Sample records for ice melting temperature

  1. Reevaluation of the reconstruction of summer temperatures from melt features in Belukha ice cores, Siberian Altai

    Microsoft Academic Search

    Sachiko Okamoto; Koji Fujita; Hideki Narita; Jun Uetake; Nozomu Takeuchi; Takayuki Miyake; Fumio Nakazawa; Vladimir B. Aizen; Stanislav A. Nikitin; Masayoshi Nakawo

    2011-01-01

    In a previous study, past summer temperatures were reconstructed from melt features in the Belukha ice core, Siberian Altai. We evaluated the climatic representativeness of net accumulation and melt features by comparing two Belukha ice cores retrieved at neighboring sites by different institutions and dated by different methods. Melt features in both cores showed a significant correlation, but the trends

  2. The Response of Ice Shelf Basal Melting to Variations in Ocean Temperature

    Microsoft Academic Search

    Paul R. Holland; Adrian Jenkins; David M. Holland

    2008-01-01

    A three-dimensional ocean general circulation model is used to study the response of idealized ice shelves to a series of ocean-warming scenarios. The model predicts that the total ice shelf basal melt increases quadratically as the ocean offshore of the ice front warms. This occurs because the melt rate is proportional to the product of ocean flow speed and temperature

  3. Reevaluation of past summer temperature reconstruction by melt features in Belukha ice cores, Russian Altai

    Microsoft Academic Search

    S. Okamoto; K. Fujita; H. Narita; J. Uetake; N. Takeuchi; T. Miyake; F. Nakazawa; V. Aizen; S. Nikitin; M. Nakawo

    2009-01-01

    Past summer temperature has been reconstructed by melt features in Belukha ice core in a previous study. We evaluated a climatic representativeness of isotope, net accumulation and melt feature by comparing two Belukha ice cores retrieved by different institutions and dated by different methods. We find a significant correlation between seasonal changes in stable isotope in precipitation and air temperature.

  4. Monitoring seasonal basal melting of ice shelves using fiber-optic distributed temperature sensing

    NASA Astrophysics Data System (ADS)

    Kobs, S.; Tyler, S. W.; Holland, D. M.; Zagorodnov, V.; Stern, A. A.

    2014-12-01

    Ice shelf basal melt rates represent an important, yet challenging measurement for understanding ice-ocean interactions and climate change. In November 2011, two moorings containing fiber-optic cables for distributed temperature sensing (DTS) were installed through the McMurdo Ice Shelf at Windless Bight, Antarctica, penetrating ~200m of ice and extending ~600m into the ice shelf cavity. Annual basal melt rates in the region are estimated to be close to the 1m resolution of the DTS system. However, the smooth thermal profile of ice shelves and high spatial resolution of DTS allows for transient monitoring of the thermal gradient close to the ice-ocean interface. By utilizing the thermal gradient near the interface we are able to resolve the interface location more precisely and at a higher spatial resolution than the field deployed DTS system. The thermal gradient near the ice-ocean interface is extrapolated to the in situ freezing temperature in order to continuously track the interface and to estimate seasonal melt rates. Maximum melting corresponds with the arrival of seasonal warm surface water in the ice shelf cavity and is estimated to be 8.5mm•d-1, approximately ten times greater than the observed winter melt rate. The development of a continuous, surface-based, measurement technique for ice shelf basal melting represents a significant advance in our ability to monitor ice shelf stability and ice-ocean interactions.

  5. Distinguishing snow and ice melt contributions using daily MODIS and a temperature index melt model in the Hunza River basin

    NASA Astrophysics Data System (ADS)

    Rittger, Karl; Brodzik, Mary J.; Racoviteanu, Adina; Barrett, Andrew; Jodha Kalsa, Siri; Armstrong, Richard

    2015-04-01

    In mountainous regions of High Asia, snow and ice both contribute to streamflow, but few in-situ observations exist that can help distinguish between the two components of melt. Our goal is to develop a melt model that can distinguish between seasonal snow and glacier ice melt at a continental scale. We use a combination of MODIS-derived data sets to distinguish three surface types at daily resolution: 1) exposed glacier ice, 2) snow over ice and 3) snow over land. We use MODICE to map glacier area and then distinguish areas of exposed ice from snow over ice using thresholds on MODIS-derived albedo or grain size products. We map snow over land using the daily MODSCAG fractional snow cover product, and use the time series of three surface types as input to a temperature index melt model. The model outputs melt volumes from exposed glacier ice, snow over ice and snow over land, respectively. To partition the glacier surface into exposed glacier ice versus snow over ice, we threshold MODIS albedo or grain size based on higher-resolution Landsat 8 imagery. During the ablation period, the high elevation mid-latitude snowpack receives intense incoming solar radiation resulting in surface albedo decreases and snow grain growth. We compare differences in modeled melt using two albedo products (Terra Daily Snow Cover algorithm (MOD10A1) and Surface Reflectance BRDF/Albedo (MCD43)) and two grain size products (MODIS Snow Covered Area and Grain Size Model (MODSCAG) and MODIS Dust Radiative Forcing in Snow (MODDRFS)). For the Hunza basin, a sub-basin of the Upper Indus basin, for the years 2001-2004, the modeled melt from exposed glacier ice accounts for: 26-44% (MOD10A1 albedo), 24-32% (MCD43 albedo), 17-28% (MODSCAG grain size) or 23-26% (MODDRFS grain size) of the combined melt from all three surface areas.

  6. 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.

  7. Surface Temperature and Melt on the Greenland Ice Sheet, 2000 - 2011

    NASA Technical Reports Server (NTRS)

    Hall, Dorothy K.; Comiso, Josefino C.; Shuman, Christopher A.; Koeing, Lora S.; Box, Jason E.; DiGirolamo, Nicolo E.

    2012-01-01

    Enhanced melting along with surface-temperature increases measured using infrared satellite data, have been documented for the Greenland Ice Sheet. Recently we developed a climate-quality data record of ice-surface temperature (IST) of the Greenland Ice Sheet using the Moderate-Resolution Imaging Spectroradiometer (MODIS) IST product -- http://modis-snow-ice.gsfc.nasa.gov.Using daily and mean-monthly MODIS IST maps from the data record we show maximum extent of melt for the ice sheet and its six major drainage basins for a 12-year period extending from March of 2000 through December of 2011. The duration of the melt season on the ice sheet varies in different drainage basins with some basins melting progressively earlier over the study period. Some (but not all) of the basins also show a progressively-longer duration of melt. The short time of the study period (approx 12 years) precludes an evaluation of statistically-significant trends. However the dataset provides valuable information on natural variability of IST, and on the ability of the MODIS instrument to capture changes in IST and melt conditions in different drainage basins of the ice sheet.

  8. Variability of Surface Temperature and Melt on the Greenland Ice Sheet, 2000-2011

    NASA Technical Reports Server (NTRS)

    Hall, Dorothy K.; Comiso, Josefino, C.; Shuman, Christopher A.; Koenig, Lora S.; DiGirolamo, Nicolo E.

    2012-01-01

    Enhanced melting along with surface-temperature increases measured using infrared satellite data, have been documented for the Greenland Ice Sheet. Recently we developed a climate-quality data record of ice-surface temperature (IST) of the Greenland Ice Sheet using the Moderate-Resolution Imaging Spectroradiometer (MODIS) 1ST product -- http://modis-snow-ice.gsfc.nasa.gov. Using daily and mean monthly MODIS 1ST maps from the data record we show maximum extent of melt for the ice sheet and its six major drainage basins for a 12-year period extending from March of 2000 through December of 2011. The duration of the melt season on the ice sheet varies in different drainage basins with some basins melting progressively earlier over the study period. Some (but not all) of the basins also show a progressively-longer duration of melt. The short time of the study period (approximately 12 years) precludes an evaluation of statistically-significant trends. However the dataset provides valuable information on natural variability of IST, and on the ability of the MODIS instrument to capture changes in IST and melt conditions indifferent drainage basins of the ice sheet.

  9. Greenland ice sheet surface temperature, melt and mass loss: 2000-06

    USGS Publications Warehouse

    Hall, D.K.; Williams, R.S., Jr.; Luthcke, S.B.; DiGirolamo, N.E.

    2008-01-01

    A daily time series of 'clear-sky' surface temperature has been compiled of the Greenland ice sheet (GIS) using 1 km resolution moderate-resolution imaging spectroradiometer (MODIS) land-surface temperature (LST) maps from 2000 to 2006. We also used mass-concentration data from the Gravity Recovery and Climate Experiment (GRACE) to study mass change in relationship to surface melt from 2003 to 2006. The mean LST of the GIS increased during the study period by ???0.27??Ca-1. The increase was especially notable in the northern half of the ice sheet during the winter months. Melt-season length and timing were also studied in each of the six major drainage basins. Rapid (<15 days) and sustained mass loss below 2000 m elevation was triggered in 2004 and 2005 as recorded by GRACE when surface melt begins. Initiation of large-scale surface melt was followed rapidly by mass loss. This indicates that surface meltwater is flowing rapidly to the base of the ice sheet, causing acceleration of outlet glaciers, thus highlighting the metastability of parts of the GIS and the vulnerability of the ice sheet to air-temperature increases. If air temperatures continue to rise over Greenland, increased surface melt will play a large role in ice-sheet mass loss.

  10. Melting of Ice under Pressure

    SciTech Connect

    Schwegler, E; Sharma, M; Gygi, F; Galli, G

    2008-07-31

    The melting of ice under pressure is investigated with a series of first principles molecular dynamics simulations. In particular, a two-phase approach is used to determine the melting temperature of the ice-VII phase in the range of 10 to 50 GPa. Our computed melting temperatures are consistent with existing diamond anvil cell experiments. We find that for pressures between 10 to 40 GPa, ice melts as a molecular solid. For pressures above {approx}45 GPa there is a sharp increase in the slope of the melting curve due to the presence of molecular dissociation and proton diffusion in the solid, prior to melting. The onset of significant proton diffusion in ice-VII as a function of increasing temperature is found to be gradual and bears many similarities to that of a type-II superionic solid.

  11. Predicting the melting temperature of ice-Ih with only electronic structure information as input.

    PubMed

    Pinnick, Eric R; Erramilli, Shyamsunder; Wang, Feng

    2012-07-01

    The melting temperature of ice-Ih was calculated with only electronic structure information as input by creating a problem-specific force field. The force field, Water model by AFM for Ice and Liquid (WAIL), was developed with the adaptive force matching (AFM) method by fitting to post-Hartree-Fock quality forces obtained in quantum mechanics?molecular mechanics calculations. WAIL predicts the ice-Ih melting temperature to be 270 K. The model also predicts the densities of ice and water, the temperature of maximum density of water, the heat of vaporizations, and the radial distribution functions for both ice and water in good agreement with experimental measurements. The non-dissociative WAIL model is very similar to a flexible version of the popular TIP4P potential and has comparable computational cost. By customizing to problem-specific configurations with the AFM approach, the resulting model is remarkably more accurate than any variants of TIP4P for simulating ice-Ih and water in the temperature range from 253 K and 293 K under ambient pressure. PMID:22779668

  12. Predicting the melting temperature of ice-Ih with only electronic structure information as input

    NASA Astrophysics Data System (ADS)

    Pinnick, Eric R.; Erramilli, Shyamsunder; Wang, Feng

    2012-07-01

    The melting temperature of ice-Ih was calculated with only electronic structure information as input by creating a problem-specific force field. The force field, Water model by AFM for Ice and Liquid (WAIL), was developed with the adaptive force matching (AFM) method by fitting to post-Hartree-Fock quality forces obtained in quantum mechanics/molecular mechanics calculations. WAIL predicts the ice-Ih melting temperature to be 270 K. The model also predicts the densities of ice and water, the temperature of maximum density of water, the heat of vaporizations, and the radial distribution functions for both ice and water in good agreement with experimental measurements. The non-dissociative WAIL model is very similar to a flexible version of the popular TIP4P potential and has comparable computational cost. By customizing to problem-specific configurations with the AFM approach, the resulting model is remarkably more accurate than any variants of TIP4P for simulating ice-Ih and water in the temperature range from 253 K and 293 K under ambient pressure.

  13. Quantum path integral simulation of isotope effects in the melting temperature of ice Ih

    Microsoft Academic Search

    R. Ramírez; C. P. Herrero

    2010-01-01

    The isotope effect in the melting temperature of ice Ih has been studied by free energy calculations within the path integral formulation of statistical mechanics. Free energy differences between isotopes are related to the dependence of their kinetic energy on the isotope mass. The water simulations were performed by using the q-TIP4P\\/F model, a point charge empirical potential that includes

  14. 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

  15. Quantum path integral simulation of isotope effects in the melting temperature of ice Ih

    E-print Network

    Ramirez, R; 10.1063/1.3503764

    2011-01-01

    The isotope effect in the melting temperature of ice Ih has been studied by free energy calculations within the path integral formulation of statistical mechanics. Free energy differences between isotopes are related to the dependence of their kinetic energy on the isotope mass. The water simulations were performed by using the q-TIP4P/F model, a point charge empirical potential that includes molecular flexibility and anharmonicity in the OH stretch of the water molecule. The reported melting temperature at ambient pressure of this model (T = 251 K) increases by 6.5+-0.5 K and 8.2+-0.5 K upon isotopic substitution of hydrogen by deuterium and tritium, respectively. These temperature shifts are larger than the experimental ones (3.8 K and 4.5 K, respectively). In the classical limit, the melting temperature is nearly the same as that for tritiated ice. This unexpected behavior is rationalized by the coupling between intermolecular interactions and molecular flexibility. This coupling makes the kinetic energy o...

  16. Novel monitoring of Antarctic ice shelf basal melting using a fiber-optic distributed temperature sensing mooring

    NASA Astrophysics Data System (ADS)

    Kobs, Scott; Holland, David M.; Zagorodnov, Victor; Stern, Alon; Tyler, Scott W.

    2014-10-01

    Measuring basal melting of ice shelves is challenging and represents a critical component toward understanding ocean-ice interactions and climate change. In November 2011, moorings containing fiber-optic cables for distributed temperature sensing (DTS) were installed through the McMurdo Ice Shelf, Antarctica, (~200 m) and extending ~600 m into the ice shelf cavity. The high spatial resolution of DTS allows for transient monitoring of the thermal gradient within the ice shelf. The gradient near the ice-ocean interface is extrapolated to the in situ freezing temperature in order to continuously track the ice-ocean interface. Seasonal melt rates are calculated to be ~1.0 mm d-1 and 8.6 mm d-1, and maximum melting corresponds to the arrival of seasonal warm surface water in the ice shelf cavity between January and April. The development of continuous, surface-based techniques for measuring basal melting represents a significant advance in monitoring ice shelf stability and ice-ocean interactions.

  17. Testing recent charge-on-spring type polarizable water models. I. Melting temperature and ice properties

    NASA Astrophysics Data System (ADS)

    Kiss, Péter T.; Bertsyk, Péter; Baranyai, András

    2012-11-01

    We determined the freezing point of eight molecular models of water. All models use the charge-on-spring (COS) method to express polarization. The studied models were the COS/G2, COS/G3 [H. Yu and W. F. van Gunsteren, J. Chem. Phys. 121, 9549 (2004), 10.1063/1.1805516], the COS/B2 [H. Yu, T. Hansson, and W. F. van Gunsteren, J. Chem. Phys. 118, 221 (2003), 10.1063/1.1523915], the SWM4-DP [G. Lamoureux, A. D. MacKerell, Jr., and B. Roux, J. Chem. Phys. 119, 5185 (2003), 10.1063/1.1598191], the SWM4-NDP [G. Lamoureux, E. Harder, I. V. Vorobyov, B. Roux, and A. D. MacKerell, Jr., Chem. Phys. Lett. 418, 245 (2006), 10.1016/j.cplett.2005.10.135], and three versions of our model, the BKd1, BKd2, and BKd3. The BKd1 is the original Gaussian model [P. T. Kiss, M. Darvas, A. Baranyai, and P. Jedlovszky, J. Chem. Phys. 136, 114706 (2012), 10.1063/1.3692602] with constant polarization and with a simple exponential repulsion. The BKd2 applies field-dependent polarizability [A. Baranyai and P. T. Kiss, J. Chem. Phys. 135, 234110 (2011), 10.1063/1.3670962], while the BKd3 model has variable size to approximate the temperature-density (T-?) curve of water [P. T. Kiss and A. Baranyai, J. Chem. Phys. 137, 084506 (2012), 10.1063/1.4746419]. We used the thermodynamic integration (TI) and the Gibbs-Helmholtz equation to determine the equality of the free energy for liquid water and hexagonal ice (Ih) at 1 bar. We used the TIP4P and the SPC/E models as reference systems of the TI. The studied models severely underestimate the experimental melting point of ice Ih. The calculated freezing points of the models are the following: COS/G2, 215 K; COS/G3, 149 K; SWM4-DP, 186 K; BKd1, 207 K; BKd2, 213 K; BKd3, 233 K. The freezing temperature of the SWM4-NDP system is certainly below 120 K. It might even be that the water phase is more stable than the ice Ih at 1 bar in the full temperature range. The COS/B2 model melts below 100 K. The best result was obtained for the BKd3 model which indicates that correct description of the (T-?) curve improves the estimation of the freezing point. We also determined and compared the densities of high-pressure polymorphs of ice for these models.

  18. Testing recent charge-on-spring type polarizable water models. I. Melting temperature and ice properties.

    PubMed

    Kiss, Péter T; Bertsyk, Péter; Baranyai, András

    2012-11-21

    We determined the freezing point of eight molecular models of water. All models use the charge-on-spring (COS) method to express polarization. The studied models were the COS/G2, COS/G3 [H. Yu and W. F. van Gunsteren, J. Chem. Phys. 121, 9549 (2004)], the COS/B2 [H. Yu, T. Hansson, and W. F. van Gunsteren, J. Chem. Phys. 118, 221 (2003)], the SWM4-DP [G. Lamoureux, A. D. MacKerell, Jr., and B. Roux, J. Chem. Phys. 119, 5185 (2003)], the SWM4-NDP [G. Lamoureux, E. Harder, I. V. Vorobyov, B. Roux, and A. D. MacKerell, Jr., Chem. Phys. Lett. 418, 245 (2006)], and three versions of our model, the BKd1, BKd2, and BKd3. The BKd1 is the original Gaussian model [P. T. Kiss, M. Darvas, A. Baranyai, and P. Jedlovszky, J. Chem. Phys. 136, 114706 (2012)] with constant polarization and with a simple exponential repulsion. The BKd2 applies field-dependent polarizability [A. Baranyai and P. T. Kiss, J. Chem. Phys. 135, 234110 (2011)], while the BKd3 model has variable size to approximate the temperature-density (T-?) curve of water [P. T. Kiss and A. Baranyai, J. Chem. Phys. 137, 084506 (2012)]. We used the thermodynamic integration (TI) and the Gibbs-Helmholtz equation to determine the equality of the free energy for liquid water and hexagonal ice (Ih) at 1 bar. We used the TIP4P and the SPC/E models as reference systems of the TI. The studied models severely underestimate the experimental melting point of ice Ih. The calculated freezing points of the models are the following: COS/G2, 215 K; COS/G3, 149 K; SWM4-DP, 186 K; BKd1, 207 K; BKd2, 213 K; BKd3, 233 K. The freezing temperature of the SWM4-NDP system is certainly below 120 K. It might even be that the water phase is more stable than the ice Ih at 1 bar in the full temperature range. The COS/B2 model melts below 100 K. The best result was obtained for the BKd3 model which indicates that correct description of the (T-?) curve improves the estimation of the freezing point. We also determined and compared the densities of high-pressure polymorphs of ice for these models. PMID:23181289

  19. Melting Temperature of Ice Ih calculated from coexisting solid-liquid phases

    SciTech Connect

    Wang, J. [University of Nebraska, Lincoln; Yoo, S. [University of Nebraska, Lincoln; Bai, J. [University of Nebraska, Lincoln; Morris, James R [ORNL; Zeng, X.C. [University of Nebraska, Lincoln

    2005-01-01

    In a previous paper we report the calculated melting temperature of the proton-disordered hexagonal ice I{sub h} using a four-site water model, the TIP4P (Ref. 2) and a five-site model, the TIP5P. In that work, we used a free-energy method. For the TIP4P model, the calculated melting temperature at 1 bar is T{sub m} = 229 {+-} 9 K, whereas for the TIP5P model, T{sub m} = 268 {+-} 6 K. For both models, the long-ranged interactions were truncated at 17 {angstrom}. Interestingly, these values of Tm are very close to T{sub m} = 232 {+-} 5 K and T{sub m} = 273.9 K reported by Sanz et al. and Vega et al. who used a slightly different free-energy method along with Ewald summation technique, although both the TIP4P and TIP5P models were originally developed for use with a truncated Coulomb interaction. The purpose of this paper is twofold: (1) to compute the melting temperature (T{sub m}) of ice I{sub h} with both TIP4P and TIP5P models by using the two-phase coexistence method and to compare with previously obtained T{sub m}; (2) to compute the T{sub m} using recently improved TIP4P and TIP5P models, namely, the TIP4P-Ew (Ref. 6) and TIP5P-Ew (Ref. 7) models. Both models are developed specifically for use with Ewald techniques. The TIP4P-Ew model, in particular, has shown substantial improvement over the original TIP4P model as it can reproduce the density maximum at about 274 K, very close to 277 K of the real water. The original TIP5P model can reproduce the measured T{sub m}. It will be of interest to see whether the improved TIP5P-Ew model can still hold the same level of prediction as far as the T{sub m} is concerned.

  20. Does Ice Dissolve or Does Halite Melt? A Low-Temperature Liquidus Experiment for Petrology Classes.

    ERIC Educational Resources Information Center

    Brady, John B.

    1992-01-01

    Measurement of the compositions and temperatures of H2O-NaCl brines in equilibrium with ice can be used as an easy in-class experimental determination of a liquidus. This experiment emphasizes the symmetry of the behavior of brines with regard to the minerals ice and halite and helps to free students from the conceptual tethers of one-component…

  1. 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).

  2. Developing Temperature Forcing for Snow and Ice Melt Runoff Models in High Mountain Regions

    NASA Astrophysics Data System (ADS)

    Barrett, A. P.; Armstrong, R. L.; Brodzik, M. J.; Khalsa, S. J. S.; Raup, B. H.; Rittger, K.

    2014-12-01

    Glaciers and snow cover are natural storage reservoirs that delay runoff on seasonal and longer time-scales. Glacier wastage and reduced snow packs will impact the volume and timing of runoff from mountain basins. Estimates of the contributions of glacier and snow melt to runoff in river systems draining mountain regions are critical for water resources planning. The USAID funded CHARIS project aims to estimate the contributions of glacier and snow melt to streamflow in the Ganges, Indus, Brahmaputra, Amu Darya and Syr Darya rivers. Most efforts to estimate glacier and snow melt contributions use temperature-index or degree-day approaches. Near-surface air temperature is a key forcing variable for such models. As with all mountain regions, meteorological stations are sparse and may have short records. Few stations exist at high elevations, with most stations located in valleys below the elevations of glaciers and seasonal snow cover. Reanalyses offer an alternative source of temperature data. However, reanalyses have coarse resolution and simplified topography, especially in the Himalaya. Surface fields are often biased. Any reanalysis product must be both bias-corrected and "downscaled" to the resolution of the melt-runoff model. We present a combined empirically-based bias-correction and downscaling procedure that uses near-surface air temperature from global atmospheric reanalyses to generate near-surface temperature forcing fields for the five river basins in the CHARIS study area. We focus on three 3rd Generation reanalyses; NASA MERRA, NCEP CFSR and ECMWF ERA-Interim. Evaluation of reanalysis temperature fields reveals differences between seasonal means of 500 hPa air temperatures for the three products are of the order of 1 °C, indicating choice of reanalysis can impact model results. The procedure accounts for these seasonal variations in biases of the reanalysis products and in lapse rates.

  3. Classical and quantum mechanical studies of ice Ih near the melting temperature

    SciTech Connect

    Gai, H.; Schenter, G.K.; Garrett, B.C. [Environmental Molecular Sciences Laboratory, Pacific Northwest Laboratory, Richland, Washington 99352 (United States)] [Environmental Molecular Sciences Laboratory, Pacific Northwest Laboratory, Richland, Washington 99352 (United States)

    1996-01-01

    Classical and path integral Monte Carlo methods have been used to study the structure and energetics of ice Ih. The water{endash}water interaction is described by the SPC water model. We compute the change in average intermolecular potential energy, radial distribution function, and structural factor as a function of temperature. It is found that near 280 K, the structural and energetic properties from quantum and classical simulations are quite different. {copyright} {ital 1996 American Institute of Physics.}

  4. Surface melting on ice shelves and icebergs

    Microsoft Academic Search

    Olga V. Sergienko

    2005-01-01

    Disintegration of Larsen Ice Shelf A and B, in 1995 and 2002, respectively, were preceded by two decades of extended summer melt seasons and by surface melt-water accumulation in ponds, surface crevasses and depressions produced by the elastic flexure of the ice. The extraordinary rapidity of ice-shelf fragmentation into large iceberg plumes following the appearance of surface melt water implies

  5. Satellite-derived, melt-season surface temperature of the Greenland Ice Sheet (2000-2005) and its relationship to mass balance

    USGS Publications Warehouse

    Hall, D.K.; Williams, R.S., Jr.; Casey, K.A.; DiGirolamo, N.E.; Wan, Z.

    2006-01-01

    Mean, clear-sky surface temperature of the Greenland Ice Sheet was measured for each melt season from 2000 to 2005 using Moderate-Resolution Imaging Spectroradiometer (MODIS)-derived land-surface temperature (LST) data-product maps. During the period of most-active melt, the mean, clear-sky surface temperature of the ice sheet was highest in 2002 (-8.29 ?? 5.29??C) and 2005 (-8.29 ?? 5.43??C), compared to a 6-year mean of -9.04 ?? 5.59??C, in agreement with recent work by other investigators showing unusually extensive melt in 2002 and 2005. Surface-temperature variability shows a correspondence with the dry-snow facies of the ice sheet; a reduction in area of the dry-snow facies would indicate a more-negative mass balance. Surface-temperature variability generally increased during the study period and is most pronounced in the 2005 melt season; this is consistent with surface instability caused by air-temperature fluctuations. Copyright 2006 by the American Geophysical Union.

  6. Monte Carlo Study of Melting of a Model Bulk Ice

    Microsoft Academic Search

    Kyu-Kwang Han

    1989-01-01

    The methods of NVT (constant number, volume and temperature) and NPT (constant number, pressure and temperature) Monte Carlo computer simulations are used to examine the melting of a periodic hexagonal ice (ice Ih) sample with a unit cell of 192 (rigid) water molecules interacting via the revised central force potentials of Stillinger and Rahman (RSL2). In NVT Monte Carlo simulation

  7. Ice-Shelf Melting Around Antarctica

    NASA Astrophysics Data System (ADS)

    Rignot, E.; Jacobs, S.; Mouginot, J.; Scheuchl, B.

    2013-07-01

    We compare the volume flux divergence of Antarctic ice shelves in 2007 and 2008 with 1979 to 2010 surface accumulation and 2003 to 2008 thinning to determine their rates of melting and mass balance. Basal melt of 1325 ± 235 gigatons per year (Gt/year) exceeds a calving flux of 1089 ± 139 Gt/year, making ice-shelf melting the largest ablation process in Antarctica. The giant cold-cavity Ross, Filchner, and Ronne ice shelves covering two-thirds of the total ice-shelf area account for only 15% of net melting. Half of the meltwater comes from 10 small, warm-cavity Southeast Pacific ice shelves occupying 8% of the area. A similar high melt/area ratio is found for six East Antarctic ice shelves, implying undocumented strong ocean thermal forcing on their deep grounding lines.

  8. Monitoring snow melt characteristics on the Greenland ice sheet using a new MODIS land surface temperature and emissivity product (MOD21)

    NASA Astrophysics Data System (ADS)

    Hulley, G. C.; Hall, D. K.; Hook, S. J.

    2013-12-01

    Land Surface Temperature (LST) and emissivity are sensitive energy-balance parameters that control melt and energy exchange between the surface and the atmosphere. MODIS LST is currently used to monitor melt zones on glaciers and can be used for glacier or ice sheet mass balance calculations. Much attention has been paid recently to the warming of the Arctic in the context of global warming, with a focus on the Greenland ice sheet because of its importance with sea-level rise. Various researchers have shown a steady decline in the extent of the Northern Hemisphere sea ice, both the total extent and the extent of the perennial or multiyear ice. Surface melt characteristics over the Greenland ice sheet have been traditionally monitored using the MODIS LST and albedo products (e.g. MOD11 and MOD10A1). Far fewer studies have used thermal emissivity data to monitor surface melt characteristics due to the lack of suitable data. In theory, longwave emissivity combined with LST information should give a more direct measure of snow melt characteristics since the emissivity is an intrinsic property of the surface, whereas the albedo is dependent on other factors such as solar zenith angle, and shadowing effects. Currently no standard emissivity product exists that can dynamically retrieve changes in longwave emissivity consistently over long time periods. This problem has been addressed with the new MOD21 product, which uses the ASTER TES algorithm to dynamically retrieve LST and spectral emissivity (bands 29, 31, 32) at 1-km resolution. In this study we show that using a new proposed index termed the snow emissivity difference index (SEDI) derived from the MOD21 longwave emissivity product, combined with the LST, will improve our understanding of snow melt and freezeup dynamics on ice sheets such as Greenland. The results also suggest that synergistic use of both thermal-based and albedo data will help to improve our understanding of snow melt dynamics on glaciers and ice sheets, and reduce uncertainties in estimating magnitudes and trends.

  9. What if the Ice Shelves Melted?

    NSDL National Science Digital Library

    LuAnn Dahlman

    This activity is a hands-on guided inquiry activity designed to highlight the role of an ice shelf on slowing the movement of continental ice sheets in Antarctica. Students build a model of Antarctica and both continental glaciers and ice shelves using paper models of the land and slime for glaciers and ice. Students use their model to explore the impact of recent and potential ice shelf melting and break-up.

  10. Mathematical Modelling of Melt Lake Formation on an Ice Shelf

    NASA Astrophysics Data System (ADS)

    Buzzard, Sammie; Feltham, Daniel; Flocco, Daniela; Sammonds, Peter

    2015-04-01

    The accumulation of surface meltwater on ice shelves can lead to the formation of melt lakes. These structures have been implicated in crevasse propagation and ice shelf collapse; the Larsen B ice shelf was observed to have a large amount of melt lakes present on its surface just before its collapse in 2002. Through modelling the transport of heat through the surface of the Larsen C ice shelf, where melt lakes have also been observed, this work aims to provide new insights into the ways in which melt lakes are forming and the effect that meltwater filling crevasses on the ice shelf will have. This will enable an assessment of the role of meltwater in triggering ice shelf collapse. The Antarctic Peninsula, where Larsen C is situated, has warmed several times the global average over the last century and this ice shelf has been suggested as a candidate for becoming fully saturated with meltwater by the end of the current century. Here we present results of a 1D mathematical model of heat transfer through an idealised ice shelf. When forced with automatic weather station data from Larsen C, surface melting and the subsequent meltwater accumulation, melt lake development and refreezing are demonstrated through the modelled results. Furthermore, the effect of lateral meltwater transport upon melt lakes is examined. This will be developed through the estimations of meltwater catchment areas and the fraction of the ice shelf where melt lakes are present. Investigating the role of meltwater in ice shelf stability is key as collapse can affect ocean circulation and temperature, and cause a loss of habitat. Additionally, it can cause a loss of the buttressing effect that ice shelves can have on their tributary glaciers, thus allowing the glaciers to accelerate, contributing to sea level rise.

  11. Ice-shelf melting around Antarctica

    NASA Astrophysics Data System (ADS)

    Rignot, E.; Jacobs, S.

    2008-12-01

    The traditional view on the mass balance of Antarctic ice shelves is that they loose mass principally from iceberg calving with bottom melting a much lower contributing factor. Because ice shelves are now known to play a fundamental role in ice sheet evolution, it is important to re-evaluate their wastage processes from a circumpolar perspective using a combination of remote sensing techniques. We present area average rates deduced from grounding line discharge, snow accumulation, firn depth correction and ice shelf topography. We find that ice shelf melting accounts for roughly half of ice-shelf ablation, with a total melt water production of 1027 Gt/yr. The attrition fraction due to in-situ melting varies from 9 to 90 percent around Antarctica. High melt producers include the Ronne, Ross, Getz, Totten, Amery, George VI, Pine Island, Abbot, Dotson/Crosson, Shackleton, Thwaites and Moscow University Ice Shelves. Low producers include the Larsen C, Princess Astrid and Ragnhild coast, Fimbul, Brunt and Filchner. Correlation between melt water production and grounding line discharge is low (R2 = 0.65). Correlation with thermal ocean forcing from the ocean are highest in the northern parts of West Antarctica where regressions yield R2 of 0.93-0.97. Melt rates in the Amundsen Sea exhibit a quadratic sensitivity to thermal ocean forcing. We conclude that ice shelf melting plays a dominant role in ice shelf mass balance, with a potential to change rapidly in response to altered ocean heat transport onto the Antarctic continental shelf.

  12. Monte Carlo Study of Melting of a Model Bulk Ice.

    NASA Astrophysics Data System (ADS)

    Han, Kyu-Kwang

    The methods of NVT (constant number, volume and temperature) and NPT (constant number, pressure and temperature) Monte Carlo computer simulations are used to examine the melting of a periodic hexagonal ice (ice Ih) sample with a unit cell of 192 (rigid) water molecules interacting via the revised central force potentials of Stillinger and Rahman (RSL2). In NVT Monte Carlo simulation of P-T plot for a constant density (0.904g/cm^3) is used to locate onset of the liquid-solid coexistence region (where the slope of the pressure changes sign) and estimate the (constant density) melting point. The slope reversal is a natural consequence of the constant density condition for substances which expand upon freezing and it is pointed out that this analysis is extremely useful for substances such as water. In this study, a sign reversal of the pressure slope is observed near 280 K, indicating that the RSL2 potentials reproduce the freezing expansion expected for water and support a bulk ice Ih system which melts <280 K. The internal energy, specific heat, and two dimensional structure factors for the constant density H_2O system are also examined at a range of temperatures between 100 and 370 K and support the P-T analysis for location of the melting point. This P-T analysis might likewise be useful for determining a (constant density) freezing point, or, with multiple simulations at appropriate densities, the triple point. For NPT Monte Carlo simulations preliminary results are presented. In this study the density, enthalpy, specific heat, and structure factor dependences on temperature are monitored during a sequential heating of the system from 100 to 370 K at a constant pressure (1 atm.). A jump in density upon melting is observed and indicates that the RSL2 potentials reproduce the melting contraction of ice. From the dependences of monitored physical properties on temperature an upper bound on the melting temperature is estimated. In this study we made the first analysis and calculation of the P-T curve for ice Ih melting at constant volume and the first NPT study of ice and of ice melting. In the NVT simulation we found for rho = 0.904g/cm^3 T_ {rm m} ~eq 280 K which is much closer to physical T_ {rm m} than any other published NVT simulation of ice. Finally it is shown that RSL2 potentials do a credible job of describing the thermodynamic properties of ice Ih near its melting point.

  13. Formation of melt channels on ice shelves

    NASA Astrophysics Data System (ADS)

    Sergienko, Olga

    2013-04-01

    Melt channels have been observed on ice shelves experiencing strong melting in both Greenland (Petermann Glacier) and Antarctica (Pine Island Glacier). Using a fully-couple ice-shelf/sub-ice-shelf-ocean flow model, it is demonstrated that these channels can form spontaneously in laterally confined ice shelves. These channels have transverse extent of a few kilometers and a vertical relief of about a few hundred meters. Meltrates and sea-water transport in the channels are significantly higher than in between the channels on the smooth flat ice bottom. In circumstances where an ice shelf has no-slip conditions at its lateral boundaries, the ice-shelf/sub-ice-shelf-cavity system exhibits equilibrium periodic states, where the same configurations repetitively appear with a periodicity of about 30-35 years. This peculiar dynamics of the system has strong implications on the interpretation of the remote and in-situ observations and inferences of the system parameters (e.g., melt rates) based on these observations. For instance, the persistent temporal changes in the ice-shelf thickness are caused by internal dynamics of the melt channels, and, in contrast to traditional interpretation, can be independent of the oceanic forcings.

  14. Greenland ice sheet melt from MODIS and associated atmospheric variability

    NASA Astrophysics Data System (ADS)

    Häkkinen, Sirpa; Hall, Dorothy K.; Shuman, Christopher A.; Worthen, Denise L.; DiGirolamo, Nicolo E.

    2014-03-01

    Daily June-July melt fraction variations over the Greenland ice sheet (GIS) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) (2000-2013) are associated with atmospheric blocking forming an omega-shape ridge over the GIS at 500 hPa height. Blocking activity with a range of time scales, from synoptic waves breaking poleward (<5 days) to full-fledged blocks (?5 days), brings warm subtropical air masses over the GIS controlling daily surface temperatures and melt. The temperature anomaly of these subtropical air mass intrusions is also important for melting. Based on the years with the greatest melt (2002 and 2012) during the MODIS era, the area-average temperature anomaly of 2 standard deviations above the 14 year June-July mean results in a melt fraction of 40% or more. Though the summer of 2007 had the most blocking days, atmospheric temperature anomalies were too small to instigate extreme melting.

  15. Mathematical Modelling of Melt Lake Formation on an Ice Shelf

    NASA Astrophysics Data System (ADS)

    Feltham, D. L.; Buzzard, S. C.; Flocco, D.; Sammonds, P. R.

    2014-12-01

    The accumulation of surface meltwater on ice shelves can lead to the formation of melt lakes. These structures have been implicated in crevasse propagation and ice shelf collapse; the Larsen B ice shelf was observed to have a large amount of melt lakes present on its surface just before its collapse in 2002. Through modelling the transport of heat through the surface of the Larsen C ice shelf, where melt lakes have also been observed, this work aims to provide new insights into the ways in which melt lakes are forming and the effect that meltwater filling crevasses on the ice shelf will have. This will enable an assessment of the role of meltwater in triggering ice shelf collapse.The Antarctic Peninsula, where Larsen C is situated, has warmed several times the global average over the last century and this ice shelf has been suggested as a candidate for becoming fully saturated with meltwater by the end of the current century. Here we present preliminary results of a mathematical model of heat transfer through an idealised ice shelf. When forced with automatic weather station data from Larsen C, surface melting and the subsequent meltwater accumulation and melt lake development are demonstrated through the modelled results. Investigating the role of meltwater in ice shelf stability is key as collapse can affect ocean circulation and temperature, and cause a loss of habitat. Additionally, it can cause a loss of the buttressing effect that ice shelves can have on their tributary glaciers, thus allowing the glaciers to accelerate, contributing to sea level rise.

  16. Ice melting and earthquake suppression in Greenland

    NASA Astrophysics Data System (ADS)

    Olivieri, M.; Spada, G.

    2015-03-01

    It has been suggested that the Greenland ice sheet is the cause of earthquake suppression in the region. With few exceptions, the observed seismicity extends only along the continental margins of Greenland, which almost coincide with the ice sheet margin. This pattern has been put forward as further validation of the earthquake suppression hypothesis. In this review, new evidence in terms of ice melting, post-glacial rebound and earthquake occurrence is gathered and discussed to re-evaluate the connection between ice mass unloading and earthquake suppression. In Greenland, the spatio-temporal distribution of earthquakes indicates that seismicity is mainly confined to regions where the thick layer of ice is absent and where significant ice melting is presently occurring. A clear correlation between seismic activity and ice melting in Greenland is not found. However, earthquake locations and corresponding depth distributions suggest two distinct governing mechanisms: post-glacial rebound promotes moderate-size crustal earthquakes at Greenland's regional scale, while current ice melting promotes shallow low magnitude seismicity locally.

  17. Turbulent exchange coefficients for the ice/ocean interface in case of rapid melting

    NASA Astrophysics Data System (ADS)

    Sirevaag, Anders

    2009-02-01

    In the marginal ice zones, drifting sea ice encounters large ocean heat fluxes and melting rates. However, as found from modelling studies and observations of ice melting, double diffusive effects at the ice/ocean interface limit the melting rates. In this paper, direct measurements of turbulent heat and salt fluxes from the marginal ice zone during rapid melting are presented. The strength of double diffusion is found to be significant and close to the range suggested from other studies. Calculated melting rates when double diffusive effects are present are compared to melting rates calculated from a traditional bulk parameterization of ocean heat flux for a range of temperatures and friction velocities often encountered within the marginal ice zones. This comparison shows that by ignoring double diffusive effects, melting rates are overestimated by several cm per day, which may have a significant impact on a predicted future ice cover.

