest that the crystallization rate of water reaches a maximum around 225 K, below which ice nuclei form faster than liquid water can equilibrate. This implies a lower limit of metastability of liquid water just below T(H) and well above its glass transition temperature, 136 K. By establishing a relationship between the structural transformation in liquid water and its anomalous thermodynamics and crystallization rate, our findings also provide mechanistic insight into the observed dependence of homogeneous ice nucleation rates on the thermodynamics of water. PMID:22113691

  17. Mechanical interactions between ice crystals and red blood cells during directional solidification.

    PubMed

    Ishiguro, H; Rubinsky, B

    1994-10-01

    Experiments in which red blood cells were frozen on a directional solidification stage under a microscope show that there is a mechanical interaction between ice crystals and cells in which cells are pushed and deformed by the ice crystals. The mechanical interaction occurs during freezing of cells in physiological saline and is significantly inhibited by the addition of 20% v/v glycerol to the solution. The addition of osmotically insignificant quantities of antifreeze proteins from the winter flounder or ocean pout to the physiological saline with 20% v/v glycerol generates strong mechanical interactions between the ice and the cells. The cells were destroyed during freezing in physiological saline, survived freezing in physiological saline with glycerol, and were completely destroyed by the addition of antifreeze proteins to the solution with glycerol. The difference in cell survival through freezing and thawing appears to be related, in part, to the habit of ice crystal growing in the suspension of red blood cells and the nature of mechanical interaction between the ice crystal and the cells. This suggests that mechanical damage may be a factor during cryopreservation of cells. PMID:7988158

  18. Modeling the Influence of Antifreeze Proteins on Three-Dimensional Ice Crystal Melt Shapes using a Geometric Approach

    E-print Network

    Liu, Jun Jie; Dolev, Maya Bar; Celik, Yeliz; Wettlaufer, J S; Braslavsky, Ido

    2012-01-01

    The melting of pure axisymmetric ice crystals has been described previously by us within the framework of so-called geometric crystal growth. Nonequilibrium ice crystal shapes evolving in the presence of hyperactive antifreeze proteins (hypAFPs) are experimentally observed to assume ellipsoidal geometries ("lemon" or "rice" shapes). To analyze such shapes we harness the underlying symmetry of hexagonal ice Ih and extend two-dimensional geometric models to three-dimensions to reproduce the experimental dissolution process. The geometrical model developed will be useful as a quantitative test of the mechanisms of interaction between hypAFPs and ice.

  19. Modeling the Influence of Antifreeze Proteins on Three-Dimensional Ice Crystal Melt Shapes using a Geometric Approach

    E-print Network

    Jun Jie Liu; Yangzong Qin; Maya Bar Dolev; Yeliz Celik; J. S. Wettlaufer; Ido Braslavsky

    2012-07-12

    The melting of pure axisymmetric ice crystals has been described previously by us within the framework of so-called geometric crystal growth. Nonequilibrium ice crystal shapes evolving in the presence of hyperactive antifreeze proteins (hypAFPs) are experimentally observed to assume ellipsoidal geometries ("lemon" or "rice" shapes). To analyze such shapes we harness the underlying symmetry of hexagonal ice Ih and extend two-dimensional geometric models to three-dimensions to reproduce the experimental dissolution process. The geometrical model developed will be useful as a quantitative test of the mechanisms of interaction between hypAFPs and ice.

  20. Exploring the relation between crystal fabric and climate history in an ice-core record

    NASA Astrophysics Data System (ADS)

    Kennedy, J. H.; Pettit, E. C.; di Prinzio, C. L.; Wilen, L. A.

    2010-12-01

    Ice crystals shear easily along the slip systems in their basal planes, while shear on the other slip systems are nearly two orders of magnitude harder. The bulk response of a glacier to shear (flow) can be significantly altered if the crystals exhibit a preferred orientation, or fabric, as see in many glaciers and ice sheets. Further, a positive feedback mechanism exists between fabric development and ice deformation which may allow the vertical variation in fabric to retain information about the climate history. We explore both the evolution of a particular climatic event as well as the bulk fabric evolution through time within Taylor Dome, East Antarctica, where an ice core was drilled to bedrock in 1991-1994. We model bulk fabric evolution driven by a stress history derived from the geometry, temperature and depth-age relation and study the sensitivity of the results to initialization of near-surface fabric and the results are validated by thin-section fabric data. A climatic event can induce a subtle change in the near surface fabric. We model the evolution of this subtle change through time under different stress scenarios. The model is based on that developed by Thorsteinsson (2002), which is based on the homogeneous stress assumption and includes crystal growth, polygonization, migration recrystallization, and the influence of neighboring crystals on each crystals rotation. Our model successfully captures the large-scale fabric variations observed in the Taylor Dome record. We find that the influence of neighboring crystals have negligible effects over millennial time scales, and small effects over longer ice-sheet time scales. Furthermore, our model suggests that the fabric-climate feedback mechanism enhances small climate-induced variations in fabric and results in crystal size variations over time.

  1. Crystal structure of an insect antifreeze protein and its implications for ice binding.

    PubMed

    Hakim, Aaron; Nguyen, Jennifer B; Basu, Koli; Zhu, Darren F; Thakral, Durga; Davies, Peter L; Isaacs, Farren J; Modis, Yorgo; Meng, Wuyi

    2013-04-26

    Antifreeze proteins (AFPs) help some organisms resist freezing by binding to ice crystals and inhibiting their growth. The molecular basis for how these proteins recognize and bind ice is not well understood. The longhorn beetle Rhagium inquisitor can supercool to below -25 °C, in part by synthesizing the most potent antifreeze protein studied thus far (RiAFP). We report the crystal structure of the 13-kDa RiAFP, determined at 1.21 ? resolution using direct methods. The structure, which contains 1,914 nonhydrogen protein atoms in the asymmetric unit, is the largest determined ab initio without heavy atoms. It reveals a compressed ?-solenoid fold in which the top and bottom sheets are held together by a silk-like interdigitation of short side chains. RiAFP is perhaps the most regular structure yet observed. It is a second independently evolved AFP type in beetles. The two beetle AFPs have in common an extremely flat ice-binding surface comprising regular outward-projecting parallel arrays of threonine residues. The more active, wider RiAFP has four (rather than two) of these arrays between which the crystal structure shows the presence of ice-like waters. Molecular dynamics simulations independently reproduce the locations of these ordered crystallographic waters and predict additional waters that together provide an extensive view of the AFP interaction with ice. By matching several planes of hexagonal ice, these waters may help freeze the AFP to the ice surface, thus providing the molecular basis of ice binding. PMID:23486477

  2. On the importance of small ice crystals in tropical anvil cirrus

    NASA Astrophysics Data System (ADS)

    Jensen, E. J.; Lawson, P.; Baker, B.; Pilson, B.; Mo, Q.; Heymsfield, A. J.; Bansemer, A.; Bui, T. P.; McGill, M.; Hlavka, D.; Heymsfield, G.; Platnick, S.; Arnold, G. T.; Tanelli, S.

    2009-03-01

    In situ measurements of ice crystal concentrations and sizes made with aircraft instrumentation over the past two decades have often indicated the presence of numerous relatively small (<50 ?m diameter) crystals in cirrus clouds. Further, these measurements frequently indicate that small crystals account for a large fraction of the extinction in cirrus clouds. The fact that the instruments used to make these measurements, such as the Forward Scattering Spectrometer Probe (FSSP) and the Cloud Aerosol Spectrometer (CAS), ingest ice crystals into the sample volume through inlets has led to suspicion that the indications of numerous small-crystals could be artifacts of large-crystal shattering on the instrument inlets. We present new aircraft measurements in anvil cirrus sampled during the Tropical Composition, Cloud, and Climate Coupling (TC4) campaign with the 2-Dimensional Stereo (2D-S) probe, which detects particles as small as 10 ?m. The 2D-S has detector "arms" instead of an inlet tube, and therefore is expected to be less susceptible to shattering artifacts than instruments such as CAS. In addition, particle inter-arrival times are used to identify and remove shattering artifacts that occur even with the 2D-S probe. The number of shattering artifacts identified by the 2D-S interarrival time analysis ranges from a negligible contribution to an order of magnitude or more enhancement in apparent ice concentration over the natural ice concentration, depending on the abundance of large crystals and the natural small-crystal concentration. The 2D-S measurements in tropical anvil cirrus suggest that natural small-crystal concentrations are typically one to two orders of magnitude lower than those inferred from CAS. The strong correlation between the CAS/2D-S ratio of small-crystal concentrations and large-crystal concentration suggests that the discrepancy is likely caused by shattering of large crystals on the CAS inlet. We argue that past measurements with CAS in cirrus with large crystals present may contain errors due to crystal shattering, and past conclusions derived from these measurements may need to be revisited. Further, we present correlations between CAS spurious concentration and 2D-S large-crystal mass from spatially uniform anvil cirrus sampling periods as an approximate guide for estimating quantitative impact of large-crystal shattering on CAS concentrations in previous datasets. We use radiative transfer calculations to demonstrate that in the maritime anvil cirrus sampled during TC4, small crystals indicated by 2D-S contribute relatively little to cloud extinction, radiative forcing, or radiative heating in the anvils, regardless of anvil age or vertical location in the clouds. While 2D-S ice concentrations in fresh anvil cirrus may often exceed 1 cm-3, and are observed to exceed 10 cm-3 in turrets, they are typically ~0.1 cm-3 and rarely exceed 1 cm-3 (<1.4% of the time) in aged anvil cirrus. It appears that the numerous small crystals detrained from convective updrafts do not persist in the anvil cirrus sampled during TC-4. We hypothesize that isolated occurrences of higher ice concentrations in aged anvil cirrus are caused by ice nucleation driven by gravity waves.

  3. On the importance of small ice crystals in tropical anvil cirrus

    NASA Astrophysics Data System (ADS)

    Jensen, E. J.; Lawson, P.; Baker, B.; Pilson, B.; Mo, Q.; Heymsfield, A. J.; Bansemer, A.; Bui, T. P.; McGill, M.; Hlavka, D.; Heymsfield, G.; Platnick, S.; Arnold, G. T.; Tanelli, S.

    2009-08-01

    In situ measurements of ice crystal concentrations and sizes made with aircraft instrumentation over the past two decades have often indicated the presence of numerous relatively small (< 50 ?m diameter) crystals in cirrus clouds. Further, these measurements frequently indicate that small crystals account for a large fraction of the extinction in cirrus clouds. The fact that the instruments used to make these measurements, such as the Forward Scattering Spectrometer Probe (FSSP) and the Cloud Aerosol Spectrometer (CAS), ingest ice crystals into the sample volume through inlets has led to suspicion that the indications of numerous small-crystals could be artifacts of large-crystal shattering on the instrument inlets. We present new aircraft measurements in anvil cirrus sampled during the Tropical Composition, Cloud, and Climate Coupling (TC4) campaign with the 2-Dimensional Stereo (2D-S) probe, which detects particles as small as 10 ?m. The 2D-S has detector "arms" instead of an inlet tube. Since the 2D-S probe surfaces are much further from the sample volume than is the case for the instruments with inlets, it is expected that 2D-S will be less susceptible to shattering artifacts. In addition, particle inter-arrival times are used to identify and remove shattering artifacts that occur even with the 2D-S probe. The number of shattering artifacts identified by the 2D-S interarrival time analysis ranges from a negligible contribution to an order of magnitude or more enhancement in apparent ice concentration over the natural ice concentration, depending on the abundance of large crystals and the natural small-crystal concentration. The 2D-S measurements in tropical anvil cirrus suggest that natural small-crystal concentrations are typically one to two orders of magnitude lower than those inferred from CAS. The strong correlation between the CAS/2D-S ratio of small-crystal concentrations and large-crystal concentration suggests that the discrepancy is likely caused by shattering of large crystals on the CAS inlet. We argue that past measurements with CAS in cirrus with large crystals present may contain errors due to crystal shattering, and past conclusions derived from these measurements may need to be revisited. Further, we present correlations between CAS spurious concentration and 2D-S large-crystal mass from spatially uniform anvil cirrus sampling periods as an approximate guide for estimating quantitative impact of large-crystal shattering on CAS concentrations in previous datasets. We use radiative transfer calculations to demonstrate that in the maritime anvil cirrus sampled during TC4, small crystals indicated by 2D-S contribute relatively little cloud extinction, radiative forcing, or radiative heating in the anvils, regardless of anvil age or vertical location in the clouds. While 2D-S ice concentrations in fresh anvil cirrus may often exceed 1 cm-3, and are observed to exceed 10 cm-3 in turrets, they are typically ~0.1 cm-3 and rarely exceed 1 cm-3 (<1.4% of the time) in aged anvil cirrus. We hypothesize that isolated occurrences of higher ice concentrations in aged anvil cirrus may be caused by ice nucleation driven by either small-scale convection or gravity waves. It appears that the numerous small crystals detrained from convective updrafts do not persist in the anvil cirrus sampled during TC-4.

  4. On the Importance of Small Ice Crystals in Tropical Anvil Cirrus

    NASA Technical Reports Server (NTRS)

    Jensen, E. J.; Lawson, P.; Baker, B.; Pilson, B.; Mo, Q.; Heymsfield, A. J.; Bansemer, A.; Bui, T. P.; McGill, M.; Hlavka, D.; Heymsfield, G.; Platnick, S.; Arnold, G. T.; Tanelli, S.

    2009-01-01

    In situ measurements of ice crystal concentrations and sizes made with aircraft instrumentation over the past two decades have often indicated the presence of numerous relatively small (< 50 m diameter) crystals in cirrus clouds. Further, these measurements frequently indicate that small crystals account for a large fraction of the extinction in cirrus clouds. The fact that the instruments used to make these measurements, such as the Forward Scattering Spectrometer Probe (FSSP) and the Cloud Aerosol Spectrometer (CAS), ingest ice crystals into the sample volume through inlets has led to suspicion that the indications of numerous small ]crystals could be artifacts of large ]crystal shattering on the instrument inlets. We present new aircraft measurements in anvil cirrus sampled during the Tropical Composition, Cloud, and Climate Coupling (TC4) campaign with the 2 ] Dimensional Stereo (2D ]S) probe, which detects particles as small as 10 m. The 2D ]S has detector "arms" instead of an inlet tube. Since the 2D ]S probe surfaces are much further from the sample volume than is the case for the instruments with inlets, it is expected that 2D ]S will be less susceptible to shattering artifacts. In addition, particle inter ]arrival times are used to identify and remove shattering artifacts that occur even with the 2D ]S probe. The number of shattering artifacts identified by the 2D ]S interarrival time analysis ranges from a negligible contribution to an order of magnitude or more enhancement in apparent ice concentration over the natural ice concentration, depending on the abundance of large crystals and the natural small ]crystal concentration. The 2D ]S measurements in tropical anvil cirrus suggest that natural small ]crystal concentrations are typically one to two orders of magnitude lower than those inferred from CAS. The strong correlation between the CAS/2D ]S ratio of small ]crystal concentrations and large ]crystal concentration suggests that the discrepancy is likely caused by shattering of large crystals on the CAS inlet. We argue that past measurements with CAS in cirrus with large crystals present may contain errors due to crystal shattering, and past conclusions derived from these measurements may need to be revisited. Further, we present correlations between CAS spurious concentration and 2D ]S large ]crystal mass from spatially uniform anvil cirrus sampling periods as an approximate guide for estimating quantitative impact of large ]crystal shattering on CAS concentrations in previous datasets. We use radiative transfer calculations to demonstrate that in the maritime anvil cirrus sampled during TC4, small crystals indicated by 2D ]S contribute relatively little cloud extinction, radiative forcing, or radiative heating in the anvils, regardless of anvil age or vertical location in the clouds. While 2D ]S ice concentrations in fresh anvil cirrus may often exceed 1 cm.3, and are observed to exceed 10 cm.3 in turrets, they are typically 0.1 cm.3 and rarely exceed 1 cm.3 (<1.4% of the time) in aged anvil cirrus. We hypothesize that isolated occurrences of higher ice concentrations in aged anvil cirrus may be caused by ice nucleation driven by either small ]scale convection or gravity waves. It appears that the numerous small crystals detrained from convective updrafts do not persist in the anvil cirrus sampled during TC ]4.

  5. Crystal alignments in the fast ice of Arctic Alaska

    SciTech Connect

    Weeks, W.F.; Gow, A.J.

    1980-02-20

    Field observations at 60 sites located in the fast or near-fast ice along a 1200-km stretch of the north coast of Alaska between the Bering Strait and Barter Island have shown that the great majority of the ice samples (95%) exhibit striking c axis alignments within the horizontal plane. In all cases the degree of preferred orientation increased with depth in the ice. Representative standard deviations around a mean direction in the horizontal plane are commonly less than +- 10/sup 0/ for samples collected near the bottom of the ice. At a given site the mean c axis direction X-bar/sub 0/ may vary as much as 20/sup 0/ with vertical location in the ice sheet. The c axis allignments in the nearshore region generally parallel the coast, with strong alignments occurring in the lagoon systems between the barrier islands and the coast and seaward of the barrier islands. In passes between islands and in entrances such as the opening to Kotzebue Sound the alignment is parallel to the channel. Only limited observations are available farther seaward over the inner (10- to 50-m isobaths) and outer (50-m isobath to shelf break) shelf regions. These indicate Ne-SW and E-W alignments, respectively, in the Beaufort Sea north of Prudhoe Bay.

  6. arXiv:1110.5828v1[cond-mat.mtrl-sci]26Oct2011 Measurements of Growth Rates of (0001) Ice Crystal Surfaces

    E-print Network

    Libbrecht, Kenneth G.

    arXiv:1110.5828v1[cond-mat.mtrl-sci]26Oct2011 Measurements of Growth Rates of (0001) Ice Crystal plays an important role in the growth dy- namics of ice crystals from water vapor [1, 2, 3]. Although holds that temperature-dependent effects of premelting on ice crystal growth are responsible for the ob

  7. A global classification of snow crystals, ice crystals, and solid precipitation based on observations from middle latitudes to polar regions

    NASA Astrophysics Data System (ADS)

    Kikuchi, Katsuhiro; Kameda, Takao; Higuchi, Keiji; Yamashita, Akira

    2013-10-01

    This paper presents an extensive revision of Magono and Lee's (1966) classification of natural snow crystals, which has been widely used in snow and ice studies to describe snow crystal shapes. The new classification catalogs snow crystals and other solid precipitation particles into 121 categories, in contrast to Magono and Lee's 80 categories. Of these, 28 categories were created to classify new types of snow crystals that have been discovered in polar regions since 1968, seven were created after reconsidering the original categories, and six categories were created to classify solid precipitation particles such as frozen cloud particles and small raindrops. Because our observational area extended from middle latitudes (Japan) to polar regions, we refer to our new classification scheme as ‘global-scale classification’ or ‘global classification’. The global classification consists of three levels - general, intermediate, and elementary - which are composed of 8, 39, and 121 categories, respectively. This paper describes the characteristics of each type of snow crystal, ice crystal, and solid precipitation particle.

  8. The bending triad of the quasi-spherical top molecule SO 2F 2 in the 550 cm -1 region

    NASA Astrophysics Data System (ADS)

    Rotger, M.; Boudon, V.; Loëte, M.; Zvereva-Loëte, N.; Margulès, L.; Demaison, J.; Merke, I.; Hegelund, F.; Bürger, H.

    2006-08-01

    The analysis of the ?3/ ?7/ ?9 bending triad of SO 2F 2 has been recently performed with the Watson's Hamiltonian up to octic terms employing 79 rovibrational parameters but including only the first order Coriolis interaction terms, fixed to ab initio values [H. Bürger, J. Demaison, F. Hegelund, L. Margulès, I. Merke, J. Mol. Struct. 612 (2002) 133-141]. Since SO 2F 2 is a quasi-spherical top, it can also be considered as derived from the SO42- sulfate ion. We have thus developed a new tensorial formalism in the O (3) ? Td ? C2 v group chain [M. Rotger, V. Boudon, M. Loëte, J. Mol. Spectrosc. 216 (2002) 297-307]. This approach allows a systematic development of rovibrational interactions and makes global analyses easier to perform even for complex polyad systems. We present here an application of this model to the analysis of the bending triad, with the same set of microwave assignments and almost the same set of infrared assignments as in the previous study of Bürger et al. It appears that we need to expand our Hamiltonian to a lower degree than the "classical" one (six instead of eight) when including also the second order Coriolis interactions. Our fit does not include more parameters. Furthermore, all of them are determined and the standard deviation of the rotational transitions is twice smaller. The analysis has been performed thanks to the C 2 v TDS program suite, which is freely available at the URL: http://www.u-bourgogne.fr/LPUB/c2vTDS.html.

  9. cm-scale variations of crystal orientation fabric in cold Alpine ice core from Colle Gnifetti

    NASA Astrophysics Data System (ADS)

    Kerch, Johanna; Weikusat, Ilka; Eisen, Olaf; Wagenbach, Dietmar; Erhardt, Tobias

    2015-04-01

    Analysis of the microstructural parameters of ice has been an important part of ice core analyses so far mainly in polar cores in order to obtain information about physical processes (e.g. deformation, recrystallisation) on the micro- and macro-scale within an ice body. More recently the influence of impurities and climatic conditions during snow accumulation on these processes has come into focus. A deeper understanding of how palaeoclimate proxies interact with physical properties of the ice matrix bears relevance for palaeoclimatic interpretations, improved geophysical measurement techniques and the furthering of ice dynamical modeling. Variations in microstructural parameters e.g. crystal orientation fabric or grain size can be observed on a scale of hundreds and tens of metres but also on a centimetre scale. The underlying processes are not necessarily the same on all scales. Especially for the short-scale variations many questions remain unanswered. We present results from a study that aims to investigate following hypotheses: 1. Variations in grain size and fabric, i.e. strong changes of the orientation of ice crystals with respect to the vertical, occur on a centimetre scale and can be observed in all depths of an ice core. 2. Palaeoclimate proxies like dust and impurities have an impact on the microstructural processes and thus are inducing the observed short-scale variations in grain size and fabric. 3. The interaction of proxies with the ice matrix leads to depth intervals that show correlating behaviour as well as ranges with anticorrelation between microstructural parameters and palaeoclimatic proxies. The respective processes need to be identified. Fabric Analyser measurements were conducted on more than 80 samples (total of 8 m) from different depth ranges of a cold Alpine ice core (72 m length) drilled in 2013 at Colle Gnifetti, Switzerland/Italy. Results were obtained by automatic image processing, providing estimates for grain size distributions and crystal orientation fabric, and comparison with data from continuous flow analysis of chemical impurities. A microstructural characterisation of the analysed core is presented with emphasis on the observed variations in crystal orientation fabric. The relevance of these results for palaeoclimate reconstruction and geophysical applications in ice are discussed.

  10. Crystallization of amorphous ice as the cause of Comet P/Halley's outburst at 14 AU

    NASA Technical Reports Server (NTRS)

    Prialnik, D.; Bar-Nun, A.

    1992-01-01

    An explanation is provided for the postperihelion eruption of Comet P/Halley, detected in February 1991 and believed to have started three months earlier, namely, the crystallization of amorphous ice taking place in the interior of the porous nucleus, at depths of a few tens of meters, accompanied by the release of trapped gases. Numerical calculations show that for a bulk density of 0.5 g/cu cm and a pore size of 1 micron crystallization occurs on the outbound leg of Comet P/Halley's orbit, at heliocentric distances between 5 AU and 17 AU. The trapped gas is released and flows to the surface through the porous medium. It may also open wider channels, as the internal pressures obtained surpass the tensile strength of cometary ice. The outflowing gas carries with it grains of ice and dust, and thus can explain the large amounts of dust observed in the coma at 14.3 AU and beyond.

  11. NASA Glenn Propulsion Systems Lab: 2012 Inaugural Ice Crystal Cloud Calibration Procedure and Results

    NASA Technical Reports Server (NTRS)

    VanZante, Judith F.; Rosine, Bryan M.

    2014-01-01

    The inaugural calibration of the ice crystal and supercooled liquid water clouds generated in NASA Glenn's engine altitude test facility, the Propulsion Systems Lab (PSL) is reported herein. This calibration was in support of the inaugural engine ice crystal validation test. During the Fall of 2012 calibration effort, cloud uniformity was documented via an icing grid, laser sheet and cloud tomography. Water content was measured via multi-wire and robust probes, and particle sizes were measured with a Cloud Droplet Probe and Cloud Imaging Probe. The environmental conditions ranged from 5,000 to 35,000 ft, Mach 0.15 to 0.55, temperature from +50 to -35 F and relative humidities from less than 1 percent to 75 percent in the plenum.

  12. 1 Polar nephelometers for light scattering by ice crystals and aerosols: design and measurements

    E-print Network

    Liou, K. N.

    1 Polar nephelometers for light scattering by ice crystals and aerosols: design and measurements. 1.1. The scattering angle () is referenced from the direction of the incident light. The particle is the cosine-weighted integral of the light scattered from a particle, is a key parameter in radiative transfer

  13. Static charging of aircraft by collisions with ice crystals (+) A. J. Illingworth and S. J. Marsh

    E-print Network

    Paris-Sud XI, Université de

    803 Static charging of aircraft by collisions with ice crystals (+) A. J. Illingworth and S. J alloys used for aircraft manufacture varied by a factor of two. Further experiments are needed, Classification Physics Abstracts 92.60 1. Introduction. When aircraft fly through clouds they generally charge up

  14. OBSERVATIONS OF SNOW AND ICE CRYSTALS WITH LOW TEMPERATURE SCANNING ELECTRON MICROSCOPY (REVIEW)

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This review summarizes the advantages of LTSEM for observations of samples of snow and ice by illustrating the type of surface information that is obtainable, the resolution that can be attained and how the depth of field allows one to observe crystals with significant topography. In addition, we i...

  15. Rearrangement of dislocation structures in the aging of ice single crystals

    E-print Network

    Miguel-Lopez, Carmen

    relaxation during aging are seen as the origin of the acceleration effect. The interplay between dislocation; Strain gradient plasticity 1. Introduction In crystalline materials, aging of the microstructure mayRearrangement of dislocation structures in the aging of ice single crystals V. Taupin a , T

  16. Distributions of ice supersaturation and ice crystals from airborne observations in relation to upper tropospheric dynamical boundaries

    NASA Astrophysics Data System (ADS)

    Diao, Minghui; Jensen, Jorgen B.; Pan, Laura L.; Homeyer, Cameron R.; Honomichl, Shawn; Bresch, James F.; Bansemer, Aaron

    2015-05-01

    Ice supersaturation (ISS) is the prerequisite condition for cirrus cloud formation. To examine multiscale dynamics' influences on ISS formation, we analyze in situ aircraft observations (~200 m scale) over North America in coordinates relative to dynamical boundaries in the upper troposphere and lower stratosphere. Two case studies demonstrate that ISS formation is likely influenced by mesoscale uplifting, small-scale waves, and turbulence. A collective analysis of 15 flights in April-June 2008 shows that the top layers of ISS and ice crystal distributions are strongly associated with thermal tropopause height. In addition, the average occurrence frequencies of ISS and ice crystals on the anticyclonic side of the jet stream are ~1.5-2 times of those on the cyclonic side. By defining five cirrus evolution phases based on the spatial relationships between ice-supersaturated and in-cloud regions, we find that their peak occurrence frequencies are located at decreasing altitudes with respect to the thermal tropopause: (phase 1) clear-sky ISS around the tropopause, (phase 2) nucleation phase around 2 km below the tropopause, (phases 3 and 4) early and later growth phases around 6 km below the tropopause, and (phase 5) sedimentation/sublimation around 2-6 km below the tropopause. Consistent with this result, chemical tracer correlation analysis shows that the majority (~80%) of the earlier cirrus phases (clear-sky ISS and nucleation) occurs inside the chemical tropopause transition layer, while the later phases happen mostly below that layer. These results shed light on the role of dynamical environment in facilitating cirrus cloud formation and evolution.

  17. Adsorption of alpha-helical antifreeze peptides on specific ice crystal surface planes.

    PubMed Central

    Knight, C A; Cheng, C C; DeVries, A L

    1991-01-01

    The noncolligative peptide and glycopeptide antifreezes found in some cold-water fish act by binding to the ice surface and preventing crystal growth, not by altering the equilibrium freezing point of the water. A simple crystal growth and etching technique allows determination of the crystallographic planes where the binding occurs. In the case of elongated molecules, such as the alpha-helical peptides in this report, it also allows a deduction of the molecular alignment on the ice surface. The structurally similar antifreeze peptides from winter flounder (Pseudopleuronectes americanus) and Alaskan plaice (Pleuronectes quadritaberulatus) adsorb onto the (2021) pyramidal planes of ice, whereas the sculpin (Myoxocephalus scorpius) peptide adsorbs on (2110), the secondary prism planes. All three are probably aligned along (0112). These antifreeze peptides have 11-amino acid sequence repeats ending with a polar residue, and each repeat constitutes a distance of 16.5 A along the helix, which nearly matches the 16.7 A repeat spacing along (0112) in ice. This structural match is undoubtedly important, but the mechanism of binding is not yet clear. The suggested mechanism of growth inhibition operates through the influence of local surface curvature upon melting point and results in complete inhibition of the crystal growth even though individual antifreeze molecules bind at only one interface orientation. Images FIGURE 2 PMID:2009357

  18. Elementary steps at the surface of ice crystals visualized by advanced optical microscopy.

    PubMed

    Sazaki, Gen; Zepeda, Salvador; Nakatsubo, Shunichi; Yokoyama, Etsuro; Furukawa, Yoshinori

    2010-11-16

    Due to the abundance of ice on earth, the phase transition of ice plays crucially important roles in various phenomena in nature. Hence, the molecular-level understanding of ice crystal surfaces holds the key to unlocking the secrets of a number of fields. In this study we demonstrate, by laser confocal microscopy combined with differential interference contrast microscopy, that elementary steps (the growing ends of ubiquitous molecular layers with the minimum height) of ice crystals and their dynamic behavior can be visualized directly at air-ice interfaces. We observed the appearance and lateral growth of two-dimensional islands on ice crystal surfaces. When the steps of neighboring two-dimensional islands coalesced, the contrast of the steps always disappeared completely. We were able to discount the occurrence of steps too small to detect directly because we never observed the associated phenomena that would indicate their presence. In addition, classical two-dimensional nucleation theory does not support the appearance of multilayered two-dimensional islands. Hence, we concluded that two-dimensional islands with elementary height (0.37 and 0.39 nm on basal and prism faces, respectively) were visualized by our optical microscopy. On basal and prism faces, we also observed the spiral growth steps generated by screw dislocations. The distance between adjacent spiral steps on a prism face was about 1/20 of that on a basal face. Hence, the step ledge energy of a prism face was 1/20 of that on a basal face, in accord with the known lower-temperature roughening transition of the prism face. PMID:20974928

  19. Determination of Ice-Phase Water Capture Temperatures Using Isotopic Composition and Habits of Ice Crystals—Relevance to Snowpack Augmentation.

    NASA Astrophysics Data System (ADS)

    Warburton, Joseph A.

    1994-09-01

    The oxygen 18/oxygen 16 (18O/16O) and deuterium/hydrogen (D/H) ratios of snowmelt have been used for estimating the weighted mean temperatures in clouds where ice-phase water capture has occurred during the precipitation-forming process. The isotopic measurements were combined with ice crystal replication and microphotographic observations of primary ice crystal habits and degrees of riming. Measurements from two complete winter seasons have enabled the development of climatological databases of these ice-phase water capture temperatures for the central Sierra Nevada and the Snowy Mountains of Australia. The results are based on the linear relationships between the temperature of formation in the clouds of ice crystals grown by vapor deposition and the departures (18O, D) of the oxygen and hydrogen isotopic ratios in these crystals from the standard mean ocean water values. It was found that precipitation falling from orographic winter storms collects most of its water substance in the lower 1 2 km of the supercooled clouds. In the Sierra Nevada, average ice-phase water capture occurred around 10°C. In the Snowy Mountains the primary capture region appears to have an average temperature of 5°C with a secondary region centered on 12°C. Such databases may be useful when designing cloud-seeding projects in regions where snow is the principal form of precipitation.

  20. Superheating of ice crystals in antifreeze protein solutions

    E-print Network

    Braslavsky, Ido

    their equilibrium melting point, and the maximum super- heating obtained was 0.44 °C. When melting commenced in this superheated regime, rapid melting of the crystals from a point on the surface was observed. This increase is known to occur even at temperatures below the bulk melting point (i.e., premelting) (5). Nevertheless

  1. Size and location of ice crystals in pork frozen by high-pressure-assisted freezing as compared to classical methods

    Microsoft Academic Search

    M. N. Martino; L. Otero; P. D. Sanz; N. E. Zaritzky

    1998-01-01

    In high-pressure-assisted freezing, samples are cooled under pressure (200 MPa) to ? 20 °C without ice formation then pressure is released (0.1 MPa) and the high super-cooling reached (approx. 20 °C), promotes uniform and rapid ice nucleation. The size and location of ice crystals in large meat pieces (Longissimus dorsi pork muscle) as a result of high-pressure-assisted freezing were compared

  2. Optical constants of ice Iwqh crystal at terahertz frequencies

    SciTech Connect

    Zhang, Chun; Lee, Kwang-Su; Zhang, X.-C.; Wei, Xing; Shen, Y. R.

    2001-07-23

    Terahertz time-domain spectroscopy was used to measure the refractive indices of Ih crystalline ice in the frequency range of 0.25--1.0 THz. With increasing frequency, the real part, n', of the refractive index increases from 1.787 to 1.793 at 243 K, and the imaginary part, n'', increases from 0.005 to 0.020. The temperature dependence of n' is less than 0.01%/K and that of n'' is {approx}1%/K. Our results connect smoothly to the data of Matsuoka and co-workers [T. Matsuoka, S. Fujita, and S. Mae, J. Appl. Phys. 80, 5884 (1996)] in the microwave range and the data in the far IR range, and can be well described by the existing theoretical models.

  3. A model predicting the evolution of ice particle size spectra and radiative properties of cirrus clouds. Part 2: Dependence of absorption and extinction on ice crystal morphology

    NASA Technical Reports Server (NTRS)

    Mitchell, David L.; Arnott, W. Patrick

    1994-01-01

    This study builds upon the microphysical modeling described in Part 1 by deriving formulations for the extinction and absorption coefficients in terms of the size distribution parameters predicted from the micro-physical model. The optical depth and single scatter albedo of a cirrus cloud can then be determined, which, along with the asymmetry parameter, are the input parameters needed by cloud radiation models. Through the use of anomalous diffraction theory, analytical expressions were developed describing the absorption and extinction coefficients and the single scatter albedo as functions of size distribution parameters, ice crystal shapes (or habits), wavelength, and refractive index. The extinction coefficient was formulated in terms of the projected area of the size distribution, while the absorption coefficient was formulated in terms of both the projected area and mass of the size distribution. These properties were formulated as explicit functions of ice crystal geometry and were not based on an 'effective radius.' Based on simulations of the second cirrus case study described in Part 1, absorption coefficients predicted in the near infrared for hexagonal columns and rosettes were up to 47% and 71% lower, respectively, than absorption coefficients predicted by using equivalent area spheres. This resulted in single scatter albedos in the near-infrared that were considerably greater than those predicted by the equivalent area sphere method. Reflectances in this region should therefore be underestimated using the equivalent area sphere approach. Cloud optical depth was found to depend on ice crystal habit. When the simulated cirrus cloud contained only bullet rosettes, the optical depth was 142% greater than when the cloud contained only hexagonal columns. This increase produced a doubling in cloud albedo. In the near-infrared (IR), the single scatter albedo also exhibited a significant dependence on ice crystal habit. More research is needed on the geometrical properties of ice crystals before the influence of ice crystal shape on cirrus radiative properties can be adequately understood. This study provides a way of coupling the radiative properties of absorption, extinction, and single scatter albedo to the microphysical properties of cirrus clouds. The dependence of extinction and absorption on ice crystal shape was not just due to geometrical differences between crystal types, but was also due to the effect these differences had on the evolution of ice particle size spectra. The ice particle growth model in Part 1 and the radiative properties treated here are based on analytical formulations, and thus represent a computationally efficient means of modeling the microphysical and radiative properties of cirrus clouds.

  4. Particle habit in tropical ice clouds during CRYSTAL-FACE: Comparison of two remote sensing techniques with in situ observations

    Microsoft Academic Search

    H. Chepfer; V. Noel; P. Minnis; D. Baumgardner; L. Nguyen; G. Raga; M. J. McGill; P. Yang

    2005-01-01

    Ice crystal shapes in tropical ice clouds are estimated with two different remote sensing methods and compared with measurements from an in situ cloud aerosol spectrometer (CAS) during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE) campaign conducted in Florida during July 2002. The remote sensing techniques use dual-satellite reflectances and lidar linear depolarization

  5. Particle habit in tropical ice clouds during CRYSTAL-FACE: Comparison of two remote sensing techniques with in situ observations

    Microsoft Academic Search

    H. Chepfer; V. Noel; P. Minnis; D. Baumgardner; L. Nguyen; G. Raga; M. J. McGill; P. Yang

    2005-01-01

    Ice crystal shapes in tropical ice clouds are estimated with two different remote sensing methods and compared with measurements from an in situ cloud aerosol spectrometer (CAS) during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers–Florida Area Cirrus Experiment (CRYSTAL-FACE) campaign conducted in Florida during July 2002. The remote sensing techniques use dual-satellite reflectances and lidar linear depolarization

  6. General equations for the motions of ice crystals and water drops in gravitational and electric fields

    NASA Technical Reports Server (NTRS)

    Nisbet, John S.

    1988-01-01

    General equations for the Reynolds number of a variety of types of ice crystals and water drops are given in terms of the Davies, Bond, and Knudsen numbers. The equations are in terms of the basic physical parameters of the system and are valid for calculating velocities in gravitational and electric fields over a very wide range of sizes and atmospheric conditions. The equations are asymptotically matched at the bottom and top of the size spectrum, useful when checking large computer codes. A numerical system for specifying the dimensional properties of ice crystals is introduced. Within the limits imposed by such variables as particle density, which have large deviations, the accuracy of velocities appears to be within 10 percent over the entire range of sizes of interest.

  7. Possible Evidence for Crystallization of Astrophysical Ice Analogs by Heavy and Energetic Cosmic Rays

    NASA Astrophysics Data System (ADS)

    Pilling, S.; Seperuelo Duarte, E.; da Silveira, E. F.; Rothard, H.; Domaracka, A.; Boduch, P.

    2011-05-01

    We present an experimental study about the alteration of the 3300 cm-1 band (?_1 vibration mode) in the infrared spectra of water-rich ices due to the bombardments with heavy, highly-charged, and energetic ions (15.7 MeV 16O5+; 46 MeV 58Ni13+). The experiments simulate the physical chemistry as well possible morphological changes induced by heavy-ion cosmic rays at water-rich astrophysical ices. The measurements were performed inside a high vacuum chamber at the heavy-ion accelerator GANIL (Grand Accelerateur National d'Ions Lourds) in Caen, France. The experiments employed pure amorphous water ice and mixed H_2O:CO_2 amorphous ices at 13 K. In-situ analysis was performed by a Fourier transform infrared spectrometer (FTIR) at different ion fluences. After the ion bombardment the center of this water band is shifted to lower frequencies (longer wavelength).We suggest this behavior may be attributed to the destruction of small water clusters (n=2,3), as well the production of larger clusters (n>5), both as a result of energy delivered by the fast ions (and its secondary electrons) along the neighborhood of the ion tracks inside the ices. The vibration of individual small water clusters are representative for the left wing of the ?_1 band in water ice while larger individual clusters are important for the right wing (lower energy). An experiment employing H_2O:CO_2 ice at 80 K, showing a small crystallization degree, does not show changes in the water ?_1 profile during the ion bombardment. The results suggest that a small degree of crystallization may be achieved in the amorphous astrophysical ices after the extensive bombardment with heavy and energetic ions. This may give us some clues about the crystalline water features observed at some cold regions in the interstellar medium such as the ices around young stellar objects, and also at some frozen surfaces of outer solar system bodies. Both regions are highly exposed to galactic cosmic rays.

  8. The mystery of low ice crystal numbers in the TTL and implications for the UTLS water vapor budget

    NASA Astrophysics Data System (ADS)

    Kraemer, M.; Spichtinger, P.

    2012-12-01

    Water vapour is the most important natural green house gas. However, in the stratosphere an increase in water vapour would possibly result in a net cooling of the earth-atmosphere system. The major entrance pathway of trace substances into the stratosphere is the tropical tropopause layer (TTL). The TTL water vapor budget, and thus the exchange between troposphere and stratosphere, depends crucially on the occurrence and properties of ice clouds in this cold region (T < 200 K). New observations indicate that very low ice crystal numbers frequently occur in the TTL. This phenomenon is not yet understood and is not compatible with the idea that homogeneous freezing of solution droplets is the major pathway of ice formation. These low ice number concentrations are consistent with observed persistent high ice supersaturations inside cold TTL cirrus clouds, which in turn control the exchange of water vapor with the stratosphere. Here, we reproduce in-situ measurements of frequencies of occurrence of ice crystal concentrations by extensive model simulations, driven by the special dynamical conditions in the TTL, namely the superposition of slow large-scale updrafts with high-frequency short waves. The simulations show that about 80% of the observed incidences of low ice crystal concentrations can be explained by 'classical' homogeneous ice nucleation in the very slow updrafts (< 1cm/s), about 19% stem from heterogeneous freezing, while the remaining of about 1% originates from homogeneous freezing in slightly faster updrafts (> 1cm/s). The mechanism limiting the ice crystal production from homogeneous freezing in an environment full of gravity waves is that freezing events are stalled -due to the shortness of the gravity waves- before a higher number concentration of ice crystals can be formed. Furthermore, the very few ice crystals cannot efficiently reduce the gas phase water vapor inside of the cirrus. As a result, high supersaturations can last for many hours thus hindering the downward transport of water by sedimenting ice crystals. Based on our new insights in both the low ice crystal numbers and subsequent persistent high supersatuartions, we propose to reasses the water transport to the stratosphere in the TTL.

  9. THE MECHANICAL PROPERTIES OF SINGLE CRYSTALS OF ICE AT LOW TEMPERATURES

    Microsoft Academic Search

    S. J. JONES; J. W. GLEN

    The mechanical properties of single crystals of ice have been investigated at various temperatures down to — 90 °C. Two methods have been used: creep tests in tension and constant strain-rate tests in compression. Results show that the activation energy for creep varies with temperature from 0.41 -_t 0.03 eV between — 50 °C and — 90 °C to 0.68

  10. The single-crystal, basal face of ice Ih investigated with sum frequency generation

    Microsoft Academic Search

    Henning Groenzin; Irene Li; Victoria Buch; Mary Jane Shultz

    2007-01-01

    Sum frequency generation spectroscopy has been used to investigate the hydrogen-bonded region of single-crystal, hexagonal ice in the temperature range of 113-178 K. The temperature and polarization dependences of the signal are used in conjunction with a recent theoretical model to suggest an interpretation of the bluest and reddest of the hydrogen-bonded peaks. The reddest feature is associated with strong

  11. The dependence of the single-scattering properties of small ice crystals on orientation average, particle shape, and wavelength

    NASA Astrophysics Data System (ADS)

    Um, J.; McFarquhar, G. M.

    2012-12-01

    Current methods of representing the bulk scattering properties of cirrus for numerical models and satellite retrieval algorithms require weighting the single-scattering properties of specific shapes and sizes of ice crystals by their observed concentrations. Thus, to determine the influence of cirrus on solar and infrared radiation, as required for climate studies, knowledge of the single-scattering properties of ice crystals is required. Except for a few large ice crystals, most ice crystals do not have preferred orientations. Thus, the corresponding single-scattering properties of ice crystals used for numerical models and remote sensing retrievals are typically calculated assuming random orientations. The Euler's angle, selected using a random number generator, has been exclusively used to determine crystals' orientation for such calculations. When more orientations are used to determine the mean scattering properties, the scattering properties are determined with higher accuracy. However, computational resources limit the number of orientations that can be used in these calculations. Past studies used several efficient orientation-averaging schemes (e.g., quasi-Monte-Carlo and optimal cubature on the sphere) for calculating light scattering properties. These studies mainly focused on small sizes and considered relatively simple shapes, such as spheres and sphere aggregates. Atmospheric ice crystals are non-spherical and their sizes are much larger than those studied previously. In this study, the minimum numbers of orientations needed to determine the single-scattering properties of four different realistically shaped atmospheric ice crystals (i.e., column, droxtal, Gaussian random sphere, and budding Bucky ball) with predefined accuracy levels are determined using the Amsterdam discrete dipole approximation (ADDA) ver. 1.0. The results of the calculations are also used to quantify how the scattering and absorption efficiency, the single-scattering albedo, asymmetry parameter, and scattering phase function depend on sphericity, a parameter that is defined as the ratio of the surface area of a sphere with the same volume of given particle to the surface area of the particle. To generate the random orientations of ice crystals, the Euler's angles are selected using a quasi-Monte-Carlo method that uses a number sequence instead of a random number generator; its efficiency is compared with that of the internal orientation average method of ADDA. Further, simulations with varying sizes of ice crystals determine the influences of ice crystal size on the minimum number of orientations required to achieve the desired accuracy of the single-scattering properties. The results are reported for three different wavelengths of incident light, non-absorbing (0.55 ?m), moderate absorbing (3.78 ?m), and strongly absorbing (11 ?m).

  12. Sea Ice

    NSDL National Science Digital Library

    In this resource, students will discover that there are notable differences between sea ice and fresh-water ice, such as density. In on segment, students learn that the first sign of freezing on the sea is an oily appearance of the water caused by the formation of needle-like crystals. The site explains the relationship between growth and the rate at which heat flows from the water and that the ice pack can alter its shape and dimension due to the movement of winds, currents, thermal expansion, and contraction of the ice. Types of ice described here include new ice, nilas, young ice, first-year ice, and old ice while the forms of ice covered include pancake ice, brash ice, ice cake, floe, and fast ice. The site also explains the meteorological and oceanographic factors that control the amount and movement of ice.

  13. Measurements of Ice Crystal Growth Rates in Air at -5C and -10C K. G. Libbrecht and H. M. Arnold

    E-print Network

    Libbrecht, Kenneth G.

    Measurements of Ice Crystal Growth Rates in Air at -5C and -10C K. G. Libbrecht and H. M. Arnold to: kgl@caltech.edu Abstract. We present experiments investigating the growth of ice crystals from understand the surface molecular dynamics that determine crystal growth rates and morphologies. [The figures

  14. Communication: Anti-icing characteristics of superhydrophobic surfaces investigated by quartz crystal microresonators

    NASA Astrophysics Data System (ADS)

    Lee, Moonchan; Yim, Changyong; Jeon, Sangmin

    2015-01-01

    We investigated the anti-icing characteristics of superhydrophobic surfaces with various morphologies by using quartz crystal microresonators. Anodic aluminum oxide (AAO) or ZnO nanorods were synthesized directly on gold-coated quartz crystal substrates and their surfaces were rendered hydrophobic via chemical modifications with octyltrichlorosilane (OTS), octadecyltrichlorosilane (ODS), or octadecanethiol (ODT). Four different hydrophobic nanostructures were prepared on the quartz crystals: ODT-modified hydrophobic plain gold (C18-Au), an OTS-modified AAO nanostructure (C8-AAO), an ODS-modified AAO nanostructure (C18-AAO), and ODT-modified ZnO nanorods (C18-ZnO). The water contact angles on the C18-Au, C8-AAO, C18-AAO, and C18-ZnO surfaces were measured to be 91.4°, 147.2°, 156.3°, and 157.8°, respectively. A sessile water droplet was placed on each quartz crystal and its freezing temperature was determined by monitoring the drastic changes in the resonance frequency and Q-factor upon freezing. The freezing temperature of a water droplet was found to decrease with decreases in the water contact radius due to the decreases in the number of active sites available for ice nucleation.

  15. Ice crystal shape effects on solar radiative properties of Arctic mixed-phase clouds—Dependence on microphysical properties

    NASA Astrophysics Data System (ADS)

    Ehrlich, André; Wendisch, Manfred; Bierwirth, Eike; Herber, Andreas; Schwarzenböck, Alfons

    Based on 1-year cloud measurements with radar and microwave radiometer broadband solar radiative transfer simulations were performed to quantify the impact of different ice crystal shapes of Arctic mixed-phase clouds on their radiative properties (reflectance, transmittance and absorptance). The ice crystal shape effects were investigated as a function of microphysical cloud properties (ice volume fraction fi, ice and liquid water content IWC and LWC, mean particle diameter DmI and DmW of ice/water particle number size distributions, NSDs). The required NSDs were statistically derived from radar data. The NSD was composed of a liquid and a solid mode defined by LWC, DmW (water mode) and IWC, DmI (ice mode). It was found that the ratio of DmI and DmW determines the magnitude of the shape effect. For mixed-phase clouds with DmI ? 27 ?m a significant shape effect was obtained. The shape effect was almost insensitive with regard to the solar zenith angle, but highly sensitive to the ice volume fraction of the mixed-phase cloud. For mixed-phase clouds containing small ice crystals ( DmI ? 27 ?m) and high ice volume fractions ( fi > 0.5) crystal shape is crucial. The largest shape effects were observed assuming aggregates and columns. If the IWC was conserved the shape effect reaches values up to 0.23 in cloud reflectance and transmittance. If the ice mode NSD was kept constant only a small shape effect was quantified (? 0.04).

  16. Ice

    NSDL National Science Digital Library

    Harris, Kathryn Louise.

    When a chunk of ice "twice the size of Manhattan" broke away from the northernmost part of the Antarctic Peninsula in February, ice was at the forefront of scientific news. Now, with the spectacular discovery of bacteria in Antarctic ice and with new evidence of slush beneath the frozen surface of Jupiter's moon Europa, water in its frozen form is once again in the news. The discovery of living organisms in the Antarctic ecosystem, described in the June 26, 1998 issue of Science, is significant because it presents a model for "how life may have arisen and persisted on other worlds." Scientists speculate that if organisms can thrive in the hard ice of Antarctica, they may possibly have done so on Europa and Mars. Galileo's closest approach to Europa occurred on July 21, 1998, offering new images of ice in space. The nine sites listed offer insights and details of the recent findings and discoveries related to ice.

  17. blowing snow as a source of ice crystals in supercooled orographic clouds

    NASA Astrophysics Data System (ADS)

    Geerts, Bart; Pokharel, Binod; Chu, Xia

    2015-04-01

    Winter storms are often accompanied by strong winds, especially over complex terrain. Under such conditions freshly fallen snow readily can be suspended. Most of that snow will be redistributed across the landscape (e.g. behind obstacles), but some may be lofted into the turbulent boundary layer, and even in the free atmosphere in areas of boundary layer separation near terrain crests, or in hydraulic jumps. These ice crystals, presumably mostly small, fractured particles, may enhance snow growth in clouds. This may explain why shallow orographic clouds, with cloud top temperatures too high for significant ice initiation, can produce (light) snowfall with remarkable persistence. Airborne radar and lidar data are presented to demonstrate the presence of blowing snow, boundary layer separation, and the glaciation of a shallow supercooled orographic cloud. Further evidence for the presence of blowing snow comes from a comparison between flight level (~700 m AGL) and ground-level snow size distributions. We will also present a parameterization for the aerial injection of ice crystals from the surface, as implemented in WRF.

  18. Polarization lidar observations of backscatter phase matrices from oriented ice crystals and rain.

    PubMed

    Hayman, Matthew; Spuler, Scott; Morley, Bruce

    2014-07-14

    Oriented particles can exhibit different polarization properties than randomly oriented particles. These properties cannot be resolved by conventional polarization lidar systems and are capable of corrupting the interpretation of depolarization ratio measurements. Additionally, the typical characteristics of backscatter phase matrices from atmospheric oriented particles are not well established. The National Center for Atmospheric Research High Spectral Resolution Lidar was outfitted in spring of 2012 to measure the backscatter phase matrix, allowing it to fully characterize the polarization properties of oriented particles. The lidar data analyzed here considers operation at 4°, 22° and 32° off zenith in Boulder, CO, USA (40.0°N,105.2°W). The HSRL has primarily observed oriented ice crystal signatures at lidar tilt angles near 32° off zenith which corresponds to an expected peak in backscatter from horizontally oriented plates. The maximum occurrence frequency of oriented ice crystals is measured at 5 km, where 2% of clouds produced significant oriented ice signatures by exhibiting diattenuation in their scattering matrices. The HSRL also observed oriented particle characteristics of rain at all three tilt angles. Oriented signatures in rain are common at all three tilt angles. As many as 70% of all rain observations made at 22° off zenith exhibited oriented signatures. The oriented rain signatures exhibit significant linear diattenuation and retardance. PMID:25090513

  19. Hydration of the lower stratosphere by ice crystal geysers over land convective systems

    NASA Astrophysics Data System (ADS)

    Khaykin, S.; Pommereau, J.-P.; Korshunov, L.; Yushkov, V.; Nielsen, J.; Larsen, N.; Christensen, T.; Garnier, A.; Lukyanov, A.; Williams, E.