  18. Floating Ice-Algal Aggregates below Melting Arctic Sea Ice

    PubMed Central

    Assmy, Philipp; Ehn, Jens K.; Fernández-Méndez, Mar; Hop, Haakon; Katlein, Christian; Sundfjord, Arild; Bluhm, Katrin; Daase, Malin; Engel, Anja; Fransson, Agneta; Granskog, Mats A.; Hudson, Stephen R.; Kristiansen, Svein; Nicolaus, Marcel; Peeken, Ilka; Renner, Angelika H. H.; Spreen, Gunnar; Tatarek, Agnieszka; Wiktor, Jozef

    2013-01-01

    During two consecutive cruises to the Eastern Central Arctic in late summer 2012, we observed floating algal aggregates in the melt-water layer below and between melting ice floes of first-year pack ice. The macroscopic (1-15 cm in diameter) aggregates had a mucous consistency and were dominated by typical ice-associated pennate diatoms embedded within the mucous matrix. Aggregates maintained buoyancy and accumulated just above a strong pycnocline that separated meltwater and seawater layers. We were able, for the first time, to obtain quantitative abundance and biomass estimates of these aggregates. Although their biomass and production on a square metre basis was small compared to ice-algal blooms, the floating ice-algal aggregates supported high levels of biological activity on the scale of the individual aggregate. In addition they constituted a food source for the ice-associated fauna as revealed by pigments indicative of zooplankton grazing, high abundance of naked ciliates, and ice amphipods associated with them. During the Arctic melt season, these floating aggregates likely play an important ecological role in an otherwise impoverished near-surface sea ice environment. Our findings provide important observations and measurements of a unique aggregate-based habitat during the 2012 record sea ice minimum year. PMID:24204642

  19. Modelling of melt ponds on a sea ice floe

    Microsoft Academic Search

    F. Scott; D. Feltham

    2009-01-01

    During winter the ocean surface at the poles freezes over to form sea ice. Sea ice floats on the ocean surface and has a matrix structure caused by the rejection of salts during freezing. In the summer sea ice melts at its surface creating melt ponds. An accurate estimate of the fraction of the upper sea-ice surface covered in melt

  20. Greenland ice sheet melt from MODIS and associated atmospheric variability

    PubMed Central

    Häkkinen, Sirpa; Hall, Dorothy K; Shuman, Christopher A; Worthen, Denise L; DiGirolamo, Nicolo E

    2014-01-01

    Daily June-July melt fraction variations over the Greenland ice sheet (GIS) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) (2000–2013) are associated with atmospheric blocking forming an omega-shape ridge over the GIS at 500 hPa height. Blocking activity with a range of time scales, from synoptic waves breaking poleward (<5 days) to full-fledged blocks (?5 days), brings warm subtropical air masses over the GIS controlling daily surface temperatures and melt. The temperature anomaly of these subtropical air mass intrusions is also important for melting. Based on the years with the greatest melt (2002 and 2012) during the MODIS era, the area-average temperature anomaly of 2 standard deviations above the 14 year June-July mean results in a melt fraction of 40% or more. Though the summer of 2007 had the most blocking days, atmospheric temperature anomalies were too small to instigate extreme melting. Key Points Short-term atmospheric blocking over Greenland contributes to melt episodes Associated temperature anomalies are equally important for the melt Duration and strength of blocking events contribute to surface melt intensity PMID:25821277

  1. Regelation: why does ice melt under pressure?

    E-print Network

    Sun, Chang Q

    2015-01-01

    Unlike other unusual materials whose bonds contract under compression, the O:H nonbond undergoes contraction and the H-O bond elongation towards O:H and H-O length symmetry in water and ice. The energy drop of the H-O bond dictates the melting point Tm depression of ice. Once the pressure is relieved, the O:H-O bond fully recovers its initial state, resulting in Regelation.

  2. Regelation: why does ice melt under pressure?

    E-print Network

    Chang Q Sun

    2015-01-28

    Unlike other unusual materials whose bonds contract under compression, the O:H nonbond undergoes contraction and the H-O bond elongation towards O:H and H-O length symmetry in water and ice. The energy drop of the H-O bond dictates the melting point Tm depression of ice. Once the pressure is relieved, the O:H-O bond fully recovers its initial state, resulting in Regelation.

  3. 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

  4. connecting the dots between Greenland ice sheet surface melting and ice flow dynamics (Invited)

    NASA Astrophysics Data System (ADS)

    Box, J. E.; Colgan, W. T.; Fettweis, X.; Phillips, T. P.; Stober, M.

    2013-12-01

    This presentation is of a 'unified theory' in glaciology that first identifies surface albedo as a key factor explaining total ice sheet mass balance and then surveys a mechanistic self-reinforcing interaction between melt water and ice flow dynamics. The theory is applied in a near-real time total Greenland mass balance retrieval based on surface albedo, a powerful integrator of the competing effects of accumulation and ablation. New snowfall reduces sunlight absorption and increases meltwater retention. Melting amplifies absorbed sunlight through thermal metamorphism and bare ice expansion in space and time. By ';following the melt'; we reveal mechanisms linking existing science into a unified theory. Increasing meltwater softens the ice sheet in three ways: 1.) sensible heating given the water temperature exceeds that of the ice sheet interior; 2.) Some infiltrating water refreezes, transferring latent heat to the ice; 3.) Friction from water turbulence heats the ice. It has been shown that for a point on the ice sheet, basal lubrication increases ice flow speed to a time when an efficient sub-glacial drainage network develops that reduces this effect. Yet, with an increasing melt duration the point where the ice sheet glides on a wet bed increases inland to a larger area. This effect draws down the ice surface elevation, contributing to the ';elevation feedback'. In a perpetual warming scenario, the elevation feedback ultimately leads to ice sheet loss reversible only through much slower ice sheet growth in an ice age environment. As the inland ice sheet accelerates, the horizontal extension pulls cracks and crevasses open, trapping more sunlight, amplifying the effect of melt accelerated ice. As the bare ice area increases, the direct sun-exposed crevassed and infiltration area increases further allowing the ice warming process to occur more broadly. Considering hydrofracture [a.k.a. hydrofracking]; surface meltwater fills cracks, attacking the ice integrity. Because water is 'heavier' than ice, water-filled cracks have unlimited capacity to hydraulically ';jack' open fractures, penetrating, fracturing and disaggregating a solid ice body. This process promotes iceberg calving at more than 150, 1km wide marine terminating Greenland glacier fronts. Resulting from a rising trend of surface melting and sea water temperature, meltwater ejection at the underwater front of marine glaciers drives a an increasing turbulent heat exchange between the glacier front and relatively warm sea water melting it faster. Underwater melting promotes an undercutting of the glacier front leading to ice berg calving. Calving through hydrofracture or marine undercutting provide a direct and immediate ice flow speed response mechanism for surface meltwater production. Ice flow speed reacts because calving reduces flow resistance. The above physical processes interact. Cooling shuts these processes down. Negative feedbacks dampen the warming impulse. Live 21 June, 2013 is a new Danish Web site1 that exploits total mass balance rate of decline as a function of albedo to predict GRACE mass rate of change with 80% explained variance. While surface mass balance explains the mass rate of change slightly higher, surface albedo is an observable quantity as is gravity change.

  5. Causes and Effects of Melting Ice

    NSDL National Science Digital Library

    Elizabeth Vernon Bell

    2012-11-14

    In this activity, learners explore the concept of density-driven currents (thermohaline circulation) and how these currents are affected by climate change. Learners use colored ice cubes, water, and salt to explore density as it relates to salinity. This activity helps learners to understand the impact of glacial melt on sea level rise.

  6. Ocean variability contributing to basal melt rate near the ice front of Ross Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Arzeno, Isabella B.; Beardsley, Robert C.; Limeburner, Richard; Owens, Breck; Padman, Laurie; Springer, Scott R.; Stewart, Craig L.; Williams, Michael J. M.

    2014-07-01

    Basal melting of ice shelves is an important, but poorly understood, cause of Antarctic ice sheet mass loss and freshwater production. We use data from two moorings deployed through Ross Ice Shelf, ˜6 and ˜16 km south of the ice front east of Ross Island, and numerical models to show how the basal melting rate near the ice front depends on sub-ice-shelf ocean variability. The moorings measured water velocity, conductivity, and temperature for ˜2 months starting in late November 2010. About half of the current velocity variance was due to tides, predominantly diurnal components, with the remainder due to subtidal oscillations with periods of a few days. Subtidal variability was dominated by barotropic currents that were large until mid-December and significantly reduced afterward. Subtidal currents were correlated between moorings but uncorrelated with local winds, suggesting the presence of waves or eddies that may be associated with the abrupt change in water column thickness and strong hydrographic gradients at the ice front. Estimated melt rate was ˜1.2 ± 0.5 m a-1 at each site during the deployment period, consistent with measured trends in ice surface elevation from GPS time series. The models predicted similar annual-averaged melt rates with a strong annual cycle related to seasonal provision of warm water to the ice base. These results show that accurately modeling the high spatial and temporal ocean variability close to the ice-shelf front is critical to predicting time-dependent and mean values of meltwater production and ice-shelf thinning.

  7. Duration of the Arctic sea ice melt season: Regional and interannual variability, 1979-2001

    USGS Publications Warehouse

    Belchansky, G.I.; Douglas, D.C.; Platonov, N.G.

    2004-01-01

    Melt onset dates, freeze onset dates, and melt season duration were estimated over Arctic sea ice, 1979-2001, using passive microwave satellite imagery and surface air temperature data. Sea ice melt duration for the entire Northern Hemisphere varied from a 104-day minimum in 1983 and 1996, to a 124-day maximum in 1989. Ranges in melt duration were highest in peripheral seas, numbering 32, 42, 44, and 51 days in the Laptev, Barents-Kara, East Siberian and Chukchi Seas, respectively. In the Arctic Ocean, average melt duration varied from a 75-day minimum in 1987 to a 103-day maximum in 1989. On average, melt onset in annual ice began 10.6 days earlier than perennial ice, and freeze onset in perennial ice commenced 18.4 days earlier than annual ice. Average annual melt dates, freeze dates, and melt durations in annual ice were significantly correlated with seasonal strength of the Arctic Oscillation (AO). Following high-index AO winters (January-March), spring melt tended to be earlier and autumn freeze later, leading to longer melt season durations. The largest increases in melt duration were observed in the eastern Siberian Arctic, coincident with cyclonic low pressure and ice motion anomalies associated with high-index AO phases. Following a positive AO shift in 1989, mean annual melt duration increased 2-3 weeks in the northern East Siberian and Chukchi Seas. Decreasing correlations between consecutive-year maps of melt onset in annual ice during 1979-2001 indicated increasing spatial variability and unpredictability in melt distributions from one year to the next. Despite recent declines in the winter AO index, recent melt distributions did not show evidence of reestablishing spatial patterns similar to those observed during the 1979-88 low-index AO period. Recent freeze distributions have become increasingly similar to those observed during 1979-88, suggesting a recurrent spatial pattern of freeze chronology under low-index AO conditions.

  8. Absence of superheating for ice Ih with a free surface: a new method of determining the melting point of different water models

    Microsoft Academic Search

    Carlos Vega; Maria Martin-Conde; Andrzej Patrykiejew

    2006-01-01

    Molecular dynamic simulations were performed for ice Ih with a free surface. The simulations were carried out at several temperatures and each run lasted more than 7?ns. At high temperatures the ice melts. It is demonstrated that the melting process starts at the surface and propagates to the bulk of the ice block. Already at the temperatures below the melting

  9. Directional close-contact melting in glacier ice

    NASA Astrophysics Data System (ADS)

    Kowalski, Julia; Schüller, Kai

    2015-04-01

    The Saturnian moon Enceladus shows incidence of liquid water underneath a thick ice sheet cover and is thought to be a potential candidate for extraterrestrial life. However, direct exploration of these subglacial aquatic ecosystems is very challenging. Within the scope of the joint research project 'Enceladus Explorer' (EnEx) (consisting of FH Aachen, RWTH Aachen, Bergische Universität Wuppertal, Universität Bremen, TU Braunschweig und Bundeswehr Universität München), initiated by the German Space Agency, a maneuverable close-contact melting probe has been developed. The force-regulated and heater-controlled probe is able to melt against gravity or even on a curved trajectory. Hence, it offers additional degrees of freedom in its melting motion, e.g. for target oriented melting or obstacle avoidance strategies. General feasibility of the concept has been demonstrated in various field tests. However, in order to optimize its design and to adopt it to extraterrestrial missions a simulation model is needed, capable of determining melting velocity and efficiency at given environmental conditions and system configurations. Within this contribution, the physical situation is abstracted into a quasi-stationary mathematical model description, and a numerical solution strategy is developed to compute melting velocity and temperature distribution within the probe and the surrounding ice. We present an inverse solution approach, in which a background velocity field of the ice mimics the melting velocity. The fundamental balance laws are solved with the corresponding melting rate. Following Newton's laws, the resulting force acting on the probe has to balance the contact force exerted by the probe and can hence be used for convergence. We present both, analytical results to a simplified head geometry, as well as results from a simulation model implemented into the open source software Elmer for arbitrary head geometries. The latter can deal with the full 3d situation, which is demonstrated through various examples. We will conclude by discussing modeling results with respect to recent laboratory experiments and field tests conducted in Antarctica.

  10. The melting temperature of the most common models of water

    Microsoft Academic Search

    C. Vega; E. Sanz; J. L. F. Abascal

    2005-01-01

    The melting temperature of ice Ih for several commonly used models of water (SPC, SPC\\/E,TIP3P,TIP4P, TIP4P\\/Ew, and TIP5P) is obtained from computer simulations at p=1 bar. Since the melting temperature of ice Ih for the TIP4P model is now known [E. Sanz, C. Vega, J. L. F. Abascal, and L. G. MacDowell, Phys. Rev. Lett. 92, 255701 (2004)], it is

  11. Past and Future Vulnerability of the West Antarctic Ice Sheet to Surface Ice-Shelf Melt

    NASA Astrophysics Data System (ADS)

    DeConto, R.; Pollard, D.; Kowalewski, D. E.

    2011-12-01

    New sediment core records from the Ross Embayment (ANDRILL) imply dramatic, orbitally paced variability of the West Antarctic Ice Sheet (WAIS) over the last five million years (Naish et al., 2009). Time-continuous model simulations of the coupled Antarctic ice sheet-shelf system over this interval are capable of simulating this implied WAIS variability, including sudden, orbitally triggered retreats and subsequent regrowth of nearly all marine ice in West Antarctica. In the model, simulated episodes of WAIS retreat are common during the warm Pliocene, but they also occur during some of the strongest interglacials of the colder Pleistocene. Clearly, the magnitude and millennial timescale of simulated WAIS retreat in response to relatively modest past forcing hints at the potential future vulnerability of the ice sheet. In previous long-term simulations (Pollard and DeConto, 2009), the ice-sheet model was driven by parameterized climatologies (surface temperature, precipitation, sea level, and oceanic sub-ice shelf melt), scaled mainly to deep- sea benthic oxygen isotope records. The model WAIS was found to be highly sensitive to sub-ice-shelf melt rates, with modest increases (~2 m/yr) capable of triggering sudden grounding-line retreat and dynamic thinning in the Ross, Weddell and Amundsen Sea sectors - largely in response to reduced ice-shelf buttressing. Here we present new ice sheet-shelf simulations of specific Pliocene and Pleistocene interglacials, using atmospheric climatologies from a new high-resolution Regional Climate Model. The results show that in addition to increased sub-ice-shelf melt rates, surface melting on ice-shelf surfaces could have been a contributing factor to past episodes of WAIS retreat, providing a simple explanation (orbital forcing of Antarctic surface air temperatures) for the orbital pacing of the events. Simulated increases in surface ice-shelf melt rates in response to elevated greenhouses gas levels are also evaluated, to assess their influence on WAIS retreat and sea-level rise in the near and long-term future.

  12. The melting history of the late Pleistocene Antarctic ice sheet

    Microsoft Academic Search

    M. Nakada; K. Lambeck

    1988-01-01

    Spatial and temporal variations in the sea levels of the past 20,000 years around the globe place constraints on the melting history of the major late Pleistocene ice sheets. The Antarctic ice sheets provided a significant contribution to the sea-level rise at a rate that was approximately synchronous with the melting of the Laurentide ice sheet, except for the interval

  13. New Equations for the Sublimation Pressure and Melting Pressure of H2O Ice Ih

    NASA Astrophysics Data System (ADS)

    Wagner, Wolfgang; Riethmann, Thomas; Feistel, Rainer; Harvey, Allan H.

    2011-12-01

    New reference equations, adopted by the International Association for the Properties of Water and Steam (IAPWS), are presented for the sublimation pressure and melting pressure of ice Ih as a function of temperature. These equations are based on input values derived from the phase-equilibrium condition between the IAPWS-95 scientific standard for thermodynamic properties of fluid H2O and the equation of state of H2O ice Ih adopted by IAPWS in 2006, making them thermodynamically consistent with the bulk-phase properties. Compared to the previous IAPWS formulations, which were empirical fits to experimental data, the new equations have significantly less uncertainty. The sublimation-pressure equation covers the temperature range from 50 K to the vapor-liquid-solid triple point at 273.16 K. The ice Ih melting-pressure equation describes the entire melting curve from 273.16 K to the ice Ih-ice III-liquid triple point at 251.165 K. For completeness, we also give the IAPWS melting-pressure equation for ice III, which is slightly adjusted to agree with the ice Ih melting-pressure equation at the corresponding triple point, and the unchanged IAPWS melting-pressure equations for ice V, ice VI, and ice VII.

  14. The refreezing of melt ponds on Arctic sea ice

    NASA Astrophysics Data System (ADS)

    Flocco, Daniela; Feltham, Daniel L.; Bailey, Eleanor; Schroeder, David

    2015-02-01

    The presence of melt ponds on the surface of Arctic sea ice significantly reduces its albedo, inducing a positive feedback leading to sea ice thinning. While the role of melt ponds in enhancing the summer melt of sea ice is well known, their impact on suppressing winter freezing of sea ice has, hitherto, received less attention. Melt ponds freeze by forming an ice lid at the upper surface, which insulates them from the atmosphere and traps pond water between the underlying sea ice and the ice lid. The pond water is a store of latent heat, which is released during refreezing. Until a pond freezes completely, there can be minimal ice growth at the base of the underlying sea ice. In this work, we present a model of the refreezing of a melt pond that includes the heat and salt balances in the ice lid, trapped pond, and underlying sea ice. The model uses a two-stream radiation model to account for radiative scattering at phase boundaries. Simulations and related sensitivity studies suggest that trapped pond water may survive for over a month. We focus on the role that pond salinity has on delaying the refreezing process and retarding basal sea ice growth. We estimate that for a typical sea ice pond coverage in autumn, excluding the impact of trapped ponds in models overestimates ice growth by up to 265 million km3, an overestimate of 26%.

  15. Melting beneath Greenland outlet glaciers and ice streams

    NASA Astrophysics Data System (ADS)

    Alexander, David; Perrette, Mahé; Beckmann, Johanna

    2015-04-01

    Basal melting of fast-flowing Greenland outlet glaciers and ice streams due to frictional heating at the ice-bed interface contributes significantly to total glacier mass balance and subglacial meltwater flux, yet modelling this basal melt process in Greenland has received minimal research attention. A one-dimensional dynamic ice-flow model is calibrated to the present day longitudinal profiles of 10 major Greenland outlet glaciers and ice streams (including the Jakobshavn Isbrae, Petermann Glacier and Helheim Glacier) and is validated against published ice flow and surface elevation measurements. Along each longitudinal profile, basal melt is calculated as a function of ice flow velocity and basal shear stress. The basal shear stress is dependent on the effective pressure (difference between ice overburden pressure and water pressure), basal roughness and a sliding parametrization. Model output indicates that where outlet glaciers and ice streams terminate into the ocean with either a small floating ice tongue or no floating tongue whatsoever, the proportion of basal melt to total melt (surface, basal and submarine melt) is 5-10% (e.g. Jakobshavn Isbrae; Daugaard-Jensen Glacier). This proportion is, however, negligible where larger ice tongues lose mass mostly by submarine melt (~1%; e.g. Nioghalvfjerdsfjorden Glacier). Modelled basal melt is highest immediately upvalley of the grounding line, with contributions typically up to 20-40% of the total melt for slippery beds and up to 30-70% for resistant beds. Additionally, modelled grounding line and calving front migration inland for all outlet glaciers and ice streams of hundreds of metres to several kilometres occurs. Including basal melt due to frictional heating in outlet glacier and ice stream models is important for more accurately modelling mass balance and subglacial meltwater flux, and therefore, more accurately modelling outlet glacier and ice stream dynamics and responses to future climate change.

  16. The melting temperature of the most common models of water

    NASA Astrophysics Data System (ADS)

    Vega, C.; Sanz, E.; Abascal, J. L. F.

    2005-03-01

    The melting temperature of ice Ih for several commonly used models of water (SPC, SPC/E,TIP3P,TIP4P, TIP4P/Ew, and TIP5P) is obtained from computer simulations at p =1bar. Since the melting temperature of ice Ih for the TIP4P model is now known [E. Sanz, C. Vega, J. L. F. Abascal, and L. G. MacDowell, Phys. Rev. Lett. 92, 255701 (2004)], it is possible to use the Gibbs-Duhem methodology [D. Kofke, J. Chem. Phys. 98, 4149 (1993)] to evaluate the melting temperature of ice Ih for other potential models of water. We have found that the melting temperatures of ice Ih for SPC, SPC/E, TIP3P, TIP4P, TIP4P/Ew, and TIP5P models are T =190K, 215K, 146K, 232K, 245K, and 274K, respectively. The relative stability of ice Ih with respect to ice II for these models has also been considered. It turns out that for SPC, SPC/E, TIP3P, and TIP5P the stable phase at the normal melting point is ice II (so that ice Ih is not a thermodynamically stable phase for these models). For TIP4P and TIP4P/Ew, ice Ih is the stable solid phase at the standard melting point. The location of the negative charge along the H-O-H bisector appears as a critical factor in the determination of the relative stability between the Ih and II ice forms. The methodology proposed in this paper can be used to investigate the effect upon a coexistence line due to a change in the potential parameters.

  17. Temperature (T) degrees Celsius (oC) arbitrary scale from 0oC at melting point of ice to 100oC at

    E-print Network

    Allan, Richard P.

    it increases the flow of energy from the body through evaporation (sweat) and sensible heat. 15oC may feel coolC at melting point of ice to 100oC at boiling point of water Also (Kelvin, K) = oC plus 273.15 0 K is absolute body has an energy balance just like the Earth (solar radiative heating, thermal radiative heating/cooling

  18. 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

  19. Regional variability in sea ice melt in a changing Arctic.

    PubMed

    Perovich, Donald K; Richter-Menge, Jacqueline A

    2015-07-13

    In recent years, the Arctic sea ice cover has undergone a precipitous decline in summer extent. The sea ice mass balance integrates heat and provides insight on atmospheric and oceanic forcing. The amount of surface melt and bottom melt that occurs during the summer melt season was measured at 41 sites over the time period 1957 to 2014. There are large regional and temporal variations in both surface and bottom melting. Combined surface and bottom melt ranged from 16 to 294?cm, with a mean of 101?cm. The mean ice equivalent surface melt was 48?cm and the mean bottom melt was 53?cm. On average, surface melting decreases moving northward from the Beaufort Sea towards the North Pole; however interannual differences in atmospheric forcing can overwhelm the influence of latitude. Substantial increases in bottom melting are a major contributor to ice losses in the Beaufort Sea, due to decreases in ice concentration. In the central Arctic, surface and bottom melting demonstrate interannual variability, but show no strong temporal trends from 2000 to 2014. This suggests that under current conditions, summer melting in the central Arctic is not large enough to completely remove the sea ice cover. PMID:26032323

  20. Estimation of surface melt and absorbed radiation on the Greenland ice sheet using passive microwave data

    NASA Astrophysics Data System (ADS)

    Joshi, Maneesha D.

    1999-09-01

    Passive microwave data from the Defense Meteorological Satellite Program (DMPS) Special Sensor Microwave/Imager (SSM/I) and Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) were used to estimate the extent of melt, melt duration and length of melt season on the Greenland ice sheet for the years 1979--1997. Three techniques---a maximum likelihood classification (MLC), a spectral technique and an edge detection method---were implemented. The MLC and spectral techniques provided estimates of the melt extent, while estimates of the melt extent, the length of the melt season and the duration of melt were obtained from the edge method. Comparisons of the surface melt results with global and coastal (Greenland) temperature data indicated that melt extents were better related to global than coastal temperatures. The reverse was noted for melt season and duration trends. The results suggest an overall increase in warmer spells in summer for the period 1979--1997, as indicated by increasing maximum melt extent on the ice sheet. However, there was no corresponding increase in the overall total melt season and total duration of melt. The annual melt extent and the total melt season/duration showed a sharp drop in 1992, due to the eruption of Mt. Pinatubo in June, 1991. The results indicated that melt extents alone cannot be used to estimate warming or cooling on the ice sheet and that melt duration and season trends should also be examined. These surface melt results were then extended to obtain the absorbed radiation flux on the Greenland ice sheet. The monthly albedo on the ice sheet was estimated by assigning an albedo value that was a function of the length of the melt season. The monthly albedo was used with a solar radiation model to estimate the monthly and annual absorbed shortwave flux on the ice sheet. The computation of absorbed radiation on the Greenland ice sheet gave results consistent with those derived from the Earth Radiation Budget Experiment (ERBE). The estimation of absorbed shortwave radiation using satellite passive microwave data demonstrates a new method for determining absorbed shortwave flux on the Greenland ice sheet.

  1. Zooplankton boom and ice amphipod bust below melting sea ice in the Amundsen Gulf, Arctic Canada

    Microsoft Academic Search

    Haakon Hop; Christopher J. Mundy; Michel Gosselin; Andrea L. Rossnagel; David G. Barber

    Early summer in the Arctic with extensive ice melt and break-up represents a dramatic change for sympagic–pelagic fauna below\\u000a seasonal sea ice. As part of the International Polar Year-Circumpolar Flaw Lead system study (IPY-CFL), this investigation\\u000a quantified zooplankton in the meltwater layer below landfast ice and remaining ice fauna below melting ice during June (2008)\\u000a in Franklin Bay and Darnley

  2. Climatic signal of ice melt features in southern Greenland

    Microsoft Academic Search

    Michael M. Herron; Susan L. Herron; Chester C. Langway

    1981-01-01

    The stratigraphie record of melt features in intermediate depth polar ice cores has provided valuable data on past summer climate1-3. The thermal drilling technique used in previous studies precluded extending this record beyond a few hundred years. Recently, however, a 901-m deep ice core was mechanically drilled in southern Greenland. The excellent core quality and improved techniques for measuring melt

  3. 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

  4. Supplemental Online Materials Shock and Post-Shock Temperatures in an Ice-Quartz Mixture: Implications for Melting During

    E-print Network

    Stewart, Sarah T.

    in multi-component hotspot fit. 9. Text S2 provides experimental details. 1 #12;Table S1: Hugoniot equation isentrope of the driver is assumed to be the reflected Hugoniot. Material 0 [g/cm3] C0 [km/s] s Reference on the principal Hugoniot of each component. The shock temperature in the H2O was determined from the 5-phase

  5. Sea ice melting and floe geometry in a simple ice-ocean model

    Microsoft Academic Search

    Michael Steele

    1992-01-01

    A coupled sea ice-ocean numerical model has been developed that addresses the role of floe geometry during summertime melting. The model contains a diagnostic equation for average floe diameter in addition to the usual prognostic equations for ice volume per unit area and ice concentration. The partition between melting on the top, bottom, and lateral (side) surfaces of flows is

  6. Ice Core Evidence of Recent Changes in Summer Melt Intensity of the Southern Greenland Ice Sheet

    Microsoft Academic Search

    S. B. Das; M. A. Fahnestock; J. McConnell; E. Hanna; K. Steffen; J. E. Box

    2004-01-01

    Knowledge of past Greenland Ice Sheet surface melting extent and intensity, and associated climatic controls, is critical to understanding the current and future mass balance of the ice sheet. Surface melting is greatest along the margins of the Greenland Ice Sheet, but leaves no simple record of past patterns or intensity at low elevations. This makes it difficult to place

  7. Climate variability, warming and ice melt on the Antarctic Peninsula over the last millennium (Invited)

    NASA Astrophysics Data System (ADS)

    Abram, N.; Mulvaney, R.; Wolff, E. W.; Triest, J.; Kipfstuhl, S.; Trusel, L. D.; Vimeux, F.; Fleet, L.; Arrowsmith, C.

    2013-12-01

    The Antarctic Peninsula has experienced rapid warming over the past 50 years, which has led to extensive summer ice melt, the collapse of ice shelves and the acceleration of glacial outflow. But the short observational records of Antarctic climate don't allow for an understanding of how unusual the recent conditions may be. We present reconstructions of temperature and melt history since 1000 AD from a highly resolved ice core record from James Ross Island on the northeastern Antarctic Peninsula. The spatial pattern of temperature variability across networks of palaeoclimate reconstructions demonstrates that the Southern Annular Mode (SAM) has been an important driver of Antarctic Peninsula climate variability over a range of time scales. Rapid warming of the Antarctic Peninsula since the mid-20th century is consistent with strengthening of the SAM by a combination of greenhouse and later ozone forcing. The rare reconstruction of summer melting, from visible melt layers in the ice core, demonstrates the non-linear response of ice melt to increasing summer temperatures. Melting in the region is now more intense than at any other time over the last 1000 years and suggests that the Antarctic Peninsula is now particularly susceptible to rapid increases in ice loss in response to relatively small increases in mean temperature.

  8. Melt-flow Acceleration Effects on the Greenland Ice Sheet

    Microsoft Academic Search

    H. J. Zwally; J. L. Saba; K. Steffen; J. Robbins

    2008-01-01

    The first observations of accelerated ice-sheet flow at the equilibrium line in West-central Greenland during summer melt periods of 1996 to 1999 indicated that surface melt-water rapidly propagated to the base and enhanced the basal sliding (Zwally et al., 2002). Additional research has confirmed that melt-water from lake drainage rapidly propagates to the base causing ice acceleration (Das et al.,

  9. Rapid Bottom Melting Widespread near Antarctic Ice Sheet Grounding Lines

    Microsoft Academic Search

    Eric Rignot; Stanley S. Jacobs

    2002-01-01

    As continental ice from Antarctica reaches the grounding line and begins to float, its underside melts into the ocean. Results obtained with satellite radar interferometry reveal that bottom melt rates experienced by large outlet glaciers near their grounding lines are far higher than generally assumed. The melting rate is positively correlated with thermal forcing, increasing by 1 meter per year

  10. THE CONTRIBUTION OF GREENLAND ICE SHEET MELTING TO

    E-print Network

    THE CONTRIBUTION OF GREENLAND ICE SHEET MELTING TO GLOBAL SEA-LEVEL CHANGE Conor Mc three major sources, the Greenland ice sheet, Antarctica, and other eustatic components. Each has its own predictable spatial signal, and particular attention was paid to the Greenland ice sheet, given

  11. The effect of footwear sole abrasion on the coefficient of friction on melting and hard ice

    Microsoft Academic Search

    Chuansi Gao; John Abeysekera; Mikko Hirvonen; Carita Aschan

    2003-01-01

    Footwear sole wear by natural use or artificial abrasion either increases or decreases slip resistance on floors with and without lubricant. The objectives of this paper were to study the effect of footwear sole abrasive wear on slip resistance on ice with respect to temperature, and to compare the slip resistance of abraded soles on melting and hard ice with

  12. Strong sensitivity of Pine Island ice-shelf melting to climatic variability.

    PubMed

    Dutrieux, Pierre; De Rydt, Jan; Jenkins, Adrian; Holland, Paul R; Ha, Ho Kyung; Lee, Sang Hoon; Steig, Eric J; Ding, Qinghua; Abrahamsen, E Povl; Schröder, Michael

    2014-01-10

    Pine Island Glacier has thinned and accelerated over recent decades, significantly contributing to global sea-level rise. Increased oceanic melting of its ice shelf is thought to have triggered those changes. Observations and numerical modeling reveal large fluctuations in the ocean heat available in the adjacent bay and enhanced sensitivity of ice-shelf melting to water temperatures at intermediate depth, as a seabed ridge blocks the deepest and warmest waters from reaching the thickest ice. Oceanic melting decreased by 50% between January 2010 and 2012, with ocean conditions in 2012 partly attributable to atmospheric forcing associated with a strong La Niña event. Both atmospheric variability and local ice shelf and seabed geometry play fundamental roles in determining the response of the Antarctic Ice Sheet to climate. PMID:24385606

  13. Basal Melt Under the Interior of the Greenland Ice Sheet: Comparison of Models, Deep Ice Cores, and Radar Observations

    NASA Astrophysics Data System (ADS)

    Rezvanbehbahani, S.; Stearns, L. A.; van der Veen, C. J.

    2014-12-01

    Basal ice temperature is a critical boundary condition for ice sheet models. It modulates the basal melt rate and sliding conditions, and also affects the ice hardness which alters the deformational velocity. Therefore, in order to obtain reliable estimates on the future mass loss of the ice sheets using numerical models, basal ice temperature is of paramount importance. In this study, the basal temperature and basal melt rate under the Greenland Ice Sheet are estimated using the Robin temperature solution. The analytical Robin solution is obtained by solving the heat conservation equation for steady state conditions, assuming that advection and diffusion are significant only in the vertical direction. In this study, the sensitivity of the basal temperature obtained from the Robin solution to changes in input parameters, including changes in atmospheric conditions, ice thickness, and geothermal heat flux is tested. Although the Robin solution is frequently used in glaciology, there has been no quantitative study to estimate the effect of neglecting the horizontal advection on basal temperatures in regions of higher velocity. Here, a two-dimensional model is applied to quantify the effect of horizontal heat advection on basal temperatures. Overall, horizontal heat advection lowers the basal temperature except in regions where surface mass balance gradients are negative along the flow. Comparing the results from the 2D temperature model to the Robin solution along multiple flowlines of the Greenland Ice Sheet suggest that the horizontal heat advection alters the basal temperatures by less than 3°C up to 30-45% of the flow distance away from the ice divide; at greater distances this difference increases rapidly. All simulations using the Robin solution predict substantial basal melting under the northeast drainage basin of the ice sheet. Our 2D model results also show that because of the negative surface mass balance gradient, horizontal heat advection increases the basal temperatures in the northeast basin. Our obtained map of basal melting area matches well with the radar detected basal water under the north and northeast drainage basins. However, low basal temperatures estimated at the Camp Century ice core location in the northwest of the ice sheet is in contrast with the radar observations.

  14. Dissociative melting of ice VII at high pressure

    SciTech Connect

    Goncharov, Alexander F.; Sanloup, Chrystele; Goldman, Nir; Crowhurst, Jonathan C.; Bastea, Sorin; Howard, W.M.; Fried, Laurence E.; Guignot, Nicolas; Mezouar, Mohamed; Meng, Yue; (UPMC); (LLNL); (CIW); (ESRF)

    2009-04-02

    We have used x-ray diffraction to determine the structure factor of water along its melting line to a static pressure of 57 GPa (570 kbar) and a temperature of more than 1500 K, conditions which correspond to the lower mantle of the Earth, and the interiors of Neptune and Uranus up to a depth of 7000 km. We have also performed corresponding first principles and classical molecular dynamics simulations. Above a pressure of 4 GPa the O-O structure factor is found to be very close to that of a simple soft sphere liquid, thus permitting us to determine the density of liquid water near the melting line. By comparing these results with the density of ice, also determined in this study, we find that the enthalpy of fusion ({Delta}H{sub f}) increases enormously along the melting line, reaching approximately 120 kJ/mole at 40 GPa (compared to 6 kJ/mole at 0 GPa), thus revealing significant molecular dissociation of water upon melting. We speculate that an extended two-phase region could occur in planetary processes involving the adiabatic compression of water.

  15. A model of the threedimensional evolution of Arctic melt ponds on firstyear and multiyear sea ice

    E-print Network

    Feltham, Daniel

    A model of the threedimensional evolution of Arctic melt ponds on firstyear and multiyear sea ice F ice. In the summer the upper layers of sea ice and snow melts producing meltwater that accumulates in Arctic melt ponds on the surface of sea ice. An accurate estimate of the fraction of the sea ice surface

  16. Quantitative Links between Amundsen Sea Heat and Pine Island Ice Shelf Melt

    NASA Astrophysics Data System (ADS)

    Bindschadler, R.; Vaughan, D. G.; Vornberger, P.

    2010-12-01

    Previous researchers have established the strong connection between the Amundsen Sea and basal melt of Pine Island Glacier’s ice shelf in Antarctica. In this presentation we extend this work by focusing on a strong spatial pattern of ice thickness undulations observed on the ice shelf and the predicted temporal pattern of pulses of Circumpolar Deep Water (CDW) upwelled onto the Amundsen Sea continental shelf by variable surface winds (Thoma et al., 2008). After converting the temporal pattern to spatial position on the ice shelf, we show a remarkable correlation over the last decade of these records that allows us to quantitatively associate an amount of heat at the front of the ice shelf, with an amount of melt that occurs at the grounding line. By considering the excess melting driven by pulses of CDW separately from the background melting, we extract a set of heat vs. melt values that suggest a linear relationship supporting the results of Rignot and Jacobs (2002) and disputing the non-linear relationship suggested by Holland et al. (2008). We infer that the current delivering the ocean’s heat is approximately 3.4 cm/sec , that most of the heat is expended by melt, and that the majority of melting is spatially limited to the grounding line vicinity. References cited: Holland, P.R., A. Jenkins and D.M. Holland, 2008. The Response of Ice Shelf Basal Melting to Variations in Ocean Temperature. Journal of Climate, Vol. 21, pp. 2558-2572, DOI: 10.1175/2007JCLI1909.1 Rignot E. and S.S. Jacobs, 2002. Rapid bottom melting widespread near Antarctic ice sheet grounding lines, Science, Vol. 296, No. 5575, p. 2020-2023. Thoma, M., A. Jenkins, D. Holland, and S. Jacobs, 2008. Modelling Circumpolar Deep Water intrusions on the Amundsen Sea continental shelf, Antarctica, Geophysical Research Letters, Vol. 35, No. 18, L18602, doi: 10.1029/2008GL034939

  17. Object-based Image Classification of Arctic Sea Ice and Melt Ponds through Aerial Photos

    NASA Astrophysics Data System (ADS)

    Miao, X.; Xie, H.; Li, Z.; Lei, R.

    2013-12-01

    The last six years have marked the lowest Arctic summer sea ice extents in the modern era, with a new record summer minimum (3.4 million km2) set on 13 September 2012. It has been predicted that the Arctic could be free of summer ice within the next 25-30. The loss of Arctic summer ice could have serious consequences, such as higher water temperature due to the positive feedback of albedo, more powerful and frequent storms, rising sea levels, diminished habitats for polar animals, and more pollution due to fossil fuel exploitation and/ or increased traffic through the Northwest/ Northeast Passage. In these processes, melt ponds play an important role in Earth's radiation balance since they strongly absorb solar radiation rather than reflecting it as snow and ice do. Therefore, it is necessary to develop the ability of predicting the sea ice/ melt pond extents and space-time evolution, which is pivotal to prepare for the variation and uncertainty of the future environment, political, economic, and military needs. A lot of efforts have been put into Arctic sea ice modeling to simulate sea ice processes. However, these sea ice models were initiated and developed based on limited field surveys, aircraft or satellite image data. Therefore, it is necessary to collect high resolution sea ice aerial photo in a systematic way to tune up, validate, and improve models. Currently there are many sea ice aerial photos available, such as Chinese Arctic Exploration (CHINARE 2008, 2010, 2012), SHEBA 1998 and HOTRAX 2005. However, manually delineating of sea ice and melt pond from these images is time-consuming and labor-intensive. In this study, we use the object-based remote sensing classification scheme to extract sea ice and melt ponds efficiently from 1,727 aerial photos taken during the CHINARE 2010. The algorithm includes three major steps as follows. (1) Image segmentation groups the neighboring pixels into objects according to the similarity of spectral and texture information; (2) random forest ensemble classifier can distinguish the following objects: water, submerged ice, shadow, and ice/snow; and (3) polygon neighbor analysis can further separate melt ponds from submerged ice according to the spatial neighboring relationship. Our results illustrate the spatial distribution and morphological characters of melt ponds in different latitudes of the Arctic Pacific sector. This method can be applied to massive photos and images taken in past years and future years, in deriving the detailed sea ice and melt pond distribution and changes through years.

  18. Observed anomalous atmospheric patterns in summers of unusual Arctic sea ice melt

    NASA Astrophysics Data System (ADS)

    Knudsen, Erlend M.; Orsolini, Yvan J.; Furevik, Tore; Hodges, Kevin I.

    2015-04-01

    The Arctic sea ice retreat has accelerated over the last decade. The negative trend is largest in summer, but substantial interannual variability still remains. Here we explore observed atmospheric conditions and feedback mechanisms during summer months of anomalous sea ice melt in the Arctic. Compositing months of anomalous low and high sea ice melt over 1979-2013, we find distinct patterns in atmospheric circulation, precipitation, radiation, and temperature. Compared to summer months of anomalous low sea ice melt, high melt months are characterized by anomalous high sea level pressure in the Arctic (up to 7 hPa), with a corresponding tendency of storms to track on a more zonal path. As a result, the Arctic receives less precipitation overall and 39% less snowfall. This lowers the albedo of the region and reduces the negative feedback the snowfall provides for the sea ice. With an anticyclonic tendency, 12 W/m2 more incoming shortwave radiation reaches the surface in the start of the season. The melting sea ice in turn promotes cloud development in the marginal ice zones and enhances downwelling longwave radiation at the surface toward the end of the season. A positive cloud feedback emerges. In midlatitudes, the more zonally tracking cyclones give stormier, cloudier, wetter, and cooler summers in most of northern Europe and around the Sea of Okhotsk. Farther south, the region from the Mediterranean Sea to East Asia experiences significant surface warming (up to 2.4°C), possibly linked to changes in the jet stream.

  19. Arctic sea ice melt in summer 2007: Surface and bottom ice ablation

    Microsoft Academic Search

    D. K. Perovich; J. A. Richter-Menge; B. C. Elder; K. J. Claffey

    2007-01-01

    Satellite observations indicate a record minimum in Arctic sea ice extent in September 2007, with a particularly large retreat in the East Siberian, Chukchi, and Beaufort Seas. Insights on the nature of this retreat, and of the summer melt season, can be gleaned from 7 autonomous buoys that were monitoring the thermodynamic mass balance of the ice during the melt

  20. Basal melt rates beneath Whillans Ice Stream, West Antarctica

    E-print Network

    Beem, Lucas H.; Jezek, Ken C.; van der Veen, Cornelis J.

    2010-08-05

    . Downstream of the onset of shear crevasses, strong basal melt (20–50 mm a?1) is concentrated beneath the relatively narrow shear margins. Farther upstream, melt rates are consistently 3–7 mm a?1 across the width of the ice stream. We show that the transition...

  1. Applying Archimedes' Law to Ice Melting in Sea Water

    Microsoft Academic Search

    Peter D. Noerdlinger; K. R. Brower

    2006-01-01

    Archimedes stated that a floating body displaces its own weight of liquid, but his law has been widely misapplied to ice floating in the oceans by scientists who assumed that equal weights correspond to equal liquid volumes. It is often said that when floating ice melts, the sea level does not rise \\

  2. On the phase diagram of water with density functional theory potentials: the melting temperature of Ice I-h with the Perdew-Burke-Ernzerhof and Becke-Lee-Yang-Parr functionals

    SciTech Connect

    Yoo, Soohaeng; Zeng, Xiao Cheng; Xantheas, Sotiris S.

    2009-06-11

    The melting temperature (Tm) of ice Ih was determined from constant enthalphy (NPH) Born-Oppenheimer Molecular Dynamics (BOMD) simulations to be 417±3 K for the Perdew-Burke-Ernzerhof (PBE) and 411±4 K for the Becke-Lee-Yang-Parr (BLYP) density functionals using a coexisting ice (Ih)-liquid phase at constant pressures of P = 2,500 and 10,000 bar and a density ? = 1 g/cm3, respectively. This suggests that ambient condition simulations at ? = 1 g/cm3 will rather describe a supercooled state that is overstructured when compared to liquid water. This work was supported by the US Department of Energy Office of Basic Energy Sciences' Chemical Sciences program. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

  3. Melting of the precipitated ice IV in LiCl aqueous solution and polyamorphism of water.

    PubMed

    Mishima, Osamu

    2011-12-01

    Melting of the precipitated ice IV in supercooled LiCl-H(2)O solution was studied in the range of 0-0.6 MPa and 160-270 K. Emulsified solution was used to detect this metastable transition. Ice IV was precipitated from the aqueous solution of 2.0 mol % LiCl (or 4.8 mol % LiCl) in each emulsion particle at low-temperature and high-pressure conditions, and the emulsion was decompressed at different temperatures. The melting of ice IV was detected from the temperature change of the emulsified sample during the decompression. There was an apparently sudden change in the slope of the ice IV melting curve (liquidus) in the pressure-temperature diagram. At the high-pressure and high-temperature side of the change, the solute-induced freezing point depression was observed. At the low-pressure and low-temperature side, ice IV transformed into ice Ih on the decompression, and the transition was almost unrelated to the concentration of LiCl. These experimental results were roughly explained by the presumed existence of two kinds of liquid water (low-density liquid water and high-density liquid water), or polyamorphism in water, and by the simple assumption that LiCl dissolved maily in high-density liquid water. PMID:21736291

  4. Response of Southern Ocean circulation to global warming may enhance basal ice shelf melting around Antarctica

    E-print Network

    Levermann, Anders

    ]. Melting sensitivities to the oceanic temperature outside of the ice shelf cavities are varied from linear one. 1 Introduction The unique zonally unblocked topography in the Southern Ocean (SO) gives rise). According to recent observations, rising atmospheric temperatures may have already caused a warming

  5. 07/06/2009 Melting Ice Could Lead to Massive Waves of Climate Refugees Treehugger 06/30/2009 MELTING GREENLAND ICE SHEETS MAY THREATEN

    E-print Network

    Hu, Aixue

    /30/2009 MELTING GREENLAND ICE SHEETS MAY THREATEN NORTHEAST U.S., CANADA Federal News Service 06/30/2009 Sea raises spectre of displaced humanity peopleandplanet.net 06/16/2009 Melting Greenland Ice Sheets May Report - Online 06/02/2009 Melting Greenland Ice Sheets May Threaten Northeast, Canada usagnet 06

  6. Modis LST as an Index of Summer Melt Conditions over Arctic Ice Caps

    NASA Astrophysics Data System (ADS)

    Geai, M. E.; Sharp, M. J.

    2011-12-01

    Despite the large area of glacier ice in the Arctic, very few in situ mass balance and air temperature measurements exist over Arctic ice caps. There is therefore a need to develop proxy records of summer melt conditions on these ice caps in order to identify spatial patterns and temporal trends in surface mass balance across the region. Analysis of Moderate Resolution Imaging Spectroradiometer (MODIS) derived land surface temperatures (LST) may provide a method to evaluate melt and climate trends over Arctic ice caps for the last decade. MODIS LST data were used to derive the seasonal mean of 8-day average values of daytime clear-sky surface temperature over 30 Arctic ice caps for each melt season from 2000 to 2010. LST was retrieved for a specified area within each individual ice cap, defined as the largest contiguous area of ice and snow within that ice cap. The melt season was defined as the period between the 10-year mean of melt onset and freeze-up dates derived from QuikScat. Given the potential biases introduced by the facts that a) LST data are available only for clear sky days and b) cloudiness likely varies substantially across the Arctic glaciated regions, there is a need to verify LST measurements against known changes in air temperature across all these regions. NCEP/NCAR R1 Reanalysis temperatures provide a single consistent dataset with which to evaluate air temperature trends. Ice caps in Alaska, the Canadian Arctic Archipelago (CAA) and Greenland display a common shift toward strong positive anomalies in the 2000's (0.45 to 1.2°C). The Iceland and Svalbard ice caps show weaker positive air temperature anomalies in the same period (0.38 to 0.4°C), while the Novaya Zemlya, Severnaya Zemlya and Franz Josef Land ice caps (Russia) display negative anomalies (-0.10 to -0.25°C). LST track the NCEP air temperature records at 700 hPa in the CAA (r2 0.6 to 0.96) and northern Svalbard (r2 0.6 to 0.76) only. This talk will explore whether the observed differences in degree of correlation between the LST and air temperature records is directly related to regional variations in the number of individual LST measurements contributing to the 8-day LST product and, if so, whether these variations are due primarily to differences in the incidence of cloud cover.

  7. The "blob of death", or how warm air advection causes rapid ice melt

    NASA Astrophysics Data System (ADS)

    Tjernström, Michael; Shupe, Matthew; Achtert, Peggy; Brooks, Barbara; Brooks, Ian; Johnston, Paul; Persson, Ola; Prytherch, John; Salisbury, Dominic; Sedlar, Joseph; Sotiropoulou, Georgia; Wolfe, Dan

    2015-04-01

    The Arctic Clouds in Summer Experiment (ACSE) program obtained measurements of surface energy fluxes, boundary-layer structure, cloud macro- and micro-physical structure, and upper-ocean thermal and salinity structure from pack-ice and open-water regions in the eastern Arctic from early July to early October 2014. ACSE was divided into two legs. The first took a route from Tromsö, Norway, to Barrow, Alaska, during late summer (early July to late August) mostly on the Siberian Shelf, while the second leg was from traversed back mostly north of the shelf during September and early October. This paper will present ACSE and show examples of some results. Energy fluxes at the surface determine the annual summer melt and autumn freeze-up of Arctic sea ice, but are strongly modulated by interactions between atmospheric, ocean, and sea-ice processes. ACSE summer measurements showed energy flux surpluses leading to significant surface melt, while late August and September measurements showed deficits, leading to freeze-up of sea ice and the ocean surface. A weeklong episode with intensive melt resulting from warm air advection from continental Russia will be presented and discussed. During this episode, temperatures up to 20 °C was observed aloft while near surface temperatures over the ice remained near melting. In the surface inversion dense fog formed that enhanced the downward longwave radiation. Together with a downward turbulent sensible heat flux this caused a rapid melt in this area.

  8. Melt channels under ice shelves: what do they tell us about ice-shelf/ocean interactions?

    NASA Astrophysics Data System (ADS)

    Sergienko, O. V.; Gladish, C. V.

    2012-12-01

    Melt channels incised upward into the bottoms of ice shelves and floating glaciers are an observational hallmark of strong melting. Their formation and dynamics are considered in this presentation. Using a fully-couple ice-shelf/sub-ice-shelf-ocean flow model, we demonstrate that melt channels can form spontaneously in laterally confined ice shelves. These channels have transverse extent of about 3-5 km and a vertical relief of about 100-150 m. Meltrates and sea-water transport in the channels are significantly higher than in between the channels on the smooth flat ice bottom. In circumstances where an ice shelf is frozen (no-slip) at its lateral boundaries, the ice-shelf/sub-ice-shelf-cavity system exhibits equilibrium periodic states, where the same configurations repetitively appear with a periodicity of about 50 years. This peculiar dynamics of the system has strong implications on the interpretation of the remote and in-situ observations and inferences of the system parameters (e.g., melt rates) based on these observations. For instance, the persistent temporal changes in the ice-shelf thickness are caused by internal dynamics of the melt channels, and, in contrast to traditional interpretation, can be independent of the oceanic forcings.

  9. Distinguishing Ice from Snow for Melt Modeling Using Daily Observations from MODIS

    NASA Astrophysics Data System (ADS)

    Rittger, K.; Brodzik, M. J.; Racoviteanu, A.; Barrett, A. P.; Khalsa, S. J. S.; Painter, T. H.; Armstrong, R. L.; Burgess, A. B.

    2014-12-01

    In Earth's mountainous regions, melt from both seasonal snow and glacier ice contributes to streamflow. Few in-situ observations exist that can help distinguish between the two components of melt, particularly across large mountain ranges. In this study, we analyze daily time series of MODIS data products to distinguish ice from snow as the seasonal snowpack recedes revealing firn and glacier ice surfaces. We run a temperature index melt model for the Hunza, a sub-basin of the Upper Indus basin using the MODIS data to discriminate between glacier ice and snow and partition the corresponding streamflow. During the ablation period, this high elevation mid-latitude snowpack receives intense incoming solar radiation resulting in snow grain growth and surface albedo decreases. To explore snow grain growth, we use estimates of grain size from both the MODIS Snow Covered Area and Grain Size Model (MODSCAG) and MODIS Dust Radiative Forcing in Snow (MODDRFS). To explore albedo reduction we use 2 standard albedo products from MODIS, the Terra Daily Snow Cover algorithm (MOD10A1) and Surface Reflectance BRDF/Albedo (MOD43). We use a threshold on the grain size and albedo products to discriminate ice from snow. We test the ability of the 4 MODIS products to discriminate snow from glacier ice using higher resolution data from the Landsat 8 sensor from July 5th and July 21st, 2013 for a subset of the study area in the Karakoram region of the Himalaya that includes the Yazghil and Hopper Glaciers that drain north and northeast in the Shimshall Valley, part of the Hunza River basin. Snow and glacier ice are mapped using band ratio techniques, and are then separated on the basis of broadband albedo values calculated from Landsat bands for comparison with MODIS-derived snow and glacier ice pixels. We run a temperature index melt model that uses gap filled snow covered area from MODSCAG and interpolated station temperature data for the Hunza River basin. The model outputs daily melt volume from three surface classifications: area of snow over land, snow over glacier ice, and exposed glacier ice. The partitioning is done using a combination of MODICE and 1 of 4 MODIS products. Melt from glacier ice accounts for 25% of the combined melt on average across the 4 MODIS products for the Hunza basin, with fluctuations based on the seasonal variability of snowfall.

  10. Modelling the Areal Evolution of Arctic Melt Ponds on Sea Ice

    Microsoft Academic Search

    D. L. Feltham; F. Scott

    2009-01-01

    During winter the ocean surface at the poles freezes over to form sea ice. Sea ice floats on the ocean surface and has a matrix structure caused by the rejection of salts during freezing. In the summer sea ice melts at its surface creating melt ponds. An accurate estimate of the fraction of the upper sea-ice surface covered in melt

  11. Inorganic carbon dynamics of melt-pond-covered first-year sea ice in the Canadian Arctic

    NASA Astrophysics Data System (ADS)

    Geilfus, N.-X.; Galley, R. J.; Crabeck, O.; Papakyriakou, T.; Landy, J.; Tison, J.-L.; Rysgaard, S.

    2015-03-01

    Melt pond formation is a common feature of spring and summer Arctic sea ice, but the role and impact of sea ice melt and pond formation on both the direction and size of CO2 fluxes between air and sea is still unknown. Here we report on the CO2-carbonate chemistry of melting sea ice, melt ponds and the underlying seawater as well as CO2 fluxes at the surface of first-year landfast sea ice in the Resolute Passage, Nunavut, in June 2012. Early in the melt season, the increase in ice temperature and the subsequent decrease in bulk ice salinity promote a strong decrease of the total alkalinity (TA), total dissolved inorganic carbon (TCO2) and partial pressure of CO2 (pCO2) within the bulk sea ice and the brine. As sea ice melt progresses, melt ponds form, mainly from melted snow, leading to a low in situ melt pond pCO2 (36 ?atm). The percolation of this low salinity and low pCO2 meltwater into the sea ice matrix decreased the brine salinity, TA and TCO2, and lowered the in situ brine pCO2 (to 20 ?atm). This initial low in situ pCO2 observed in brine and melt ponds results in air-ice CO2 fluxes ranging between -0.04 and -5.4 mmol m-2 day-1 (negative sign for fluxes from the atmosphere into the ocean). As melt ponds strive to reach pCO2 equilibrium with the atmosphere, their in situ pCO2 increases (up to 380 ?atm) with time and the percolation of this relatively high concentration pCO2 meltwater increases the in situ brine pCO2 within the sea ice matrix as the melt season progresses. As the melt pond pCO2 increases, the uptake of atmospheric CO2 becomes less significant. However, since melt ponds are continuously supplied by meltwater, their in situ pCO2 remains undersaturated with respect to the atmosphere, promoting a continuous but moderate uptake of CO2 (~ -1 mmol m-2 day-1) into the ocean. Considering the Arctic seasonal sea ice extent during the melt period (90 days), we estimate an uptake of atmospheric CO2 of -10.4 Tg of C yr-1. This represents an additional uptake of CO2 associated with Arctic sea ice that needs to be further explored and considered in the estimation of the Arctic Ocean's overall CO2 budget.

  12. 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

  13. An edge detection technique to estimate melt duration, season and melt extent on the Greenland ice sheet using passive microwave data

    Microsoft Academic Search

    Maneesha Joshi; Carolyn J. Merry; Kenneth C. Jezek; John F. Bolzan

    2001-01-01

    The melt extent, duration and melt season on the Greenland ice sheet were estimated using an edge detection technique on passive microwave data from the SSM\\/I and SMMR instruments (18\\/19V GHz channel) for the period 1979 to 1997. The annual brightness temperature (Tb) time series at a pixel location that experiences summer melt has a steep rise and drop in

  14. Antarctic ice sheet response to combined surface and oceanic sub-ice shelf melt during past interglacials and in the future

    NASA Astrophysics Data System (ADS)

    DeConto, R.; Pollard, D.; Kowalewski, D.

    2012-04-01

    New sediment core records from the Ross Embayment (ANDRILL; Naish et al., Nature, 2009) and time-continuous modeling of the Antarctic ice sheet-shelf system (Pollard and DeConto, Nature, 2009) imply dramatic, orbitally paced variability of the West Antarctic Ice Sheet (WAIS) through the Plio-Pleistocene. Model-simulated episodes of WAIS retreat are common during the warm Pliocene, but they also occur during some interglacials in the colder Pleistocene. The relatively modest forcing of these simulated past retreats hints at the future vulnerability of the ice sheet. In our previous long-term simulations, the ice-sheet model was driven by parameterized climatologies (surface temperature, precipitation, sea level, and oceanic sub-ice shelf melt) scaled mainly to deep-sea benthic oxygen isotope records. In the model, WAIS was found to be highly sensitive to sub-ice-shelf melt rates, with modest increases (~2 m/yr) capable of triggering sudden grounding-line retreat and dynamic thinning in the Ross, Weddell and Amundsen Sea sectors- largely in response to reduced ice-shelf buttressing. Here we present new ice sheet-shelf simulations of specific past interglacials and future scenarios with elevated greenhouse gasses. The model is driven by atmospheric climatologies from a new high-resolution Regional Climate Model adapted to the South Polar region and modest increases in circum-Antarctic ocean temperatures. The model (accounting for past greenhouse gas and orbital forcing) shows that melt on ice-shelf surfaces played a contributing role in prior Pleistocene WAIS retreats, but increased oceanic sub ice-shelf melt was likely the dominant mechanism driving those past retreats. At levels of atmospheric CO2 exceeding 2x preindustrial levels (560 ppmv), surface melt on ice-shelf surfaces becomes increasingly important. As CO2 levels approach 4x preindustrial levels, surface melt on ice shelves and the low-elevation flanks of WAIS is sufficient to cause near complete WAIS collapse within several thousand years, without any increase in ocean temperature and oceanic sub-ice melt. On millennial timescales, the loss of WAIS ice is partially compensated by increased accumulation on East Antarctica, but the transfer of mass from West to East Antarctica has significant implications for local relative sea level adjustment. These results suggest oceanic sub-ice melt likely played the dominant role in previous Pleistocene WAIS retreats, but surface melt will begin to play an increasingly important role in the long-term future dynamic response of WAIS in response to elevated greenhouse gas concentrations.

  15. Ranking spatially and temporally variable Greenland ice surface melt factors

    NASA Astrophysics Data System (ADS)

    Box, Jason; Mottram, Ruth; Langen, Peter; Boberg, Fredrik; Promice Team

    2014-05-01

    Greenland ice sheet surface melt water production is evaluated via a spatially distributed surface energy budget analysis of the 14 summers spanning 2000-2013. Key ingredients are DMI HIRHAM5 5km x 5km output and NASA MOD10A1 daily albedo. The HIRHAM5 simulated downward solar and infrared fluxes and turbulent fluxes are compared with in-situ data from the Danish PROMICE.org automatic weather stations. The seasonally and spatially evolving relative importance of individual surface energy budget components yields detailed insight into physical processes driving melt variability with some surprising implications to ice sheet surface mass balance sensitivity to climate change.

  16. Divergent trajectories of Antarctic ice shelf surface melt under 21st century climate scenarios

    NASA Astrophysics Data System (ADS)

    Trusel, L. D.; Frey, K. E.; Das, S. B.; Kuipers Munneke, P.; van Meijgaard, E.

    2014-12-01

    Antarctic ice shelves represent a critical interface between continental ice masses and the surrounding ocean. Breakup events of several ice shelves in recent decades have been linked to an increase in intense surface melting, and have in turn lead to cascading effects including accelerated glacier discharge into the ocean. In this study, we utilized sophisticated regional and global climate models (GCMs) to assess potential future surface melt trajectories across Antarctica under two climate scenarios (RCP4.5 and RCP8.5). RACMO2.1, a polar-adapted regional atmospheric climate model, was forced by the ERA-Interim reanalysis (1980-2010) and by two GCMs, EC-EARTH and HadGEM2-ES (2007-2100). Using RACMO2.1, we observed an exponential growth function well represents the relationship between ice shelf surface meltwater production and mean summer (DJF) 2-meter air temperature (t2m). We employed this melt-t2m relationship to project melt using t2m output from an ensemble of five CMIP5-based GCMs incorporating the NCAR Community Land Model 4 (CLM4), following spatial downscaling and bias correction using t2m from ERA-Interim-forced RACMO2.1. Our resulting GCM-derived melt projections provide an independent and methodologically unique perspective into potential future melt pathways, complementary to those derived from RACMO2.1. Most notably, both RACMO2.1 and the CMIP5 ensemble reveal divergent trajectories of meltwater production beyond 2050 under the two climate scenarios. For many ice shelves in RCP4.5, meltwater production through 2100 remains at levels comparable to present. Conversely, under RCP8.5 all methods indicate non-linear melt intensification, resulting in a four-fold increase in the Antarctic-wide meltwater volume by the end of the 21st century. For some ice shelves, including Larsen C and Wilkins (Antarctic Peninsula), and Shackleton and West (Wilkes Land), spatially averaged end-of-century meltwater production within RCP8.5 approaches or surpasses levels historically associated with collapse of Antarctic Peninsula ice shelves (~600 mm w.e. a-1). While many factors influence ice shelf stability, these projections indicate a strong sensitivity of ice shelf melting to future climate pathways with potentially profound effects on future ice shelf stability.

  17. How does the mantle melt?How does the mantle melt? 1) Increase the temperature

    E-print Network

    Siebel, Wolfgang

    : ­ Decompression melting · Passive asthenospheric upwelling at mid- ocean ridges · Rising plume head at "hot spotsHow does the mantle melt?How does the mantle melt? 1) Increase the temperature Melting by raising the temperatureMelting by raising the temperature Solidus: Temperature of melting, increases with depth (P) #12

  18. Arctic sea ice surviving the summer melt: interannual variability and decreasing trend

    Microsoft Academic Search

    H. Jay Zwally; Per Gloersen

    2008-01-01

    Sea ice surviving the summer melt season to become multi-year ice in the Arctic Ocean is of interest because multi-year ice significantly affects the ice-thickness distribution and the dynamics and thermodynamics of the ice pack in subsequent seasons. However, the amount of ice surviving summer melting has not been well determined because the time of the minimum ice area varies

  19. Absence of superheating for ice Ih with a free surface : a new method of determining the melting point of different water models

    E-print Network

    Carlos Vega; Maria Martin-Conde; Andrzej Patrykiejew

    2013-04-18

    Molecular dynamic simulations were performed for ice Ih with a free surface. The simulations were carried out at several temperatures and each run lasted more than 7ns. At high temperatures the ice melts. It is demonstrated that the melting process starts at the surface and propagates to the bulk of the ice block. Already at the temperatures below the melting point, we observe a thin liquid layer at the ice surface, but the block of ice remains stable along the run. As soon as the temperature reaches the melting point the entire ice block melts. Our results demonstrate that, unlike in the case of conventional simulations in the NpT ensemble, overheating of the ice Ih with a free surface does not occur. That allows to estimate the melting point of ice at zero pressure. We applied the method to the following models of water: SPC/E, TIP4P, TIP4P/Ew, TIP4P/Ice and TIP4P/2005, and found good agreement between the melting temperatures obtained by this procedure and the values obtained either from free energy calculations or from direct simulations of the ice/water interface.

  20. Onset and end of the summer melt season over sea ice: thermal structure and surface energy perspective from SHEBA

    Microsoft Academic Search

    P. Ola G. Persson

    2011-01-01

    Various measurements from the Surface Heat Flux of the Arctic Ocean (SHEBA) experiment have been combined to study structures and processes producing the onset and end of summer melt over Arctic sea ice. The analysis links the surface energy budget to free-troposphere synoptic variables, clouds, precipitation, and in-ice temperatures. The key results are (1) SHEBA melt-season transitions are associated with

  1. Did Davy melt Ice by Friction in a Vacuum?

    Microsoft Academic Search

    Florian Cajori

    1926-01-01

    QUITE firmly entrenched in scientific literature, including some very recent English histories of science, is the statement that Sir Humphry Davy contrived a clockwork by which two pieces of ice were rubbed together and made to melt under the exhausted receiver of an air-pump. This is incorrect. A reference to Davy's works (Davy, ``Collected Works'', vol. 2, 1839, p. 11,

  2. The melting point of ice Ih for common water models calculated from direct coexistence of the solid-liquid interface

    Microsoft Academic Search

    Ramón García Fernández; José L. F. Abascal; Carlos Vega

    2006-01-01

    In this work we present an implementation for the calculation of the melting point of ice Ih from direct coexistence of the solid-liquid interface. We use molecular dynamics simulations of boxes containing liquid water and ice in contact. The implementation is based on the analysis of the evolution of the total energy along NpT simulations at different temperatures. We report

  3. Update on the Greenland Ice Sheet Melt Extent: 1979-1999

    NASA Technical Reports Server (NTRS)

    Abdalati, Waleed; Steffen, Konrad

    2000-01-01

    Analysis of melt extent on the Greenland ice sheet is updated to span the time period 1979-1999 is examined along with its spatial and temporal variability using passive microwave satellite data. In order to acquire the full record, the issue of continuity between previous passive microwave sensors (SMMR, SSM/I F-8, and SSM/I F-11), and the most recent SSM/I F-13 sensor is addressed. The F-13 Cross-polarized gradient ratio (XPGR) melt-classification threshold is determined to be -0.0154. Results show that for the 21-year record, an increasing melt trend of nearly 1 %/yr is observed, and this trend is driven by conditions on in the western portion of the ice sheet, rather than the east, where melt appears to have decreased slightly. Moreover, the eruption of Mt. Pinatubo in 1991 is likely to have had some impact the melt, but not as much as previously suspected. The 1992 melt anomaly is 1.7 standard deviations from the mean. Finally, the relationship between coastal temperatures and melt extent suggest an increase in surface runoff contribution to sea level of 0.31 mm/yr for a 1 C temperature rise.

  4. Shock and post-shock temperatures in an icequartz mixture: implications for melting during planetary impact events

    E-print Network

    Stewart, Sarah T.

    Shock and post-shock temperatures in an ice­quartz mixture: implications for melting during November 2009 Edited by: T. Spohn Keywords: shock temperature impact cratering melting water ice equation the components of a shocked mixture is still an open question in the shock physics community. Knowledge of how

  5. Spatial and temporal observations of summer ice melt using ERS-1 SAR imagery

    Microsoft Academic Search

    B. Holt; S. Martin

    1995-01-01

    This study examines the spatial and temporal character of ice melt. Using ERS-1 SAR imagery, the authors examine the development of small floes formed by melt and deformation, and changes in the fraction of open water, small floes and larger floes. They also examine the spatial variations in melt from the marginal ice zone up into the central Arctic ice

  6. Surface Melt-Induced Acceleration of Greenland Ice-Sheet Flow

    Microsoft Academic Search

    H. Jay Zwally; Waleed Abdalati; Tom Herring; Kristine Larson; Jack Saba; Konrad Steffen

    2002-01-01

    Ice flow at a location in the equilibrium zone of the west-central Greenland Ice Sheet accelerates above the midwinter average rate during periods of summer melting. The near coincidence of the ice acceleration with the duration of surface melting, followed by deceleration after the melting ceases, indicates that glacial sliding is enhanced by rapid migration of surface meltwater to the

  7. Simulating Ice Particle Melting using Smooth Particle Hydrodynamics

    NASA Astrophysics Data System (ADS)

    Kuo, Kwo-Sen; Pelissier, Craig

    2015-04-01

    To measure precipitation from space requires an accurate estimation of the collective scattering properties of particles suspended in a precipitating column. It is well known that the complicated and typically unknowable shapes of the solid precipitation particles cause much uncertainty in the retrievals involving such particles. This remote-sensing problem becomes even more difficult with the "melting layer" containing partially melted ice particles, where both the geometric shape and liquid-solid fraction of the hydrometeors are variables.. For the scattering properties of these particles depend not only on their shapes, but also their melt-water fraction,and the spatial distribution of liquid and ice within. To obtain an accurate estimation thus requires a set of "realistic" particle geometries and a method to determine the melt-water distribution at various stages in the melting process. Once this is achieved, a suitable method can be used to compute the scattering properties. In previous work, the growth of a set of astoundingly realistic ice particles has been simulated using the "Snowfake" algorithm of Gravner and Griffeath. To simulate the melting process of these particles, the method of Smooth Particle Hydrodynamics (SPH) is used. SPH is a mesh-less particle-based approach where kinematic and thermal dynamics is controlled entirely through two-body interactions between neighboring SPH particles. An important property of SPH is that the interaction at boundaries between air/ice/water is implicitly taken care of. This is crucial for this work since those boundaries are complex and vary throughout the melting process. We present the SPH implementation and a simulation, using highly parallel Graphic Processing Units (GPUs), with ~1 million SPH particles to represent one of the generated ice particle geometries. We plan to use this method, especially its parallelized version, to simulate the melting of all the "Snowfake" particles (~10,000 of them) in our collection, to form the basis for the construction of an extensive scattering database of the melting particles. Such a database will be invaluable to the characterization of uncertainty for precipitation retrievals.

  8. Antarctic ice-sheet loss driven by basal melting of ice shelves.

    PubMed

    Pritchard, H D; Ligtenberg, S R M; Fricker, H A; Vaughan, D G; van den Broeke, M R; Padman, L

    2012-04-26

    Accurate prediction of global sea-level rise requires that we understand the cause of recent, widespread and intensifying glacier acceleration along Antarctic ice-sheet coastal margins. Atmospheric and oceanic forcing have the potential to reduce the thickness and extent of floating ice shelves, potentially limiting their ability to buttress the flow of grounded tributary glaciers. Indeed, recent ice-shelf collapse led to retreat and acceleration of several glaciers on the Antarctic Peninsula. But the extent and magnitude of ice-shelf thickness change, the underlying causes of such change, and its link to glacier flow rate are so poorly understood that its future impact on the ice sheets cannot yet be predicted. Here we use satellite laser altimetry and modelling of the surface firn layer to reveal the circum-Antarctic pattern of ice-shelf thinning through increased basal melt. We deduce that this increased melt is the primary control of Antarctic ice-sheet loss, through a reduction in buttressing of the adjacent ice sheet leading to accelerated glacier flow. The highest thinning rates occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf. Wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of Antarctic ice shelves, through ocean upwelling in the Amundsen and Bellingshausen seas, and atmospheric warming on the Antarctic Peninsula. This implies that climate forcing through changing winds influences Antarctic ice-sheet mass balance, and hence global sea level, on annual to decadal timescales. PMID:22538614

  9. The response of grounded ice to ocean temperature forcing in a coupled ice sheet-ice shelf-ocean cavity model

    NASA Astrophysics Data System (ADS)

    Goldberg, D. N.; Little, C. M.; Sergienko, O. V.; Gnanadesikan, A.

    2010-12-01

    Ice shelves provide a pathway for the heat content of the ocean to influence continental ice sheets. Changes in the rate or location of basal melting can alter their geometry and effect changes in stress conditions at the grounding line, leading to a grounded ice response. Recent observations of ice streams and ice shelves in the Amundsen Sea sector of West Antarctica have been consistent with this story. On the other hand, ice dynamics in the grounding zone control flux into the shelf and thus ice shelf geometry, which has a strong influence on the circulation in the cavity beneath the shelf. Thus the coupling between the two systems, ocean and ice sheet-ice shelf, can be quite strong. We examine the response of the ice sheet-ice shelf-ocean cavity system to changes in ocean temperature using a recently developed coupled model. The coupled model consists a 3-D ocean model (GFDL's Generalized Ocean Layered Dynamics model, or GOLD) to a two-dimensional ice sheet-ice shelf model (Goldberg et al, 2009), and allows for changing cavity geometry and a migrating grounding line. Steady states of the coupled system are found even under considerable forcing. The ice shelf morphology and basal melt rate patterns of the steady states exhibit detailed structure, and furthermore seem to be unique and robust. The relationship between temperature forcing and area-averaged melt rate is influenced by the response of ice shelf morphology to thermal forcing, and is found to be sublinear in the range of forcing considered. However, results suggest that area-averaged melt rate is not the best predictor of overall system response, as grounding line stability depends on local aspects of the basal melt field. Goldberg, D N, D M Holland and C G Schoof, 2009. Grounding line movement and ice shelf buttressing in marine ice sheets, Journal of Geophysical Research-Earth Surfaces, 114, F04026.

  10. Observation of melt onset on multiyear Arctic sea ice using the ERS 1 synthetic aperture radar

    NASA Technical Reports Server (NTRS)

    Winebrenner, D. P.; Nelson, E. D.; Colony, R.; West, R. D.

    1994-01-01

    We present nearly coincident observations of backscattering from the Earth Remote-Sensing Satellite (ERS) 1 synthetic aperture radar (SAR) and of near-surface temperature from six drifting buoys in the Beaufort Sea, showing that the onset of melting in snow on multiyear sea ice is clearly detectable in the SAR data. Melt onset is marked by a clean, steep decrease in the backscattering cross section of multiyear ice at 5.3 GHz and VV polarization. We investigate the scattering physics responsible for the signature change and find that the cross section decrease is due solely to the appearance of liquid water in the snow cover overlying the ice. A thin layer of moist snow is sufficient to cause the observed decrease. We present a prototype algorithm to estimate the date of melt onset using the ERS 1 SAR and apply the algorithm first to the SAR data for which we have corresponding buoy temperatures. The melt onset dates estimated by the SAR algorithm agree with those obtained independently from the temperature data to within 4 days or less, with the exception of one case in which temperatures oscillated about 0 C for several weeks. Lastly, we apply the algorithm to the entire ERS 1 SAR data record acquired by the Alaska SAR Facility for the Beaufort Sea north of 73 deg N during the spring of 1992, to produce a map of the dates of melt onset over an area roughly 1000 km on a side. The progression of melt onset is primarily poleward but shows a weak meridional dependence at latitudes of approximately 76 deg-77 deg N. Melting begins in the southern part of the study region on June 13 and by June 20 has progressed to the northermost part of the region.

  11. Sea Ice Melt in Summer 2013 Figure 1. Results from six ice mass balance buoys that operated throughout the summer of 2013. The red

    E-print Network

    Sea Ice Melt in Summer 2013 Figure 1. Results from six ice mass balance buoys that operated is the MASIE ice extent on 28 August 2013 mapped on Google Earth. The 2013 Arctic sea ice melt season was observed at a buoy near the ice edge in the Beaufort Sea. This buoy had the largest total amount of melt

  12. Sea ice melting increase in the eastern Barents Sea during the last ca. 500 years

    NASA Astrophysics Data System (ADS)

    Rueda, G.; Rosell-Melé, A.; Massé, G.; Polyak, L.

    2012-04-01

    Climate conditions in the Arctic have changed considerably in the last decades. Sea ice cover is declining, temperatures are rising and the latest projections point to an ice free Arctic ocean at around 2040. To understand better climatic processes on such a sensitive and climatically significant region on the globe it is necessary to gain knowledge on the drivers of climate over time. Here we show a reconstruction of past sea ice and sea surface temperature (SST) variations in the eastern Barents Sea from sediment core PL96-126 (73° 37.5' N, 50° 43.0' E; 270m water depth) that spans the last ca. 4.400 years (Voronina et al. 2001). To achieve this goal, we used a recently developed biomarker based on highly branched isoprenoid lipid (IP25) synthesized by sea ice diatoms (Belt et al. 2007) to infer variations in past sea ice cover, together with the concentration of alkenones - algae synthesized lipids - from which we also estimated past SST (UK37' index) and fresh water mass variation (%C37:4). At lower resolution, we also analyzed the distributions of terrigenous lipids to obtain information on the origin of the organic matter, and finally the glycerol dialkyl glycerol tetraethers (GDGTs) which give an estimate of past sea surface temperature (TEX86) and air temperature (MBT/CBT indices). Three climatically distinct periods can be distinguished in the sediment record under study. A period from ca. 4.4 to 2.5 Kyr BP, had a generally stable sea ice cover and relatively short ice melting season, as inferred from the low IP25 and algal lipids concentrations, together with cold and freshened surface water. From ca. 2.5 to 1 Kyr BP there was a transition period with rather unstable conditions characterized by fluctuations in the biomarker indices. From ca. 1 Kyr BP until present, our data indicate a gradual increase in ice melting that accelerated during the last ca. 0.5 Kyr BP. This is in agreement with a previous reconstruction (Vare et al. 2010) suggesting a reduced sea ice cover for the last centuries. In contrast, a reconstruction for the last 7 Kyr BP from the central Canadian Arctic Archipelago (Belt et al. 2010) interpreted an increase in IP25 flux for the last 0.8 Kyr as higher sea ice occurrence. Here we interpret our IP25 data as suggested by Müller et al. (2011). The recent increase in IP25 represents an acceleration in ice melting during the last 500 years in the Barents Sea.

  13. 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.

  14. Calving fluxes and basal melt rates of Antarctic ice shelves.

    PubMed

    Depoorter, M A; Bamber, J L; Griggs, J A; Lenaerts, J T M; Ligtenberg, S R M; van den Broeke, M R; Moholdt, G

    2013-10-01

    Iceberg calving has been assumed to be the dominant cause of mass loss for the Antarctic ice sheet, with previous estimates of the calving flux exceeding 2,000?gigatonnes per year. More recently, the importance of melting by the ocean has been demonstrated close to the grounding line and near the calving front. So far, however, no study has reliably quantified the calving flux and the basal mass balance (the balance between accretion and ablation at the ice-shelf base) for the whole of Antarctica. The distribution of fresh water in the Southern Ocean and its partitioning between the liquid and solid phases is therefore poorly constrained. Here we estimate the mass balance components for all ice shelves in Antarctica, using satellite measurements of calving flux and grounding-line flux, modelled ice-shelf snow accumulation rates and a regional scaling that accounts for unsurveyed areas. We obtain a total calving flux of 1,321?±?144?gigatonnes per year and a total basal mass balance of -1,454?±?174?gigatonnes per year. This means that about half of the ice-sheet surface mass gain is lost through oceanic erosion before reaching the ice front, and the calving flux is about 34 per cent less than previous estimates derived from iceberg tracking. In addition, the fraction of mass loss due to basal processes varies from about 10 to 90 per cent between ice shelves. We find a significant positive correlation between basal mass loss and surface elevation change for ice shelves experiencing surface lowering and enhanced discharge. We suggest that basal mass loss is a valuable metric for predicting future ice-shelf vulnerability to oceanic forcing. PMID:24037377

  15. Bacterial Communities of Surface Mixed Layer in the Pacific Sector of the Western Arctic Ocean during Sea-Ice Melting

    PubMed Central

    Ha, Ho Kyung; Kim, Hyun Cheol; Kim, Ok-Sun; Lee, Bang Yong; Cho, Jang-Cheon; Hur, Hor-Gil; Lee, Yoo Kyung

    2014-01-01

    From July to August 2010, the IBRV ARAON journeyed to the Pacific sector of the Arctic Ocean to monitor bacterial variation in Arctic summer surface-waters, and temperature, salinity, fluorescence, and nutrient concentrations were determined during the ice-melting season. Among the measured physicochemical parameters, we observed a strong negative correlation between temperature and salinity, and consequently hypothesized that the melting ice decreased water salinity. The bacterial community compositions of 15 samples, includicng seawater, sea-ice, and melting pond water, were determined using a pyrosequencing approach and were categorized into three habitats: (1) surface seawater, (2) ice core, and (3) melting pond. Analysis of these samples indicated the presence of local bacterial communities; a deduction that was further corroborated by the discovery of seawater- and ice-specific bacterial phylotypes. In all samples, the Alphaproteobacteria, Flavobacteria, and Gammaproteobacteria taxa composed the majority of the bacterial communities. Among these, Alphaproteobacteria was the most abundant and present in all samples, and its variation differed among the habitats studied. Linear regression analysis suggested that changes in salinity could affect the relative proportion of Alphaproteobacteria in the surface water. In addition, the species-sorting model was applied to evaluate the population dynamics and environmental heterogeneity in the bacterial communities of surface mixed layer in the Arctic Ocean during sea-ice melting. PMID:24497990

  16. What Will Happen if Climate Variability and Change Cause Glacier and Polar Ice Cap Melting?

    NSDL National Science Digital Library

    2012-08-03

    This demonstration will show how increased temperatures will hasten the melting of ice in the environment, contributing to a rise in sea level and subsequent flooding of coastal areas. Materials required include 2 aquariums, plastic wrap, a clamp light with a 60 watt bulb, modeling clay, ice, pebbles and rocks, and a ruler. Teacher background information, student worksheets and a scoring rubric are included. This is Activity 3 of the learning module, Too Many Blankets, part of the lesson series, The Potential Consequences of Climate Variability and Change.