    2008-08-01

    The possible impact of deep convective overshooting over land has been explored by six simultaneous soundings of water vapour, particles and ozone in the lower stratosphere next to MesoScale Convective Systems (MCSs) during the monsoon season over West Africa in Niamey, Niger in August 2006. The water vapour measurements were carried out using a fast response FLASH-B Lyman-alpha hygrometer. The high vertical resolution observations of this instrument show the presence of enhanced water vapour layers between the tropopause at 370 K and the 450 K level. Most of these moist layers are shown connected with overshooting events occurring upwind as identified from satellite IR images, over which the air mass probed by the sondes passed during the three previous days. In the case of a local overshoot identified by echo top turrets up to 18.5 km by the MIT C-band radar also in Niamey, tight coincidence was found between enhanced water vapour, ice crystal and ozone dip layers indicative of fast uplift of tropospheric air across the tropopause. The water vapour mixing ratio in the enriched layers, up to 8 ppmv higher than that of saturation at the tropopause, and the coincidence with the presence of ice crystals strongly suggest hydration of the lower stratosphere by geyser-like injection of ice particles over overshooting turrets. The pile-like structure of the water vapour seen by the high-resolution hygrometer in contrast to smooth profiles reported by a coarse vertical-resolution satellite observation, suggests that the hydration mechanism described above may be responsible for the known summer seasonal increase of moisture in the lower stratosphere. If this interpretation is correct, hydration by ice geysers across the tropopause may be an important contributor to the stratospheric water vapour budget.

  20. Hydration of the lower stratosphere by ice crystal geysers over land convective systems

    NASA Astrophysics Data System (ADS)

    Khaykin, S.; Pommereau, J.-P.; Korshunov, L.; Yushkov, V.; Nielsen, J.; Larsen, N.; Christensen, T.; Garnier, A.; Lukyanov, A.; Williams, E.

    2009-03-01

    The possible impact of deep convective overshooting over land has been explored by six simultaneous soundings of water vapour, particles and ozone in the lower stratosphere next to Mesoscale Convective Systems (MCSs) during the monsoon season over West Africa in Niamey, Niger in August 2006. The water vapour measurements were carried out using a fast response FLASH-B Lyman-alpha hygrometer. The high vertical resolution observations of the instrument show the presence of accumulation of enhanced water vapour layers between the tropopause at 370 K and the 420 K level. Most of these moist layers are shown connected with overshooting events occurring upwind as identified from satellite IR images over which the air mass probed by the sondes passed during the three previous days. In the case of a local overshoot identified by echo top turrets above the tropopause by the MIT C-band radar also in Niamey, tight coincidence was found between enhanced water vapour, ice crystal and ozone dip layers indicative of fast uplift of tropospheric air across the tropopause. The water vapour mixing ratio in the enriched layers exceeds frequently by 1-3 ppmv the average 6 ppmv saturation ratio at the tropopause and by up to 7 ppmv in the extreme case of local storm in coincidence with the presence of ice crystals. The presence of such layers strongly suggests hydration of the lower stratosphere by geyser-like injection of ice particles over overshooting turrets. The pile-like increase of water vapour up to 19 km seen by the high-resolution hygrometer during the season of maximum temperature of the tropopause, suggests that the above hydration mechanism may contribute to the summer maximum moisture in the lower stratosphere. If this interpretation is correct, hydration by ice geysers across the tropopause might be an important contributor to the stratospheric water vapour budget.

  1. Quasi-spherical approach for seismic wave modeling in a 2-D slice of a global Earth model with lateral heterogeneity

    NASA Astrophysics Data System (ADS)

    Toyokuni, Genti; Takenaka, Hiroshi; Wang, Yanbin; Kennett, Brian L. N.

    2005-05-01

    For iterative calculations of synthetic seismograms with limited computer resources, a fast and accurate modeling method is needed. Axisymmetric modeling has often been used in global seismology to restrict computational time and storage. This approach can correctly model 3-D geometrical spreading effects with computational times comparable to 2-D methods, but cannot treat asymmetric structures about the source axis. To overcome this problem, a new approach is proposed for seismic wave propagation in a 2-D slice through a global Earth model with lateral heterogeneity. The elastodynamic equation for spherical coordinates is not solved in the conventional spherical domain but instead in the ``quasi-spherical domain'' using the finite-difference method. The validity and efficiency of this technique is illustrated with numerical examples including subduction zone structures.

  2. Electromagnetic scattering and absorption by thin walled dielectric cylinders with application to ice crystals

    NASA Technical Reports Server (NTRS)

    Senior, T. B. A.; Weil, H.

    1977-01-01

    Important in the atmospheric heat balance are the reflection, transmission, and absorption of visible and infrared radiation by clouds and polluted atmospheres. Integral equations are derived to evaluate the scattering and absorption of electromagnetic radiation from thin cylindrical dielectric shells of arbitrary cross section when irradiated by a plane wave of any polarization incident in a plane perpendicular to the generators. Application of the method to infinitely long hexagonal cylinders has yielded numerical scattering and absorption data which simulate columnar sheath ice crystals. It is found that the numerical procedures are economical for cylinders having perimeters less than approximately fifteen free-space wavelengths.

  3. A discussion of mechanisms proposed to explain habit changes of vapor-grown ice crystals

    NASA Astrophysics Data System (ADS)

    Levi, Laura; Nasello, Olga B.

    In the present work, surface kinetics processes that can contribute to the growth behavior of ice crystals from the vapor phase are revised and proposed interpretations of crystal habit changes are discussed. Following the main initial papers on this subject by Hallet, Mason et al. and Kobayashi, relationships are considered between linear growth rate and step velocity. More recent results obtained by Sei and Gonda (SG2) for molecular steps naturally formed on basal and prism surfaces are shown to confirm Hallet's interpretation of previous curves obtained for the velocity of giant steps that were artificially formed on basal surfaces only. The different behavior of the condensation coefficient ?( T) characterizing growth in pure water vapor, observed by Lamb and Scott for surfaces intersecting a substrate and by Sei and Gonda for free surfaces, is discussed by considering that ? is the product of the adsorption and accommodation coefficients ? and ?, respectively. It is noted that, as in previous works, ?=1 was assumed, the variations of ? discussed to interpret crystal habit changes were made to coincide with variations of ?. However, Sei and Gonda's results show that in the temperature range where crystal habit changes are observed, values of ?( T)?1 are found. As these depend on surface orientation, they should play an important role in the phenomenon. The dependence of crystal habits on two-dimensional nucleation is also discussed on the basis of measurements carried out by Nelson and Knight of the critical supersaturation ?cr on the basal and prism surfaces. A possible relationship between the curves for ?cr( T) and those of ?( T) derived from Sei and Gonda's results is suggested. The mechanisms determining the large anisotropy exhibited by crystals grown in atmospheric conditions are discussed by taking into account that the growth rate curves R( T) on the basal and prism surfaces show a correlation between maximum and minimum values, which are not observed for crystals grown in pure vapor.

  4. Radiative properties of visible and subvisible Cirrus: Scattering on hexagonal ice crystals

    NASA Technical Reports Server (NTRS)

    Flatau, Piotr J.; Stephens, Graeme L.; Draine, Bruce T.

    1990-01-01

    One of the main objectives of the First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE) is to provide a better understanding of the physics of upper level clouds. The focus is on just one specific aspect of cirrus physics, namely on characterizing the radiative properties of single, nonspherical ice particles. The basis for further more extensive studies of the radiative transfer through upper level clouds is provided. Radiation provides a potential mechanism for strong feedback between the divergence of in-cloud radiative flux and the cloud microphysics and ultimately on the dynamics of the cloud. Some aspects of ice cloud microphysics that are relevant to the radiation calculations are described. Next, the Discrete Dipole Approximation (DDA) is introduced and some new results of scattering by irregular crystals are presented. The Anomalous Diffraction Theory (ADT) was adopted to investigate the scattering properties of even larger crystals. In this way the scattering properties of nonspherical particles were determined over a range of particle sizes.

  5. Comparison in Schemes for Simulating Depositional Growth of Ice Crystal between Theoretical and Laboratory Data

    NASA Astrophysics Data System (ADS)

    Zhai, Guoqing; Li, Xiaofan

    2015-04-01

    The Bergeron-Findeisen process has been simulated using the parameterization scheme for the depositional growth of ice crystal with the temperature-dependent theoretically predicted parameters in the past decades. Recently, Westbrook and Heymsfield (2011) calculated these parameters using the laboratory data from Takahashi and Fukuta (1988) and Takahashi et al. (1991) and found significant differences between the two parameter sets. There are two schemes that parameterize the depositional growth of ice crystal: Hsie et al. (1980), Krueger et al. (1995) and Zeng et al. (2008). In this study, we conducted three pairs of sensitivity experiments using three parameterization schemes and the two parameter sets. The pre-summer torrential rainfall event is chosen as the simulated rainfall case in this study. The analysis of root-mean-squared difference and correlation coefficient between the simulation and observation of surface rain rate shows that the experiment with the Krueger scheme and the Takahashi laboratory-derived parameters produces the best rain-rate simulation. The mean simulated rain rates are higher than the mean observational rain rate. The calculations of 5-day and model domain mean rain rates reveal that the three schemes with Takahashi laboratory-derived parameters tend to reduce the mean rain rate. The Krueger scheme together with the Takahashi laboratory-derived parameters generate the closest mean rain rate to the mean observational rain rate. The decrease in the mean rain rate caused by the Takahashi laboratory-derived parameters in the experiment with the Krueger scheme is associated with the reductions in the mean net condensation and the mean hydrometeor loss. These reductions correspond to the suppressed mean infrared radiative cooling due to the enhanced cloud ice and snow in the upper troposphere.

  6. A 4-D dataset for validation of crystal growth in a complex three-phase material, ice cream

    NASA Astrophysics Data System (ADS)

    Rockett, P.; Karagadde, S.; Guo, E.; Bent, J.; Hazekamp, J.; Kingsley, M.; Vila-Comamala, J.; Lee, P. D.

    2015-06-01

    Four dimensional (4D, or 3D plus time) X-ray tomographic imaging of phase changes in materials is quickly becoming an accepted tool for quantifying the development of microstructures to both inform and validate models. However, most of the systems studied have been relatively simple binary compositions with only two phases. In this study we present a quantitative dataset of the phase evolution in a complex three-phase material, ice cream. The microstructure of ice cream is an important parameter in terms of sensorial perception, and therefore quantification and modelling of the evolution of the microstructure with time and temperature is key to understanding its fabrication and storage. The microstructure consists of three phases, air cells, ice crystals, and unfrozen matrix. We perform in situ synchrotron X-ray imaging of ice cream samples using in-line phase contrast tomography, housed within a purpose built cold-stage (-40 to +20oC) with finely controlled variation in specimen temperature. The size and distribution of ice crystals and air cells during programmed temperature cycling are determined using 3D quantification. The microstructural evolution of three-phase materials has many other important applications ranging from biological to structural and functional material, hence this dataset can act as a validation case for numerical investigations on faceted and non-faceted crystal growth in a range of materials.

  7. Crystal growth investigations of ice?water interfaces from molecular dynamics simulations: Profile functions and average properties.

    PubMed

    Razul, M S Gulam; Kusalik, P G

    2011-01-01

    Attempts to simulate crystal growth of ice from liquid water and to provide a consistent microscopic description of this process have been challenging tasks. In this paper we have adapted our previously developed molecular dynamics simulation methodology to enable the investigation of steady-state directional crystal growth?melting of ice. Specifically, we examine ice?water systems of the (001), (110), and (111) faces of ice Ic and the (0001), (1010), and (1120) faces of ice Ih, where the TIP4P, TIP4P-Ew, and SPC?E water models have been utilized. The influence of different growth?melting conditions (temperature gradients and growth velocities) is investigated. Profile functions of properties of interest across the interface are obtained from nonequilibrium steady-state simulations and provide consistent descriptions of ice?water interfaces. The widths of the various crystallographic faces are found to increase in the apparent order Ic111, Ih0001 < Ih1010 < Ih1120 < Ic001 < Ic110. The observed growth rates were in agreement with experimental values and the possible dependence on the various faces is explored. The melting temperatures obtained with the present methodology for the different models are in good agreement with estimates from other work. PMID:21219023

  8. Detection of ice crystal particles preferably oriented in the atmosphere by use of the specular component of scattered light.

    PubMed

    Borovoi, Anatoli; Galileiskii, Victor; Morozov, Alexander; Cohen, Ariel

    2008-05-26

    A new method to retrieve sizes and flutter of ice crystals in the atmosphere when they reveal their preferably horizontal orientation is proposed and realized. The method consists of the measurement of angular width for the specular component of scattered light in the bistatic sounding scheme. The technique is realized with a floodlight beam and a CCD camera as a detector. PMID:18545469

  9. Finite-difference time domain method for light scattering by small ice crystals in three-dimensional space

    Microsoft Academic Search

    Ping Yang; K. N. Liou

    1996-01-01

    The finite-difference time domain (FDTD) method for the solution of light scattering by nonspherical particles has been developed for small ice crystals of hexagonal shapes including solid and hollow columns, plates, and bullet rosettes commonly occurring in cirrus clouds. To account for absorption, we have introduced the effec- tive permittivity and conductivity to circumvent the required complex calculations in the

  10. Effects of size on the dynamics of dislocations in ice single crystals.

    PubMed

    Taupin, V; Varadhan, S; Chevy, J; Fressengeas, C; Beaudoin, A J; Montagnat, M; Duval, P

    2007-10-12

    Single crystals of ice subjected to primary creep in torsion exhibit a softening behavior: the plastic strain rate increases with time. In a cylindrical sample, the size of the radius affects this response. The smaller the radius of the sample becomes while keeping constant the average shear stress across a section, the softer the response. The size-dependent behavior is interpreted by using a field dislocation theory, in terms of the coupled dynamics of excess screw dislocations gliding in basal planes and statistical dislocations developed through cross slip occurring in prismatic planes. The differences in the results caused by sample height effects and variations in the initial dislocation microstructure are discussed. PMID:17995184

  11. Convective Troposphere-Stratosphere Transport in the Tropics and Hydration by ice Crystals Geysers

    NASA Astrophysics Data System (ADS)

    Pommereau, J.

    2008-12-01

    Twenty-five years ago the suggestion was made by Danielsen of direct fast convective penetration of tropospheric air in the stratosphere over land convective systems. Although the existence of the mechanism is accepted, it was thought to be rare and thus its contribution to Troposphere-Stratosphere Transport (TST) of chemical species and water vapour at global scale unimportant at global scale. In contrast to this assumption, observations of temperature, water vapour, ice particles, long-lived tropospheric species during HIBISCUS, TROCCINOX and SCOUT-O3 over Brazil, Australia and Africa and more recently CALIPSO aerosols observations suggest that it is a general feature of tropical land convective regions in the summer. Particularly relevant to stratospheric water vapour is the observation of geyser like ice crystals in the TTL over overshooting events which may result in the moistening of the stratosphere. Although such events successfully captured by small scale Cloud-Resolving Models may have a significant impact on stratospheric ozone chemistry and climate, they are currently totally ignored by NWPs, CTMs and CCMs. Several recent balloon and aircraft observations of overshoots and CRM simulations will be shown illustrating the mechanism, as well as observations from a variety of satellites suggesting a significant impact at global scale.

  12. Estimation of Cirrus Cloud Effective Ice Crystal Shapes using Visible Reflectances from Dual-Satellite Measurements

    NASA Technical Reports Server (NTRS)

    Chepfer, Helene; Minnis, Patrick; Young, David; Nguyen, Louis; Arduini, Robert F.

    2002-01-01

    This study develops and examines a multiangle, multisatellite method for determining effective cloud particle shapes from reflectances observed at visible wavelengths. The technique exploits the significant differences in the various cloud particle shape phase functions near the backscatter direction to infer particle shape from a combination of views from a near-backscatter angle and a side scattering angle. Adding-doubling calculations confirm that the optimal viewing combinations include one near-backscatter angle and another between 60" and 150". Sensitivity to shape increases with solar zenith angle. A total of 28 collocated, visible images from pairs of currently operating meteorological satellites with the desired viewing combinations were analyzed for particle shape. Matching reflectances from images with optimal viewing angles clearly separates water droplet from ice crystal clouds. Reflectance pairs from matched pixels containing ice crystals can be explained by the range of selected microphysical models. The most common retrieved shapes correspond to combinations of hexagonal compacts (aspect ratio of unity), hexagonal columns, and bullet rosettes. Although no single microphysical model can account for the observed variability, taken together, the models used for retrieving cloud particle size by the Clouds and the Earth's Radiant Energy System and the Moderate Resolution Imaging Spectroradiometer Projects can account for most of the reflectance variability observed in this limited data set. Additional studies are needed to assess the uncertainties in retrieved shapes due to temporal and spatial mismatches, anisotropic and bright background reflectances, and calibration errors and to validate the retrieved shapes. While applicable to a limited number of dual-satellite viewing combinations for current research and operational meteorological satellites, this approach could be used most extensively to derive effective particle size, shape, and optical depth from a combination of an imaging satellite in an L1 orbit, like Triana, and any other lower Earth orbiting Satellites.

  13. Isothermal ice crystallization kinetics in the gas-diffusion layer of a proton-exchange-membrane fuel cell.

    PubMed

    Dursch, T J; Ciontea, M A; Radke, C J; Weber, A Z

    2012-01-17

    Nucleation and growth of ice in the fibrous gas-diffusion layer (GDL) of a proton-exchange membrane fuel cell (PEMFC) are investigated using isothermal differential scanning calorimetry (DSC). Isothermal crystallization rates and pseudo-steady-state nucleation rates are obtained as a function of subcooling from heat-flow and induction-time measurements. Kinetics of ice nucleation and growth are studied at two polytetrafluoroethylene (PTFE) loadings (0 and 10 wt %) in a commercial GDL for temperatures between 240 and 273 K. A nonlinear ice-crystallization rate expression is developed using Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory, in which the heat-transfer-limited growth rate is determined from the moving-boundary Stefan problem. Induction times follow a Poisson distribution and increase upon addition of PTFE, indicating that nucleation occurs more slowly on a hydrophobic fiber than on a hydrophilic fiber. The determined nucleation rates and induction times follow expected trends from classical nucleation theory. A validated rate expression is now available for predicting ice-crystallization kinetics in GDLs. PMID:22133053

  14. Dependence on accelerating voltage of crystal structural changes in water ice thin film under electron beam irradiation

    NASA Astrophysics Data System (ADS)

    Kobayashi, Keita; Yasuda, Hidehiro

    2013-02-01

    The dependence on accelerating voltage of crystal structural changes in water ice thin film under electron beam irradiation was investigated by cryogenic transmission electron microscopy (cryo-TEM) at 95 K and accelerating voltages of 25, 50, 75, 100, or 125 kV. Ice thin film was prepared by depositing residual moisture in the TEM column onto both sides of a carbon membrane at 95 K. The major phase of the deposited film at 95 K was identified as ice Ic by transmission electron diffractometry. We found that the mass loss rate of the ice thin film decreased sharply as the accelerating voltage was increased. From this result, we conclude the mass loss mechanism was the ionization of water by inelastic scattering of incident electrons. Moreover, the phase transition from ice Ic to ice Ih was observed at accelerating voltages of 75 kV or greater. At 50 kV or lower, however, the phase transition was hardly observed by TEM. Because the phase transition can also be attributed to inelastic scattering of incident electrons, the results suggest that whether mass loss or a phase transition occurs depends primarily on the accelerating voltage.

  15. Simulation of the Extinction Efficiency, the Absorption Efficiency and the Asymmetry Factor of Ice Crystals and Relevant Applications to the Study of Cirrus Cloud Radiative Properties

    E-print Network

    Lu, Kai

    2010-10-12

    can generate reasonably accurate single-scattering properties of ice crystals, and can result in reasonable upward IR and solar fluxes at top of atmosphere (TOA), downward IR fluxes at the surface, and net heating rates....

  16. Formation of ridges on Europa above crystallizing water bodies inside the ice shell

    NASA Astrophysics Data System (ADS)

    Johnston, Stephanie A.; Montési, Laurent G. J.

    2014-07-01

    Jupiter’s second Galilean satellite, Europa, is a Moon-sized body with an icy shell and global ocean approximately 100 km thick surrounding a rocky interior. Its surface displays extensive tectonic activity in a geologically recent past. Europa’s most ubiquitous surface features, double ridges, have a central trough flanked by two raised edifices. Double ridges can extend hundreds of kilometers and appear genetically related to cracks formed in the Europan ice shell. The origin of the raised flanks has been the center of much debate and many models have been proposed. There are also ridges without a central trough, single ridges. These ridges are far less common than their double ridge counterparts. However, there are locations where along-strike changes in ridge type appear to occur. We explore an elastic model in which the ridges form in response to crystallization of a liquid water intrusion. In our model, liquid water fills tension cracks that open in the Europan crust in response to tidal stress or perhaps overpressure of a subsurface ocean. The crack would be long and essentially continuous, similar to dikes on Earth, explaining the remarkable continuity and lack of segmentation of Europan ridges. The freezing of the water would cause a volume expansion, compressing and buckling the adjacent crust. We find that the geometry of the intruding water body controls the shape of the resulting ridges, with single ridges forming above sill-like intrusions and double ridges above dike-like intrusions. In order to match the ridge heights observed for double ridges we would need approximately 1.5 km2 of water intruded at a shallow depth in the ice shell, potentially over the course of multiple events. Deeper intrusions result in a broader, lower amplitude ridge than shallow intrusions.

  17. 162 J. Opt. Soc. Am. A/Vol. 12, No. 1/January 1995 P. Yang and K. N. Liou Light scattering by hexagonal ice crystals

    E-print Network

    Liou, K. N.

    162 J. Opt. Soc. Am. A/Vol. 12, No. 1/January 1995 P. Yang and K. N. Liou Light scattering geometric ray-tracing model for the calculation of light scattering by hexagonal ice crystals. In the FDTD surface cannot be imposed. For this rea- son research on light scattering by hexagonal ice crys- tals

  18. Tightly integrated single- and multi-crystal data collection strategy calculation and parallelized data processing in JBluIce beamline control system

    PubMed Central

    Pothineni, Sudhir Babu; Venugopalan, Nagarajan; Ogata, Craig M.; Hilgart, Mark C.; Stepanov, Sergey; Sanishvili, Ruslan; Becker, Michael; Winter, Graeme; Sauter, Nicholas K.; Smith, Janet L.; Fischetti, Robert F.

    2014-01-01

    The calculation of single- and multi-crystal data collection strategies and a data processing pipeline have been tightly integrated into the macromolecular crystallographic data acquisition and beamline control software JBluIce. Both tasks employ wrapper scripts around existing crystallographic software. JBluIce executes scripts through a distributed resource management system to make efficient use of all available computing resources through parallel processing. The JBluIce single-crystal data collection strategy feature uses a choice of strategy programs to help users rank sample crystals and collect data. The strategy results can be conveniently exported to a data collection run. The JBluIce multi-crystal strategy feature calculates a collection strategy to optimize coverage of reciprocal space in cases where incomplete data are available from previous samples. The JBluIce data processing runs simultaneously with data collection using a choice of data reduction wrappers for integration and scaling of newly collected data, with an option for merging with pre-existing data. Data are processed separately if collected from multiple sites on a crystal or from multiple crystals, then scaled and merged. Results from all strategy and processing calculations are displayed in relevant tabs of JBluIce. PMID:25484844

  19. Tightly integrated single- and multi-crystal data collection strategy calculation and parallelized data processing in JBluIce beamline control system.

    PubMed

    Pothineni, Sudhir Babu; Venugopalan, Nagarajan; Ogata, Craig M; Hilgart, Mark C; Stepanov, Sergey; Sanishvili, Ruslan; Becker, Michael; Winter, Graeme; Sauter, Nicholas K; Smith, Janet L; Fischetti, Robert F

    2014-12-01

    The calculation of single- and multi-crystal data collection strategies and a data processing pipeline have been tightly integrated into the macromolecular crystallographic data acquisition and beamline control software JBluIce. Both tasks employ wrapper scripts around existing crystallographic software. JBluIce executes scripts through a distributed resource management system to make efficient use of all available computing resources through parallel processing. The JBluIce single-crystal data collection strategy feature uses a choice of strategy programs to help users rank sample crystals and collect data. The strategy results can be conveniently exported to a data collection run. The JBluIce multi-crystal strategy feature calculates a collection strategy to optimize coverage of reciprocal space in cases where incomplete data are available from previous samples. The JBluIce data processing runs simultaneously with data collection using a choice of data reduction wrappers for integration and scaling of newly collected data, with an option for merging with pre-existing data. Data are processed separately if collected from multiple sites on a crystal or from multiple crystals, then scaled and merged. Results from all strategy and processing calculations are displayed in relevant tabs of JBluIce. PMID:25484844

  20. The effect of ice crystal surface roughness on the retrieval of ice cloud microphysical and optical properties 

    E-print Network

    Xie, Yu

    2007-09-17

    on the retrieval of ice cloud effective particle size, optical thickness and cloud-top temperature. Three particle surface conditions, smooth, moderately rough and deeply rough, are considered in the visible and near-infrared channels (0.65 and 3.75 Ã...

  1. Crystal Field Disorder in the Quantum Spin Ice Ground State of Tb2Sn2 xTixO7

    SciTech Connect

    Gaulin, Bruce D. [McMaster University; Zhang, J. [McMaster University; Dahlberg, M. L. [Pennsylvania State University; Matthews, Maria J. [Pennsylvania State University; Bert, F. [Universite Paris Sud, Orsay, France; Kermarrec, E. [Universite Paris Sud, Orsay, France; Fritsch, Katharina [McMaster University; Granroth, Garrett E [ORNL; Jiramongkolchai, P. [Princeton University; Amato, A. [Paul Scherrer Institut, Villigen, Switzerland; Baines, C. [Paul Scherrer Institut, Villigen, Switzerland; Cava, R. J. [Princeton University; Mendels, P. [Universite Paris Sud, Orsay, France; Schiffer, P [Pennsylvania State University

    2015-01-01

    Spin ice physics marries that of hydrogen disorder in water ice, first discussed almost 60 years ago by Pauling, and that of low temperature magnetism on certain networks of connected tetrahedra. Recently the classical spin ice mag- nets Ho2Ti2O7 and Dy2Ti2O7 have shown an emergent artificial magneto- statics , which manifests itself as Coulombic spin correlations and excitations behaving as diffusive magnetic monopoles. The related pyrochlore magnet, Tb2Ti2O7, has been proposed as a quantum variant of spin ice, stabilized by 1 virtual excitations between the crystal field (CF) ground state doublet appro- priate to Tb3+, and its low lying excited state doublet. Isostructural Tb2Sn2O7 displays soft spin ice order, and its Tb3+ ground and excited CF eigenstates are known to differ relative to those of Tb2Ti2O7. We present a comprehensive study of Tb2Sn2 xTixO7 showing a novel, dynamic spin liquid state for all x other than the end members (0, 2). This state is the result of disorder in the low lying Tb3+ CF environments which de-stabilizes the mechanism by which quantum fluctuations contribute to ground state selection in Tb2Sn2 xTixO7.

  2. Dynamics of Arctic Mixed Phase Clouds: A focus on the effects of ice crystal habits and nucleation

    NASA Astrophysics Data System (ADS)

    Komurcu, M.; Harrington, J. Y.

    2010-12-01

    The Arctic is warming significantly; this warming is greater than any other region on Earth. To understand the future atmospheric state of the Arctic, climate models are typically run through different climate scenarios. The common conclusion of all climate model simulations is that a warming in Arctic will occur. The degree of warming for the same scenarios, however, is inconsistent among the climate models. Clouds are ubiquitous over the Arctic and they strongly affect the surface radiative and energy budget. This result makes clouds a key component of the Arctic climate. Recent studies using regional climate models show that models are not capable of reproducing the supercooled liquid observed in clouds during the cold season. Large discrepancies exist in the partitioning of phase between ice and liquid water among different models. It is currently thought that these discrepancies are due to the way ice crystal habits are parameterized and the way ice is nucleated in models. However, the evolution of ice within clouds, and ice nucleation, depend critically on the dynamics that drive cloud scale motions. We will present results that attempt to separate the influences of microphysics and dynamics, with a view to understanding how dynamic processes affect the production and maintenance of supercooled liquid within Arctic cloud systems.

  3. Midlatitude Cirrus Clouds Derived from Hurricane Nora: A Case Study with Implications for Ice Crystal Nucleation and Shape.

    NASA Astrophysics Data System (ADS)

    Sassen, Kenneth; Arnott, W. Patrick; O'C. Starr, David; Mace, Gerald G.; Wang, Zhien; Poellot, Michael R.

    2003-04-01

    Hurricane Nora traveled up the Baja Peninsula coast in the unusually warm El Niño waters of September 1997 until rapidly decaying as it approached southern California on 24 September. The anvil cirrus blowoff from the final surge of tropical convection became embedded in subtropical flow that advected the cirrus across the western United States, where it was studied from the Facility for Atmospheric Remote Sensing (FARS) in Salt Lake City, Utah, on 25 September. A day later, the cirrus shield remnants were redirected southward by midlatitude circulations into the southern Great Plains, providing a case study opportunity for the research aircraft and ground-based remote sensors assembled at the Clouds and Radiation Testbed (CART) site in northern Oklahoma. Using these comprehensive resources and new remote sensing cloud retrieval algorithms, the microphysical and radiative cloud properties of this unusual cirrus event are uniquely characterized.Importantly, at both the FARS and CART sites the cirrus generated spectacular halos and arcs, which acted as a tracer for the hurricane cirrus, despite the limited lifetimes of individual ice crystals. Lidar depolarization data indicate widespread regions of uniform ice plate orientations, and in situ particle replicator data show a preponderance of pristine, solid hexagonal plates and columns. It is suggested that these unusual aspects are the result of the mode of cirrus particle nucleation, presumably involving the lofting of sea salt nuclei in strong thunderstorm updrafts into the upper troposphere. This created a reservoir of haze particles that continued to produce halide-salt-contaminated ice crystals during the extended period of cirrus cloud maintenance. The inference that marine microbiota are embedded in the replicas of some ice crystals collected over the CART site points to the longevity of marine effects. Various nucleation scenarios proposed for cirrus clouds based on this and other studies, and the implications for understanding cirrus radiative properties on a global scale, are discussed.

  4. Numerical simulation of the flow fields around falling ice crystals with inclined orientation and the hydrodynamic torque

    NASA Astrophysics Data System (ADS)

    Hashino, Tempei; Chiruta, Mihai; Polzin, Dierk; Kubicek, Alexander; Wang, Pao K.

    2014-12-01

    The flow field and orientation of ice particles are fundamental information to understand cloud microphysical processes, optical phenomena, and electric-field induced orientation and to improve remote sensing of ice clouds. The purpose of this study is to investigate the flow fields and hydrodynamic torques of falling ice columns and hexagonal plates with their largest dimension inclined with respect to the airflow. The Reynolds numbers range from 2 to 70 for columns and 2 to 120 for plates. The flow fields are obtained by numerically solving the relevant Navier-Stokes equations under the assumption of air incompressibility. It was found that for the intermediate Reynolds number the streamlines around the inclined crystals exhibit less spiral rotation behind them than those around the stable posture. The vorticity magnitude was larger in the upstream side and broader in the downstream than the one without inclination. For plates, a high-pressure dome on the center of the lower basal face disappears with inclination, possibly leading to an increase of riming there. The torques acting on the crystals have a local maximum over the inclined angle and exhibit almost symmetric around 45° over the range of Reynolds numbers. The torque parameterization was performed under pressures of 300, 500, and 800 hPa as a function of Reynolds number and aspect ratio. It was found that the time scale of rotation for plates is smaller than the one for columns. Furthermore, the torque formula was applied to assess alignment of crystals along electric fields. It was found that these crystals of millimeter size require 120 kV/m for the electrical alignment, which agrees with previous studies.

  5. Catalytic crystallization of ices by small silicate smokes at temperatures less than 20K

    NASA Astrophysics Data System (ADS)

    Moore, M.; Ferrante, R.; Hudson, R.; Tanabe, T.; Nuth, J.

    1993-03-01

    Samples of methanol and water ices condensed from the vapor onto aluminum substrates at low temperatures (below approximately 80 K) form amorphous ices; annealing at temperatures in excess of 140-155 K is usually required to convert such amorphous samples to crystalline ices. However, we have found that when either methanol or water vapor is deposited on to aluminum substrates that have been coated with a thin (0.1-0.5 mm) layer of amorphous silicate smoke, the ices condense in crystalline form. We believe that crystalline ice forms as the result of energy liberated at the ice/silicate interface perhaps due to weak bonding of the ice at defect sites on the grains and the very high surface to volume ratio and defect density of these smokes. Annealing of amorphous water ice mixed with more volatile components such as methane, carbon monoxide, etc., has been suggested as an efficient way to produce clatherates in the outer solar nebula and thus explain the volatile content of comets and icy satellites of the outer planets. This hypothesis may need to be re-examined if amorphous ice does not form on cold silicate grains.

  6. Catalytic crystallization of ices by small silicate smokes at temperatures less than 20K

    NASA Technical Reports Server (NTRS)

    Moore, M.; Ferrante, R.; Hudson, R.; Tanabe, T.; Nuth, J.

    1993-01-01

    Samples of methanol and water ices condensed from the vapor onto aluminum substrates at low temperatures (below approximately 80 K) form amorphous ices; annealing at temperatures in excess of 140-155 K is usually required to convert such amorphous samples to crystalline ices. However, we have found that when either methanol or water vapor is deposited on to aluminum substrates that have been coated with a thin (0.1-0.5 mm) layer of amorphous silicate smoke, the ices condense in crystalline form. We believe that crystalline ice forms as the result of energy liberated at the ice/silicate interface perhaps due to weak bonding of the ice at defect sites on the grains and the very high surface to volume ratio and defect density of these smokes. Annealing of amorphous water ice mixed with more volatile components such as methane, carbon monoxide, etc., has been suggested as an efficient way to produce clatherates in the outer solar nebula and thus explain the volatile content of comets and icy satellites of the outer planets. This hypothesis may need to be re-examined if amorphous ice does not form on cold silicate grains.

  7. Reversible pressure-induced crystal-amorphous structural transformation in ice Ih

    NASA Astrophysics Data System (ADS)

    English, Niall J.; Tse, John S.

    2014-08-01

    Molecular dynamics (MD) simulation of depressurised high-density amorphous ice (HDA) at 80 K and at negative pressures has been performed. Over several attempts, HDA recrystallised to a form close to hexagonal ice Ih, albeit with some defects. The results support the hypothesis that compression of ice-Ih to HDA is a reversible first-order phase transition, with a large hysteresis. Therefore, it would appear that LDA is not truly amorphous. The elastic energy estimated from the area of the hysteresis loop is ca. 4.5 kJ/mol, in some way consistent with experimentally-determined accumulated successive heats of transformations from recovered HDA ? ice Ih.

  8. Snow crystal imaging using scanning electron microscopy: III. Glacier ice, snow and biota

    Microsoft Academic Search

    A. RANGO; W. P. WERGIN; E. F. ERBE; E. G. JOSBERGER

    2000-01-01

    Low-temperature scanning electron microscopy (SEM) was used to observe metamorphosed snow, glacial firn, and glacial ice obtained from South Cascade Glacier in Washington State, USA. Biotic samples consisting of algae (Chlamydomonas nivalis) and ice worms (a species of oligochaetes) were also collected and imaged. In the field, the snow and biological samples were mounted on copper plates, cooled in liquid

  9. Validation and Determination of Ice Water Content - Radar Reflectivity Relationships during CRYSTAL-FACE: Flight Requirements for Future Comparisons

    NASA Technical Reports Server (NTRS)

    Sayres, D. S.; Smith, J. B.; Pittman, J. V.; Weinstock, E. M.; Anderson, J. G.; Heymsfield, G.; Fridland, A. M.; Ackerman, A. S.

    2007-01-01

    In order for clouds to be more accurately represented in global circulation models (GCM), there is need for improved understanding of the properties of ice such as the total water in ice clouds, called ice water content (IWC), ice particle sizes and their shapes. Improved representation of clouds in models will enable GCMs to better predict for example, how changes in emissions of pollutants affect cloud formation and evolution, upper tropospheric water vapor, and the radiative budget of the atmosphere that is crucial for climate change studies. An extensive cloud measurement campaign called CRYSTAL-FACE was conducted during Summer 2002 using instrumented aircraft and a variety of instruments to measure properties of ice clouds. This paper deals with the measurement of IWC using the Harvard water vapor and total water instruments on the NASA WB-57 high-altitude aircraft. The IWC is measured directly by these instruments at the altitude of the WB-57, and it is compared with remote measurements from the Goddard Cloud Radar System (CRS) on the NASA ER-2. CRS measures vertical profiles of radar reflectivity from which IWC can be estimated at the WB-57 altitude. The IWC measurements obtained from the Harvard instruments and CRS were found to be within 20-30% of each other. Part of this difference was attributed to errors associated with comparing two measurements that are not collocated in time an space since both aircraft were not in identical locations. This study provides some credibility to the Harvard and CRS-derived IWC measurements that are in general difficult to validate except through consistency checks using different measurement approaches.

  10. Part A: Cirrus ice crystal nucleation and growth. Part B: Automated analysis of aircraft ice particle data

    NASA Technical Reports Server (NTRS)

    Arnott, William P.; Hallett, John; Hudson, James G.

    1995-01-01

    Specific measurement of cirrus crystals by aircraft and temperature modified CN are used to specify measurements necessary to provide a basis for a conceptual model of cirrus particle formation. Key to this is the ability to measure the complete spectrum of particles at cirrus levels. The most difficult regions for such measurement is from a few to 100 microns, and uses a replicator. The details of the system to automate replicator data analysis are given, together with an example case study of the system provided from a cirrus cloud in FIRE 2, with particles detectable by replicator and FSSP, but not 2DC.

  11. Meth (Crank, Ice) Facts

    MedlinePLUS

    Listen to this page Meth (Crank, Ice) Facts Methamphetamine—meth for short—is a white, bitter powder. ... names for meth are: Crank Ice Crystal Glass Chalk En español "Heart disease runs in some families. ...

  12. Supercooled Droplets and Ice Crystals in Mixed-Phase Clouds: Numerical Simulations Considering Isotropic Turbulence of the Ambient Flow Field

    NASA Astrophysics Data System (ADS)

    Siewert, Christoph; Kunnen, Rudie; Meinke, Matthias; Schröder, Wolfgang; Beheng, Klaus

    2013-04-01

    In midlatitudes the formation and evolution of precipitation is the result of a chain of processes taking place in mixed-phase clouds. Due to the coexistence of supercooled water drops and ice particles in such clouds mutual interactions by collisions, i.e. riming and aggregation, take place leading to ice hydrometeors of a large precipitation size. In the past these collision mechanisms have been investigated - besides laboratory measurements - by numerical simulations of the collision process where trajectories of the participating hydrometeors have been calculated as occurring in an environment at rest (Pruppacher and Klett, Kluwer Academic Publishers, Dordrecht, 1997). However, as it is well-known the flow field in clouds is almost always turbulent (Siebert et al., Atmos. Res. 97 (2010) 426-437) except in undiluted updrafts of single strong convective clouds. And it has been argued that turbulence may enhance precipitation formation. As a consequence turbulence effects on the collisional interaction of cloud and other heavy particles came into focus during the last decade and gave rise to the description in terms of radial distribution function, mean radial relative velocity and the collection efficiency all derived from numerical simulations. Up to now mostly the turbulence influence on cloud droplet/cloud droplet collisions has been investigated (Ayala et al., New J. Phys. 10 (2008) 075015), (Bec et al., J. Fluid Mech. 646 (2010) 527-536). Much less is known about the influence of turbulence on particles in mixed phase clouds. This is mainly due to the various and complex shapes of the ice particles depending on the temperature, the supersaturation, and their life time. Hence, our knowledge about the behavior of ice crystals in turbulence is based on wind tunnel experiments. In the early stage ice crystals often have the shape of hexagonal plates or needles. In theoretical and numerical studies these are commonly approximated by ellipsoids. However, except in (Pinsky and Khain, Atmos. Res. 47-48 (1998) 69-86) only laminar flows have been considered so far. Therefore we have developed a numerical experiment with a novel setup (Kunnen et al., under review in Atmos. Res. (2013)). Therein synthetic turbulence is generated at the inflow and is then advected by a mean flow through the domain. The full Navier-Stokes equations are solved using a DNS method on an Eulerian Cartesian grid. The evolving decaying turbulence shares similarities with the grid-generated turbulence of wind tunnels. In this flow several million particle spheres as well as ellipsoids are advanced in a Lagrangian manner in order to represent the supercooled droplets and ice crystals out of a small region of a mixed-phase cloud. Statistics will be gathered about the orientation, the sedimentation velocities, the clustering, and the relative velocities of these particles. From this basis collision kernels can be calculated. These are input parameters for cloud models estimating the evolution of precipitation.

  13. Evidence of ice crystals at cloud top of Arctic boundary-layer mixed-phase clouds derived from airborne remote sensing

    Microsoft Academic Search

    A. Ehrlich; M. Wendisch; E. Bierwirth; J.-F. Gayet; G. Mioche; A. Lampert; B. Mayer

    2009-01-01

    The vertical distribution of ice crystals in Arctic boundary-layer mixed-phase (ABM) clouds was investigated by airborne remote sensing and in situ measurements during the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR) campaign in March and April 2007. From airborne measurements of spectral solar radiation reflected by the ABM clouds information on the spectral absorption of solar radiation by

  14. Ice rule correlations in stuffed spin ice

    NASA Astrophysics Data System (ADS)

    Aldus, R. J.; Fennell, T.; Deen, P. P.; Ressouche, E.; Lau, G. C.; Cava, R. J.; Bramwell, S. T.

    2013-01-01

    Stuffed spin ice is a chemical variation of a spin ice material like Ho2Ti2O7 in which extra magnetic ions are inserted into the crystal structure. Previous studies have shown that the degree of stuffing has very little effect on the residual entropy in the system, which takes a value very close to the spin ice entropy. We argue, however, that the observation of this entropy does not imply long range coherence of the ice rules, that determine the local spin configurations. We have characterized deviations from the ice rules by means of a polarized neutron diffraction study of a single crystal of Ho2+?Ti2-?O7-?/2 with ? = 0.3. Our results demonstrate that the ice rules in stuffed spin ice are strictly valid only over a relatively short range, and that at longer range stuffed spin ice exhibits some characteristics of a ‘cluster glass’, with a tendency to more conventional ferromagnetic correlations.

  15. ICE PRODUCTION IN A FLUIDISED BED CRYSTALLISER

    Microsoft Academic Search

    M. A. VAN DER GUN; J. W. MEEWISSE; C. A. INFANTE FERREIRA

    The fluidised bed ice slurry generator is analysed with respect to size and shape of the ice crystals produced. The different steps of ice crystallisation are discussed, which are supersaturation, nucleation and crystal growth. Additional effects as attrition, agglomeration and Ostwald ripening are also analysed for their influence on ice slurries produced in fluidised bed ice generators. Microscopic pictures taken

  16. Diffusion of nitrogen gas in ice Ih

    Microsoft Academic Search

    Tomoko Ikeda-Fukazawa; Katsuyuki Kawamura; Takeo Hondoh

    2004-01-01

    Diffusion of N2 in ice crystal has been found from Raman scattering of the natural ice from the Antarctic ice sheet. In order to investigate the diffusion mechanism, we perform molecular dynamics simulations of diffusion of N2 in ice. The results show that the N2 molecule hops in the crystal by breaking hydrogen bonds in the ice lattice. The diffusion

  17. Effects of nuclei concentrations, ice nucleation mechanisms and crystal habits on the dynamics and microphysics of Arctic mixed-phase clouds

    NASA Astrophysics Data System (ADS)

    Komurcu, Muge

    There is a significant warming in the Arctic that is evident in both observations and in the future climate predictions. The Arctic warming is greater than any other region on Earth, however, the degree of warming is inconsistent among the climate models even for the same emission scenarios. Clouds, especially low-level clouds, are a prevailing feature of the Arctic atmosphere. They strongly affect the surface radiative and energy budgets, which make them a key component of the Arctic climate. Recent inter-comparison studies using regional climate models show that models are incapable of reproducing the supercooled liquid water observed in clouds during the cold season. Large discrepancies exist in the partitioning of phase between ice and liquid water among different models. It is currently thought that these discrepancies are due to the uncertainties in ice nuclei concentrations, ice nucleation, and ice crystal habits used in models. Predicting these physical processes controls the partitioning between liquid and ice, and hence the impact of mixed-phase clouds on the surface energy budget. There is a need to improve model cloud predictions in the Arctic, however, the microphysical uncertainties mentioned above are tied directly to the cloud dynamics that help maintain persistent mixed-phase clouds. Therefore, this dissertation analyzes and inter-compares the impacts of different ice nuclei concentrations, ice nucleation mechanisms and ice crystal habits on mixedphase cloud dynamics. Separate simulations using different ice nuclei concentrations, ice nucleation mechanisms, and crystal habits are performed. It is found that the choice of habits in models alters the water paths and cloud dynamics strongly. Next, the relative importance of and interactions among the processes that influence the dynamics of the cloud, such as the radiative cooling at cloud top, and the ice precipitation induced cloudbase stabilization are investigated. To examine these processes in detail, sensitivity studies are performed by fixing the radiative cooling, and the diabatic influences of ice precipitation. In addition, simulations with increasing ice nuclei concentrations, different nucleation mechanisms, and crystal habits are repeated with surface fluxes and largescale forcing included. The influence of surface fluxes is important as it can compensate for the water mass that is lost through ice precipitation if the ice precipitation is weak. Surface fluxes can also lead to the coupling of the liquid cloud layer with the sub-cloud layer. The cloud-base stability is diminished with the inclusion of the surface fluxes, and the effect of entrainment is enhanced. Sensitivity tests are also repeated with the added surface fluxes. Using the results of the sensitivity analysis, a ratio identifying the decoupling of the cloud and subcloud layers is generated, and also with the sensitivity analysis cloud dynamic and microphysical interactions within Arctic mixed-phase clouds are explained.

  18. Magnetic vortex crystal formation in the antidot complement of square artificial spin ice

    SciTech Connect

    Araujo, C. I. L. de, E-mail: dearaujo@ufv.br; Silva, R. C.; Ribeiro, I. R. B.; Nascimento, F. S.; Felix, J. F.; Ferreira, S. O.; Moura-Melo, W. A.; Pereira, A. R. [Departamento de Física, Universidade Federal de Viçosa, Viçosa 36570-900, Minas Gerais (Brazil); Mól, L. A. S. [Departamento de Física, ICEx, Universidade Federal de Minas Gerais, Belo Horizonte 31270-901, Minas Gerais (Brazil)

    2014-03-03

    We have studied ferromagnetic nickel thin films patterned with square lattices of elongated antidots that are negative analogues of square artificial spin ice. Micromagnetic simulations and direct current magnetic moment measurements reveal in-plane anisotropy of the magnetic hysteresis loops, and the formation of a dense array of magnetic vortices with random polarization and chirality. These multiply-connected antidot arrays could be superior to lattices of disconnected nanodisks for investigations of vortex switching by applied electric current.

  19. Hydrohalite in cold sea ice: Laboratory observations of single crystals, surface accumulations, and migration rates under a temperature gradient, with application to “Snowball Earth”

    NASA Astrophysics Data System (ADS)

    Light, Bonnie; Brandt, Richard E.; Warren, Stephen G.

    2009-07-01

    When NaCl precipitates out of a saturated solution, it forms anhydrous crystals of halite at temperatures above +0.11°C, but at temperatures below this threshold it instead precipitates as the dihydrate "hydrohalite," NaCl · 2H2O. When sea ice is cooled, hydrohalite begins to precipitate within brine inclusions at about -23°C. In this work, hydrohalite crystals are examined in laboratory experiments: their formation, their shape, and their response to warming and desiccation. Sublimation of a sea ice surface at low temperature leaves a lag deposit of hydrohalite, which has the character of a fine powder. The precipitation of hydrohalite in brine inclusions raises the albedo of sea ice, and the subsequent formation of a surface accumulation further raises the albedo. Although these processes have limited climatic importance on the modern Earth, they would have been important in determining the surface types present in regions of net sublimation on the tropical ocean in the cold phase of a Snowball Earth event. However, brine inclusions in sea ice migrate downward to warmer ice, so whether salt can accumulate on the surface depends on the relative rates of sublimation and migration. The migration rates are measured in a laboratory experiment at temperatures from -2°C to -32°C; the migration appears to be too slow to prevent formation of a salt crust on Snowball Earth.

  20. Ice forming experiment

    NASA Technical Reports Server (NTRS)

    Vali, G.

    1982-01-01

    A low gravity experiment to assess the effect of the presence of supercooled cloud droplets on the diffusional growth rate of ice crystals is described. The theoretical work and the feasibility studies are summarized. The nucleation of ice crystals in supercooled clouds is also discussed.

  1. Crystal Distortion of Dy2Ti2O7 at the Spin Ice Transition Temperature

    SciTech Connect

    Suzuki, H.; Hata, F.; Xue, Y.; Kaneko, H.; Hosomichi, A.; Abe, S. [Department of Physics, Kanazawa University, Kakuma-machi, Kanazawa 920-1192 (Japan); Higashinaka, R.; Nakatsuji, S.; Maeno, Y. [Department of Physics, Kyoto University, Kyoto 606-8502 (Japan)

    2006-09-07

    Dy2Ti2O7 with the pyrochlore structure shows a spin ice transition at about 1 K. The Dy3+ ion in this compound has an effective spin Seff=1/2. The Dy ions reside on the vertices of corner-linked tetrahedra. Due to a strong single-ion anisotropy, the ground state of Dy3+ is well expressed by an Ising doublet with local <111> quantization axes. We measured the x-ray diffraction for a Dy2Ti2O7 powder sample between 0.15 K. and 20 K. The lattice spacing increases drastically between 1.5 K and about 1 K, with decreasing temperature. The lattice spacing of the (222) diffraction is considerably larger than the other directions.

  2. Crystal and molecular structure of dihydroxynaphthalene isomers. Effect of structure on ice-forming properties

    Microsoft Academic Search

    V. K. Bel'skii; E. V. Kharchenko; A. N. Sobolev; V. E. Zavodnik; N. A. Kolomiets; G. S. Prober; L. P. Oleksenko

    1991-01-01

    X-ray diffraction structural analysis established the structures of three dihydroxynaphthalene isomers: 1,5-dihydroxynaphthalene (space group P21\\/n, Z = 2(r), R = 0.035), 2,5-dihydroxynaphthalene (space group P21\\/a , Z --- 4(12), R = 0.058), and 2,3-dihydroxynaphthalene (space group Pcab, Z = 16(12), R = 0.032). The molecules of the dihydroxynaphthalene isomers in the crystals are connected by hydrogen bond systems. The existence

  3. MEAT, POULTRY, Still contains ice

    E-print Network

    Liskiewicz, Maciej

    MEAT, POULTRY, SEAFOOD Still contains ice crystals and feels as cold, there will be some texture and Clavor loss. Discard DAIRY Still contains ice crystals and feels Ice cream, frozen yogurt Discard Discard Cheese (soft and semi-soft) Refreeze. May

  4. Ice is a Mineral

    NSDL National Science Digital Library

    This is a lesson about the characteristics of ice as a mineral and how it compares to other minerals with respect to hardness. Learners will observe ice crystals, develop a hardness scale and position ice on it. Learners will also practice working collaboratively in a team. Activities include small group miming, speaking, drawing, and/or writing. This is lesson 3 of 12 in the unit, Exploring Ice in the Solar System.

  5. On the characterization of crystallization and ice adhesion on smooth and rough surfaces using molecular dynamics

    NASA Astrophysics Data System (ADS)

    Singh, Jayant K.; Müller-Plathe, Florian

    2014-01-01

    Coarse-grained molecular dynamics is utilized to quantify the behavior of a supercooled water drop on smooth and rough surfaces. Crystallization on rough surface is characterized based on wetting states. Freezing temperature and work of adhesion of water droplet are linearly associated with roughness parameters corresponding to the Cassie-Baxter and Wenzel states. The behavior is insensitive to different surface-fluid affinity. We show in general, for Wenzel states, work of adhesion is higher than that of Cassie-Baxter state for surfaces that have identical freezing temperatures.

  6. Study of Horizontally Oriented Ice Crystals with CALIPSO Observations and Comparison with Monte Carlo Radiative Transfer Simulations

    E-print Network

    Baum, Bryan A.

    ice clouds. 1. Introduction In current satellite-based retrievals of ice cloud optical thickness scattering computation of the bulk ice cloud optical properties, predefined size and habit (shape) dis) ABSTRACT Data from the Cloud­Aerosol Lidar with Orthogonal Polarization (CALIOP) indicate that horizontally

  7. Optimal numerical methods for determining the orientation averages of single-scattering properties of atmospheric ice crystals

    NASA Astrophysics Data System (ADS)

    Um, Junshik; McFarquhar, Greg M.

    2013-09-01

    The optimal orientation averaging scheme (regular lattice grid scheme or quasi Monte Carlo (QMC) method), the minimum number of orientations, and the corresponding computing time required to calculate the average single-scattering properties (i.e., asymmetry parameter (g), single-scattering albedo (?o), extinction efficiency (Qext), scattering efficiency (Qsca), absorption efficiency (Qabs), and scattering phase function at scattering angles of 90° (P11 (90°)), and 180° (P11 (180°))) within a predefined accuracy level (i.e., 1.0%) were determined for four different nonspherical atmospheric ice crystal models (Gaussian random sphere, droxtal, budding Bucky ball, and column) with maximum dimension D=10?m using the Amsterdam discrete dipole approximation at ?=0.55, 3.78, and 11.0?m.The QMC required fewer orientations and less computing time than the lattice grid. The calculations of P11 (90°) and P11 (180°) required more orientations than the calculations of integrated scattering properties (i.e., g, ?o, Qext, Qsca, and Qabs) regardless of the orientation average scheme. The fewest orientations were required for calculating g and ?o. The minimum number of orientations and the corresponding computing time for single-scattering calculations decreased with an increase of wavelength, whereas they increased with the surface-area ratio that defines particle nonsphericity.

  8. Application of the Discontinuous Galerkin method to computation of ice crystal scattering properties

    NASA Astrophysics Data System (ADS)

    Tang, G.; Panetta, R. L.; Yang, P.

    2009-12-01

    The Discontinuous Galerkin (DG) method has recently proven successful in numerical simulations of solutions to electromagnetic and fluid dynamic equations. Here we use the method to compute optical properties of single ice particles with circular and hexagonal cross-sections, in two-dimensional geometry. The method presents two distinct advantages over finite difference methods: use of an unstructured grid allows a good fit to particle shape, and the use of polynomial interpolants on grid elements allows choice of grid resolution on the order of a half-wavelength, a factor of 10 larger than in finite difference methods. The computations are done in the time domain, with a fourth order Runga-Kutta time-stepping method. Our interest is in the regime of large particle size. We show results for two particle sizes, ka=50 and ka=100, and two wavelengths: one non-absorptive, corresponding to the peak in solar shortwave radiation, and one absorptive, corresponding to the peak in terrestrial longwave radiation. In each case, phase matrices for circular cross-sections computed using the DG method compare very favorably with analytical solutions. In the case of hexagonal cross-section, where analytical solutions are not available, we show good agreement of results from DG computations with results from ray-tracing calculations. We consider random orientations and discuss some fine structure features of the far-field scattered wave in the hexagonal case that have not been reported before.

  9. Categorizing Ice Crystals Using Airborne APR-2 and HVPS Observations during GCPEx

    NASA Astrophysics Data System (ADS)

    Martinez, M., III; Bennartz, R.; Turk, F. J.; Tanelli, S.; Sy, O. O.; Bansemer, A.; Kuo, K. S.

    2014-12-01

    Current and planned millimeter-wave passive and active satellite sensors are proposed for future low Earth-orbiting satellite platforms. For accurate modeling and sensor simulation of ice clouds at these wavelengths, realistic particle shapes and size distributions (PSD) need to be used. During the Jan-Feb 2012 Global Precipitation Measurement (GPM) Cold Season Precipitation Experiment (GCPEx) near Toronto, Canada, the Jet Propulsion Laboratory (JPL) dual-frequency (Ku/Ka-band) Airborne Precipitation Radar (APR-2) flew onboard the NASA DC-8 aircraft. Coordinated flights were carried out with the Univ. of North Dakota Citation aircraft carrying the High Volume Precipitation Spectrometer (HVPS-3), to collect cloud PSD and particle imagery. Selected flights enabled collection of coincident sampling volumes from the APR-2 and the HVPS. This unique dataset enables the scattering properties of the frozen hydrometeors to be modeled using the HVPS-provided particle distributions, and compared with APR-2 observations. The wide variety of fractal-like particle shapes measured in the HVPS data were separated into size bins and presented as 2 dimensional histograms with bins defined by Aspect (As) and Area (Ar) ratio. Individual histograms were previously characterized by the mean As and Ar values, ignoring the preferential linear trend between As and Ar visible for data points within most particle sizes. To facilitate the scattering models, we attempted to partition particles by shape within four size-invariant As and Ar categories. The four unique PSD, created by particle shape segregation, were then used to forward model the Ku and Ka- band radar reflectivities to locate the particle characteristics that provided the best agreement with actual APR-2 observations. In future work, these PSD will be used for passive microwave satellite sensor simulations of cold season precipitation and compared to actual satellite observations.

  10. Examining Crystal Fabric Develoment in Ice: Cryo EBSD, Deformation Experiments and the Link to En-glacial Reflectivity

    NASA Astrophysics Data System (ADS)

    Vaughan, Matthew; Prior, David; Seidemann, Meike; Gorman, Andrew; Lilly, Kat; Langhorne, Pat; Easingwood, Richard; Golding, Narayana; Durham, Bill

    2014-05-01

    Over the past few years, cryogenic electron back-scatter diffraction (Cryo-EBSD) has been increasingly used to examine micro-structures in both natural and experimentally deformed ice samples on a micron-scale. Experiments that investigate grain size-sensitive behavior require working on fine-grained ice. These samples present a number of experimental challenges. Issues that present particular difficulties include stable mounting of ice samples, transport of mounted samples and producing a planar, frost-free and damage-free surface. Recent work at the new Otago Ice Deformation Lab has led to the development of a number of experimental methods that help overcome these challenges and enable routine EBSD analysis of fine-grained ice. A brief outline of these experimental methods and some EBSD results from variably deformed ice samples will be presented. Shear deformation experiments on polycrystalline ice are being conducted in order to further explore the relationships between deformation, processes of recrystallization, and the development of anisotropic fabrics that lead to en-glacial seismic reflections. Self-contained, refrigerated deformation units fitted with digital controllers and hardware have been designed for unconfined deformation experiments on polycrystalline synthetic ice. Methods of analysis, from time-lapse photography to random-point tracking, are being employed for monitoring strain in real time. Various methods have been explored for monitoring the development of anisotropic fabrics in ice during progressive deformation. Ultra-sonic transducers can be used to monitor wave velocity changes in various orientations in materials under strain. These experiments have been designed with the objective of quantifying the relationship between deformation fabrics and en-glacial seismic reflectivity observed in thick grounded ice sheets.

  11. Influence of particle size and shape on the backscattering linear depolarisation ratio of small ice crystals - cloud chamber measurements in the context of contrail and cirrus microphysics

    NASA Astrophysics Data System (ADS)

    Schnaiter, M.; Büttner, S.; Möhler, O.; Skrotzki, J.; Vragel, M.; Wagner, R.

    2012-11-01

    The article presents the laser scattering and depolarisation instrument SIMONE that is installed at the large aerosol and cloud chamber facility AIDA of the Karlsruhe Institute of Technology. SIMONE uses a 488 nm cw laser to probe simulated atmospheric clouds by measuring the scattered light from the 1.8° and 178.2° directions. At 178.2°, the scattered light is analysed for the linear polarisation state to deduce the particle linear depolarisation ratio ?p which is a common measurement parameter of atmospheric lidar applications. The optical setup and the mathematical formalism of the depolarisation detection concept are given. SIMONE depolarisation measurements in spheroidal hematite aerosol and supercooled liquid clouds are used to validate the instrument. SIMONE data from a series of AIDA ice nucleation experiments at temperatures between 195 and 225 K were analysed in terms of the impact of the ice particle microphysics on ?p. We found strong depolarisation values of up to 0.4 in case of small growing and sublimating ice particles with volume equivalent diameters of only a few micrometers. Modelling runs with the T-matrix method showed that the measured depolarisation ratios can be accurately reproduced assuming spheroidal and cylindrical particles with a size distribution that has been constrained by IR extinction spectroscopy. Based on the T-matrix modelling runs, we demonstrate that in case of small ice crystals the SIMONE depolarisation results are representative for the lidar depolarisation ratio which is measured at exact backscattering direction of 180°. The relevance of our results for the interpretation of recent lidar observations in cirrus and contrails is discussed. In view of our results, the high depolarisation ratios observed by the spaceborne lidar CALIOP in the tropical upper troposphere might be a hint for the presence of small (sublimating) ice particles in the outflows of deep convective systems.

  12. Influence of particle size and shape on the backscattering linear depolarisation ratio of small ice crystals - cloud chamber measurements in the context of contrail and cirrus microphysics

    NASA Astrophysics Data System (ADS)

    Schnaiter, M.; Büttner, S.; Möhler, O.; Skrotzki, J.; Vragel, M.; Wagner, R.

    2012-06-01

    The article presents the laser scattering and depolarisation instrument SIMONE that is installed at the large aerosol and cloud chamber facility AIDA of the Karlsruhe Institute of Technology. SIMONE uses a 488 nm cw laser to probe simulated atmospheric clouds by measuring the scattered light from the 1.8° and 178.2° directions. At 178.2°, the scattered light is analysed for the linear polarisation state to deduce the linear depolarisation ratio ?l which is a common measurement parameter of atmospheric LIDAR applications. The optical setup and the mathematical formalism of the depolarisation detection concept are given. SIMONE depolarisation measurements in spheroidal hematite aerosol and supercooled liquid clouds are used to validate the instrument. SIMONE data from a series of AIDA ice nucleation experiments at temperatures between 195 and 225 K were analysed in terms of the impact of the ice particle microphysics on ?l. We found strong depolarisation values of up to 0.4 in case of small growing and sublimating ice particles with volume equivalent diameters of only a few micrometers. Modelling runs with the T-matrix method showed that the measured depolarisation ratios can be accurately reproduced assuming spheroidal and cylindrical particles with a size distribution that has been constrained by IR extinction spectroscopy. Based on the T-matrix modelling runs, we demonstrate that in case of small ice crystals the SIMONE depolarisation results are representative for the LIDAR depolarisation ratio which is measured at exact backscattering direction of 180°. The relevance of our results for the interpretation of recent LIDAR observations in cirrus and contrails is discussed. In view of our results, the high depolarisation ratios observed by the spaceborne LIDAR CALIOP in the tropical upper troposphere might be a hint for the presence of small (sublimating) ice particles in the outflows of deep convective systems.

  13. Crystals

    NSDL National Science Digital Library

    Lawrence Hall of Science

    2009-01-01

    In this earth science/math/art activity, learners use simple ingredients to grow crystals and examine the repeating geometric shapes and patterns. Learners compare the growth of crystals from four types of crystal-starters (table salt, Borax, sand, and Epsom salt) to see which starter grows the most crystals in 14 days. Learners report their results online and find out what other learners discovered. Afterward, learners can use the crystals they grew to create works of art.

  14. Quasi-spherical collapse with cosmological constant

    E-print Network

    Ujjal Debnath; Soma Nath; Subenoy Chakraborty

    2006-04-21

    The junction conditions between static and non-static space-times are studied for analyzing gravitational collapse in the presence of a cosmological constant. We have discussed about the apparent horizon and their physical significance. We also show the effect of cosmological constant in the collapse and it has been shown that cosmological constant slows down the collapse of matter.

  15. On the ice nucleation spectrum

    NASA Astrophysics Data System (ADS)

    Barahona, D.

    2011-11-01

    This work presents a novel formulation of the ice nucleation spectrum, i.e. the function relating the ice crystal concentration to cloud formation conditions and aerosol properties. The new formulation relies on a statistical view of the ice nucleation process and explicitly accounts for the dependency of the ice crystal concentration on temperature, supersaturation, cooling rate, and particle size, and, in the case of heterogeneous ice nucleation, on the distributions of particle area and surface composition. The new formulation is used to generate ice nucleation parameterizations for the homogeneous freezing of cloud droplets and the heterogeneous deposition ice nucleation on dust and soot ice nuclei. For homogeneous freezing, it was found that by increasing the dispersion in the droplet volume distribution the fraction of supercooled droplets in the population increases. For heterogeneous ice nucleation it was found that ice nucleation on efficient ice nuclei (IN) shows features consistent with the singular hypothesis (characterized by a lack of temporal dependency of the ice nucleation spectrum) whereas less efficient IN tend to display stochastic behavior. Analysis of empirical nucleation spectra suggested that inferring the aerosol heterogeneous ice nucleation properties from measurements of the onset supersaturation and temperature may carry significant error as the variability in ice nucleation properties within the aerosol population is not accounted for. This work provides a simple and rigorous ice nucleation framework were theoretical predictions, laboratory measurements and field campaign data can be reconciled, and that is suitable for application in atmospheric modeling studies.

  16. The Spectral Signature of Mixed-Phase Clouds Composed of Non-Spherical Ice Crystals and Spherical Liquid Droplets in the Terrestrial Window Region

    SciTech Connect

    Yang, P.; Wei, H.- L.; Bryan, B. A.; Huang, H.- L.; Heymsfield, Andrew J.; Hu, Yong X.; Gao, B.- C.; Turner, David D.

    2003-06-01

    An outstanding problem facing the cloud modeling and remote sensing community is to improve satellite-derived cloud microphysical and macrophysical properties when a single cloud layer exists within a temperature range for which a combination of water and ice particles may be present. This is typically known as a ''mixed-phase'' cloud condition, and is prevalent when the cloud-top temperature lies between -40C and 0C. In this paper, we report on a sensitivity study of the spectral signature of mixed-phase clouds in the infrared terrestrial window (8-13 um). Mixed clouds are assumed to be a vertically uniform cloud layer composed of a mixture of pristine hexagonal crystals and spherical water droplets. Unlike the conventional approach that derives the bulk scattering properties of the mixed-phase clouds by a linear weighting of the contributions of ice and water components, the bulk single-scattering properties of mixed-phase clouds are formulated on the basis of fundamental physics. With the aid of a line-by-line radiative transfer model and a discrete ordinates radiative transfer (DISORT) computational program, we investigate the high-resolution spectral signature, expressed in terms of brightness temperature, of mixed-phase clouds with various effective sizes, ice fraction ratios, and optical thicknesses. Small particles are found to have a significant impact on the infrared spectral signature of mixed-phase clouds when the size discrepancy between the ice and water particles is large. Furthermore, the simulation results show that the infrared radiative spectrum associated with cirrus clouds can be quite different from their mixed-phase counterparts even if only a small amount of water droplets exist in the mixed-phase cloud layer.

  17. Stacking disorder in ice I.

    PubMed

    Malkin, Tamsin L; Murray, Benjamin J; Salzmann, Christoph G; Molinero, Valeria; Pickering, Steven J; Whale, Thomas F

    2015-01-01

    Traditionally, ice I was considered to exist in two well-defined crystalline forms at ambient pressure: stable hexagonal ice (ice Ih) and metastable cubic ice (ice Ic). However, it is becoming increasingly evident that what has been called cubic ice in the past does not have a structure consistent with the cubic crystal system. Instead, it is a stacking-disordered material containing cubic sequences interlaced with hexagonal sequences, which is termed stacking-disordered ice (ice Isd). In this article, we summarise previous work on ice with stacking disorder including ice that was called cubic ice in the past. We also present new experimental data which shows that ice which crystallises after heterogeneous nucleation in water droplets containing solid inclusions also contains stacking disorder even at freezing temperatures of around -15 °C. This supports the results from molecular simulations, that the structure of ice that crystallises initially from supercooled water is always stacking-disordered and that this metastable ice can transform to the stable hexagonal phase subject to the kinetics of recrystallization. We also show that stacking disorder in ice which forms from water droplets is quantitatively distinct from ice made via other routes. The emerging picture of ice I is that of a very complex material which frequently contains stacking disorder and this stacking disorder can vary in complexity depending on the route of formation and thermal history. PMID:25380218

  18. Ice particle crystallization in the presence of ethanol: an in situ study by Raman and X-ray diffraction.

    PubMed

    Facq, Sébastien; Danède, Florence; Chazallon, Bertrand

    2013-06-13

    Two distinct ethanol aqueous solution droplets ((X(EtOH))L = 8.7 wt % and 46.5 wt %) are investigated by in situ Raman spectroscopy and X-ray diffraction between 253 and 88 K. Structural changes are identified by modifications in the O-H and C-H stretching modes (2800-3800 cm(-1) spectral region) during freezing and annealing events. They are attributed to the formation of ice and/or different hydrate structures in the EtOH-water system. At high initial ethanol concentration, the particle is found to be composed of a modified clathrate I (cubic structure) at 211 K on cooling and transformed into an ethanol hydrate II (monoclinic structure) on annealing between ?143 and 173 K. This latter decomposes at ?200 K and leaves an aqueous solution and ice Ih which further dissociates above ?230 K. At low initial concentration, ice first forms on cooling and the particle consists of a crystalline ice core embedded in a liquid layer of high ethanol content at ~200 K (or an amorphous layer at lower T). A new hydrate (IV) of distinct structure (orthorhombic) is observed on annealing (from 100 K) between ?123 K and ?142 K (depending on initial composition), which transforms into the ethanol hydrate II at ?160 K. The hydrate II decomposes at ?200 K, and ice Ih remains (and dissociate above ?220 K) in coexistence with the liquid layer of high ethanol content. It is proposed that the complex crystalline ice particles formed may have the potential to impact several atmospherical processes differently in comparison to the pure ice case. PMID:23682626

  19. Ice slurry production using supercooling phenomenon

    Microsoft Academic Search

    Jean-Pierre Bédécarrats; Thomas David; Jean Castaing-Lasvignottes

    2010-01-01

    The studied ice slurry production consists in generating ice from a flow of supercooled water or aqueous solution. After leaving the evaporator of the refrigerating plant, the supercooled flow is physically disturbed in order to generate ice crystals. The influence of different parameters on the crystallization have been studied: the level of supercooling, the flow rate and the refrigerant temperature.

  20. Eutectic freeze crystallization in a new apparatus: the cooled disk column crystallizer

    Microsoft Academic Search

    Frank van der Ham; Marcelo Martins Seckler; Geert Jan Witkamp

    2004-01-01

    Eutectic freeze crystallization (EFC) is a technique for simultaneous crystallization of ice and salt that is energetically more efficient than conventional evaporative crystallization. In this paper, a new type of crystallizer is introduced for simultaneously conducting EFC and separating the ice from the salt crystals, the cooled disk column crystallizer (CDCC). Crystallization is achieved by indirect cooling with wiped disks

  1. Ice slurry generation involving moving parts

    Microsoft Academic Search

    E. Stamatiou; J. W. Meewisse; M. Kawaji

    2005-01-01

    Efficient ice slurry generation systems continuously produce ice crystals of desired size offering high cooling rates without any wall freeze-up. Although several ice slurry generation technologies have been and are being developed, currently only the scraped surface and supercooling type have been widely used in commercial applications. Typical ice slurry generators require the use of mechanical devices such as scraper

  2. Interpreting ancient ice in a shallow ice core from the South Yamato (Antarctica) blue ice area using flow modeling and compositional matching to deep ice cores

    Microsoft Academic Search

    John C. Moore; Fumihiko Nishio; Shuji Fujita; Hideki Narita; Elizabeth Pasteur; Aslak Grinsted; Anna Sinisalo; Norikazu Maeno

    2006-01-01

    We explore methods of dating a 101 m ice core from a bare ice ablation area in the Yamato Mountains, Dronning Maud Land, East Antarctica. There are two unknowns, the age of the ice at the surface and the age spanned by the core. The ice crystal growth rate was used to estimate the age span of the core at

  3. Three-dimensional rocking curve imaging to measure the effective distortion in the neighbourhood of a defect within a crystal: an ice example

    PubMed Central

    Philip, Armelle; Meyssonnier, Jacques; Kluender, Rafael T.; Baruchel, José

    2013-01-01

    Rocking curve imaging (RCI) is a quantitative version of monochromatic beam diffraction topography that involves using a two-dimensional detector, each pixel of which records its own ‘local’ rocking curve. From these local rocking curves one can reconstruct maps of particularly relevant quantities (e.g. integrated intensity, angular position of the centre of gravity, FWHM). Up to now RCI images have been exploited in the reflection case, giving a quantitative picture of the features present in a several-micrometre-thick subsurface layer. Recently, a three-dimensional Bragg diffraction imaging technique, which combines RCI with ‘pinhole’ and ‘section’ diffraction topography in the transmission case, was implemented. It allows three-dimensional images of defects to be obtained and measurement of three-dimensional distortions within a 50?×?50?×?50?µm elementary volume inside the crystal with angular misorientations down to 10?5–10?6?rad. In the present paper, this three-dimensional-RCI (3D-RCI) technique is used to study one of the grains of a three-grained ice polycrystal. The inception of the deformation process is followed by reconstructing virtual slices in the crystal bulk. 3D-RCI capabilities allow the effective distortion in the bulk of the crystal to be investigated, and the predictions of diffraction theories to be checked, well beyond what has been possible up to now. PMID:24046486

  4. Optical spectra of orientationally disordered crystals. VI. The Raman spectrum of the translational lattice vibrations of ice Ih

    Microsoft Academic Search

    P. T. T. Wong; E. Whalley

    1976-01-01

    The Raman spectrum of the translational vibrations of polycrystalline ice Ih has been investigated in the range 350-20 cm-1. All the vibrations are Raman active, and there is much fine structure, presumably due to particular points in the Brillouin zone. Tentative assignments are suggested for some of the features. The theory of the Raman scattering by the translational vibrations of

  5. Characterization of ice binding proteins from sea ice algae.

    PubMed

    Bayer-Giraldi, Maddalena; Jin, EonSeon; Wilson, Peter W

    2014-01-01

    Several polar microalgae are able to live and thrive in the extreme environment found within sea ice, where growing ice crystals may cause mechanical damage to the cells and reduce the organisms' living space. Among the strategies adopted by these organisms to cope with the harsh conditions in their environment, ice binding proteins (IBPs) seem to play a key role and possibly contribute to their success in sea ice. IBPs have the ability to control ice crystal growth. In nature they are widespread among sea ice microalgae, and their mechanism of function is of interest for manifold potential applications. Here we describe methods for a classical determination of the IBP activity (thermal hysteresis, recrystallization inhibition) and further methods for protein characterization (ice pitting assay, determination of the nucleating temperature). PMID:24852640

  6. Measurements of growth rates of an ice crystal from supercooled heavy water under microgravity conditions: basal face growth rate and tip velocity of a dendrite.

    PubMed

    Yokoyama, Etsuro; Yoshizaki, Izumi; Shimaoka, Taro; Sone, Takehiko; Kiyota, Tatsuo; Furukawa, Yoshinori

    2011-07-14

    The growth of single ice crystals from supercooled heavy water was studied under microgravity conditions in the Japanese Experiment Module ''KIBO'' of the International Space Station (ISS). The velocities of dendrite tips parallel to the a axis and the growth rates of basal faces parallel to the c axis were both analyzed under supercooling ranging from 0.03 to 2.0 K. The velocities of dendrite tips agree with the theory for larger amounts of supercooling when the growth on the basal faces are not zero. At very low supercooling there is no growth on the basal faces. With increasing supercooling the basal faces start to grow, the growth rate changing as a function of supercooling with a power law with an exponent of about 2, with the exponent approaching 1 as supercooling increases further. We interpret the growth on the basal faces as being controlled by two-dimensional nucleation under low supercooling, with a change in the growth kinetics to spiral growth with the aid of screw dislocations with increasing supercooling then to a linear growth law. We discuss the combined effect of tip velocity and basal face kinetics on pattern formation during the growth of ice. PMID:21631108

  7. Ice Nucleation in Deep Convection

    NASA Technical Reports Server (NTRS)

    Jensen, Eric; Ackerman, Andrew; Stevens, David; Gore, Warren J. (Technical Monitor)

    2001-01-01

    The processes controlling production of ice crystals in deep, rapidly ascending convective columns are poorly understood due to the difficulties involved with either modeling or in situ sampling of these violent clouds. A large number of ice crystals are no doubt generated when droplets freeze at about -40 C. However, at higher levels, these crystals are likely depleted due to precipitation and detrainment. As the ice surface area decreases, the relative humidity can increase well above ice saturation, resulting in bursts of ice nucleation. We will present simulations of these processes using a large-eddy simulation model with detailed microphysics. Size bins are included for aerosols, liquid droplets, ice crystals, and mixed-phase (ice/liquid) hydrometers. Microphysical processes simulated include droplet activation, freezing, melting, homogeneous freezing of sulfate aerosols, and heterogeneous ice nucleation. We are focusing on the importance of ice nucleation events in the upper part of the cloud at temperatures below -40 C. We will show that the ultimate evolution of the cloud in this region (and the anvil produced by the convection) is sensitive to these ice nucleation events, and hence to the composition of upper tropospheric aerosols that get entrained into the convective column.

  8. An ab initio study of the OH stretching frequencies in ice II, ice VIII, and ice IX

    Microsoft Academic Search

    Sören Knuts; Lars Ojamäe; Kersti Hermansson

    1993-01-01

    Abinitio studies of the uncoupled, anharmonic OH and OD stretching frequency shifts in the three proton-ordered ice phases known, ice II, ice VIII, and ice IX, are presented. The ice structures are simulated by (H2O)5 supermolecules surrounded by point charges representing the correct crystal potentials. The calculations include electron correlation at the MP2 (DZP) level. For the eight different OH

  9. On the ice nucleation spectrum

    NASA Astrophysics Data System (ADS)

    Barahona, D.

    2012-04-01

    This work presents a novel formulation of the ice nucleation spectrum, i.e. the function relating the ice crystal concentration to cloud formation conditions and aerosol properties. The new formulation is physically-based and explicitly accounts for the dependency of the ice crystal concentration on temperature, supersaturation, cooling rate, and particle size, surface area and composition. This is achieved by introducing the concepts of ice nucleation coefficient (the number of ice germs present in a particle) and nucleation probability dispersion function (the distribution of ice nucleation coefficients within the aerosol population). The new formulation is used to generate ice nucleation parameterizations for the homogeneous freezing of cloud droplets and the heterogeneous deposition ice nucleation on dust and soot ice nuclei. For homogeneous freezing, it was found that by increasing the dispersion in the droplet volume distribution the fraction of supercooled droplets in the population increases. For heterogeneous ice nucleation the new formulation consistently describes singular and stochastic behavior within a single framework. Using a fundamentally stochastic approach, both cooling rate independence and constancy of the ice nucleation fraction over time, features typically associated with singular behavior, were reproduced. Analysis of the temporal dependency of the ice nucleation spectrum suggested that experimental methods that measure the ice nucleation fraction over few seconds would tend to underestimate the ice nuclei concentration. It is shown that inferring the aerosol heterogeneous ice nucleation properties from measurements of the onset supersaturation and temperature may carry significant error as the variability in ice nucleation properties within the aerosol population is not accounted for. This work provides a simple and rigorous ice nucleation framework where theoretical predictions, laboratory measurements and field campaign data can be reconciled, and that is suitable for application in atmospheric modeling studies.

  10. On the Ice Nucleation Spectrum

    NASA Technical Reports Server (NTRS)

    Barahona, D.

    2012-01-01

    This work presents a novel formulation of the ice nucleation spectrum, i.e. the function relating the ice crystal concentration to cloud formation conditions and aerosol properties. The new formulation is physically-based and explicitly accounts for the dependency of the ice crystal concentration on temperature, supersaturation, cooling rate, and particle size, surface area and composition. This is achieved by introducing the concepts of ice nucleation coefficient (the number of ice germs present in a particle) and nucleation probability dispersion function (the distribution of ice nucleation coefficients within the aerosol population). The new formulation is used to generate ice nucleation parameterizations for the homogeneous freezing of cloud droplets and the heterogeneous deposition ice nucleation on dust and soot ice nuclei. For homogeneous freezing, it was found that by increasing the dispersion in the droplet volume distribution the fraction of supercooled droplets in the population increases. For heterogeneous ice nucleation the new formulation consistently describes singular and stochastic behavior within a single framework. Using a fundamentally stochastic approach, both cooling rate independence and constancy of the ice nucleation fraction over time, features typically associated with singular behavior, were reproduced. Analysis of the temporal dependency of the ice nucleation spectrum suggested that experimental methods that measure the ice nucleation fraction over few seconds would tend to underestimate the ice nuclei concentration. It is shown that inferring the aerosol heterogeneous ice nucleation properties from measurements of the onset supersaturation and temperature may carry significant error as the variability in ice nucleation properties within the aerosol population is not accounted for. This work provides a simple and rigorous ice nucleation framework where theoretical predictions, laboratory measurements and field campaign data can be reconciled, and that is suitable for application in atmospheric modeling studies.

  11. Simulating Ice Accretion Effects on Engine Performance

    NASA Technical Reports Server (NTRS)

    Jorgenson, Philip C. E.; Veres, Joseph P.; Wright, William

    2011-01-01

    Develop a modeling tool that can be used to predict the onset of engine icing due to ice crystal ingestion. The tool will be capable of modeling the effects of ice build up as well as its effect on engine performance. Perform a parametric study of an engine with simulated ice blockage effects at altitude conditions. Using the tool, estimate the effect of blockage in the low pressure compressor due to ice buildup (accretion), and its effects on engine performance.

  12. A comparison of heterogeneous ice nucleation parameterizations using a parcel model framework

    Microsoft Academic Search

    Trude Eidhammer; Paul J. DeMott; Sonia M. Kreidenweis

    2009-01-01

    A liquid-phase Lagrangian parcel model was expanded to include nucleation and growth of ice crystals. Intercomparisons between three heterogeneous ice nucleation parameterizations that link aerosol type and number to ice crystal concentration were conducted. Results indicate large differences in the prediction of ice formation in modestly supercooled clouds and in the susceptibility of cirrus to heterogeneous ice nucleation for the

  13. DIFFRACTION STUDIES OF ICE Alexe BOSAK

    E-print Network

    Titov, Anatoly

    as a seed crystal, and causes the solidification of the entire body of water which quickly crystallizes as ice-nine [K. Vonnegut, Cat's Cradle] #12;Phase diagram of water #12;Phase diagram of water Here we are

  14. Ice/hydrohalite crystallization structures in sub-eutectic freezing experiments in the system NaCl-H20 and possible implications for the properties of frozen brines in Europa: A preliminary report

    NASA Astrophysics Data System (ADS)

    Rieck, K.; Kirby, S. H.; Stern, L. A.

    2005-12-01

    Sulfates are likely to be the most abundant solutes in the subsurface Europan liquid ocean. NaCl may also be a significant component of such liquids based on the compositions of stony meteorites like those thought to be among the source materials for the silicates in Europa's interior. The system NaCl-H20 exhibits a eutectic at -20.8°C and 23.3 weight percent NaCl between ice Ih and hydrohalite (NaCl.2H20). This low eutectic temperature compared to Mg and Na sulfate hydrate/ice eutectics indicates that hydrohalite should be among the last salts to crystallize in brine upwellings along rifts and other places where resurfacing by melt extrusion occurs on Europa. We conducted a suite of freezing experiments on NaCl brines with 20.3, 23.3, and 26.6 (saturated) weight percent NaCl by holding these liquids at a few degrees below the eutectic temperature. These runs produced ice-rich, eutectic and hydrohalite-rich aggregates of both phases, respectively, as confirmed by cryogenic x-ray diffraction and x-ray fluorescence spectroscopy. Based on direct observations of crystals forming at the tops and bottoms of the sample chambers and on refractive index measurements of subsequently melted sample material, marked fractional crystallization and segregation by density of ice, hydrohalite, and residual liquids occurred in the 20.3 and 26.6% samples and less so in for the eutectic composition. Crystallization of very fine grained eutectic intergrowths was recognized in cryogenic SEM images of all these samples and they were especially prominent in samples frozen from saturated brine. These samples were very difficult to cleave compared to pure polycrystalline ice, and hence are likely to have high fracture toughness. Direct measurements of this property and also the effects of partial melting on ductile flow rates are planned on such samples. Refracturing of such regions of fine eutectoid ice/hydrohalite intergrowths is likely to be inhibited in refrozen rifts compared to more ice-rich regions on Europa.

  15. Influence of ice crystal shape on retrieval of cirrus optical thickness and effective radius: A case study

    Microsoft Academic Search

    H. Eichler; A. Ehrlich; M. Wendisch; G. Mioche; J.-F. Gayet; M. Wirth; C. Emde; A. Minikin

    2009-01-01

    Airborne measurements of spectral upwelling radiances (350–2200 nm) reflected by cirrus using the Spectral Modular Airborne Radiation measurement sysTem (SMART)-Albedometer were made over land and water surfaces. Based on these data, cloud optical thickness ? and effective radius Reff of the observed cirrus were retrieved. By using different crystal shape assumptions (hexagonal plates, solid and hollow columns, rough aggregates, planar

  16. Creep and friction of ice.

    PubMed

    Tabor, D; Walker, J C

    1970-10-10

    The creep of polycrystalline ice in uniaxial compression has been studied over a very wide range of strain rates. The creep is far too slow to explain the friction of ice observed at very low sliding speeds, but experiments with single crystals show that sliding produces recrystallization at the interface, the ice presenting an orientation favourable to easy glide in directions tangential to the interface. PMID:16058445

  17. A New Parameterisation of Frazil and Grease Ice Formation in a Climate Sea Ice Model

    NASA Astrophysics Data System (ADS)

    Feltham, D. L.; Heorton, H. D.; Wilchinsky, A. V.

    2014-12-01

    An idealised model describing frazil ice formation in the ocean mixed layer beneath a lead in the sea ice cover is developed and incorporated into the sea ice climate model CICE. The frazil ice model assumes a steady state formation of single size frazil ice crystals. The crystals are uniformly distributed under the lead over the mixed layer depth and the lead width. The basic processes affecting the frazil ice mass balance is the rate of frazil ice formation due to the heat loss from the open water to the atmosphere, advection of heat and frazil ice volume into the lead from the water under sea ice, and precipitation of frazil ice crystals to the ocean surface and formation of grease ice. The grease ice is pushed against one of the lead edges by wind and water drag keeping the lead open. The frazil ice model is incorporated into CICE and used to simulate the sea ice state in the Arctic Basin and Southern Ocean.In contrast to the original frazil ice treatment in CICE which produces sea ice with only around 10% frazil ice fraction, the new model produces of order of 50% of frazil-derived sea ice, which corresponds better to observations. While the original model can be re-tuned in order to produce a similar average fraction of frazil ice by having a frazil collection thickness of 30 cm in the Antarctic and 5 cm in the Arctic, the new model's collection thickness is dynamically calculated, allowing for a larger collection thickness in large leads whereas the old model assumes it to be equal for wide and narrow leads. The new model keeps leads open for a longer period thus increasing the period of frazil ice formation. This is particularly important in the central Arctic where the new model's increased frazil ice production results in sea ice 0.5 m thicker than in the old model.

  18. Ice nucleation on soot particles

    Microsoft Academic Search

    B Gorbunov; A Baklanov; N Kakutkina; H. L Windsor; R Toumi

    2001-01-01

    The ice-forming activity of soot particles of various sizes has been studied in a cloud chamber under temperatures ranging from ?5 to ?20°C. It was found that the fraction of aerosol particles forming ice crystals was influenced by the temperature, the mean radius of aerosol particles and the degree of oxidising of the soot particle surface. It was suggested that

  19. A Reanalyis of the Contribution of Meteoric Ice, Flooding and Snow Ice Formation to the Mass Balance of Antarctic Sea Ice

    Microsoft Academic Search

    T. Maksym; M. Jeffries

    2003-01-01

    Sea ice core data from five autumn to early spring cruises in the Ross, Amundsen, and Bellingshausen Seas from 1993 to 1998 are reanalyzed to determine the role of meteoric ice, flooding and snow ice formation in the mass balance of Antarctic Sea Ice. Previous analysis of crystal texture and oxygen isotope data have determined that 15% to 38% of

  20. Chemical characterization of individual particles and residuals of cloud droplets and ice crystals collected on board research aircraft in the ISDAC 2008 study

    NASA Astrophysics Data System (ADS)

    Hiranuma, N.; Brooks, S. D.; Moffet, R. C.; Glen, A.; Laskin, A.; Gilles, M. K.; Liu, P.; MacDonald, A. M.; Strapp, J. W.; McFarquhar, G. M.

    2013-06-01

    Ambient particles and the dry residuals of mixed-phase cloud droplets and ice crystals were collected during the Indirect and Semi-Direct Aerosol Campaign (ISDAC) near Barrow, Alaska, in spring of 2008. The collected particles were analyzed using Computer Controlled Scanning Electron Microscopy with Energy Dispersive X-ray analysis and Scanning Transmission X-ray Microscopy coupled with Near Edge X-ray Absorption Fine Structure spectroscopy to identify physico-chemical properties that differentiate cloud-nucleating particles from the total aerosol population. A wide range of individually mixed components was identified in the ambient particles and residuals including organic carbon compounds, inorganics, carbonates, and black carbon. Our results show that cloud droplet residuals differ from the ambient particles in both size and composition, suggesting that both properties may impact the cloud-nucleating ability of aerosols in mixed-phase clouds. The percentage of residual particles which contained carbonates (47%) was almost four times higher than those in ambient samples. Residual populations were also enhanced in sea salt and black carbon and reduced in organic compounds relative to the ambient particles. Further, our measurements suggest that chemical processing of aerosols may improve their cloud-nucleating ability. Comparison of results for various time periods within ISDAC suggests that the number and composition of cloud-nucleating particles over Alaska can be influenced by episodic events bringing aerosols from both the local vicinity and as far away as Siberia.

  1. A direct evidence of vibrationally delocalized response at ice surface

    SciTech Connect

    Ishiyama, Tatsuya; Morita, Akihiro, E-mail: morita@m.tohoku.ac.jp [Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578 (Japan)

    2014-11-14

    Surface-specific vibrational spectroscopic responses at isotope diluted ice and amorphous ice are investigated by molecular dynamics (MD) simulations combined with quantum mechanics/molecular mechanics calculations. The intense response specific to the ordinary crystal ice surface is predicted to be significantly suppressed in the isotopically diluted and amorphous ices, demonstrating the vibrational delocalization at the ordinary ice surface. The collective vibration at the ice surface is also analyzed with varying temperature by the MD simulation.

  2. A direct evidence of vibrationally delocalized response at ice surface

    NASA Astrophysics Data System (ADS)

    Ishiyama, Tatsuya; Morita, Akihiro

    2014-11-01

    Surface-specific vibrational spectroscopic responses at isotope diluted ice and amorphous ice are investigated by molecular dynamics (MD) simulations combined with quantum mechanics/molecular mechanics calculations. The intense response specific to the ordinary crystal ice surface is predicted to be significantly suppressed in the isotopically diluted and amorphous ices, demonstrating the vibrational delocalization at the ordinary ice surface. The collective vibration at the ice surface is also analyzed with varying temperature by the MD simulation.

  3. A direct evidence of vibrationally delocalized response at ice surface.

    PubMed

    Ishiyama, Tatsuya; Morita, Akihiro

    2014-11-14

    Surface-specific vibrational spectroscopic responses at isotope diluted ice and amorphous ice are investigated by molecular dynamics (MD) simulations combined with quantum mechanics/molecular mechanics calculations. The intense response specific to the ordinary crystal ice surface is predicted to be significantly suppressed in the isotopically diluted and amorphous ices, demonstrating the vibrational delocalization at the ordinary ice surface. The collective vibration at the ice surface is also analyzed with varying temperature by the MD simulation. PMID:25399168

  4. Overview of Icing Research at NASA Glenn

    NASA Technical Reports Server (NTRS)

    Kreeger, Richard E.

    2013-01-01

    The aviation industry continues to deal with icing-related incidents and accidents on a regular basis. Air traffic continues to increase, placing more aircraft in adverse icing conditions more frequently and for longer periods. Icing conditions once considered rare or of little consequence, such as super-cooled large droplet icing or high altitude ice crystals, have emerged as major concerns for modern aviation. Because of this, there is a need to better understand the atmospheric environment, the fundamental mechanisms and characteristics of ice growth, and the aerodynamic effects due to icing, as well as how best to protect these aircraft. The icing branch at NASA Glenn continues to develop icing simulation methods and engineering tools to address current aviation safety issues in airframe, engine and rotorcraft icing.

  5. Ice Slurry Formation in a Cocurrent Liquid-Liquid Flow

    Microsoft Academic Search

    Zhengbiao PENG; Zhulin YUAN; Kunfeng LIANG; Jie CAI

    2008-01-01

    A new technique for ice slurry production was explored. Multiple small water-drops were formed in another immiscible chilled liquid by a single-nozzled atomizer and frozen in the fluidized bed by direct contact heat transfer. Experiments were conducted to investigate the dynamic behaviors of the ice crystal making system. The results demonstrate that the ice crystals could be produced continuously and

  6. Evaluation of NCAR Ice Nucleus Counter. Part I: Basic Operation

    Microsoft Academic Search

    G. Langer

    1973-01-01

    A detailed examination was made of the variables affecting the operation of the National Center for Atmospheric Research (NCAR) ice nucleus counter. The design criteria for proper flow control to achieve consistent cloud formation were established. The loss of ice crystals by settling to the bottom of the cloud chamber instead of exiting to the ice crystal counter was found

  7. Pressure melting of ice

    Microsoft Academic Search

    Thomas A. Weber; Frank H. Stillinger

    1984-01-01

    A 250-molecule ice Ih crystallite has been melted at a pressure of about 2 kbars using molecular dynamics computer simulation. The ST2 potential has been used to represent molecular interactions. Melting was observed to begin at the crystallite surface and to proceed inward until the entire crystal was converted to an amorphous droplet. The melting point was found to be

  8. Diffuse scattering in Ih ice.

    PubMed

    Wehinger, Björn; Chernyshov, Dmitry; Krisch, Michael; Bulat, Sergey; Ezhov, Victor; Bosak, Alexeï

    2014-07-01

    Single crystals of ice Ih, extracted from the subglacial Lake Vostok accretion ice layer (3621 m depth) were investigated by means of diffuse x-ray scattering and inelastic x-ray scattering. The diffuse scattering was identified as mainly inelastic and rationalized in the frame of ab initio calculations for the ordered ice XI approximant. Together with Monte-Carlo modelling, our data allowed reconsidering previously available neutron diffuse scattering data of heavy ice as the sum of thermal diffuse scattering and static disorder contribution. PMID:24912550

  9. Ice Sheets

    NSDL National Science Digital Library

    This educational brief describes the nature and properties of the Greenland and Antarctica ice sheets. Topics include the thickness and aereal extent of the ice sheets, volume of water contained in them, mass balance, and the mechanisms by which ice is lost from or accumulated by the ice sheets.

  10. The Development of Measurement Techniques to Identify and Characterize Dusts and Ice Nuclei in the Atmosphere

    E-print Network

    Glen, Andrew

    2014-01-15

    Mineral dusts and ice crystals directly influence the Earth's radiative budget through radiative scattering and absorption. The interaction of spherical particles on the radiative budget are well known, however mineral dusts and ice crystals...

  11. crystals

    NASA Astrophysics Data System (ADS)

    Badalyan, A.; Hovsepyan, R.; Mantashyan, P.; Mekhitaryan, V.; Drampyan, R.

    2014-07-01

    A novel combined interferometric-mask method for the formation of micro- and nanometric scale three-dimensional (3D) rotational symmetry quasi-crystalline refractive lattice structures in photorefractive materials is demonstrated experimentally. The method is based on micrometric scale spatial modulation of the light by amplitude mask in the radial directions and along the azimuthal angle and the use of counter-propagating beam geometry building up Gaussian standing wave, which defines the light modulation in the axial direction with half-wavelength periodicity. 3D intensity pattern can be represented as numerous mask-generated 2D quasi-periodic structures located in each anti-node of the standing wave. The formed 3D intensity distributions of the optical beams can be imparted into the photorefractive medium thus creating the micro- and sub-micrometric scale 3D refractive index volume lattices. The used optical scheme allows also the formation of 2D lattices by removing the back-reflecting mirror. 2D and 3D refractive lattices were recorded with the use of 532 nm laser beam and rotational symmetry mask in doped lithium niobate crystals and were tested by the probe beam far-field diffraction pattern imaging and direct observation by phase microscope. The formed rotational symmetry 3D refractive structures have the periods of 20-60 ?m in the radial directions, 60 ?m along the azimuthal angle and half-wavelength 266 nm in the axial direction.

  12. SCM Simulations of Tropical Ice Clouds Using Observationally Based Parameterizations of Microphysics

    Microsoft Academic Search

    Greg M. McFarquhar; Sam Iacobellis; Richard C. J. Somerville

    2003-01-01

    ABSTRACT A new bulk parameterization of the dependence,of ice cloud effective radius (re) on ice water content (IWC) is developed,using in situ observations of the size and shape of ice crystals in tropical anvils. This work extends previous parameterizations because information about the number, size, and shape of ice crystals with diameters smaller than 100 mm is included and in

  13. The Influence of Platelet Ice and Snow on Antarctic Land-fast Sea Ice

    NASA Astrophysics Data System (ADS)

    Hoppmann, M.; Nicolaus, M.

    2011-12-01

    Sea ice fastened to coasts, icebergs and ice shelves is of crucial importance for climate- and ecosystems. Near Antarctic ice shelves, this land-fast sea ice exhibits two unique characteristics that distinguish it from most other sea ice: a sub-ice layer of ice platelets and a highly stratified and thick snow cover. Ice platelets are flat, plate-like ice crystals forming and growing in a layer of super-cooled water which originates from ice shelf cavities. During growth, heat is lost to the super-cooled ocean rather than conducted to the atmosphere. The crystals accumulate beneath the solid sea-ice cover, forming a layer of loose platelets and eventually becoming incorporated into the sea-ice fabric as platelet ice. Considering the fact that the amount of platelet ice contributes between 10 and 60% to the mass of the land-fast sea ice around Antarctica, very little is known about its spatial and temporal variability. A thick and partly multi-year snow cover develops on top of the Antarctic fast ice, ultimately altering the sea-ice surface and affecting the sea-ice thermodynamics and mass balance. It typically leads to snow-ice formation, surface flooding, and the development of superimposed ice from snow melt water. In order to investigate the role of platelet ice and snow for Antarctic fast ice, we have initiated a regular observation program on the land-fast sea ice of Atka Bay as part of the international Antarctic Fast Ice Network (AFIN). We performed manual measurements of sea-ice and snow thicknesses from June to December 2010 and 2011. Additionally, a mass balance buoy and an automatic weather station were deployed in 2011 and ice cores were taken. Our measurements will reveal insight into the spatial and temporal variability of sea-ice and snow thickness distributions on Atka Bay fast ice. First results show that sea-ice thickness is lowest in the eastern part of the Bay, where a thick snow cover leads to extensive surface flooding. In the West, dynamic conditions lead to high thickness and high local variability. Ice platelets were observed regularly in the boreholes, but measurement techniques have to be improved to assess the thickness of the platelet layer.

  14. J. Non-Newtonian Fluid Mech. 134 (2006) 3343 Flow-induced anisotropy in polar ice and related

    E-print Network

    Gagliardini, Olivier

    2006-01-01

    ice crystallizes in the hexagonal system (ice Ih). The viscoplastic deformation of the ice Ih single to the hexagonal symmetry axis, called the c-axis [1]. As a consequence, ice Ih is one of the most anisotropicJ. Non-Newtonian Fluid Mech. 134 (2006) 33­43 Flow-induced anisotropy in polar ice and related ice

  15. PSL Icing Facility Upgrade Overview

    NASA Technical Reports Server (NTRS)

    Griffin, Thomas A.; Dicki, Dennis J.; Lizanich, Paul J.

    2014-01-01

    The NASA Glenn Research Center Propulsion Systems Lab (PSL) was recently upgraded to perform engine inlet ice crystal testing in an altitude environment. The system installed 10 spray bars in the inlet plenum for ice crystal generation using 222 spray nozzles. As an altitude test chamber, the PSL is capable of simulating icing events at altitude in a groundtest facility. The system was designed to operate at altitudes from 4,000 to 40,000 ft at Mach numbers up to 0.8M and inlet total temperatures from -60 to +15 degF. This paper and presentation will be part of a series of presentations on PSL Icing and will cover the development of the icing capability through design, developmental testing, installation, initial calibration, and validation engine testing. Information will be presented on the design criteria and process, spray bar developmental testing at Cox and Co., system capabilities, and initial calibration and engine validation test. The PSL icing system was designed to provide NASA and the icing community with a facility that could be used for research studies of engine icing by duplicating in-flight events in a controlled ground-test facility. With the system and the altitude chamber we can produce flight conditions and cloud environments to simulate those encountered in flight. The icing system can be controlled to set various cloud uniformities, droplet median volumetric diameter (MVD), and icing water content (IWC) through a wide variety of conditions. The PSL chamber can set altitudes, Mach numbers, and temperatures of interest to the icing community and also has the instrumentation capability of measuring engine performance during icing testing. PSL last year completed the calibration and initial engine validation of the facility utilizing a Honeywell ALF502-R5 engine and has duplicated in-flight roll back conditions experienced during flight testing. This paper will summarize the modifications and buildup of the facility to accomplish these tests.

  16. Basal ice facies and supraglacial melt-out till of the Laurentide Ice Sheet, Tuktoyaktuk Coastlands, western Arctic Canada

    NASA Astrophysics Data System (ADS)

    Murton, J. B.; Whiteman, C. A.; Waller, R. I.; Pollard, W. H.; Clark, I. D.; Dallimore, S. R.

    2005-03-01

    Glacially-deformed massive ice and icy sediments (MI-IS) in the Eskimo Lakes Fingerlands and Summer Island area of the Tuktoyaktuk Coastlands, western Arctic Canada, show, in the same stratigraphic sequences, features characteristic of both basal glacier ice and intrasedimental ice. Basal-ice features comprise (1) ice facies and facies groupings similar to those from the basal ice layers of contemporary glaciers and ice sheets in Alaska, Greenland and Iceland; (2) ice crystal fabrics similar to those from basal ice in Antarctica and ice-cored moraines on Axel Heiberg Island, Canada; and (3) a thaw or erosional unconformity along the top of the MI-IS, buried by glacigenic or aeolian sediments. Intrasedimental ice consists of pore ice and segregated ice formed within Pleistocene sands deposited before glacial overriding. The co-existence of basal and intrasedimental ice within the MI-IS records their occurrence within the basal ice layer of the Laurentide Ice Sheet. Stagnation of the ice sheet and melt-out of till from the ice surface allowed burial and preservation of the basal ice layer on a regional scale. The widespread occurrence of supraglacial melt-out till with clast fabrics similar to those in the underlying ice suggests that such till can be well preserved during partial thaw of a continental ice sheet in lowlands underlain by continuous permafrost.

  17. Food Crystalization and Eggs

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Food Crystalization and Eggs Deana R. Jones, Ph.D. USDA Agricultural Research Service Egg Safety and Quality Research Unit Athens, Georgia, USA Deana.Jones@ars.usda.gov Sugar, salt, lactose, tartaric acid and ice are examples of constituents than can crystallize in foods. Crystallization in a foo...

  18. Mixed Phase Modeling in GlennICE with Application to Engine Icing

    NASA Technical Reports Server (NTRS)

    Wright, William B.; Jorgenson, Philip C. E.; Veres, Joseph P.

    2011-01-01

    A capability for modeling ice crystals and mixed phase icing has been added to GlennICE. Modifications have been made to the particle trajectory algorithm and energy balance to model this behavior. This capability has been added as part of a larger effort to model ice crystal ingestion in aircraft engines. Comparisons have been made to four mixed phase ice accretions performed in the Cox icing tunnel in order to calibrate an ice erosion model. A sample ice ingestion case was performed using the Energy Efficient Engine (E3) model in order to illustrate current capabilities. Engine performance characteristics were supplied using the Numerical Propulsion System Simulation (NPSS) model for this test case.

  19. Finite-difference time domain method for light scattering by small ice

    E-print Network

    Liou, K. N.