  17. Little Ice Age Cold Interval in West Antarctica: Evidence from Borehole Temperature at the West Antarctic Ice Sheet (WAIS) Divide.

    E-print Network

    Severinghaus, Jeffrey P.

    is the key evolving parameter. Preliminary measurements of the 3400m deep borehole indicate melting Model Description The forward firn and ice model is based on the 1 dimensional heat and ice flow the heat capacity, T the temperature, t the time, z the depth, w the downward velocity of the firn

  18. Svalbard summer melting, continentality, and sea ice extent from the Lomonosovfonna ice core

    Microsoft Academic Search

    Aslak Grinsted; John C. Moore; Veijo Pohjola; Tõnu Martma; Elisabeth Isaksson

    2006-01-01

    We develop a continentality proxy (1600-1930) based on amplitudes of the annual signal in oxygen isotopes in an ice core. We show via modeling that by using 5 and 15 year average amplitudes the effects of diffusion and varying layer thickness can be minimized, such that amplitudes then reflect real seasonal changes in delta18O under the influence of melt. A

  19. Svalbard summer melting, continentality, and sea ice extent from the Lomonosovfonna ice core

    Microsoft Academic Search

    Aslak Grinsted; John C. Moore; Veijo Pohjola; Tõnu Martma; Elisabeth Isaksson

    2006-01-01

    We develop a continentality proxy (1600–1930) based on amplitudes of the annual signal in oxygen isotopes in an ice core. We show via modeling that by using 5 and 15 year average amplitudes the effects of diffusion and varying layer thickness can be minimized, such that amplitudes then reflect real seasonal changes in ?18O under the influence of melt. A

  20. Influence of NaCl on ice VI and ice VII melting curves up to 6 GPa, implications for large icy moons

    NASA Astrophysics Data System (ADS)

    Journaux, B.; Daniel, I.; Caracas, R.; Montagnac, G.; Cardon, H.

    2013-09-01

    The influence of sodium chloride salt on the liquidus of ice VI and ice VII has been measured for concentrations ranging between 0.01 and 4 mol kg-1 NaCl. Dissolved NaCl significantly increases the melting pressure or decreases the melting temperature as a function of the salt concentration and induces a density crossover between ice VI and the brine. For NaCl concentrations higher than 2.5 mol kg-1 ice VI is more buoyant than the brine. The liquidus points are fitted to a second order polynomial law and a model is provided to predict the melting pressures of ice VI and ice VII (Pm,VI and Pm,VII), respectively as a function of temperature T (K) and NaCl concentration XNaCl (mol kg-1): Pm,VI(T,XNaCl)=9.27+0.996XNaCl-(6.99×10-2+7.6×10-3XNaCl)·T+(1.414×10-4+1.541×10-5XNaCl)·T2 Pm,VII(T,XNaCl)=-0.133+0.122XNaCl-(1.28×10-4+4.17×10-4XNaCl)·T+(1.86×10-5+8.56×10-7XNaCl)·T2 The temperature of the triple point between ice VI, ice VII and the brine shifts of -7 K/XNaCl along the 2.17 GPa isobar. The consequences of potentially dissolved NaCl for the internal structure of water rich planetary bodies are discussed. The density crossover between ice VI and brines suggests that migration of brines through a deep ice VI layer is enhanced for high thermal profiles and is unlikely for colder thermal conditions. It also suggests that patches of brines may actually be gravitationally stable at the interface between the bedrock and a deep ice VI basal layer allowing for a potential new class of exobiological habitat.

  1. The spatial distribution of solar radiation under a melting Arctic sea ice cover

    NASA Astrophysics Data System (ADS)

    Frey, Karen E.; Perovich, Donald K.; Light, Bonnie

    2011-11-01

    The sea ice cover of the Chukchi and Beaufort Seas is currently undergoing a fundamental shift from multiyear ice to first-year ice. Field observations of sea ice physical and optical properties were collected in this region during June-July 2010, revealing unexpectedly complex spatial distributions of solar radiation under the melt-season ice cover. Based on our optical measurements of first-year ice, we found the under-ice light field in the upper ocean to be spatially heterogeneous and dependent on wavelength, ice thickness, and the areal and geometric distribution of melt ponded and bare ice surfaces. Much of the observed complexity in radiation fields arose because the transmission of light through ponded ice was generally an order of magnitude greater than through bare, unponded ice. Furthermore, while many sites exhibited a consistent, exponential decay in light transmission through both ponded and bare ice surfaces, light transmission under bare ice was also observed to increase with depth (reaching maximum values ˜5-10 m below the bottom of the ice). A simple geometric model shows these transmission peaks are a result of scattering in the ice and the interspersion of bare and ponded sea ice surfaces. These new observations of complex radiation fields beneath melt-season first-year sea ice have significant implications for biological production, biogeochemical processes, and the heat balance of sea ice and under-ice ocean waters and should be carefully considered when modeling these sea ice-related phenomena.

  2. Recent Changes in Arctic Sea Ice Melt Onset, Freeze-Up, and Melt Season Length

    NASA Technical Reports Server (NTRS)

    Markus, Thorsten; Stroeve, Julienne C.; Miller, Jeffrey

    2010-01-01

    In order to explore changes and trends in the timing of Arctic sea ice melt onset and freeze-up and therefore melt season length, we developed a method that obtains this information directly from satellite passive microwave data, creating a consistent data set from 1979 through present. We furthermore distinguish between early melt (the first day of the year when melt is detected) and the first day of continuous melt. A similar distinction is made for the freeze-up. Using this method we analyze trends in melt onset and freeze-up for 10 different Arctic regions. In all regions except for the Sea of Okhotsk, which shows a very slight and statistically insignificant positive trend (O.4 days/decade), trends in melt onset are negative, i.e. towards earlier melt. The trends range from -1.0day/decade for the Bering Sea to -7.3 days/decade for the East Greenland Sea. Except for the Sea of Okhotsk all areas also show a trend towards later autumn freeze onset. The Chukchi/Beaufort Seas and Laptev/East Siberian Seas observe the strongest trends with 7 days/decade. For the entire Arctic, the melt season length has increased by about 20 days over the last 30 years. Largest trends of over 1O days/decade are seen for Hudson Bay, the East Greenland Sea the Laptev/East Siberian Seas, and the Chukchi/Beaufort Seas. Those trends are statistically significant a1 the 99% level.

  3. The dynamics of sea ice spring melt: Ramifications for high latitude marine ecosystems

    NASA Astrophysics Data System (ADS)

    Geiger, C. A.; Perovich, D. K.

    2006-12-01

    Oscillatory motion of sea ice nearly matching the local inertial period (i.e., near-inertial) is examined using two ice drifting buoys separated by one degree latitude around 66S in the Marguerite Bay region west of the Antarctic Peninsula. The oscillations are examined with respect to the kinematics involved in the breakup process of sea ice. These include hourly resolved manifestation of circular trajectories, semi-circular oscillations with compressed trajectory cusps, and "accordion-like" compressions along straight line trajectories. Oscillations are found in all trajectory types over the lifetime of both buoys (several months). Traditional circular and semi-circular oscillations are particularly prominent during two episodes, one of which is preceded by strong wind events and a substantial decrease in ice thickness and concentration. These episodes combine with seasonally warming temperatures to break up and melt the sea ice cover. We discuss potential relationships between the degradation of the ice pack during spring breakup and the increase in energy at near-inertial frequencies including a non-linear cascade of energy within the ice from the low frequencies (commensurate with storms and fortnightly tides) to semi-diurnal frequencies. We find these near- inertial oscillations are at their peak during the final decay of sea ice when springtime primary productivity begins. We further comment on the implications this type of high-frequency motion has on local biological ecosystems. Specifically, the oscillatory motion of sea ice not only serves as an effective mixing agent within the ice-ocean mixed layer, but also serves as an effective seeding platform for distributing phyto- and zooplankton that have over-wintered within and around the ice floes. This type of bio-physical coupling is very important from the modeling perspective of bio-physical processes and biomass productivity. These processes are currently in a dynamic-thermodynamic balance with air temperatures, light, nutrients, and the frequency of spring storms. Alternations of the climate may resort in differing phase shifts of the ice melt onset and storm frequency thereby creating new stresses to the local ecosystem.

  4. Multiparameter Radar Modeling and Observations of Melting Ice.

    NASA Astrophysics Data System (ADS)

    Vivekanandan, J.; Bringi, V. N.; Raghavan, R.

    1990-03-01

    This paper uses a microphysically detailed graupel and hail melting model, described by Rasmussen and Heymsfield, which is coupled to a radar model that computes multiparameter variables such as differential reflectivity, linear depolarization ratio, the specific propagation differential phase shift and X-band specific attenuation. The microphysical model is initialized with two different summer-time sounding profiles (Colorado and Alabama). Sensitivity studies are performed with respect to particle shape and orientation distributions. The hail melting model is also initialized with a summertime sounding from the Munich, FRG area, and C-band differential reflectivity is computed for application to radar data from the DFVLR radar. A simple spherical hail melting model is also used to study the effects of absorption and scattering on the X-band attenuation. NCAR CP-2 radar measurements from the MIST (Microburst and Severe Thunderstorm) project and from CINDE (Convective Initiation and Downburst Experiment) are used to illustrate the usefulness of multiparameter data in studying the melting of ice in convective storms.

  5. Evaluation of Surface and Near-Surface Melt Characteristics on the Greenland Ice Sheet using MODIS and QuikSCAT Data

    NASA Technical Reports Server (NTRS)

    Hall, Dorothy K.; Nghiem, Son V.; Schaaf, Crystal B.; DiGirolamo, Nicolo E.

    2009-01-01

    The Greenland Ice Sheet has been the focus of much attention recently because of increasing melt in response to regional climate warming. To improve our ability to measure surface melt, we use remote-sensing data products to study surface and near-surface melt characteristics of the Greenland Ice Sheet for the 2007 melt season when record melt extent and runoff occurred. Moderate Resolution Imaging Spectroradiometer (MODIS) daily land-surface temperature (LST), MODIS daily snow albedo, and a special diurnal melt product derived from QuikSCAT (QS) scatterometer data, are all effective in measuring the evolution of melt on the ice sheet. These daily products, produced from different parts of the electromagnetic spectrum, are sensitive to different geophysical features, though QS- and MODIS-derived melt generally show excellent correspondence when surface melt is present on the ice sheet. Values derived from the daily MODIS snow albedo product drop in response to melt, and change with apparent grain-size changes. For the 2007 melt season, the QS and MODIS LST products detect 862,769 square kilometers and 766,184 square kilometers of melt, respectively. The QS product detects about 11% greater melt extent than is detected by the MODIS LST product probably because QS is more sensitive to surface melt, and can detect subsurface melt. The consistency of the response of the different products demonstrates unequivocally that physically-meaningful melt/freeze boundaries can be detected. We have demonstrated that these products, used together, can improve the precision in mapping surface and near-surface melt extent on the Greenland Ice Sheet.

  6. Real-time Non-contact Millimeter Wave Characterization of Water-Freezing and Ice-Melting Dynamics

    SciTech Connect

    Sundaram, S. K.; Woskov, Paul P.

    2008-11-12

    We applied millimeter wave radiometry for the first time to monitor water-freezing and ice-melting dynamics in real-time non-contact. The measurements were completed at a frequency of 137 GHz. Small amounts (about 2 mL) of freshwater or saltwater were frozen over a Peltier cooler and the freezing and melting sequence was recorded. Saltwater was prepared in the laboratory that contained 3.5% of table salt to simulate the ocean water. The dynamics of freezing-melting was observed by measuring the millimeter wave temperature as well as the changes in the ice or water surface reflectivity and position. This was repeated using large amounts of freshwater and saltwater (800 mL) mimicking glaciers. Millimeter wave surface level fluctuations indicated as the top surface melted, the light ice below floated up indicating lower surface temperature until the ice completely melted. Our results are useful for remote sensing and tracking temperature for potentially large-scale environmental applications, e.g., global warming.

  7. Processes and imagery of first-year fast sea ice during the melt season

    NASA Technical Reports Server (NTRS)

    Holt, B.; Digby, S. A.

    1985-01-01

    In June and July 1982, a field program was conducted in the Canadian Arctic on Prince Patrick Island to study sea ice during the melt season with in situ measurements and microwave instrumentation operated near the surface and from aircraft. The objective of the program was to measure physical characteristics together with microwave backscatter and emission coefficients of sea ice during this major period of transition. The present paper is concerned with a study of both surface measurements and imagery of first-year fast ice during the melt season. The melting process observed in first-year fast ice was found to begin with the gradual reduction of the snow cover. For a two- to three-day period in this melt stage, a layer of superimposed ice nodules formed at the snow/ice interface as meltwater froze around ice and snow grains.

  8. Strong isotope effects on melting dynamics and ice crystallisation processes in cryo vitrification solutions.

    PubMed

    Kirichek, Oleg; Soper, Alan; Dzyuba, Boris; Callear, Sam; Fuller, Barry

    2015-01-01

    The nucleation and growth of crystalline ice during cooling, and further crystallization processes during re-warming are considered to be key processes determining the success of low temperature storage of biological objects, as used in medical, agricultural and nature conservation applications. To avoid these problems a method, termed vitrification, is being developed to inhibit ice formation by use of high concentration of cryoprotectants and ultra-rapid cooling, but this is only successful across a limited number of biological objects and in small volume applications. This study explores physical processes of ice crystal formation in a model cryoprotective solution used previously in trials on vitrification of complex biological systems, to improve our understanding of the process and identify limiting biophysical factors. Here we present results of neutron scattering experiments which show that even if ice crystal formation has been suppressed during quench cooling, the water molecules, mobilised during warming, can crystallise as detectable ice. The crystallisation happens right after melting of the glass phase formed during quench cooling, whilst the sample is still transiting deep cryogenic temperatures. We also observe strong water isotope effects on ice crystallisation processes in the cryoprotectant mixture. In the neutron scattering experiment with a fully protiated water component, we observe ready crystallisation occurring just after the glass melting transition. On the contrary with a fully deuteriated water component, the process of crystallisation is either completely or substantially supressed. This behaviour might be explained by nuclear quantum effects in water. The strong isotope effect, observed here, may play an important role in development of new cryopreservation strategies. PMID:25815751

  9. Variability of ice sheet thickness and water temperature in Arctic major rivers

    NASA Astrophysics Data System (ADS)

    PARK, H.; Yoshikawa, Y.; Oshima, K.

    2014-12-01

    Increasing river discharge to the Arctic Ocean is a very significant change in the Arctic system. Increase in surface temperature in the Arctic over the past decades was exceptionally higher in the history of arctic observations. The increased temperature resulted in changes in ice freezing and melting and water temperature in Arctic rivers. However, there are significant knowledge gaps in our understanding of the river-ice dynamics and river water temperature. Therefore, we assessed changes in ice sheet thickness, the timing of ice freezing and melting, and water temperature in Arctic major rivers during the period 1979-2009, based on observations and a hydrological model. The model can estimate ice thickness and water temperature using air temperature, snow depth, and river discharge. The calculated ice thickness and water temperature were compared with observations, showing generally significant correlations. The observed and calculated maximum ice thickness indicated decreasing trends at the outlet and inner points of rivers. The timing of ice breakup was also advanced. These changes were mostly significant during the recent three decades when the increase in air temperature was significant. The model also estimated increasing water temperatures, which is consistent with the observations. The warming of water temperature suggests influences on heat budget in the Arctic Ocean. This study validated the applicability for river-ice calculation of the hydrological model, and the model simulation provided useful information relating to the changing river-ice environments in the Arctic rivers.

  10. Observing the Arctic Ocean under melting ice - the UNDER-ICE project

    NASA Astrophysics Data System (ADS)

    Sagen, Hanne; Ullgren, Jenny; Geyer, Florian; Bergh, Jon; Hamre, Torill; Sandven, Stein; Beszczynska-Möller, Agnieszka; Falck, Eva; Gammelsrød, Tor; Worcester, Peter

    2014-05-01

    The sea ice cover of the Arctic Ocean is gradually diminishing in area and thickness. The variability of the ice cover is determined by heat exchange with both the atmosphere and the ocean. A cold water layer with a strong salinity gradient insulates the sea ice from below, preventing direct contact with the underlying warm Atlantic water. Changes in water column stratification might therefore lead to faster erosion of the ice. As the ice recedes, larger areas of surface water are open to wind mixing; the effect this might have on the water column structure is not yet clear. The heat content in the Arctic strongly depends on heat transport from other oceans. The Fram Strait is a crucial pathway for the exchange between the Arctic and the Atlantic Ocean. Two processes of importance for the Arctic heat and freshwater budget and the Atlantic meridional overturning circulation take place here: poleward heat transport by the West Spitzbergen Current and freshwater export by the East Greenland Current. A new project, Arctic Ocean under Melting Ice (UNDER-ICE), aims to improve our understanding of the ocean circulation, water mass distribution, fluxes, and mixing processes, sea ice processes, and net community primary production in ice-covered areas and the marginal ice zone in the Fram Strait and northward towards the Gakkel Ridge. The interdisciplinary project brings together ocean acoustics, physical oceanography, marine biology, and sea ice research. A new programme of observations, integrated with satellite data and state-of-the-art numerical models, will be started in order to improve the estimates of heat, mass, and freshwater transport between the North Atlantic and the Arctic Ocean. On this poster we present the UNDER-ICE project, funded by the Research Council of Norway and GDF Suez E&P Norge AS for the years 2014-2017, and place it in context of the legacy of earlier projects in the area, such as ACOBAR. A mooring array for acoustic tomography combined with "standard" oceanographic measurements of current velocity and water mass properties will be deployed in the Fram Strait in September 2014. The dynamic processes in the marginal ice zone, in particular internal waves, mesoscale eddies, and front instabilities, will be explored using model experiments and high temporal resolution measurements. The results of the observational data analysis and model simulations will be integrated and compared with global climate model simulations (CMIP5). Satellite-derived data products will also be included in the synthesis. As part of the UNDER-ICE project, a web portal for Arctic data will be developed, that will offer open access to metadata and observational and model data products to support studies of Arctic climate and climate change.

  11. Documenting Melting Features of the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Tedesco, M.

    2011-12-01

    There is an increasing interest in studying the Greenland Ice Sheet, its hydrology and dynamics over the short term and longer term because of the potential impact of a warming Arctic. Major studies concern about whether increased surface melting will lead to changes in production of supraglacial lakes and subglacial water pressures and hence , potentially, rates of ice movement. In this talk I will show movies recorded over the past three years form fieldwork activities carried out over the West Greenland ice sheet. In particular, I will project and comment movies concerning surface streams and supraglacial lakes, as the one at http://www.youtube.com/watch?v=QbuFphwJn4c. I will discuss the importance of observing such phenomena and how the recorded videos can be used to summarize scientific studies and communicate the relevance of scientific findings. I will also show, for the first time, the video of the drainage of a supraglacial lake, an event during which a lake ~ 6 m deep and ~ 1 km drained in ~ 1.5 hours. This section of the movie is under development as video material was collected during our latest expedition in June 2011.

  12. A Five-Year Record of Summer Melt on Eurasian Arctic Ice Caps

    Microsoft Academic Search

    Martin Sharp; Libo Wang

    2009-01-01

    Climatologies and annual anomaly patterns (2000-04) of melt season duration and dates of melt onset\\/ freeze-up on Eurasian Arctic ice masses were derived from Quick Scatterometer (QuikSCAT) backscatter data. Severnaya Zemlya, Russia, has later melt onset, earlier freeze-up, and shorter melt seasons than Svalbard, Norway\\/Novaya Zemlya, Russia. In all three archipelagos 2001 was the longest melt season and 2000 was

  13. J. Phys. Chem. 1903, 87, 4277-4201 4277 Molecular Dynamics Study of Ice Crystallite Melting

    E-print Network

    Stillinger, Frank

    J. Phys. Chem. 1903, 87, 4277-4201 4277 Molecular Dynamics Study of Ice Crystallite Melting Thomas been used to examine the melting process for a 250-moleculeice Ih crystallite. The ST2 potential moves inward eventuallyto consumethe entire hexagonal ice crystallite with which the simulation began

  14. 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

  15. Rapidly Melting Ice Caps of Northern Baffin Island: Insights From Cosmogenic and Conventional Radiocarbon Dating

    Microsoft Academic Search

    R. K. Anderson; G. H. Miller; J. P. Briner; N. Lifton; S. B. Devogel

    2006-01-01

    The interior plateau of northern Baffin Island in the eastern Canadian Arctic is home to several small (< 50 km2) ice caps whose melt has been well recorded since 1949. Modern equilibrium line altitude (ELA) is well above all existing ice and a continuation of current climatic conditions will lead to the disappearance of all ice on the plateau in

  16. Measurement of Latent Heat of Melting of Thermal Storage Materials for Dynamic Type Ice Thermal Storage

    NASA Astrophysics Data System (ADS)

    Sawada, Hisashi; Okada, Masashi; Nakagawa, Shinji

    In order to measure the latent heat of melting of ice slurries with various solute concentrations, an adiabatic calorimeter was constructed. Ice slurries were made from each aqueous solution of ethanol, ethylene glycol and silane coupling agent. The latent heat of melting of ice made from tap water was measured with the present calorimeter and the uncertainty of the result was one percent. Ice slurries were made both by mixing ice particles made from water with each aqueous solution and by freezing each aqueous solution with stirring in a vessel. The latent heat of melting of these ice slurries was measured with various concentrations of solution. The latent heat of melting decreased as the solute concentration or the freezing point depression increased. The latent heat of ice slurries made from ethanol or ethylene glycol aqueous solution agreed with that of ice made from pure water known already. The latent heat of melting of ice slurries made from silane coupling agent aqueous solution got smaller than that of ice made from pure water as the freezing point depression increased.

  17. Object-Based Aerial Photos Analysis for Arctic Sea Ice Melt Ponds and Pressure Ridges

    NASA Astrophysics Data System (ADS)

    Miao, X.; Xie, H.; Ke, C.; Lei, R.

    2014-12-01

    High resolution aerial photographs can provide detailed distribution of sea ice features so as to extract physical parameters to refine, validate, and improve climate models. For example, melt ponds play an important role in Earth's radiation balance since they strongly absorb solar radiation rather than reflecting it as snow and ice do. Furthermore, no previous studies have ever considered shadow in sea ice detection, which is ubiquitous in the aerial photographs especially in multi-year ice regions and during late melting phase. Based on our previous study, an object-based classification scheme is used to extract sea ice features including melt ponds and shadow from 163 selected aerial photographs taken during the Chinese National Arctic Research Expedition (CHINARE 2010). The classification algorithm includes three major steps as follows. (1) Image segmentation groups the neighboring pixels into objects according to the similarity of spectral and texture information; (2) random forest ensemble classifier can distinguish the following objects: water, general submerged ice, shadow, and ice/snow; and (3) polygon neighbor analysis can further separate melt ponds from general submerged ice according to the spatial neighboring relationship. Finally, the shadows are used to estimate the sea ice ridge distribution based on local solar illumination geometry. Our results illustrate the spatial distribution and morphological characters of melt ponds and ridges in different latitudes of the Arctic Pacific sector. This method can be applied to massive photos and images taken in past years and future years, in deriving the detailed sea ice feature distribution and changes through years.

  18. Analysis of summer 2002 melt extent on the Greenland ice sheet using MODIS and SSM/I data

    USGS Publications Warehouse

    Hall, D.K.; Williams, R.S., Jr.; Steffen, K.; Chien, J.Y.L.

    2004-01-01

    Previous work has shown that the summer of 2002 had the greatest area of snow melt extent on the Greenland ice sheet ever recorded using passive-microwave data. In this paper, we compare the 0?? isotherm derived from the Moderate-Resolution Imaging Spectroradiometer (MODIS) instrument, with Special Sensor Microwave/Imager (SSM/I)-derived melt, at the time of the maximum melt extent in 2002. To validate the MODIS-derived land-surface temperatures (LSTs), we compared the MODIS LSTs with air temperatures from nine stations (using 11 different data points) and found that they agreed to within 2.3??2.09??C, with station temperatures consistently lower than the MODIS LSTs. According to the MODIS LST, the maximum surface melt extended to ???2300 m in southern Greenland; while the SSM/I measurements showed that the maximum melt extended to nearly 2700 m in southeastern Greenland. The MODIS and SSM/I data are complementary in providing detailed information about the progression of surface and near-surface melt on the Greenland ice sheet.

  19. Analysis of Summer 2002 Melt Extent on the Greenland Ice Sheet using MODIS and SSM/I Data

    NASA Technical Reports Server (NTRS)

    Hall, Dorothy K.; Williams, Richard S., Jr.; Steffen, Konrad; Chien, Y. L.; Foster, James L.; Robinson, David A.; Riggs, George A.

    2004-01-01

    Previous work has shown that the summer of 2002 had the greatest area of snow melt extent on the Greenland ice sheet ever recorded using passive-microwave data. In this paper, we compare the 0 degree isotherm derived from the Moderate-Resolution Imaging Spectroradiometer (MODIS) instrument, with Special Sensor Microwave/Imager (SSM/I)-derived melt, at the time of the maximum melt extent in 2002. To validate the MODIS-derived land-surface temperatures (LSTs), we compared the MODIS LSTs with air temperatures from nine stations (using 11 different data points) and found that they agreed to within 2.3 plus or minus 2.09 C, with station temperatures consistently lower than the MODIS LSTs. According to the MODIS LST, the maximum surface melt extended to approximately 2300 m in southern Greenland; while the SSM/I measurements showed that the maximum melt extended to nearly 2700 m in southeastern Greenland. The MODIS and SSM/I data are complementary in providing detailed information about the progression of surface and near-surface melt on the Greenland ice sheet.

  20. Analysis of Summer 2002 Melt Extent on the Greenland Ice Sheet using MODIS and SSM/I Data

    NASA Technical Reports Server (NTRS)

    Hall, Dorothy K.; Williams, Richard S.; Steffen, Konrad; Chien, Janet Y. L.

    2004-01-01

    Previous work has shown that the summer of 2002 had the greatest area of snow melt extent on the Greenland ice sheet ever recorded using passive-microwave data. In this paper, we compare the 0 deg. isotherm derived from the Moderate-Resolution Imaging Spectroradiometer (MODIS) instrument, with Special Sensor Microwave/Imager (SSM/I)-derived melt, at the time of the maximum melt extent in 2002. To validate the MODIS derived land-surface temperatures (LSTs), we compared the MODIS LSTs with air temperatures from nine stations (using 11 different data points) and found that they agreed to within 2.3 +/- 2.09 C, with station temperatures consistently lower than the MODIS LSTs. According to the MODIS LST, the maximum surface melt extended to approx. 2300 m in southern Greenland; while the SSM/I measurements showed that the maximum melt extended to nearly 2700 m in southeastern Greenland. The MODIS and SSM/I data are complementary in providing detailed information about the progression of surface and near- surface melt on the Greenland ice sheet.

  1. Ice-melt collapse pits and associated features in the 1991 lahar deposits of Volcán Hudson, Chile: criteria to distinguish eruption-induced glacier melt

    Microsoft Academic Search

    Michael J. Branney; Jennie S. Gilbert

    1995-01-01

    In subaerial volcaniclastic sequences, structures formed by ice blocks can provide information about a volcano's history of lahar generation by glacier melt. At Volcán Hudson in Chile, catastrophic lahars were initiated by eruption-induced melting of glacier ice in August and October 1991. They transported large ice blocks 50?km down the Rio de los Huemules valley to the sea. Large current

  2. Ice-melt collapse pits and associated features in the 1991 lahar deposits of Volcán Hudson, Chile: criteria to distinguish eruption-induced glacier melt

    Microsoft Academic Search

    M. J. Branney; J. S. Gilbert

    1995-01-01

    In subaerial volcaniclastic sequences structures formed by ice blocks can provide information about a volcano's history of lahar generation by glacier melt. At Volcán Hudson in Chile, catastrophic lahars were initiated by eruption-induced melting of glacier ice in August and October 1991. They transported large ice blocks 50 km down the Rio de los Huemules valley to the sea. Large

  3. Simulation of Melting Ice-Phase Precipitation Hydrometeors for Use in Passive and Active Microwave Remote-Sensing Algorithms

    NASA Astrophysics Data System (ADS)

    Johnson, B. T.

    2014-12-01

    The Global Precipitation Measurement (GPM) mission, with active and passive microwave remote-sensing instruments, was designed to be sensitive to precipitation-sized particles. The shape of these particles naturally influences the distribution of scattered microwaves. Therefore, we seek to simulate ice-phase precipitation using accurate models of the physical properties of individual snowflakes and aggregate ice crystals, similar to those observed in precipitating clouds. A number of researchers have examined the single-scattering properties of individual ice crystals and aggregates, but only a few have started to look at the properties of melting these particles. One of the key difficulties, from a simulation perspective, is characterizing the distribution of melt-water on a melting particle. Previous studies by the author and others have shown that even for spherical particles, the relative distribution of liquid water on an ice-particle can have significant effects on the computed scattering and absorption properties in the microwave regime. This, in turn, strongly influences forward model simulations of passive microwave TBs, radar reflectivities, and path-integrated attenuation. The present study examines the sensitivity of the single scattering properties of melting ice-crystals and aggregates to variations in the volume fraction of melt water, and the distribution of meltwater. We make some simple simulations 1-D vertical profiles having melting layers, and compute the radar reflectivities consistent with the GPM DPR at Ku- and Ka-band. We also compute the top-of-the-atmosphere brightness temperatures at GPM GMI channels for the same vertical profiles, and discuss the sensitivities to variances in the aforementioned physical properties.

  4. Two-stage melting of the ice Ih (0001) surface by molecular dynamics: A molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Kuga, Mizuki; Iyetomi, Hiroshi

    2014-03-01

    We report a molecular dynamics simulation study of the structure and energetics of Ice Ih with a free basal (0001) surface. Especially we cast a new light on the formation of a quasi-liquid layer (QLL) at the surface prior to the melting of bulk ice. Detailed analysis of functional behavior of the total and potential energies with respect to temperature clearly separates the surface melting process into two stages. As temperature is increased, the outermost bilayer of the ideal surface first starts disordering in a progressive way with detachment of water molecules from the surface. During this first stage of surface melting, the energies show no discontinuous change as a function of temperature. Subsequently to fully developed disordering of the top layer, the surface shows stepwise melting in a narrow temperature range of around 10 K . This second stage of surface melting has first-order phase-transition-like characteristics as demonstrated by structural relaxation from an initial metastable (super-heating) state to the stable state during which the surface is liquefied layer by layer. Accordingly, it turns out that each of the stable QLL states designated by the number of liquefied bilayers has its own branch of the potential energy.

  5. Changes in Arctic Melt Season and Implications for Sea Ice Loss

    NASA Technical Reports Server (NTRS)

    Stroeve, J. C.; Markus, T.; Boisvert, L.; Miller, J.; Barrett, A.

    2014-01-01

    The Arctic-wide melt season has lengthened at a rate of 5 days dec-1 from 1979 to 2013, dominated by later autumn freeze-up within the Kara, Laptev, East Siberian, Chukchi and Beaufort seas between 6 and 11 days dec(exp -1). While melt onset trends are generally smaller, the timing of melt onset has a large influence on the total amount of solar energy absorbed during summer. The additional heat stored in the upper ocean of approximately 752MJ m(exp -2) during the last decade, increases sea surface temperatures by 0.5 to 1.5 C and largely explains the observed delays in autumn freeze-up within the Arctic Ocean's adjacent seas. Cumulative anomalies in total absorbed solar radiation from May through September for the most recent pentad locally exceed 300-400 MJ m(exp -2) in the Beaufort, Chukchi and East Siberian seas. This extra solar energy is equivalent to melting 0.97 to 1.3 m of ice during the summer.

  6. Delineation of Surface and Near-Surface Melt on the Greenland Ice Sheet Using MODIS and QuikSCAT data

    NASA Technical Reports Server (NTRS)

    Hall, Dorothy K.; Nghiem, Son V.; DiGirolamo, Nicolo E.; Neumann, Gregory; Schaaf, Crystal B.

    2010-01-01

    This slide presentation reviews the use of MODIS and QuikSCAT data to measure the surface and sub-surface melting on the Greenland Ice Sheet. The project demonstrated the consistence of this technique for measuring the ice melt on the Greenland Ice Sheet. The blending of the two instruments data allows for determination of surface vs subsurface melting. Also, the use of albedo maps can provide information about the intensity of the melting.

  7. Snow to Ice to Water: Melt Ponds, Moulins, and Surging Glaciers

    NSDL National Science Digital Library

    Carol Landis

    This article describes the work of Dr. Jason Box, a researcher studying summer melt ponds on Greenland's ice sheets and the response of glaciers to try to explain the changes in climate that are being observed in the polar regions.

  8. Sum-frequency spectroscopic studies: I. Surface melting of ice, II. Surface alignment of polymers

    SciTech Connect

    Wei, Xing

    2000-12-21

    Surface vibrational spectroscopy via infrared-visible sum-frequency generation (SFG) has been established as a useful tool to study the structures of different kinds of surfaces and interfaces. This technique was used to study the (0001) face of hexagonal ice (Ih). SFG spectra in the O-H stretch frequency range were obtained at various sample temperatures. For the vapor(air)/ice interface, the degree of orientational order of the dangling OH bonds at the surface was measured as a function of temperature. Disordering sets in around 200 K and increases dramatically with temperature, which is strong evidence of surface melting of ice. For the other ice interfaces (silica/OTS/ice and silica/ice), a similar temperature dependence of the hydrogen bonded OH stretch peak was observed; the free OH stretch mode, however, appears to be different from that of the vapor (air)/ice interface due to interactions at the interfaces. The technique was also used to measure the orientational distributions of the polymer chains on a rubbed polyvinyl alcohol surface. Results show that the polymer chains at the surface appear to be well aligned by rubbing, and the adsorbed liquid crystal molecules are aligned, in turn, by the surface polymer chains. A strong correlation exists between the orientational distributions of the polymer chains and the liquid crystal molecules, indicating that the surface-induced bulk alignment of a liquid crystal film by rubbed polymer surfaces is via an orientational epitaxy-like mechanism. This thesis also contains studies on some related issues that are crucial to the above applications. An experiment was designed to measure SFG spectra in both reflection and transmission. The result confirms that SFG in reflection is generally dominated by the surface contribution. Another issue is the motional effect due to fast orientational motion of molecules at a surface or interface. Calculations show that the effect is significant if the molecular orientation varies over a broad range within the vibrational relaxation time. The stretch vibration of the free OH bonds at the vapor/water interface is used to illustrate the importance of the effect.

  9. An experimental investigation into the icing and melting process of a water droplet impinging onto a superhydrophobic surface

    NASA Astrophysics Data System (ADS)

    Jin, ZheYan; Jin, SongYue; Yang, ZhiGang

    2013-11-01

    The freezing and melting process of a small water droplet on a superhydrophobic cold surface was investigated using the Laser Induced Fluorescence (LIF) technique. The superhydrophobic surface was prepared using a sol-gel method on a red copper test plate. From the obtained fluorescence images, the phase transition characteristics during the freezing and melting process of a water droplet were clearly observed. It was found that, at the beginning of the droplet freezing process, liquid water turned into ice at a very fast rate. Such phase transition process decreased gradually with time and the volume of frozen ice approached a constant value at the end of the icing process. In addition, the freezing time was found to reduce with the decrease of the test plate temperature. Besides, when the test plate temperature is relatively high, the effect of droplet volume on the freezing time is very significant. Over all, we provide some tentative insights into the microphysical process related to the icing and melting process of water droplets.

  10. Characteristics of two distinct high-light acclimated algal communities during advanced stages of sea ice melt

    Microsoft Academic Search

    C. J. Mundy; Michel Gosselin; Jens K. Ehn; Claude Belzile; Michel Poulin; Eva Alou; Suzanne Roy; Haakon Hop; Sylvie Lessard; Tim N. Papakyriakou; David G. Barber; Jeremy Stewart

    Biological characteristics of ice-associated algal communities were studied in Darnley Bay (western Canadian Arctic) during\\u000a a 2-week period in July 2008 when the landfast ice cover had reached an advanced stage of melt. We found two distinct and\\u000a separate algal communities: (1) an interior ice community confined to brine channel networks beneath white ice covers; and\\u000a (2) an ice melt

  11. Sensitivity of the Weddell Sea sector ice streams to sub-shelf melting and surface accumulation

    NASA Astrophysics Data System (ADS)

    Wright, A. P.; Le Brocq, A. M.; Cornford, S. L.; Bingham, R. G.; Corr, H. F. J.; Ferraccioli, F.; Jordan, T. A.; Payne, A. J.; Rippin, D. M.; Ross, N.; Siegert, M. J.

    2014-11-01

    A recent ocean modelling study indicates that possible changes in circulation may bring warm deep-ocean water into direct contact with the grounding lines of the Filchner-Ronne ice streams, suggesting the potential for future ice losses from this sector equivalent to ~0.3 m of sea-level rise. Significant advancements have been made in our knowledge of both the basal topography and ice velocity in the Weddell Sea sector, and the ability to accurately model marine ice sheet dynamics, thus enabling an assessment to be made of the relative sensitivities of the diverse collection of ice streams feeding the Filchner-Ronne Ice Shelf. Here we use the BISICLES ice sheet model, which employs adaptive-mesh refinement to resolve grounding line dynamics, to carry out such an assessment. The impact of realistic perturbations to the surface and sub-shelf mass balance forcing fields from our 2000-year "reference" model run indicate that both the Institute and Möller ice streams are highly sensitive to changes in basal melting either near to their respective grounding lines, or in the region of the ice rises within the Filchner-Ronne Ice Shelf. These same perturbations have little impact, however, on the Rutford, Carlson or Foundation ice streams, while the Evans Ice Stream is found to enter a phase of unstable retreat only after melt at its grounding line has increased by 50% of likely present-day values.

  12. Ocean Properties and Submarine Melt of Ice Shelves in a High-Arctic Fiord (Milne Fiord)

    NASA Astrophysics Data System (ADS)

    Hamilton, A.; Mueller, D.; Laval, B.

    2014-12-01

    The role of ambient stratification, the vertical distribution of heat, and fiord circulation on submarine melt rates in glacial fiords in the Canadian Arctic are largely unknown despite recent widespread collapse of ice shelves in this region. A 3-year field study was conducted to investigate ocean influence on ice loss from an ice shelf and glacier tongue in Milne Fiord (82oN), Ellesmere Island. Direct ocean observations of the sub-ice cavities from through-ice profiles showed a vertically stratified water column consisting of a perennial fresh ice-dammed epishelf lake at the surface, above cold relatively fresh Polar Water, and warm saline waters from the upper halocline of the Atlantic layer at depth. The broad continental shelf and a topographic sill prevented the warmest waters of the Atlantic layer from entering the 450 m deep fiord. Meltwater concentrations were highest near the glacier grounding line, with meltwater exported at depth due to the strong ambient stratification. There was little evidence of increased buoyancy-driven melt in summer from subglacial discharge as observed in sub-Arctic fiords (e.g. southern Greenland), suggesting that circulation in high-latitude fiords is largely melt-driven convection with less pronounced seasonality. Basal melt rates estimated using three methods, meltwater flux, divergence of ice flux, and an ocean thermodynamic model, were broadly consistent. Average melt rates of 0.75 ± 0.46 m a-1 and 1.14 ± 0.83 m a-1 were found for the Milne Ice Shelf and Milne Glacier Tongue, respectively, although showed high spatial variability. The highest melt rates (~4 m a-1) were found near the glacier grounding line and were driven by warm upper halocline waters. Similar melt rates occurred in near-surface waters driven by solar heating of the epishelf lake, enhancing melt along the margins of the glacier tongue and the landward edge of the ice shelf. The Milne Ice Shelf and Milne Glacier Tongue are in a state of negative mass balance; with submarine ice melt accounting for the majority of mass loss over the duration of the study. Submarine melt rates in this region are influenced by the thickness (and presence) of the epishelf lake, and are sensitive to external changes in the Arctic Ocean, including variations in the depth of the upper halocline and the heat content of polar surface waters.