    Finite-difference time domain method for light scattering by small ice crystals in three for the solution of light scattering by nonspherical particles has been developed for small ice crystals the scattering of light by hexagonal ice crystals.7­10 However, the geometric optics approxima- tion is valid

  20. Sea Ice, an Antarctic Habitat

    NSDL National Science Digital Library

    A 'click-and-learn' sub site hosted by the Alfred Wegener Institute Foundation for Polar and Marine Research (AWI), this is a succinct, educational tour of sea-ice and its associated ecological communities. Short synopses introduce the dynamics of sea-ice formation, the microstructure of sea-ice (including crystal structure, brine channels, and ice algae), the effects of ice melt on resident organisms, the logistics of sea-ice research, and _land fast-ice_ and platelet ice habitats. Introductions also exist for the following organisms: krill; whales (i.e., Orcas, southern bottlenosesd dolphins, minke whales); sea birds (i.e., skuas and snow petrals), penguins (i.e., emperor, adelie, and chinstraps), and seals (i.e., weddell, crabeater, leopard, and ross.) Enlargeable thumbnail images accompany the habitat and inhabitant descriptions. Further investigations (at an accelerated level) are prompted with the inclusion of bibliographic references and scientific research presentations (in PDF format) on fast-ice and platelet ice, as well as links to the main site for the AWI.

  1. Optical Properties of Ice Particles in Young Contrails

    NASA Technical Reports Server (NTRS)

    Hong, Gang; Feng, Qian; Yang, Ping; Kattawar, George; Minnis, Patrick; Hu, Yong X.

    2008-01-01

    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 micrometers using Mie codes from coated spheres. The four types of ice crystals have distinct differences in their single-scattering properties because of the embedded black carbon. 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 degrees using a vector radiative transfer model based on the adding-doubling technique. The Stokes parameters at a wavelength of 0.65 micrometers show pronounced differences for the four types of ice crystals. Those at a wavelength of 2.13 micrometers show similar variations with the viewing zenith angle and relative azimuth angle, but their values are noticeably different.

  2. Extreme Ice

    NSDL National Science Digital Library

    Margy Kuntz

    This activity students through the ways scientists monitor changes in Earth's glaciers, ice caps, and ice sheets. Students investigate about glacier locations, glacial movement, and impacts of climate change on glaciers depending on the depth of research. It is linked to 2009 PBS Nova program entitled Extreme Ice.

  3. Ice Ages

    NSDL National Science Digital Library

    During most of the last one billion years the globe had no permanent ice. However, sometimes large areas of the globe were covered with vast ice sheets. Users can read and view pictures which help explain what ice ages are, when they occurred, and why they occur. This site, sponsored by the Illinois State Museum, has links to web pages on paleontology of the midwestern United States during the last ice age and to an animation showing the advance and retreat of the ice sheet in North America 20,000 years ago.

  4. Ice Flows

    NSDL National Science Digital Library

    This is a lesson about how and why ice flows, especially in a large mass such as a glacier. Learners will experience the qualities of viscoelastic materials and view videos of glacial ice flows. They will observe ice flows and materials other than ice flowing differently under stress, and will investigate landscape changes as a result of large scale glacial movement. Activities include small group miming, speaking, drawing, and/or writing. This is lesson 5 of 12 in the unit, Exploring Ice in the Solar System.

  5. Ice Nuclei Production in Volcanic Clouds

    NASA Astrophysics Data System (ADS)

    Few, A. A.

    2012-12-01

    The paper [Durant et al., 2008] includes a review of research on ice nucleation in explosive volcanic clouds in addition to reporting their own research on laboratory measurements focused on single-particle ice nucleation. Their research as well as the research they reviewed were concerned with the freezing of supercooled water drops (250 to 260 K) by volcanic ash particles acting as ice freezing nuclei. Among their conclusions are: Fine volcanic ash particles are very efficient ice freezing nuclei. Volcanic clouds likely contain fine ash concentrations 104 to 105 times greater than found in meteorological clouds. This overabundance of ice nuclei will produce a cloud with many small ice crystals that will not grow larger as they do in meteorological clouds because the cloud water content is widely distributed among the numerous small ice crystals. The small ice crystals have a small fall velocity, thus volcanic clouds are very stable. The small ice crystals are easily lofted into the stratosphere transporting water and adsorbed trace gasses. In this paper we examine the mechanism for the production of the small ice nuclei and develop a simple model for calculating the size of the ice nuclei based upon the distribution of magma around imbedded bubbles. We also have acquired a volcanic bomb that exhibits bubble remnants on its entire surface. The naturally occurring fragments from the volcanic bomb reveal a size distribution consistent with that predicted by the simple model. Durant, A. J., R. A. Shaw, W. I. Rose, Y. Mi, and G. G. J. Ernst (2008), Ice nucleation and overseeding of ice in volcanic clouds, J. Geophys. Res., 113, D09206, doi:10.1029/2007JD009064.

  6. The phase diagram of the water-hydrogen system in the crystallization field of solid solutions based on ices Ih and II at high pressures

    Microsoft Academic Search

    Yu. A. Dyadin; E. Ya. Aladko

    1994-01-01

    The decomposition curves of the solid solutions based on ices Ih (a-solutions) and II (ß-solutions) in the water-hydrogen system were studied by the DTA technique at pressures up to 7 kbar. The a-solution is destabilized by pressure but to a lesser degree than ice Ih and is stable up to 2.3 kbar. Theß-solution is stabilized by pressure and at 7

  7. Sea ice terminology

    SciTech Connect

    Not Available

    1980-09-01

    A group of definitions of terms related to sea ice is presented, as well as a graphic representation of late winter ice zonation of the Beaufort Sea Coast. Terms included in the definition list are belt, bergy bit, bight, brash ice, calving, close pack ice, compacting, compact pack ice, concentration, consolidated pack ice, crack, diffuse ice edge, fast ice, fast-ice boundary, fast-ice edge, first-year ice, flaw, flaw lead, floe, flooded ice, fractured, fractured zone, fracturing, glacier, grey ice, grey-white ice, growler, hummock, iceberg, iceberg tongue, ice blink, ice boundary, ice cake, ice edge, ice foot, ice free, ice island, ice shelf, large fracture, lead, medium fracture, multiyear ice, nilas, old ice, open pack ice, open water, pack ice, polar ice, polynya, puddle, rafted ice, rafting, ram, ridge, rotten ice, second-year ice, shearing, shore lead, shore polynya, small fracture, strip, tabular berg, thaw holes, very close pack ice, very open pack ice, water sky, young coastal ice, and young ice.

  8. Oily Ice

    NSDL National Science Digital Library

    Mission Science Workshop

    2013-01-01

    In this activity, learners experiment with the density of ice, water, and oil. Learners will discover that the density of a liquid determines whether it will float above or sink below another liquid. Learners will be surprised to find that ice floats and water sinks in oil, even though ice and water are made of the same thing. Learners will also examine the hydrophilic properties of water and the hydrophobic nature of oil.

  9. Sea Ice

    NASA Technical Reports Server (NTRS)

    Perovich, D.; Gerland, S.; Hendricks, S.; Meier, Walter N.; Nicolaus, M.; Richter-Menge, J.; Tschudi, M.

    2013-01-01

    During 2013, Arctic sea ice extent remained well below normal, but the September 2013 minimum extent was substantially higher than the record-breaking minimum in 2012. Nonetheless, the minimum was still much lower than normal and the long-term trend Arctic September extent is -13.7 per decade relative to the 1981-2010 average. The less extreme conditions this year compared to 2012 were due to cooler temperatures and wind patterns that favored retention of ice through the summer. Sea ice thickness and volume remained near record-low levels, though indications are of slightly thicker ice compared to the record low of 2012.

  10. Climate Impacts of Ice Nucleation

    NASA Technical Reports Server (NTRS)

    Gettelman, Andrew; Liu, Xiaohong; Barahona, Donifan; Lohmann, Ulrike; Chen, Celia

    2012-01-01

    Several different ice nucleation parameterizations in two different General Circulation Models (GCMs) are used to understand the effects of ice nucleation on the mean climate state, and the Aerosol Indirect Effects (AIE) of cirrus clouds on climate. Simulations have a range of ice microphysical states that are consistent with the spread of observations, but many simulations have higher present-day ice crystal number concentrations than in-situ observations. These different states result from different parameterizations of ice cloud nucleation processes, and feature different balances of homogeneous and heterogeneous nucleation. Black carbon aerosols have a small (0.06 Wm(exp-2) and not statistically significant AIE when included as ice nuclei, for nucleation efficiencies within the range of laboratory measurements. Indirect effects of anthropogenic aerosols on cirrus clouds occur as a consequence of increasing anthropogenic sulfur emissions with different mechanisms important in different models. In one model this is due to increases in homogeneous nucleation fraction, and in the other due to increases in heterogeneous nucleation with coated dust. The magnitude of the effect is the same however. The resulting ice AIE does not seem strongly dependent on the balance between homogeneous and heterogeneous ice nucleation. Regional effects can reach several Wm2. Indirect effects are slightly larger for those states with less homogeneous nucleation and lower ice number concentration in the base state. The total ice AIE is estimated at 0.27 +/- 0.10 Wm(exp-2) (1 sigma uncertainty). This represents a 20% offset of the simulated total shortwave AIE for ice and liquid clouds of 1.6 Wm(sup-2).

  11. A new horizontal gradient, continuous flow, ice thermal diffusion chamber

    Microsoft Academic Search

    E. M. Tomlinson; N. Fukuta

    1985-01-01

    A continuous-flow, horizontal gradient, ice thermal diffusion chamber has been developed and tested for heterogeneous ice nucleation of aerosol particles under accurately controlled supersaturations and supercooling in the absence of a substrate. The chamber consists of preprocessing, main, and crystal settling sections. In the preprocessing and main sections, top and bottom plates are coated with clear, smooth ice by a

  12. Ice Floats

    NSDL National Science Digital Library

    2012-08-03

    This is a lesson about displacement, buoyancy, and density. Learners will understand why ice floats. Includes background information, teacher notes, assessment criteria, and related resources; activities are differentiated for Pre-K-grade 2 and grades 3-5. This is lesson 4 of the unit Exploring Ice in the Solar System.

  13. Surface Studies of Ice

    NASA Astrophysics Data System (ADS)

    Wang, Enge

    2014-03-01

    Despite ice being a ubiquitous and well-studied substance, it is surprising that some basic questions about its surface properties are still debated. Here computer simulations are used to study the unusual structure and dynamics of ice surface at atomic scale. An order parameter, which defines the ice surface energy, is identified for the first time. A classical electrostatic model proves useful to explain the physics inside. We predict that the proton order-disorder transition, which occurs in the bulk at ~ 72 K, will not occur at the surface at any temperature below surface melting. In addition, we find that the surface of crystalline ice exhibits a remarkable variance in vacancy formation energies that is more characteristic of an amorphous material. A fraction of surface molecules are bound by less than the strength of a single hydrogen bond, yet other sites are more strongly bound than those in the crystal interior. Vacancy energies are found to be as low as ~ 0.1eV at the surface, leading to a higher than expected concentration of vacancies at the external layer. Once a surface vacancy is formed, the energetic cost of forming neighbouring vacancies is greatly reduced, facilitating pits on the surface and other processes that may contribute to the phenomenon of pre-melting and quasi-liquid layer formation. Finally, we show that the distribution of local arrangement of dangling atoms, characterized by a surface proton order parameter, is also of crucial importance for the adsorption of water monomer on ice surface. The positive correlation of adsorption energy of water monomer with surface proton ordering suggests that the adsorption may prefer to firstly occur in the inhomogeneous surface, which sheds light on our understanding of the ice nucleation and growth as well as other physical/chemical reactivity in high altitude clouds. This work was supported by NSF and MOST of China.

  14. Population balance and computational fluid dynamics modelling of ice crystallisation in a scraped surface freezer

    Microsoft Academic Search

    Guoping Lian; Steve Moore; Luke Heeney

    2006-01-01

    Ice crystallisation in a scraped surface freezer is exceedingly complex and there is very limited fundamental understanding of the influences of fluid flow and heat transfer on ice crystal size, number and shape. This paper presents a computer modelling study that combines population balance method and computational fluid dynamics method. Ice crystal nucleation and growth kinetics has been described by

  15. Study of Ice Cloud Properties from Synergetic Use of Satellite Observations and Modeling Capabilities 

    E-print Network

    Xie, Yu

    2011-02-22

    in comparison with the case of bubble-free ice crystals. Cloud reflectance look-up tables were generated at the wavelengths of 0.65 ?m and 2.13 ?m to examine the impact of accounting for air bubbles in ice crystal morphology on the retrieval of ice cloud optical...

  16. JOURNAL OF GEOPHYSICAL RESEARCH, VOL. ???, XXXX, DOI:10.1029/, Frazil Deposition Under Growing Sea Ice

    E-print Network

    McGuinness, Mark

    - erates stirring sufficient to prevent frazil ice from attaching to the interface, forcing some of it to remain in suspension until ice growth rate and brine rejection slow to the point that frazil can stick the term frazil to refer to small ice crystals that drift in the water columns and display as crystals up

  17. The DC-8 Submillimeter-Wave Cloud Ice Radiometer

    NASA Technical Reports Server (NTRS)

    Walter, Steven; Batelaan, Paul; Siegel, Peter; Evans, K. Franklin; Evans, Aaron; Balachandra, Balu; Gannon, Jade; Guldalian, John; Raz, Guy; Shea, James; Smith, Christopher; Thomassen, John

    2000-01-01

    Submillimeter-wave cloud ice radiometry is an innovative technique for determining the amount of ice present in cirrus clouds, measuring median crystal size, and constraining crystal shape. The radiometer described in this poster is being developed to acquire data to validate radiometric retrievals of cloud ice at submillimeter wavelengths. The goal of this effort is to develop a technique to enable spaceborne characterization of cirrus, meeting key climate modeling and NASA measurement needs.

  18. Laboratory study of frazil ice accumulation under wave conditions

    NASA Astrophysics Data System (ADS)

    de La Rosa, S.; Maus, S.

    2011-07-01

    Ice growth in turbulent seawater is often accompanied by the accumulation of frazil ice crystals at its surface. The thickness and volume fraction of this ice layer play an important role in shaping the gradual transition from a loose to a solid ice cover, however, observations are very sparse. Here we analyse an extensive set of observations of frazil ice, grown in two parallel tanks with controlled wave conditions and thermal forcing, focusing on the first one to two days of grease ice accumulation. The following unresolved issues are addressed: (i) at which volume fraction the frazil crystal rising process starts and how densely they accumulate at the surface, (ii) how the grease ice solid fraction evolves with time until solid ice starts to form and (iii) how do these conditions affect, and are affected by, waves and heat loss from the ice. We obtained estimates of the initial frazil ice solid fraction (0.04-0.05), the maximum solid fraction to which it accumulates (0.24-0.28), as well as the time-scale of packing, at which 95 % of the frazil reaches the maximum solid fraction (12-18 h). Comparison of ice thickness and wave observations also indicates that grease ice first begins to affect the wave field significantly when its thickness exceeds the initial wave amplitude. These results are relevant for modelling frazil ice accumulation and freeze-up of leads, polynyas and the seasonal ice zone.

  19. Ice nucleation inhibition: mechanism of antifreeze by antifreeze protein.

    PubMed

    Du, Ning; Liu, Xiang Y; Hew, Choy Leong

    2003-09-19

    The effect of antifreeze protein type III (one type of fish antifreeze protein) on ice crystallization was examined quantitatively based on a "micro-sized ice nucleation" technique. It was found for the first time that antifreeze proteins can inhibit the ice nucleation process by adsorbing onto both the surfaces of ice nuclei and dust particles. This leads to an increase of the ice nucleation barrier and the desolvation kink kinetics barrier, respectively. Based on the latest nucleation model, the increases in the ice nucleation barrier and the kink kinetics barrier were measured. This enables us to quantitatively examine the antifreeze mechanism of antifreeze proteins for the first time. PMID:12829706

  20. Effects of Birefringence Within Ice Sheets on Obliquely Propagating Radio Waves

    Microsoft Academic Search

    Kenichi Matsuoka; Larry Wilen; Shawn P. Hurley; Charles F. Raymond

    2009-01-01

    In this paper, effects of birefringence on radio waves obliquely propagating though polar ice sheets are examined to facilitate interpretations of bistatic and side-looking radar data. A formalism applicable for arbitrary radar configurations is developed to predict the returned power from within and beneath the ice sheets that have arbitrary alignments of ice crystals (ice fabrics). We applied this formalism

  1. Seismic anisotropy in ice: numerical modelling, ice core measurements and in-situ observations

    NASA Astrophysics Data System (ADS)

    Kendall, J. M.; Baird, A. F.; Walker, A.; Wookey, J. M.; Lloyd, G. E.; Stuart, G. W.; Harland, S.; Obbard, R. W.; Smith, A.; Brisbourne, A.

    2013-12-01

    The stress distribution and style of flow in ice produces elastic and rheological anisotropy, which informs ice flow modelling as to how ice masses respond to external changes such as global warming. Here observations of shear wave splitting from three-component icequake seismograms are used to characterise ice anisotropy in the Rutford ice stream, West Antarctica. Over 110 high quality measurements are made on 41 events recorded at five stations temporarily deployed near the ice stream grounding line. The magnitude of the splitting ranges from 2ms to 80ms and suggest a maximum of 6% shear wave splitting. The fast shear wave polarisation direction is roughly perpendicular to the ice flow direction. Motivated by these observations, we consider mechanisms for seismic anisotropy in ice using numerical modelling of the development of crystal preferred orientation of ice and measurement of crystal alignment in an ice core using electron back-scattered diffraction (EBSD). These results suggest transitions in the style of anisotropy both with depth and laterally within an ice stream. Seismic anisotropy is developed with increasing hydrostatic pressure producing a VTI fabric with a vertical alignment of c-axes (so-called cluster fabric). However, convergence in the ice flow and along-flow extension leads to girdles of c-axes (and an HTI fabric). Based on the Rutford shear-wave splitting observations we can rule out a cluster fabric as the sole cause of anisotropy - an HTI component is needed, which may be due extension in the direction of flow forming a girdle fabric or the alignment of cracks or ice-films in the plane perpendicular to the flow direction. Cumulatively, our observations suggest a combination of anisotropy mechanisms are at play in deforming ice sheets. We discuss seismic measurements that can be made to better discriminate between plausible mechanisms for our shear-wave splitting observations and how these different mechanisms may in turn alter ice flow and glacial response to external changes.

  2. Archimedean Ice

    E-print Network

    Kari Eloranta

    2009-09-22

    The striking boundary dependency (the Arctic Circle phenomenon) exhibited in the ice model on the square lattice extends to other planar set-ups. We present these findings for the triangular and the Kagome lattices. Critical connectivity results guarantee that ice configurations can be generated using the simplest and most efficient local actions. Height functions are utilized throughout the analysis. At the end there is a surprise in store: on the remaining Archimedean lattice for which the ice model can be defined, the 3.4.6.4. lattice, the long range behavior is completely different from the other cases.

  3. The dynamics of frazil ice formation in leads and its role in the mass balance of the sea ice pack.

    NASA Astrophysics Data System (ADS)

    Heorton, Harry; Feltham, Daniel

    2015-04-01

    Lead are cracks in sea ice that expose the ocean to the cold atmosphere resulting in the supercooling of the ocean and the formation of frazil ice crystals within the mixed layer. Here we present two studies of ice formation in leads: a single lead model focussing on frazil crystals of varying size within the vertical structure of the mixed layer; a new module explicitly describing frazil ice formation in leads incorporated into the Los Alamos sea ice model (CICE). Both studies consider the supercooling of the ocean, the concentration of frazil crystals within the ocean and their precipitation to the ocean surface as grease ice pushed against one of the lead edges by wind and water drag. The results from the single lead model show how the vertical structure of the mixed layer develops after the lead opens. Sensitivity studies reveal how changing wind speeds play the greatest role in the time taken to refreeze a lead. In the CICE model the new module slows down the refreezing of leads resulting in an longer period of frazil ice production when compared to the original model code. The fraction of frazil-derived sea ice increases from 10% to 50% with the inclusion of the new module. Ice formation rates are increased in areas of high ice concentration and thus has a greater impact within multiyear ice than in the marginal seas. The thickness of sea ice in the central Arctic increases by over 0.5 m whereas within the Antarctic it remains unchanged.

  4. SURVIVAL OF AMORPHOUS WATER ICE ON CENTAURS

    SciTech Connect

    Guilbert-Lepoutre, Aurelie, E-mail: aguilbert@ucla.edu [Department of Earth and Space Sciences, UCLA, Los Angeles, CA 90095 (United States)

    2012-10-01

    Centaurs are believed to be Kuiper Belt objects in transition between Jupiter and Neptune before possibly becoming Jupiter family comets. Some indirect observational evidence is consistent with the presence of amorphous water ice in Centaurs. Some of them also display a cometary activity, probably triggered by the crystallization of the amorphous water ice, as suggested by Jewitt and this work. Indeed, we investigate the survival of amorphous water ice against crystallization, using a fully three-dimensional thermal evolution model. Simulations are performed for varying heliocentric distances and obliquities. They suggest that crystallization can be triggered as far as 16 AU, though amorphous ice can survive beyond 10 AU. The phase transition is an efficient source of outgassing up to 10-12 AU, which is broadly consistent with the observations of the active Centaurs. The most extreme case is 167P/CINEOS, which barely crystallizes in our simulations. However, amorphous ice can be preserved inside Centaurs in many heliocentric distance-obliquity combinations, below a {approx}5-10 m crystallized crust. We also find that outgassing due to crystallization cannot be sustained for a time longer than 10{sup 4}-10{sup 4} years, leading to the hypothesis that active Centaurs might have recently suffered from orbital changes. This could be supported by both observations (although limited) and dynamical studies.

  5. Determination of Ice Cloud Models Using MODIS and MISR Data

    NASA Technical Reports Server (NTRS)

    Xie, Yu; Yang, Ping; Kattawar, George W.; Minnis, Patrick; Hu, Yongxiang; Wu, Dong L.

    2012-01-01

    Representation of ice clouds in radiative transfer simulations is subject to uncertainties associated with the shapes and sizes of ice crystals within cirrus clouds. In this study, we examined several ice cloud models consisting of smooth, roughened, homogeneous and inhomogeneous hexagonal ice crystals with various aspect ratios. The sensitivity of the bulk scattering properties and solar reflectances of cirrus clouds to specific ice cloud models is investigated using the improved geometric optics method (IGOM) and the discrete ordinates radiative transfer (DISORT) model. The ice crystal habit fractions in the ice cloud model may significantly affect the simulations of cloud reflectances. A new algorithm was developed to help determine an appropriate ice cloud model for application to the satellite-based retrieval of ice cloud properties. The ice cloud particle size retrieved from Moderate Resolution Imaging Spectroradiometer (MODIS) data, collocated with Multi-angle Imaging Spectroradiometer (MISR) observations, is used to infer the optical thicknesses of ice clouds for nine MISR viewing angles. The relative differences between view-dependent cloud optical thickness and the averaged value over the nine MISR viewing angles can vary from -0.5 to 0.5 and are used to evaluate the ice cloud models. In the case for 2 July 2009, the ice cloud model with mixed ice crystal habits is the best fit to the observations (the root mean square (RMS) error of cloud optical thickness reaches 0.365). This ice cloud model also produces consistent cloud property retrievals for the nine MISR viewing configurations within the measurement uncertainties.

  6. laser ultrasonic characterization of ice cores

    NASA Astrophysics Data System (ADS)

    van Wijk, K.; Otheim, L. T.; Marshall, H.; Kurbatov, A.; Spaulding, N. E.

    2013-12-01

    We present preliminary measurements on ice cores of elastic wave forms at ultrasonic frequencies. The aim of the project is to map out internal properties of the ice to improve our understanding of the processes responsible for the ice structure. Annual layering is one of the targets, but the alignment of ice crystals is another.We use a system based on laser sources and receivers for a number of reasons. First, the lasers allow us to probe the ice in a non-destructive and non-contacting matter through optical windows into our cold room. Second, the lasers/core system is controlled via computerized stages, which allow us to have unprecedented data density, repeatable data acquisition, and high fidelity in each waveform. We calibrated layering properties with man-made ice structures, and we will present ongoing tests on Antarctic cores from various depths and locations.

  7. A simulated Antarctic fast ice ecosystem

    NASA Technical Reports Server (NTRS)

    Arrigo, Kevin R.; Kremer, James N.; Sullivan, Cornelius W.

    1993-01-01

    A 2D numerical ecosystem model of Antarctic land fast ice is developed to elucidate the primary production with the Antarctic sea ice zone. The physical component employs atmospheric data to simulate congelation ice growth, initial brine entrapment, desalination, and nutrient flux. The biological component is based on the concept of a maximum temperature-dependent algal growth rate which is reduced by limitations imposed from insufficient light or nutrients, as well as suboptimal salinity. Preliminary simulations indicate that, during a bloom, microalgae are able to maintain their vertical position relative to the lower congelation ice margin and are not incorporated into the crystal matrix as the ice sheet thickens. It is inferred that land fast sea ice contains numerous microhabitats that are functionally distinct based upon the unique set of processes that control microalgal growth and accumulation within each.

  8. Forecasting Aviation Icing: Icing Type and Severity

    NSDL National Science Digital Library

    COMET

    1998-03-13

    This module discusses the current theories of atmospheric conditions associated with aircraft icing and applies the theories to the icing diagnosis and forecast process. The contribution of liquid water content, temperature, and droplet size parameters to icing are examined. Identification of icing type, icing severity, and the hazards associated with icing features are presented. Tools to help diagnose atmospheric processes that may be contributing to icing and the special case of supercooled large drop (SLD) icing are examined and applied in short exercises. The use of graphics, animations, and interactive exercises in Forecasting Aviation Icing: Icing Type and Severity helps the forecaster to gain an understanding of icing processes, to identify icing hazards, and to apply diagnosis and forecast tools as aids to evaluate and anticipate potential aircraft icing threats. The subject matter expert for this module is Dr. Marcia Politovich of NCAR/Research Applications Program. This module is also available in French.

  9. Predominance of Homogeneous Ice nucleation during the Formation of Cirrus Clouds

    NASA Astrophysics Data System (ADS)

    Barahona, Donifan

    2014-05-01

    Cirrus cloud formation proceeds either by homogeneous freezing (HOM) of liquid droplets or by heterogeneous ice nucleation (HET) on ice nuclei. Liquid droplets are ubiquitous in the upper troposphere and HOM is commonly associated with high concentrations of ice crystals. On the other hand ice nuclei are very scarce in the upper troposphere and cirrus clouds produced by HET tend to have low ice crystal concentration. Recent studies have suggested that observed ice crystal concentration in cirrus is more consistent with a HET scenario than with cirrus clouds formed by HOM. Here we revised such picture and show that although heterogeneous ice nucleation has a significant influence on cirrus formation, when considered over a global basis homogeneous ice nucleation is the predominant mechanism of ice formation. Modeling experiments were carried out with NASA Global Observing System (GEOS). The ice nucleation parameterization in GEOS has been updated to account for the effect of competition between HOM and HET mechanisms, water vapor deposition onto preexisting ice crystals, and parcel history during cirrus cloud formation. When these factors are considered, the ice crystal concentration produced by HOM and HET become comparable. Moreover, over extended areas in the West coast of North and South America, as well as Central Asia HET becomes the predominant path of the ice crystal production. These regions are typically the focus of field campaigns and this may explain the predominance of heterogeneous ice nucleation observed in collected ice crystal residuals. However over the rest of the world, and particularly over most of the Southern Hemisphere, ice crystal production is dominated by HOM. This picture reconciles model results and field campaign observations.

  10. CO2 (dry ice) cleaning system

    NASA Technical Reports Server (NTRS)

    Barnett, Donald M.

    1995-01-01

    Tomco Equipment Company has participated in the dry ice (solid carbon dioxide, CO2) cleaning industry for over ten years as a pioneer in the manufacturer of high density, dry ice cleaning pellet production equipment. For over four years Tomco high density pelletizers have been available to the dry ice cleaning industry. Approximately one year ago Tomco introduced the DI-250, a new dry ice blast unit making Tomco a single source supplier for sublimable media, particle blast, cleaning systems. This new blast unit is an all pneumatic, single discharge hose device. It meters the insertion of 1/8 inch diameter (or smaller), high density, dry ice pellets into a high pressure, propellant gas stream. The dry ice and propellant streams are controlled and mixed from the blast cabinet. From there the mixture is transported to the nozzle where the pellets are accelerated to an appropriate blasting velocity. When directed to impact upon a target area, these dry ice pellets have sufficient energy to effectively remove most surface coatings through dry, abrasive contact. The meta-stable, dry ice pellets used for CO2 cleaning, while labeled 'high density,' are less dense than alternate, abrasive, particle blast media. In addition, after contacting the target surface, they return to their equilibrium condition: a superheated gas state. Most currently used grit blasting media are silicon dioxide based, which possess a sharp tetrahedral molecular structure. Silicon dioxide crystal structures will always produce smaller sharp-edged replicas of the original crystal upon fracture. Larger, softer dry ice pellets do not share the same sharp-edged crystalline structures as their non-sublimable counterparts when broken. In fact, upon contact with the target surface, dry ice pellets will plastically deform and break apart. As such, dry ice cleaning is less harmful to sensitive substrates, workers and the environment than chemical or abrasive cleaning systems. Dry ice cleaning system components include: a dry ice pellet supply, a non-reactive propellant gas source, a pellet and propellant metering device, and a media transport and acceleration hose and nozzle arrangement. Dry ice cleaning system operating parameters include: choice of propellant gas, its pressure and temperature, dry ice mass flow rate, dry ice pellet size and shape, and acceleration nozzle configuration. These parameters may be modified to fit different applications. The growth of the dry ice cleaning industry will depend upon timely data acquisition of the effects that independent changes in these parameters have on cleaning rates, with respect to different surface coating and substrate combinations. With this data, optimization of cleaning rates for particular applications will be possible. The analysis of the applicable range of modulation of these parameters, within system component mechanical constraints, has just begun.

  11. Microphysical Consequences of the Spatial Distribution of Ice Nucleation in Mixed-Phase Stratiform Clouds

    SciTech Connect

    Yang, Fan; Ovchinnikov, Mikhail; Shaw, Raymond A.

    2014-07-28

    Mixed-phase stratiform clouds can persist even with steady ice precipitation fluxes, and the origin and microphysical properties of the ice crystals are of interest. Vapor deposition growth and sedimentation of ice particles along with a uniform volume source of ice nucleation, leads to a power law relation between ice water content wi and ice number concentration ni with exponent 2.5. The result is independent of assumptions about the vertical velocity structure of the cloud and is therefore more general than the related expression of Yang et al. [2013]. The sensitivity of the wi-ni relationship to the spatial distribution of ice nucleation is confirmed by Lagrangian tracking and ice growth with cloud-volume, cloud-top, and cloud-base sources of ice particles through a time-dependent cloud field. Based on observed wi and ni from ISDAC, a lower bound of 0.006 m^3/s is obtained for the ice crystal formation rate.

  12. High density amorphous ice at room temperature.

    PubMed

    Chen, Jing-Yin; Yoo, Choong-Shik

    2011-05-10

    The phase diagram of water is both unusual and complex, exhibiting a wide range of polymorphs including proton-ordered or disordered forms. In addition, a variety of stable and metastable forms are observed. The richness of H(2)O phases attests the versatility of hydrogen-bonded network structures that include kinetically stable amorphous ices. Information of the amorphous solids, however, is rarely available especially for the stability field and transformation dynamics--but all reported to exist below the crystallization temperature of approximately 150-170 K below 4-5 GPa. Here, we present the evidence of high density amorphous (HDA) ice formed well above the crystallization temperature at 1 GPa--well inside the so-called "no-man's land." It is formed from metastable ice VII in the stability field of ice VI under rapid compression using dynamic-diamond anvil cell (d-DAC) and results from structural similarities between HDA and ice VII. The formation follows an interfacial growth mechanism unlike the melting process. Nevertheless, the occurrence of HDA along the extrapolated melt line of ice VII resembles the ice Ih-to-HDA transition, indicating that structural instabilities of parent ice VII and Ih drive the pressure-induced amorphization. PMID:21518902

  13. De-icing: recovery of diffraction intensities in the presence of ice rings

    SciTech Connect

    Chapman, Michael S.; Somasundaram, Thayumanasamy (Oregon State U.); (FSU)

    2010-11-03

    Macromolecular structures are routinely determined at cryotemperatures using samples flash-cooled in the presence of cryoprotectants. However, sometimes the best diffraction is obtained under conditions where ice formation is not completely ablated, with the result that characteristic ice rings are superimposed on the macromolecular diffraction. In data processing, the reflections that are most affected by the ice rings are usually excluded. Here, an alternative approach of subtracting the ice diffraction is tested. High completeness can be retained with little adverse effect upon the quality of the integrated data. This offers an alternate strategy when high levels of cryoprotectant lead to loss of crystal quality.

  14. Laboratory study of frazil ice accumulation under wave conditions

    NASA Astrophysics Data System (ADS)

    de La Rosa, S.; Maus, S.

    2012-02-01

    Ice growth in turbulent seawater is often accompanied by the accumulation of frazil ice crystals at its surface, forming a grease ice layer. The thickness and volume fraction of this ice layer play an important role in shaping the gradual transition from a loose to a solid ice cover, however, observations are very sparse. Here we analyse an extensive set of observations of frazil ice, grown in two parallel tanks with controlled wave conditions and thermal forcing, focusing on the first one to two days of grease ice accumulation. The following unresolved issues are addressed: (i) at which volume fraction the frazil crystals' rising process starts and how densely they accumulate at the surface, (ii) how the grease ice solid fraction and salinity evolve with time until solid ice starts to form and (iii) how do these conditions affect, and are affected by, waves and heat loss from the ice. We obtained estimates of the minimum initial grease ice solid fraction (0.03-0.05) and the maximum solid fraction to which it accumulates before freezing into pancakes (0.23-0.31). The equivalent thickness of solid ice that needs to be accumulated until grease ice packs close to maximum (95% of the compaction accomplished), was estimated as 0.4 to 1.2 cm. Comparison of grease ice thickness and wave observations indicates that a grease ice layer first begins to affect the wave field significantly when its thickness exceeds the initial wave amplitude. These results are relevant for modelling frazil ice accumulation and freeze-up of leads, polynyas and along the seasonal ice zone.

  15. Forces Generated by High Velocity Impact of Ice on a Rigid Structure

    NASA Technical Reports Server (NTRS)

    Pereira, J. Michael; Padula, Santo A., II; Revilock, Duane M.; Melis, Matthew E.

    2006-01-01

    Tests were conducted to measure the impact forces generated by cylindrical ice projectiles striking a relatively rigid target. Two types of ice projectiles were used, solid clear ice and lower density fabricated ice. Three forms of solid clear ice were tested: single crystal, poly-crystal, and "rejected" poly-crystal (poly-crystal ice in which defects were detected during inspection.) The solid ice had a density of approximately 56 lb/cu ft (0.9 gm/cu cm). A second set of test specimens, termed "low density ice" was manufactured by molding shaved ice into a cylindrical die to produce ice with a density of approximately 40 lb/cu ft (0.65 gm/cu cm). Both the static mechanical characteristics and the crystalline structure of the ice were found to have little effect on the observed transient response. The impact forces generated by low density ice projectiles, which had very low mechanical strength, were comparable to those of full density solid ice. This supports the hypothesis that at a velocity significantly greater than that required to produce fracture in the ice, the mechanical properties become relatively insignificant, and the impact forces are governed by the shape and mass of the projectile.

  16. High pressure ices

    PubMed Central

    Hermann, Andreas; Ashcroft, N. W.; Hoffmann, Roald

    2012-01-01

    H2O will be more resistant to metallization than previously thought. From computational evolutionary structure searches, we find a sequence of new stable and meta-stable structures for the ground state of ice in the 1–5 TPa (10 to 50 Mbar) regime, in the static approximation. The previously proposed Pbcm structure is superseded by a Pmc21 phase at p = 930 GPa, followed by a predicted transition to a P21 crystal structure at p = 1.3 TPa. This phase, featuring higher coordination at O and H, is stable over a wide pressure range, reaching 4.8 TPa. We analyze carefully the geometrical changes in the calculated structures, especially the buckling at the H in O-H-O motifs. All structures are insulating—chemistry burns a deep and (with pressure increase) lasting hole in the density of states near the highest occupied electronic levels of what might be component metallic lattices. Metallization of ice in our calculations occurs only near 4.8 TPa, where the metallic C2/m phase becomes most stable. In this regime, zero-point energies much larger than typical enthalpy differences suggest possible melting of the H sublattice, or even the entire crystal. PMID:22207625

  17. Sensitivity of cirrus properties to ice nuclei abundance

    NASA Astrophysics Data System (ADS)

    Jensen, E. J.

    2014-12-01

    The relative importance of heterogeneous and homogeneous ice nucleation for cirrus formation remains an active area of debate in the cloud physics community. From a theoretical perspective, a number of modeling studies have investigated the sensitivity of ice number concentration to the nucleation mechanism and the abundance of ice nuclei. However, these studies typically only addressed ice concentration immediately after ice nucleation. Recent modeling work has shown that the high ice concentrations produced by homogeneous freezing may not persist very long, which is consistent with the low frequency of occurrence of high ice concentrations indicated by cirrus measurements. Here, I use idealized simulations to investigate the impact of ice nucleation mechanism and ice nuclei abundance on the full lifecycle of cirrus clouds. The primary modeling framework used includes different modes of ice nucleation, deposition growth/sublimation, aggregation, sedimentation, and radiation. A limited number of cloud-resolving simulations that treat radiation/dynamics interactions will also been presented. I will show that for typical synoptic situations with mesoscale waves present, the time-averaged cirrus ice crystal size distributions and bulk cloud properties are less sensitive to ice nucleation processes than might be expected from the earlier simple ice nucleation calculations. I will evaluate the magnitude of the ice nuclei impact on cirrus for a range of temperatures and mesoscale wave specifications, and I will discuss the implications for cirrus aerosol indirect effects in general.

  18. Iced Tea

    NSDL National Science Digital Library

    Richard Konicek-Moran

    2009-04-01

    Dissolving things in the universal solvent water is an everyday experience for almost all of us. We don't have a lot of trouble dissolving honey in our hot tea, but when it comes to sweetening cold iced tea, it is quite a task, if not almost impossible. O

  19. Relationship between melting and amorphization of ice

    Microsoft Academic Search

    Osamu Mishima

    1996-01-01

    THE discovery1 in 1984 that an ice crystal can be transformed by pressure to an amorphous phase has since been followed by other examples of pressure-induced amorphization2. This transition, like melting, involves loss of long-ranged order, prompting the question of whether the two transitions are related. Here I describe experiments probing this relationship for a form of crystalline ice (denoted

  20. Significant alterations in anisotropic ice growth rate induced by the ice nucleation-active bacteria Xanthomonas campestris

    NASA Astrophysics Data System (ADS)

    Nada, Hiroki; Zepeda, Salvador; Miura, Hitoshi; Furukawa, Yoshinori

    2010-09-01

    In the present study, we found that the ice nucleation-active bacteria Xanthomonas campestris significantly altered anisotropic ice growth rate. Results of ice growth experiments in the presence of X. campestris showed that this bacterium decreased the ice crystal growth rate in the c-axis, whereas it increased growth rates in directions normal to the c-axis. These results indicate that these alterations in anisotropic growth rate are the result of selective binding of bacterial ice-nucleating proteins along the {0 0 0 1} basal plane.

  1. Smart Icing Systems for Aircraft Icing Safety

    Microsoft Academic Search

    Michael B. Bragg; Tamer Basar; William R. Perkins; Michael S. Selig

    2002-01-01

    Ice accretion affects the performance and control of an aircraft and in extreme situations can lead to incidents and accidents. However, changes in performance and control are difficult to sense. As a result, the icing sensors currently in use sense primarily ice accretion, not the effect of the ice. No processed aircraft performance degradation information is available to the pilot.

  2. Parameterizing Size Distribution in Ice Clouds

    SciTech Connect

    DeSlover, Daniel; Mitchell, David L.

    2009-09-25

    PARAMETERIZING SIZE DISTRIBUTIONS IN ICE CLOUDS David L. Mitchell and Daniel H. DeSlover ABSTRACT An outstanding problem that contributes considerable uncertainty to Global Climate Model (GCM) predictions of future climate is the characterization of ice particle sizes in cirrus clouds. Recent parameterizations of ice cloud effective diameter differ by a factor of three, which, for overcast conditions, often translate to changes in outgoing longwave radiation (OLR) of 55 W m-2 or more. Much of this uncertainty in cirrus particle sizes is related to the problem of ice particle shattering during in situ sampling of the ice particle size distribution (PSD). Ice particles often shatter into many smaller ice fragments upon collision with the rim of the probe inlet tube. These small ice artifacts are counted as real ice crystals, resulting in anomalously high concentrations of small ice crystals (D < 100 µm) and underestimates of the mean and effective size of the PSD. Half of the cirrus cloud optical depth calculated from these in situ measurements can be due to this shattering phenomenon. Another challenge is the determination of ice and liquid water amounts in mixed phase clouds. Mixed phase clouds in the Arctic contain mostly liquid water, and the presence of ice is important for determining their lifecycle. Colder high clouds between -20 and -36 oC may also be mixed phase but in this case their condensate is mostly ice with low levels of liquid water. Rather than affecting their lifecycle, the presence of liquid dramatically affects the cloud optical properties, which affects cloud-climate feedback processes in GCMs. This project has made advancements in solving both of these problems. Regarding the first problem, PSD in ice clouds are uncertain due to the inability to reliably measure the concentrations of the smallest crystals (D < 100 µm), known as the “small mode”. Rather than using in situ probe measurements aboard aircraft, we employed a treatment of ice cloud optical properties formulated in terms of PSD parameters in combination with remote measurements of thermal radiances to characterize the small mode. This is possible since the absorption efficiency (Qabs) of small mode crystals is larger at 12 µm wavelength relative to 11 µm wavelength due to the process of wave resonance or photon tunneling more active at 12 µm. This makes the 12/11 µm absorption optical depth ratio (or equivalently the 12/11 µm Qabs ratio) a means for detecting the relative concentration of small ice particles in cirrus. Using this principle, this project tested and developed PSD schemes that can help characterize cirrus clouds at each of the three ARM sites: SGP, NSA and TWP. This was the main effort of this project. These PSD schemes and ice sedimentation velocities predicted from them have been used to test the new cirrus microphysics parameterization in the GCM known as the Community Climate Systems Model (CCSM) as part of an ongoing collaboration with NCAR. Regarding the second problem, we developed and did preliminary testing on a passive thermal method for retrieving the total water path (TWP) of Arctic mixed phase clouds where TWPs are often in the range of 20 to 130 g m-2 (difficult for microwave radiometers to accurately measure). We also developed a new radar method for retrieving the cloud ice water content (IWC), which can be vertically integrated to yield the ice water path (IWP). These techniques were combined to determine the IWP and liquid water path (LWP) in Arctic clouds, and hence the fraction of ice and liquid water. We have tested this approach using a case study from the ARM field campaign called M-PACE (Mixed-Phase Arctic Cloud Experiment). This research led to a new satellite remote sensing method that appears promising for detecting low levels of liquid water in high clouds typically between -20 and -36 oC. We hope to develop this method in future research.

  3. Phase Transformation and Intense 2.7??m Emission from Er3+ Doped YF3/YOF Submicron-crystals

    PubMed Central

    Chai, Guanqi; Dong, Guoping; Qiu, Jianrong; Zhang, Qinyuan; Yang, Zhongmin

    2013-01-01

    Yttrium fluoride YF3:Er3+ and yttrium oxyfluoride YOF:Er3+ submicron-crystals with mid-infrared fluorescent emissions were synthesized for the first time. The rhombohedral phase YOF submicron-crystals were synthesized by the crystalline phase transformation from pure orthorhombic YF3 submicron-crystals, which were prepared by co-precipitation method. The composition and morphology were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM), which showed that submicron-crystals were quasi-spherical with the particle size of ~400?nm. A novel formation mechanism of YOF submicron-crystals was proposed. Photoluminescence (PL) spectra indicated the 2.7??m emission of Er3+ has remarkably enhanced with the increase of Er3+ doping concentration, and a novel dynamic circulatory energy transfer mechanism was proposed. Fourier transform infrared spectra (FTIR) were used to demonstrate the change of hydroxyl content. These oxyfluoride submicron-crystals provide a new material for nano/submicron-crystals-glass composites, and open a brand new field for the realization of mid-infrared micro/nano-lasers. PMID:23604234

  4. Ice crystals growth driving assembly of porous nitrogen-doped graphene for catalyzing oxygen reduction probed by in situ fluorescence electrochemistry

    PubMed Central

    Wang, Jiong; Wang, Huai-Song; Wang, Kang; Wang, Feng-Bin; Xia, Xing-Hua

    2014-01-01

    In recent years, doped carbonaceous materials as alternative catalysts for oxygen reduction reaction (ORR) have received considerable attention due to the low cost and high CO tolerance capability. Different theoretical studies have suggested that oxygen is reduced in a rapid sequence intermediated by diverse oxygen-containing reactive intermediates (ORI). However, due to the short lifetimes of the possible ORI, direct experimental evidence is very difficult to be obtained. Here, we report the synthesis of an ultralight and porous nitrogen-doped graphene (NG) by annealing graphite oxide (GO)-melamine scaffold shaped in ice template. The resultant NG exhibits excellent electrocatalytic activity toward 4e-reduction of oxygen with the onset potential as low as ?0.05?V vs. Ag/AgCl in alkaline media. Using this material as model study, sensitive in situ fluorescence spectroelectrochemistry is applied to demonstrate the presence the reactive ORI. The global ORR pathway is unraveled as stepwise electron transfer involving hydroxyl radical as the important intermediate via both inner- and outer-sphere process. This result would likely provide a new insight into the further understanding of ORR mechanism on those intrinsic carbonaceous materials. PMID:25335571

  5. Square ice in graphene nanocapillaries

    NASA Astrophysics Data System (ADS)

    Algara-Siller, G.; Lehtinen, O.; Wang, F. C.; Nair, R. R.; Kaiser, U.; Wu, H. A.; Geim, A. K.; Grigorieva, I. V.

    2015-03-01

    Bulk water exists in many forms, including liquid, vapour and numerous crystalline and amorphous phases of ice, with hexagonal ice being responsible for the fascinating variety of snowflakes. Much less noticeable but equally ubiquitous is water adsorbed at interfaces and confined in microscopic pores. Such low-dimensional water determines aspects of various phenomena in materials science, geology, biology, tribology and nanotechnology. Theory suggests many possible phases for adsorbed and confined water, but it has proved challenging to assess its crystal structure experimentally. Here we report high-resolution electron microscopy imaging of water locked between two graphene sheets, an archetypal example of hydrophobic confinement. The observations show that the nanoconfined water at room temperature forms `square ice'--a phase having symmetry qualitatively different from the conventional tetrahedral geometry of hydrogen bonding between water molecules. Square ice has a high packing density with a lattice constant of 2.83 Å and can assemble in bilayer and trilayer crystallites. Molecular dynamics simulations indicate that square ice should be present inside hydrophobic nanochannels independently of their exact atomic nature.

  6. Study of ice cloud properties using infrared spectral data 

    E-print Network

    Garrett, Kevin James

    2009-05-15

    August 2007 Major Subject: Atmospheric Sciences ii ABSTRACT Study of Ice Cloud Properties Using Infrared Spectral Data. (August 2007) Kevin James Garet, B.S., Syracuse University Chair of Advisory Commite: Dr. Ping Yang The research... Page 1 Images of the 6 non-spherical ice crystal habits included in the single- scatering property database of Yang et al. [56]???.????..????..10 2 The refractive index of ice over the IASI spectrum for a) real part and b) imaginary part...

  7. Periodic density functional theory and local-MP2 study of the librational modes of Ice XI

    Microsoft Academic Search

    Alessandro Erba; Silvia Casassa; Roberto Dovesi; Lorenzo Maschio; Cesare Pisani

    2009-01-01

    Two periodic codes, CRYSTAL and CRYSCOR, are here used to simulate and characterize the librational modes of the nuR band of Ice XI: this band has been found experimentally to be the region of the vibrational spectrum of ordinary ice most affected by the transition from the proton-disordered (Ice Ih) to the proton-ordered (Ice XI) phase. With CRYSTAL, the problem

  8. Physiochemical Properties of Sodium Chloride Particles on Laboratory Ice Surfaces

    NASA Astrophysics Data System (ADS)

    Gleason, E. P.; Simpson, W. R.

    2013-12-01

    Aqueous halides (e.g. Cl- and Br-) on environmental ice surfaces are converted to reactive gases through heterogeneous chemistry that has broad consequences for springtime Arctic tropospheric oxidation chemistry. Recent studies indicate that atmospherically contaminated snow (e.g. more acidic snow) is more effective at activating halogens than frozen seawater. This study investigates the microstructure created by the addition of salts onto ice surfaces as a function of temperature. Microscopic sodium chloride salt crystals were labeled with a fluorescent dye (fluorescein) and placed onto laboratory ice surface below the hydrohalite (NaCl 2H2O)-water eutectic temperature. As temperature was increased above the eutectic, a discrete brine area formed around the crystal. Size and morphology of the brine area was determined using an Axioscope II epifluorescence microscope. Initially, the salt crystal did not entirely dissolve and three distinct phases (solid salt, brine, ice) were present for some time. Timescales for crystal dissolving, brine formation, and wetting across the ice surfaces where thus constrained. Similar experiments using a fluorescently labeled, laboratory-generated sea salt aerosol particles were also carried out and compared to the larger microscopic sodium chloride crystals. This work gives insight into how atmospheric particles deliver contaminants to ice surfaces, how those contaminants interact with ice surfaces and thus how they may impact halogen activation.

  9. The Influence of Polysaccharides on the Glass Transition in Frozen Sucrose Solutions and Ice Cream

    Microsoft Academic Search

    H. D. Goff; K. B. Caldwell; D. W. Stanley; T. J. Maurice

    1993-01-01

    The objective of this study was to describe further the mechanism by which polysaccharide stabilizers contribute to stability of frozen dairy desserts. The influence of stabilizers on the thermal properties and viscosity of carbohydrate solutions at subzero temperatures, on the thermal properties of ice cream mix, and on ice crystallization and growth in ice cream were investigated. Polysaccharide stabilizers did

  10. Understanding ice supersaturation, particle growth, and number concentration in cirrus clouds

    Microsoft Academic Search

    Jennifer M. Comstock; Ruei-Fong Lin; David O'C. Starr; Ping Yang

    2008-01-01

    Many factors control the ice supersaturation and microphysical properties in cirrus clouds. We explore the effects of dynamic forcing, ice nucleation mechanisms, and ice crystal growth rate on the evolution and distribution of water vapor and cloud properties in nighttime cirrus clouds using a one-dimensional cloud model with bin microphysics and remote sensing measurements obtained at the Department of Energy's

  11. Understanding Ice Supersaturation, Particle Growth, and Number Concentration in Cirrus Clouds

    Microsoft Academic Search

    Jennifer M. Comstock; Ruei-Fong Lin; David O'C. Starr; Ping Yang

    2008-01-01

    Many factors control the ice supersaturation and microphysical properties in cirrus clouds. We explore the effects of dynamic forcing, ice nucleation mechanisms, and ice crystal growth rate on the evolution and distribution of water vapor and cloud properties in cirrus clouds using a detailed microphysical model and remote sensing measurements obtained at the Department of Energys Atmospheric Radiation Measurement (ARM)

  12. Thermodynamics and Kinetics of the Solid Solution of HCl in Ice Emmanuel Thibert and Florent Domine*,

    E-print Network

    Domine, Florent

    solubility of HCl in ice Ih has been measured as a function of temperature and HCl partial pressure, betweenThermodynamics and Kinetics of the Solid Solution of HCl in Ice Emmanuel Thibert and Florent Domine -8 and -35 °C by doping large ice single crystals with gaseous HCl for several weeks. Results

  13. 9422 Stratospheric ice catalyzes chlorine reactions 9428 Fusing silk and silica

    E-print Network

    McFadden, Geoff

    9422 Stratospheric ice catalyzes chlorine reactions 9428 Fusing silk and silica 9482 Identifying deteriorates with age CHEMISTRY Stratospheric ice catalyzes chlorine reactions To explain how ice crystals can catalyze chlorine reactions in the stratosphere, Faye McNeill et al. report that small amounts

  14. The sub-ice platelet layer and its influence on freeboard to thickness conversion of Antarctic sea ice

    NASA Astrophysics Data System (ADS)

    Price, D.; Rack, W.; Langhorne, P. J.; Haas, C.; Leonard, G.; Barnsdale, K.

    2014-06-01

    This is an investigation to quantify the influence of the sub-ice platelet layer on satellite measurements of total freeboard and their conversion to thickness of Antarctic sea ice. The sub-ice platelet layer forms as a result of the seaward advection of supercooled ice shelf water from beneath ice shelves. This ice shelf water provides an oceanic heat sink promoting the formation of platelet crystals which accumulate at the sea ice-ocean interface. The build-up of this porous layer increases sea ice freeboard, and if not accounted for, leads to overestimates of sea ice thickness from surface elevation measurements. In order to quantify this buoyant effect, the solid fraction of the sub-ice platelet layer must be estimated. An extensive in situ data set measured in 2011 in McMurdo Sound in the southwestern Ross Sea is used to achieve this. We use drill-hole measurements and the hydrostatic equilibrium assumption to estimate a mean value for the solid fraction of this sub-ice platelet layer of 0.16. This is highly dependent upon the uncertainty in sea ice density. We test this value with independent Global Navigation Satellite System (GNSS) surface elevation data to estimate sea ice thickness. We find that sea ice thickness can be overestimated by up to 19%, with a mean deviation of 12% as a result of the influence of the sub-ice platelet layer. It is concluded that within 100 km of an ice shelf this influence might need to be considered when undertaking sea ice thickness investigations using remote sensing surface elevation measurements.

  15. The sub-ice platelet layer and its influence on freeboard to thickness conversion of Antarctic sea ice

    NASA Astrophysics Data System (ADS)

    Price, D.; Rack, W.; Langhorne, P. J.; Haas, C.; Leonard, G.; Barnsdale, K.

    2014-02-01

    This is an investigation to quantify the influence of the sub-ice platelet layer on satellite measurements of total freeboard and their conversion to thickness of Antarctic sea ice. The sub-ice platelet layer forms as a result of the seaward advection of supercooled ice shelf water from beneath ice shelves. This ice shelf water provides an oceanic heat sink promoting the formation of platelet crystals which accumulate at the sea ice-ocean interface. The build-up of this porous layer increases sea ice freeboard, and if not accounted for, leads to overestimates of sea ice thickness from surface elevation measurements. In order to quantify this buoyant effect, the solid fraction of the sub-ice platelet layer must be estimated. An extensive in situ data set measured in 2011 in McMurdo Sound in the south-western Ross Sea is used to achieve this. We use drill-hole measurements and the hydrostatic equilibrium assumption to estimate a mean value for the solid fraction of this sub-ice platelet layer of 0.16. This is highly dependent upon the uncertainty in sea ice density. We test this value with independent Global Navigation Satellite System (GNSS) surface elevation data to estimate sea ice thickness. We find that sea ice thickness can be overestimated by up to 19%, with a mean deviation of 12% as a result of the influence of the sub-ice platelet layer. It is concluded that in close proximity to ice shelves this influence should be considered universally when undertaking sea ice thickness investigations using remote sensing surface elevation measurements.

  16. Detections of Trans-Neptunian Ice in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    McClure, M. K.; Espaillat, C.; Calvet, N.; Bergin, E.; D'Alessio, P.; Watson, D. M.; Manoj, P.; Sargent, B.; Cleeves, L. I.

    2015-02-01

    We present Herschel Space Observatory PACS spectra of T Tauri stars, in which we detect amorphous and crystalline water ice features. Using irradiated accretion disk models, we determine the disk structure and ice abundance in each of the systems. Combining a model-independent comparison of the ice feature strength and disk size with a detailed analysis of the model ice location, we estimate that the ice emitting region is at disk radii >30 AU, consistent with a proto-Kuiper belt. Vertically, the ice emits most below the photodesorption zone, consistent with Herschel observations of cold water vapor. The presence of crystallized water ice at a disk location (1) colder than its crystallization temperature and (2) where it should have been re-amorphized in ~1 Myr suggests that localized generation is occurring; the most likely cause appears to be micrometeorite impact or planetesimal collisions. Based on simple tests with UV models and different ice distributions, we suggest that the SED shape from 20 to 50 ?m may probe the location of the water ice snowline in the disk upper layers. This project represents one of the first extra-solar probes of the spatial structure of the cometary ice reservoir thought to deliver water to terrestrial planets.

  17. Lattice Boltzmann Simulation of Kinetic Isotope Effect During Snow Crystal Formation

    Microsoft Academic Search

    G. Lu; D. J. Depaolo; Q. Kang; D. Zhang

    2007-01-01

    The isotopic composition of precipitation, especially that of snow, plays a special role in the global hydrological cycle and in reconstruction of past climates using polar ice cores. The fractionation of the major water isotope species (HHO, HDO, HHO-18) during ice crystal formation is critical to understanding the global distribution of isotopes in precipitation. Ice crystal growth in clouds is

  18. Minimalist Model of Ice Microphysics in Mixed-phase Stratiform Clouds

    SciTech Connect

    Yang, F.; Ovchinnikov, Mikhail; Shaw, Raymond A.

    2013-07-28

    The question of whether persistent ice crystal precipitation from super cooled layer clouds can be explained by time-dependent, stochastic ice nucleation is explored using an approximate, analytical model, and a large-eddy simulation (LES) cloud model. The updraft velocity in the cloud defines an accumulation zone, where small ice particles cannot fall out until they are large enough, which will increase the residence time of ice particles in the cloud. Ice particles reach a quasi-steady state between growth by vapor deposition and fall speed at cloud base. The analytical model predicts that ice water content (wi) has a 2.5 power law relationship with ice number concentration ni. wi and ni from a LES cloud model with stochastic ice nucleation also confirm the 2.5 power law relationship. The prefactor of the power law is proportional to the ice nucleation rate, and therefore provides a quantitative link to observations of ice microphysical properties.

  19. Growth Rates of the Principal Facets of Ice between -10 C to -40 C

    E-print Network

    Libbrecht, Kenneth G.

    Growth Rates of the Principal Facets of Ice between -10 C to -40 C K G. L 1 Norman Bridge to the Journal of Crystal Growth, with revisions, August 21, 2002] Abstract. We describe measurements of the growth rates of the basal and prism facets of ice crystals grown from the vapor phase at temperatures -39

  20. Color Reveals Translucent Seasonal Ice

    NASA Technical Reports Server (NTRS)

    2007-01-01

    [figure removed for brevity, see original site] Figure 1

    In a region near the south pole of Mars translucent carbon dioxide ice covers the ground seasonally. For the first time we can 'see' the translucent ice by the affect it has on the appearance of the surface below.

    Dark fans of dust (figure 1) from the surface drape over the top of the seasonal ice. The surface would be the same color as the dust except that the seasonal ice affecting its appearance. Bright bluish streaks are frost that has re-crystallized from the atmosphere.

    Sunlight can penetrate through the seasonal layer of translucent ice to warm the ground below. That causes the seasonal ice layer to sublime (evaporate) from the bottom rather than the top.

    Observation Geometry Image PSP_002942_0935 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on 13-Mar-2007. The complete image is centered at -86.4 degrees latitude, 99.2 degrees East longitude. The range to the target site was 245.4 km (153.4 miles). At this distance the image scale is 49.1 cm/pixel (with 2 x 2 binning) so objects 147 cm across are resolved. The image shown here has been map-projected to 50 cm/pixel . The image was taken at a local Mars time of 06:41 PM and the scene is illuminated from the west with a solar incidence angle of 82 degrees, thus the sun was about 8 degrees above the horizon. At a solar longitude of 199.6 degrees, the season on Mars is Northern Autumn.

  1. Ice Zones: Where We Look for Ice

    NSDL National Science Digital Library

    In this activity, learners draw conclusions about where on a planetary body scientists might look for ice and why. They use a clay ball, ice cubes, and a heat lamp to model the permanently-shadowed polar regions of planets and moons that may harbor ice. They learn that our Moon, and even Mercury, may have areas with ice. This activity is part of Explore! To the Moon and Beyond! - a resource developed specifically for use in libraries.

  2. Examination of Icing Induced Loss of Control and Its Mitigations

    NASA Technical Reports Server (NTRS)

    Reehorst, Andrew L.; Addy, Harold E., Jr.; Colantonio, Renato O.

    2010-01-01

    Factors external to the aircraft are often a significant causal factor in loss of control (LOC) accidents. In today s aviation world, very few accidents stem from a single cause and typically have a number of causal factors that culminate in a LOC accident. Very often the "trigger" that initiates an accident sequence is an external environment factor. In a recent NASA statistical analysis of LOC accidents, aircraft icing was shown to be the most common external environmental LOC causal factor for scheduled operations. When investigating LOC accident or incidents aircraft icing causal factors can be categorized into groups of 1) in-flight encounter with super-cooled liquid water clouds, 2) take-off with ice contamination, or 3) in-flight encounter with high concentrations of ice crystals. As with other flight hazards, icing induced LOC accidents can be prevented through avoidance, detection, and recovery mitigations. For icing hazards, avoidance can take the form of avoiding flight into icing conditions or avoiding the hazard of icing by making the aircraft tolerant to icing conditions. Icing detection mitigations can take the form of detecting icing conditions or detecting early performance degradation caused by icing. Recovery from icing induced LOC requires flight crew or automated systems capable of accounting for reduced aircraft performance and degraded control authority during the recovery maneuvers. In this report we review the icing induced LOC accident mitigations defined in a recent LOC study and for each mitigation describe a research topic required to enable or strengthen the mitigation. Many of these research topics are already included in ongoing or planned NASA icing research activities or are being addressed by members of the icing research community. These research activities are described and the status of the ongoing or planned research to address the technology needs is discussed

  3. A dynamic model of Ostwald ripening in ice suspensions

    NASA Astrophysics Data System (ADS)

    Pronk, P.; Infante Ferreira, C. A.; Witkamp, G. J.

    2005-02-01

    A computer-based dynamic model of Ostwald ripening in ice suspensions in a storage tank containing crystal growth kinetics, population, mass and energy balances has been developed to simulate the development of ice crystal size distributions during adiabatic ice slurry storage. The model assumed a homogeneously mixed storage tank with neither inlet nor outlet of mass. Growth and melting of ice crystals were caused by differences in equilibrium temperatures between differently sized crystals and crystal growth kinetics were based on heat and mass transfer. Validation with experimental results for different types and concentration of solutes, different ice fractions and different mixing rates showed that the model is able to predict the development of the average crystal size in time. Especially, the former two parameters have a strong effect on the ripening process, while the effect of the latter two is small. A difference between experimental and simulation results was found for the shape of the crystal size distribution curve after storage, which had a slightly longer tail during the experiments.

  4. Cirrus Uncinus Generating Cells and the Evolution of Cirrdorm Clouds. Part III: Numerical Computations of the Growth of the Ice Phase

    Microsoft Academic Search

    Andrew Heymsneid

    1975-01-01

    Equations were developed to calculate the growth of the ice phase in cirrus clouds. Calculations indicated that nucleation of ice crystals in cirrus uncinus heads forming at temperatures lower than 35°C generally should occur near the upwind base of the head, and in cirrostratus clouds at the top of the cloud.The growth of ice crystals and the resulting shape of

  5. When are antifreeze proteins in solution essential for ice growth inhibition?

    PubMed

    Drori, Ran; Davies, Peter L; Braslavsky, Ido

    2015-06-01

    Antifreeze proteins (AFPs) are a widespread class of proteins that bind to ice and facilitate the survival of organisms under freezing conditions. AFPs have enormous potential in applications that require control over ice growth. However, the nature of the binding interaction between AFPs and ice remains the subject of debate. Using a microfluidics system developed in-house we previously showed that hyperactive AFP from the Tenebrio molitor beetle, TmAFP, remains bound to an ice crystal surface after exchanging the solution surrounding the ice crystal to an AFP-free solution. Furthermore, these surface-adsorbed TmAFP molecules sufficed to prevent ice growth. These experiments provided compelling evidence for the irreversible binding of hyperactive AFPs to ice. Here, we tested a moderately active type III AFP (AFPIII) from a fish in a similar microfluidics system. We found, in solution exchange experiments that the AFPIIIs were also irreversibly bound to the ice crystals. However, some crystals displayed "burst" growth during the solution exchange. AFPIII, like other moderately active fish AFPs, is unable to bind to the basal plane of an ice crystal. We showed that although moderate AFPs bound to ice irreversibly, moderate AFPs in solution were needed to inhibit ice growth from the bipyramidal crystal tips. Instead of binding to the basal plane, these AFPs minimized the basal face size by stabilizing other crystal planes that converge to form the crystal tips. Furthermore, when access of solution to the basal plane was physically blocked by the microfluidics device walls, we observed enhancement of the antifreeze activity. These findings provide direct evidence that the weak point of ice growth inhibition by fish AFPs is the basal plane, whereas insect AFPs, which can bind to the basal plane, are able to inhibit its growth and thereby increase antifreeze activity. PMID:25946514

  6. Preferred crystal orientations due to melt convection during directional solidification

    Microsoft Academic Search

    Michael I. Bergman; David M. Cole; Jackson R. Jones

    2002-01-01

    Directional solidification of salt water results in a preferred crystallographic orientation, with ice platelets growing with their short dimension (the c axis of the hexagonal close packed (hcp) ice crystal) transverse to the growth direction. In the absence of a mean saltwater flow parallel to the solidification interface, the ice platelets, and hence the c axes, are arbitrarily oriented in

  7. Friction of ice on ice

    NASA Astrophysics Data System (ADS)

    Schulson, Erland M.; Fortt, Andrew L.

    2012-12-01

    New measurements have been made of the friction coefficient of freshwater polycrystalline ice sliding slowly (5 × 10-8 to 1 × 10-3 m s-1) upon itself at temperatures from 98 to 263 K under low normal stresses (?98 kPa). Sliding obeys Coulomb's law: the shear stress is directly proportional to the normal stress across the interface, while cohesion offers little contribution to frictional resistance. The coefficient of kinetic friction of smooth surfaces varies from ?k = 0.15 to 0.76 and, at elevated temperatures (?223 K), exhibits both velocity strengthening at lower velocities (<10-5 to 10-4 m s-1) and velocity weakening at higher velocities. Strengthening and weakening are attributed to creep deformation of asperities and localized melting, respectively. At intermediate temperatures of 173 and 133 K, the kinetic coefficient appears to not exhibit significant dependence upon velocity. However, at the low temperature of 98 K the coefficient of kinetic friction exhibits moderate velocity strengthening at both the lowest and the highest velocities but velocity independence over the range of intermediate velocities. No effect was detected of either grain size or texture. Over the range of roughness 0.4 × 10-6 m ? Ra ? 12 × 10-6 m, a moderate effect was detected, where ?k ? Ra0.08. Slide-hold-slide experiments revealed that the coefficient of static friction increases by an amount that scales logarithmically with holding time. Implications of the results are discussed in relation to shearing across "tiger stripe" faults within the icy crust of Saturn's Enceladus, sliding of the arctic sea ice cover and brittle compressive failure of cold ice.

  8. Effects of storage in slurry ice on the microbial, chemical and sensory quality and on the shelf life of farmed turbot ( Psetta maxima)

    Microsoft Academic Search

    Óscar Rodríguez; Jorge Barros-Velázquez; Carmen Piñeiro; José M. Gallardo; Santiago P. Aubourg

    2006-01-01

    The application of slurry ice, a binary mixture of small spherical ice crystals surrounded by seawater at subzero temperature, is a potentially new preservation method for farmed turbot (Psetta maxima), a flat fish species of increasing commercial interest. Comparative biochemical, microbiological and sensory analyses were carried on turbot specimens stored in either slurry ice or flake ice for up to

  9. Scrambled Ice

    NASA Technical Reports Server (NTRS)

    1998-01-01

    This complex area on the side of Europa which faces away from Jupiter shows several types of features which are formed by disruptions of Europa's icy crust. North is to the top of the image, taken by NASA's Galileo spacecraft, and the Sun illuminates the surface from the left. The prominent wide, dark bands are up to 20 kilometers (12 miles) wide and over 50 kilometers (30 miles) long. They are believed to have formed when Europa's icy crust fractured, separated and filled in with darker, 'dirtier' ice or slush from below. A relatively rare type of feature on Europa is the 15-kilometer-diameter (9.3-mile) impact crater in the lower left corner. The small number of impact craters on Europa's surface is an indication of its relatively young age. A region of chaotic terrain south of this impact crater contains crustal plates which have broken apart and rafted into new positions. Some of these 'ice rafts' are nearly 1 kilometer (about half a mile) across. Other regions of chaotic terrain are visible and indicate heating and disruption of Europa's icy crust from below. The youngest features in this scene are the long, narrow cracks in the ice which cut across all other features. One of these cracks is about 30 kilometers (18 miles) to the right of the impact crater and extends for hundreds of miles from the top to the bottom of the image.

    The image, centered near 23 degrees south latitude and 179 degrees longitude, covers an area about 240 by 215 kilometers (150 by 130 miles) across. The finest details that can be discerned in this picture are about 460 meters (500 yards) across. The image was taken as Galileo flew by Europa on March 29, 1998. The image was taken by the onboard solid state imaging system camera from an altitude of 23,000 kilometers (14,000 miles).

    The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is an operating division of California Institute of Technology (Caltech).

    This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

  10. Global Ice Viewer

    NSDL National Science Digital Library

    This website explores the sentinels of climate change with a 3D interactive global ice viewer. View the effects of climate change on glaciers, sea ice, and continental ice sheets worldwide, in Greenland, Arctic and Antarctica through time lapse movies of ice melt and trends, comparison photographs and maps. Links to NASA satellites and their missions are provided.

  11. Make Ice Cream

    NSDL National Science Digital Library

    2014-02-03

    Learners add salt to ice to chill it lower than its freezing point. This chilled ice can then be used to freeze milk and sugar into ice cream. Learners can experiment by adding different flavors such as fruit juices and candy to the ice cream mix.

  12. Ice Particle Growth Rates Under Upper Troposphere Conditions

    NASA Technical Reports Server (NTRS)

    Peterson, Harold; Bailey, Matthew; Hallett, John

    2010-01-01

    Atmospheric conditions for growth of ice crystals (temperature and ice supersaturation) are often not well constrained and it is necessary to simulate such conditions in the laboratory to investigate such growth under well controlled conditions over many hours. The growth of ice crystals from the vapour in both prism and basal planes was observed at temperatures of -60 C and -70 C under ice supersaturation up to 100% (200% relative humidity) at pressures derived from the standard atmosphere in a static diffusion chamber. Crystals grew outward from a vertical glass filament, thickening in the basal plane by addition of macroscopic layers greater than 2 m, leading to growth in the prism plane by passing of successive layers conveniently viewed by time lapse video.

  13. Ice Particle Growth Under Conditions of the Upper Troposphere

    NASA Technical Reports Server (NTRS)

    Peterson, Harold S.; Bailey, Matthew; Hallett, John

    2010-01-01

    Atmospheric conditions for growth of ice crystals (temperature and ice supersaturation) are often not well constrained and it is necessary to simulate such conditions in the laboratory to investigate such growth under well controlled conditions over many hours. The growth of ice crystals from the vapour in both prism and basal planes was observed at temperatures of -60 C and -70 C under ice supersaturation up to 100% (200% relative humidity) at pressures derived from the standard atmosphere in a static diffusion chamber. Crystals grew outward from a vertical glass filament, thickening in the basal plane by addition of macroscopic layers greater than 2 microns, leading to growth in the prism plane by passing of successive layers conveniently viewed by time lapse video.

  14. Ice sheet margins and ice shelves

    NASA Technical Reports Server (NTRS)

    Thomas, R. H.

    1984-01-01

    The effect of climate warming on the size of ice sheet margins in polar regions is considered. Particular attention is given to the possibility of a rapid response to warming on the order of tens to hundreds of years. It is found that the early response of the polar regions to climate warming would be an increase in the area of summer melt on the ice sheets and ice shelves. For sufficiently large warming (5-10C) the delayed effects would include the breakup of the ice shelves by an increase in ice drainage rates, particularly from the ice sheets. On the basis of published data for periodic changes in the thickness and melting rates of the marine ice sheets and fjord glaciers in Greenland and Antarctica, it is shown that the rate of retreat (or advance) of an ice sheet is primarily determined by: bedrock topography; the basal conditions of the grounded ice sheet; and the ice shelf condition downstream of the grounding line. A program of satellite and ground measurements to monitor the state of ice sheet equilibrium is recommended.

  15. Icing: Accretion, Detection, Protection

    NASA Technical Reports Server (NTRS)

    Reinmann, John J.

    1994-01-01

    The global aircraft industry and its regulatory agencies are currently involved in three major icing efforts: ground icing; advanced technologies for in-flight icing; and tailplane icing. These three major icing topics correspondingly support the three major segments of any aircraft flight profile: takeoff; cruise and hold; and approach and land. This lecture addressess these three topics in the same sequence as they appear in flight, starting with ground deicing, followed by advanced technologies for in-flight ice protection, and ending with tailplane icing.

  16. Polarimetric Signatures of Sea Ice. Part 1; Theoretical Model

    NASA Technical Reports Server (NTRS)

    Nghiem, S. V.; Kwok, R.; Yueh, S. H.; Drinkwater, M. R.

    1995-01-01

    Physical, structural, and electromagnetic properties and interrelating processes in sea ice are used to develop a composite model for polarimetric backscattering signatures of sea ice. Physical properties of sea ice constituents such as ice, brine, air, and salt are presented in terms of their effects on electromagnetic wave interactions. Sea ice structure and geometry of scatterers are related to wave propagation, attenuation, and scattering. Temperature and salinity, which are determining factors for the thermodynamic phase distribution in sea ice, are consistently used to derive both effective permittivities and polarimetric scattering coefficients. Polarimetric signatures of sea ice depend on crystal sizes and brine volumes, which are affected by ice growth rates. Desalination by brine expulsion, drainage, or other mechanisms modifies wave penetration and scattering. Sea ice signatures are further complicated by surface conditions such as rough interfaces, hummocks, snow cover, brine skim, or slush layer. Based on the same set of geophysical parameters characterizing sea ice, a composite model is developed to calculate effective permittivities and backscattering covariance matrices at microwave frequencies for interpretation of sea ice polarimetric signatures.

  17. Polarimetric signatures of sea ice. 1: Theoretical model

    NASA Technical Reports Server (NTRS)

    Nghiem, S. V.; Kwok, R.; Yueh, S. H.; Drinkwater, M. R.

    1995-01-01

    Physical, structral, and electromagnetic properties and interrelating processes in sea ice are used to develop a composite model for polarimetric backscattering signatures of sea ice. Physical properties of sea ice constituents such as ice, brine, air, and salt are presented in terms of their effects on electromagnetic wave interactions. Sea ice structure and geometry of scatterers are related to wave propagation, attenuation, and scattering. Temperature and salinity, which are determining factors for the thermodynamic phase distribution in sea ice, are consistently used to derive both effective permittivities and polarimetric scattering coefficients. Polarmetric signatures of sea ice depend on crystal sizes and brine volumes, which are affected by ice growth rates. Desalination by brine expulsion, drainage, or other mechanisms modifies wave penetration and scattering. Sea ice signatures are further complicated by surface conditions such as rough interfaces, hummocks, snow cover, brine skim, or slush layer. Based on the same set of geophysical parameters characterizing sea ice, a composite model is developed to calculate effective permittivities and backscattering covariance matrices at microwave frequencies to interpretation of sea ice polarimetric signatures.

  18. Cirrus cloud model parameterizations: Incorporating realistic ice particle generation

    NASA Technical Reports Server (NTRS)

    Sassen, Kenneth; Dodd, G. C.; Starr, David OC.

    1990-01-01

    Recent cirrus cloud modeling studies have involved the application of a time-dependent, two dimensional Eulerian model, with generalized cloud microphysical parameterizations drawn from experimental findings. For computing the ice versus vapor phase changes, the ice mass content is linked to the maintenance of a relative humidity with respect to ice (RHI) of 105 percent; ice growth occurs both with regard to the introduction of new particles and the growth of existing particles. In a simplified cloud model designed to investigate the basic role of various physical processes in the growth and maintenance of cirrus clouds, these parametric relations are justifiable. In comparison, the one dimensional cloud microphysical model recently applied to evaluating the nucleation and growth of ice crystals in cirrus clouds explicitly treated populations of haze and cloud droplets, and ice crystals. Although these two modeling approaches are clearly incompatible, the goal of the present numerical study is to develop a parametric treatment of new ice particle generation, on the basis of detailed microphysical model findings, for incorporation into improved cirrus growth models. For example, the relation between temperature and the relative humidity required to generate ice crystals from ammonium sulfate haze droplets, whose probability of freezing through the homogeneous nucleation mode are a combined function of time and droplet molality, volume, and temperature. As an example of this approach, the results of cloud microphysical simulations are presented showing the rather narrow domain in the temperature/humidity field where new ice crystals can be generated. The microphysical simulations point out the need for detailed CCN studies at cirrus altitudes and haze droplet measurements within cirrus clouds, but also suggest that a relatively simple treatment of ice particle generation, which includes cloud chemistry, can be incorporated into cirrus cloud growth.

  19. Arctic ice islands

    SciTech Connect

    Sackinger, W.M.; Jeffries, M.O.; Lu, M.C.; Li, F.C.

    1988-01-01

    The development of offshore oil and gas resources in the Arctic waters of Alaska requires offshore structures which successfully resist the lateral forces due to moving, drifting ice. Ice islands are floating, a tabular icebergs, up to 60 meters thick, of solid ice throughout their thickness. The ice islands are thus regarded as the strongest ice features in the Arctic; fixed offshore structures which can directly withstand the impact of ice islands are possible but in some locations may be so expensive as to make oilfield development uneconomic. The resolution of the ice island problem requires two research steps: (1) calculation of the probability of interaction between an ice island and an offshore structure in a given region; and (2) if the probability if sufficiently large, then the study of possible interactions between ice island and structure, to discover mitigative measures to deal with the moving ice island. The ice island research conducted during the 1983-1988 interval, which is summarized in this report, was concerned with the first step. Monte Carlo simulations of ice island generation and movement suggest that ice island lifetimes range from 0 to 70 years, and that 85% of the lifetimes are less then 35 years. The simulation shows a mean value of 18 ice islands present at any time in the Arctic Ocean, with a 90% probability of less than 30 ice islands. At this time, approximately 34 ice islands are known, from observations, to exist in the Arctic Ocean, not including the 10-meter thick class of ice islands. Return interval plots from the simulation show that coastal zones of the Beaufort and Chukchi Seas, already leased for oil development, have ice island recurrences of 10 to 100 years. This implies that the ice island hazard must be considered thoroughly, and appropriate safety measures adopted, when offshore oil production plans are formulated for the Alaskan Arctic offshore. 132 refs., 161 figs., 17 tabs.

  20. Homogeneous ice nucleation from supercooled water.

    PubMed

    Li, Tianshu; Donadio, Davide; Russo, Giovanna; Galli, Giulia

    2011-11-28

    Homogeneous ice nucleation from supercooled water was studied in the temperature range of 220-240 K through combining the forward flux sampling method (Allen et al., J. Chem. Phys., 2006, 124, 024102) with molecular dynamics simulations (FFS/MD), based on a recently developed coarse-grained water model (mW) (Molinero et al., J. Phys. Chem. B, 2009, 113, 4008). The calculated ice nucleation rates display a strong temperature dependence, ranging from 2.148 ± 0.635 × 10(25) m(-3) s(-1) at 220 K to 1.672 ± 0.970 × 10(-7) m(-3) s(-1) at 240 K. These rates can be fitted according to the classical nucleation theory, yielding an estimate of the effective ice-water interface energy ?(ls) of 31.01 ± 0.21 mJ m(-2) for the mW water model. Compared to experiments, our calculation underestimates the homogeneous ice nucleation rate by a few orders of magnitude. Possible reasons for the discrepancy are discussed. The nucleating ice embryo contains both cubic ice Ic and hexagonal ice Ih, with the fraction of each structure being roughly 50% when the critical size is reached. In particular, a novel defect structure containing nearly five-fold twin boundaries is identified in the ice clusters formed during nucleation. The way such defect structure is formed is found to be different from mechanisms proposed for the formation of the same defect in metallic nanoparticles and thin film. The quasi five-fold twin boundary structure found here is expected to occur in the crystallization of a wide range of materials with the diamond cubic structure, including ice. PMID:21989826

  1. Dust ice nuclei effects on cirrus clouds in ECHAM5-HAM

    NASA Astrophysics Data System (ADS)

    Lohmann, Ulrike; Kübbeler, Miriam; Hendricks, Johannes; Kärcher, Bernd

    2013-05-01

    Aerosol-cloud interactions are one of the main uncertainties in climate research. Up to now a lot of research has been conducted on aerosol-cloud interactions in warm clouds. The impact of aerosols on ice or mixed-phase clouds is much less understood. Cirrus clouds in an unpolluted environment are assumed to form mainly via homogeneous freezing. The presence of heterogeneous ice nuclei can lead to earlier ice crystal formation and change the microphysical properties of cirrus clouds. Recent box model studies even suggest that heterogeneous freezing can suppress homogeneous freezing, if several conditions are fulfilled. Most likely this would lead to cirrus clouds containing fewer and larger ice crystals. If homogeneous and heterogeneous freezing compete either freezing mechanism may dominate depending mainly on vertical velocity and number density of ice nuclei. Thus, it is not clear yet how number and size of ice crystals are affected.

  2. Observation of Sea Ice Surface Thermal States Under Cloud Cover

    NASA Technical Reports Server (NTRS)

    Nghiem, S. V.; Perovich, D. K.; Gow, A. J.; Kwok, R.; Barber, D. G.; Comiso, J. C.; Zukor, Dorothy J. (Technical Monitor)

    2001-01-01

    Clouds interfere with the distribution of short-wave and long-wave radiations over sea ice, and thereby strongly affect the surface energy balance in polar regions. To evaluate the overall effects of clouds on climatic feedback processes in the atmosphere-ice-ocean system, the challenge is to observe sea ice surface thermal states under both clear sky and cloudy conditions. From laboratory experiments, we show that C-band radar (transparent to clouds) backscatter is very sensitive to the surface temperature of first-year sea ice. The effect of sea ice surface temperature on the magnitude of backscatter change depends on the thermal regimes of sea ice thermodynamic states. For the temperature range above the mirabilite (Na2SO4.10H20) crystallization point (-8.2 C), C-band data show sea ice backscatter changes by 8-10 dB for incident angles from 20 to 35 deg at both horizontal and vertical polarizations. For temperatures below the mirabilite point but above the crystallization point of MgCl2.8H2O (-18.0 C), relatively strong backwater changes between 4-6 dB are observed. These backscatter changes correspond to approximately 8 C change in temperature for both cases. The backscattering mechanism is related to the temperature which determines the thermodynamic distribution of brine volume in the sea ice surface layer. The backscatter is positively correlated to temperature and the process is reversible with thermodynamic variations such as diurnal insolation effects. From two different dates in May 1993 with clear and overcast conditions determined by the Advanced Very High Resolution Radiometer (AVHRR), concurrent Earth Resources Satellite 1 (ERS-1) C-band ice observed with increases in backscatter over first-year sea ice, and verified by increases in in-situ sea ice surface temperatures measured at the Collaborative-Interdisciplinary Cryosphere Experiment (C-ICE) site.

  3. Diatom assemblages promote ice formation in large lakes

    PubMed Central

    D'souza, N A; Kawarasaki, Y; Gantz, J D; Lee, R E; Beall, B F N; Shtarkman, Y M; Koçer, Z A; Rogers, S O; Wildschutte, H; Bullerjahn, G S; McKay, R M L

    2013-01-01

    We present evidence for the directed formation of ice by planktonic communities dominated by filamentous diatoms sampled from the ice-covered Laurentian Great Lakes. We hypothesize that ice formation promotes attachment of these non-motile phytoplankton to overlying ice, thereby maintaining a favorable position for the diatoms in the photic zone. However, it is unclear whether the diatoms themselves are responsible for ice nucleation. Scanning electron microscopy revealed associations of bacterial epiphytes with the dominant diatoms of the phytoplankton assemblage, and bacteria isolated from the phytoplankton showed elevated temperatures of crystallization (Tc) as high as ?3?°C. Ice nucleation-active bacteria were identified as belonging to the genus Pseudomonas, but we could not demonstrate that they were sufficiently abundant to incite the observed freezing. Regardless of the source of ice nucleation activity, the resulting production of frazil ice may provide a means for the diatoms to be recruited to the overlying lake ice, thereby increasing their fitness. Bacterial epiphytes are likewise expected to benefit from their association with the diatoms as recipients of organic carbon excreted by their hosts. This novel mechanism illuminates a previously undescribed stage of the life cycle of the meroplanktonic diatoms that bloom in Lake Erie and other Great Lakes during winter and offers a model relevant to aquatic ecosystems having seasonal ice cover around the world. PMID:23552624

  4. Ice-templated structures for biomedical tissue repair: From physics to final scaffolds

    NASA Astrophysics Data System (ADS)

    Pawelec, K. M.; Husmann, A.; Best, S. M.; Cameron, R. E.

    2014-06-01

    Ice-templating techniques, including freeze-drying and freeze casting, are extremely versatile and can be used with a variety of materials systems. The process relies on the freezing of a water based solution. During freezing, ice nucleates within the solution and concentrates the solute in the regions between the growing crystals. Once the ice is removed via sublimation, the solute remains in a porous structure, which is a negative of the ice. As the final structure of the ice relies on the freezing of the solution, the variables which influence ice nucleation and growth alter the structure of ice-templated scaffolds. Nucleation, the initial step of freezing, can be altered by the type and concentration of solutes within the solution, as well as the set cooling rate before freezing. After nucleation, crystal growth and annealing processes, such as Ostwald ripening, determine the features of the final scaffold. Both crystal growth and annealing are sensitive to many factors including the set freezing temperature and solutes. The porous structures created using ice-templating allow scaffolds to be used for many diverse applications, from microfluidics to biomedical tissue engineering. Within the field of tissue engineering, scaffold structure can influence cellular behavior, and is thus critical for determining the biological stimulus supplied by the scaffold. The research focusing on controlling the ice-templated structure serves as a model for how other ice-templating systems might be tailored, to expand the applications of ice-templated structures to their full potential.

  5. Sea ice and icing risk for offshore wind turbines

    Microsoft Academic Search

    L. Battisti; R. Fedrizzi; A. Brighenti; T. Laakso

    There are two important issues related to wind turbines performances in offshore sites that locate in cold cli- mates: sea ice (flows, driving ice, land-fast ice) and the presence of atmospheric icing (due to water in the air as in-cloud operation, rainfall and sea sprays) which may potentially lead to ice formation on turbines' struc- tures. Icing of rotor blades

  6. Creep and plasticity of glacier ice: a material science perspective Paul DUVAL, Maurine MONTAGNAT, Fanny GRENNERAT, Jerome WEISS,

    E-print Network

    Weiss, Jérôme

    Creep and plasticity of glacier ice: a material science perspective Paul DUVAL, Maurine MONTAGNAT the plasticity of ice have been made during the past 60 years with the development of studies of the flow experimental investigations clearly show that the plastic deformation of the ice single crystal and polycrystal

  7. Inhibition of chemical changes related to freshness loss during storage of horse mackerel ( Trachurus trachurus) in slurry ice

    Microsoft Academic Search

    Vanesa Losada; Carmen Piñeiro; Jorge Barros-Velázquez; Santiago P. Aubourg

    2005-01-01

    Slurry ice is a biphasic system consisting of small spherical ice crystals surrounded by seawater at subzero temperature. Its employment was evaluated in the present work as a new chilled storage method for whole horse mackerel (Trachurus trachurus) and compared with traditional flake icing. Different chemical analyses (nucleotide degradation, lipid hydrolysis and oxidation, interaction compounds formation and electrophoretic protein profiles)

  8. TEMPERATURE DEPENDENCE OF THE 306 AND 227 cm-1 RAMAN LINES IN HEXAGONAL ICE BETWEEN 250 AND 80 K

    E-print Network

    Paris-Sud XI, Université de

    and discussion. - The single crystal of ice Ih was of the same origin as those studied by Brillouin scattering1457 TEMPERATURE DEPENDENCE OF THE 306 AND 227 cm-1 RAMAN LINES IN HEXAGONAL ICE BETWEEN 250 AND 80 of the translational vibrational modes at 227 cm-1and 306 cm-1 in hexagonal ice were studied as a function

  9. Eutectic freeze crystallization: Application to process streams and waste water purification

    Microsoft Academic Search

    F. van der Ham; G. J. Witkamp; J. de Graauw; G. M. van Rosmalen

    1998-01-01

    Two case studies are presented using eutectic freeze crystallization (EFC) as an alternative for evaporative crystallization: a 7.8 ton day?1 35 w% aqueous sodium nitrate and a 24 ton day?1 12 w% copper sulfate stream. The proposed crystallizer is a cooled disk column crystallizer (CDCC), using indirect cooling for heat transfer. In single stage operation, the formed ice crystals are

  10. Nares Strait Ice Flux

    NASA Astrophysics Data System (ADS)

    Kwok, R.

    2005-12-01

    Six years (1996-2002) of Arctic Ocean ice flux through Nares Strait are estimated using ice motion from RADARSAT. Across an ~30 km gate at the entrance to Robeson Channel, the average annual (Sept-Aug) ice area flux is 33x103 km2 and ranges from 16x103 km2 in 2000 to 48x103 km2 in 1999. Uncertainties in the ice displacements from high-resolution synthetic aperture radar imagery, at ~100-300 m, are small. Assuming sea ice that is 3 m thick, the average volume flux amounts to ~100 km3 (~3 mSv); this is ~5% of the mean annual Fram Strait ice flux (1978-2003). Seasonally, ice flux is most active after July, ceases after the formation of an ice arch in mid- to late-winter, and re-commences after breakup in the late spring. The multiyear ice coverage of the area poleward of the gate is high (>80%). South of the gate, the multiyear ice coverage is highly variable and is reduced as individual floes, small enough to fit through the channel, are broken off the Arctic pack. After the formation of an ice arch in winter, the channel may be filled with multiyear or seasonal ice. The details of the ice flux estimates are presented.

  11. NOAA Great Lakes Ice Atlas

    NSDL National Science Digital Library

    This website presents the results of the analysis of Great Lakes ice charts dating back to 1960. After learning about the methods used to produce this online atlas, users can view the original ice charts. Researchers can find data on first ice, last ice, ice duration, and other ice related statistics. Students and educators can learn about variations in ice cover through the animations of ice cover time series. The website offers downloads of a few of the references and technical issues.

  12. A study on ice formation by means of direct-contact heat transfer between water and coolant

    SciTech Connect

    Noma, Tsuyoshi; Yamashita, Katsuya; Hachimonji, Takayuki; Watanabe, Yutaka [Toshiba Corp., Yokohama (Japan). Heavy Apparatus Engineering Lab.

    1995-12-31

    Ice storage systems are attracting interest as a way to avoid the peak demand charges imposed by many electric utilities. The authors have developed a new type of ice storage system that is entirely different from the systems in use until now. The ice storage system produces extremely thin discoidal crystals of ice several millimeters in diameter. This ice is similar in shape to frazil ice observed in the arctic. Characteristically, this system has high efficiency in producing ice, and since the ice melts easily, cool energy in the form of cold water can be provided immediately. In this paper the authors show that ice production by means of direct-contact heat transfer between water and coolant is possible. They also show the similarity between the ice and that which occurs in nature.

  13. Cubic ice from liquid water

    Microsoft Academic Search

    Erwin Mayer; Andreas Hallbrucker

    1987-01-01

    Hexagonal ice (ice Ih) is the only form of ice that is known to occur naturally on the Earth. Recently it has been suggested that small droplets of water in the upper atmosphere may often freeze first to cubic ice (ice Ic), which is metastable relative to ice Ih. The evidence is Scheiner's halo, a rare halo that occurs at

  14. Doped Colloidal Artificial Ice

    E-print Network

    A. Libal; C. J. Olson Reichhardt; C. Reichhardt

    2015-07-02

    We examine square and kagome artificial spin ice for colloids confined in arrays of double-well traps. Unlike magnetic artificial spin ices, colloidal and vortex artificial spin ice realizations allow creation of doping sites through double occupation of individual traps. We find that doping square and kagome ice geometries produces opposite effects. For square ice, doping creates local excitations in the ground state configuration that produce a local melting effect as the temperature is raised. In contrast, the kagome ice ground state can absorb the doping charge without generating non-ground-state excitations, while at elevated temperatures the hopping of individual colloids is suppressed near the doping sites. These results indicate that in the square ice, doping adds degeneracy to the ordered ground state and creates local weak spots, while in the kagome ice, which has a highly degenerate ground state, doping locally decreases the degeneracy and creates local hard regions.

  15. Structure of ice Ih and ice Ic as described in the language of Delaunay simplices.

    PubMed

    Naberukhin, Yu I; Voloshin, V P

    2011-11-01

    Classification of the Delaunay simplex forms is carried out for the ideal structures of ice Ih and ice Ic. Classification according to the number of edges of different length reveals six types of simplices, while classification according to the number and mutual positions of edges of the unit length (equal to the length of the hydrogen bond) reveals five types of indices. Ice Ic is composed of simplices of three types (one of which has the form of a perfect tetrahedron), ice Ih from six simplices. Degeneracy is removed in computer models of slightly distorted ice by means of insignificant shifting of water molecules from their ideal positions. This makes it possible to provide the unambiguous partition of the crystal structure into Delaunay simplices. It is found that degeneracy removal results in the appearance of Delaunay simplices of specific forms with a very small volume (Kije simplices). The shape characteristics of simplices of different types and their percentage are calculated in the large computer models of ice. In particular, the fraction of the Kije simplices is found to be about 7.5% in ice Ih. PMID:22011465

  16. Sublimation Coefficient of Water Ice

    NASA Astrophysics Data System (ADS)

    Kossacki, K. J.; Markiewicz, W. J.; Skorov, Y.; Koemle, N. I.

    1999-09-01

    In simulations of evolution of cometary nuclei it is commonly assumed that the coefficients of sublimation and condensation of the volatiles are both equal to one. However, the laboratory investigation of water ice samples under cometary-like conditions (Kossacki et al., 1997) suggests, that the sublimation flux calculated with the Hertz-Knudsen formula and the above assumption is nearly an order of magnitude too high. A similar conclusion can be drawn from the results of various experiments on growth from vapour phase and sublimation of ice crystals (Lamb and Scott, 1972; Beckmann and Lacmann, 1982; Sei and Gonda, 1989). These results imply that the sublimation coefficient can be as low as 0.1. The above coefficients depend on various parameters such as temperature, concentration of surface impurities as well as deviation of the vapour pressure from that of the phase equilibrium. In this work we discuss the temperature dependence of both of these coefficients. We also propose an empirical formula to fit the temperature dependence. This new formulation is also used to analyse the implications for the thermal conductivity of a porous cometary-like ice.

  17. Ice Concentration Retrieval in Stratiform Mixed-phase Clouds Using Cloud Radar Reflectivity Measurements and 1D Ice Growth Model Simulations

    SciTech Connect

    Zhang, Damao; Wang, Zhien; Heymsfield, Andrew J.; Fan, Jiwen; Luo, Tao

    2014-10-01

    Measurement of ice number concentration in clouds is important but still challenging. Stratiform mixed-phase clouds (SMCs) provide a simple scenario for retrieving ice number concentration from remote sensing measurements. The simple ice generation and growth pattern in SMCs offers opportunities to use cloud radar reflectivity (Ze) measurements and other cloud properties to infer ice number concentration quantitatively. To understand the strong temperature dependency of ice habit and growth rate quantitatively, we develop a 1-D ice growth model to calculate the ice diffusional growth along its falling trajectory in SMCs. The radar reflectivity and fall velocity profiles of ice crystals calculated from the 1-D ice growth model are evaluated with the Atmospheric Radiation Measurements (ARM) Climate Research Facility (ACRF) ground-based high vertical resolution radar measurements. Combining Ze measurements and 1-D ice growth model simulations, we develop a method to retrieve the ice number concentrations in SMCs at given cloud top temperature (CTT) and liquid water path (LWP). The retrieved ice concentrations in SMCs are evaluated with in situ measurements and with a three-dimensional cloud-resolving model simulation with a bin microphysical scheme. These comparisons show that the retrieved ice number concentrations are within an uncertainty of a factor of 2, statistically.

  18. Ice electrode electrolytic cell

    DOEpatents

    Glenn, David F. (Idaho Falls, ID); Suciu, Dan F. (Idaho Falls, ID); Harris, Taryl L. (Idaho Falls, ID); Ingram, Jani C. (Idaho Falls, ID)

    1993-01-01

    This invention relates to a method and apparatus for removing heavy metals from waste water, soils, or process streams by electrolytic cell means. The method includes cooling a cell cathode to form an ice layer over the cathode and then applying an electric current to deposit a layer of the heavy metal over the ice. The metal is then easily removed after melting the ice. In a second embodiment, the same ice-covered electrode can be employed to form powdered metals.

  19. Ice Drilling Gallonmilkjugs

    E-print Network

    Saffman, Mark

    Ice Drilling Materials · Gallonmilkjugs · Syringes,largeand small · Pitchers · Spraybottles · 13x9? ·Isitbettertosquirtthewaterslowlyorasquicklyaspossible? ·Doestherateatwhichyousquirtthewaterchangethediameteroftheholes? ·Doesthetypeof`drill

  20. Stability of ferroelectric ice

    E-print Network

    Iitaka, Toshiaki

    2010-01-01

    We theoretically study the stability conditions of the ferroelectric ice of the Cmc21 structure, which has been considered, for decades, one of the most promising candidates of the low temperature proton-ordered phase of pure ice Ih. It turned out that the Cmc21 structure is stable only with a certain amount of dopant and the true proton-ordered phase of pure ice Ih remains to be found at lower temperature. Implication for spin ice is mentioned.

  1. Nares Strait Ice Flux

    Microsoft Academic Search

    R. Kwok

    2005-01-01

    Six years (1996-2002) of Arctic Ocean ice flux through Nares Strait are estimated using ice motion from RADARSAT. Across an ~30 km gate at the entrance to Robeson Channel, the average annual (Sept-Aug) ice area flux is 33x103 km2 and ranges from 16x103 km2 in 2000 to 48x103 km2 in 1999. Uncertainties in the ice displacements from high-resolution synthetic aperture

  2. Deformation in the Rutford ice stream, West Antarctica: measuring shear-wave anisotropy from icequakes

    NASA Astrophysics Data System (ADS)

    Kendall, Michael; Harland, Sophie; Stuart, Graham; Baird, Alan; Lloyd, Geoff; Smith, Andy; Pritchard, Hamish; Brisbourne, Alex

    2013-04-01

    Ice streams provide major drainage pathways for the Antarctic ice sheet. The stress distribution and style of flow in such ice streams produces elastic and rheological anisotropy, which informs ice flow modelling as to how ice masses respond to external changes such as global warming. Here we analyse elastic anisotropy in the Rutford ice stream, West Antarctica, using observations of shear wave splitting from three-component icequake seismograms to characterise ice deformation via crystal preferred orientation. Over 110 high quality measurements are made on 41 events recorded at five stations temporarily deployed near the ice stream grounding line. To the best of our knowledge this is the first well-documented observation of shear wave splitting from Antarctic icequakes. The magnitude of the splitting ranges from 2ms to 80ms and suggest a maximum of 6% shear wave splitting. The fast shear wave polarisation direction is roughly perpendicular to ice flow direction. We consider three mechanisms for ice anisotropy: a cluster model (VTI model); a girdle model (and HTI model); and crack-induced anisotropy (an HTI model). Based on the data we can rule out a VTI mechanism as the sole cause of anisotropy - an HTI component is needed, which may be due to ice crystal a-axis alignment in the direction of flow or the alignment of cracks or ice-films in the plane perpendicular to the flow direction. The results may suggest a combination of mechanisms are at play, which represent vertical variations in the symmetry of ice-crystal anisotropy in an ice stream, as predicted by ice fabric models.

  3. Heterogeneous ice nucleation ability of crystalline sodium chloride dihydrate particles

    NASA Astrophysics Data System (ADS)

    Wagner, Robert; MöHler, Ottmar

    2013-05-01

    The aerosol and cloud chamber AIDA (Aerosol Interactions and Dynamics in the Atmosphere) of the Karlsruhe Institute of Technology has been used to quantify the deposition mode ice nucleation ability of airborne crystalline sodium chloride dihydrate (NaCl • 2H2O) particles with median diameters between 0.06 and 1.1 µm. For this purpose, expansion cooling experiments with starting temperatures from 235 to 216 K were conducted. Recently, supermicron-sized NaCl • 2H2O particles deposited onto a surface have been observed to be ice-active in the deposition mode at temperatures below 238 K, requiring a median threshold ice saturation ratio of only 1.02 in the range from 238 to 221 K. In AIDA, heterogeneous ice nucleation by NaCl • 2H2O was first detected at a temperature of 227.1 K with a concomitant threshold ice saturation ratio of 1.25. Above that temperature, the crystallized salt particles underwent a deliquescence transition to form aqueous NaCl solution droplets upon increasing relative humidity. At nucleation temperatures below 225 K, the inferred threshold ice saturation ratios varied between 1.15 and 1.20. The number concentration of the nucleated ice crystals was related to the surface area of the seed aerosol particles to deduce the ice nucleation active surface site (INAS) density of the aerosol population as a function of the ice supersaturation. Maximum INAS densities of about 6 ? 1010 m-2 at an ice saturation ratio of 1.20 were found for temperatures below 225 K. These INAS densities are similar to those recently derived for deposition mode ice nucleation on mineral dust particles.

  4. Piscataquis River Ice Measurement

    USGS Multimedia Gallery

    In this photo Terrence Talbot, a student with the Maine Office, drills holes with an ice auger in preparation for a discharge measurement through the ice at the USGS station on the Piscataquis River near Dover-Foxcroft, Maine.  After drilling 20-30 holes through the ice at known intervals we a...

  5. Ice Jam Remnants

    USGS Multimedia Gallery

    On April 29, hydrologic technicians Anthony Underwood and Jeremiah Pomerleau visited the USGS gaging station on the St. John River at Ninemile Bridge and found a sea of broken up, dirty ice left behind by a recent ice jam. According to Anthony, photos don't do the size and scale of the ice chunks a...

  6. Vote for Ice Cream

    NSDL National Science Digital Library

    chris worley

    2012-04-20

    This lesson will pique your students' interest by reading about Curious George and his ice cream adventure. Students will move from George's adventure to a class chart of favorite ice cream flavors to organizing and completing their own ice cream chart.

  7. Seasat and floating ice

    Microsoft Academic Search

    1974-01-01

    Data collected by SEASAT would be useful in developing predictive physical models for the drift and deformation of sea ice, for estimating the heat budget of the polar seas, for the optimum routing of shipping through pack ice areas, for the design of both offshore structures and shipping capable of surviving in heavy pack ice, and for the tracking of

  8. Ice on the Moon

    NSDL National Science Digital Library

    David Williams

    2003-01-22

    This information about the Lunar Prospector mission to the Moon discusses the possibility that ice exists on the lunar surface. The article indicates that no native water ice has been found on the moon. If ice has been found, it most likely originated from meteors and meteorites which periodically bombard the lunar surface.

  9. Radio-wave depolarization and scattering within ice sheets: a matrix-based model to link radar and ice-core measurements and its application

    Microsoft Academic Search

    Shuji Fujita; Hideo Maeno; Kenichi Matsuoka

    2006-01-01

    Crystal-orientation fabric (COF) has a large influence on ice-sheet flow. Earlier radar studies have shown that COF-based birefringence occurs within ice sheets. Radio-wave scattering in polar ice results from changing physical properties of permittivity and conductivity that arise from differing values of density, acidity and COF. We present an improved mathematical model that can handle all these phenomena together. We

  10. Continuous Production of Ice Slurry by Control of Solute Concentration with Ultrasonic Vibration

    NASA Astrophysics Data System (ADS)

    Tada, Yukio; Takimoto, Akira; Miyamoto, Tomoaki; Mikami, Hiroko; Hayashi, Yujiro

    A method to making ice slurry is one of key technology for cold-energy Storage system. This study has been conducted to clarify continuous production of ice slurry by utilizing constitutional supercooling promoted by mixing of two aqueous solutions whose solute concentrations are different. In this technique, fine ice crystals are made under volume-catalyzed nucleation without heat transfer surface. In the experiments, cooled sucrose solution and water were mixed in the cylindrical vessel, and ultrasonic vibration was applied to promote nucleation in the supercooled solution. It was found that the ice making process is classified into three characteristic patterns; stable ice making, ice making in stratified concentration layer due to defect in solute-mixing, and no ice making due to no supercooling by mixing. The characteristics of ice making were discussed with the mixing ratio and total flow rate of solutions.

  11. Layers of Ice

    NSDL National Science Digital Library

    This is a lesson about the formation of glaciers, ice layering and stratigraphy, and the cryosphere and cryobotics. Learners will collect evidence of layering, explore the science story that layering tells, study snow and ice for insights into climate change, and learn about the tools used to explore ice layers on Earth and in the solar system. Connections between rings of a tree and rings in an ice core will be made. Activities include small group miming, speaking, drawing, and/or writing. This is lesson 7 of 12 in the unit, Exploring Ice in the Solar System.