  13. Assessing Antarctica's Ice Shelves for Vulnerability to Surface-Melt-Induced Collapse Using Scatterometry

    NASA Astrophysics Data System (ADS)

    Alley, K. E.; Scambos, T. A.; Long, D. G.

    2014-12-01

    The disintegration of several ice shelves on the Antarctic Peninsula since 1995 initiated a rapid increase in ice flow, altering the regional mass balance. A key element of disintegration appears to be the formation of surface melt ponds, which can trigger a run-away hydrofracturing process. A shelf's firn layer must be saturated with ice for ponds to form at the surface. This study presents a comparison of wintertime satellite-derived active microwave backscatter and surface melt-day data, revealing a distinctive pattern that can be used to assess the state of ice shelf firn. Low melt areas (1 to 10 days of melting per year) have few refrozen meltwater lenses within the firn to serve as scatterers, so they have low backscatter values (-10 to -5 dB ?o). As the mean number of melt days and therefore the abundance of ice lenses in the firn increases, backscatter values rise significantly to a peak at approximately 30 to 50 days of melt and approximately -1 dB ?o. With increasing melt beyond this threshold, mean wintertime backscatter declines, reaching -5 dB ?o at 80 to 100 melt days/year. This drop in backscatter reflects an increase in specular reflections from an ice-saturated firn layer. All ice shelves that have previously collapsed plot above this threshold. This pattern mirrors the characteristics of snow facies as observed in these same data types for transects across the Greenland Ice Sheet. Backscatter values on Antarctic ice shelves are also sensitive to accumulation rate, with higher accumulation requiring more melt days to produce the same level of backscatter increase. We hypothesize that, as the atmosphere warms in the future, ice shelves will evolve upwards along this pattern until they reach the firn saturation threshold where collapse is imminent. Therefore, a comprehensive survey of Antarctic ice shelves using scatterometry indicates which shelves are presently most vulnerable to surface-melt-induced collapse, and which shelves are likely to be vulnerable in the relatively near future.

  14. Can Arctic Sea Ice Summer Melt be Accelerated by Changes in Spring Cloud Properties?

    Microsoft Academic Search

    I. Gorodetskaya; B. Tremblay; B. Liepert; M. Cane

    2006-01-01

    Ice-albedo feedback remains the major factor accelerating recently observed decline in the Arctic sea ice extent and thickness. The immediate effect of this feedback is offset by clouds, which decrease the amount of solar radiation reaching the surface in summer. However, once the surface albedo is decreased due to an increase in the open water fraction or enhanced snow melt,

  15. Predominance of ß-proteobacteria in summer melt pools on Arctic pack ice

    Microsoft Academic Search

    Robin Brinkmeyer; Frank-Oliver Glöckner; Elisabeth Helmke; Rudolf Amann

    2004-01-01

    The diversity and community structure of bacteria in melt pools on Arctic pack ice floes were dominated by b- proteobacteria. Thirty-five percent of the pure cultures isolated in 1997 from pack ice floes north of Svalbard and in the Fram Strait were from the b-proteobacteria group. Within this group, there were only two phylotypes clus- tering within the widespread Beta

  16. 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

  17. 2 Internal melting in Antarctic sea ice: Development of ``gap layers'' 3 S. F. Ackley,1

    E-print Network

    Texas at San Antonio, University of

    2 Internal melting in Antarctic sea ice: Development of ``gap layers'' 3 S. F. Ackley,1 M. J. Lewis April 2008; published XX Month 2008. 6 [1] An internal ``gap'' layer of deteriorated sea ice is co- 7 located with a significant microbial biological community in 8 late first year and second year Antarctic

  18. Melting of the Patagonian Ice Sheet and deglacial perturbations of the nitrogen cycle in the eastern South Pacific

    E-print Network

    Demouchy, Sylvie

    Melting of the Patagonian Ice Sheet and deglacial perturbations of the nitrogen cycle of the Patagonian Ice Sheet. We consequently attribute the deglacial onset of marine denitrification in the area), Melting of the Patagonian Ice Sheet and deglacial perturbations of the nitrogen cycle in the eastern South

  19. Honeycomb artificial spin ice at low temperatures

    NASA Astrophysics Data System (ADS)

    Zeissler, Katharina; Chadha, Megha; Cohen, Lesley; Branford, Will

    2015-03-01

    Artificial spin ice is a macroscopic playground for magnetically frustrated systems. It consists of a geometrically ordered but magnetically frustrated arrangement of ferromagnetic macros spins, e.g. an arrangement of single domain ferromagnetic nanowires on a honeycomb lattice. Permalloy and cobalt which have critical temperature scales far above 290 K, are commonly used in the construction of such systems. Previous measurements have shown unusual features in the magnetotransport signature of cobalt honeycomb artificial spin ice at temperatures below 50 K which are due to changes in the artificial spin ice's magnetic reversal. In that case, the artificial spin ice bars were 1 micron long, 100 nm wide and 20 nm thick. Here we explore the low temperature magnetic behavior of honeycomb artificial spin ice structures with a variety of bar dimensions, indirectly via electrical transport, as well as, directly using low temperature magnetic imaging techniques. We discuss the extent to which this change in the magnetic reversal at low temperatures is generic to the honeycomb artificial spin ice geometry and whether the bar dimensions have an influence on its onset temperature. The EPSRC (Grant No. EP/G004765/1; Grant No. EP/L504786/1) and the Leverhulme Trust (Grant No. RPG 2012-692) funded this scientific work.

  20. A three-phase free boundary problem with melting ice and dissolving gas

    E-print Network

    Maurizio Ceseri; John M. Stockie

    2014-11-05

    We develop a mathematical model for a three-phase free boundary problem in one dimension that involves the interactions between gas, water and ice. The dynamics are driven by melting of the ice layer, while the pressurized gas also dissolves within the meltwater. The model incorporates a Stefan condition at the water-ice interface along with Henry's law for dissolution of gas at the gas-water interface. We employ a quasi-steady approximation for the phase temperatures and then derive a series solution for the interface positions. A non-standard feature of the model is an integral free boundary condition that arises from mass conservation owing to changes in gas density at the gas-water interface, which makes the problem non-self-adjoint. We derive a two-scale asymptotic series solution for the dissolved gas concentration, which because of the non-self-adjointness gives rise to a Fourier series expansion in eigenfunctions that do not satisfy the usual orthogonality conditions. Numerical simulations of the original governing equations are used to validate the series approximations.

  1. Natural and human contribution to recent Arctic sea-ice melting patterns

    NASA Astrophysics Data System (ADS)

    Min, Seung-Ki; Heo, Joonghyeok; Kim, Baek-Min; Kim, Seong-Joong

    2015-04-01

    Arctic sea-ice has declined sharply during recent three decades with seasonally and regionally different melting patterns. Identifying causes of the spatial patterns of Arctic sea-ice loss is critical to better understanding of global and regional impacts of Arctic cryosphere, but it remains uncertain. This study conducts a quantitative analysis of recent sea-ice melting by comparing observed and model-simulated trend patterns using an optimal fingerprinting technique. Satellite observations show overall decreasing trends across all seasons with stronger melting occurring over Kara-Laptev Seas, E. Siberia-Chukchi Seas, and Barents Seas during warm seasons. The CMIP5 multi-model simulations including greenhouse-gas forcings can largely capture the observed trend patterns, enabling detection of human influence, but with weaker amplitude. As natural factors of observed sea-ice melting, the Arctic Oscillation (AO) and Atlantic Multidecadal Oscillation (AMO) are further considered. AMO exhibits a significant impact on regional variation of sea-ice melting patterns while AO impact is found very weak. Good agreement can be obtained between observed and model-simulated trend patterns when taking account of the AMO influence on observations. This result suggests contribution of both human and natural factors to the recent abrupt reduction in Arctic sea ice.

  2. Links Between Acceleration, Melting, and Supraglacial Lake Drainage of the Western Greenland Ice Sheet

    NASA Technical Reports Server (NTRS)

    Hoffman, M. J.; Catania, G. A.; Newmann, T. A.; Andrews, L. C.; Rumrill, J. A.

    2012-01-01

    The impact of increasing summer melt on the dynamics and stability of the Greenland Ice Sheet is not fully understood. Mounting evidence suggests seasonal evolution of subglacial drainage mitigates or counteracts the ability of surface runoff to increase basal sliding. Here, we compare subdaily ice velocity and uplift derived from nine Global Positioning System stations in the upper ablation zone in west Greenland to surface melt and supraglacial lake drainage during summer 2007. Starting around day 173, we observe speedups of 6-41% above spring velocity lasting approximately 40 days accompanied by sustained surface uplift at most stations, followed by a late summer slowdown. After initial speedup, we see a spatially uniform velocity response across the ablation zone and strong diurnal velocity variations during periods of melting. Most lake drainages were undetectable in the velocity record, and those that were detected only perturbed velocities for approximately 1 day, suggesting preexisting drainage systems could efficiently drain large volumes of water. The dynamic response to melt forcing appears to 1) be driven by changes in subglacial storage of water that is delivered in diurnal and episodic pulses, and 2) decrease over the course of the summer, presumably as the subglacial drainage system evolves to greater efficiency. The relationship between hydrology and ice dynamics observed is similar to that observed on mountain glaciers, suggesting that seasonally large water pressures under the ice sheet largely compensate for the greater ice thickness considered here. Thus, increases in summer melting may not guarantee faster seasonal ice flow.

  3. Mechanisms and implications of ?-HCH enrichment in melt pond water on Arctic sea ice.

    PubMed

    Pu?ko, M; Stern, G A; Barber, D G; Macdonald, R W; Warner, K-A; Fuchs, C

    2012-11-01

    During the summer of 2009, we sampled 14 partially refrozen melt ponds and the top 1 m of old ice in the pond vicinity for ?-hexachlorocyclohexane (?-HCH) concentrations and enantiomer fractions (EFs) in the Beaufort Sea. ?-HCH concentrations were 3 - 9 times higher in melt ponds than in the old ice. We identify two routes of ?-HCH enrichment in the ice over the summer. First, atmospheric gas deposition results in an increase of ?-HCH concentration from 0.07 ± 0.02 ng/L (old ice) to 0.34 ± 0.08 ng/L, or ~20% less than the atmosphere-water equilibrium partitioning concentration (0.43 ng/L). Second, late-season ice permeability and/or complete ice thawing at the bottom of ponds permit ?-HCH rich seawater (~0.88 ng/L) to replenish pond water, bringing concentrations up to 0.75 ± 0.06 ng/L. ?-HCH pond enrichment may lead to substantial concentration patchiness in old ice floes, and changed exposures to biota as the surface meltwater eventually reaches the ocean through various drainage mechanisms. Melt pond concentrations of ?-HCH were relatively high prior to the late 1980-s, with a Melt pond Enrichment Factor >1 (MEF; a ratio of concentration in surface meltwater to surface seawater), providing for the potential of increased biological exposures. PMID:23039929

  4. Circulation of modified Circumpolar Deep Water and basal melt beneath the Amery Ice Shelf, East Antarctica

    NASA Astrophysics Data System (ADS)

    Herraiz-Borreguero, Laura; Coleman, Richard; Allison, Ian; Rintoul, Stephen R.; Craven, Mike; Williams, Guy D.

    2015-04-01

    Antarctic ice sheet mass loss has been linked to an increase in oceanic heat supply, which enhances basal melt and thinning of ice shelves. Here we detail the interaction of modified Circumpolar Deep Water (mCDW) with the Amery Ice Shelf, the largest ice shelf in East Antarctica, and provide the first estimates of basal melting due to mCDW. We use subice shelf ocean observations from a borehole site (AM02) situated ˜70 km inshore of the ice shelf front, together with open ocean observations in Prydz Bay. We find that mCDW transport into the cavity is about 0.22 ± 0.06 Sv (1 Sv = 106 m3 s-1). The inflow of mCDW drives a net basal melt rate of up to 2 ± 0.5 m yr-1 during 2001 (23.9 ± 6.52 Gt yr-1 from under about 12,800 km2 of the north-eastern flank of the ice shelf). The heat content flux by mCDW at AM02 shows high intra-annual variability (up to 40%). Our results suggest two main modes of subice shelf circulation and basal melt regimes: (1) the "ice pump"/high salinity shelf water circulation, on the western flank and (2) the mCDW meltwater-driven circulation in conjunction with the "ice pump," on the eastern flank. These results highlight the sensitivity of the Amery's basal melting to changes in mCDW inflow. Improved understanding of such ice shelf-ocean interaction is crucial to refining projections of mass loss and associated sea level rise.

  5. Comparison of DMSP SSM/I and Landsat 7 ETM+ Sea Ice Concentrations During Summer Melt

    NASA Technical Reports Server (NTRS)

    Cavalieri, Donald J.; Markus, Thorsten; Ivanoff, Alvaro; Koblinsky, Chester J. (Technical Monitor)

    2001-01-01

    As part of NASA's EOS Aqua sea ice validation program for the Advanced Microwave Scanning Radiometer (AMSR-E), Landsat 7 Enhanced Thematic Mapper (ETM+) images were acquired to develop a sea ice concentration data set with which to validate AMSR-E sea ice concentration retrievals. The standard AMSR-E Arctic sea ice concentration product will be obtained with the enhanced NASA Team (NT2) algorithm. The goal of this study is to assess the accuracy to which the NT2 algorithm, using DMSP Special Sensor Microwave Imager radiances, retrieves sea ice concentrations under summer melt conditions. Melt ponds are currently the largest source of error in the determination of Arctic sea ice concentrations with satellite passive microwave sensors. To accomplish this goal, Landsat 7 ETM+ images of Baffin Bay were acquired under clear sky conditions on the 26th and 27th of June 2000 and used to generate high-resolution sea ice concentration maps with which to compare the NT2 retrievals. Based on a linear regression analysis of 116 25-km samples, we find that overall the NT2 retrievals agree well with the Landsat concentrations. The regression analysis yields a correlation coefficient of 0.98. In areas of high melt ponding, the NT2 retrievals underestimate the sea ice concentrations by about 12% compared to the Landsat values.

  6. Investigation of the effects of summer melt on the calculation of sea ice concentration using active and passive microwave data

    Microsoft Academic Search

    Donald J. Cavalieri; Barbara A. Burns; Robert G. Onstott

    1990-01-01

    Active and passive microwave data sets acquired during the 1984 Marginal Ice Zone (MIZ) Experiment aircraft flights in the Fram Strait region are used to examine the effects of ice surface melt on microwave signatures and their resulting error in the calculation of sea ice concentration. Conditions examined with the active-passive data set include ice floes with moist and dry

  7. Internal stress-induced melting below melting temperature at high-rate laser heating

    SciTech Connect

    Hwang, Yong Seok, E-mail: yshwang@iastate.edu [Department of Aerospace Engineering, Iowa State University, Ames, Iowa 50011 (United States); Levitas, Valery I., E-mail: vlevitas@iastate.edu [Departments of Aerospace Engineering, Mechanical Engineering, and Material Science and Engineering, Iowa State University, Ames, Iowa 50011 (United States)

    2014-06-30

    In this Letter, continuum thermodynamic and phase field approaches (PFAs) predicted internal stress-induced reduction in melting temperature for laser-irradiated heating of a nanolayer. Internal stresses appear due to thermal strain under constrained conditions and completely relax during melting, producing an additional thermodynamic driving force for melting. Thermodynamic melting temperature for Al reduces from 933.67?K for a stress-free condition down to 898.1?K for uniaxial strain and to 920.8?K for plane strain. Our PFA simulations demonstrated barrierless surface-induced melt nucleation below these temperatures and propagation of two solid-melt interfaces toward each other at the temperatures very close to the corresponding predicted thermodynamic equilibrium temperatures for the heating rate Q?1.51×10{sup 10}K/s. At higher heating rates, kinetic superheating competes with a reduction in melting temperature and melting under uniaxial strain occurs at 902.1?K for Q?=?1.51?×?10{sup 11?}K/s and 936.9?K for Q?=?1.46?×?10{sup 12?}K/s.

  8. Internal stress-induced melting below melting temperature at high-rate laser heating

    NASA Astrophysics Data System (ADS)

    Hwang, Yong Seok; Levitas, Valery I.

    2014-06-01

    In this Letter, continuum thermodynamic and phase field approaches (PFAs) predicted internal stress-induced reduction in melting temperature for laser-irradiated heating of a nanolayer. Internal stresses appear due to thermal strain under constrained conditions and completely relax during melting, producing an additional thermodynamic driving force for melting. Thermodynamic melting temperature for Al reduces from 933.67 K for a stress-free condition down to 898.1 K for uniaxial strain and to 920.8 K for plane strain. Our PFA simulations demonstrated barrierless surface-induced melt nucleation below these temperatures and propagation of two solid-melt interfaces toward each other at the temperatures very close to the corresponding predicted thermodynamic equilibrium temperatures for the heating rate Q ?1.51×1010K/s. At higher heating rates, kinetic superheating competes with a reduction in melting temperature and melting under uniaxial strain occurs at 902.1 K for Q = 1.51 × 1011 K/s and 936.9 K for Q = 1.46 × 1012 K/s.

  9. Impact of ice temperature on microwave emissivity of thin newly formed sea ice

    Microsoft Academic Search

    Byong Jun Hwang; Jens K. Ehn; David G. Barber

    2008-01-01

    This study examines the impact of ice temperature on microwave emissivity over thin, newly formed sea ice at 6, 19, and 37 GHz during October 2003 in the southern Beaufort Sea, where the physical properties of newly formed sea ice were coincidently measured with microwave emissions. Six ice stations with distinct properties were selected and divided according to ice surface

  10. Aluminosilicate melts: structure, composition and temperature

    Microsoft Academic Search

    Bjorn Mysen

    1997-01-01

    The anionic structure of aluminosilicate melts of intermediate degree of polymerization (NBO\\/T = 0.5) and with along the composition join (LS4-LA4) has been examined in-situ to ˜1480?°C, and compared with recent data for melts along the analog composition join\\u000a and with less polymerized melts along the join and O_5. With , the anionic equilibrium, (1) , adequately describes the structure.

  11. Integral solutions for ice formation and melting outward of the external wall of a pipe with internal and external convection

    SciTech Connect

    Neto, J.H.M.; Krarti, M. [Univ. of Colorado, Boulder, CO (United States). Dept. of Civil Engineering

    1995-12-31

    Outward formation and melting of ice around the external wall of a coil-tubing is common in ice-storage tanks which use indirect brine solution (e.g. ethylene or propylene glycol water mixtures) to freeze the water and melt the ice around a build-in spiral coil-tubing heat-exchanger. In this paper, Integral Solutions are derived and analytically solved for ice formation and melting outward a pipe wall, with internal and external convection. Parametric analysis show the effect of the pipe radius, the Stefan number, and the convection heat transfer coefficients, on the ice formation and melting thickness layer. It was found that the ice or water layer thickness increases with the pipe radius but decreases with the convection heat transfer coefficients. The Stefan number has no significant effect. This model can be useful as a limiting case to validate freezing-melting problems outward tubing.

  12. Contribution of glacial melt water to the recent Southern Ocean sea ice increase

    NASA Astrophysics Data System (ADS)

    Haid, Verena; Iovino, Dorotea

    2015-04-01

    In recent years climate change and global warming are topics that are discussed everywhere. Big concerns are the melting of land ice, the reduced summer sea ice cover in the Arctic Ocean, and the general decline of the cryosphere. In contrast to those scenarios, the response of Antarctic sea ice to a warming climate is elaborate and puzzling: sea ice extent has been slightly increasing on a circumpolar scale during the last decades. Atmospheric data analysis ascribed this expansion to changes in the wind dynamics; simulations with climate-scale ocean model suggest that accelerated basal melting of ice shelves plays a major role. We investigate the influence of the glacial melt water on the sea ice of the Southern Ocean on the circumpolar and regional scales employing the ocean/sea ice NEMO-LIM coupled system at eddy-permitting resolution. The forcing of the sea ice-ocean model is supplied from the ERA-Interim data set. After a 25-year spin-up period the reference run supplies a realistic simulation of the period 2004-2013. Different volumes and distributions of melt water are applied in individual model runs spanning the same period and results are compared with the reference run. The results of this study will increase our understanding of the effect of climate change on the Southern Ocean at present and thus also of the future development. Questions like how long the increasing trend in sea ice will last or how fast it will be reversed once the tipping point is reached will be able to be addressed with more accuracy.

  13. Export of algal biomass from the melting Arctic sea ice.

    PubMed

    Boetius, Antje; Albrecht, Sebastian; Bakker, Karel; Bienhold, Christina; Felden, Janine; Fernández-Méndez, Mar; Hendricks, Stefan; Katlein, Christian; Lalande, Catherine; Krumpen, Thomas; Nicolaus, Marcel; Peeken, Ilka; Rabe, Benjamin; Rogacheva, Antonina; Rybakova, Elena; Somavilla, Raquel; Wenzhöfer, Frank

    2013-03-22

    In the Arctic, under-ice primary production is limited to summer months and is restricted not only by ice thickness and snow cover but also by the stratification of the water column, which constrains nutrient supply for algal growth. Research Vessel Polarstern visited the ice-covered eastern-central basins between 82° to 89°N and 30° to 130°E in summer 2012, when Arctic sea ice declined to a record minimum. During this cruise, we observed a widespread deposition of ice algal biomass of on average 9 grams of carbon per square meter to the deep-sea floor of the central Arctic basins. Data from this cruise will contribute to assessing the effect of current climate change on Arctic productivity, biodiversity, and ecological function. PMID:23413190

  14. IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 44, NO. 9, SEPTEMBER 2006 2461 Melt Detection in Antarctic Ice Shelves Using

    E-print Network

    Long, David G.

    the surface melt of Arctic sea ice, e.g., [1]­[3], Antarctic ice sheets [4]­[6], and the Greenland ice sheet more limited has been the use of these instruments in detecting surface melt on Antarctic sea ice [10 Detection in Antarctic Ice Shelves Using Scatterometers and Microwave Radiometers Lukas B. Kunz and David G

  15. Magma-Hydrothermal Heat Transfer and Ice Melting During the Non-Eruptive Event at Mt. Spurr, Alaska, 2002-2006

    NASA Astrophysics Data System (ADS)

    Mercier, D.; Lowell, R. P.

    2012-12-01

    Mount Spurr, a volcano on the eastern edge of the Aleutian Arc in Alaska showed signs of magma emplacement and heat transfer between 2002 and 2006 that did not culminate in an eruptive event. Seismic activity was recorded approximately 2 km west of the Mt. Spurr summit as early as 20 October 2002 at a depth of approximately 4-5 km below sea level, suggesting possible emplacement of a magmatic intrusion. Around 20 June 2004, a time difference of approximately 20 months, ice and snow on the summit of the volcano began melting, as evidenced by aerial photography and ground observations. Approximately 5.4 x 106 m3 of ice melted during a period of approximately 23 months, ending around 22 Mar 2006. Activity then ceased and no eruption occurred. We have developed a preliminary heat transfer model assuming that a sill-like magma intrusion emplaced at a depth of 4 km beneath the Mt Spurr summit drove an overlying hydrothermal system, which in turn led to the ice melting event. We show that heat transfer from the cooling sill could easily be ~ 100 W/m2, which could result in melting approximately a 20 m thick layer of ice within two years. This calculation results in a potential hydrothermal heating area of 2.7x105 m2. Using scale analysis we argue that hydrothermal flow velocities would be ~ 10-5 - 10-6 m/s, which in turn would suggest that crustal permeability would be ~ 10-10 to 10-11 m2. These estimates assume ice at its melting temperature, that the melt water is not heated, and that all the magmatic heat is used to melt the ice. We also neglect heat transport by magmatic volatiles, which were observed to discharge from the summit during this time.

  16. Melting West Antarctic ice-shelves: role of coastal warming versus changes in cavity geometries

    NASA Astrophysics Data System (ADS)

    Jourdain, Nicolas; Mathiot, Pierre; Durand, Gael; Le Sommer, Julien; Spence, Paul

    2015-04-01

    The mass loss of West Antarctic glaciers has accelerated over the last 15 years, most likely in response to ocean warming in Antarctic coastal waters. This oceanic warming in Antarctic coastal waters has recently been suggested to be caused by the positive trend of the Southern Annular Mode. But the mechanisms controlling he changes in melt rates underneath outlet glaciers are still poorly understood. For instance, despite recent developments in glacier modeling, melt rates are usually prescribed in glacier models. This strongly limits the ability of glacier models to predict the future evolution of West Antarctic glaciers. Several ocean models are now able to simulate ocean circulation beneath ice-shelves, therefore allowing a direct study of the mechanisms controlling the changes in melting rates underneath outlet glaciers. Building upon these developments, we here investigate the relative influence of ocean warming in coastal waters and changes in ice-shelves cavern geometries on melting rates underneath West Antarctic glaciers. To this purpose, we use a regional ocean/sea-ice model configuration based on NEMO, centered on the Admundsen sea, that explicitly represents flows in ice-shelves cavities. A series of sensitivity experiments is conducted with different cavern geometries and under different atmospheric forcing scenarios in order to identify the leading mechanism controlling the changes in melt rates underneath West Antarctic glaciers over the 21st century. Our results provide a first assessment on the importance of coupling glacier models to ocean models for predicting the future evolution of outlet glaciers.

  17. Seasonal to interannual variability in Antarctic sea-ice surface melt

    Microsoft Academic Search

    Mark R. Drinkwater; Xiang Liu

    2000-01-01

    Satellite remote sensing time-series images are used to illustrate the spatial and temporal variability in Antarctic-wide sea-ice surface melting during the austral summer. Combinations of collocated data from the Active Microwave Instrument onboard the ERS-1\\/2 spacecraft, RadarSat synthetic aperture radar (SAR), and special sensor microwave\\/imager (SSM\\/I) passive microwave radiometer are used in characterizing the effects of surface melting on measured

  18. Is Global Warming Melting the Greenland Ice Sheet?

    Microsoft Academic Search

    E. Hanna; P. Huybrechts; I. Janssens; J. McConnell; S. Das; J. Cappelen; K. Steffen; W. Krabill; R. Thomas; A. Stephens

    2004-01-01

    Concerted observational and modelling programmes are underway to determine the mass balance of the Greenland Ice Sheet, and therefore help predict its response to future climatic change. We present results of meteorological modelling based on ERA-40 reanalysis data from the European Centre for Medium Range Weather Forecasts (ECMWF). Our novel surface-mass-balance history of the ice sheet for 1958-2003, is based

  19. EOS Aqua AMSR-E Arctic Sea Ice Validation Program: Intercomparison Between Modeled and Measured Sea Ice Brightness Temperatures

    NASA Technical Reports Server (NTRS)

    Stroeve, J.; Markus, T.; Cavalieri, D. J.; Maslanik, J.; Sturm, M.; Henrichs, J.; Gasiewski, A.; Klein, M.

    2004-01-01

    During March 2003, an extensive field campaign was conducted near Barrow, Alaska to validate AQUA Advanced Microwave Scanning Radiometer (AMSR) sea ice products. Field, airborne and satellite data were collected over three different types of sea ice: 1) first year ice with little deformation, 2) first year ice with various amounts of deformation and 3) mixed first year ice and multi-year ice with various degrees of deformation. The validation plan relies primarily on comparisons between satellite, aircraft flights and ground-based measurements. Although these efforts are important, key aspects such as the effects of atmospheric conditions, snow properties, surface roughness, melt processes, etc on the sea ice algorithms are not sufficiently well understood or documented. To improve our understanding of these effects, we combined the detailed, in-situ data collection from the 2003 field campaign with radiance modeling using a radiative transfer model to simulate the top of the atmosphere AMSR brightness temperatures. This study reports on the results of the simulations for a variety of snow and ice types and compares the results with the National Oceanographic and Atmospheric Administration Environmental Technology Laboratory Polarimetric Scanning Radiometer (NOAA) (ETL) (PSR) microwave radiometer that was flown on the NASA P-3.

  20. Method for synthesizing extremely high-temperature melting materials

    DOEpatents

    Saboungi, Marie-Louise (Chicago, IL); Glorieux, Benoit (Perpignan, FR)

    2007-11-06

    The invention relates to a method of synthesizing high-temperature melting materials. More specifically the invention relates to a containerless method of synthesizing very high temperature melting materials such as carbides and transition-metal, lanthanide and actinide oxides, using an aerodynamic levitator and a laser. The object of the invention is to provide a method for synthesizing extremely high-temperature melting materials that are otherwise difficult to produce, without the use of containers, allowing the manipulation of the phase (amorphous/crystalline/metastable) and permitting changes of the environment such as different gaseous compositions.

  1. Method For Synthesizing Extremely High-Temperature Melting Materials

    DOEpatents

    Saboungi, Marie-Louise (Chicago, IL); Glorieux, Benoit (Perpignan, FR)

    2005-11-22

    The invention relates to a method of synthesizing high-temperature melting materials. More specifically the invention relates to a containerless method of synthesizing very high temperature melting materials such as borides, carbides and transition-metal, lanthanide and actinide oxides, using an Aerodynamic Levitator and a laser. The object of the invention is to provide a method for synthesizing extremely high-temperature melting materials that are otherwise difficult to produce, without the use of containers, allowing the manipulation of the phase (amorphous/crystalline/metastable) and permitting changes of the environment such as different gaseous compositions.

  2. Distinguishing ice from snow for melt modeling using daily observations from MODIS

    NASA Astrophysics Data System (ADS)

    Rittger, Karl; Bryant, Anne C.; Brodzik, Mary J.; Painter, Thomas H.; Armstrong, Richard

    2014-05-01

    In high mountainous regions of the Earth during melt periods, both seasonal snow and glacier ice melt may contribute to surface water and ground water feeding streams. In these regions there are often few in-situ observations that can help distinguish between the two components of melt, particularly across large mountain ranges. Understanding the contribution of melt water from the seasonal snow and glacier ice sources informs us about the current state of the water cycle and how a changing climate may alter the water cycle. In this study, we analyze daily time series of MODIS data products to distinguish ice from snow as the seasonal snowpack recedes, revealing melt over glacier ice surfaces. Broadband albedo increases as ice is exposed because of larger grain sizes and dust/debris on the glacier surface. To investigate the grain sizes we use estimates from the MODIS Snow Covered Area and Grain Size Model (MODSCAG) and MODIS Dust Radiative Forcing in Snow (MODDRFS) derived from MODIS surface reflectance (MOD09GA). MODSCAG uses the shape of the spectrum selected by a spectral mixture analysis model while MODDRFS uses the Normalized Difference Grain Size Index (NDGSI). Comparison of the grain sizes with grain sizes derived from the Airborne Visible/Infrared Imaging Spectrometer have demonstrated higher accuracy for the NDGSI approach. In addition to analysis of grain sizes, we use 2 standard albedo products from the MODIS, the Terra Daily Snow Cover algorithm (MOD10A1) that uses a narrow-to-broadband conversion scheme to create an integrated broadband albedo and Surface Reflectance BRDF/Albedo (MOD43) product that provides albedo in three broad bands. We focus on the Hunza River basin, in the Upper Indus located in Northern Pakistan. We use the annual minimum ice and snow from the MODICE Persistent Ice and Snow (MODICE) algorithm to identify glaciated regions for analysis. The methods (MODSCAG, MODDRFS, MOD10A1, MOD43) all show sensitivity to exposed glacier surfaces. Further work will use a time series of melt modeling in this region to determine the contributions from seasonal snow versus glacier ice melt.

  3. Record summer melt in Greenland in 2010

    Microsoft Academic Search

    M. Tedesco; X. Fettweis; M. R. van den Broeke; C. J. P. P. Smeets; W. J. van de Berg; M. C. Serreze; J. E. Box

    2011-01-01

    As Arctic temperatures increase, there is growing concern about the melting of the Greenland ice sheet, which reached a new record during the summer of 2010. Understanding the changing surface mass balance of the Greenland ice sheet requires appreciation of the close links among changes in surface air temperature, surface melting, albedo, and snow accumulation. Increased melting accelerates surface snow

  4. Heat sources for glacial ice melt in a west Greenland tidewater outlet glacier fjord: The role of subglacial freshwater discharge

    NASA Astrophysics Data System (ADS)

    Bendtsen, Jørgen; Mortensen, John; Lennert, Kunuk; Rysgaard, Søren

    2015-05-01

    The melting of tidewater outlet glaciers from the Greenland Ice Sheet contributes significantly to global sea level rise. Accelerated mass loss is related to melt processes in front of calving glaciers, yet the role of ocean heat transports is poorly understood. Here we present the first direct measurements from a subglacial plume in front of a calving tidewater outlet glacier. Surface salinity in the plume corresponded to a meltwater content of 7%, which is indicative of significant entrainment of warm bottom water and, according to plume model calculations, significant ice melt. Energy balance of the area near the glacier showed that ice melt was mainly due to ocean heat transport and that direct plume-associated melt was only important in periods with high meltwater discharge rates of ~100 m3 s-1. Ocean mixing outside of the plume area was thus the primary heat source for melting glacier ice.

  5. Development of ice thickness retrieval algorithms for large northern lakes from AMSR-E brightness temperature measurements

    Microsoft Academic Search

    K. Kang; C. R. Duguay; J. Lemmetyinen; Y. Gel

    2010-01-01

    Ice cover on lakes is a very sensitive to climate variability and change. With climate warming, lakes have the potential to greatly increase their energy and moisture exchanges with the atmosphere due to earlier break-up and warmer lake temperature during the open water season. Lake ice growth occurs between ice-on date and melt-onset as a result of energy loss by

  6. Sensitive response of the Greenland Ice Sheet to surface melt drainage over a soft bed.

    PubMed

    Bougamont, M; Christoffersen, P; Hubbard, A L; Fitzpatrick, A A; Doyle, S H; Carter, S P

    2014-01-01

    The dynamic response of the Greenland Ice Sheet (GrIS) depends on feedbacks between surface meltwater delivery to the subglacial environment and ice flow. Recent work has highlighted an important role of hydrological processes in regulating the ice flow, but models have so far overlooked the mechanical effect of soft basal sediment. Here we use a three-dimensional model to investigate hydrological controls on a GrIS soft-bedded region. Our results demonstrate that weakening and strengthening of subglacial sediment, associated with the seasonal delivery of surface meltwater to the bed, modulates ice flow consistent with observations. We propose that sedimentary control on ice flow is a viable alternative to existing models of evolving hydrological systems, and find a strong link between the annual flow stability, and the frequency of high meltwater discharge events. Consequently, the observed GrIS resilience to enhanced melt could be compromised if runoff variability increases further with future climate warming. PMID:25262753

  7. Vegetation structure in gullies developed by the melting of ice wedges along Kolyma River, northern Siberia

    Microsoft Academic Search

    Shiro Tsuyuzaki; Takeshi Ishizaki; Toshiyuki Sato

    1999-01-01

    Vegetation structure was surveyed in gullies developed by the melting of ice wedges along the Kolyma River, northern Siberia, using 72–50 × 50 cm plots. The mean total plant cover was approximately 50% on gley soils, which were only distributed in the gullies. Based on twinspan cluster analysis, four vegetation types were recognized: (i) Agrostis purpurascens grassland with Ceratodon purpureus

  8. A NEW METHOD FOR MELT DETECTION ON ANTARCTIC ICE-SHELVES AND SCATTEROMETER CALIBRATION

    E-print Network

    Long, David G.

    Winds on ADEOS-2 (SeaWinds) scat- terometers are identical radar sensors on different spaceborne platforms of Science Ku-band dual-polarization radar backscatter measurements from the SeaWinds on Quik to determine periods of surface melt and freeze in the Antarctic ice-shelves. The normalized radar backscatter

  9. Melt Detection in Antarctic Ice-Sheets Using Spaceborne Scatterometers and Radiometers

    E-print Network

    Long, David G.

    Melt Detection in Antarctic Ice-Sheets Using Spaceborne Scatterometers and Radiometers Lukas B, and Section VII contains conclusions from this work. II. BACKGROUND Spaceborne scatterometers observe the normalized radar backscatter (o ) of the Earth's surface and are particularly sensitive to the water content

  10. GREENLAND INLAND ICE MELT-OFF: ANALYSIS OF GLOBAL GRAVITY DATA FROM THE GRACE SATELLITES

    E-print Network

    GREENLAND INLAND ICE MELT-OFF: ANALYSIS OF GLOBAL GRAVITY DATA FROM THE GRACE SATELLITES Allan A) in meters starting at 29 July 2002 and ending at 25 August 2010. Results focussing on Greenland show indications of a transition taking place in the mass loss in Greenland from mid-2004 to early 2006. Index

  11. Fundamentals of ice making by convection cooling followed by contact melting

    Microsoft Academic Search

    J. V. C. Vargas; A. Bejan

    1995-01-01

    In this paper we show that the production of ice by convection cooling followed by contact melting can be maximized by properly selecting the frequency of the intermittent freezing and removal cycle. In the first part of the paper, this principle is illustrated in three configurations: water freezing inside a tube cooled externally by convection, freezing on the outside of

  12. Satellite observation of winter season subsurface liquid melt water retention on the Greenland ice sheet using spectroradiometer and scatterometer data

    NASA Astrophysics Data System (ADS)

    Miller, J. Z.; Forster, R. R.; Long, D. G.; Brewer, S.

    2013-12-01

    The recently discovered perennial firn aquifer (PFA) represents a new glacier facie and a previously undefined liquid water storage mechanism on the Greenland ice sheet (GrIS). The current hypothesis suggests that at least two geophysical processes control the formation of the PFA: 1) high melt rates that saturate snow and firn layers with liquid water during the melt season, and 2) high snow accumulation rates that subsequently insulate this saturated layer allowing it to be retained in liquid form during the winter season. The PFA is potentially an important component in ice sheet mass and energy budget calculations, however, large-scale observations linking surface melt, subsurface liquid melt water retention, and the PFA currently do not exist. Satellite-borne spectroradiometers and scatterometers are frequently used to detect the presence of liquid water content over the GrIS. The sensor's penetration depth is dependent on the frequency (which determines wavelength) and time-varying geophysical properties (which determine absorption and scattering characteristics). At shorter spectral wavelengths, penetration depths are limited at the interface between the ice sheet surface and the atmosphere. Spectroradiometer-derived retrievals of liquid water content represent an integrated response on the order of a few millimeters. At longer microwave wavelengths (C- and Ku-band), penetration depths are increased. Scatterometer-derived retrievals of liquid water content represent an integrated response on the order of a few centimeters to several meters. We combine spectroradiometer data acquired from the Moderate Resolution Imaging Spectroradiometer aboard Terra and Aqua (MODIS) and C- and Ku-band scatterometer data acquired from MetOP-A (ASCAT) and OceanSAT-2 (OSCAT) to investigate the spatiotemporal variability of subsurface liquid water content on the GrIS. Penetration depth differences are exploited to distinguish between the detection of liquid water content controlled by surface heat flux and the detection of subsurface liquid water content controlled by the retention process. Surface freeze-up is identified using MODIS-derived ice surface temperatures. We then identify distinct microwave signatures suggesting the presence of subsurface liquid water content, characterize the stratigraphy and geophysical processes controlling the observed response, and derive a retrieval algorithm using a simple radiative transfer model. Over the 4 year time series (2009-2013), results indicate subsurface liquid melt water persists within Ku-band penetration depth up to ~1 month and within C-band penetration depth between ~1-5 months following surface-freeze-up. Detection occurs exclusively in regions where the PFA has previously been mapped using field (Arctic Circle Traverse) and airborne (IceBridge) observations and the spatial extent is consistent with regional climate model (RACMO2) simulations.

  13. Towards Estimate of Present Day Ice Melting in Polar Regions From Altimetry, Gravity, Ocean Bottom Pressure and GPS Observations

    NASA Astrophysics Data System (ADS)

    Jiang, Y.; Wu, X.; van den Broeke, M. R.; Munneke, P. K.; Simonsen, S. B.; van der Wal, W.; Vermeersen, B. L.