  12. On a nearly proton-ordered structure for ice IX

    Microsoft Academic Search

    Sam J. La Placa; Walter C. Hamilton; Barclay Kamb; Anand Prakash

    1973-01-01

    Single-crystal neutron diffraction shows that ice IX, the low-temperature modification of ice III, has an almost completely proton-ordered structure in which the ordered component contains two types of water molecules, type 1 in a site of no point symmetry, and type 2 on a twofold axis, each forming four hydrogen bonds in a three-dimensional framework. The configuration of the water

  13. Diffusion and solubility of HCHO in ice: preliminary results

    Microsoft Academic Search

    S. Perrier; P. Sassin; F. Domine

    2003-01-01

    The diffusion and solubility of formaldehyde (HCHO) in ice were measured at -15degrees by exposing large single crystals of ice to low vapor pressures of HCHO (P-HCHO) for several days. The solubility was found to be ( 30 +\\/- 3) x 10(-6) mol L-1 at -15degrees under P-HCHO = 1.7 x 10(-2) Pa. The diffusion coefficient is of the order

  14. Bench Scale Test of Absorption Slurry-ice Maker

    NASA Astrophysics Data System (ADS)

    Sasao, Hiroyuki; Yoshida, Takashi

    Slurry ice system is desirable as cold heat source for air conditioning, because it requires less conveyance power or less pipe size. On the other hand, recently absorption refrigerator is reevaluated because it can utilize various types of waste heat and it does not use fluorocarbon refrigerant. But it had been regarded to be difficult to make ice by absorption refrigerator because the refrigerant is water. However making slurry ice is possible, of cource, if the slurry ice generated by partial freezing of water is continuously taken away from the evaporator. This method was certified experimentally with a bench scale model. For ice making continuously, ice had not to be frozen stiff at water surface or inside wall of the evaporator. Then refrigerant water in the evaporator was raised swirl flow. And inside wall of the evaporator was finished by water repellent coating, and heated from outside wall. This slurry ice was adaptable to hydraulic transportation, because ice was needle crystal with about 5 mm length and ice temperature was 0°C.

  15. Mechanisms of ice gouging

    SciTech Connect

    Kioka, Shinji; Saeki, Hiroshi [Hokkaido Univ., Sapporo (Japan)

    1995-12-31

    Sea ice is carried to the cost of Hokkaido by wind and water currents every year. In low pressure systems or when there is much sea ice, it drifts out toward the Pacific Ocean. When sea ice moves in shallow water areas, the sandy subgrade on the sea bottom is gouged by the sea ice. This phenomenon is generally called ``ice gouging``. Substantial damage to sea food i.e. (shellfish) and to structures embedded in the seabed is reported every year. However, the mechanisms and behavior of ice gouging is not known sufficiently enough for discussion. Therefore, the authors have conducted a suitable experiment to clarify this phenomenon and have suggested formulas to measure ice gouging.

  16. River Ice Processes

    NSDL National Science Digital Library

    COMET

    2006-11-10

    The “River Ice Processes” module provides information on flooding associated with river ice jams. In this webcast, Dr. Kate White, nationally-recognized expert on river ice, explores basic river ice processes including the formation, growth, breakup, and transport of river ice and how it can become jammed, triggering floods. In addition, Dr. White covers the current, state-of-the-art ice jam forecasting, and current ice-modeling research and development being conducted by the U.S. Army Corps of Engineers. As a foundation topic for the Basic Hydrologic Science course, this module may be taken on its own, but it will also be available as a supporting topic providing factual scientific information to support students in completion of the case-based forecasting modules.

  17. ICE SLURRY APPLICATIONS.

    PubMed

    Kauffeld, M; Wang, M J; Goldstein, V; Kasza, K E

    2010-12-01

    The role of secondary refrigerants is expected to grow as the focus on the reduction of greenhouse gas emissions increases. The effectiveness of secondary refrigerants can be improved when phase changing media are introduced in place of single phase media. Operating at temperatures below the freezing point of water, ice slurry facilitates several efficiency improvements such as reductions in pumping energy consumption as well as lowering the required temperature difference in heat exchangers due to the beneficial thermo-physical properties of ice slurry. Research has shown that ice slurry can be engineered to have ideal ice particle characteristics so that it can be easily stored in tanks without agglomeration and then be extractable for pumping at very high ice fraction without plugging. In addition ice slurry can be used in many direct contact food and medical protective cooling applications. This paper provides an overview of the latest developments in ice slurry technology. PMID:21528014

  18. ICE SLURRY APPLICATIONS

    PubMed Central

    Kauffeld, M.; WANG, M. J.; Goldstein, V.; Kasza, K. E.

    2011-01-01

    The role of secondary refrigerants is expected to grow as the focus on the reduction of greenhouse gas emissions increases. The effectiveness of secondary refrigerants can be improved when phase changing media are introduced in place of single phase media. Operating at temperatures below the freezing point of water, ice slurry facilitates several efficiency improvements such as reductions in pumping energy consumption as well as lowering the required temperature difference in heat exchangers due to the beneficial thermo-physical properties of ice slurry. Research has shown that ice slurry can be engineered to have ideal ice particle characteristics so that it can be easily stored in tanks without agglomeration and then be extractable for pumping at very high ice fraction without plugging. In addition ice slurry can be used in many direct contact food and medical protective cooling applications. This paper provides an overview of the latest developments in ice slurry technology. PMID:21528014

  19. Anomalous Proton Dynamics in Ice at Low Temperatures

    SciTech Connect

    Bove, L. E.; Klotz, S. [IMPMC, CNRS-UMR 7590, Universite P and M Curie, F-75252 Paris (France); Paciaroni, A.; Sacchetti, F. [CNR-INFM CRS-Soft, c/o Dipartimento di Fisica, Universita di Perugia, I-06123 Perugia (Italy)

    2009-10-16

    We present incoherent quasielastic neutron scattering measurements on ice Ih (ordinary ice) and Ic (cubic ice) which show the existence of nonharmonic motion of hydrogen at low temperatures, down to 5 K. We show that this dynamics is localized, nonvibrational, and related to the hydrogen disorder since it is absent in ordered ice VIII. A main jump distance of 0.75 A is identified, hence close to the distance between the two possible proton sites along the oxygen-oxygen bond. The dynamics is non-Arrhenius, has a large time rate of 2.7x10{sup 11} s{sup -1}, and affects only a few percent of the total number of hydrogen atoms in the crystal. These results give evidence for the existence of concerted proton tunneling in these ice phases.

  20. Relative importance of acid coating on ice nuclei in the deposition and contact modes for wintertime Arctic clouds and radiation

    NASA Astrophysics Data System (ADS)

    Girard, Eric; Sokhandan Asl, Niloofar

    2014-01-01

    Aerosols emitted from volcanic activities and polluted mid-latitudes regions are efficiently transported over the Arctic during winter by the large-scale atmospheric circulation. These aerosols are highly acidic. The acid coating on ice nuclei, which are present among these aerosols, alters their ability to nucleate ice crystals. In this research, the effect of acid coating on deposition and contact ice nuclei on the Arctic cloud and radiation is evaluated for January 2007 using a regional climate model. Results show that the suppression of contact freezing by acid coating on ice nuclei leads to small changes of the cloud microstructure and has no significant effect on the cloud radiative forcing (CRF) at the top of the atmosphere when compared with the effect of the alteration of deposition ice nucleation by acid coating on deposition ice nuclei. There is a negative feedback by which the suppression of contact freezing leads to an increase of the ice crystal nucleation rate by deposition ice nucleation. As a result, the suppression of contact freezing leads to an increase of the cloud ice crystal concentration. Changes in the cloud liquid and ice water contents remain small and the CRF is not significantly modified. The alteration of deposition ice nucleation by acid coating on ice nuclei is dominant over the alteration of contact freezing.

  1. Cloud structure and crystal growth in nimbostratus clouds. Mengistu Wolde*

    E-print Network

    Vali, Gabor

    1 Cloud structure and crystal growth in nimbostratus clouds. Mengistu Wolde* , Gabor Vali-mail: mengistu.wolde@nrc.ca. #12;2 Abstract Cloud structure and crystal growth in two nimbostratus were examined made available by large scale lifting was taken up by depositional growth of the ice crystals

  2. LOW TEMPERATURE SCANNING ELECTRON MICROSCOPY OF IRREGULAR SNOW CRYSTALS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Snow crystals occur in eight basic types: columns, needles, plates, dendrites, irregular crystals, graupel, hail and ice pellets. Most of these types have been described and photographed. However, our understanding of "irregular crystals" remains vague because the limited resolution and depth-of-f...

  3. A Global View of Ice Generation in Supercooled Stratiform Altocumulus Clouds Based on CALIPSO and CloudSat Measurements

    NASA Astrophysics Data System (ADS)

    Zhang, D.; Wang, Z.; Liu, D.

    2008-12-01

    Ice generation in atmospheric clouds is still poorly understood. Supercooled stratiform altocumulus (Ac) clouds represent a simple scenario to study ice generation in clouds. Because radar is more sensitive to large ice crystals than small water droplets in mixed-phase clouds, radar measurements provide a good indication of ice generation in supercooled stratiform Ac clouds. The first year CALIPSO (lidar) and CloudSat (radar) satellite data are analyzed to provide a global view of ice generation in supercooled stratiform Ac clouds. Two distinct ice formation zones, cloud top temperature (CTT) colder or warmer than -18 C, can be identified from the distributions of Ac occurrence in terms of CTT and layer maximum radar reflectivity factor (Zmax). For all latitude ranges, ice crystals are detectable in some of the stratiform Ac clouds when cloud top temperature colder than -10 C, and the Zmax of ice crystals increase with CTT decrease in an similar slope and reach the maximum value ~ -16 C. Ice generation in stratiform Ac with CTT colder than -18 C show significant latitude differences. The contrast of ice generation in these two zones indicate different dominate ice generation mechanisms among them. The ice occurrence and mean ice water path are proved as a function of CTT. Aerosol size and chemical compositions have great impacts on ice formation characteristics, and mineral dust is effective ice nuclei (IN). By separating stratiform Ac in the "dust bel" regions into dusty Ac (affected by dust) and non-dusty Ac, we found strong dust impacts on ice generation in stratiform Ac. For dusty Ac, ice are detected in all clouds when CTT reaches ~ -20 C.

  4. A van der Waals density functional study of ice Ih.

    PubMed

    Hamada, Ikutaro

    2010-12-01

    Density functional theory with the van der Waals density functional (vdW-DF) is used to calculate equilibrium crystal structure, binding energy, and bulk modulus of ice Ih. It is found that although it overestimates the equilibrium volume, vdW-DF predicts accurate binding energy of ice Ih, as compared with high level quantum chemistry calculations and experiment. Inclusion of the nonlocal correlation, i.e., van der Waals interaction, leads to an overall improvement over the standard generalized gradient approximation in describing water ice. PMID:21142304

  5. Incorporation of crude and fuel oil into salt-and freshwater ice

    SciTech Connect

    Taylor, S.; Perron, N.

    1995-02-01

    North Slope Crude, no. 2 fuel oil, and vegetable oil were each released under columnar freshwater and saltwater ice grown in a laboratory coldroom. Because the thermal conductivity of all the oils is lower than that of water or ice, thinner ice grew under the oil and resulted in a concave ice/water interface. Both the fresh and saline ice encapsulated the oils, but the saline ice did so more slowly. Thin sections of the ice blocks containing the crude and fuel oils show how the columnar ice crystals bend around and under the oil patches. The movement of the vegetable oil during melting was photographed, and spectral reflectance measurements of the ice surface were made to determine if the oil could be detected remotely. Although we could detect the presence of oil under 10 cm of ice, under field conditions the optical detectability of oil will depend upon the depth of the oil within the ice, the type of ice, and the contrast between the under-ice oil and the background against which it is being viewed.

  6. Near-Infrared Spectral Monitoring of Pluto's Ices II: Recent Decline of CO and N$_2$ Ice Absorptions

    E-print Network

    Grundy, W M; Young, L A; Holler, B J

    2014-01-01

    IRTF/SpeX observations of Pluto's near-infrared reflectance spectrum during 2013 show vibrational absorption features of CO and N$_2$ ices at 1.58 and 2.15 {\\mu}m, respectively, that are weaker than had been observed during the preceding decade. To reconcile declining volatile ice absorptions with a lack of decline in Pluto's atmospheric pressure, we suggest these ices could be getting harder to see because of increasing scattering by small CH$_4$ crystals, rather than because they are disappearing from the observed hemisphere.

  7. Dynamics enhanced by HCl doping triggers full Pauling entropy release at the ice XII-XIV transition.

    PubMed

    Köster, K W; Fuentes-Landete, V; Raidt, A; Seidl, M; Gainaru, C; Loerting, T; Böhmer, R

    2015-01-01

    The pressure-temperature phase diagram of ice displays a perplexing variety of structurally distinct phases. In the century-long history of scientific research on ice, the proton-ordered ice phases numbered XIII through XV were discovered only recently. Despite considerable effort, none of the transitions leading from the low-temperature ordered ices VIII, IX, XI, XIII, XIV and XV to their high-temperature disordered counterparts were experimentally found to display the full Pauling entropy. Here we report calorimetric measurements on suitably high-pressure-treated, hydrogen chloride-doped ice XIV that demonstrate just this at the transition to ice XII. Dielectric spectroscopy on undoped and on variously doped ice XII crystals reveals that addition of hydrogen chloride, the agent triggering complete proton order in ice XIV, enhances the precursor dynamics strongest. These discoveries provide new insights into the puzzling observation that different dopants trigger the formation of different proton-ordered ice phases. PMID:26076946

  8. Dynamics enhanced by HCl doping triggers full Pauling entropy release at the ice XII–XIV transition

    PubMed Central

    Köster, K. W.; Fuentes-Landete, V.; Raidt, A.; Seidl, M.; Gainaru, C.; Loerting, T.; Böhmer, R.

    2015-01-01

    The pressure–temperature phase diagram of ice displays a perplexing variety of structurally distinct phases. In the century-long history of scientific research on ice, the proton-ordered ice phases numbered XIII through XV were discovered only recently. Despite considerable effort, none of the transitions leading from the low-temperature ordered ices VIII, IX, XI, XIII, XIV and XV to their high-temperature disordered counterparts were experimentally found to display the full Pauling entropy. Here we report calorimetric measurements on suitably high-pressure-treated, hydrogen chloride-doped ice XIV that demonstrate just this at the transition to ice XII. Dielectric spectroscopy on undoped and on variously doped ice XII crystals reveals that addition of hydrogen chloride, the agent triggering complete proton order in ice XIV, enhances the precursor dynamics strongest. These discoveries provide new insights into the puzzling observation that different dopants trigger the formation of different proton-ordered ice phases. PMID:26076946

  9. Sea Ice and Oceanographic Conditions.

    ERIC Educational Resources Information Center

    Oceanus, 1986

    1986-01-01

    The coastal waters of the Beaufort Sea are covered with ice three-fourths of the year. These waters (during winter) are discussed by considering: consolidation of coastal ice; under-ice water; brine circulation; biological energy; life under the ice (including kelp and larger animals); food chains; and ice break-up. (JN)

  10. Investigating ice nucleation in cirrus clouds with an aerosol-enabled Multiscale Modeling Framework

    SciTech Connect

    Zhang, Chengzhu; Wang, Minghuai; Morrison, H.; Somerville, Richard C.; Zhang, Kai; Liu, Xiaohong; Li, J-L F.

    2014-12-01

    In this study, an aerosol-dependent ice nucleation scheme [Liu and Penner, 2005] has been implemented in an aerosol-enabled multi-scale modeling framework (PNNL MMF) to study ice formation in upper troposphere cirrus clouds through both homogeneous and heterogeneous nucleation. The MMF model represents cloud scale processes by embedding a cloud-resolving model (CRM) within each vertical column of a GCM grid. By explicitly linking ice nucleation to aerosol number concentration, CRM-scale temperature, relative humidity and vertical velocity, the new MMF model simulates the persistent high ice supersaturation and low ice number concentration (10 to 100/L) at cirrus temperatures. The low ice number is attributed to the dominance of heterogeneous nucleation in ice formation. The new model simulates the observed shift of the ice supersaturation PDF towards higher values at low temperatures following homogeneous nucleation threshold. The MMF models predict a higher frequency of midlatitude supersaturation in the Southern hemisphere and winter hemisphere, which is consistent with previous satellite and in-situ observations. It is shown that compared to a conventional GCM, the MMF is a more powerful model to emulate parameters that evolve over short time scales such as supersaturation. Sensitivity tests suggest that the simulated global distribution of ice clouds is sensitive to the ice nucleation schemes and the distribution of sulfate and dust aerosols. Simulations are also performed to test empirical parameters related to auto-conversion of ice crystals to snow. Results show that with a value of 250 ?m for the critical diameter, Dcs, that distinguishes ice crystals from snow, the model can produce good agreement to the satellite retrieved products in terms of cloud ice water path and ice water content, while the total ice water is not sensitive to the specification of Dcs value.

  11. Prospecting for Martian Ice

    NASA Technical Reports Server (NTRS)

    McBride, S. A.; Allen, C. C.; Bell, M. S.

    2005-01-01

    During high Martian obliquity, ice is stable to lower latitudes than predicted by models of present conditions and observed by the Gamma Ray Spectrometer (approx. 60 deg N). An ice-rich layer deposited at mid-latitudes could persist to the present day; ablation of the top 1 m of ice leaving a thin insulating cover could account for lack of its detection by GRS. The presence of an ice-layer in the mid-latitudes is suggested by a network of polygons, interpreted as ice-wedge cracks. This study focuses on an exceptional concentration of polygons in Western Utopia (section of Casius quadrangle, roughly 40 deg - 50 deg N, 255 deg - 300 deg W). We attempt to determine the thickness and age of this ice layer through crater-polygons relations.

  12. A new optical ice particle counter at LACIS

    NASA Astrophysics Data System (ADS)

    Bieligk, Henner; Voelker, Georg Sebastian; Clauss, Tina; Grundmann, Marius; Stratmann, Frank

    2014-05-01

    Clouds play an important role within the climate system, especially for the radiative energy budget of the earth. The radiative properties of a cloud depend strongly on the fractions of ice crystals and water droplets, their size distributions, and the ice crystal shapes within the particular cloud. One option to gain this kind of information is using optical particle counters. A new optical particle counter is developed for laboratory work and is based on the concept of the Thermostabilized Optical Particle Spectrometer for the Detection of Ice Particles (TOPS-Ice, Clauss et al., 2013). TOPS-Ice uses linearly polarized green laser light and the depolarization of the scattered light at a scattering angle of 42.5° to discriminate between liquid water droplets and ice crystals in the lower ?m range. However, the measurements are usually limited to ice fractions in the order of 1%. To improve the determination of the ice fraction, several modifications of the original setup are implemented including an additional detection system at another scattering angle. The new scattering angle is optimized for least interference between the droplet and ice signals. This is achieved by finding the angle with the maximum difference in scattered intensity of water droplets compared to ice crystals with the same volume equivalent diameter. The suitable scattering angle of 100° for linearly polarized light was chosen based on calculations using T-Matrix method, Lorenz-Mie theory, Müller matrices and distribution theory. The new optical setup is designed to run in combination with a laminar flow tube, the so-called Leipzig Aerosol Cloud Interaction Simulator (LACIS, Stratmann et al., 2004; Hartmann et al., 2011). Using LACIS and its precisely controlled thermodynamic conditions, we are able to form small water droplets and ice crystals which will then be detected, classified and sized by our new optical device. This setup is planned to be tested in ice measurements including Snomax® and several dusts (e.g. illite, kaolinite, ATD) as ice nuclei which all show different behaviors in ice formation. Furthermore, a detailed comparison of both instruments TOPS-Ice and the new setup is planned. This project is part of the Leipzig Graduate School on Clouds, Aerosols and Radiation and is partly supported by the German Research Foundation (DFG project WE 4722/1-1) within the DFG Research Unit FOR 1525 INUIT. Clauss, T., Kiselev, A., Hartmann, S., Augustin, S., Pfeifer, S., Niedermeier, D., Wex, H., and Stratmann, F, 2013, Application of linear polarized light for the discrimination of frozen and liquid droplets in ice nucleation experiments, Atmos. Meas. Tech., 6, 1041-1052. Hartmann, S., Niedermeier, D., Voigtländer, J., Clauss, T., Shaw, R. A., Kiselev, A., and Stratmann, F., 2011, Homogeneous and heterogeneous ice nucleation at LACIS: operating principle and theoretical studies, Atmos. Chem. Phys., 11, 1753-1767. Stratmann, F., Kiselev, A., Wurzler, S., Wendisch, M., Heintzenberg, J., Charlson, R. J., Diehl, K., Wex, H., and Schmidt, S., 2004, Laboratory Studies and Numerical Simulations of Cloud Droplet Formation under Realistic Supersaturation Conditions, J. Atmos. Oceanic. Technol., 21, 876-887.

  13. Anisotropic elastocreep in glacial ice: A mechanism for intergranular melt and recrystallization

    Microsoft Academic Search

    Steven M. Jepsen; Edward E. Adams

    2008-01-01

    Bonded ice crystals under pressure are in a heterogeneous stress state because of the mechanical anisotropy of constituent grains. This condition plays a role in intergranular melt and recrystallization, which in turn influence properties such as permeability and biologic habitability. To examine this, we develop an anisotropic elastocreep model simulating subgrain-scale stresses in polycrystalline ice, choosing in particular the thermal

  14. Ice microstructure and fabric: an up-to-date approach for measuring textures

    E-print Network

    Gagliardini, Olivier

    Ice microstructure and fabric: an up-to-date approach for measuring textures Gae¨l DURAND,1 O for analysis of ice crystal texture. Such an increase in the quality and quantity of data allows for stricter statistical estimates. The current textural parameters, i.e. fabric (crystallographic orientations

  15. The Structural Properties of Vapor Deposited Water Ice and Astrophysical Implications

    NASA Technical Reports Server (NTRS)

    Jenniskens, P.; Blake, D. F.; Chang, Sherwood (Technical Monitor)

    1996-01-01

    Films of vapor deposited water ice at low temperature (T<30 K) show a number of interesting structural changes during a gradual warmup. We would like to talk about the structure of the low temperature high density amorphous form of water ice, the process of crystallization, and some recent work on the morphological changes of water ice films at high temperature. The studies of the high density amorphous form are from in-situ electron microscopy as well as numerical simulations of molecular dynamics and have lead to new insights into the physical distinction between this high density amorphous form and the low density amorphous form. For the process of crystallization, we propose a model that describes the crystallization of water ice from the amorphous phase to cubic ice in terms of the nucleation of small domains in the ice. This model agrees well with the behavior of water ice in our electron microscopy studies and finds that pure water above the glass transition is a strong liquid. In more recent work, we have concentrated on temperatures above the crystallization temperature and we find interesting morphological changes related to the decrease in viscosity of the amorphous component in the cubic crystalline regime. Given enough time, we would like to put these results in an astrophysical context and discuss some observed features of the frost on interstellar grains and the bulk ice in comets.

  16. Modeling equilibrium concentrations of Bjerrum and molecular point defects and their complexes in ice Ih

    Microsoft Academic Search

    Maurice de Koning; Alex Antonelli

    2008-01-01

    We present a model for the determination of the thermal equilibrium concentrations of Bjerrum defects, molecular point defects, and their aggregates in ice Ih. First, using a procedure which minimizes the free energy of an ice crystal with respect to the numbers of defect species, we derive a set of equations for the equilibrium concentrations of free Bjerrum and point

  17. Ice in the Shadows

    NSDL National Science Digital Library

    This is a lesson about detecting ice on the permanently shadowed craters of Mercury and the Moon. Learners will consider what might be in that ice and will examine why the polar regions of Earth, Mercury and the Moon are colder than elsewhere on the planets. Activities include small group miming, speaking, drawing, and/or writing. This is the lesson 12 of 12 in the unit, Exploring Ice in the Solar System.

  18. Characterization of Arctic ice cloud properties observed during ISDAC

    NASA Astrophysics Data System (ADS)

    Jouan, Caroline; Girard, Eric; Pelon, Jacques; Gultepe, Ismail; Delanoë, Julien; Blanchet, Jean-Pierre

    2012-12-01

    Extensive measurements from ground-based sites and satellite remote sensing (CloudSat and CALIPSO) reveal the existence of two types of ice clouds (TICs) in the Arctic during the polar night and early spring. The first type (TIC-2A), being topped by a cover of nonprecipitating very small (radar unseen) ice crystals (TIC-1), is found more frequently in pristine environment, whereas the second type (TIC-2B), detected by both sensors, is associated preferentially with a high concentration of aerosols. To further investigate the microphysical properties of TIC-1/2A and TIC-2B, airborne in situ and satellite measurements of specific cases observed during Indirect and Semi-Direct Aerosol Campaign (ISDAC) have been analyzed. For the first time, Arctic TIC-1/2A and TIC-2B microstructures are compared using in situ cloud observations. Results show that the differences between them are confined in the upper part of the clouds where ice nucleation occurs. TIC-2B clouds are characterized by fewer (by more than 1 order of magnitude) and larger (by a factor of 2 to 3) ice crystals and a larger ice supersaturation (of 15-20%) compared to TIC-1/2A. Ice crystal growth in TIC-2B clouds seems explosive, whereas it seems more gradual in TIC-1/2A. It is hypothesized that these differences are linked to the number concentration and the chemical composition of aerosols. The ice crystal growth rate in very cold conditions impinges on the precipitation efficiency, dehydration and radiation balance. These results represent an essential and important first step to relate previous modeling, remote sensing and laboratory studies with TICs cloud in situ observations.

  19. Ice formation in Saharan dust over central Europe observed with temperature/humidity/aerosol Raman lidar

    NASA Astrophysics Data System (ADS)

    Ansmann, Albert; Mattis, Ina; Müller, Detlef; Wandinger, Ulla; Radlach, Marcus; Althausen, Dietrich; Damoah, Richard

    2005-09-01

    Three gravity-wave-induced clouds and a glaciating altocumulus layer were continuously monitored with lidar at Leipzig, Germany, on 21 November 2003. The midtropospheric clouds formed in Saharan dust at heights from 3.5 km (-9°C) to 6.5 km (-27°C). Distinct ice formation in the altocumulus was triggered by the gravity wave. For the first time, an aerosol/cloud study presents height profiles of temperature, water vapor mixing ratio, relative humidity, dust, and cloud optical properties (volume extinction and backscatter coefficients, lidar ratio, depolarization ratio) within the same air column, solely derived from lidar data. The three gravity-wave-induced clouds did not show any sign of ice formation. The aged dust particles below 4.5-km height were probably partly coated and mixed with hygroscopic material and thus deactivated concerning ice nucleation. Ice crystals were generated in isolated air parcels at the cloud edges of a young, optically thin altocumulus layer between 5- and 6.5-km height. An aged altocumulus deck composed of a geometrically thin liquid water layer at cloud top and an extended ice crystal layer (ice virga) was observed 2 hours later in the same height range. Strong ice formation occurred in the altocumulus during the downdraft induced by the gravity wave. Contact freezing was probably the main reason for the observed ice formation on dust particles. Ice depolarization ratios were relatively low with values from 10 to 15% in the altocumulus and indicate plate-like crystals.

  20. An ice lithography instrument.

    PubMed

    Han, Anpan; Chervinsky, John; Branton, Daniel; Golovchenko, J A

    2011-06-01

    We describe the design of an instrument that can fully implement a new nanopatterning method called ice lithography, where ice is used as the resist. Water vapor is introduced into a scanning electron microscope (SEM) vacuum chamber above a sample cooled down to 110 K. The vapor condenses, covering the sample with an amorphous layer of ice. To form a lift-off mask, ice is removed by the SEM electron beam (e-beam) guided by an e-beam lithography system. Without breaking vacuum, the sample with the ice mask is then transferred into a metal deposition chamber where metals are deposited by sputtering. The cold sample is then unloaded from the vacuum system and immersed in isopropanol at room temperature. As the ice melts, metal deposited on the ice disperses while the metals deposited on the sample where the ice had been removed by the e-beam remains. The instrument combines a high beam-current thermal field emission SEM fitted with an e-beam lithography system, cryogenic systems, and a high vacuum metal deposition system in a design that optimizes ice lithography for high throughput nanodevice fabrication. The nanoscale capability of the instrument is demonstrated with the fabrication of nanoscale metal lines. PMID:21721733

  1. An ice lithography instrument

    SciTech Connect

    Han, Anpan [Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States); Chervinsky, John [School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 (United States); Branton, Daniel [Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138 (United States); Golovchenko, J. A. [Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States); School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 (United States)

    2011-06-15

    We describe the design of an instrument that can fully implement a new nanopatterning method called ice lithography, where ice is used as the resist. Water vapor is introduced into a scanning electron microscope (SEM) vacuum chamber above a sample cooled down to 110 K. The vapor condenses, covering the sample with an amorphous layer of ice. To form a lift-off mask, ice is removed by the SEM electron beam (e-beam) guided by an e-beam lithography system. Without breaking vacuum, the sample with the ice mask is then transferred into a metal deposition chamber where metals are deposited by sputtering. The cold sample is then unloaded from the vacuum system and immersed in isopropanol at room temperature. As the ice melts, metal deposited on the ice disperses while the metals deposited on the sample where the ice had been removed by the e-beam remains. The instrument combines a high beam-current thermal field emission SEM fitted with an e-beam lithography system, cryogenic systems, and a high vacuum metal deposition system in a design that optimizes ice lithography for high throughput nanodevice fabrication. The nanoscale capability of the instrument is demonstrated with the fabrication of nanoscale metal lines.

  2. An ice lithography instrument

    PubMed Central

    Han, Anpan; Chervinsky, John; Branton, Daniel; Golovchenko, J. A.

    2011-01-01

    We describe the design of an instrument that can fully implement a new nanopatterning method called ice lithography, where ice is used as the resist. Water vapor is introduced into a scanning electron microscope (SEM) vacuum chamber above a sample cooled down to 110 K. The vapor condenses, covering the sample with an amorphous layer of ice. To form a lift-off mask, ice is removed by the SEM electron beam (e-beam) guided by an e-beam lithography system. Without breaking vacuum, the sample with the ice mask is then transferred into a metal deposition chamber where metals are deposited by sputtering. The cold sample is then unloaded from the vacuum system and immersed in isopropanol at room temperature. As the ice melts, metal deposited on the ice disperses while the metals deposited on the sample where the ice had been removed by the e-beam remains. The instrument combines a high beam-current thermal field emission SEM fitted with an e-beam lithography system, cryogenic systems, and a high vacuum metal deposition system in a design that optimizes ice lithography for high throughput nanodevice fabrication. The nanoscale capability of the instrument is demonstrated with the fabrication of nanoscale metal lines. PMID:21721733

  3. Ice age paleotopography

    SciTech Connect

    Peltier, W.R. (Univ. of Toronto, Ontario (Canada))

    1994-07-08

    A gravitationally self-consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the Last Glacial Maximum (LGM). The results show that LGM ice volume was approximately 35 percent lower than suggested by the CLIMAP reconstruction and the maximum heights of the main Laurentian and Fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level. Use of these Ice Age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the CLIMAP data set.

  4. New simulation model of multicomponent crystal growth and inhibition.

    PubMed

    Wathen, Brent; Kuiper, Michael; Walker, Virginia; Jia, Zongchao

    2004-04-01

    We review a novel computational model for the study of crystal structures both on their own and in conjunction with inhibitor molecules. The model advances existing Monte Carlo (MC) simulation techniques by extending them from modeling 3D crystal surface patches to modeling entire 3D crystals, and by including the use of "complex" multicomponent molecules within the simulations. These advances makes it possible to incorporate the 3D shape and non-uniform surface properties of inhibitors into simulations, and to study what effect these inhibitor properties have on the growth of whole crystals containing up to tens of millions of molecules. The application of this extended MC model to the study of antifreeze proteins (AFPs) and their effects on ice formation is reported, including the success of the technique in achieving AFP-induced ice-growth inhibition with concurrent changes to ice morphology that mimic experimental results. Simulations of ice-growth inhibition suggest that the degree of inhibition afforded by an AFP is a function of its ice-binding position relative to the underlying anisotropic growth pattern of ice. This extended MC technique is applicable to other crystal and crystal-inhibitor systems, including more complex crystal systems such as clathrates. PMID:15054746

  5. Proton ordering in tetragonal and monoclinic H2O ice

    E-print Network

    Yen, Fei; Berlie, Adam; Liu, Xiaodi; Goncharov, Alexander F

    2015-01-01

    H2O ice remains one of the most enigmatic materials as its phase diagram reveals up to sixteen solid phases. While the crystal structure of these phases has been determined, the phase boundaries and mechanisms of formation of the proton-ordered phases remain unclear. From high precision measurements of the complex dielectric constant, we probe directly the degree of ordering of the protons in H2O tetragonal ice III and monoclinic ice V down to 80 K. A broadened first-order phase transition is found to occur near 202 K we attribute to a quenched disorder of the protons which causes a continuous disordering of the protons during cooling and metastable behavior. At 126 K the protons in ice III become fully ordered, and for the case of ice V becoming fully ordered at 113 K forming ice XIII. Two triple points are proposed to exist: one at 0.35 GPa and 126 K where ices III, IX and V coexist; and another at 0.35 GPa and 113 K where ices V, IX and XIII coexist. Our findings unravel the underlying mechanism driving th...

  6. Thermal desorption of circumstellar and cometary ice analogs

    NASA Astrophysics Data System (ADS)

    Martín-Doménech, R.; Muñoz Caro, G. M.; Bueno, J.; Goesmann, F.

    2014-04-01

    Context. Thermal annealing of interstellar ices takes place in several stages of star formation. Knowledge of this process comes from a combination of astronomical observations and laboratory simulations under astrophysically relevant conditions. Aims: For the first time we present the results of temperature programmed desorption (TPD) experiments with pre-cometary ice analogs composed of up to five molecular components: H2O, CO, CO2, CH3OH, and NH3. Methods: The experiments were performed with an ultra-high vacuum chamber. A gas line with a novel design allows the controlled preparation of mixtures with up to five molecular components. Volatiles desorbing to the gas phase were monitored using a quadrupole mass spectrometer, while changes in the ice structure and composition were studied by means of infrared spectroscopy. Results: The TPD curves of water ice containing CO, CO2, CH3OH, and NH3 present desorption peaks at temperatures near those observed in pure ice experiments, volcano desorption peaks after water ice crystallization, and co-desorption peaks with water. Desorption peaks of CH3OH and NH3 at temperatures similar to the pure ices takes place when their abundance relative to water is above ~3% in the ice matrix. We found that CO, CO2, and NH3 also present co-desorption peaks with CH3OH, which cannot be reproduced in experiments with binary water-rich ice mixtures. These are extensively used in the study of thermal desorption of interstellar ices. Conclusions: These results reproduce the heating of circumstellar ices in hot cores and can be also applied to the late thermal evolution of comets. In particular, TPD curves represent a benchmark for the analysis of the measurements that mass spectrometers on board the ESA-Rosetta cometary mission will perform on the coma of comet 67P/Churyumov-Gerasimenko, which will be active before the arrival of Rosetta according to our predictions.

  7. Why is intracellular ice lethal? A microscopical study showing evidence of programmed cell death in cryo-exposed embryonic axes of recalcitrant seeds of Acer saccharinum

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Intracellular ice formed in rapidly cooled embryonic axes of Acer saccharinum and was not necessarily lethal when ice crystals were small. This study seeks to understand the nature and extent of damage from intracellular ice, and the course of recovery and regrowth in surviving tissues. Embryonic a...

  8. Ice Formation and Its Removal Phenomena of Flowing Solution in Cooled Pipe

    NASA Astrophysics Data System (ADS)

    Hirata, Tetsuo; Ishikawa, Masaaki; Kanbara, Kanta

    Ice formation phenomena of ethylene-glycol solution flow in a cooled vertical pipe have been examined experimentally. As a cooled pipe, polyvinyl chloride has been used. The concentrations of the ethylene-glycol solution are 2,6,10 wt%. It is shown that the crystal ice formed in the pipe is removed from the pipe surface and drift away downstream with the solution flow. It suggests the possibility of “liquid-like ice” formation by this method. It is found that the heat transfer coefficient in the pipe is strongly affected by ice formation and ice removal phenomena, and that the ice formation rate increases with decreasing Reynolds number. The ice removal phenomenon becomes not to occur for smaller Reynolds numbers and for larger cooling heat fluxes.

  9. [Tail Plane Icing

    NASA Technical Reports Server (NTRS)

    1997-01-01

    The Aviation Safety Program initiated by NASA in 1997 has put greater emphasis in safety related research activities. Ice-contaminated-tailplane stall (ICTS) has been identified by the NASA Lewis Icing Technology Branch as an important activity for aircraft safety related research. The ICTS phenomenon is characterized as a sudden, often uncontrollable aircraft nose- down pitching moment, which occurs due to increased angle-of-attack of the horizontal tailplane resulting in tailplane stall. Typically, this phenomenon occurs when lowering the flaps during final approach while operating in or recently departing from icing conditions. Ice formation on the tailplane leading edge can reduce tailplane angle-of-attack range and cause flow separation resulting in a significant reduction or complete loss of aircraft pitch control. In 1993, the Federal Aviation Authority (FAA) and NASA embarked upon a four-year research program to address the problem of tailplane stall and to quantify the effect of tailplane ice accretion on aircraft performance and handling characteristics. The goals of this program, which was completed in March 1998, were to collect aerodynamic data for an aircraft tail with and without ice contamination and to develop analytical methods for predicting the effects of tailplane ice contamination. Extensive dry air and icing tunnel tests which resulted in a database of the aerodynamic effects associated with tailplane ice contamination. Although the FAA/NASA tailplane icing program generated some answers regarding ice-contaminated-tailplane stall (ICTS) phenomena, NASA researchers have found many open questions that warrant further investigation into ICTS. In addition, several aircraft manufacturers have expressed interest in a second research program to expand the database to other tail configurations and to develop experimental and computational methodologies for evaluating the ICTS phenomenon. In 1998, the icing branch at NASA Lewis initiated a second multi-phase research program for tailplane icing (TIP II) to develop test methodologies and tailplane performance and handling qualities evaluation tools. The main objectives of this new NASA/Industry/Academia collaborative research programs were: (1) define and evaluate a sub-scale wind tunnel test methodology for determining tailplane performance degradation due to icing. (2) develop an experimental database of tailplane aerodynamic performance with and without ice contamination for a range of tailplane configurations. Wind tunnel tests were planned with representative general aviation aircraft, i.e., the Learjet 45, and a twin engine low speed aircraft. This report summarizes the research performed during the first year of the study, and outlines the work tasks for the second year.

  10. Modelling biogeochemical tracer transport in sea ice due to gravity drainage

    NASA Astrophysics Data System (ADS)

    Hitchen, Joseph; Wells, Andrew

    2014-05-01

    Sea ice is a porous material, formed of an evolving array of solid ice crystals bathed in liquid brine. The liquid-filled pore space provides a habitat for life within the ice, and, when the ice is permeable, provides a pathway for exchange of gases and other chemicals between the ice, ocean, and atmosphere. This coupling between the physical, chemical, and biological evolution of sea ice has poorly constrained implications for biogeochemical processes, such as the impact of sea ice on the carbon cycle. During winter ice growth, so-called gravity drainage drives a convective exchange of brine between the ocean and the porous interior of sea ice. Here, we use two-dimensional mushy-layer simulations of convective flow to provide insight into the resulting transport of passive biogeochemical tracers through the ice. We quantify the chemical concentration in the liquid during periods of quasi-steady growth rate, and determine a scaling law for the total chemical tracer fluxes through the region of active convection inside the ice. Chemical concentrations show spatial heterogeneity, and our results predict enhanced chemical concentrations in the pore space near to brine channels. These results may provide useful insight for interpreting studies of sea-ice biogeochemistry, and offer a framework to develop models of physical, chemical, and biological interactions.

  11. Spectroscopic signature for ferroelectric ice

    NASA Astrophysics Data System (ADS)

    Wójcik, Marek J.; G?ug, Maciej; Boczar, Marek; Boda, ?ukasz

    2014-09-01

    Various forms of ice exist within our galaxy. Particularly intriguing type of ice - ‘ferroelectric ice' was discovered experimentally and is stable in temperatures below 72 K. This form of ice can generate enormous electric fields and can play an important role in planetary formation. In this letter we present Car-Parrinello simulation of infrared spectra of ferroelectric ice and compare them with spectra of hexagonal ice. Librational region of the spectra can be treated as spectroscopic signature of ice XI and can be of help to identify ferroelectric ice in the Universe.

  12. Initiation of the ice phase by marine biogenic surfaces in supersaturated gas and supercooled aqueous phases.

    PubMed

    Alpert, Peter A; Aller, Josephine Y; Knopf, Daniel A

    2011-11-28

    Biogenic particles have the potential to affect the formation of ice crystals in the atmosphere with subsequent consequences for the hydrological cycle and climate. We present laboratory observations of heterogeneous ice nucleation in immersion and deposition modes under atmospherically relevant conditions initiated by Nannochloris atomus and Emiliania huxleyi, marine phytoplankton with structurally and chemically distinct cell walls. Temperatures at which freezing, melting, and water uptake occur are observed using optical microscopy. The intact and fragmented unarmoured cells of N. atomus in aqueous NaCl droplets enhance ice nucleation by 10-20 K over the homogeneous freezing limit and can be described by a modified water activity based ice nucleation approach. E. huxleyi cells covered by calcite plates do not enhance droplet freezing temperatures. Both species nucleate ice in the deposition mode at an ice saturation ratio, S(ice), as low as ~1.2 and below 240 K, however, for each, different nucleation modes occur at warmer temperatures. These observations show that markedly different biogenic surfaces have both comparable and contrasting effects on ice nucleation behaviour depending on the presence of the aqueous phase and the extent of supercooling and water vapour supersaturation. We derive heterogeneous ice nucleation rate coefficients, J(het), and cumulative ice nuclei spectra, K, for quantification and analysis using time-dependent and time-independent approaches, respectively. Contact angles, ?, derived from J(het)via immersion freezing depend on T, a(w), and S(ice). For deposition freezing, ? can be described as a function of S(ice) only. The different approaches yield different predictions of atmospheric ice crystal numbers primarily due to the time evolution allowed for the time-dependent approach with implications for the evolution of mixed-phase and ice clouds. PMID:21912788

  13. Evaluating and Constraining Ice Cloud Parameterizations in CAM5 using Aircraft Measurements from the SPARTICUS Campaign

    SciTech Connect

    Zhang, Kai; Liu, Xiaohong; Wang, Minghuai; Comstock, Jennifer M.; Mitchell, David; Mishra, Subhashree; Mace, Gerald G.

    2013-01-01

    This study uses aircraft measurements of relative humidity and ice crystal size distribution collected in synoptic cirrus during the SPARTICUS (Small PARTicles In CirrUS) field campaign to evaluate and constrain ice cloud parameterizations in the Community Atmosphere Model version 5. The probability density function (PDF) of ice crystal number concentration (Ni) derived from high frequency (1 Hz) measurements features a strong dependence on ambient temperature. As temperature decreases from -35°C to -62°C, the peak in the PDF shifts from 10-20 L-1 to 200-1000 L-1, while the ice crystal number concentration shows a factor of 6-7 increase. Model simulations are performed with two different insitu ice nucleation schemes. One of the schemes can reproduce a clear increase of Ni with decreasing temperature, by using either an observation based ice nuclei spectrum or a classical theory based spectrum with a relatively low (5%-10%) maximum freezing ratio for dust aerosols. The simulation with the other scheme, which assumes a high maximum freezing ratio (100%), shows much weaker temperature dependence of Ni. Simulations are also performed to test empirical parameters related to water vapor deposition and the auto-conversion of ice crystals to snow. Results show that a value between 0.05 and 0.1 for the water vapor deposition coefficient and 250 um for the critical ice crystal size can produce good agreements between model simulation and the SPARTICUS measurements in terms of ice crystal number concentration and effective radius. The climate impact of perturbing these parameters is also discussed.

  14. Investigating Ice Worlds

    NSDL National Science Digital Library

    2012-12-27

    In this activity about the solar system, learners use various light sources to examine ice with different components to understand how NASA studies planets and moons from space. This detailed lesson guide includes background information about distant ice worlds in the outer solar system, literature connections, instructions for a pre-activity demonstration, modified activities by age, tips, discussion questions, and resources.

  15. Antarctic Ice Velocity Data

    NSDL National Science Digital Library

    1999-01-01

    The National Snow and Ice Data Center (NSIDC) (described in the October 2, 1998 Scout Report) provides the Antarctic Ice Velocity Data set. This set contains large satellite image maps along with latitude, longitude, speed, bearing, and error ranges data. Data for this set is available via FTP.

  16. A Changing Ice Sheet

    NSDL National Science Digital Library

    This animation shows the retreat of glacial ice, changes in the shoreline, and the disappearance of the land bridge across the Bering Sea which occurred at the end of the last ice age, beginning just over 21,000 years ago.

  17. Antarctica: Sea Ice

    NSDL National Science Digital Library

    This video segment, adapted from a NOVA broadcast, shows how sea ice forms in the Southern Ocean around Antarctica and how its seasonal fluctuation dramatically changes the continent. The segment, two minutes thirty-five seconds in length, includes rare footage of the destruction of the British ship 'Endurance', trapped and crushed by sea ice in 1914.

  18. Naled ice growth

    Microsoft Academic Search

    G. A. Schohl; R. Ettema

    1986-01-01

    Based on theoretical formulation and dimensional analysis, supported by the results of laboratory experiments, a theory and a detailed description of naled ice growth are presented. The theory, concepts, and data should be of interest to engineers concerned with the effects of naleds (also referred to as aufeis or icings) on engineering works. The growth of a two dimensional, or

  19. Global Ice Viewer

    NSDL National Science Digital Library

    Laura Tenenbaum

    With this simulation from the NASA Climate website, learners explore different examples of how ice is melting due to climate change in four places where large quantities of ice are found. The photo comparisons, graphs, animations, and especially the time lapse video clips of glaciers receding are astonishing and dramatic.

  20. Sea ice: Antarctic aspects

    Microsoft Academic Search

    P. SCHWERDTFEGER

    The relevance and limitations of theoretical and laboratory investiga- tions of sea ice to the Antarctic is discussed. Because of the complex thermal and mechanical perturbations suffered by sea ice under such oceanic conditions, analogue computations are suggested as being amongst the most promising methods of analysis. In the light of basic heat economy determinations, it is suggested that the

  1. Ice making apparatus

    Microsoft Academic Search

    1987-01-01

    An ice-making apparatus is described including a housing defining a substantially cylindrical freezing chamber, refrigeration means adjacent the freezing chamber, means for supplying ice make-up water to the freezing chamber, an axially extending auger rotatably mounted in the freezing chamber. The improvement includes a central body portion, at least one flight portion extending in a generally spiral path along at

  2. Ice maker safety control

    Microsoft Academic Search

    Linstromberg

    1988-01-01

    In a refrigeration apparatus including an evaporator, a defrost heater for defrosting the evaporator, a defrost thermostat having a switch for de-energizing the defrost heater at a preselected high temperature of the evaporator, and an ice making apparatus having a mold, a mold heater, and a control circuit controllably energized the mold heater, a safety control for the ice making

  3. Sea Ice 1987 - 2012

    NSDL National Science Digital Library

    This site features a video that illustrates both seasonal patterns and long-term changes in sea ice distribution across the Arctic Ocean. It draws data from two satellite instruments that measure emitted microwave radiation, which helps distinguish open ocean from ice. It shows that during the winter months, a layer of ice forms across vast expanses of the Arctic Ocean and each summer, more than half of that ice vanishes. Students discover that this natural cycle of freezing and thawing is influenced both by seasonal temperature variations and long-term climate change and that scientists are using satellite images to measure the distribution of Arctic sea ice in order to gain a better understanding of how it is linked to Earth's climate system.

  4. All About Sea Ice

    NSDL National Science Digital Library

    Launched by the National Snow and Ice Data Center, the "All About Sea Ice" website is designed as an introduction to sea ice: what it is, how it forms, how it is studied, how it affected historical expeditions in the polar regions, and what role it plays in the global climate. The site contains over 80 pages of information on sea ice, including a glossary of sea ice terms and links to more information. The primary focus of the site is as a resource for the general public, educators and students in middle school and above. It may also be useful to researchers as a source of imagery, sample data, references, and basic information.

  5. Tensile properties of impact ices

    NASA Technical Reports Server (NTRS)

    Chu, M. L.; Scavuzzo, R. J.; Kellackey, C. J.

    1992-01-01

    A special test apparatus was developed to measure the tensile strength of impact ices perpendicular to the direction of growth. The apparatus consists of a split tube carefully machined to minimize the effect of the joint on impact ice strength. The tube is supported in the wind tunnel by two carefully aligned bearings. During accretion the tube is turned slowly in the icing cloud to form a uniform coating of ice on the split tube specimen. The two halves of the split tube are secured firmly by a longitudinal bolt to prevent relative motion between the two halves during ice accretion and handling. Tensile test strength results for a variety of icing conditions were obtained. Both glaze and rime ice conditions were investigated. In general, the tensile strength of impact ice was significantly less than refrigerator ice. Based on the limited data taken, the median strength of rime ice was less than glaze ice. However, the mean values were similar.

  6. Proton ordering in cubic ice and hexagonal ice; a potential new ice phase--XIc.

    PubMed

    Raza, Zamaan; Alfè, Dario; Salzmann, Christoph G; Klimeš, Ji?í; Michaelides, Angelos; Slater, Ben

    2011-11-28

    Ordinary water ice forms under ambient conditions and has two polytypes, hexagonal ice (Ih) and cubic ice (Ic). From a careful comparison of proton ordering arrangements in Ih and Ic using periodic density functional theory (DFT) and diffusion Monte Carlo (DMC) approaches, we find that the most stable arrangement of water molecules in cubic ice is isoenergetic with that of the proton ordered form of hexagonal ice (known as ice XI). We denote this potential new polytype of ice XI as XIc and discuss a possible route for preparing ice XIc. PMID:22009223

  7. Snow Crystals

    NSDL National Science Digital Library

    Kenneth Libbrecht

    1999-02-01

    This site is all about snow crystals and snowflakes. The many facets of snow crystals are described here, along with attempts to understand their formation. This site includes collections of super-high-resolution snow crystal photos, as well as links to learn about snow crystal classifications and how to make snow crystal fossils. Included in the study of how snow crystals form, these researchers have created snow crystals in the laboratory. Their snow crystal galleries include selections of images and movies of laboratory-grown snow crystals, as well as information on how to make your own snow crystals. The snow crystal primer describes what snow crystals are, how they form, and why they form the way they do. There is also a section on snow crystal physics.

  8. Morphology changes in stacking-disordered ice Ich as a function of time and temperature

    NASA Astrophysics Data System (ADS)

    Kuhs, Werner F.; Falenty, Andrzej; Hansen, Thomas C.

    2015-04-01

    Laboratory experiments have shown that ice I crystallizing from water vapour [1] or undercooled liquid water [2] under atmospheric conditions initially forms a stacking disordered arrangement of high complexity; the stacking arrangement is different depending on the starting phase[1]. Both cubic and hexagonal components are locally present and various names of this form of ice have been proposed recently: so-called ice Ic or 'ice Ic'[1], ice Isd [2] or ice Ich[3]. It is has been shown that ice Ich undergoes a progressive transformation of cubic into hexagonal stackings with time and/or increasing temperature [1]. As a mechanisms for this annealing we had proposed the cooperative action of Bjerrrum defects and moving dislocations which become active on a time-scale of minutes at temperatures close to 240K [4]. Here we show from electron-microscopic images that the presence of stacking faults is linked to numerous kinks on the prismatic faces of the trigonal ice crystals of ice Ich [1]. We present details on the annealing kinetics in the temperature range between 170 and 240K and suggest that the kinks of ice Ich crystals may be responsible for the roughness deduced from some air-borne light-scattering experiments, an increased reactivity in particular at temperatures below ~ 200K as well as curvature-induced higher vapour pressures of ice Ich as compared to normal ice Ih. [1] W.F.Kuhs, C.Sippel, T.C.Hansen (2012) PNAS 109:21259-21264 [2] T.Malkin, B.J.Murray, A.V.Brukhno, J.Anwar, C.G.Salzmann (2012) PNAS 109: 1041-1045 [3] T.C.Hansen, C.Sippel, W.F.Kuhs (2014) Z.Krist. DOI 10.1515/zkri-2014-1780 [4] W.F.Kuhs, G.Genov, D.K.Staykova, T.Hansen (2004) 6:4917-4920

  9. Amorphous ice and the behavior of cometary nuclei

    NASA Technical Reports Server (NTRS)

    Smoluchowski, R.

    1981-01-01

    The gradual heating of the nucleus of a comet approaching the sun may produce solid-state phase changes that are of particular importance for new comets, which may never have been heated before. The water-ice component of new comets is expected to be amorphous rather than crystalline, and its subsequent crystallization should produce gaseous tails and flareups at heliocentric distances about 70% greater than those expected for crystalline nuclei. These distances and the size of the flareups depend strongly on the inclination of the rotation axis and on the porosity of the ice. The effect should be weaker for older comets, but it may be related to the behavior of P/Schwassmann-Wachmann 1 if the layers of the crystallized ice peel off.

  10. Instant Ice Cream with a Dry Ice Bath

    NSDL National Science Digital Library

    Sean Michael Ragan

    2011-01-01

    In this chemistry meets cooking activity, learners make carbonated, vanilla ice cream using dry ice and denatured ethanol, which are both inexpensive and accessible. This process to make ice cream is faster than using rock salt and water ice as the refrigerant. Use this activity to introduce learners to the process of sublimation and phase change and to provide a fun treat.

  11. Surface Crystallization of Supercooled Water in Clouds

    NASA Technical Reports Server (NTRS)

    Tabazadeh, Azadeh; Gore, Warren J. (Technical Monitor)

    2002-01-01

    The process by which liquid cloud droplets homogeneously crystallize into ice is still not well-understood. The ice nucleation process based on the standard and classical theory of homogeneous freezing, initiates within the interior volume of a cloud droplet. Current experimental data on homogeneous freezing rates of ice in droplets of supercooled water, both in air and emulsion oil samples, show considerable scatter. For example, at -33 C, the reported volume-based freezing rates of ice in supercooled water vary by as much as 5 orders of magnitude, which is well outside the range of measurement uncertainties. Here, we show that the process of ice nucleus formation at the air (or oil)-liquid water interface may help to explain why experimental results on ice nucleation rates yield different results in different ambient phases. Our results also suggest that surface crystallization of ice in cloud droplets can explain why low amounts of supercooled water have been observed in the atmosphere near -40 C.

  12. Surface crystallization of supercooled water in clouds

    PubMed Central

    Tabazadeh, A.; Djikaev, Y. S.; Reiss, H.

    2002-01-01

    The process by which liquid cloud droplets homogeneously crystallize into ice is still not well understood. The ice nucleation process based on the standard and classical theory of homogeneous freezing initiates within the interior volume of a cloud droplet. Current experimental data on homogeneous freezing rates of ice in droplets of supercooled water, both in air and emulsion oil samples, show considerable scatter. For example, at ?33°C, the reported volume-based freezing rates of ice in supercooled water vary by as many as 5 orders of magnitude, which is well outside the range of measurement uncertainties. Here, we show that the process of ice nucleus formation at the air (or oil)-liquid water interface may help to explain why experimental results on ice nucleation rates yield different results in different ambient phases. Our results also suggest that surface crystallization of ice in cloud droplets can explain why low amounts of supercooled water have been observed in the atmosphere near ?40°C. PMID:12456877

  13. Measurements of sea ice proxies from Antarctic coastal shallow cores

    NASA Astrophysics Data System (ADS)

    Maffezzoli, Niccolò; Vallelonga, Paul; Spolaor, Andrea; Barbante, Carlo; Frezzotti, Massimo

    2015-04-01

    Despite its close relationship with climate, the climatic impact of sea ice remains only partially understood: an indication of this is the Arctic sea ice which is declining at a faster rate than models predict. Thus, the need for reliable sea ice proxies is of crucial importance. Among the sea ice proxies that can be extracted from ice cores, interest has recently been shown in the halogens Iodine (I) and Bromine (Br) (Spolaor, A., et al., 2013a, 2013b). The production of sea ice is a source of Sodium and Bromine aerosols through frost flower crystal formation and sublimation of salty blowing snow, while Iodine is emitted by the algae living underneath sea ice. We present here the results of Na, Br and I measurements in Antarctic shallow cores, drilled during a traverse made in late 2013 - early 2014 from Talos Dome (72° 00'S, 159°12'E) to GV7 (70° 41'S, 158° 51'E) seeking for sea ice signature. The samples were kept frozen until the analyses, that were carried out by Sector Field Mass Spectroscopy Inductive Coupled Plasma (SFMS-ICP): special precautions and experimental steps were adopted for the detection of such elements. The coastal location of the cores allows a clear signal from the nearby sea ice masses. The multiple cores are located about 50 km from each other and can help us to infer the provenance of the sea ice that contributed to the proxy signature. Moreover, by simultaneously determining other chemical elements and compounds in the snow, it is possible to determine the relative timing of their deposition, thus helping us to understand their processes of emission and deposition.

  14. Polarization dependence of radiowave propagation through Antarctic ice

    E-print Network

    Besson, Dave Z

    2008-01-01

    Using a bistatic radar system on the ice surface, we have studied radiofrequency reflections off internal layers in Antarctic ice at the South Pole. In our measurement, the total propagation time of ~ns-duration, vertically broadcast radio signals, as a function of polarization axis in the horizontal plane, provides a direct probe of the geometry-dependence of the ice permittivity to depths of 1--2 km. Previous studies in East Antarctica have interpreted the measured azimuthal dependence of reflected signals as evidence for birefringent-induced interference effects, which are proposed to result from preferred alignment of the crystal orientation fabric (COF) axis. To the extent that COF alignment results from the bulk flow of ice across the Antarctic continent, we would expect a measurable birefringent asymmetry at South Pole, as well. Although we also observe clear dependence of reflected amplitude on polarization angle in our measurements, we do not observe direct evidence for birefringent-induced time-dela...

  15. Cosmogenic Activation in the DM-Ice Experiment

    NASA Astrophysics Data System (ADS)

    Pettus, Walter

    2013-04-01

    DM-Ice is a quarter-ton-scale dark matter experiment planned for deployment deep in the ice at the South Pole. This experiment will search for the expected annual modulation signature in the dark matter signal using low-background NaI(Tl) scintillating crystals. Cosmogenic activation of the detectors during transport to and storage at the South Pole (altitude 9,186 feet) has the potential to produce long-lived radioisotopes which will add a significant source of background and threaten the discovery potential of this experiment. We present simulation studies in the rate of activation and the spectral affect these additional radioactive decays will have. In data from the presently operating DM-Ice17 detectors, we compare the simulated activation spectra with decaying spectral regions. For the full-scale DM-Ice, we discuss the possible effects of this activation, and mitigation strategies being explored.

  16. Principles and biotechnological applications of bacterial ice nucleation.

    PubMed

    Margaritis, A; Bassi, A S

    1991-01-01

    Certain aerobic, Gram-negative bacteria, including the epiphytic plant pathogen, Pseudomonas syringae, possess a membrane protein that enables them to nucleate crystallization in supercooled water. Currently, these ice-nucleating (IN) bacteria are being used in snow making and have potential applications in the production and texturing of frozen foods, and as a replacement of silver iodide in cloud seeding. A negative aspect of these IN bacteria is frost damage to plant surfaces. Thus, of the various types of biological ice nucleators, bacteria have been the subject of most research and also appear relevant to the anticipated practical uses. The intent of this review is to explain the identification and ecology of the ice-nucleating bacteria, as well as to discuss aspects of molecular biology related to ice nucleation and consider existing and potential applications of this unique phenomenon. PMID:1760850

  17. Comparison of PARASOL Observations with Polarized Reflectances Simulated Using Different Ice Habit Mixtures

    NASA Technical Reports Server (NTRS)

    Cole, Benjamin H.; Yang, Ping; Baum, Bryan A.; Riedi, Jerome; Labonnote, Laurent C.; Thieuleux, Francois; Platnick, Steven

    2012-01-01

    Insufficient knowledge of the habit distribution and the degree of surface roughness of ice crystals within ice clouds is a source of uncertainty in the forward light scattering and radiative transfer simulations required in downstream applications involving these clouds. The widely used MODerate Resolution Imaging Spectroradiometer (MODIS) Collection 5 ice microphysical model assumes a mixture of various ice crystal shapes with smooth-facets except aggregates of columns for which a moderately rough condition is assumed. When compared with PARASOL (Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar) polarized reflection data, simulations of polarized reflectance using smooth particles show a poor fit to the measurements, whereas very rough-faceted particles provide an improved fit to the polarized reflectance. In this study a new microphysical model based on a mixture of 9 different ice crystal habits with severely roughened facets is developed. Simulated polarized reflectance using the new ice habit distribution is calculated using a vector adding-doubling radiative transfer model, and the simulations closely agree with the polarized reflectance observed by PARASOL. The new general habit mixture is also tested using a spherical albedo differences analysis, and surface roughening is found to improve the consistency of multi-angular observations. It is suggested that an ice model incorporating an ensemble of different habits with severely roughened surfaces would potentially be an adequate choice for global ice cloud retrievals.

  18. Crystal Creations.

    ERIC Educational Resources Information Center

    Whipple, Nona; Whitmore, Sherry

    1989-01-01

    Presents a many-faceted learning approach to the study of crystals. Provides instructions for performing activities including crystal growth and patterns, creating miniature simulations of crystal-containing rock formations, charcoal and sponge gardens, and snowflakes. (RT)

  19. Ice Stream Dynamics during Deglaciation of the Laurentide Ice Sheet

    NASA Astrophysics Data System (ADS)

    Stokes, C.; Margold, M.; Clark, C.

    2014-12-01

    Ice streams can rapidly drain large sectors of ice sheet interiors. At present, they account for approximately 50% and 90% of the mass loss from Greenland and Antarctica, respectively, but there are concerns over recent increases in ice discharge. This has been linked to atmospheric and oceanic warming, but the longer-term implications for ice sheet deglaciation are less clear. A key question is whether the activity of ice streams is predictably linked to climate-driven ice sheet mass balance, or whether their activity might accelerate deglaciation. To explore this, we analyse ice streaming during deglaciation of the Laurentide Ice Sheet (LIS) from ~18 to ~7 ka. Following a recent mapping inventory, we bracket the timing of >100 ice streams using published ice margin chronologies. At the Last Glacial Maximum (LGM), ice streams formed a drainage network similar to modern ice sheets. Numerous ice streams were located in topographic troughs and likely operated for thousands of years from the LGM. These drained the marine-based sectors of the northern and eastern margins of the ice sheet until ~11 ka and show a degree of spatial self-organisation. Other ice streams operated on much shorter time-scales and turned on and off, perhaps in as little as a few hundred years. These include large ice streams that switched positions over sedimentary bedrock at the western and southern terrestrial margins until ~13 ka. As the LIS retreated onto its low-relief and predominantly crystalline bedrock interior (after ~11 ka), a smaller number of large ice streams operated that were very wide (50-100 km), and have no modern analogue. Overall, the number of ice streams decreased during deglaciation and they drained a smaller proportion of the ice sheet margin: 30% at the LGM (similar to present-day Antarctica), 15% at 12 ka, and 12% at 10 ka. We use simple scaling relationships to estimate the mass loss delivered by ice streams and examine their role during deglaciation.

  20. Analysis of iced wings

    NASA Technical Reports Server (NTRS)

    Cebeci, Tuncer; Chen, H. H.; Kaups, K.; Schimke, S.; Shin, Jaiwon

    1992-01-01

    A method for computing ice shapes along the leading edge of a wing and a method for predicting its aerodynamic performance degradation due to icing is described. Ice shapes are computed using an extension of the LEWICE code which was developed for airfoils. The aerodynamic properties of the iced wing are determined with an interactive scheme in which the solutions of the inviscid flow equations are obtained from a panel method and the solutions of the viscous flow equations are obtained from an inverse three-dimensional finite-difference boundary-layer method. A new interaction law is used to couple the inviscid and viscous flow solutions. The application of the LEWICE wing code to the calculation of ice shapes on a MS-317 swept wing show good agreement with measurements. The interactive boundary layer method is applied to a tapered iced wing in order to study the effect of icing on the aerodynamic properties of the wing at several angles of attack.

  1. High Speed Ice Friction

    NASA Astrophysics Data System (ADS)

    Seymour-Pierce, Alexandra; Sammonds, Peter; Lishman, Ben

    2014-05-01

    Many different tribological experiments have been run to determine the frictional behaviour of ice at high speeds, ostensibly with the intention of applying results to everyday fields such as winter tyres and sports. However, experiments have only been conducted up to linear speeds of several metres a second, with few additional subject specific studies reaching speeds comparable to these applications. Experiments were conducted in the cold rooms of the Rock and Ice Physics Laboratory, UCL, on a custom built rotational tribometer based on previous literature designs. Preliminary results from experiments run at 2m/s for ice temperatures of 271 and 263K indicate that colder ice has a higher coefficient of friction, in accordance with the literature. These results will be presented, along with data from further experiments conducted at temperatures between 259-273K (in order to cover a wide range of the temperature dependent behaviour of ice) and speeds of 2-15m/s to produce a temperature-velocity-friction map for ice. The effect of temperature, speed and slider geometry on the deformation of ice will also be investigated. These speeds are approaching those exhibited by sports such as the luge (where athletes slide downhill on an icy track), placing the tribological work in context.

  2. Pyroelectricity of Water Ice

    SciTech Connect

    Wang, Hanfu; Bell, Richard C.; Iedema, Martin J.; Schenter, Gregory K.; Wu, Kai; Cowin, James P.

    2008-05-22

    Water ice usually is though to have zero pyroelectricity by symmetry. But biasing it with ions breaks the symmetry because of the induced partially dipole-aligned. This unmasks a large pyroelectricity. Ions were soft-landed upon 1 micron films of water ice at ? 160K. When cooled below 140 to 150 K this locks-in the dipole-alignment. Workfunction measurements of these films then show high and reversible pyroelectric activity from 30 to 150K. For an initial ~10V induced by the deposited ions, the at 160K, the observed bias below 150K varies approximately as 10V*(T/150K)2 This implies water has pyroelectric coefficients as large as that of many commercial pyroelectrics such as lead zirconate titanate (“PZT”). The pyroelectricity of water ice, not previously reported, is in reasonable agreement with that predicted via a monte carlo simulation of TIP4P ice. This is observed in crystalline and compact amorphous ice, deuterated or not. This implies that for water ice between 0 and 150K (such as astrophysical ices), temperature changes can induce strong electric fields (~10,000,000 V/m) that can influence their chemistry and trajectories or binding.

  3. Skylab floating ice experiment

    NASA Technical Reports Server (NTRS)

    Campbell, W. J. (principal investigator); Ramseier, R. O.; Weaver, R. J.; Weeks, W. F.

    1975-01-01

    The author has identified the following significant results. Coupling of the aircraft data with the ground truth observations proved to be highly successful with interesting results being obtained with IR and SLAR passive microwave techniques, and standard photography. Of particular interest were the results of the PMIS system which operated at 10.69 GHz with both vertical and horizontal polarizations. This was the first time that dual polarized images were obtained from floating ice. In both sea and lake ice, it was possible to distinguish a wide variety of thin ice types because of their large differences in brightness temperatures. It was found that the higher brightness temperature was invariably obtained in the vertically polarized mode, and as the age of the ice increases the brightness temperature increases in both polarizations. Associated with this change in age, the difference in temperature was observed as the different polarizations decreased. It appears that the horizontally polarized data is the most sensitive to variations in ice type for both fresh water and sea ice. The study also showed the great amount of information on ice surface roughness and deformation patterns that can be obtained from X-band SLAR observations.

  4. Creep of ice: Further studies

    NASA Technical Reports Server (NTRS)

    Heard, H. C.; Durham, W. B.; Kirby, S. H.

    1987-01-01

    Detailed studies have been done of ice creep as related to the icy satellites, Ganymede and Callisto. Included were: (1) the flow of high-pressure water ices II, III, and V, and (2) frictional sliding of ice I sub h. Work was also begun on the study of the effects of impurities on the flow of ice. Test results are summarized.

  5. How Do Plants Survive Ice?

    Microsoft Academic Search

    C. J. ANDREWS

    1996-01-01

    Plant species have had to adapt to freezing and the presence of ice in many climatic zones. Annual plants avoid ice by seed dispersal but, for biennials and perennials to survive they must cope with ice in various forms. Most plants that are regularly exposed to ice during their life cycles have acquired a dormant or quiescent winter period, when

  6. Investigating ice nucleation in cirrus clouds with an aerosol-enabled Multiscale Modeling Framework

    NASA Astrophysics Data System (ADS)

    Zhang, Chengzhu; Wang, Minghuai; Morrison, Hugh; Somerville, Richard C. J.; Zhang, Kai; Liu, Xiaohong; Li, Jui-Lin F.

    2014-12-01

    In this study, an aerosol-dependent ice nucleation scheme has been implemented in an aerosol-enabled Multiscale Modeling Framework (PNNL MMF) to study ice formation in upper troposphere cirrus clouds through both homogeneous and heterogeneous nucleation. The MMF model represents cloud scale processes by embedding a cloud-resolving model (CRM) within each vertical column of a GCM grid. By explicitly linking ice nucleation to aerosol number concentration, CRM-scale temperature, relative humidity and vertical velocity, the new MMF model simulates the persistent high ice supersaturation and low ice number concentration (10-100/L) at cirrus temperatures. The new model simulates the observed shift of the ice supersaturation PDF toward higher values at low temperatures following the homogeneous nucleation threshold. The MMF model predicts a higher frequency of midlatitude supersaturation in the Southern Hemisphere and winter hemisphere, which is consistent with previous satellite and in situ observations. It is shown that compared to a conventional GCM, the MMF is a more powerful model to simulate parameters that evolve over short time scales such as supersaturation. Sensitivity tests suggest that the simulated global distribution of ice clouds is sensitive to the ice nucleation scheme and the distribution of sulfate and dust aerosols. Simulations are also performed to test empirical parameters related to auto-conversion of ice crystals to snow. Results show that with a value of 250 ?m for the critical diameter, Dcs, that distinguishes ice crystals from snow, the model can produce good agreement with the satellite-retrieved products in terms of cloud ice water path and ice water content, while the total ice water is not sensitive to the specification of Dcs value.

  7. Engineering and Design: Ice Engineering

    NSDL National Science Digital Library

    As part of the US Army Corps of Engineers, the Ice Engineering Group solves problems stemming from ice and its effects on equipment and operations. This broad area includes ice jams that impede maritime navigation, maintenance issues, and "the destructive forces that moving ice exerts on river or coastal structures." Released on Oct. 30, 2002, the Ice Engineering Manual, given on this site, is divided into three parts. The first describes the difficulties presented by ice accumulation and how they are solved. Next, preventative measures are introduced that minimize the problem of ice jams. The last part discusses how boats navigate dangerous inland waterways during the winter.

  8. Engineering and Design: Ice Engineering

    NSDL National Science Digital Library

    2002-01-01

    As part of the US Army Corps of Engineers, the Ice Engineering Group solves problems stemming from ice and its effects on equipment and operations. This broad area includes ice jams that impede maritime navigation, maintenance issues, and "the destructive forces that moving ice exerts on river or coastal structures." Released on Oct. 30, 2002, the Ice Engineering Manual, given on this site, is divided into three parts. The first describes the difficulties presented by ice accumulation and how they are solved. Next, preventative measures are introduced that minimize the problem of ice jams. The last part discusses how boats navigate dangerous inland waterways during the winter.

  9. Vortex ice in nanostructured superconductors

    SciTech Connect

    Reichhardt, Charles [Los Alamos National Laboratory; Reichhardt, Cynthia J [Los Alamos National Laboratory; Libal, Andras J [Los Alamos National Laboratory

    2008-01-01

    We demonstrate using numerical simulations of nanostructured superconductors that it is possible to realize vortex ice states that are analogous to square and kagome ice. The system can be brought into a state that obeys either global or local ice rules by applying an external current according to an annealing protocol. We explore the breakdown of the ice rules due to disorder in the nanostructure array and show that in square ice, topological defects appear along grain boundaries, while in kagome ice, individual defects appear. We argue that the vortex system offers significant advantages over other artificial ice systems.

  10. Ice nucleation terminology

    NASA Astrophysics Data System (ADS)

    Vali, G.; DeMott, P.; Möhler, O.; Whale, T. F.

    2014-08-01

    Progress in the understanding of ice nucleation is being hampered by the lack of uniformity in how some terms are used in the literature. This even extends to some ambiguity of meanings attached to some terms. Suggestions are put forward here for common use of terms. Some are already well established and clear of ambiguities. Others are less engrained and will need a conscious effort in adoption. Evolution in the range of systems where ice nucleation is being studied enhances the need for a clear nomenclature. The ultimate limit in the clarity of definitions is, of course, the limited degree to which ice nucleation processes are understood.

  11. Under ice oil barrier

    SciTech Connect

    Bickham, K.L.

    1984-02-14

    A method and apparatus are provided for containing and collecting oil spilled under ice over water having a current by deploying a buoyant boom or barrier under the ice downstream of the oil spill and crossing the current flow, and stopping the flow of the oil with the boom or barrier. Preferably, the boom or barrier is constructed of two tubes connected by a spreader which are inflatable in situ under the ice and which form a water space above the spreader and between the tubes which subsequently freezes to anchor the boom or barrier in place.

  12. Global Ice Core Research

    NSDL National Science Digital Library

    This informative site from the US Geological Survey (USGS) covers the latest ice-core research projects from around the world, including sites in Nepal, Norway, and Kyrghyzstan. Authored by researchers at the Global Ice core Research Office, the site contains an overview of the mid-latitude and polar glaciers, isotopic methods in glacial research, and applications to paleoclimatology. Links to maps, figures, and in some cases, full-text articles (HTML) about specific glaciers are available, and the site is peppered with color photos of glacial environments. Links to biographies of the scientists involved in the project, contacts, and other snow and ice sites are also listed.

  13. An ice shelf breakup

    SciTech Connect

    Fahnestock, M. [Univ. of Maryland, College Park, MD (United States)

    1996-02-09

    Glaciers and ice sheets are controlled by the climate and must change if the conditions that led to their current configurations are changing. These ice masses exist at the interface between the atmosphere, which provides sustaining snowfall and thermal regulation, and the land, which provides a stable base and in many cases the elevation required to reach suitably cold conditions. Ice sheets and glaciers are distributed around the globe and can serve as potential indicators of past climate variability and current climatic trends. 9 refs.

  14. The Great Ice Age

    NSDL National Science Digital Library

    Louis Ray

    The Great Ice Age, a recent chapter in the Earth's history, was a period of recurring widespread glaciations. Mountain glaciers formed on all continents, the ice caps of Antarctica and Greenland were more extensive and thicker than today, and vast glaciers, in places as much as several thousand feet thick, spread across North America and Eurasia. This ice age, the most recent in the history of the Earth, took place from 20 million years to 6 thousand years ago (Quaternary Period). The development of our understanding and the evidence for this worldwide event are covered in this United States Geological Survey (USGS) publication.

  15. Middle Pleistocene (?) buried glacial ice on Bylot Island, Canadian Arctic Archipleago

    NASA Astrophysics Data System (ADS)

    Fortier, D.; Godin, E.; Kanevskiy, M. Z.; Allard, M.

    2009-12-01

    Bylot Island is located north of Baffin Island (73°N, 80°W). More than the half of the island is covered by an ice cap and its outlet glaciers flowing towards the arctic lowland of the Lancaster formation. The study site comprises four main stratigraphic units. Overlying the shales (Tertiary) of the Lancaster Formation (500 m a.s.l.), a diamicton (unit 1) is covered by a “fossil forest-tundra” sequence (unit 2) containing abundant remains of trees and plants (Allard et al., submitted). Paleontological correlation of extinct species and reverse to normal palomagnetism polarities suggest a Late Pliocene to Early Pleistocene age for this unit. A sequence (unit 3) of ice-contact proximal to distal glacio-fluvial sediments overlies the organic beds. Paleomagnetic analysis showed that the upper glacio-fluvial sediments were likely deposited during the Brunhes polarity chron (younger than 0.73 Ma). The uppermost unit (unit 4) consists in a lodgement till containing clasts of Paleozoic limestone erratics. Based on amino acid ratios of shells fragments in the drift, Klassen (1993) suggested that this “foreign drift” was probably deposited during an "old" Quaternary glaciation named “Baffin glaciation” During July 2009 several active-layer detachment slides at the head of large gullies exposed large massive ice bodies located at the junction between units 3 and 4. A preliminary analysis of the ice facies and ice crystals revealed the presence of two distinct types of massive ice: 1) clear-ice bodies with very few sediments and no organic inclusions. The ice crystals were large (cm) and air bubbles were observed at the junction of crystals. These characteristics could potentially indicate an englacial origin for these clear ice bodies. In some places, the ice was stratified with undulating layers of sands and gravels. These micro-structures are very similar to basal ice facies we observed at the Matanuska Glacier in Alaska. The exposed massive ice sections were a few tens of meter wide and about 2 to 4 m deep but the real width and thickness of these ice masses are unknown. The upper part of the clear ice and stratified massive ice bodies were always in contact with various types of glacio-fluvial sediments which suggest that their preservation were likely related to rapid burial of the ice and refreezing of the overlying sediments following permafrost aggradation. 2) large, white to milky, epigenetic ice wedges with a typical sub-vertical foliated structure. The ice wedges were formed in unit 4 and, in some places, penetrated into the clear massive ice bodies described above which created a sharp visual contrast between the two types of ice. This also indicates that ice wedge development post-date the massive ice burial. Based on the chrono-stratigraphic context and on the similarities between 1) the clear ice masses and the contemporary englacial ice facies (e.g. on Bylot Island); and 2) the cryostructures of the stratified massive ice at the study site and the contemporary basal ice cryostructures observed at the Matanuska glaciers, we propose that the massive ice bodies exposed on Bylot Island are related to a Middle Pleistocene glaciation.

  16. Understanding Ice Supersaturation, Particle Growth, and Number Concentration in Cirrus Clouds

    SciTech Connect

    Comstock, Jennifer M.; Lin, Ruei-Fong; Starr, David O.; Yang, P.

    2008-12-10

    Many factors control the ice supersaturation and microphysical properties in cirrus clouds. We explore the effects of dynamic forcing, ice nucleation mechanisms, and ice crystal growth rate on the evolution and distribution of water vapor and cloud properties in cirrus clouds using a detailed microphysical model and remote sensing measurements obtained at the Department of Energy’s Atmospheric Radiation Measurement (ARM) Climate Research Facility located near Lamont, OK. To help understand dynamic scales important in cirrus formation, we force the model using both large-scale forcing derived using ARM variational analysis, and mean mesoscale velocity derived from radar Doppler velocity measurements. Both heterogeneous and homogeneous nucleation processes are explored, where we have implemented a rigorous classical theory heterogeneous nucleation scheme to compare with empirical representations. We evaluate model simulations by examining both bulk cloud properties and distributions of measured radar reflectivity, lidar extinction, and water vapor profiles, as well as retrieved cloud microphysical properties. This approach allows for independent verification of both the large and small particle modes of the particle size distribution. Our results suggest that mesoscale variability is the primary mechanism needed to reproduce observed quantities, while nucleation mechanism is secondary. Slow ice crystal growth tends to overestimate the number of small ice crystals, but does not seem to influence bulk properties such as ice water path and cloud thickness. The most realistic simulations as compared with observations are forced using mesoscale waves, include fast ice crystal growth, and initiate ice by either homogeneous or heterogeneous nucleation. Ice crystal number concentrations on the order of 10-100 L-1 produce results consistent with both lidar and radar observations during a cirrus event observed on 7 December 1999, which has an optical depth range typical of midlatitude cirrus.

  17. Designing for effective stationkeeping in ice

    E-print Network

    Nørvåg, Kjetil

    . Sea ice management Sea ice observation and monitoring: · Ice concentration, floe size distribution, etc. · Ice geometry, ice age, density, salinity, etc. · Sea ice tracking (drift speed and directionDesigning for effective stationkeeping in ice CeSOS Highlights and AMOS Visions Conference

  18. Field and Laboratory Studies of Ice Nucleation in Winter Orographic Clouds.

    NASA Astrophysics Data System (ADS)

    Rogers, David Clark

    The present research was divided into two separate but related areas: (1) Cloud microphysical data from instrumented aircraft flights through winter clouds over Elk Mountain were analyzed to assess the formation of ice crystals under natural conditions. The results indicated that for these supercooled clouds, most crystals form near the upwind edge of the cloud, where water vapor condenses on available cloud condensation nuclei (CCN). Two possible explanations were offered: the active nuclei are either very small contact ice nuclei, or they are a subset of the CCN known as "condensation -freezing ice nuclei ". Furthermore, this formation was indicated as likely to be a primary nucleation process since there was a strong temperature dependence of crystal concentration: the ensemble of data showed typical concentrations of one per liter at -15(DEGREES)C and changed by a factor 10(DEGREES) for a 9(DEGREES)C temperature change. (2) In order to assess the contribution made by condensation-freezing nuclei, natural concentrations of both deposition and condensation -freezing nuclei were measured with a continuous flow thermal gradient diffusion chamber (CFC). Significant characteristics of the chamber design included: concentric cylinder geometry, vertical axis alignment and flow, ice covered walls of ebonized copper, and optical detection of ice crystals which form and grow on active ice nuclei. As an aid to instrument design and data interpretation, a mathematical model of the temperature and vapor fields in the chamber and of the growth and fallout of water and ice particles was constructed. Its predictions compared favorably with those of another numerical model. Laboratory experiments were performed with artificial aerosols and confirmed both the ability of the chamber to detect known ice nuclei and of the optical-electronic system to distinguish crystals from droplets. Ice nucleus measurements were obtained for natural aerosols over the range of temperatures -7(DEGREES)C to -20(DEGREES)C and water supersaturation, SSw, -5% to +5%. Values for the concentration of deposition nuclei (SSw < 0%) were generally larger than usually accepted values based on the membrane filter technique. Over the range of operating conditions, concentrations (per liter) of deposition ice nuclei were described well by .20 x SSi (ice supersaturation, %) and of condensation-freezing plus deposition ice nuclei at -15(DEGREES)C and warmer by 1.07 + .20 x SSi. Greater concentrations of condensation-freezing nuclei were indicated at -20(DEGREES)C. The ice nucleus measurements fit within the temperature-crystal concentration envelope of research aircraft observations in Elk Mountain cap clouds.

  19. TOWARDS ICE FORMATION CLOSURE IN MIXED-PHASE BOUNDARY LAYER CLOUDS DURING ISDAC

    NASA Astrophysics Data System (ADS)

    Avramov, A.; Ackerman, A. S.; Fridlind, A. M.; van Diedenhoven, B.; Korolev, A. V.

    2009-12-01

    Mixed-phase stratus clouds are ubiquitous in the Arctic during the winter and transition seasons. Despite their important role in various climate feedback mechanisms they are not well understood and are difficult to represent faithfully in cloud models. In particular, models of all types experience difficulties reproducing observed ice concentrations and liquid/ice water partitioning in these clouds. Previous studies have demonstrated that simulated ice concentrations and ice water content are critically dependent on ice nucleation modes and ice crystal habit assumed in simulations. In this study we use large-eddy simulations with size-resolved microphysics to determine whether uncertainties in ice nucleus concentrations, ice nucleation mechanisms, ice crystal habits and large-scale forcing are sufficient to account for the difference between simulated and observed quantities. We present results of simulations of two case studies based on observations taken during the recent Indirect and Semi-Direct Aerosol Campaign (ISDAC) on April 8 and 26, 2008. The model simulations are evaluated through extensive comparison with in-situ observations and ground-based remote sensing measurements.

  20. Field and Laboratory Studies of Ice Nucleation in Winter Orographic Clouds

    Microsoft Academic Search

    David Clark Rogers

    1982-01-01

    The present research was divided into two separate but related areas: (1) Cloud microphysical data from instrumented aircraft flights through winter clouds over Elk Mountain were analyzed to assess the formation of ice crystals under natural conditions. The results indicated that for these supercooled clouds, most crystals form near the upwind edge of the cloud, where water vapor condenses on

  1. River Ice Processes - Short Version

    NSDL National Science Digital Library

    COMET

    2010-07-13

    This module provides information on flooding associated with river ice jams. Based on a presentation by Dr. Kate White, a nationally-recognized expert on river ice, this webcast explores basic river ice processes including the formation, growth, breakup, and transport of river ice and how it can become jammed, triggering floods. This shorter version of the previously published module "River Ice Processes", has less focus on the US National Weather Service, making it more broadly applicable, including to an international audience.

  2. Origin of massive ice at Cape Marre-Sale, Yamal Peninsula, Siberia, Russia: contrasting views

    NASA Astrophysics Data System (ADS)

    Fortier, D.; Kurchatova, A. N.; Jorgenson, M. T.; Godin, E.; M-Lepage, J.; Stephani, E.; Kanevskiy, M. Z.; Shur, Y.

    2012-12-01

    The origin of permafrost and ground ice of the Cape Marre-Sale polar station area, Western Yamal Peninsula, Russia, has been debated for decades. This can be explained by the extremely complex morphology of sedimentary strata and cryofacies exposed along the costal bluffs. Here, we report massive ice observations realized during summer 2012 as well as numerous laboratory and field analysis previously conducted on the massive ice bodies and reported in the literature. Our objective is to present contrasting views currently being proposed to explain the origin of massive ice at Cape Marre-Sale. Several types of massive ice bodies can be observed along the exposures. One striking cryofacies observed shows alternating cm-thick ice lenses and cm-to-dm thick bands of sediment-rich ice, which are commonly folded with an amplitude of several meters. This very ice-rich cryofacies is interpreted either as buried basal ice of the Eurasian ice-sheet or alternatively as massive segregated ice formed during epigenetic permafrost aggradation. This cryofacies comprised meters large clasts of stratified sand with organics, with some of these stratifications being folded and faulted and showing boudinage structure. The location of these large sand clasts within the foliated ice-rich massive ice could be explained either by glacio-tectonic activity (glacio-dislocation during ice flow) or alternatively by regional tectonic activity. Large m-thick and meters-long pure ice bodies were also observed within the foliated massive ice. The first type is withish and contains a very large amount of air bubbles without any clear orientation. The second type is made of blueish to clear ice and contains a few air bubbles and rare, randomly distributed, fine-grained sediment inclusions suspended in the ice. Ice crystallography revealed the presence of large (cm) ice crystals in both types of ice. These pure ice bodies cross-cut the massive foliated ice. They could be interpreted as refrozen water trapped in intra-glacial tunnels formed within the basal ice (oxygen-rich water and suspension freezing of fine-grained sediments) of the ice-sheet or alternatively as groundwater injection (and subsequent refreezing) during freezing of taliks following lake drainage. Finally, wedge-shaped massive ice can also be observed near the top of the exposures. The first type is yellowish, vertically foliated, extends downward for several meters in the massive foliated ice and contains a significant amount of fine-grained sediment. This is either interpreted as Pleistocene ice wedge (frost-cracking) or alternatively as hydrolaccolith formed by the upward intrusion/expulsion of water within the foliated massive ice, likely due to the joint action of groundwater, permafrost aggradation and tectonic processes. The second type of wedge ice is withish in color and foliated and has been interpreted unanimously as Holocene ice wedges (frost-cracking). The contrasting views presented here represent new and reasonable working hypothesis to explain the genesis of massive ice at Cape Marre-Sale. These hypotheses have considerable implications for the reconstruction of paleoclimates and paleoenvironments of Western Siberia.

  3. NOVA - Extreme Ice

    NSDL National Science Digital Library

    WGBH Educational Foundation

    This one-hour program is divided into 6 parts which can be watched individually or as a set. The chapters document ice loss across the world due to climate change with focuses on Alaska, Greenland, and Antarctica.

  4. Global ice sheet modeling

    SciTech Connect

    Hughes, T.J.; Fastook, J.L. [Univ. of Maine, Orono, ME (United States). Institute for Quaternary Studies

    1994-05-01

    The University of Maine conducted this study for Pacific Northwest Laboratory (PNL) as part of a global climate modeling task for site characterization of the potential nuclear waste respository site at Yucca Mountain, NV. The purpose of the study was to develop a global ice sheet dynamics model that will forecast the three-dimensional configuration of global ice sheets for specific climate change scenarios. The objective of the third (final) year of the work was to produce ice sheet data for glaciation scenarios covering the next 100,000 years. This was accomplished using both the map-plane and flowband solutions of our time-dependent, finite-element gridpoint model. The theory and equations used to develop the ice sheet models are presented. Three future scenarios were simulated by the model and results are discussed.

  5. Cryosphere: Entry beneath ice

    NASA Astrophysics Data System (ADS)

    Fretwell, Peter

    2015-04-01

    Ice shelves in West Antarctica have been shown to melt where warm circumpolar deep water enters a sub-shelf cavity. A bathymetric reconstruction of Totten Glacier in East Antarctica suggests that the same process may be at work there.

  6. Ice in Space

    NSDL National Science Digital Library

    This is a detailed lesson about space and how Earth fits in it. Learners will consider the essential question, "What is space?" Activities include small group miming, speaking, drawing, and/or writing about space and the evidence for ice in space. Included are detailed games and dialogue. Native stories are shared. This is lesson 9 of 12 in the unit, Exploring Ice in the Solar System.

  7. Ice On Venus

    NSDL National Science Digital Library

    This resource is part of the Science Education Gateway (SEGway) project, funded by NASA, which is a national consortium of scientists, museums, and educators working together to bring the latest science to students, teachers, and the general public. Is there ice on Venus? If so, what kind of ice is it? In this activity, students find the answers to these questions by using internet resources. The teacher's page contains teaching strategies, vocabulary, homework ideas, and assessment possibilities.

  8. Mars: retention of ice.

    PubMed

    Smoluchowski, R

    1968-03-22

    Water in the form of ice can exist on Mars as permafrost that is either in equilibrium with the water content of the atmosphere or gradually evaporating through a protective layer of soil. The latter situation is evaluated quantitatively, and the required thicknesses of the protective layers are estimated. The presence of subsurface ice may explain the higher radar reflectivity of the dark areas than of the bright areas. Observation of its seasonal variations is suggested. PMID:17791161

  9. Probing ice nucleation events on individual particles relevant to cloud formation

    NASA Astrophysics Data System (ADS)

    Wang, B.; Knopf, D. A.; Gilles, M. K.; Kulkarni, G.; Kathmann, S. M.; Kovarik, L.; Laskin, A.

    2014-12-01

    Atmospheric ice crystal formation in clouds can proceed by homogeneous and heterogeneous nucleation. Better understanding of heterogeneous ice nucleation is of critical importance to elucidate fundamental processes of aerosol-cloud interactions - one of the most challenging problems for predictive understanding of Earth's climate change. We develop and apply microscopy approaches for fundamental studies of heterogeneous ice nucleation on atmospheric particles. Hosted by environmental scanning electron microscope, we expand experimental observations of individual ice nucleation events at atmospherically relevant conditions. Applying multi-modal micro-spectroscopy methods, the physical and chemical properties of the identified ice nuclei can be characterized. Combined with theoretical chemistry calculations, the experimental data will be analyzed to gain better understanding of ice nucleation and parameterizations for cloud modelling studies.

  10. Cubic ice and large humidity with respect to ice in cold cirrus clouds

    NASA Astrophysics Data System (ADS)

    Bogdan, A.; Loerting, T.

    2009-04-01

    Recently several studies have reported about the possible formation of cubic ice in upper-tropospheric cirrus ice clouds and its role in the observed elevated relative humidity with respect to hexagonal ice, RHi, within the clouds. Since cubic ice is metastable with respect to stable hexagonal ice, its vapour pressure is higher. A key issue in determining the ratio of vapour pressures of cubic ice Pc and hexagonal ice Ph is the enthalpy of transformation from cubic to hexagonal ice Hcâ??h. By dividing the two integrated forms of the Clausius-Clapeyron equation for cubic ice and hexagonal ice, one obtains the relationship (1): ln Pc-- ln P*c-=--(Hcâ??h--) Ph P*h R 1T-- 1T* (1) from which the importance of Hcâ??h is evident. In many literature studies the approximation (2) is used: ln Pc-= Hc-â??h. Ph RT (2) Using this approximated form one can predict the ratio of vapour pressures by measuring Hcâ??h. Unfortunately, the measurement of Hcâ??h is difficult. First, the enthalpy difference is very small, and the transition takes place over a broad temperature range, e.g., between 230 K and 260 K in some of our calorimetry experiments. Second, cubic ice (by contrast to hexagonal ice) can not be produced as a pure crystal. It always contains hexagonal stacking faults, which are evidenced by the (111)-hexagonal Bragg peak in the powder diffractogram. If the number of hexagonal stacking faults in cubic ice is high, then one could even consider this material as hexagonal ice with cubic stacking faults. Using the largest literature value of the change of enthalpy of transformation from cubic to hexagonal ice, Hcâ??h ? 160 J/mol, Murphy and Koop (2005) calculated that Pc would be ~10% higher than that of hexagonal ice Phat 180 K - 190 K, which agrees with the measurements obtained later by Shilling et al. (2006). Based on this result Shilling et al. concluded that "the formation of cubic ice at T < 202 K may significantly contribute to the persistent in-cloud water supersaturations" in the upper-tropospheric cold cirrus clouds. Using instead the value of Hcâ??h ? 50 J/mol (Handa et al., 1986; Mayer and Hallbrucker, 1987) the calculation gives that Pc is only ~3% larger than that of Ph. Recently it has been reported that emulsified water droplets freeze to cubic ice when being cooled at a rate of 10 K/min (Murray and Bertram, 2006,). We prepared emulsified droplets using the same emulsification technique and studied them with a differential scanning calorimeter (DSC) between 278 and 180 K using a scanning rate of 10 K/min. During the warming of the samples we observed a very broad, tiny exothermal peak approximately between 230 and 260 K. Kohl et al. (2000) observed exothermal peak at ~230 K during the warming at 30 K/min of several samples of hyperquenched glassy water (HGW) prepared at temperature between 130 and 190 K. They attributed this peak to the cubic-to-hexagonal ice transition and estimated Hcâ??h to be between ~33 and 75 J/mol. Johari (2005) used the value of Hcâ??h ? 37 J/mol. Assuming that in our case the broad peak between 230 and 260 K is also due to the cubic-to-hexagonal ice transition we obtained approximately between 10 and 25 J/mol for Hcâ??h. This low enthalpy of transformation suggests that cubic ice in the atmosphere contains many hexagonal stacking faults. Using these values of Hcâ??h for cubic ice as produced at atmospheric cooling rates, the above mentioned formula gives that Pc is larger than that of Ph only by ~1%. We, therefore, suggest that the difference in the water vapor pressures between ice Ic and ice Ih is small and does not play a significant role in the elevation of RHi in cold cirrus clouds. Murphy, D. M., and T. Koop (2005), Q. J. R. Meteorol. Soc. 131, 1539-1565. Shilling, J. E. et al. (2006). Geophys. Res. Lett. 33, L17801, doi:1029/2006GL026671. Handa, P. Y., D. D. Klug, and E. Whalley (1986). J. Chem. Phys. 84, 7009-7010. Mayer, E., and A. Hallbr

  11. Ice Stream Dynamics during Deglaciation of the Laurentide Ice Sheet

    NASA Astrophysics Data System (ADS)

    Margold, Martin; Stokes, Chris R.; Clark, Chris D.

    2015-04-01

    Ice streams rapidly drain large sectors of ice sheet interiors. At present, they account for approximately 50% and 90% of the mass loss from Greenland and Antarctica, respectively, but there are concerns over recent increases in ice discharge. This has been linked to atmospheric and oceanic warming, but the longer-term implications for ice sheet deglaciation are less clear. A key question is whether the activity of ice streams is predictably linked to climate-driven ice sheet mass balance, or whether their activity might accelerate deglaciation. To explore this, we analyse ice streaming during deglaciation of the Laurentide Ice Sheet (LIS) from ~18 to ~7 ka. Following a recent mapping inventory, we bracket the timing of >100 ice streams using existing ice margin chronologies. At the Last Glacial Maximum (LGM), ice streams formed a drainage network similar to modern ice sheets. Numerous ice streams were located in topographic troughs and likely operated for thousands of years from the LGM. These drained the marine-based sectors of the northern and eastern margins of the ice sheet until ~11 ka and show a degree of spatial self-organisation. Other ice streams operated over much shorter time-scales and switched on and off, perhaps active for as little as a few hundred years. These include large ice streams that switched positions over sedimentary bedrock at the western and southern terrestrial margins. As the LIS retreated onto its low-relief and predominantly crystalline bedrock interior (after ~11 ka), a smaller number of large ice streams operated that were very wide (50-100 km), and have no modern analogue. Overall, the number of ice streams decreased during deglaciation and they represented a small proportion of the ice sheet circumference. We use simple scaling relationships, based on a data-set of modern Antarctic and Greenland ice stream dimensions and velocities, to estimate the mass loss delivered by ice streams. Our estimated total flux from ice streams is relatively stable until 13 ka and drops rapidly thereafter. We therefore find no evidence for major ice sheet instabilities linked to ice stream activity and conclude that deglaciation was largely driven by surface melt.

  12. Magnetic resonance diffusion and relaxation characterization of water in the unfrozen vein network in polycrystalline ice and its response to microbial metabolic products

    NASA Astrophysics Data System (ADS)

    Brown, Jennifer R.; Brox, Timothy I.; Vogt, Sarah J.; Seymour, Joseph D.; Skidmore, Mark L.; Codd, Sarah L.

    2012-12-01

    Polycrystalline ice, as found in glaciers and the ice sheets of Antarctica, is a low porosity porous media consisting of a complicated and dynamic pore structure of liquid-filled intercrystalline veins within a solid ice matrix. In this work, Nuclear Magnetic Resonance measurements of relaxation rates and molecular diffusion, useful for probing pore structure and transport dynamics in porous systems, were used to physically characterize the unfrozen vein network structure in ice and its response to the presence of metabolic products produced by V3519-10, a cold tolerant microorganism isolated from the Vostok ice core. Recent research has found microorganisms that can remain viable and even metabolically active within icy environments at sub-zero temperatures. One potential mechanism of survival for V3519-10 is secretion of an extracellular ice binding protein that binds to the prism face of ice crystals and inhibits ice recrystallization, a coarsening process resulting in crystal growth with ice aging. Understanding the impact of ice binding activity on the bulk vein network structure in ice is important to modeling of frozen geophysical systems and in development of ice interacting proteins for biotechnology applications, such as cryopreservation of cell lines, and manufacturing processes in food sciences. Here, we present the first observations of recrystallization inhibition in low porosity ice containing V3519-10 extracellular protein extract as measured with Nuclear Magnetic Resonance and Magnetic Resonance Imaging.

  13. Observations of small ice in mixed phase clouds using an airborne SID2 Small Ice Detector

    NASA Astrophysics Data System (ADS)

    Barrett, Paul; Blyth, Alan; Brown, Phil; Ulanowski, Joseph

    2015-04-01

    Here we present observations of small ice crystals in mixed phase cloud systems using an aircraft mounted SID2 (Small Ice Detector 2) probe. It is likely that these small ice particles have formed through an immersion freezing process from the underlying liquid cloud population. The exact nature of the immersion freezing mechanisms at work in the real atmosphere is uncertain and may include contributions from singular and stochastic processes as well as hybrid processes such as Contact Nucleation Inside Out. Observations of the number and position in the cloud structure of the first ice in mixed phase clouds are essential if we are to understand the microphysical mechanisms responsible for the conversion of liquid cloud drops into ice particles. The SID2 probe is able to observe particles smaller than 10 microns and so is useful when assessing the properties of ice that has formed from liquid cloud particles. Using the scattering patterns produced by SID2 it is possible to distinguish between liquid drops and non-spherical particles. A liquid cloud drop will produce a scattering pattern containing concentric rings whereas a non-spherical particle will not. The SID2 probe has a relatively large sample volume, and while this is good in the low concentrations found in typical cirrus clouds it presents difficulties in liquid clouds where concentrations can be orders of magnitude greater. Coincidence events, where two or more spherical particles are co-located within the extended sample volume, do not produce the typical scattering pattern associated with a liquid particle and are therefore more difficult to distinguish from ice. There are, however, some characteristic features of the scattering pattern from a coincidence event. Here we present an algorithm to identify coincidence events from analysis of individual scattering patterns. Results are presented that show that it is possible to obtain an estimate of the concentration of small ice in clouds which have relatively low concentrations of liquid cloud drops (<100/cc). Observations are presented of the occurrence of small ice in a mixed phase altocumulus cloud relative to cloud top. The significance of these observations in relation to the potential freezing mechanism is discussed.

  14. Imprints of air bubbles & crystal orientation fabric on RES signature

    NASA Astrophysics Data System (ADS)

    Drews, R.; Bohleber, P.; Eisen, O.; Steinhage, D.; Hamann, I.; Wilhelms, F.; Freitag, J.

    2009-04-01

    Radio echo sounding (RES) enables mapping of bedrock topography and internal structure in large ice bodies. Via multi-frequency and multi-polarization sounding, internal reflections can be assigned to non-uniformities in density, conductivity and crystal orientation fabric (COF). The isochronous character of density and conductivity variations allows to deduce a multitude of glaciological parameters (e.g. accumulation, linking of ice cores). The formation of COF interrelates with ice flow and gives insight into ice dynamical behavior. Polarization dependent backscatter has been observed in numerous cases in Greenland and Antarctica. It is often attributed to changing COF superimposed with birefringence. Radar profiles close to the EPICA ice core drill site in Dronning Maud Land (EDML), Antarctica, are a show-case for varying anisotropy along the ice column. In the upper 900 m, the backscattered power is maximal for polarization perpendicular to the ice divide, whereas below 900 m the maximum is parallel to the ice divide. For the observed anisotropy in deep ice, COF seems to be the dominant factor, as short scale variations (circ. 20 m) have been measured in the micro-structure of the nearby ice core. However, high resolution (circ. 1 m) COF data along depth are missing so far. In the upper ice column the COF distribution is initially isotropic and slowly evolves into an anisotropic girdle towards greater depth. The depth of rotation in anisotropy coincides with the clathrate transition at EDML. We therefore conclude that the anisotropy in the upper ice column might also be related to an anisotropic distribution of air bubbles caused by ice flow. We examine the effect of statistical variations in COF as well as anisotropic air bubble distribution on the radar response. This is linked to in-situ measurements of COF and air bubble distribution in the EDML ice core. Eventually we aim at reconstructing stress and strain rates in ice from the observed anisotropy in the radar data.

  15. Scattering and absorption of light by ice particles: Solution by a new physical-geometric optics hybrid method

    E-print Network

    Baum, Bryan A.