    2013-12-01

    The ice sheet in Polar Regions stores the largest freshwater bodies on Earth, sufficient to elevate global sea level by more than 65 meters if melted. The earth may have entered an intensive ice-melting episode, possibly due to anthropogenic global warming rather than natural orbit variations. Determining present-day ice mass balance, however, is complicated by the fact that most observations contain both present day ice melting signal and residual signals from past glacier melting. Despite decades of progress in geodynamic modeling and new observations, significant uncertainties remain in both. The key to separate present-day ice mass change and signals from past melting is to include data of different physical characteristics. We conducted a new global kinematic inversion scheme to estimate both present-day ice melting and past glacier signatures simultaneously and assess their contribution to current and future global mean sea level change. Our approach is designed to invert and separate present-day melting signal in the spherical harmonic domain using a globally distributed interdisciplinary data with distinct physical information. Interesting results with unprecedented precisions have been achieved so far. We will present our results of the estimated present-day ice mass balance trend in both Greenland and Antarctica ice sheet as well as other regions where significant mass change occurs.

  14. Substrate effect on the melting temperature of gold nanoparticles

    NASA Astrophysics Data System (ADS)

    Luo, Wenhua; Su, Kalin; Li, Kemin; Liao, Gaohua; Hu, Nengwen; Jia, Ming

    2012-06-01

    Previous experimental, molecular dynamics, and thermodynamic researches on the melting temperature of Au nanoparticles on tungsten substrate provide entirely different results. To account for the substrate effect upon the melting point of nanoparticles, three different substrates were tested by using a thermodynamic model: tungsten, amorphous carbon, and graphite. The results reveal that the melting point suppression of a substrate-supported Au nanoparticle is principally ruled by the free surface-to-volume ratio of the particle or the contact angle between the particle and the substrate. When the contact angle ? is less than 90°, a stronger size-dependent melting point depression compared with those for free nanoparticles is predicted; when the contact angle ? is greater than 90°, the melting temperature of the supported Au nanoparticles are somewhat higher than those for free nanoparticles.

  15. Estimating the time of melt onset and freeze onset over Arctic sea-ice area using active and passive microwave data

    USGS Publications Warehouse

    Belchansky, G.I.; Douglas, D.C.; Mordvintsev, I.N.; Platonov, N.G.

    2004-01-01

    Accurate calculation of the time of melt onset, freeze onset, and melt duration over Arctic sea-ice area is crucial for climate and global change studies because it affects accuracy of surface energy balance estimates. This comparative study evaluates several methods used to estimate sea-ice melt and freeze onset dates: (1) the melt onset database derived from SSM/I passive microwave brightness temperatures (Tbs) using Drobot and Anderson's [J. Geophys. Res. 106 (2001) 24033] Advanced Horizontal Range Algorithm (AHRA) and distributed by the National Snow and Ice Data Center (NSIDC); (2) the International Arctic Buoy Program/Polar Exchange at the Sea (IABP/POLES) surface air temperatures (SATs); (3) an elaborated version of the AHRA that uses IABP/POLES to avoid anomalous results (Passive Microwave and Surface Temperature Analysis [PMSTA]); (4) another elaborated version of the AHRA that uses T b variance to avoid anomalous results (Mean Differences and Standard Deviation Analysis [MDSDA]); (5) Smith's [J. Geophys. Res. 103 (1998) 27753] vertically polarized Tb algorithm for estimating melt onset in multiyear (MY) ice (SSM/I 19V-37V); and (6) analyses of concurrent backscattering cross section (????) and brightness temperature (T b) from OKEAN-01 satellite series. Melt onset and freeze onset maps were created and compared to understand how the estimates vary between different satellite instruments and methods over different Arctic sea-ice regions. Comparisons were made to evaluate relative sensitivities among the methods to slight adjustments of the Tb calibration coefficients and algorithm threshold values. Compared to the PMSTA method, the AHRA method tended to estimate significantly earlier melt dates, likely caused by the AHRA's susceptibility to prematurely identify melt onset conditions. In contrast, the IABP/POLES surface air temperature data tended to estimate later melt and earlier freeze in all but perennial ice. The MDSDA method was least sensitive to small adjustments of the SMMR-SSM/I inter-satellite calibration coefficients. Differences among methods varied by latitude. Freeze onset dates among methods were most disparate in southern latitudes, and tended to converge northward. Surface air temperatures (IABP/POLES) indicated freeze onset well before the MDSDA method, especially in southern peripheral seas, while PMSTA freeze estimates were generally intermediate. Surface air temperature data estimated latest melt onset dates in southern latitudes, but earliest melt onset in northern latitudes. The PMSTA estimated earliest melt onset dates in southern regions, and converged with the MDSDA northward. Because sea-ice melt and freeze are dynamical transitional processes, differences among these methods are associated with differing sensitivities to changing stages of environmental and physical development. These studies contribute to the growing body of documentation about the levels of disparity obtained when Arctic seasonal transition parameters are estimated using various types of microwave data and algorithms. ?? 2004 Elsevier Inc. All rights reserved.

  16. Surface and basal sea ice melt from autonomous buoy arrays during the 2014 sea ice retreat in the Beaufort/Chukchi Seas

    NASA Astrophysics Data System (ADS)

    Maksym, T. L.; Wilkinson, J.; Hwang, P. B.

    2014-12-01

    As the Arctic continues its transition to a seasonal ice cover, the nature and role of the processes driving sea ice retreat are expected to change. Key questions revolve around how the coupling between dynamics and thermodynamic processes and potential changes in the role of melt ponds contribute to an accelerated seasonal ice retreat. To address these issues, 44 autonomous platforms were deployed in four arrays in the Beaufort Sea in March, 2014, with an additional array deployed in August in the Chukchi Sea to monitor the evolution of ice conditions during the seasonal sea ice retreat. Each "5-dice" array included four or five co-sited ice mass balance buoys (IMB) and wave buoys with digital cameras, and one automatic weather station (AWS) at the array center. The sensors on these buoys, combined with satellite imagery monitoring the large-scale evolution of the ice cover, provide a near-complete history of the processes involved in the seasonal melt of sea ice. We present a preliminary analysis of the contributions of several key processes to the seasonal ice decay. The evolution of surface ponding was observed at several sites with differing ice types and surface morphologies. The records of surface melt and ice thickness demonstrate a key role of ice type in driving the evolution of the ice cover. Analysis of the surface forcing and estimates of solar energy partitioning between the surface and upper ocean is compared to the surface and basal mass balance from the IMBs. The role of ice divergence and deformation in driving sea ice decay - in particular its role in accelerating thermodynamic melt processes - is discussed.

  17. Polycrystalline methane hydrate: Synthesis from superheated ice, and low-temperature mechanical properties

    USGS Publications Warehouse

    Stern, L.A.; Kirby, S.H.; Durham, W.B.

    1998-01-01

    We describe a new and efficient technique to grow aggregates of pure methane hydrate in quantities suitable for physical and material properties testing. Test specimens were grown under static conditions by combining cold, pressurized CH4 gas with granulated H2O ice, and then warming the reactants to promote the reaction CH4(g) + 6H2O(s???1) ??? CH4??6H2O (methane hydrate). Hydrate formation evidently occurs at the nascent ice/liquid water interface on ice grain surfaces, and complete reaction was achieved by warming the system above the ice melting point and up to 290 K, at 25-30 MPa, for approximately 8 h. The resulting material is pure, cohesive, polycrystalline methane hydrate with controlled grain size and random orientation. Synthesis conditions placed the H2O ice well above its melting temperature while reaction progressed, yet samples and run records showed no evidence for bulk melting of the unreacted portions of ice grains. Control experiments using Ne, a non-hydrate-forming gas, showed that under otherwise identical conditions, the pressure reduction and latent heat associated with ice melting are easily detectable in our fabrication apparatus. These results suggest that under hydrate-forming conditions, H2O ice can persist metastably to temperatures well above its ordinary melting point while reacting to form hydrate. Direct observations of the hydrate growth process in a small, high-pressure optical cell verified these conclusions and revealed additional details of the hydrate growth process. Methane hydrate samples were then tested in constant-strain-rate deformation experiments at T = 140-200 K, Pc = 50-100 MPa, and ?? = 10-4 10-6 s-1. Measurements in both the brittle and ductile fields showed that methane hydrate has measurably different strength than H2O ice, and work hardens to an unusually high degree compared to other ices as well as to most metals and ceramics at high homologous temperatures. This work hardening may be related to a changing stoichiometry under pressure during plastic deformation; X-ray analyses showed that methane hydrate undergoes a process of solid-state disproportionation or exsolution during deformation at conditions well within its conventional stability field.

  18. Unusually loud ambient noise in tidewater glacier fjords: a signal of ice melt

    USGS Publications Warehouse

    Pettit, Erin C.; Lee, Kevin M.; Brann, Joel P.; Nystuen, Jeffrey A.; Wilson, Preston S.; O'Neel, Shad R.

    2015-01-01

    In glacierized fjords, the ice-ocean boundary is a physically and biologically dynamic environment that is sensitive to both glacier flow and ocean circulation. Ocean ambient noise offers insight into processes and change at the ice-ocean boundary. Here we characterize fjord ambient noise and show that the average noise levels are louder than nearly all measured natural oceanic environments (significantly louder than sea ice and non-glacierized fjords). Icy Bay, Alaska has an annual average sound pressure level of 120?dB (re 1 ?Pa) with a broad peak between 1000 and 3000?Hz. Bubble formation in the water column as glacier ice melts is the noise source, with variability driven by fjord circulation patterns. Measurements from two additional fjords, in Alaska and Antarctica, support that this unusually loud ambient noise in Icy Bay is representative of glacierized fjords. These high noise levels likely alter the behavior of marine mammals.

  19. Melting probes as a means to access the subsurface of Mars' polar caps and Jupiter's ice moons

    NASA Astrophysics Data System (ADS)

    Biele, J.; Ulamec, S.; Funke, O.; Engelhardt, M.

    There is a high scientific interest in exploring certain planetary icy environments in the solar system (Mars' polar caps, Europa and other icy satellites) motivated by the search for traces of life in these extreme environments as well as interest in planetary climate history as in the case of Mars. A promising technique to penetrate thick ice layers with small and reliable probes which do not require the heavy, complex and expensive equipment of a drilling rig is by melting. Contamination avoidance with respect to planetary protection requirements can be fulfilled using melting probes, since the melting channel refreezes behind the probe and shuts off the contact to the surface; also, in-situ decontamination of the probe is possible. Melting probes can be equipped with a suite of scientific instruments that are capable e.g. of determining the chemical and isotopic composition of the embedded or dissolved materials, of the ices themselves, of the dust content and possible traces of indigenous biological activity. Due to the still rather high energy demand to overcome the melting enthalpy, in case of extraterrestrial application (e.g. Europa or polar caps of Mars), only heating with radioactive isotopes seems feasible for reaching greater depths. The necessary power is driven by the desired penetration velocity (linearly) and the dimensions of the probe (proportional to the cross section). On Mars, however, solar cells could be used to power small tethered melting probes in polar summer. While such probes have successfully been used for terrestrial applications, e.g., in Antarctica in the 1990ies, the technology is not yet mature for space applications; for example, the behaviour in vacuum (below the triple point pressure of water, i.e., 611 Pa) needs to be assessed. We will report briefly on our laboratory tests with melting probes in vacuum and under very low temperatures to this end. Practical issues (impact of dust on the performance, gravity dependence, prevention of blocking, attitude control, power supply, communications) and engineering concepts will be discussed. For future missions to Europa (in particular in view of the ESA Cosmic Vision Programme), if planned to include a Surface Package, a melting probe may be the most adequate (and most easily realized) way to access the subsurface areas, protected from the intense ionising radiation in the Jovian system and most interesting from a biochemical and biological point of view.

  20. Estimating the time of melt onset and freeze onset over Arctic sea-ice area using active and passive microwave data

    USGS Publications Warehouse

    Belchansky, G.I.; Douglas, D.C.; Mordvintsev, I.N.; Platonov, N.G.

    2004-01-01

    Accurate calculation of the time of melt onset, freeze onset, and melt duration over Arctic sea-ice area is crucial for climate and global change studies because it affects accuracy of surface energy balance estimates. This comparative study evaluates several methods used to estimate sea-ice melt and freeze onset dates: (1) the melt onset database derived from SSM/I passive microwave brightness temperatures (Tbs) using Drobot and Anderson's [J. Geophys. Res. 106 (2001) 24033] Advanced Horizontal Range Algorithm (AHRA) and distributed by the National Snow and Ice Data Center (NSIDC); (2) the International Arctic Buoy Program/Polar Exchange at the Sea (IABP/POLES) surface air temperatures (SATs); (3) an elaborated version of the AHRA that uses IABP/POLES to avoid anomalous results (Passive Microwave and Surface Temperature Analysis [PMSTA]); (4) another elaborated version of the AHRA that uses Tb variance to avoid anomalous results (Mean Differences and Standard Deviation Analysis [MDSDA]); (5) Smith's [J. Geophys. Res. 103 (1998) 27753] vertically polarized Tb algorithm for estimating melt onset in multiyear (MY) ice (SSM/I 19V - 37V); and (6) analyses of concurrent backscattering cross section (rj) and brightness temperature (Tb) from OKEAN-01 satellite series. Melt onset and freeze onset maps were created and compared to understand how the estimates vary between different satellite instruments and methods over different Arctic seaice regions. Comparisons were made to evaluate relative sensitivities among the methods to slight adjustments of the Tb calibration coefficients and algorithm threshold values. Compared to the PMSTA method, the AHRA method tended to estimate significantly earlier melt dates, likely caused by the AHRA's susceptibility to prematurely identify melt onset conditions. In contrast, the IABP/POLES surface air temperature data tended to estimate later melt and earlier freeze in all but perennial ice. The MDSDA method was least sensitive to small adjustments of the SMMR-SSM/I inter-satellite calibration coefficients. Differences among methods varied by latitude. Freeze onset dates among methods were most disparate in southern latitudes, and tended to converge northward. Surface air temperatures (IABP/POLES) indicated freeze onset well before the MDSDA method, especially in southern peripheral seas, while PMSTA freeze estimates were generally intermediate. Surface air temperature data estimated latest melt onset dates in southern latitudes, but earliest melt onset in northern latitudes. The PMSTA estimated earliest melt onset dates in southern regions, and converged with the MDSDA northward. Because sea-ice melt and freeze are dynamical transitional processes, differences among these methods are associated with differing sensitivities to changing stages of environmental and physical development. These studies contribute to the growing body of documentation about the levels of disparity obtained when Arctic seasonal transition parameters are estimated using various types of microwave data and algorithms.

  1. Low melting temperature alloy deployment mechanism and recent experiments

    NASA Technical Reports Server (NTRS)

    Madden, M. J.

    1993-01-01

    This paper describes the concept of a low melting temperature alloy deployment mechanism, U.S. Patent 4,842,106. It begins with a brief history of conventional dimethyl-silicone fluid damped mechanisms. Design fundamentals of the new melting alloy mechanism are then introduced. Benefits of the new over the old are compared and contrasted. Recent experiments and lessons learned complete this paper.

  2. Substrate effect on the melting temperature of thin polyethylenefilms

    SciTech Connect

    Wang, Y.; Rafailovich, M.; Sokolov, J.; Gersappe, D.; Araki, T.; Zou, Y.; Kilcoyne, A.D.L.; Ade, H.; Marom, G.; Lustiger, A.

    2006-01-17

    Strong dependence of the crystal orientation, morphology,and melting temperature (Tm) on the substrate is observed in thesemicrystalline polyethylene thin films. The Tm decreases with the filmthickness when the film is thinner that a certain critical thickness andthe magnitude of the depression increases with increasing surfaceinteraction. We attribute the large Tm depression to the decrease in theoverall free energy on melting, which is caused by the substrateattraction force to the chains that competes against the interchain forcewhich drives the chains to crystallization.

  3. Investigation of the effects of summer melt on the calculation of sea ice concentration using active and passive microwave data

    NASA Technical Reports Server (NTRS)

    Cavalieri, Donald J.; Burns, Barbara A.; Onstott, Robert G.

    1990-01-01

    The effects of ice surface melt on microwave signatures and errors in the calculation of sea ice concentration are examined, using active and passive microwave data sets from the Marginal Ice Zone Experiment aircraft flights in the Fram Strait region. Consideration is given to the possibility of using SAR to supplement passive microwave data to unambiguously discriminate between open water areas and ponded floes. Coincident active multichannel microwave radiometer and SAR measurements of individual floes are used to describe the effects of surface melt on sea ice concentration calculations.

  4. Pitted rock surfaces on Mars: A mechanism of formation by transient melting of snow and ice

    E-print Network

    Marchant, David R.

    pressure exceeding the triple point pressure of H2O; an available source of solid water to melt). We find point of water by sunlight. We examine the conditions under which a similar process might explain the pitted rocks seen on the surface of Mars (rock surface temperatures above the melting point; atmospheric

  5. Communication: The Effect of Dispersion Corrections on the Melting Temperature of Liquid Water

    SciTech Connect

    Yoo, Soohaeng; Xantheas, Sotiris S.

    2011-03-28

    We report the results of the melting temperature (Tm) of liquid water for the Becke-Lee- Yang-Parr (BLYP) density functional including Dispersion corrections (BLYP-D) and the TTM3-F ab-initio based classical potential via constant pressure and constant enthalpy (NPH) ensemble molecular dynamics simulations of an ice Ih-liquid coexisting system. The inclusion of dispersion corrections to BLYP lowers the melting temperature of liquid water to Tm=360 K, which is a large improvement over the value of Tm > 400 K obtained with the original BLYP functional. The ab-initio based flexible, polarizable Thole-type model (TTM3-F) produces Tm=248 K from classical molecular dynamics simulations.

  6. A Microwave Technique for Mapping Ice Temperature in the Arctic Seasonal Sea Ice Zone

    NASA Technical Reports Server (NTRS)

    St.Germain, Karen M.; Cavalieri, Donald J.

    1997-01-01

    A technique for deriving ice temperature in the Arctic seasonal sea ice zone from passive microwave radiances has been developed. The algorithm operates on brightness temperatures derived from the Special Sensor Microwave/Imager (SSM/I) and uses ice concentration and type from a previously developed thin ice algorithm to estimate the surface emissivity. Comparisons of the microwave derived temperatures with estimates derived from infrared imagery of the Bering Strait yield a correlation coefficient of 0.93 and an RMS difference of 2.1 K when coastal and cloud contaminated pixels are removed. SSM/I temperatures were also compared with a time series of air temperature observations from Gambell on St. Lawrence Island and from Point Barrow, AK weather stations. These comparisons indicate that the relationship between the air temperature and the ice temperature depends on ice type.

  7. A microwave technique for mapping ice temperature in the Arctic seasonal sea ice zone

    SciTech Connect

    St. Germain, K.M. [Naval Research Lab., Washington, DC (United States). Remote Sensing Div.] [Naval Research Lab., Washington, DC (United States). Remote Sensing Div.; Cavalieri, D.J. [National Aeronautics and Space Administration, Greenbelt, MD (United States). Goddard Space Flight Center] [National Aeronautics and Space Administration, Greenbelt, MD (United States). Goddard Space Flight Center

    1997-07-01

    A technique for deriving ice temperature in the Arctic seasonal sea ice zone from passive microwave radiances has been developed. The algorithm operates on brightness temperatures derived from the Special Sensor Microwave/Imager (SSM/I) and uses ice concentration and type from a previously developed thin ice algorithm to estimate the surface emissivity. Comparisons of the microwave derived temperatures with estimates derived from infrared imagery of the Bering Strait yield a correlation coefficient of 0.93 and an RMS difference of 2.1 K when coastal and cloud contaminated pixels are removed. SSM/I temperatures were also compared with a time series of air temperature observations from Gambell on St. Lawrence Island and from Point Barrow, AK weather stations. These comparisons indicate that the relationship between the air temperature and the ice temperature depends on ice type.

  8. Real time thermal imaging of high temperature semiconductor melts

    NASA Technical Reports Server (NTRS)

    Wargo, Michael J.

    1988-01-01

    A real time thermal imaging system with temperature resolution better than + or - 1 C and spatial resolution of better than 0.5 mm was developed and applied to the analysis of melt surface thermal field distributions in both Czochralski and liquid encapsulated Czochralski (LEC) growth configurations. The melt is viewed in near normal incidence by a high resolution charge coupled device camera to which is attached a very narrow bandpass filter. The resulting image is digitized and processed using a pipelined pixel processor operating at an effective 40 million operations per second thus permitting real time high frequency spatial and temporal filtering of the high temperature scene. A multi-pixel averaging algorithm was developed which permits localized, low noise sensing of temperature variations at any location in the hot zone as a function of time. This signial is used to implement initial elements of a feedforward growth control scheme which is aimed at reducing disturbances to the melt caused by the batch nature of the growth process. The effect of magnetic melt stabilization on radial melt temperature distributions was measured using this technique. Problems associated with residual internal reflections and non-optimized path geometry are discussed.

  9. Austral Summer Sea Ice Melt Revealed in Antarctic ERS-1\\/2 and NSCAT Scatterometer Data

    Microsoft Academic Search

    Mark R. Drinkwater; Xiang Liu

    IntroductionThe first in-situ field observations of Antarctic austral summer sea-ice melt were made in theBellingshausen Sea by Arctowski (1908) on Belgica in 1899, and later by Wordie (1921)during the ill-fated drift of Endurance in the Weddell Sea from 1914-1916. It has been 100years since these pioneering ship drift experiments, yet little more is known about the spatialextent, duration, frequency of

  10. InSAR and GPS Observations Show Seasonal Speedup of Ice Flow in Greenland Following the Onset of Summer Melting

    Microsoft Academic Search

    I. Joughin; S. B. Das; M. A. King; B. Smith; I. Howat; T. Moon

    2007-01-01

    We have assembled a comprehensive set of InSAR and GPS observations that reveal both spatial and temporal changes in velocity during the summer melt season along a several-hundred kilometer stretch of the ice-sheet margin near Jakobshavn Isbrae, Greenland. In the bare ice zone, we obtain InSAR (speckle\\/feature tracking) results throughout the melt season that agree well with results from two

  11. Physical and ecological processes in the marginal ice zone of the northern Barents Sea during the summer melt period

    Microsoft Academic Search

    Stig Falk-Petersen; Haakon Hop; W. Paul Budgell; Else N. Hegseth; Reinert Korsnes; Terje B. Løyning; Jon Børre Ørbæk; Toshiyuki Kawamura; Kunio Shirasawa

    2000-01-01

    The main physical and ecological processes associated with the summer melt period in the marginal ice zone (MIZ) were investigated in a multidisciplinary research programme (ICE-BAR), which was carried out in the northern Barents Sea during June–August 1995–1996. This study provided simultaneous observations of a wide range of physical and chemical factors of importance for the melting processes of sea

  12. Revisiting the potential of melt pond fraction as a predictor for the seasonal Arctic sea ice extent minimum

    NASA Astrophysics Data System (ADS)

    Liu, Jiping; Song, Mirong; Horton, Radley M.; Hu, Yongyun

    2015-05-01

    The rapid change in Arctic sea ice in recent decades has led to a rising demand for seasonal sea ice prediction. A recent modeling study that employed a prognostic melt pond model in a stand-alone sea ice model found that September Arctic sea ice extent can be accurately predicted from the melt pond fraction in May. Here we show that satellite observations show no evidence of predictive skill in May. However, we find that a significantly strong relationship (high predictability) first emerges as the melt pond fraction is integrated from early May to late June, with a persistent strong relationship only occurring after late July. Our results highlight that late spring to mid summer melt pond information is required to improve the prediction skill of the seasonal sea ice minimum. Furthermore, satellite observations indicate a much higher percentage of melt pond formation in May than does the aforementioned model simulation, which points to the need to reconcile model simulations and observations, in order to better understand key mechanisms of melt pond formation and evolution and their influence on sea ice state.

  13. The WAIS Melt Monitor: An automated ice core melting system for meltwater sample handling and the collection of high resolution microparticle size distribution data

    NASA Astrophysics Data System (ADS)

    Breton, D. J.; Koffman, B. G.; Kreutz, K. J.; Hamilton, G. S.

    2010-12-01

    Paleoclimate data are often extracted from ice cores by careful geochemical analysis of meltwater samples. The analysis of the microparticles found in ice cores can also yield unique clues about atmospheric dust loading and transport, dust provenance and past environmental conditions. Determination of microparticle concentration, size distribution and chemical makeup as a function of depth is especially difficult because the particle size measurement either consumes or contaminates the meltwater, preventing further geochemical analysis. Here we describe a microcontroller-based ice core melting system which allows the collection of separate microparticle and chemistry samples from the same depth intervals in the ice core, while logging and accurately depth-tagging real-time electrical conductivity and particle size distribution data. This system was designed specifically to support microparticle analysis of the WAIS Divide WDC06A deep ice core, but many of the subsystems are applicable to more general ice core melting operations. Major system components include: a rotary encoder to measure ice core melt displacement with 0.1 millimeter accuracy, a meltwater tracking system to assign core depths to conductivity, particle and sample vial data, an optical debubbler level control system to protect the Abakus laser particle counter from damage due to air bubbles, a Rabbit 3700 microcontroller which communicates with a host PC, collects encoder and optical sensor data and autonomously operates Gilson peristaltic pumps and fraction collectors to provide automatic sample handling, melt monitor control software operating on a standard PC allowing the user to control and view the status of the system, data logging software operating on the same PC to collect data from the melting, electrical conductivity and microparticle measurement systems. Because microparticle samples can easily be contaminated, we use optical air bubble sensors and high resolution ice core density profiles to guide the melting process. The combination of these data allow us to analyze melt head performance, minimize outer-to-inner fraction contamination and avoid melt head flooding. The WAIS Melt Monitor system allows the collection of real-time, sub-annual microparticle and electrical conductivity data while producing and storing enough sample for traditional Coulter-Counter particle measurements as well long term acid leaching of bioactive metals (e.g., Fe, Co, Cd, Cu, Zn) prior to chemical analysis.

  14. Communication: The effect of dispersion corrections on the melting temperature of liquid water

    NASA Astrophysics Data System (ADS)

    Yoo, Soohaeng; Xantheas, Sotiris S.

    2011-03-01

    The melting temperature (Tm) of liquid water with the Becke-Lee-Yang-Parr (BLYP) density functional including dispersion corrections (BLYP-D) and the Thole-type, version 3 (TTM3-F) ab-initio based flexible, polarizable classical potential is reported via constant pressure and constant enthalpy (NPH) molecular dynamics simulations of an ice Ih-liquid coexisting system. Dispersion corrections to BLYP lower Tm to about 360 K, a large improvement over the value of Tm > 400 K previously obtained with the original BLYP functional under the same simulation conditions. For TTM3-F, Tm = 248 K from classical molecular dynamics simulations.

  15. Radar attenuation and temperature within the Greenland Ice Sheet

    USGS Publications Warehouse

    MacGregor, Joseph A; Li, Jilu; Paden, John D; Catania, Ginny A; Clow, Gary D.; Fahnestock, Mark A; Gogineni, S. Prasad; Grimm, Robert E.; Morlighem, Mathieu; Nandi, Soumyaroop; Seroussi, Helene; Stillman, David E

    2015-01-01

    The flow of ice is temperature-dependent, but direct measurements of englacial temperature are sparse. The dielectric attenuation of radio waves through ice is also temperature-dependent, and radar sounding of ice sheets is sensitive to this attenuation. Here we estimate depth-averaged radar-attenuation rates within the Greenland Ice Sheet from airborne radar-sounding data and its associated radiostratigraphy. Using existing empirical relationships between temperature, chemistry, and radar attenuation, we then infer the depth-averaged englacial temperature. The dated radiostratigraphy permits a correction for the confounding effect of spatially varying ice chemistry. Where radar transects intersect boreholes, radar-inferred temperature is consistently higher than that measured directly. We attribute this discrepancy to the poorly recognized frequency dependence of the radar-attenuation rate and correct for this effect empirically, resulting in a robust relationship between radar-inferred and borehole-measured depth-averaged temperature. Radar-inferred englacial temperature is often lower than modern surface temperature and that of a steady state ice-sheet model, particularly in southern Greenland. This pattern suggests that past changes in surface boundary conditions (temperature and accumulation rate) affect the ice sheet's present temperature structure over a much larger area than previously recognized. This radar-inferred temperature structure provides a new constraint for thermomechanical models of the Greenland Ice Sheet.

  16. 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

  17. An Experimental Investigation of Ice Melting and Heat Transfer Characteristics from Submerged Jets of Hot Water, Implications for Subglacial Volcanic Eruptions

    NASA Astrophysics Data System (ADS)

    Jamshidnia, H.; Gudmundsson, M. T.

    2014-12-01

    The rates and processes of energy transfer in water-filled cavities formed under glaciers by geothermal and volcanic activity has been investigated by designing, developing, and using an experimental setup in which hot water jets can impinge on an ice block. Systematic sets of experimental runs typically lasting 60-90 seconds with water jet temperatures in the range 10° - 90°C have been performed with initial ice block temparature. It is quantitatively found that heat flux from flowing water to ice is linearly dependent on temperature of the jet flow. The hot water jet meltes out a cavity into the ice block during the process. The cavities had steep to vertical sides with a doming roof. Some of the ice blocks used had trapped air bubbles. In these cases melting of the ice lead to the trapping of air at the top of the cavity, partially insulating the roof from the hot water jet. Such cavities had lower aspect ratios (height/width) and flatter and less dome shaped roofs than did cavities in ice blocks with little or no air bubbles. The overall heat transfer rate in cavity formation varied with jet temperature from <100 kW m-2 to ~900 kW m-2 while melting rates in the vertical direction yield heat transfer rates of 200-1200 kW m-2. The observed experimental heat transfer rates can be compared to data on subglacial melting observed for ice cauldrons in various settings in Iceland. For the lowest experimental temperatures the numbers are comparable to those found for geothermal water in cool, subglacial water bodies and above subglacial flowpaths of jökulhlaups. However, the highest experimental rates for 80-90°C jets are 3-10 times less than inferred from observations of recent subglacial eruptions (2000-4000 kW m-2). This can indicate that single phase liquid water convection alone is not sufficient to explain the rates seen in recent subglacial eruptions in Iceland, suggesting that during such eruptions forced two-phase (liquid and steam) or three phase (liquid, steam and pyroclasts) convection is common. Further recommendations may also be presented for future research in this field.

  18. Effects of locust bean gum and mono- and diglyceride concentrations on particle size and melting rates of ice cream.

    PubMed

    Cropper, S L; Kocaoglu-Vurma, N A; Tharp, B W; Harper, W J

    2013-06-01

    The objective of this study was to determine how varying concentrations of the stabilizer, locust bean gum (LBG), and different levels of the emulsifier, mono- and diglycerides (MDGs), influenced fat aggregation and melting characteristics of ice cream. Ice creams were made containing MDGs and LBG singly and in combination at concentrations ranging between 0.0% to 0.14% and 0.0% to 0.23%, respectively. Particle size analysis, conducted on both the mixes and ice cream, and melting rate testing on the ice cream were used to determine fat aggregation. No significant differences (P < 0.05) were found between particle size values for experimental ice cream mixes. However, higher concentrations of both LBG and MDG in the ice creams resulted in values that were larger than the control. This study also found an increase in the particle size values when MDG levels were held constant and LBG amounts were increased in the ice cream. Ice creams with higher concentrations of MDG and LBG together had the greatest difference in the rate of melting than the control. The melting rate decreased with increasing LBG concentrations at constant MDG levels. These results illustrated that fat aggregation may not only be affected by emulsifiers, but that stabilizers may play a role in contributing to the destabilization of fat globules. PMID:23772704

  19. Shock Melting of Permafrost on Mars: Water Ice Multiphase Equation of State for Numerical Modeling and Its Testing

    NASA Technical Reports Server (NTRS)

    Ivanov, B. A.

    2005-01-01

    The presence of water/ice/brine in upper layers of Martian crust affects many processes of impact cratering. Modeling of these effects promises better understanding of Martian cratering records. We present here the new ANEOS-based multiphase equation of state for water/ice constructed for usage in hydrocodes and first numerical experiments on permafrost shock melting. Preliminary results show that due to multiple shock compression of ice inclusions in rocks the entropy jump in shocked ice is smaller than in pure ice for the same shock pressure. Hence previous estimates of ice melting during impact cratering on Mars should be re-evaluated. Additional information is included in the original extended abstract.

  20. Formation of relief on Europa's surface and analysis of a melting probe movement through the ice

    NASA Astrophysics Data System (ADS)

    Erokhina, O. S.; Chumachenko, E. N.; Dunham, D. W.; Aksenov, S. A.; Logashina, I. V.

    2013-12-01

    These days, studies of planetary bodies' are of great interest. And of special interest are the icy moons of the giant planets like Jupiter and Saturn. Analysis of 'Voyager 1', 'Voyager 2', 'Galileo' and 'Cassini' spacecraft data showed that icy covers were observed on Jupiter's moons Ganymede, Europa and Calisto, and Saturn's moons Titan and Enceladus. Of particular interest is the relatively smooth surface of Europa. The entire surface is covered by a system of bands, valleys, and ridges. These structures are explained by the mobility of surface ice, and the impact of stress and large-scale tectonic processes. Also conditions on these moons allow speculation about possible life, considering these moons from an astrobiological point of view. To study the planetary icy body in future space missions, one of the problems to solve is the problem of design of a special device capable of penetrating through the ice, as well as the choice of the landing site of this probe. To select a possible landing site, analysis of Europa's surface relief formation is studied. This analysis showed that compression, extention, shearing, and bending can influence some arbitrarily separated section of Europe's icy surface. The computer simulation with the finite element method (FEM) was performed to see what types of defects could arise from such effects. The analysis showed that fractures and cracks could have various forms depending on the stress-strained state arising in their vicinity. Also the problem of a melting probe's movement through the ice is considered: How the probe will move in low gravity and low atmospheric pressure; whether the hole formed in the ice will be closed when the probe penetrates far enough or not; what is the influence of the probe's characteristics on the melting process; what would be the order of magnitude of the penetration velocity. This study explores the technique based on elasto-plastic theory and so-called 'solid water' theory to estimate the melting velocity and to study the melting process. Based on this technique, several cases of melting probe motion are considered, the velocity of the melting probe is estimated, the influence of different factors are studied and discussed, and an easy way to optimize the parameters of the probe is proposed.

  1. Analysis of summer 2002 melt extent on the Greenland ice sheet using MODIS and SSM\\/I data

    Microsoft Academic Search

    Dorothy K. Hall; Richard S. Williams; Konrad Steffen; J. Y. L. Chien

    2004-01-01

    Previous work has shown that the summer of 2002 had the greatest area of snow melt extent on the Greenland ice sheet ever recorded using passive-microwave data. In this paper, we compare the 0deg isotherm derived from the Moderate-Resolution Imaging Spectroradiometer (MODIS) instrument, with Special Sensor Microwave\\/Imager (SSM\\/I)-derived melt, at the time of the maximum melt extent in 2002. To

  2. Development of ice thickness retrieval algorithms for large northern lakes from AMSR-E brightness temperature measurements

    NASA Astrophysics Data System (ADS)

    Kang, K.; Duguay, C. R.; Lemmetyinen, J.; Gel, Y.

    2010-12-01

    Ice cover on lakes is a very sensitive to climate variability and change. With climate warming, lakes have the potential to greatly increase their energy and moisture exchanges with the atmosphere due to earlier break-up and warmer lake temperature during the open water season. Lake ice growth occurs between ice-on date and melt-onset as a result of energy loss by the conductive heat flow to the atmosphere above from the water under the ice to the ice/snow interface. Previous studies have suggested the potential of using brightness temperatures measured from low-frequency passive microwave sensors to estimate lake ice thickness. In this respect, brightness temperatures from current satellite passive microwave platforms (i.e. AMSR-E and SSM/I) are a viable data source for the development of ice thickness retrieval algorithms from space. The major objective of this study is to develop ice algorithms to estimate ice thickness from brightness temperature (TB) measurements obtained from AMSR-E 18.7 GHz channel over large lakes in northern Canada (e.g. Great Bear Lake and Great Slave Lake). The evolution of the horizontally and vertically polarized TB derived from AMSR-E L2A products was compared with ice thickness obtained with a previously validated lake ice model over the course of seven winter seasons (2002-2009). Given that much of the variations in TB could be explained by ice growth, as demonstrated through the use of a recent version of the Helsinki University of Technology (HUT) model, this relation was exploited to develop global and regional ice thickness retrieval algorithms. Following the application of the algorithms, estimated lake ice thickness on GBL is found to be on average 10-20 cm thicker than on GSL. Overall, this study shows that regression-based algorithms using AMSR-E TB data as input can be used to estimate lake ice thickness routinely on the two large northern lakes.

  3. Shock temperatures and melting of iron at Earth core conditions

    Microsoft Academic Search

    C. S. Yoo; N. C. Holmes; M. Ross; D. J. Webb; C. Pike

    1993-01-01

    The temperature of shock compressed iron has been measured to 340 GPa, using well characterized iron films sputtered on transparent diamond substrates and a 1 ns time-resolved optical method. We find a knee on the ([ital P],[ital T]) iron Hugoniot indicating melting at 6350 K and 235 GPa and at 6720 K and 300 GPa. An extrapolation yields an iron

  4. A Climate-Data Record (CDR) of the "Clear-Sky" Surface Temperature of the Greenland Ice Sheet

    NASA Technical Reports Server (NTRS)

    Hall, Dorothy K.; Comiso, Josefino C.; DiGirolamo, Nocolo E.; Shuman, Christopher A.

    2011-01-01

    We have developed a climate-data record (CDR) of "clear-sky" ice-surface temperature (IST) of the Greenland Ice Sheet using Moderate-Resolution Imaging Spectroradiometer (MODIS) data. The CDR provides daily and monthly-mean IST from March 2000 through December 2010 on a polar stereographic projection at a resolution of 6.25 km. The CDR is amenable to extension into the future using Visible/Infrared Imager Radiometer Suite (VIIRS) data. Regional "clear-sky" surface temperature increases since the early 1980s in the Arctic, measured using Advanced Very High Resolution Radiometer (AVHRR) infrared data, range from 0.57 +/- 0.02 to 0.72 +/- 0.1 c per decade. Arctic warming has important implications for ice-sheet mass balance because much of the periphery of the Greenland Ice Sheet is already near O C during the melt season, and is thus vulnerable to rapid melting if temperatures continue to increase. An increase in melting of the ice sheet would accelerate sea-level rise, an issue affecting potentially billions of people worldwide. The IST CDR will provide a convenient data set for modelers and for climatologists to track changes of the surface temperature of the ice sheet as a whole and of the individual drainage basins on the ice sheet. The daily and monthly maps will provide information on surface melt as well as "clear-sky" temperature. The CDR will be further validated by comparing results with automatic-weather station data and with satellite-derived surface-temperature products.

  5. A Shift to Melted Sea Ice From Runoff as the Major Component of Chukchi Shelf Open Water Freshwater Fractions, 1993-2013

    NASA Astrophysics Data System (ADS)

    Cooper, L. W.; Frey, K. E.; Logvinova, C. L.; Biasatti, D. M.; Grebmeier, J. M.

    2014-12-01

    The freshwater fraction of water that is derived from melted sea ice has increased significantly on the Chukchi shelf relative to runoff within the past decade, based upon analysis of salinity and ?18O mixing lines from a number of research cruises from 1993-2013. The shift to summertime dominance of melted sea ice (freshwater end-member ?18O >-10 per mil) relative to runoff occurred within the past ten years with a transition primarily observed from runoff dominance to sea ice melt after 2004. This shift is localized to the Chukchi shelf and does not reflect large amounts of melted sea ice flowing north through Bering Strait, which still largely transports a freshwater component with runoff origins (freshwater end-member ?18O ~-20 per mil). These observations have implications for understanding high latitude shelf biogeochemical cycling as melted sea ice carries much lower fractions of dissolved organic carbon (DOC) than runoff, allowing for greater light penetration, including through melt ponds in sea ice, and potential changes in productivity. Lower alkalinity and buffering capacity in melted sea ice compared to runoff will also increase the vulnerability of shelf organisms to water column acidification. Melted sea ice, with low DOC relative to runoff can dominate the freshwater budget in Chukchi shelf waters even under apparently continuous ice coverage. The higher transmission of light through melted sea ice with low DOC may be in part responsible for recent reported under-ice blooms on the Chukchi shelf. Since these blooms occur in waters with the freshwater budget dominated by melted sea ice, they can reasonably interpreted as being part of a continuum with other ice melt-associated blooms and not independent of sea ice retreat and dissolution.

  6. Frictional melt and seismic slip

    Microsoft Academic Search

    S. Nielsen; G. Di Toro; T. Hirose; T. Shimamoto

    2008-01-01

    Frictional melt is implied in a variety of processes such as seismic slip, ice skating, and meteorite combustion. A steady state can be reached when melt is continuously produced and extruded from the sliding interface, as shown recently in a number of laboratory rock friction experiments. A thin, low-viscosity, high-temperature melt layer is formed resulting in low shear resistance. A

  7. Recent increase in snow-melt area in the Greenland Ice sheet as an indicator of the effect of reduced surface albedo by snow impurities

    NASA Astrophysics Data System (ADS)

    Rikiishi, K.

    2008-12-01

    Recent rapid decline of cryosphere including mountain glaciers, sea ice, and seasonal snow cover tends to be associated with global warming. However, positive feedback is likely to operate between the cryosphere and air temperature, and then it may not be so simple to decide the cause-and-effect relation between them. The theory of heat budget for snow surface tells us that sensible heat transfer from the air to the snow by atmospheric warming by 1°C is about 10 W/m2, which is comparable with heat supply introduced by reduction of the snow surface albedo by only 0.02. Since snow impurities such as black carbon and soil- origin dusts have been accumulated every year on the snow surface in snow-melting season, it is very important to examine whether the snow-melting on the ice sheets, mountain glaciers, and sea ice is caused by global warming or by accumulated snow impurities originated from atmospheric pollutants. In this paper we analyze the dataset of snow-melt area in the Greenland ice sheet for the years 1979 - 2007 (available from the National Snow and Ice Data Center), which is reduced empirically from the satellite micro-wave observations by SMMR and SMM/I. It has been found that, seasonally, the snow-melt area extends most significantly from the second half of June to the first half of July when the sun is highest and sunshine duration is longest, while it doesn't extend any more from the second half of July to the first half of August when the air temperature is highest. This fact may imply that sensible heat required for snow-melting comes from the solar radiation rather than from the atmosphere. As for the interannual variation of snow-melt area, on the other hand, we have found that the growth rate of snow-melt area gradually increases from July, to August, and to the first half of September as the impurities come out to and accumulated at the snow surface. However, the growth rate is almost zero in June and the second half of September when fresh snow of high albedo covers the surface. This fact may imply that the combined operation of solar radiation and snow impurities is responsible for the recent global decline of cryosphere. Discussion about other research works will be given in the presentation in order to support the above idea.

  8. Antarctic Sea ice variations and seasonal air temperature relationships

    NASA Technical Reports Server (NTRS)

    Weatherly, John W.; Walsh, John E.; Zwally, H. J.

    1991-01-01

    Data through 1987 are used to determine the regional and seasonal dependencies of recent trends of Antarctic temperature and sea ice. Lead-lag relationships involving regional sea ice and air temperature are systematically evaluated, with an eye toward the ice-temperature feedbacks that may influence climatic change. Over the 1958-1087 period the temperature trends are positive in all seasons. For the 15 years (l973-l987) for which ice data are available, the trends are predominantly positive only in winter and summer, and are most strongly positive over the Antarctic Peninsula. The spatially aggregated trend of temperature for this latter period is small but positive, while the corresponding trend of ice coverage is small but negative. Lag correlations between seasonal anomalies of the two variables are generally stronger with ice lagging the summer temperatures and with ice leading the winter temperatures. The implication is that summer temperatures predispose the near-surface waters to above-or below-normal ice coverage in the following fall and winter.

  9. Melting behavior of H[subscript 2]O at high pressures and temperatures

    SciTech Connect

    Lin, Jung-Fu; Gregoryanz, Eugene; Struzhkin, Viktor V.; Somayazulu, Maddury; Mao, H.-K.; Hemley, R.J. (CIW)

    2010-07-19

    Water plays an important role in the physics and chemistry of planetary interiors. In situ high pressure-temperature Raman spectroscopy and synchrotron x-ray diffraction have been used to examine the phase diagram of H{sub 2}O. A discontinuous change in the melting curve of H{sub 2}O is observed at approximately 35 GPa and 1040 K, indicating a triple point on the melting line. The melting curve of H{sub 2}O increases significantly above the triple point and may intersect the isentropes of Neptune and Uranus. Solid ice could therefore form in stratified layers at depth within these icy planets. The extrapolated melting curve may also intersect with the geotherm of Earth's lower mantle above 60 GPa. The presence of solid H{sub 2}O would result in a jump in the viscosity of the mid-lower mantle and provides an additional explanation for the observed higher viscosity of the mid-lower mantle.

  10. Effect of the potential melting of the Greenland Ice Sheet on the Meridional Overturning Circulation and global climate in the future

    E-print Network

    Han, Weiqing

    Effect of the potential melting of the Greenland Ice Sheet on the Meridional Overturning February 2011 Keywords: Atlantic Meridional Overturning Circulation Sea level Greenland Ice Sheet Global of the Greenland Ice Sheet since the mid-1990s. This increased ice sheet mass loss might be an evidence of global

  11. 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.

  12. 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.

  13. High Resolution Estimates of Sea Ice Melt-Freeze Transitions in the Northern Canadian Arctic Archipelago from Radarsat

    NASA Astrophysics Data System (ADS)

    Mahmud, M. S.; Yackel, J.; Howell, S.

    2014-12-01

    The northern Canadian Arctic Archipelago (CAA) historically contains high concentration of multi-year ice (MYI). Previous research has shown that this region receives a continuous supply of MYI from the Arctic Ocean that is subsequently flushed southward into the Western Perry Channel during the summer melt season. This amount has never been quantified and the controls on southward advection have only been crudely investigated using coarse spatial resolution passive microwave observations that do not provide sufficient information regarding dynamics and thermodynamics for the sea ice in the northern CAA. This paper evaluates the utility of high spatial resolution synthetic aperture radar (SAR) to better understand the controls on sea ice dynamics within the northern CAA. SAR data was acquired from RADARSAT-1 between April and October, 2005, with an average temporal resolution of 3 days and spatial resolution of 100 m. A melt-freeze transition algorithm was developed to estimate the melt onset date. This is based on the temporal evolution of the backscatter coefficient (?o), which can be thresholded into melt onset for both seasonal first year ice (FYI) and MYI. The amount of sea ice flowing through the northern CAA was determined using the Canadian Ice Service Automated Ice Tracking System. Results indicate that melt onset dates for FYI are observed approximately two weeks earlier than MYI. The earlier melt onset date for FYI resulted in an increased open water area within the CAA, which provided more leeway for southward flow of MYI from the Arctic Ocean, via the northern CAA; leading to earlier than expected MYI flushed into the Western Parry Channel.

  14. Modeling Regolith Temperatures and Volatile Ice Processes (Invited)

    NASA Astrophysics Data System (ADS)

    Mellon, M. T.

    2013-12-01

    Surface and subsurface temperatures are an important tool for exploring the distribution and dynamics of volatile ices on and within planetary regoliths. I will review thermal-analysis approaches and recent applications in the studies of volatile ice processes. Numerical models of regolith temperatures allow us to examine the response of ices to periodic and secular changes in heat sources such as insolation. Used in conjunction with spatially and temporally distributed remotely-sensed temperatures, numerical models can: 1) constrain the stability and dynamics of volatile ices; 2) define the partitioning between phases of ice, gas, liquid, and adsorbate; and 3) in some instances be used to probe the distribution of ice hidden from view beneath the surface. The vapor pressure of volatile ices (such as water, carbon dioxide, and methane) depends exponentially on temperature. Small changes in temperature can result in transitions between stable phases. Cyclic temperatures and the propagation of thermal waves into the subsurface can produce a strong hysteresis in the population and partitioning of various phases (such as between ice, vapor, and adsorbate) and result in bulk transport. Condensation of ice will also have a pronounced effect on the thermal properties of otherwise loose particulate regolith. Cementing grains at their contacts through ice deposition will increase the thermal conductivity, and may enhance the stability of additional ice. Likewise sintering of grains within a predominantly icy regolith will increase the thermal conductivity. Subsurface layers that result from ice redistribution can be discriminated by remote sensing when combined with numerical modeling. Applications of these techniques include modeling of seasonal carbon dioxide frosts on Mars, predicting and interpreting the subsurface ice distribution on Mars and in Antarctica, and estimating the current depth of ice-rich permafrost on Mars. Additionally, understanding cold trapping ices in regions of the regolith of airless bodies, such as Mercury and the Moon, are aided by numerical modeling of regolith temperatures. Thermally driven sublimation of volatiles (water ice on Mars and more exotic species on icy moons in the outer solar system) can result in terrain degradation and collapse.

  15. An 800-kyr Record of Global Surface Ocean ?18Osw and Implications for Ice Volume-Temperature Coupling

    NASA Astrophysics Data System (ADS)

    Shakun, J. D.; Lea, D. W.; Lisiecki, L. E.; Raymo, M. E.

    2014-12-01

    We use 49 paired sea surface temperature (SST)-planktonic ?18O records to extract the mean ?18O of surface ocean seawater (?18Osw) over the past 800 kyr, which we interpret to dominantly reflect global ice volume, and compare it to SST variability on the same stratigraphy. This analysis suggests that ice volume and temperature contribute to the marine isotope record in ~60/40 proportions, but they show consistently different patterns over glacial cycles. Global temperature cools early during each cycle while major ice sheet growth occurs later, suggesting that ice volume may have exhibited a threshold response to cooling and also had relatively little feedback on it. Multivariate regression analysis suggests that the rate of ice volume change through time is largely determined by the combined influence of orbital forcing, global temperature, and ice volume itself (r2 = 0.70 at zero-lag for 0-400 ka), with sea level rising faster with stronger insolation and warmer temperatures and when there is more ice available to melt. Indeed, cross-spectral analysis indicates that ice volume exhibits a smaller phase lag and larger gain relative to SST at the 41 and 23 kyr periods than at the 100 kyr period, consistent with additional forcing from insolation at the obliquity and precession time scales. Removing the surface ocean ?18Osw signal from the global benthic ?18O stack produces a reconstruction of deep ocean temperature that bears considerable similarity to the Antarctic ice core temperature record (r2 = 0.80 for 0-400 ka), including cooler interglacials before 400 ka. Overall, we find a close association between global surface temperature, deep ocean temperature, and atmospheric CO2. Additionally, we find that rapid cooling precedes the gradual buildup of large continental ice sheets, which may then be instrumental in terminating the cycle.

  16. Potential methane emission from north-temperate lakes following ice melt

    USGS Publications Warehouse

    Michmerhuizen, C.M.; Striegl, R.G.; McDonald, M.E.

    1996-01-01

    Methane, a radiatively active 'greenhouse' gas, is emitted from lakes to the atmosphere throughout the open-water season. However, annual lake CH4 emissions calculated solely from open-water measurements that exclude the time of spring ice melt may substantially underestimate the lake CH4 source strength. We estimated potential spring CH4 emission at the time of ice melt for 19 lakes in northern Minnesota and Wisconsin. Lakes ranged in area from 2.7 to 57,300 ha and varied in littoral zone sediment type. Regression analyses indicated that lake area explained 38% of the variance in potential CH4 emission for relatively undisturbed lakes; as lake area increases potential CH4 emission per unit area decreases. Inclusion of a second term accounting for the presence or absence of soft organic-rich littoral-zone sediments explained 83% of the variance in potential spring CH4 emission. Total estimated spring CH4 emission for 1993 for all Minnesota lakes north of 45?? with areas ???4 ha was 1.5 x 108 mol CH4 assuming a 1 : 1 ratio of soft littoral sediment to hard littoral sediment lakes. Emission estimates ranged from 5.3 x 107 tool assuming no lakes have soft organic-rich littoral sediments to 4.5 x 108 mol assuming all lakes have soft organic-rich littoral sediments. This spring CH4 pulse may make up as much as 40% of the CH4 annually emitted to the atmosphere by small lakes.

  17. Light absorption and partitioning in Arctic Ocean surface waters: impact of multi year ice melting

    NASA Astrophysics Data System (ADS)

    Bélanger, S.; Cizmeli, S. A.; Ehn, J.; Matsuoka, A.; Doxaran, D.; Hooker, S.; Babin, M.

    2013-03-01

    Ice melting in the Arctic Ocean exposes the surface water to more radiative energy with poorly understood effects on photo-biogeochemical processes and heat deposition in the upper ocean. In August 2009, we documented the vertical variability of light absorbing components at 37 stations located in the southeastern Beaufort Sea including both Mackenzie river-influenced waters and polar mixed layer waters. We found that melting multi-year ice released significant amount of non-algal particulates (NAP) near the sea surface relative to sub-surface waters. NAP absorption coefficients at 440 nm (aNAP(440)) immediately below the sea surface (0-) were on average 3-fold (up to 10-fold) higher compared to sub-surface values measured at 2-3 m depth. The impact of this unusual feature on the light transmission and remote sensing reflectance (Rrs) was further examined using a radiative transfer model. A 10-fold particle enrichment homogeneously distributed in the first meter of the water column slightly reduced photosynthetically available and usable radiation (PAR and PUR) by ~6% and ~8%, respectively, relative to a fully homogenous water column with low particles concentration. In terms of Rrs, the particle enrichment significantly flattered the spectrum by reducing the Rrs by up to 20% in the blue-green spectral region (400-550 nm). These results highlight the impact of melt water on the concentration of particles at sea surface, and the need for considering nonuniform vertical distribution of particles in such systems when interpreting remotely sensed ocean color. Spectral slope of aNAP spectra calculated in the UV domain decreased with depth suggesting that this parameter is sensitive to detritus composition and/or diagenesis state (e.g., POM photobleaching).

  18. Seasonal sea ice melt pond fraction and pond freezing estimation using dual-polarisation C-band synthetic aperture radar

    NASA Astrophysics Data System (ADS)

    Scharien, R. K.; Landy, J.; Howell, S.; Warner, K.; Barber, D. G.

    2014-12-01

    Sea ice melt ponds play an important role in spring-summer radiation absorption and upper ocean warming, light transmittance and under-ice primary production, and biogeochemical exchanges. With a larger portion of Arctic first-year sea ice (FYI) compared to multiyear ice observed in recent years comes the expectation of greater melt pond fraction due to the absence of topographical controls on FYI. Despite progress in our understanding and modelling of pond fraction evolution and coupled processes at the local scale, a reliable means for monitoring variations at regional or greater scales, uninhibited by cloud cover, is lacking. In this study we demonstrate the ability of dual-polarisation C-band synthetic aperture radar (SAR) for estimating pond fraction and freezing conditions on level FYI in the Canadian Arctic Archipelago. We use a combination of in situ C-band scatterometer and radar-scale surface roughness observations to study the dual-polarisation channel (VV+HH and HV+HH) and channel ratio characteristics of individual melt ponds and ice patches. Aerial surveys of pond fraction are used to evaluate retrieval approaches from Radarsat-2 SAR fine quad-polarisation mode imagery. Accurate retrievals of pond fraction are found using the VV/HH polarisation ratio during melting conditions. Results demonstrate the potential of dual-polarisation SAR for regional scale observations with temporal frequency suitable for contributing to process-scale studies and improvements to model parameterizations.

  19. Burnup dependence of melting temperature of FBR mixed oxide fuels irradiated to high burnup

    NASA Astrophysics Data System (ADS)

    Hirosawa, Takashi; Sato, Isamu

    2011-11-01

    The melting temperatures of FBR MOX fuels with Pu content of 28-30 wt.% irradiated to from 22.5 to 112.5 MWd kg -1 were measured using a rhenium inner capsule to hold the specimens. The rhenium inner capsule could prevent chemical reactions between fuels and tungsten materials which decrease the melting temperature. The melting temperatures were about 30 K higher than the previous data using tungsten capsules. The melting temperature decreases in a linear manner with burnup due to solid solution of fission products in fuels. However, the slopes of the lines plotting melting temperature versus burnup are almost similar to the previous data.

  20. Electronic Desorption from Internal Surfaces of Porous Low Temperature Ice

    NASA Astrophysics Data System (ADS)

    Grieves, G. A.; Orlando, T. M.

    2006-05-01

    Radiation induced surface desorption from low temperature water ice plays a crucial role in the astrochemistry of icy planetary surfaces, comets and ice-covered interstellar grains. Excitations from low energy electrons (5- 100 eV) or VUV photons can hop between the strongly coupled hydrogen bonding network and migrate until they encounter a surface or a defect where they localize and induce dissociation. Ices deposited at very low temperatures, such as those in interstellar space, exhibit an exceptionally low density and have a highly porous amorphous structure. These pores represent large open structures and enclose a volume of vacuum and give the porous ice an enormous internal surface area. These pores are also likely to play an important role in spontaneous segregation of hydrophobic organic contaminants. The electronic structure of ice at the interface of these pores should resemble that of the outer surface vacuum interface. The effects of porosity and morphology of amorphous and crystalline D2O ices on the electron stimulated generation and trapping of D2 and O2 have been studied by post-irradiation thermal desorption. Molecular deuterium is released in the temperature range from 55 - 105 K for each of the samples, with two notable bursts at 115 and 132 K for porous amorphous ice. The majority of trapped O2 coevolves with desorption of the ice matrix, suggesting that clathrate hydrates may be important trapping sites. Production and trapping of organic polymers within pores from coadsorbed methane and ammonia are also discussed.

  1. Numerical evidence of quantum melting of spin ice: quantum-classical crossover

    NASA Astrophysics Data System (ADS)

    Kato, Yasuyuki; Onoda, Shigeki

    2015-03-01

    Unbiased quantum Monte-Carlo simulations are performed on the simplest case of the quantum spin ice model, namely, the nearest-neighbor spin-1/2 XXZ model on the pyrochlore lattice with an antiferromagnetic longitudinal and a weak ferromagnetic transverse exchange couplings, J and J?. On cooling across TCSI ~ 0 . 2 J , the specific heat shows a broad peak associated with a crossover to a classical Coulomb liquid regime characterized by a remnant of the pinch-point singularity in longitudinal spin correlations as well as the Pauling ice entropy for | J? | << J , as in classical spin ice. On further cooling, the entropy restarts gradually decaying to zero for J? >J? c ~ - 0 . 104 J , as expected for bosonic quantum Coulomb liquids. With negatively increasing J? across J? c, a first-order transition occurs at a nonzero temperature from the quantum Coulomb liquid to an XY ferromagnet. Relevance to magnetic rare-earth pyrochlore oxides is discussed.

  2. Development of a Climate-Data Record (CDR) of the Surface Temperature of the Greenland Ice Sheet

    NASA Technical Reports Server (NTRS)

    Hall, Dorthy K.; Comiso, Josefino C.; Shuman, Christopher A.; DiGirolamo, Nicolo E.; Stock, Larry V.

    2010-01-01

    Regional "clear sky" surface temperature increases since the early 1980s in the Arctic, measured using Advanced Very High Resolution Radiometer (AVHRR) infrared data, range from 0.57+/-0.02 deg C to 72+/-0.10 deg C per decade. Arctic warming has important implications for ice-sheet mass balance because much of the periphery of the Greenland Ice Sheet is already near 0 deg C during the melt season, and is thus vulnerable to rapid melting if temperatures continue to increase. An increase in melting of the ice sheet would accelerate sea-level rise, an issue affecting potentially billions of people worldwide. To quantify the ice-surface temperature (IST) of the Greenland Ice Sheet, and to provide an IST dataset of Greenland for modelers that provides uncertainties, we are developing a climate-data record (CDR) of daily "clear-sky" IST of the Greenland Ice Sheet, from 1982 to the present using AVHRR (1982 - present) and Moderate-Resolution Imaging Spectroradiometer (MODIS) data (2000 - present) at a resolution of approximately 5 km. Known issues being addressed in the production of the CDR are: time-series bias caused by cloud cover (surface temperatures can be different under clouds vs. clear areas) and cross-calibration in the overlap period between AVHRR instruments, and between AVHRR and MODIS instruments. Because of uncertainties, mainly due to clouds, time-series of satellite IST do not necessarily correspond with actual surface temperatures. The CDR will be validated by comparing results with automatic-weather station data and with satellite-derived surface-temperature products and biases will be calculated.

  3. Low temperature melting of copper nanorod arrays Tansel Karabacak,a

    E-print Network

    Wang, Gwo-Ching

    Low temperature melting of copper nanorod arrays Tansel Karabacak,a James S. DeLuca, and Pei-I Wang arrays of copper at temperatures much lower than its bulk melting point 1083 °C . The Cu nanorods were that the melting behavior of nanometer-size particles can be quite different from that of bulk materials see Refs

  4. arXiv:1408.2487v2[physics.ao-ph]22Aug2014 Ising model for melt ponds on Arctic sea ice

    E-print Network

    Golden, Kenneth M.

    arXiv:1408.2487v2[physics.ao-ph]22Aug2014 Ising model for melt ponds on Arctic sea ice Yi-Ping Ma,1, USA The albedo of melting Arctic sea ice, a key parameter in climate modeling, is determined by pools of about 100 square meters. To explain this behavior and provide a statistical physics approach to sea ice

  5. Equations of state of ice VI and ice VII at high pressure and high temperature

    NASA Astrophysics Data System (ADS)

    Bezacier, Lucile; Journaux, Baptiste; Perrillat, Jean-Philippe; Cardon, Hervé; Hanfland, Michael; Daniel, Isabelle

    2014-09-01

    High-pressure H2O polymorphs among which ice VI and ice VII are abundant in the interiors of large icy satellites and exo-planets. Knowledge of the elastic properties of these pure H2O ices at high-temperature and high-pressure is thus crucial to decipher the internal structure of icy bodies. In this study we assess for the first time the pressure-volume-temperature (PVT) relations of both polycrystalline pure ice VI and ice VII at high pressures and temperatures from 1 to 9 GPa and 300 to 450 K, respectively, by using in situ synchrotron X-ray diffraction. The PVT data are adjusted to a second-order Birch-Murnaghan equation of state and give V0 = 14.17(2) cm3 mol-1, K0 = 14.05(23) GPa, and ?0 = 14.6(14) × 10-5 K-1 for ice VI and V0 = 12.49(1) cm3 mol-1, K0 = 20.15(16) GPa, and ?0 = 11.6(5) × 10-5 K-1 for ice VII.

  6. Reply to “Comment on ‘Determination of the bulk melting temperature of nickel using Monte Carlo simulations: Inaccuracy of extrapolation from cluster melting temperatures' ”

    E-print Network

    Los, J. H.

    The thermodynamic integration (TI) method for determining the melting temperature has to be performed with great care to ensure accuracy. Since the slopes of the Gibbs free energy curves as a function of temperature (or ...

  7. CO2 isotopes as tracers of firn air diffusion and age in an Arctic ice cap with summer melting, Devon Island, Canada

    E-print Network

    Chappellaz, Jérôme

    CO2 isotopes as tracers of firn air diffusion and age in an Arctic ice cap with summer melting and the effects of summer melting. The 14 CO2 profile from the permeable firn includes the 1963 thermonuclear peak no indication of alteration by summer melting, which is attributed to a high degree of convective and diffusive

  8. Light absorption and partitioning in Arctic Ocean surface waters: impact of multiyear ice melting

    NASA Astrophysics Data System (ADS)

    Bélanger, S.; Cizmeli, S. A.; Ehn, J.; Matsuoka, A.; Doxaran, D.; Hooker, S.; Babin, M.

    2013-10-01

    Ice melting in the Arctic Ocean exposes the surface water to more radiative energy with poorly understood effects on photo-biogeochemical processes and heat deposition in the upper ocean. In August 2009, we documented the vertical variability of light absorbing components at 37 stations located in the southeastern Beaufort Sea including both Mackenzie River-influenced waters and polar mixed layer waters. We found that melting multiyear ice released significant amount of non-algal particulates (NAP) near the sea surface relative to subsurface waters. NAP absorption coefficients at 440 nm (aNAP(440)) immediately below the sea surface were on average 3-fold (up to 10-fold) higher compared to subsurface values measured at 2-3 m depth. The impact of this unusual feature on the light transmission and remote sensing reflectance (Rrs) was further examined using a radiative transfer model. A 10-fold particle enrichment homogeneously distributed in the first meter of the water column slightly reduced photosynthetically available and usable radiation (PAR and PUR) by ∼6 and ∼8%, respectively, relative to a fully homogenous water column with low particle concentration. In terms of Rrs, the particle enrichment significantly flattered the spectrum by reducing the Rrs by up to 20% in the blue-green spectral region (400-550 nm). These results highlight the impact of meltwater on the concentration of particles at sea surface, and the need for considering non-uniform vertical distribution of particles in such systems when interpreting remotely sensed ocean color. Spectral slope of aNAP spectra calculated in the UV (ultraviolet) domain decreased with depth suggesting that this parameter is sensitive to detritus composition and/or diagenesis state (e.g., POM (particulate organic matter) photobleaching).

  9. 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.

  10. Correlations between Inter-Annual Variations in Arctic Sea Ice Extent, Greenland Surface Melt, and Boreal Snow Cover

    NASA Technical Reports Server (NTRS)

    Markus, Thorstena; Stroeve, Julienne C.; Armstrong, Richard L.

    2004-01-01

    Intensification of global warming in recent decades has caused a rise of interest in year-to-year and decadal-scale climate variability in the Arctic. This is because the Arctic is believed to be one of the most sensitive and vulnerable regions to climatic changes. For over two decades satellite passive microwave observations have been utilized to continuously monitor the Arctic environment. Derived parameters include sea ice cover, snow cover and snow water equivalent over land, and Greenland melt extent and length of melt season. Most studies have primarily concentrated on trends and variations of individual variables. In this study we investigated how variations in sea ice cover, Greenland surface melt, and boreal snow cover are correlated. This was done on hemispheric as well as on regional scales. Latest results will be presented including data from the summer of 2004.

  11. 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.

  12. Measurements of restitution coefficients of ice at low temperatures

    Microsoft Academic Search

    M. Higa; M. Arakawa; N. Maeno

    1996-01-01

    Measurements of the restitution coefficient (?) of a smooth water ice sphere (radius = 1.5 cm) are made in a wide range of impact velocities (1??i?700cms?1) and temperatures (113?T?269K). The impact velocity dependence of ? is different in the quasi-elastic and inelastic regimes separated by a critical velocity (?c) at which fracture deformation occurs at the impact point of ice

  13. The Atlantic Meridional Overturning Circulation Stability Influenced by the Melting of the Greenland Ice Sheet under Various Warming Scenarios

    NASA Astrophysics Data System (ADS)

    Gierz, P.; Lohmann, G.; Wei, W.; Barbi, D.

    2012-12-01

    In this study, we aim to model melting processes of the Greenland ice sheet over the next 1000 years using the Earth system model COSMOS with a dynamic ice sheet module. Of primary interest is the resulting impact on the Atlantic meridional overturning circulation (GMOC/AMOC), which is expected to slow in response to a large freshwater (eg melt water) input. Six warming scenarios will be considered, one set corresponding to the IPCC's RPC Scenario 6, and another set corresponding to RPC Scenario 4.5, each time with 0.5, 1, and 2% increase of greenhouse gas concentration per year. It is expected that the freshwater input will slow down the AMOC overturning; each scenario producing a unique braking signal corresponding to how rapidly the Greenland ice sheet is forced to melt. It will be interesting to see if there is a CO2 threshold level at which the slowdown of the AMOC begins and the melting phenomena becomes unstable and positively reinforces itself or instead, as previous studies have demonstrated with a prescribed amount of melting, if the freshwater input always allows for an eventual recovery of the AMOC to a stable state regardless of the rapidity with which the salinity anomalies develop. The primary difference between this set of experiments and those in previous studies shall be the dynamic nature of the ice sheet model, as we will allow the Greenland ice sheet to melt solely based upon atmospheric conditions rather than prescribing a salinity change directly into the ocean model. It is expected that higher levels of greenhouse gases will result in more rapid melting, which in turn will have a stronger braking affect on the AMOC, possibly with longer recovery times to the starting equilibrium point. It will additionally be of interest to see if it is possible to create a shift in this equilibrium, suggesting that the rapidity with which density anomalies are introduced may create a new stable deep water formation rate. PRELIMINARY RESULTS - AMOC downwelling strength with changes in dynamically modeled Ice Sheet volume. AMOC seems to decrease with varying magnitudes depending upon the rate of carbon dioxide release and the amount of meltwater generated.

  14. Self-consistent ice-sheet properties: ice dynamics, temperature, accumulation, delta-age and chronologies for ice cores and radar isochrones

    NASA Astrophysics Data System (ADS)

    Lundin, J.; Waddington, E. D.; Conway, H.

    2011-12-01

    Ice sheet behavior has not previously been modeled to force self-consistency, to determine histories of accumulation, temperature, and ice dynamics that incorporate the ice-age/gas-age offset (delta-age) and sparse depth-age measurements from ice cores. An iterative scheme is used to combine several modular components into one self-consistent model. The goal is to determine a suite of histories constrained by the depth-age data from ice cores and ice radar that are part of a physically self-consistent ice sheet. The model is tested using a synthetic data set resembling WAIS divide. Using synthetic data provides proof of concept that histories of accumulation, temperature and ice dynamics can be recovered by the self-consistent model, and that the depth-age from ice cores and ice radar can be matched. Results from synthetic data show we can recover the ice-sheet properties used to generate the data and we can improve the depth-age chronologies by interpolating with an ice-flow model where data are sparse. When this self-consistent model can be applied to field data, results will (1) improve chronologies for ice cores and radar layers, (2) determine histories of accumulation for GCM modelling, and (3) improve estimates of past ice sheet configurations, incorporating data from ice cores and ice radar.

  15. In situ high-pressure and high-temperature bubble growth in silicic melts

    E-print Network

    Paris-Sud XI, Université de

    in a superheated infinite one-phase system [2] to many identical cells of one bubble surrounded by melt, in which diffusion in the melt, viscous deformation of the melt, and mass balance of volatiles at the bubble temperature using heating stage devices [8, 9 and 10]. These in situ methods allow the direct observation

  16. Substrate Effect on the Melting Temperature of Thin Polyethylene Films M. Rafailovich,1,* J. Sokolov,1

    E-print Network

    technique, lateral scanning force modulation, was used to determine the melting point of the semicrystalline of surface interactions, as well as crystalline orientation and morphology, on the melting point of crysSubstrate Effect on the Melting Temperature of Thin Polyethylene Films Y. Wang,1 M. Rafailovich,1

  17. Pressure dependence of the melting temperature of solids - Rare-gas solids

    NASA Technical Reports Server (NTRS)

    Schlosser, Herbert; Ferrante, John

    1991-01-01

    A method presented by Schlosser et al. (1989) for analyzing the pressure dependence of experimental melting-temperature data is applied to rare-gas solids. The plots of the logarithm of the reduced melting temperature vs that of the reduced pressure are straight lines in the absence of phase transitions. The plots of the reduced melting temperatures for Ar, Kr, and Xe are shown to be approximately straight lines.

  18. Structure and dynamics of magnesium in silicate melts: A high-temperature 25Mg NMR study

    Microsoft Academic Search

    ANNA M. GEORGE; JONATHAN F. STEBBINS

    Mg NMR spectra for several silicate and aluminosilicate melts were obtained from 1000-1470 8C. The peaks are initially very broad, but narrow with increasing temperature to near 500 Hz at the highest temperatures. The peak positions for most of the melts do not shift noticeably with temperature in the range studied, except for a sodium magnesium silicate composition that was

  19. Short Communication: Atmospheric moisture transport, the bridge between ocean evaporation and Arctic ice melting

    NASA Astrophysics Data System (ADS)

    Gimeno, L.; Vázquez, M.; Nieto, R.; Trigo, R. M.

    2015-06-01

    If we could choose a region where the effects of global warming are likely to be pronounced and considerable, and at the same time one where the changes could affect the global climate in similarly asymmetric way with respect to other regions, this would unequivocally be the Arctic. The atmospheric branch of the hydrological cycle lies behind the linkages between the Arctic system and the global climate. Changes in the atmospheric moisture transport have been proposed as a vehicle for interpreting the most significant changes in the Arctic region. This is because the transport of moisture from the extratropical regions to the Arctic has increased in recent decades, and is expected to increase within a warming climate. This increase could be due either to changes in circulation patterns which have altered the moisture sources, or to changes in the intensity of the moisture sources because of enhanced evaporation, or a combination of these two mechanisms. In this short communication we focus on the assessing more objectively the strong link between ocean evaporation trends and Arctic Sea ice melting. We will critically analyze several recent results suggesting links between moisture transport and the extent of sea-ice in the Arctic, this being one of the most distinct indicators of continuous climate change both in the Arctic and on a global scale. To do this we will use a sophisticated Lagrangian approach to develop a more robust framework on some of these previous disconnect ng results, using new information and insights. Among the many mechanisms that could be involved are hydrological (increased Arctic river discharges), radiative (increase of cloud cover and water vapour) and meteorological (increase in summer storms crossing the Arctic, or increments in precipitation).

  20. Perchlorate Found by Phoenix Could Provide a Mobile Brine Sludge at the Bed of Mars Northern Ice Cap that Would Allow Flow with Very Low Basal Temperatures: Possible Mechanism for Water Table Re-Charge

    NASA Astrophysics Data System (ADS)

    Fisher, D. A.; Hecht, M.; Kounaves, S.; Catling, D.

    2009-03-01

    The north cap of Mars has basal temperature that precludes the flow of ice. Phoenix discovered polar soils contain perchlorate salts. These salts depress the melting point so it could form a sludge that provides a mobile bed that moves the ice outwards.

  1. Ice moderator experiments at very low temperatures

    NASA Astrophysics Data System (ADS)

    Nünighoff, K.; Pohl, Ch.; Bollini, V.; Bubak, A.; Conrad, H.; Filges, D.; Glückler, H.; Goldenbaum, F.; Hansen, G.; Lensing, B.; Neef, R.-D.; Paul, N.; Prasuhn, D.; Pysz, K.; Schaal, H.; Soltner, H.; Stelzer, H.; Tietze-Jaensch, H.; Bernnat, W.; Keinert, J.; Mattes, M.; Ninaus, W.; Koulikov, S.; Smirnov, A.; Wohlmuther, M.

    2004-12-01

    In this article measured time-of-flight spectra and energy spectra of a water moderator operated at various temperatures between 20K and room temperature are described. These data are used to validate generated and processed neutron scattering law data. It was possible to simulate the leakage spectrum of a water moderator at cryogenic temperatures and compare it with experimental results.

  2. Phase change nanocomposites with tunable melting temperature and thermal energy storage density.

    PubMed

    Liu, Minglu; Wang, Robert Y

    2013-08-21

    Size-dependent melting decouples melting temperature from chemical composition and provides a new design variable for phase change material applications. To demonstrate this potential, we create nanocomposites that exhibit stable and tunable melting temperatures through numerous melt-freeze cycles. These composites consist of a monodisperse ensemble of Bi nanoparticles (NPs) embedded in a polyimide (PI) resin matrix. The Bi NPs operate as the phase change component whereas the PI resin matrix prevents nanoparticle coalescence during melt-freeze cycles. We tune melting temperature and enthalpy of fusion in these composites by varying the NP diameter. Adjusting the NP volume fraction also controls the composite's thermal energy storage density. Hence it is possible to leverage size effects to tune phase change temperature and energy density in phase change materials. PMID:23835614

  3. Using pan-Arctic, springtime, surface radiation observations to quantify atmospheric preconditioning processes that impact the sea ice melt season

    NASA Astrophysics Data System (ADS)

    Cox, Christopher; Uttal, Taneil; Starkweather, Sandy; Intrieri, Janet; Maturilli, Marion; Kustov, Vasily; Konopleva, Elena; Crepinsek, Sara; Long, Chuck

    2015-04-01

    Accurate, seasonal-scale forecasts of sea ice extent and distribution are critical for weather forecasting, transportation, the energy industry and local Arctic communities. Current forecasting methods capture an overall trend of decreasing sea ice on decadal scales, but do not reliably predict inter-annual variability. Recent work using satellite observations identified a relationship between spring-time, cloud modulated, shortwave radiation, and late season sea-ice extent; this relationship suggested an atmospheric preconditioning process that modulates the ice-albedo feedback and sets the stage for the melt season. Due to a general lack of emphasis on the role of the atmosphere on the evolution of the summer sea-ice, compounded by biases in cloud properties within models, this preconditioning process is poorly represented in current forecasting methods. Longwave and shortwave radiation data collected at the surface from stations surrounding the Arctic Basin as part of the Baseline Surface Radiation Network (BSRN) provide high-quality, continuous observations of the surface radiation budget. This includes downwelling fluxes and surface-cloud radiative interactions which cannot be directly acquired by satellites. These BSRN data are used to investigate the role of the atmosphere and clouds in seasonal scale variability of sea ice conditions, and the potential for improving predictability by incorporating these atmospheric observations into prediction strategies. We find that the downwelling fluxes measured at the land stations in spring are well correlated with sea ice conditions in September, especially in regions of the Arctic Ocean where late summer sea ice concentration has large inter-annual variability. Using observations of the total radiative flux (longwave + shortwave) at the surface, it is possible to make a seasonal sea-ice extent forecast that is within the range of uncertainty of forecasts currently incorporated into the Sea Ice Prediction Network (SIPN). Cloud variability and associated shortwave modulation of the ice-albedo feedback are found to be important, but the shortwave anomaly alone is insufficient unless combined with the longwave anomaly, which dominates and is opposite in sign in the presence of clouds. The amount of open water in the Western Arctic in September and October then controls cloud cover during the autumn freeze-up, potentially revealing a preconditioning mechanism that persists into the following melt season.

  4. Limits to future expansion of surface-melt-enhanced ice flow into the interior of western Greenland

    NASA Astrophysics Data System (ADS)

    Poinar, Kristin; Joughin, Ian; Das, Sarah B.; Behn, Mark D.; Lenaerts, Jan T. M.; Broeke, Michiel R.

    2015-03-01

    Moulins are important conduits for surface meltwater to reach the bed of the Greenland Ice Sheet. It has been proposed that in a warming climate, newly formed moulins associated with the inland migration of supraglacial lakes could introduce surface melt to new regions of the bed, introducing or enhancing sliding there. By examining surface strain rates, we found that the upper limit to where crevasses, and therefore moulins, are likely to form is ~1600 m. This is also roughly the elevation above which lakes do not drain completely. Thus, meltwater above this elevation will largely flow tens of kilometers through surface streams into existing moulins downstream. Furthermore, results from a thermal ice sheet model indicate that the ~1600 m crevassing limit is well below the wet-frozen basal transition (~2000 m). Together, these data sets suggest that new supraglacial lakes will have a limited effect on the inland expansion of melt-induced seasonal acceleration.

  5. High-Temperature Vibrational Properties and Melting Curve of Aluminum

    NASA Astrophysics Data System (ADS)

    Bhatt, N. K.; Thakore, B. Y.; Vyas, P. R.; Jani, A. R.

    2010-12-01

    The mean-field theory due to Wang and Li (Phys Rev B 63:196, 2000) to calculate the effective mean potential experienced by vibrating ions in a crystal is used to compute the ion-motional free energy. An improvement is sought by treating the parameter ?, entering an expression of the mean-field potential (MFP), as a free parameter for the case of aluminum. Although a corresponding expression for the Grüneisen parameter ( ?) is significantly different then the known cases, namely, those due to (i) Slater, (ii) Dugdale and MacDonald, (iii) free volume theory, and (iv) Barton and Stacey, its value is very close to the experimental result. Significant improvement is observed for high-temperature thermodynamics of aluminum with the new choice of ?, or equivalently ?. Also, the present improved scheme is extended to measure the vibrational response of the crystal. Recently, Bhatt et al. (Philos Mag 90:1599, 2010) have demonstrated that the mean frequency ( ?') calculated by the MFP approach in conjunction with the density-dependent local pseudopotential suffices to characterize the crystal at finite temperatures. Relating ?' to the Debye frequency, vibrational properties like the Debye temperature, the mean-square displacement, and entropy are obtained as a function of temperature. Further, a generalized melting law is derived by combining the MFP approach to Lindemann's law, where the effect of different choices of the parameter ? is now explicitly included into the description. Results so obtained for different physical properties are analyzed and discussed in the light of recent first principles and experimental findings.

  6. Sea-ice melt CO2-carbonate chemistry in the western Arctic Ocean: meltwater contributions to air-sea CO2 gas exchange, mixed-layer properties and rates of net community production under sea ice

    NASA Astrophysics Data System (ADS)

    Bates, N. R.; Garley, R.; Frey, K. E.; Shake, K. L.; Mathis, J. T.