    Scattering and absorption of light by ice particles: Solution by a new physical-geometric optics: Light scattering Geometric optics Physical optics Hexagonal ice crystal a b s t r a c t A new physical of the scattering and absorption of light by non- spherical particles [1­5]. Rigorous techniques developed

  16. Comparisons of Cubed Ice, Crushed Ice, and Wetted Ice on Intramuscular and Surface Temperature Changes

    PubMed Central

    Dykstra, Joseph H; Hill, Holly M; Miller, Michael G; Cheatham, Christopher C; Michael, Timothy J; Baker, Robert J

    2009-01-01

    Context: Many researchers have investigated the effectiveness of different types of cold application, including cold whirlpools, ice packs, and chemical packs. However, few have investigated the effectiveness of different types of ice used in ice packs, even though ice is one of the most common forms of cold application. Objective: To evaluate and compare the cooling effectiveness of ice packs made with cubed, crushed, and wetted ice on intramuscular and skin surface temperatures. Design: Repeated-measures counterbalanced design. Setting: Human performance research laboratory. Patients or Other Participants: Twelve healthy participants (6 men, 6 women) with no history of musculoskeletal disease and no known preexisting inflammatory conditions or recent orthopaedic injuries to the lower extremities. Intervention(s): Ice packs made with cubed, crushed, or wetted ice were applied to a standardized area on the posterior aspect of the right gastrocnemius for 20 minutes. Each participant was given separate ice pack treatments, with at least 4 days between treatment sessions. Main Outcome Measure(s): Cutaneous and intramuscular (2 cm plus one-half skinfold measurement) temperatures of the right gastrocnemius were measured every 30 seconds during a 20-minute baseline period, a 20-minute treatment period, and a 120-minute recovery period. Results: Differences were observed among all treatments. Compared with the crushed-ice treatment, the cubed-ice and wetted-ice treatments produced lower surface and intramuscular temperatures. Wetted ice produced the greatest overall temperature change during treatment and recovery, and crushed ice produced the smallest change. Conclusions: As administered in our protocol, wetted ice was superior to cubed or crushed ice at reducing surface temperatures, whereas both cubed ice and wetted ice were superior to crushed ice at reducing intramuscular temperatures. PMID:19295957

  17. Effects of crushed ice and wetted ice on hamstring flexibility.

    PubMed

    Larsen, Chelsea C; Troiano, Jean M; Ramirez, Rebecca J; Miller, Michael G; Holcomb, William R

    2015-02-01

    Flexibility, which is the ability to move freely through a full range of motion (ROM), is desired to enhance the performance and decrease the likelihood of muscle injury. There are different techniques used to increase ROM and cryotherapy techniques to facilitation flexibility gains. However, the combination of stretching and type of cryotherapy agents are still confounding. The purpose was to determine which type of cryotherapy, crushed or wetted ice, would produce the greatest gains in hamstring ROM when followed by proprioceptive neuromuscular facilitation (PNF) stretching. Fifteen healthy subjects underwent 3 treatment conditions: crushed ice bag (crushed ice), wetted ice bag (wetted ice), and no ice bag (no ice). Subject's hamstring ROM was measured at baseline, then again after a 20-minute cryotherapy treatment session. Subjects were then stretched using a slow-reversal-hold-relax PNF technique followed by a final ROM measurement. A repeated measures analysis of variance showed significant differences between cryotherapy and measurement conditions. Post hoc testing indicated that no ice (75.49 ± 12.19° C) was significantly different from wetted ice (81.73 ± 10.34° C) and crushed ice (81.62 ± 13.19° C) at the end of the treatment session, and that no ice (85.27 ± 13.83° C) was significantly different than wetted ice (89.44 ± 11.31° C) and crushed ice (89.16 ± 13.78° C) after the stretching session. However, there were no differences between wetted ice and crushed ice. Results indicate that strength and conditioning specialists can increase ROM with both forms of ice in combination with PNF stretching more so than when using no ice at all. PMID:24378663

  18. A New Way to Measure Cirrus Ice Water Content by Using Ice Raman Scatter with Raman Lidar

    NASA Technical Reports Server (NTRS)

    Wang, Zhien; Whiteman, David N.; Demoz, Belay; Veselovskii, Igor

    2004-01-01

    High and cold cirrus clouds mainly contain irregular ice crystals, such as, columns, hexagonal plates, bullet rosettes, and dendrites, and have different impacts on the climate system than low-level clouds, such as stratus, stratocumulus, and cumulus. The radiative effects of cirrus clouds on the current and future climate depend strongly on cirrus cloud microphysical properties including ice water content (IWC) and ice crystal sizes, which are mostly an unknown aspect of cinus clouds. Because of the natural complexity of cirrus clouds and their high locations, it is a challenging task to get them accurately by both remote sensing and in situ sampling. This study presents a new method to remotely sense cirrus microphysical properties by using ice Raman scatter with a Raman lidar. The intensity of Raman scattering is fundamentally proportional to the number of molecules involved. Therefore, ice Raman scattering signal provides a more direct way to measure IWC than other remote sensing methods. Case studies show that this method has the potential to provide essential information of cirrus microphysical properties to study cloud physical processes in cirrus clouds.

  19. Antarctic Ice Movement Part II

    NSDL National Science Digital Library

    For the most part, an ice sheet moves down slope slowly because the ice is in direct contact with underlying bedrock. In some places, however, ice races along much faster than the rest of the sheet. These areas of fast-moving flow, called ice streams, are believed to be caused by a thin, lubricating layer of water and mud between the ice and the land. In this video segment adapted from NOVA, a team of scientists seeks evidence to support their hypothesis that atmospheric warming -- either now or in the past -- may explain why water has formed beneath the ice sheet.

  20. Intracellular ice and cell survival in cryo-exposed embryonic axes of recalcitrant seeds of Acer saccharinum: an ultrastructural study of factors affecting cell and ice structures

    PubMed Central

    Wesley-Smith, James; Berjak, Patricia; Pammenter, N. W.; Walters, Christina

    2014-01-01

    Background and Aims Cryopreservation is the only long-term conservation strategy available for germplasm of recalcitrant-seeded species. Efforts to cryopreserve this form of germplasm are hampered by potentially lethal intracellular freezing events; thus, it is important to understand the relationships among cryo-exposure techniques, water content, structure and survival. Methods Undried embryonic axes of Acer saccharinum and those rapidly dried to two different water contents were cooled at three rates and re-warmed at two rates. Ultrastructural observations were carried out on radicle and shoot tips prepared by freeze-fracture and freeze-substitution to assess immediate (i.e. pre-thaw) responses to cooling treatments. Survival of axes was assessed in vitro. Key Results Intracellular ice formation was not necessarily lethal. Embryo cells survived when crystal diameter was between 0·2 and 0·4 µm and fewer than 20 crystals were distributed per ?m2 in the cytoplasm. Ice was not uniformly distributed within the cells. In fully hydrated axes cooled at an intermediate rate, the interiors of many organelles were apparently ice-free; this may have prevented the disruption of vital intracellular machinery. Intracytoplasmic ice formation did not apparently impact the integrity of the plasmalemma. The maximum number of ice crystals was far greater in shoot apices, which were more sensitive than radicles to cryo-exposure. Conclusions The findings challenge the accepted paradigm that intracellular ice formation is always lethal, as the results show that cells can survive intracellular ice if crystals are small and localized in the cytoplasm. Further understanding of the interactions among water content, cooling rate, cell structure and ice structure is required to optimize cryopreservation treatments without undue reliance on empirical approaches. PMID:24368198

  1. Inhibition of Ice Growth and Recrystallization by Zirconium Acetate and Zirconium Acetate Hydroxide

    PubMed Central

    Mizrahy, Ortal; Bar-Dolev, Maya; Guy, Shlomit; Braslavsky, Ido

    2013-01-01

    The control over ice crystal growth, melting, and shaping is important in a variety of fields, including cell and food preservation and ice templating for the production of composite materials. Control over ice growth remains a challenge in industry, and the demand for new cryoprotectants is high. Naturally occurring cryoprotectants, such as antifreeze proteins (AFPs), present one solution for modulating ice crystal growth; however, the production of AFPs is expensive and inefficient. These obstacles can be overcome by identifying synthetic substitutes with similar AFP properties. Zirconium acetate (ZRA) was recently found to induce the formation of hexagonal cavities in materials prepared by ice templating. Here, we continue this line of study and examine the effects of ZRA and a related compound, zirconium acetate hydroxide (ZRAH), on ice growth, shaping, and recrystallization. We found that the growth rate of ice crystals was significantly reduced in the presence of ZRA and ZRAH, and that solutions containing these compounds display a small degree of thermal hysteresis, depending on the solution pH. The compounds were found to inhibit recrystallization in a manner similar to that observed in the presence of AFPs. The favorable properties of ZRA and ZRAH suggest tremendous potential utility in industrial applications. PMID:23555701

  2. Understanding Ice Supersaturation, Particle Growth, and Number Concentration in Cirrus Clouds

    NASA Technical Reports Server (NTRS)

    Comstock, Jennifer M.; Lin, Ruei-Fong; Starr, David O'C.; Yang, Ping

    2008-01-01

    Many factors control the ice supersaturation and microphysical properties in cirrus clouds. We explore the effects of dynamic forcing, ice nucleation mechanisms, and ice crystal growth rate on the evolution and distribution of water vapor and cloud properties in nighttime cirrus clouds using a one-dimensional cloud model with bin microphysics and remote sensing measurements obtained at the Department of Energy's Atmospheric Radiation Measurement (ARM) Climate Research Facility located near Lamont, OK. We forced the model using both large-scale vertical ascent and, for the first time, mean mesoscale velocity derived from radar Doppler velocity measurements. Both heterogeneous and homogeneous nucleation processes are explored, where a classical theory heterogeneous scheme is compared with empirical representations. We evaluated model simulations by examining both bulk cloud properties and distributions of measured radar reflectivity, lidar extinction, and water vapor profiles, as well as retrieved cloud microphysical properties. Our results suggest that mesoscale variability is the primary mechanism needed to reproduce observed quantities. Model sensitivity to the ice growth rate is also investigated. The most realistic simulations as compared with observations are forced using mesoscale waves, include fast ice crystal growth, and initiate ice by either homogeneous or heterogeneous nucleation. Simulated ice crystal number concentrations (tens to hundreds particles per liter) are typically two orders of magnitude smaller than previously published results based on aircraft measurements in cirrus clouds, although higher concentrations are possible in isolated pockets within the nucleation zone.

  3. Inhibition of ice growth and recrystallization by zirconium acetate and zirconium acetate hydroxide.

    PubMed

    Mizrahy, Ortal; Bar-Dolev, Maya; Guy, Shlomit; Braslavsky, Ido

    2013-01-01

    The control over ice crystal growth, melting, and shaping is important in a variety of fields, including cell and food preservation and ice templating for the production of composite materials. Control over ice growth remains a challenge in industry, and the demand for new cryoprotectants is high. Naturally occurring cryoprotectants, such as antifreeze proteins (AFPs), present one solution for modulating ice crystal growth; however, the production of AFPs is expensive and inefficient. These obstacles can be overcome by identifying synthetic substitutes with similar AFP properties. Zirconium acetate (ZRA) was recently found to induce the formation of hexagonal cavities in materials prepared by ice templating. Here, we continue this line of study and examine the effects of ZRA and a related compound, zirconium acetate hydroxide (ZRAH), on ice growth, shaping, and recrystallization. We found that the growth rate of ice crystals was significantly reduced in the presence of ZRA and ZRAH, and that solutions containing these compounds display a small degree of thermal hysteresis, depending on the solution pH. The compounds were found to inhibit recrystallization in a manner similar to that observed in the presence of AFPs. The favorable properties of ZRA and ZRAH suggest tremendous potential utility in industrial applications. PMID:23555701

  4. Comparisons of Fabric Strength and Development in Polycrystalline Ice at Atmospheric and Basal Hydrostatic Pressures

    NASA Astrophysics Data System (ADS)

    Breton, Daniel; Baker, Ian; Cole, David

    2013-04-01

    Understanding and predicting the flow of polycrystalline ice is crucial to ice sheet modeling and paleoclimate reconstruction from ice cores. Ice flow rates depend strongly on the fabric (i.e. the distribution of grain sizes and crystallographic orientations) which evolves over time and enhances the flow rate in the direction of applied stress. The mechanisms for fabric evolution in ice have been extensively studied at atmospheric pressures, but little work has been done to observe these processes at the high pressures experienced deep within ice sheets where long-term changes in ice rheology are expected to have significance. We conducted compressive creep tests to ~10% strain on 917 kg m-3, initially randomly-oriented polycrystalline ice specimens at 0.1 (atmospheric) and 20 MPa (simulating ~2,000 m depth) hydrostatic pressures, performing microstructural analyses on the resulting deformed specimens to characterize the evolution and strength of crystal fabric. Our microstructural analysis technique simultaneously collects grain shape and size data from Scanning Electron Microscope (SEM) micrographs and obtains crystallographic orientation data via Electron BackScatter Diffraction (EBSD). Combining these measurements allows rapid analysis of the ice fabric over large numbers of grains, yielding statistically useful numbers of grain size and orientation data. We present creep and microstructural data to demonstrate pressure-dependent effects on the mechanical and microstructural evolution of polycrystalline ice and discuss possible mechanisms for the observed differences.

  5. Response of Simulated Mixed-Phase Arctic Stratus Clouds to Slowly Activated Ice Nuclei

    NASA Astrophysics Data System (ADS)

    Fridlind, A. M.; Avramov, A.; Ackerman, A. S.; Alpert, P. A.; Knopf, D. A.

    2014-12-01

    Supercooled mixed-phase cloud decks are common in the Arctic, often persisting for days. Individual ice crystals in such clouds have relatively short lifetimes, typically an hour or less. Thus new ice crystals must be generated continuously in such long-lived cloud layers. Field campaigns investigating the microphysics of the simplest such clouds—unseeded single-layer cases in coupled or decoupled boundary layers—have aimed to measure the background ice nuclei (IN) required to initiate ice formation processes, specifically by measuring the concentration of IN above cloud top that are active at water saturation at cloud-top temperature. In previous detailed simulations of observed case studies, we demonstrated that if all ambient IN are assumed to be activated rapidly, and if there is no surface source of IN over pack ice or efficient multiplication process in the absence of riming, as commonly assumed, then overlying IN concentrations must exceed those of in-cloud ice crystals by a factor of order 10-100 or more, generally much higher than measured. However, under such conditions, entrainment and rapid activation quickly achieve a long-lived quasi-steady cloud microphysical state in simulations that seems consistent with that commonly observed. These previous studies made the assumption that all relevant IN have a lifetime of roughly one second at water saturation under cloud-top conditions, using a singular ice nucleation scheme. Here we investigate the behavior of the same cloud systems in the presence of IN with longer activation time scales, including those only available in the contact mode and those with a wider range of lifetimes under in-cloud conditions. We make a range of assumptions about IN properties to constrain ice nucleation schemes to the degree possible using field data. When ice crystals are primarily sustained by slowly activated IN, we find that the relative depletion rate of the boundary-layer reservoir of IN impacts the degree of quasi-steady behavior.

  6. Clathrate hydrate formation in amorphous cometary ice analogs in vacuo

    NASA Technical Reports Server (NTRS)

    Blake, David; Allamandola, Louis; Sandford, Scott; Hudgins, Doug; Freund, Friedemann

    1991-01-01

    Experiments conducted in clathrate hydrates with a modified electron microscope have demonstrated the possibility of such compounds' formation during the warming of vapor-deposited amorphous ices in vacuo, through rearrangements in the solid state. Subsolidus crystallization of compositionally complex amorphous ices may therefore be a general and ubiquitous process. Phase separations and microporous textures thus formed may be able to account for such anomalous cometary phenomena as the release of gas at large radial distances from the sun and the retention of volatiles to elevated temperatures.

  7. Bacteria Assists in Formation of Ice and Snow

    NSDL National Science Digital Library

    NPR Talk of the Nation Science Friday Audio Story: New work in the journal Science suggests that bacteria may have played an important role in guiding the formation of the snow and rain forming ice crystals found in high-level clouds. The researchers looked at snow samples from around the globe — including Montana, France and Antarctica — and found that cells and cell fragments were a significant part of the aerosol particles that lead to the formation of ice and raindrops. Brent C. Christner, a member from the research team, talks with guest host Joe Palca about the connection between microbiology and meteorology.

  8. Ice deformation near SHEBA R. W. Lindsay

    E-print Network

    Lindsay, Ron

    Oceanography: General: Artic and Antartic oceanography; 4275 Oceanography: General: Remote sensing and electromagnetic processes (0689); 4540 Oceanography: Physical: Ice mechanics and air/sea/ice exchange processes; 4594 Oceanography: Physical: Instruments and techniques; KEYWORDS: sea ice, ice deformation, SHEBA

  9. Vostok Ice Core: Excel (Mac or PC)

    NSDL National Science Digital Library

    Professor Stephanie Pfirman, Barnard College. Based on data of J. Chapellaz, Laboratoire de Glaciologie et Geophysique de l'Environment, Grenoble. Archived at: Lamont-Dohert Earth Observatory (more info) . Starting Point page organized by R.M. MacKay.

    Students use Excel to graph and analyze Vostok ice core data (160,000 years of Ice core data from Vostok Station). Data includes ice age, ice depth, carbon dioxide, methane, dust, and deuterium isotope relative abundance.

  10. Effect of gravity wave temperature variations on homogeneous ice nucleation

    NASA Astrophysics Data System (ADS)

    Dinh, Tra; Podglajen, Aurélien; Hertzog, Albert; Legras, Bernard; Plougonven, Riwal

    2015-04-01

    Observations of cirrus clouds in the tropical tropopause layer (TTL) have shown various ice number concentrations (INC) (e.g., Jensen et al. 2013), which has lead to a puzzle regarding their formation. In particular, the frequently observed low numbers of ice crystals seemed hard to reconcile with homogeneous nucleation knowing the ubuquity of gravity waves with vertical velocity of the order of 0.1 m/s. Using artificial time series, Spichtinger and Krämer (2013) have illustrated that the variation of vertical velocity during a nucleation event could terminate it and limit the INC. However, their study was limited to constructed temperature time series. Here, we carry out numerical simulations of homogeneous ice nucleation forced by temperature time series data collected by isopycnic balloon flights near the tropical tropopause. The balloons collected data at high frequency (30 s), so gravity wave signals are well resolved in the temperature time series. With the observed temperature time series, the numerical simulations with homogeneous freezing show a full range of ice number concentrations (INC) as previously observed in the tropical upper troposphere. The simulations confirm that the dynamical time scale of temperature variations (as seen from observations) can be shorter than the nucleation time scale. They show the existence of two regimes for homogeneous ice nucleation : one limited by the depletion of water vapor by the nucleated ice crystals (those we name vapor events) and one limited by the reincrease of temperature after its initial decrease (temperature events). Low INC may thus be obtained for temperature events when the gravity wave perturbations produce a non-persistent cooling rate (even with large magnitude) such that the absolute change in temperature remains small during nucleation. This result for temperature events is explained analytically by a dependence of the INC on the absolute drop in temperature (and not on the cooling rate). This work supports the hypothesis that even acting alone homogeneous ice nucleation is not necessarily inconsistent with observations of low INC. Spichtinger, P. and Krämer, M.: Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers, Atmos. Chem. Phys., 13, 9801-9818, doi:10.5194/acp-13-9801-2013, 2013. Jensen, E. J., Diskin, G., Lawson, R. P., Lance, S., Bui, T. P., Hlavka, D., McGill, M., Pfister, L., Toon, O. B., and Gao, R.: Ice nucleation and dehydration in the Tropical Tropopause Layer, Proc. Nat. Acad. Sci., 110, 2041-2046, doi:10.1073/pnas.1217104110, 2013.

  11. Analytical Tools for Cloudscope Ice Measurement

    NASA Technical Reports Server (NTRS)

    Arnott, W. Patrick

    1998-01-01

    The cloudscope is a ground or aircraft instrument for viewing ice crystals impacted on a sapphire window. It is essentially a simple optical microscope with an attached compact CCD video camera whose output is recorded on a Hi-8 mm video cassette recorder equipped with digital time and date recording capability. In aircraft operation the window is at a stagnation point of the flow so adiabatic compression heats the window to sublimate the ice crystals so that later impacting crystals can be imaged as well. A film heater is used for ground based operation to provide sublimation, and it can also be used to provide extra heat for aircraft operation. The compact video camera can be focused manually by the operator, and a beam splitter - miniature bulb combination provide illumination for night operation. Several shutter speeds are available to accommodate daytime illumination conditions by direct sunlight. The video images can be directly used to qualitatively assess the crystal content of cirrus clouds and contrails. Quantitative size spectra are obtained with the tools described in this report. Selected portions of the video images are digitized using a PCI bus frame grabber to form a short movie segment or stack using NIH (National Institute of Health) Image software with custom macros developed at DRI. The stack can be Fourier transform filtered with custom, easy to design filters to reduce most objectionable video artifacts. Particle quantification of each slice of the stack is performed using digital image analysis. Data recorded for each particle include particle number and centroid, frame number in the stack, particle area, perimeter, equivalent ellipse maximum and minimum radii, ellipse angle, and pixel number. Each valid particle in the stack is stamped with a unique number. This output can be used to obtain a semiquantitative appreciation of the crystal content. The particle information becomes the raw input for a subsequent program (FORTRAN) that synthesizes each slice and separates the new from the sublimating particles. The new particle information is used to generate quantitative particle concentration, area, and mass size spectra along with total concentration, solar extinction coefficient, and ice water content. This program directly creates output in html format for viewing with a web browser.

  12. IceCube

    NSDL National Science Digital Library

    This is the home page for IceCube, a one-cubic-kilometer international high-energy neutrino observatory being built and installed in the clear deep ice below the South Pole Station. IceCube will open unexplored bands for astronomy, including the ten to the fifteenth electrovolt energy region, where the universe is opaque to high energy gamma rays originating from beyond the edge of our own galaxy, and where cosmic rays do not carry directional information because of their deflection by magnetic fields. IceCube will provide a totally novel viewpoint on the multi-messenger astronomy of gamma ray bursts, which have been identified as a possible source of the highest energy particles in nature. Information includes an overview of the project, a downloadable brochure, popular pieces and frequently asked questions. Other pages include publications and documents, education and outreach, and a multimedia page. In addition, information is available about the Antarctic Muon and Neutrino Detector Array at the South Pole (AMANDA) which will be incorporated into IceCube. Information about the organizational structure of the project is also available.

  13. Larsen Ice Shelf, Antarctica

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Warmer surface temperatures over just a few months in the Antarctic can splinter an ice shelf and prime it for a major collapse, NASA and university scientists report in the latest issue of the Journal of Glaciology. Using satellite images of tell-tale melt water on the ice surface and a sophisticated computer simulation of the motions and forces within an ice shelf, the scientists demonstrated that added pressure from surface water filling crevasses can crack the ice entirely through. The process can be expected to become more widespread if Antarctic summer temperatures increase. This true-color image from Landsat 7, acquired on February 21, 2000, shows pools of melt water on the surface of the Larsen Ice Shelf, and drifting icebergs that have split from the shelf. The upper image is an overview of the shelf's edge, while the lower image is displayed at full resolution of 30 meters (98 feet) per pixel. The labeled pond in the lower image measures roughly 1.6 by 1.6 km (1.0 x 1.0 miles). Full text of Press Release More Images and Animations Image courtesy Landsat 7 Science Team and NASA GSFC

  14. Effective viscosity of grease ice in linearized gravity waves

    NASA Astrophysics Data System (ADS)

    de Carolis, G.; Olla, P.; Pignagnoli, L.

    2005-07-01

    Grease ice is an agglomeration of disk-shaped ice crystals, named frazil ice, which forms in turbulent waters of the Polar Oceans and in rivers as well. It has been recognized that the property of grease ice that it damps surface gravity waves could be explained in terms of the effective viscosity of the ice slurry. This paper is devoted to the study of the dynamics of a suspension of disk-shaped particles in a gravity wave field. For dilute suspensions, depending on the strength and frequency of the external wave flow, two orientation regimes of the particles are predicted: a preferential orientation regime with the particles rotating in coherent fashion with the wave field, and a random orientation regime in which the particles oscillate around their initial orientation while diffusing under the effect of Brownian motion. For both motion regimes, the effective viscosity has been derived as a function of the wave frequency, wave amplitude and aspect ratio of the particles. Model predictions have been compared to wave attenuation data in frazil ice layers grown in wave tanks.

  15. Development of a VIIRS Radiance Simulator for Ice Clouds

    NASA Astrophysics Data System (ADS)

    Ding, S.; Wang, C.; Yang, P.; Nasiri, S. L.

    2012-12-01

    The objective of this study is to develop a Visible Infrared Imaging Radiometer Suite (VIIRS) radiance simulator, particularly, a fast radiative transfer model for single-layer ice clouds. The first step of this effort is to develop the lookup tables of the bidirectional reflectance of ice clouds for the VIIRS solar channels. The bulk scattering models of ice clouds for each VIIRS channels are derived by using the updated single scattering properties database of various nonspherical ice crystal habits, which include droxtals, hexagonal plates, hexagonal hollow columns and solid columns, three-dimensional bullet rosettes, and several types of aggregates with both smooth surface and severely roughened surface. The bulk scattering properties are utilized as inputs to the discrete ordinate radiative transfer model (DISORT) to calculate the lookup tables (LUTs) of ice clouds bidirectional reflectance for VIIRS solar channels. We also developed a set of correlated K distribution (CKD) models for the VIIRS channels to account for atmospheric trace gas absorption. The CKD model keeps tracking of spectral information and incorporates details of the instrument's response function. And it is also quite efficient for treating the overlapping absorption. Finally, for the purpose of validation, the VIIRS reflectances of ice clouds are simulated by using the developed simulator and compared with observations.

  16. Bacterial Standing Stock, Activity, and Carbon Production during Formation and Growth of Sea Ice in the Weddell Sea, Antarctica †

    PubMed Central

    Grossmann, Sönnke; Dieckmann, Gerhard S.

    1994-01-01

    Bacterial response to formation and growth of sea ice was investigated during autumn in the northeastern Weddell Sea. Changes in standing stock, activity, and carbon production of bacteria were determined in successive stages of ice development. During initial ice formation, concentrations of bacterial cells, in the order of 1 × 108 to 3 × 108 liter-1, were not enhanced within the ice matrix. This suggests that physical enrichment of bacteria by ice crystals is not effective. Due to low concentrations of phytoplankton in the water column during freezing, incorporation of bacteria into newly formed ice via attachment to algal cells or aggregates was not recorded in this study. As soon as the ice had formed, the general metabolic activity of bacterial populations was strongly suppressed. Furthermore, the ratio of [3H]leucine incorporation into proteins to [3H]thymidine incorporation into DNA changed during ice growth. In thick pack ice, bacterial activity recovered and growth rates up to 0.6 day-1 indicated actively dividing populations. However, biomass-specific utilization of organic compounds remained lower than in open water. Bacterial concentrations of up to 2.8 × 109 cells liter-1 along with considerably enlarged cell volumes accumulated within thick pack ice, suggesting reduced mortality rates of bacteria within the small brine pores. In the course of ice development, bacterial carbon production increased from about 0.01 to 0.4 ?g of C liter-1 h-1. In thick ice, bacterial secondary production exceeded primary production of microalgae. PMID:16349347

  17. Sublimation coefficient of water ice under simulated cometary-like conditions

    NASA Astrophysics Data System (ADS)

    Kossacki, Konrad J.; Markiewicz, Wojciech J.; Skorov, Yuri; Kömle, Norbert. I.

    1999-12-01

    In papers dealing with evolution of cometary nuclei it is commonly assumed that the coefficients of sublimation ?s and condensation ?c of vapour are both equal to one. The experimental investigation of ice samples under simulated cometary-like conditions (Kossacki, K.J., Kömle, N.I., Leliwa-Kopysty?ski, J., Kargl, G., 1997. Thermal and structural evolution of cometary subsurface layer: selfconsistent model and experimental verification. Icarus 128, 127-144) suggests, however, that the sublimation flux calculated with the Hertz-Knudsen formula and the above assumption is nearly an order of magnitude too high. This may imply that actual values of ?s for the ice/dust sample used in these experiments are of the order of 0.1. A similar conclusion can be drawn for ?c from the results of various experiments concerning growth of ice crystals from the vapour phase and their sublimation (Lamb, D., Scott, W.D., 1972. Linear growth rates of ice crystals grown from the vapor phase. Journal of Crystal Growth 12, 21-31; Beckmann, W., Lacmann, R., 1982. Interface kinetics of growth and evaporation of ice II. Journal of Crystal Growth 58, 433-442; Sei, T., Gonda, T., 1989. The growth mechanism and the habit change of ice crystals growing from the vapour phase. Journal of Crystal Growth 94, 697-707). The exact values of both of these coefficients depend on various parameters such as temperature, concentration of surface impurities and deviation of the vapour pressure from that of the phase equilibrium. In this work the temperature dependence of the sublimation and condensation coefficients is discussed and an appropriate formula is proposed to fit the experimental results. This new formulation is then used to analyse the implications for the thermal conductivity of a porous cometary-like ice and the rate of vapour flux from a cometary nucleus.

  18. Perturbation of bacterial ice nucleation activity by a grass antifreeze protein.

    PubMed

    Tomalty, Heather E; Walker, Virginia K

    2014-09-26

    Certain plant-associating bacteria produce ice nucleation proteins (INPs) which allow the crystallization of water at high subzero temperatures. Many of these microbes are considered plant pathogens since the formed ice can damage tissues, allowing access to nutrients. Intriguingly, certain plants that host these bacteria synthesize antifreeze proteins (AFPs). Once freezing has occurred, plant AFPs likely function to inhibit the growth of large damaging ice crystals. However, we postulated that such AFPs might also serve as defensive mechanisms against bacterial-mediated ice nucleation. Recombinant AFP derived from the perennial ryegrass Lolium perenne (LpAFP) was combined with INP preparations originating from the grass epiphyte, Pseudomonas syringae. The presence of INPs had no effect on AFP activity, including thermal hysteresis and ice recrystallization inhibition. Strikingly, the ice nucleation point of the INP was depressed up to 1.9°C in the presence of LpAFP, but a recombinant fish AFP did not lower the INP-imposed freezing point. Assays with mutant LpAFPs and the visualization of bacterially-displayed fluorescent plant AFP suggest that INP and LpAFP can interact. Thus, we postulate that in addition to controlling ice growth, plant AFPs may also function as a defensive strategy against the damaging effects of ice-nucleating bacteria. PMID:25193694

  19. Dielectric Properties of Heavy Ice Ih (D2O Ice)

    Microsoft Academic Search

    Shuji Kawada

    1979-01-01

    Dielectric anisotropy of heavy ice Ih is examined in a wide temperature range by measuring the complex dielectric constants parallel and normal to the c axis, and it is compared with that of ordinary ice Ih (H2O ice). The increased anisotropy in the static dielectric constants including only the shift of the extrapolated Curie-Weiss temperature to 55 K was observed.

  20. Mixed-phased particles in polar stratospheric ice clouds

    NASA Astrophysics Data System (ADS)

    Bogdan, Anatoli; Molina, Mario J.; Loerting, Thomas

    2010-05-01

    Keywords: polar stratospheric clouds (PSCs), ozone depletion, differential scanning calorimeter. The rate of chlorine activation reactions, which lead to ozone depletion in the winter/spring polar stratosphere (Molina, 1994), depends on the phase state of the surface of polar stratospheric cloud (PSC) ice crystals (McNeil et al., 2006). PSCs are thought to consist of solid ice and NAT (nitric acid trihydrate, HNO3× 3H2O) particles and supercooled HNO3/H2SO4/H2O droplets. The corresponding PSCs are called Type II, Ia, and Ib PSCs, respectively (Zondlo et al., 1998). Type II PSCs are formed in the Antarctic region below the ice frost point of 189 K by homogeneous freezing of HNO3/H2SO4/H2O droplets (Chang et al., 1999) with the excess of HNO3. The PSC ice crystals are thought to be solid. However, the fate of H+, NO3-, SO42- ions during freezing was not investigated. Our differential scanning calorimetry (DSC) studies of freezing emulsified HNO3/H2SO4/H2O droplets of sizes and compositions representative of the polar stratosphere demonstrate that during the freezing of the droplets, H+, NO3-, SO42- are expelled from the ice lattice. The expelled ions form a residual solution around the formed ice crystals. The residual solution does not freeze but transforms to glassy state at ~150 K (Bogdan et al., 2010). By contrast to glass-formation in these nitric-acid rich ternary mixtures the residual solution freezes in the case of sulphuric-acid rich ternary mixtures (Bogdan and Molina, 2009). For example, we can consider the phase separation into ice and a residual solution during the freezing of 23/3 wt% HNO3/H2SO4/H2O droplets. On cooling, ice is formed at ~189 K. This is inferred from the fact that the corresponding melting peak at ~248 K exactly matches the melting point of ice in the phase diagram of HNO3/H2SO4/H2O containing 3 wt % H2SO4. After the ice has formed, the glass transition occurs at Tg ? 150 K. The appearance of the glass transition indicates that the droplets do not freeze completely. After freezing, a fraction of each droplet remains liquid until its transformation to glass. The liquid, which remains unfrozen, is a residual solution formed by the expulsion of H+, NO3-, SO42- ions from the ice lattice during freezing. The residual solution undergoes the glass transition even if the cooling rate as small as 0.05 K/min (3 K/h) is applied. This cooling rate is similar to synoptic temperature change. Thus our results indicate that Type II PSC ice crystals cannot be completely solid, as is usually thought, but are enveloped by a supercooled HNO3/H2SO4/H2O coating. These results also suggest that chlorine-activation reactions are better studied on supercooled HNO3/H2SO4/H2O solutions than on a pure ice surface. Molina, M. J. (1994), The chemistry of the atmosphere: The impact of global change. Ed. Calvet, J. G. (Blackwell, Boston) pp. 27-38. McNeil, V. F., Loerting, T., Geiger, F. M., Trout, B. L. & Molina, M. J. (2006), Proc. Nat. Acad. Sci., 103, 9422.

  1. Ice-Borehole Probe

    NASA Technical Reports Server (NTRS)

    Behar, Alberto; Carsey, Frank; Lane, Arthur; Engelhardt, Herman

    2006-01-01

    An instrumentation system has been developed for studying interactions between a glacier or ice sheet and the underlying rock and/or soil. Prior borehole imaging systems have been used in well-drilling and mineral-exploration applications and for studying relatively thin valley glaciers, but have not been used for studying thick ice sheets like those of Antarctica. The system includes a cylindrical imaging probe that is lowered into a hole that has been bored through the ice to the ice/bedrock interface by use of an established hot-water-jet technique. The images acquired by the cameras yield information on the movement of the ice relative to the bedrock and on visible features of the lower structure of the ice sheet, including ice layers formed at different times, bubbles, and mineralogical inclusions. At the time of reporting the information for this article, the system was just deployed in two boreholes on the Amery ice shelf in East Antarctica and after successful 2000 2001 deployments in 4 boreholes at Ice Stream C, West Antarctica, and in 2002 at Black Rapids Glacier, Alaska. The probe is designed to operate at temperatures from 40 to +40 C and to withstand the cold, wet, high-pressure [130-atm (13.20-MPa)] environment at the bottom of a water-filled borehole in ice as deep as 1.6 km. A current version is being outfitted to service 2.4-km-deep boreholes at the Rutford Ice Stream in West Antarctica. The probe (see figure) contains a sidelooking charge-coupled-device (CCD) camera that generates both a real-time analog video signal and a sequence of still-image data, and contains a digital videotape recorder. The probe also contains a downward-looking CCD analog video camera, plus halogen lamps to illuminate the fields of view of both cameras. The analog video outputs of the cameras are converted to optical signals that are transmitted to a surface station via optical fibers in a cable. Electric power is supplied to the probe through wires in the cable at a potential of 170 VDC. A DC-to-DC converter steps the supply down to 12 VDC for the lights, cameras, and image-data-transmission circuitry. Heat generated by dissipation of electric power in the probe is removed simply by conduction through the probe housing to the visible features of the lower structure of the ice sheet, including ice layers formed at different times, bubbles, and mineralogical inclusions. At the time of reporting the information for this article, the system was just deployed in two boreholes on the Amery ice shelf in East Antarctica and after successful 2000 2001 deployments in 4 boreholes at Ice Stream C, West Antarctica, and in 2002 at Black Rapids Glacier, Alaska. The probe is designed to operate at temperatures from 40 to +40 C and to withstand the cold, wet, high-pressure [130-atm (13.20-MPa)] environment at the bottom of a water-filled borehole in ice as deep as 1.6 km. A current version is being outfitted to service 2.4-km-deep boreholes at the Rutford Ice Stream in West Antarctica. The probe (see figure) contains a sidelooking charge-coupled-device (CCD) camera that generates both a real-time analog video signal and a sequence of still-image data, and contains a digital videotape recorder. The probe also contains a downward-looking CCD analog video camera, plus halogen lamps to illuminate the fields of view of both cameras. The analog video outputs of the cameras are converted to optical signals that are transmitted to a surface station via optical fibers in a cable. Electric power is supplied to the probe through wires in the cable at a potential of 170 VDC. A DC-to-DC converter steps the supply down to 12 VDC for the lights, cameras, and image-datatransmission circuitry. Heat generated by dissipation of electric power in the probe is removed simply by conduction through the probe housing to the visible features of the lower structure of the ice sheet, including ice layers formed at different times, bubbles, and mineralogical inclusions. At thime of reporting the information for this article, the system was just deployed in two boreholes

  2. Safety hazard of aircraft icing

    NASA Technical Reports Server (NTRS)

    Mclean, J. C., Jr.

    1979-01-01

    The problem of aircraft icing is reported as well as the type of aircraft affected, the pilots involved, and an identification of the areas where reduction in icing accidents are readily accomplished.

  3. Aircraft icing research at NASA

    NASA Technical Reports Server (NTRS)

    Reinmann, J. J.; Shaw, R. J.; Olsen, W. A., Jr.

    1982-01-01

    Research activity is described for: ice protection systems, icing instrumentation, experimental methods, analytical modeling for the above, and in flight research. The renewed interest in aircraft icing has come about because of the new need for All-Weather Helicopters and General Aviation aircraft. Because of increased fuel costs, tomorrow's Commercial Transport aircraft will also require new types of ice protection systems and better estimates of the aeropenalties caused by ice on unprotected surfaces. The physics of aircraft icing is very similar to the icing that occurs on ground structures and structures at sea; all involve droplets that freeze on the surfaces because of the cold air. Therefore all icing research groups will benefit greatly by sharing their research information.

  4. Background Simulation and Verification for DM-Ice

    NASA Astrophysics Data System (ADS)

    Reilly, Bethany

    DM-Ice is an experiment designed for a direct detection search for dark matter. Using a NaI(Tl) target, DM-Ice searches for WIMP (weakly interacting massive particles) dark matter via scintillation associated with nuclear recoil in the crystal, which is then observed by PMTs. DM-Ice can test the DAMA/LIBRA result, using the same target material while running in the Southern Hemisphere. The DM-Ice prototype runs at the South Pole station, deployed underneath the IceCube Neutrino Observatory. This thesis describes the simulation work performed in order to understand the prototype detector, DM-Ice17. Dark matter background, evidence, and current understanding are discussed by way of introduction to the field. Description and discussion of detection methods and current experimental dark matter detection results follows. The DM-Ice detector itself is then considered in detail, in terms of motivation, design, and function. The assembly, deployment and operation of DM-Ice17 is also discussed. The purpose of simulating the radioactive backgrounds present in the DM-Ice17 detector is to understand the detector and the contamination levels present in each of its components, and to provide information needed for design and material selection for the full-scale DM-Ice detector. The Geant4 simulation toolkit was used to simulate the detector. The simulation is described in terms of geometry, particle decay and propagation, and producing an energy spectrum. This simulated energy spectrum was then used to characterize the detector, and this process is described as well. This thesis demonstrates that the simulation I have created aligns well with the data from DM-Ice17. This simulation allows insight into and verification of the radioactive contamination of each of the component of the detector, as well as that of its surroundings. The simulation also allows for detailed consideration of the contamination levels in different materials, which is needed in order to select materials and designs for the full-scale DM-Ice detector. Details regarding contributions of different isotopes in each region of the detector to the region of interest (low-energy; approximately 0-10 keV) are extracted from the simulation, which allows optimization of understanding what degree of cleanliness is needed for purposes of our dark matter search.

  5. New Instrument INKA for Ice Nucleation and Growth Experiments

    NASA Astrophysics Data System (ADS)

    Schmitt, Thea; Levin, Ezra; Höhler, Kristina; Nadolny, Jens; Möhler, Ottmar; DeMott, Paul

    2015-04-01

    Microphysical processes in clouds, such as the formation and growth of ice crystals, significantly influence the weather and the climate. Particularly the transition from the supercooled water to the solid ice phase is of great relevance since ice formation initiates the formation of precipitation and thereby strongly affects the cloud structure and life time. However, the formulation and parameterization of these processes and further laboratory studies are needed to obtain quantitative information on the ice activity of various atmospheric aerosol species. Therefore, we have constructed and built a new continuous flow diffusion chamber (CFDC) called INKA (Ice Nucleation Instrument of the KArlsruhe Institut of Technology) to be used both in the AIDA laboratory for detailed studies of ice nucleation and growth processes and in field applications for measuring the temperature-dependent abundance of ice nucleating particles (INPs). The CFDC design was originally developed and theoretically described by Rogers et al. (1988). The main part of the new INKA instrument, the chamber, consists of two vertically-oriented, concentric tubes with a total length of 150 cm. Together with particle-free, dry sheath air, the sampled aerosol particles flow through the annular space between these two cylinders. The wall temperatures of the cylinders can be adjusted and the walls of the annular gap are coated with thin ice layers. The bottom part (about 50 cm) of the outer cylinder of INKA is separately cooled, which allows operation in two different modes: In the ice nucleation mode, the CFDC is operated with a nucleation and growth section, covering the upper 100 cm of its length, which exposes the aerosol particles to a defined temperature and supersaturation. The bottom part is the so called droplet evaporation section which allows the ice particles to grow to a detectable size on the expense of present droplets. In the ice growth mode, the full length of the cylinders is operated as one large nucleation and growth section. Since the wall temperatures can be reduced to values as low as -80 °C, ice nucleation and growth of both mixed-phase and cirrus clouds can be investigated under well controlled temperature and humidity conditions. In this contribution, we will present the setup of INKA and show first measurements.

  6. The premelting of ice

    SciTech Connect

    Bluhm, Hendrik; Ogletree, D. Frank; Fadley, Charles S.; Salmeron,Miquel; Hussain, Zahid

    2001-02-01

    We address the century-old puzzle of the existence of a liquid-like layer at the ice surface near its melting point with new photoelectron spectroscopic tools using synchrotron radiation. Near-edge x-ray absorption shows that a liquid-like film exists at temperatures as low as -20 degrees C. Near 0 degrees C this film is about 20 Angstroms thick, i.e., 6 bilayers. With high-pressure x-ray photoelectron spectroscopy, we have further investigated for the first time the effect of surface contamination, which is ubiquitous in natural environments, on the state of the ice. Our results show that the premelting of ice can be strongly enhanced by the presence of hydrocarbon contamination.

  7. The Great Ice Age

    USGS Publications Warehouse

    Ray, Louis L.

    1992-01-01

    The Great Ice Age, a recent chapter in the Earth's history, was a period of recurring widespread glaciations. During the Pleistocene Epoch of the geologic time scale, which began about a million or more years ago, mountain glaciers formed on all continents, the icecaps of Antarctica and Greenland were more extensive and thicker than today, and vast glaciers, in places as much as several thousand feet thick, spread across northern North America and Eurasia. So extensive were these glaciers that almost a third of the present land surface of the Earth was intermittently covered by ice. Even today remnants of the great glaciers cover almost a tenth of the land, indicating that conditions somewhat similar to those which produced the Great Ice Age are still operating in polar and subpolar climates.

  8. Concord Consortium: Melting Ice

    NSDL National Science Digital Library

    2011-05-17

    This activity combines a hands-on lab with a computer simulation, as students investigate and graph the changing temperature of a melting ice cube. In the first step, learners use a sensor to monitor temperature as ice melts in a cup of water. In the second step, the ice cube is melted in a cup of salt water. Interactive graphs allow easy plotting of Temperature vs. Time. The activity concludes with a simulation of the atomic structure of a hot liquid and a cold liquid. Click "Withdraw the Barrier" and watch the changing kinetic energy of the cold liquid particles as they mix with the hot liquid. This item is part of the Concord Consortium, a nonprofit research and development organization dedicated to transforming education through technology.

  9. Structural-optical relationships in first-year sea ice

    NASA Astrophysics Data System (ADS)

    Light, Bonnie

    2000-12-01

    The optical properties of sea ice are governed by the distribution of brine and gas inclusions, and precipitated salt crystals within the ice. Laboratory experiments designed to understand structural-optical relationships and their dependence on temperature in first-year sea ice were carried out. Detailed observations of the microstructure of isothermal samples of natural sea ice were obtained for temperatures between -33 and -2°C. Changes in apparent optical properties of cylindrical samples cut from the same ice core were monitored simultaneously. A cylindrical Monte Carlo radiative transfer model was developed to infer inherent optical properties from the radiance data. Experimental results were used to develop and test a structural-optical model necessary for detailed radiative transfer modeling in sea ice. Microstructure observations were initially carried out at -15°C to obtain inclusion size distributions. Brine pocket dimensions were found to range from 0.01 mm to 10 mm, with number densities averaging about 30 mm-3. Observed vapor bubbles had radii less than 0.2 mm and number densities approximately 1 mm-3. Both these estimates are an order of magnitude larger than number densities previously reported. Results indicate that structural-optical relationships in sea ice can be described by three regimes. At temperatures below -23°C, optical properties change dramatically, and are most affected by the precipitation of hydrohalite. At temperatures between -23 and -8°C, they remain fairly constant where effects from changes in the mass of precipitated mirabilite crystals are offset by changes in the size of brine inclusions. At temperatures between -8 and -2°C, only small changes in the optical properties of the ice were observed, despite large observed increases in the cross-sectional area of the inclusions. This was discovered to be related to a significant increase in bulk asymmetry parameter resulting from a decrease in the refractive index of brine. We expect this general pattern will be found in most types of sea ice, regardless of the exact distribution of inclusions. These results suggest that it is possible to develop simple parameterizations of radiative transfer in sea ice appropriate for incorporation into large-scale climate models and GCMs.

  10. Evolution of Interstellar Ices

    NASA Astrophysics Data System (ADS)

    Allamandola, Louis J.; Bernstein, Max P.; Sandford, Scott A.; Walker, Robert L.

    1999-10-01

    Infrared observations, combined with realistic laboratory simulations, have revolutionized our understanding of interstellar ice and dust, the building blocks of comets. Ices in molecular clouds are dominated by the very simple molecules H2O, CH3OH, NH3, CO, CO2, and probably H2CO and H2. More complex species including nitriles, ketones, and esters are also present, but at lower concentrations. The evidence for these, as well as the abundant, carbon-rich, interstellar, polycyclic aromatic hydrocarbons (PAHs) is reviewed. Other possible contributors to the interstellar/pre-cometary ice composition include accretion of gas-phase molecules and in situ photochemical processing. By virtue of their low abundance, accretion of simple gas-phase species is shown to be the least important of the processes considered in determining ice composition. On the other hand, photochemical processing does play an important role in driving dust evolution and the composition of minor species. Ultraviolet photolysis of realistic laboratory analogs readily produces H2, H2CO, CO2, CO, CH4, HCO, and the moderately complex organic molecules: CH3CH2OH (ethanol), HC(=O)NH2 (formamide), CH3C(=O)NH2 (acetamide), R-CN (nitriles), and hexamethylenetetramine (HMT, C6H12N4), as well as more complex species including amides, ketones, and polyoxymethylenes (POMs). Inclusion of PAHs in the ices produces many species similar to those found in meteorites including aromatic alcohols, quinones and ethers. Photon assisted PAH-ice deuterium exchange also occurs. All of these species are readily formed and are therefore likely cometary constituents.

  11. MODIS Snow and Ice Production

    NASA Technical Reports Server (NTRS)

    Hall, Dorthoy K.; Hoser, Paul (Technical Monitor)

    2002-01-01

    Daily, global snow cover maps, and sea ice cover and sea ice surface temperature (IST) maps are derived from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS), are available at no cost through the National Snow and Ice Data Center (NSIDC). Included on this CD-ROM are samples of the MODIS snow and ice products. In addition, an animation, done by the Scientific Visualization studio at Goddard Space Flight Center, is also included.

  12. Arctic Sea Ice

    NSDL National Science Digital Library

    2012-06-26

    In this activity, learners explore how the area of Arctic sea ice has changed over recent years. First, learners graph the area of Arctic sea ice over time from 1979 to 2007. Then, learners use this information to extrapolate what the area will be in 2018 and graph their predictions. In part two of the activity, learners make a flip book to simulate the sea changes they just graphed. This resource includes background information related to the Northwest Passage and questions for learners to answer after completing this activity.

  13. Antifreeze protein-induced superheating of ice inside Antarctic notothenioid fishes inhibits melting during summer warming.

    PubMed

    Cziko, Paul A; DeVries, Arthur L; Evans, Clive W; Cheng, Chi-Hing Christina

    2014-10-01

    Antifreeze proteins (AFPs) of polar marine teleost fishes are widely recognized as an evolutionary innovation of vast adaptive value in that, by adsorbing to and inhibiting the growth of internalized environmental ice crystals, they prevent death by inoculative freezing. Paradoxically, systemic accumulation of AFP-stabilized ice could also be lethal. Whether or how fishes eliminate internal ice is unknown. To investigate if ice inside high-latitude Antarctic notothenioid fishes could melt seasonally, we measured its melting point and obtained a decadal temperature record from a shallow benthic fish habitat in McMurdo Sound, Antarctica. We found that AFP-stabilized ice resists melting at temperatures above the expected equilibrium freezing/melting point (eqFMP), both in vitro and in vivo. Superheated ice was directly observed in notothenioid serum samples and in solutions of purified AFPs, and ice was found to persist inside live fishes at temperatures more than 1 °C above their eqFMP for at least 24 h, and at a lower temperature for at least several days. Field experiments confirmed that superheated ice occurs naturally inside wild fishes. Over the long-term record (1999-2012), seawater temperature surpassed the fish eqFMP in most summers, but never exceeded the highest temperature at which ice persisted inside experimental fishes. Thus, because of the effects of AFP-induced melting inhibition, summer warming may not reliably eliminate internal ice. Our results expose a potentially antagonistic pleiotropic effect of AFPs: beneficial freezing avoidance is accompanied by melting inhibition that may contribute to lifelong accumulation of detrimental internal ice crystals. PMID:25246548

  14. Assimilation of ice motion observations and comparisons with submarine ice thickness data

    E-print Network

    Lindsay, Ron

    and satellite SSM/I (85 Ghz) ice motion data on simulation of Arctic sea ice. The sea-ice model is a thickness; 4540 Oceanography: Physical: Ice mechanics and air/sea/ice exchange processes; KEYWORDS: sea ice thickness data, J. Geophys. Res., 108(C6), 3170, doi:10.1029/2001JC001041, 2003. 1. Introduction [2] Sea ice

  15. Passive solar roof ice melter

    Microsoft Academic Search

    Deutz

    1981-01-01

    An elongated passive solar roof ice melter is placed on top of accumulated ice and snow including an ice dam along the lower edge of a roof of a heated building and is held against longitudinal movement with respect to itself. The melter includes a bottom wall having an upper surface highly absorbent to radiant solar energy; a first window

  16. Why does salt melt ice?

    NSDL National Science Digital Library

    Fred Senese

    This tutorial on the chemical interaction between salt and ice explains how molecules on the surface of the ice escape into the water (melting), and how molecules of water are captured on the surface of the ice (freezing). It was created by the Chemistry Department at Frostburg State University (no, really).

  17. Art with Salt and Ice

    NSDL National Science Digital Library

    KCET

    2007-01-01

    This open-ended art project allows learners to create their own colorful ice sculpture by using rock salt and food coloring on a solid block of ice. The entire activity is like a mini-science lesson because it teaches learners the physical reaction of salt on ice.

  18. Aerodynamics of runback ice accretions

    Microsoft Academic Search

    Edward A. Whalen

    2007-01-01

    An experimental study of the effects of simulated runback ice accretions has been performed in order to describe their aerodynamic performance penalties and investigate their scaling for use in sub-scale aerodynamic testing. Runback ice accretions corresponding to three flight conditions, warm hold, cold hold and descent, were simulated and tested on the NACA 23012 and NACA 3415. The ice shapes

  19. Ice Roughness in Short Duration SLD Icing Events

    NASA Technical Reports Server (NTRS)

    McClain, Stephen T.; Reed, Dana; Vargas, Mario; Kreeger, Richard E.; Tsao, Jen-Ching

    2014-01-01

    Ice accretion codes depend on models of roughness parameters to account for the enhanced heat transfer during the ice accretion process. While mitigating supercooled large droplet (SLD or Appendix O) icing is a significant concern for manufacturers seeking future vehicle certification due to the pending regulation, historical ice roughness studies have been performed using Appendix C icing clouds which exhibit mean volumetric diameters (MVD) much smaller than SLD clouds. Further, the historical studies of roughness focused on extracting parametric representations of ice roughness using multiple images of roughness elements. In this study, the ice roughness developed on a 21-in. NACA 0012 at 0deg angle of attack exposed to short duration SLD icing events was measured in the Icing Research Tunnel at the NASA Glenn Research Center. The MVD's used in the study ranged from 100 micrometer to 200 micrometers, in a 67 m/s flow, with liquid water contents of either 0.6 gm/cubic meters or 0.75 gm/cubic meters. The ice surfaces were measured using a Romer Absolute Arm laser scanning system. The roughness associated with each surface point cloud was measured using the two-dimensional self-organizing map approach developed by McClain and Kreeger (2013) resulting in statistical descriptions of the ice roughness.

  20. Anti-ice coating inspired by ice skating.

    PubMed

    Chen, Jing; Luo, Zhiqiang; Fan, Qinrui; Lv, Jianyong; Wang, Jianjun

    2014-11-01

    Accumulation of ice to surfaces brings dangerous and costly problems to our daily life. In this paper, an anti-ice coating inspired by ice skating is reported. Hyaluronic acid is used in the anti-ice coating to form aqueous lubricating layer benefitting from its high water absorbing property. Dopamine, the main component of the mussel adhesive protein, is introduced to anchor the hyaluronic acid to the solid surfaces to render the coating applicable to all types of solid surfaces. At the same time it serves as the crosslinking agent for hyaluronic acid, thus the thickness of the water collecting film could be easily varied. Ice adhesion strength on surfaces coated with such kind of coating could be more than one order of magnitude lower than that of uncoated ones. The results indicate that this anti-ice coating with the aqueous lubricating layer has great potential for fighting against icing problems. PMID:25145961