    2014-12-01

    The carbon dioxide (CO2)-carbonate chemistry of sea-ice melt and co-located, contemporaneous seawater has rarely been studied in sea-ice-covered oceans. Here, we describe the CO2-carbonate chemistry of sea-ice melt (both above sea-ice as "melt ponds" and below sea-ice as "interface waters") and mixed-layer properties in the western Arctic Ocean in the early summer of 2010 and 2011. At 19 stations, the salinity (∼0.5 to <6.5), dissolved inorganic carbon (DIC; ∼20 to <550 ?mol kg-1) and total alkalinity (TA; ∼30 to <500 ?mol kg-1) of above-ice melt pond water was low compared to the co-located underlying mixed layer. The partial pressure of CO2 (pCO2) in these melt ponds was highly variable (∼<10 to >1500 ?atm) with the majority of melt ponds acting as potentially strong sources of CO2 to the atmosphere. The pH of melt pond waters was also highly variable ranging from mildly acidic (6.1 to 7) to slightly more alkaline than underlying seawater (>8.2 to 10.8). All of the observed melt ponds had very low (<0.1) saturation states (?) for calcium carbonate (CaCO3) minerals such as aragonite (?aragonite). Our data suggest that sea-ice generated alkaline or acidic type melt pond water. This melt water chemistry dictates whether the ponds are sources of CO2 to the atmosphere or CO2 sinks. Below-ice interface water CO2-carbonate chemistry data also indicated substantial generation of alkalinity, presumably owing to dissolution of CaCO3 in sea-ice. The interface waters generally had lower pCO2 and higher pH/?aragonite than the co-located mixed layer beneath. Sea-ice melt thus contributed to the suppression of mixed-layer pCO2, thereby enhancing the surface ocean's capacity to uptake CO2 from the atmosphere. Our observations contribute to growing evidence that sea-ice CO2-carbonate chemistry is highly variable and its contribution to the complex factors that influence the balance of CO2 sinks and sources (and thereby ocean acidification) is difficult to predict in an era of rapid warming and sea-ice loss in the Arctic Ocean.

  7. Effect of melting temperature and time on iron valence and crystallization of iron phosphate glasses

    Microsoft Academic Search

    C. S Ray; X Fang; M Karabulut; G. K Marasinghe; D. E Day

    1999-01-01

    The effect of melting temperature and time on iron valence, dissolution rate (DR) in deionized water, and crystallization of iron phosphate glasses was investigated using a 40Fe2O3–60P2O5, mol%, batch composition. The concentration of Fe2+ ions in these glasses increased from 17% to 57% as melting temperature increased from 1150°C to 1450°C, but remained nearly constant at about 20% for melting

  8. Temperatures in Earth's Core Based on Melting and Phase Transformation Experiments on Iron

    Microsoft Academic Search

    S. K. Saxena; G. Shen; P. Lazor

    1994-01-01

    Experiments on melting and phase transformations on iron in a laser-heated, diamondanvil cell to a pressure of 150 gigapascals (approximately 1.5 million atmospheres) show that iron melts at the central core pressure of 363.85 gigapascals at 6350 ± 350 kelvin. The central core temperature corresponding to the upper temperature of iron melting is 6150 kelvin. The pressure dependence of iron

  9. Bubble nucleation in rhyolite and dacite melts: temperature dependence of surface tension

    Microsoft Academic Search

    James E. GardnerRichard; Richard A. Ketcham

    Surface tension (?) profoundly influences the ability of gas bubbles to nucleate in silicate melts. To determine how temperature impacts ?, experiments were carried out in which high-silica rhyolite melts with 5 wt% dissolved water were decompressed at temperatures\\u000a that ranged from 775 to 1,085°C. Decompressions were also carried out using dacite melts with 4.3 wt% dissolved water at 1,150°C.\\u000a Water bubbles

  10. Impact experiments in low-temperature ice

    NASA Astrophysics Data System (ADS)

    Lange, M. A.; Ahrens, T. J.

    1987-03-01

    Cubic and cylindrical water ice targets at 257 and 81 K have been subjected to impact velocities between 0.1 and 0.64 km/sec and impact energies of 10 to the 9th-10 to the 10th ergs, yielding craters that are 2-3 times larger than those obtained through equal energy impacts in basaltic targets. On the basis of a similarity analysis, general scaling laws are derived for strength-controlled crater formation and applied in a consideration of crater formation on the icy Galilean and Saturnian satellites. Surface ages are predicted by the analysis to appear greater than those for a silicate crust experiencing the same impact history, on the basis of icy crust impact crater statistics.

  11. Physical, dielectric, and C band microwave scattering properties of first-year sea ice during advanced melt

    Microsoft Academic Search

    Randall K. Scharien; Torsten Geldsetzer; David G. Barber; John J. Yackel; A. Langlois

    2010-01-01

    This paper investigates the influence of solar heating and intermittent cloud cover on the physical and dielectric properties of naturally snow-free, warm (>?2°), first-year sea ice (FYI) in the southeastern margin of the Beaufort Sea during advanced melt. A simple three-layer physical model describing the surface is introduced and copolarized C band microwave signatures are simulated using a multilayer scattering

  12. Carbon dioxide partial pressure and 13C content of north temperate and boreal lakes at spring ice melt

    USGS Publications Warehouse

    Striegl, R.G.; Kortelainen, P.; Chanton, J.P.; Wickland, K.P.; Bugna, G.C.; Rantakari, M.

    2001-01-01

    Carbon dioxide (CO2) accumulates under lake ice in winter and degasses to the atmosphere after ice melt. This large springtime CO2 pulse is not typically considered in surface-atmosphere flux estimates, because most field studies have not sampled through ice during late winter. Measured CO2 partial pressure (pCO2) of lake surface water ranged from 8.6 to 4,290 Pa (85-4,230 ??atm) in 234 north temperate and boreal lakes prior to ice melt during 1998 and 1999. Only four lakes had surface pCO2 less than or equal to atmospheric pCO2, whereas 75% had pCO2 >5 times atmospheric. The ??13CDIC (DIC = ??CO2) of 142 of the lakes ranged from -26.28??? to +0.95.???. Lakes with the greatest pCO2 also had the lightest ??13CDIC, which indicates respiration as their primary CO2 source. Finnish lakes that received large amounts of dissolved organic carbon from surrounding peatlands had the greatest pCO2. Lakes set in noncarbonate till and bedrock in Minnesota and Wisconsin had the smallest pCO2 and the heaviest ??13CDIC, which indicates atmospheric and/or mineral sources of C for those lakes. Potential emissions for the period after ice melt were 2.36 ?? 1.44 mol CO2 m-2 for lakes with average pCO2 values and were as large as 13.7 ?? 8.4 mol CO2 m-2 for lakes with high pCO2 values.

  13. The Effect of Seasonal Pack Ice Melting on the Sea Water Polychlorobiphenyl Contents at Gerlache Inlet and Wood Bay (Ross Sea - Antarctica)

    Microsoft Academic Search

    Roger Fuoco; Stefania Giannarelli; Carlo Abete; Massimo Onor; Marco Termine

    1999-01-01

    The effect of seasonal formation\\/melting process of pack ice on the PCB level of sea water at Gerlache Inlet and Wood Bay (Ross Sea, Antarctica) was investigated during four Italian expeditions, i.e. 1988–89, 1990–91, 1991–92, and 1993–94. Surface sea water samples from Gerlache Inlet and Wood Bay before pack ice melting showed a typical total PCB concentration of 133 pg\\/l

  14. Melt ponds on sea ice in the Canadian Archipelago 2. On the use of RADARSAT-1 synthetic aperture radar for geophysical inversion

    Microsoft Academic Search

    J. J. Yackel; D. G. Barber

    2000-01-01

    Microwave scattering from a first-year sea ice (FYI) melt ponded surface is examined using RADARSAT-1 synthetic aperture radar (SAR) data collected during the 1997 Collaborative-Interdisciplinary Cryospheric Experiment (C-ICE'97) near Resolute Bay, Nunavut. This paper (1) investigates the utility of time series of microwave scattering to detect melt pond formation and (2) investigates approaches toward geophysically inverting information on the physical

  15. Aerosolization of two strains (ice+ and ice-) of Pseudomonas syringae in a Collison nebulizer at different temperatures

    NASA Astrophysics Data System (ADS)

    Pietsch, Renee; David, Ray; Marr, Linsey; Vinatzer, Boris; Schmale, David

    2015-04-01

    The aerosolization of microorganisms from aquatic environments is understudied. In this study, an ice nucleation active (ice+) strain and a non-ice nucleation active (ice-) strain of the bacterium Pseudomonas syringae were aerosolized from aqueous suspensions under artificial laboratory conditions using a Collison nebulizer. The aerosolization of P. syringae was not influenced by water temperatures between 5° and 30°C. In general, the culturability (viability) of P. syringae in aerosols increased with temperature between 5 and 30°C. The ice+ strain was aerosolized in greater numbers than the ice- strain at all temperatures studied, suggesting a possible connection between the ice nucleation phenotype and aerosol production. Together, our results suggest that P. syringae has the potential to be aerosolized from natural aquatic environments, such as streams, rivers, ponds, and lakes; known reservoirs of P. syringae. Future work is needed to elucidate the mechanisms of aerosolization of P. syringae from natural aquatic systems.

  16. Temperature Dependence of Absorption in Ice at 532 nm

    Microsoft Academic Search

    Kurt Woschnagg; P. Buford Price

    2001-01-01

    A YAG laser was used to emit nanosecond pulses of light at 532 nm at depths from 1185 to 2200 m in Antarctic ice, corresponding to temperatures increasing from 229 to 249 K. From the timing distributions of photons arriving at phototubes at distances up to 100 m and at similar depths, the scattering and absorption coefficients were measured, and

  17. Sea Ice Brightness Temperature as a Function of Ice Thickness, Part II: Computed curves for thermodynamically modelled ice profiles

    E-print Network

    Mills, Peter

    2012-01-01

    Ice thickness is an important variable for climate scientists and is still an unsolved problem for satellite remote sensing specialists. There has been some success detecting the thickness of thin ice from microwave radiometers, and with this in mind this study attempts to model the thickness-radiance relation of sea ice at frequencies employed by the Soil Moisture and Ocean Salinity (SMOS) radiometer and the Advanced Microwave Scanning Radiometer (AMSR): between 1.4 and 89 GHz. In the first part of the study, the salinity of the ice was determined by a pair of empirical relationships, while the temperature was determined by a thermodynamic model. Because the thermodynamic model can be used as a simple ice growth model, in this, second part, the salinities are determined by the growth model. Because the model uses two, constant-weather scenarios representing two extremes ("fall freeze-up" and "winter cold snap"), brine expulsion is modelled with a single correction-step founded on mass conservation. The growt...

  18. Melting temperature distribution characteristic of ash deposits of black liquor coal slurry on furnace wall

    Microsoft Academic Search

    Ze-quan LAN; Xin-yu CAO; Jun-hu ZHOU; Jian-zhong LIU; Ke-fa CEN

    2009-01-01

    To investigate the distribution characteristic of melting temperature of ash deposits deposited on different locations of furnace wall, comparison test on two combustion work conditions was made in trial furnace of black liquor coal slurry. Analysis was made on melting temperature, chemical composition, and mineral phase of ash deposits on furnace wall along journey of fume. The result shows that

  19. Copper Partitioning between Amphibole and Silicate Melts: the Effects of Temperature, Melt Compositions, Oxygen Fugacity and Water Concentrations

    NASA Astrophysics Data System (ADS)

    Hsu, Y. J.; Zajacz, Z.; Ulmer, P.; Heinrich, C. A.

    2014-12-01

    Porphyry copper deposits commonly occur in arc-related settings where ore-metals are transported by magmas from the mantle wedge to shallow depths, and subsequently partition into the exsolving volatile phase. The partitioning of Cu between crystallizing silicate, oxide and sulfide minerals, sulfide melts and magmatic volatiles will determine the efficiency of Cu transfer into the magmatic-hydrothermal system. Understanding the Cu partitioning behavior between crystallizing mineral phases and silicate melt during crystallization fractionation is therefore fundamentally important. Among the crystallizing phases, amphibole is stable across a wide pressure (P) - temperature (T) range in hydrous arc magmas. Therefore, if the partition coefficients of Cu between amphibole and silicate melts are well constrained, the measured variation of Cu concentrations in natural amphibole crystals can be used to reconstruct the evolution of the Cu concentration in the silicate melt. In this study, a series of experiments were conducted by piston cylinder apparatus over a wide range of melt compositions (andesitic to rhyolitic) to determine the amphibole/melt partition coefficient of Cu. The experiments were run at T = 740 - 990 °C, P = 0.7 GPa, and oxygen fugacity (fO2) between NNO +0.75 and NNO +2. The metal activities were imposed by using Au97Cu3 and Au92Cu8 alloy capsules. The apparent Cu solubilities in both the silicate melt and amphibole phases decrease with decreasing temperature. The Cu concentrations in a dacite melt increase approximately by factor of 3 while fO2 increases from NNO +0.75 to NNO +2. However, the amphibole/melt partition coefficient of Cu remains nearly constant at a value of 0.067 ± 0.013 (1 ?), indicating that the partitioning of Cu is not significantly affected by melt composition, fO2 and water concentrations. Therefore, determination of Cu concentrations in amphiboles may be a suitable tool to monitor the evolution of the Cu budget of ore-related magma reservoirs during magma evolution in porphyry cooper systems. In addition, our results showed that Cu is always incompatible in amphibole; therefore, occasionally measured high Cu concentrations in amphibole are likely an artifact of the presence of submicroscopic sulfide inclusions.

  20. Diffractometer for synchrotron radiation structural studies of high temperature melts

    NASA Astrophysics Data System (ADS)

    Marumo, F.; Morikawa, H.; Shimizugawa, Y.; Tokonami, M.; Miyake, M.; Ohsumi, K.; Sasaki, S.

    1989-07-01

    A diffractometer has been constructed for structural studies of high-temperature melt with synchrotron radiation. It was designed to measure diffracted intensities from the free surface of a molten sample by scanning a scintillation counter with a fixed glancing angle of the incident beam. In order to heat samples up to 1500 °C, a small electric furnace is attached to the diffractometer. It carries a hemicircular (100 mm in diameter) cover, which has a window for the passage of x rays. The window is covered with a Kapton film. The sample container made of 30 Rh-Pt is mounted at the center of the furnace. A test measurement was performed on GeO2. Monochromatic beams with ?=1.32 A and its second harmonics were taken out of synchrotron radiation by a ?-alumina crystal (d002=11.3 A) and used as incident beams. To partial scattering curves obtained with ? and ?/2 were combined to a single curve after correction for absorption. The radial distribution function obtained from these data is in good agreement with that previously reported which was derived from diffraction data collected on a conventional diffractometer.

  1. Sea Ice and Ice Temperature Variability as Observed by Microwave and Infrared Satellite Data

    NASA Technical Reports Server (NTRS)

    Comiso, Josefino C.; Koblinsky, Chester J. (Technical Monitor)

    2001-01-01

    Recent reports of a retreating and thinning sea ice cover in the Arctic have pointed to a strong suggestion of significant warming in the polar regions. It is especially important to understand what these reports mean in light of the observed global warning and because the polar regions are expected to be most sensitive to changes in climate. To gain insight into this phenomenon, co-registered ice concentrations and surface temperatures derived from two decades of satellite microwave and infrared data have been processed and analyzed. While observations from meteorological stations indicate consistent surface warming in both regions during the last fifty years, the last 20 years of the same data set show warming in the Arctic but a slight cooling in the Antarctic. These results are consistent with the retreat in the Arctic ice cover and the advance in the Antarctic ice cover as revealed by historical satellite passive microwave data. Surface temperatures derived from satellite infrared data are shown to be consistent within 3 K with surface temperature data from the limited number of stations. While not as accurate, the former provides spatially detailed changes over the twenty year period. In the Arctic, for example, much of the warming occurred in the Beaufort Sea and the North American region in 1998 while slight cooling actually happened in parts of the Laptev Sea and Northern Siberia during the same time period. Big warming anomalies are also observed during the last five years but a periodic cycle of about ten years is apparent suggesting a possible influence of the North Atlantic Oscillation. In the Antarctic, large interannual and seasonal changes are also observed in the circumpolar ice cover with regional changes showing good coherence with surface temperature anomalies. However, a mode 3 is observed to be more dominant than the mode 2 wave reported in the literature. Some of these spatial and temporal changes appear to be influenced by the Antarctic Circumpolar Wave (ACW) and changes in coastal polynya activities.

  2. Dependence of Eemian Greenland temperature reconstructions on the ice sheet topography

    NASA Astrophysics Data System (ADS)

    Merz, Niklaus; Born, Andreas; Raible, Christoph; Fischer, Hubertus; Stocker, Thomas

    2014-05-01

    The impact of a reduced Greenland ice sheet (GrIS) on Greenland's surface climate during the Eemian interglacial is investigated employing the CCSM4 climate model. We find a distinct impact of changes in the GrIS topography on Greenland's surface air temperatures (SAT) even when correcting for changes in surface elevation which influences SAT through the lapse rate effect. The resulting lapse rate corrected SAT anomalies are driven by changes in the surface energy balance. In winter, the variable reacting strongest to changes in the topography is the sensible heat flux (SHFLX). The reason is its dependence on surface winds, which themselves are controlled to a large extent by the shape of the GrIS. Hence, regions where a receding GrIS causes higher surface wind velocities also experience anomalous warming through increased SHFLX. Vice-versa, regions that become flat and ice-free are characterized by low wind speeds, low SHFLX and anomalous cold winter temperatures. In summer, we find surface warming induced by a decrease in surface albedo in deglaciated areas and regions which experience surface melting. The results have implications for the interpretation of Eemian temperature reconstructions based on Greenland proxy archives such as the NEEM ice core. Changing the GrIS topography acts as a local forcing for Greenland's climate, whereas the effect on the climate outside of Greenland is small and mostly negligible. For the NEEM ice core site, our model suggests that up to 3.2 °C of the annual mean Eemian warming can be attributed to these topography-related processes and hence is not linked to large-scale climate variations.

  3. A survey and new measurements of ice vapor pressure at temperatures between 170 and 250K

    Microsoft Academic Search

    James Marti; Konrad Mauersberger

    1993-01-01

    Saturated vapor pressures of ice at temperatures below 200K have become more important since the discovery of ice clouds in the polar stratosphere and upper mesosphere. Direct measurements of ice vapor pressures at such low temperatures are sparse and unreliable. This paper summarizes published vapor pressure data and presents new measurements at temperatures between 170 and 250K, extending the range

  4. 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.

  5. A Comparison of Sea Ice Type, Sea Ice Temperature, and Snow Thickness Distributions in the Arctic Seasonal Ice Zones with the DMSP SSM/I

    NASA Technical Reports Server (NTRS)

    St.Germain, Karen; Cavalieri, Donald J.; Markus, Thorsten

    1997-01-01

    Global climate studies have shown that sea ice is a critical component in the global climate system through its effect on the ocean and atmosphere, and on the earth's radiation balance. Polar energy studies have further shown that the distribution of thin ice and open water largely controls the distribution of surface heat exchange between the ocean and atmosphere within the winter Arctic ice pack. The thickness of the ice, the depth of snow on the ice, and the temperature profile of the snow/ice composite are all important parameters in calculating surface heat fluxes. In recent years, researchers have used various combinations of DMSP SSMI channels to independently estimate the thin ice type (which is related to ice thickness), the thin ice temperature, and the depth of snow on the ice. In each case validation efforts provided encouraging results, but taken individually each algorithm gives only one piece of the information necessary to compute the energy fluxes through the ice and snow. In this paper we present a comparison of the results from each of these algorithms to provide a more comprehensive picture of the seasonal ice zone using passive microwave observations.

  6. Subpixel variability of MODIS albedo retrievals and its importance for ice sheet surface melting in southwestern Greenland's ablation zone

    NASA Astrophysics Data System (ADS)

    Moustafa, S.; Rennermalm, A. K.; Roman, M. O.; Koenig, L.; Smith, L. C.; Schaaf, C.; Wang, Z.; Mioduszewski, J.

    2013-12-01

    On the Greenland ice sheet, albedo declined across 70% of its surface since 2000, with the greatest reduction in the lower 600 m of the southwestern ablation zone. Because albedo plays a prominent role in the ice sheet surface energy balance, its decline has resulted in near doubling of meltwater production. To characterize ice sheet albedo, Moderate Imaging Spectrometer (MODIS) surface albedo products are typically used. However, it is unclear how the spatial variability of albedo within a MODIS pixel influences surface melting and whether it can be considered a linear function of albedo. In this study, high spatiotemporal resolution measurements of spectral albedo and ice sheet surface ablation were collected along a ~ 1.3 km transect during June 2013 within the Akuliarusiarsuup Kuua (AK) River watershed in southwest Greenland. Spectral measurements were made at 325-1075 nm using a Analytical Spectral Devices (ASD) spectroradiometer, fitted with a Remote Cosine Receptor (RCR). In situ albedo measurements are compared with the daily MODIS albedo product (MCD43A) to analyze how space, time, surface heterogeneity, atmospheric conditions, and solar zenith angle geometry govern albedo at different scales. Finally, analysis of sub-pixel albedo and ablation reveal its importance on meltwater production in the lower parts of the ice sheet margin.

  7. Methane efflux from high-latitude lakes during spring ice melt

    Microsoft Academic Search

    Allan R. Phelps; Kim M. Peterson; Martin O. Jeffries

    1998-01-01

    Ice cores removed from shallow ice-covered tundra lakes near Barrow, Alaska, and taiga lakes near Anchorage, Alaska, exhibit increasing concentrations of methane with depth. Methane concentrations in the ice cores increased from 0 (tM in the top 15 cm sections to a maximum of 23 (tM in the lowest 15 cm sections of tundra lake ice and to a maximum

  8. High Strain-Rate Response of High Purity Aluminum at Temperatures Approaching Melt

    SciTech Connect

    Grunschel, S E; Clifton, R J; Jiao, T

    2010-01-28

    High-temperature, pressure-shear plate impact experiments were conducted to investigate the rate-controlling mechanisms of the plastic response of high-purity aluminum at high strain rates (10{sup 6} s{sup -1}) and at temperatures approaching melt. Since the melting temperature of aluminum is pressure dependent, and a typical pressure-shear plate impact experiment subjects the sample to large pressures (2 GPa-7 GPa), a pressure-release type experiment was used to reduce the pressure in order to measure the shearing resistance at temperatures up to 95% of the current melting temperature. The measured shearing resistance was remarkably large (50 MPa at a shear strain of 2.5) for temperatures this near melt. Numerical simulations conducted using a version of the Nemat-Nasser/Isaacs constitutive equation, modified to model the mechanism of geometric softening, appear to capture adequately the hardening/softening behavior observed experimentally.

  9. Sediment plume response to surface melting and supraglacial lake drainages on the Greenland ice sheet

    Microsoft Academic Search

    Vena W. Chu; Laurence C. Smith; Asa K. Rennermalm; Richard R. Forster; Jason E. Box; Niels Reehy

    2009-01-01

    Increased mass losses from the Greenland ice sheet and inferred contributions to sea-level rise have heightened the need for hydrologic observations of meltwater exiting the ice sheet. We explore whether temporal variations in ice-sheet surface hydrology can be linked to the development of a downstream sediment plume in Kangerlussuaq Fjord by comparing: (1) plume area and suspended sediment concentration from

  10. Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century

    E-print Network

    Global analyses of sea surface temperature, sea ice, and night marine air temperature since and sea surface temperature (SST) data set, HadISST1, and the nighttime marine air temperature (NMAT) data set, HadMAT1. HadISST1 replaces the global sea ice and sea surface temperature (GISST) data sets

  11. Airborne Remote Sensing of Sea Surface Temperature Using the Ball Experimental Sea Surface Temperature (BESST) Radiometer With A Discussion of the 2013 Marginal Ice Zone Observation Processes EXperiment.

    NASA Astrophysics Data System (ADS)

    Tooth, M.; Emery, W. J.

    2014-12-01

    Airborne remote sensing has opened up new possibilities for scientists to study oceanic and atmospheric problems that are relevant to industry, environmental groups, and the scientific community as a whole. Data obtained from these platforms can provide much higher resolution imagery in comparison to satellite observations that allow for more detailed analyses of important regions. Sea surface temperature (SST) data obtained from instruments like the BESST radiometer can be used to provide more insight into issues like natural disasters and oceanographic problems of interest; such as the influence of melting sea ice on SST. During the 2013 Marginal Ice Zone Observation Processes EXperiment (MIZOPEX), BESST was flown on a Scan Eagle UAS in the Alaskan Marginal Ice Zone to acquire SST data. These observations will be discussed, along with possible future uses for the BESST radiometer.

  12. Temperature profile for glacial ice at the South Pole: implications for life in a nearby subglacial lake.

    PubMed

    Price, P Buford; Nagornov, Oleg V; Bay, Ryan; Chirkin, Dmitry; He, Yudong; Miocinovic, Predrag; Richards, Austin; Woschnagg, Kurt; Koci, Bruce; Zagorodnov, Victor

    2002-06-11

    Airborne radar has detected approximately 100 lakes under the Antarctic ice cap, the largest of which is Lake Vostok. International planning is underway to search in Lake Vostok for microbial life that may have evolved in isolation from surface life for millions of years. It is thought, however, that the lakes may be hydraulically interconnected. If so, unsterile drilling would contaminate not just one but many of them. Here we report measurements of temperature vs. depth down to 2,345 m in ice at the South Pole, within 10 km from a subglacial lake seen by airborne radar profiling. We infer a temperature at the 2,810-m deep base of the South Pole ice and at the lake of -9 degrees C, which is 7 degrees C below the pressure-induced melting temperature of freshwater ice. To produce the strong radar signal, the frozen lake must consist of a mix of sediment and ice in a flat bed, formed before permanent Antarctic glaciation. It may, like Siberian and Antarctic permafrost, be rich in microbial life. Because of its hydraulic isolation, proximity to South Pole Station infrastructure, and analog to a Martian polar cap, it is an ideal place to test a sterile drill before risking contamination of Lake Vostok. From the semiempirical expression for strain rate vs. shear stress, we estimate shear vs. depth and show that the IceCube neutrino observatory will be able to map the three-dimensional ice-flow field within a larger volume (0.5 km(3)) and at lower temperatures (-20 degrees C to -35 degrees C) than has heretofore been possible. PMID:12060731

  13. Analysis of Temperature Gradients during Simultaneous Laser Beam Melting of Polymers

    NASA Astrophysics Data System (ADS)

    Laumer, Tobias; Stichel, Thomas; Amend, Philipp; Roth, Stephan; Schmidt, Michael

    By simultaneous laser beam melting (SLBM), different polymer powders can be processed to multi-material parts, which offers the potential to enlarge the field of application for conventional LBM. In a SLBM process, a powder bed consisting of different polymers and therefore with different melting and crystallization temperatures is deposited. Besides the use of infrared emitters for preheating the lower melting polymer, a CO2 laser distributes the necessary preheating temperature of the higher melting polymer. In the last step, a thulium fibre laser distributes the energy necessary for melting the two preheated powders simultaneously. In order to analyze the temperature gradients of the process on the powder surface and in deeper layers, a high-resolution thermal imaging system and thermocouples are used.

  14. The temperature jump at a growing ice-water interface

    NASA Astrophysics Data System (ADS)

    Elif Genceli Güner, F.; Wåhlin, Johan; Hinge, Mogens; Kjelstrup, Signe

    2015-02-01

    During an ice growth rate of around 0.02 mm/s, we report a temperature jump at an ice-water interface above 0 °C up to 1.68 °C (0.01 ± °C), as measured with thermochromatic-liquid-crystals. This gives experimental proof for the existence of an interfacial temperature jump during a liquid-solid phase transition, confirming similar results for liquid-vapour transition, and supporting idea of the surface as a separate thermodynamic system. The fact that there is no continuity in intensive variables across the interface, unlike what is assumed in standard engineering models, has a bearing on the understanding and modelling of coupled heat and mass transport at interfaces in nature and man-made applications.

  15. Comparative study on size dependence of melting temperatures of pure metal and alloy nanoparticles

    SciTech Connect

    Chen, C. L. [Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, 7-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); WPI Research Center, Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Lee, J.-G. [Functional Materials Division, Korea Institute of Materials Science, 531 Changwondaero, Changwon, Gyeongnam 641-831 (Korea, Republic of); Arakawa, K.; Mori, H. [Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, 7-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan)

    2011-07-04

    A comparative study on the size dependence of the melting temperatures of pure metal and alloy nanoparticles has been carried out. It was found that the melting temperatures of Bi-Sn, In-Sn, and Pb-Sn alloy nanoparticles decreased more rapidly with decreasing particle size than those of the constituent metal nanoparticles (Bi, In, Pb, Sn). Namely, the size dependence of the melting temperature was stronger for the alloy nanoparticles than that for the constituent metal nanoparticles. Results calculated with a thermodynamic model were in good agreement with the experimental observations.

  16. Formation of high density amorphous ice by decompression of ice VII and ice VIII at 135 K

    E-print Network

    McBride, Carl

    of ice Ih and are found to have very similar structures. By cooling liquid water along the water/Ih that the melting curve of ice Ih extrapolates to 10 kbar at the liquid nitrogen temperature T 77 K. With this in mind an experiment was undertaken which squeezed ice Ih at 77 K. At 10 1 kbars they saw the onset

  17. Dependence of Eemian Greenland temperature reconstructions on the ice sheet topography

    NASA Astrophysics Data System (ADS)

    Merz, N.; Born, A.; Raible, C. C.; Fischer, H.; Stocker, T. F.

    2014-06-01

    The influence of a reduced Greenland Ice Sheet (GrIS) on Greenland's surface climate during the Eemian interglacial is studied using a set of simulations with different GrIS realizations performed with a comprehensive climate model. We find a distinct impact of changes in the GrIS topography on Greenland's surface air temperatures (SAT) even when correcting for changes in surface elevation, which influences SAT through the lapse rate effect. The resulting lapse-rate-corrected SAT anomalies are thermodynamically driven by changes in the local surface energy balance rather than dynamically caused through anomalous advection of warm/cold air masses. The large-scale circulation is indeed very stable among all sensitivity experiments and the Northern Hemisphere (NH) flow pattern does not depend on Greenland's topography in the Eemian. In contrast, Greenland's surface energy balance is clearly influenced by changes in the GrIS topography and this impact is seasonally diverse. In winter, the variable reacting strongest to changes in the topography is the sensible heat flux (SHF). The reason is its dependence on surface winds, which themselves are controlled to a large extent by the shape of the GrIS. Hence, regions where a receding GrIS causes higher surface wind velocities also experience anomalous warming through SHF. Vice-versa, regions that become flat and ice-free are characterized by low wind speeds, low SHF, and anomalous low winter temperatures. In summer, we find surface warming induced by a decrease in surface albedo in deglaciated areas and regions which experience surface melting. The Eemian temperature records derived from Greenland proxies, thus, likely include a temperature signal arising from changes in the GrIS topography. For the Eemian ice found in the NEEM core, our model suggests that up to 3.1 °C of the annual mean Eemian warming can be attributed to these topography-related processes and hence is not necessarily linked to large-scale climate variations.

  18. Dependence of Eemian Greenland temperature reconstructions on the ice sheet topography

    NASA Astrophysics Data System (ADS)

    Merz, N.; Born, A.; Raible, C. C.; Fischer, H.; Stocker, T. F.

    2013-12-01

    The influence of a reduced Greenland ice sheet (GrIS) on Greenland's surface climate during the Eemian interglacial is studied using a comprehensive climate model. We find a distinct impact of changes in the GrIS topography on Greenland's surface air temperatures (SAT) even when correcting for changes in surface elevation which influences SAT through the lapse rate effect. The resulting lapse rate corrected SAT anomalies are thermodynamically driven by changes in the local surface energy balance rather than dynamically caused through anomalous advection of warm/cold air masses. The large-scale circulation is indeed very stable among all sensitivity experiments and the NH flow pattern does not depend on Greenland's topography in the Eemian. In contrast, Greenland's surface energy balance is clearly influenced by changes in the GrIS topography and this impact is seasonally diverse. In winter, the variable reacting strongest to changes in the topography is the sensible heat flux (SHFLX). The reason is its dependence on surface winds, which themselves are controlled to a large extent by the shape of the GrIS. Hence, regions where a receding GrIS causes higher surface wind velocities also experience anomalous warming through SHFLX. Vice-versa, regions that become flat and ice-free are characterized by low wind speeds, low SHFLX and anomalous cold winter temperatures. In summer, we find surface warming induced by a decrease in surface albedo in deglaciated areas and regions which experience surface melting. The Eemian temperature records derived from Greenland proxies, thus, likely include a temperature signal arising from changes in the GrIS topography. For the NEEM ice core site, our model suggests that up to 3.2 °C of the annual mean Eemian warming can be attributed to these topography-related processes and hence is not necessarily linked to large-scale climate variations.

  19. 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.

  20. Liquid structure and temperature invariance of sound velocity in supercooled Bi melt

    SciTech Connect

    Emuna, M.; Mayo, M.; Makov, G. [Materials Engineering Department, Ben-Gurion University of the Negev, 84105 Beer-Sheva (Israel)] [Materials Engineering Department, Ben-Gurion University of the Negev, 84105 Beer-Sheva (Israel); Greenberg, Y.; Caspi, E. N.; Yahel, E. [Physics Department, Nuclear Research Centre-Negev, 84190 Beer-Sheva (Israel)] [Physics Department, Nuclear Research Centre-Negev, 84190 Beer-Sheva (Israel); Beuneu, B. [Laboratoire Léon Brillouin CEA/Saclay, 91191 Gif-Sur-Yvette Cedex (France)] [Laboratoire Léon Brillouin CEA/Saclay, 91191 Gif-Sur-Yvette Cedex (France)

    2014-03-07

    Structural rearrangement of liquid Bi in the vicinity of the melting point has been proposed due to the unique temperature invariant sound velocity observed above the melting temperature, the low symmetry of Bi in the solid phase and the necessity of overheating to achieve supercooling. The existence of this structural rearrangement is examined by measurements on supercooled Bi. The sound velocity of liquid Bi was measured into the supercooled region to high accuracy and it was found to be invariant over a temperature range of ?60°, from 35° above the melting point to ?25° into the supercooled region. The structural origin of this phenomenon was explored by neutron diffraction structural measurements in the supercooled temperature range. These measurements indicate a continuous modification of the short range order in the melt. The structure of the liquid is analyzed within a quasi-crystalline model and is found to evolve continuously, similar to other known liquid pnictide systems. The results are discussed in the context of two competing hypotheses proposed to explain properties of liquid Bi near the melting: (i) liquid bismuth undergoes a structural rearrangement slightly above melting and (ii) liquid Bi exhibits a broad maximum in the sound velocity located incidentally at the melting temperature.

  1. Observations of the annual cycle of sea ice temperature and mass balance

    Microsoft Academic Search

    Donald K. Perovich; Bruce C. Elder; Jacqueline A. Richter-Menge

    1997-01-01

    A vertical array of thermistors coupled with an autonomous data-logging system was used to obtain a 15-month record of ice temperature profiles in a multiyear floe in the Beaufort Sea. This record was used to monitor atmosphere, ice, and ocean temperatures, determine changes in the ice mass balance, and infer estimates of the ocean heat flux and the snow thermal

  2. Observations of the annual cycle of sea ice temperature and mass balance

    Microsoft Academic Search

    Donald K. Perovich; Bruce C. Elder

    1997-01-01

    A vertical array of thermistors coupled with an au- tonomous data-logging system was used to obtain a 15-month record of ice temperature profiles in a multiyear floe in the Beau- fort Sea. This record was used to monitor atmosphere, ice and ocean temperatures, determine changes in the ice mass balance, and infer estimates of the ocean heat flux and the

  3. Temperature dependence of the zero point kinetic energy in ice and water above room temperature

    NASA Astrophysics Data System (ADS)

    Senesi, R.; Romanelli, G.; Adams, M. A.; Andreani, C.

    2013-12-01

    By means of Deep Inelastic Neutron Scattering we determined the temperature dependence of the proton kinetic energy in polycrystalline ice Ih between 5 K and 271 K. We compare our results with predictions form Path Integral quantum simulations and semiclassical quasi-harmonic models with phase-dependent frequencies. The latter show the best agreement with the experiment if the librational contribution is properly taken into account. The kinetic energy increase with temperature in ice is also found to be approximately a factor ? 5 smaller than in the case of liquid water above room temperature, highlighting the role played by anharmonic quantum fluctuations in the two phases.

  4. Tracking sea ice floes from the Lincoln Sea to Nares Strait and deriving large scale melt from coincident spring and summer (2009) aerial EM thickness surveys

    NASA Astrophysics Data System (ADS)

    Lange, B. A.; Haas, C.; Beckers, J.; Hendricks, S.

    2011-12-01

    Satellite observations demonstrate a decreasing summer Arctic sea ice extent over the past ~40 years, as well as a smaller perennial sea ice zone, with a significantly accelerated decline in the last decade. Recent ice extent observations are significantly lower than predicted by any model employed by the Intergovernmental Panel on Climate Change. The disagreement of the modeled and observed results, along with the large variability of model results, can be in part attributed to a lack of consistent and long term sea ice mass balance observations for the High Arctic. This study presents the derivation of large scale (individual floe) seasonal sea ice mass balance in the Lincoln Sea and Nares Strait. Large scale melt estimates are derived by comparing aerial borne electromagnetic induction thickness surveys conducted in spring with surveys conducted in summer 2009. The comparison of coincident floes is ensured by tracking sea ice using ENIVSAT ASAR and MODIS satellite imagery. Only EM thickness survey sections of floes that were surveyed in both spring and summer are analyzed and the resulting modal thicknesses of the distributions, which represent the most abundant ice type, are compared to determine the difference in thickness and therefore total melt (snow+basal ice+surface ice melt). Preliminary analyses demonstrate a bulk (regional ice tracking) seasonal total thickness variability of 1.1m, Lincoln Sea modal thickness 3.7m (April, 2009) and Nares Strait modal thickness 2.6m (August 2009)(Fig1). More detailed floe tracking, in depth analysis of EM surveys and removal of deformed ridged/rafted sea ice (due to inaccuracies over deformed ice) will result in more accurate melt estimates for this region and will be presented. The physical structure of deformed sea ice and the footprint of the EM instrument typically underestimate the total thicknesses observed. Seasonal variations of sea ice properties can add additional uncertainty to the response of the EM instrument over deformed ridged/rafted sea ice. Here we will present additional analysis of the data comparing total thickness to ridge height that will provide some insight into the magnitude of seasonal discrepancies experienced by the EM instrument over deformed ice.

  5. Alkanediyl-alpha,omega-bis(dimethylalkylammonium bromide) surfactants: II. Krafft temperature and melting temperature.

    PubMed

    Zana, Raoul

    2002-08-01

    The melting temperature T(M) of two series of dimeric (gemini) surfactants, the alkanediyl-alpha,omega-bis(dodecyl and hexadecyl dimethylammonium bromide), referred to as 12-s-12 and 16-s-16, respectively (s = carbon number of the alkanediyl spacer), and the Krafft temperature T(K) of 1 wt% aqueous solutions of these surfactants have been measured. The melting temperature of the solid surfactant increases with the carbon number m of the alkyl chain. For each surfactant series, T(M) goes through a maximum at s close to 5, irrespective of the value of m. For the 12-s-12 series, T(M) goes through a minimum at s = 10 to 12. At a constant value of s, the value of T(K) increases with m. The variations of T(M) and T(K) with s show some correlation, with T(K) decreasing when T(M) increases and vice versa. The results are discussed in relation to the solution properties of the investigated surfactants. PMID:16290787

  6. Thermal Diffusivity for III-VI Semiconductor Melts at Different Temperatures

    NASA Technical Reports Server (NTRS)

    Ban, H.; Li, C.; Lin, B.; Emoto, K.; Scripa, R. N.; Su, C.-H.; Lehoczky, S. L.

    2004-01-01

    The change of the thermal properties of semiconductor melts reflects the structural changes inside the melts, and a fundamental understanding of this structural transformation is essential for high quality semiconductor crystal growth process. This paper focused on the technical development and the measurement of thermal properties of III-VI semiconductor melts at high temperatures. Our previous work has improved the laser flash method for the specialized quartz sample cell. In this paper, we reported the results of our recent progress in further improvements of the measurement system by minimizing the free convection of the melt, adding a front IR detector, and placing the sample cell in a vacuum environment. The results for tellurium and selenium based compounds, some of which have never been reported in the literature, were obtained at different temperatures as a function of time. The data were compared with other measured thermophysical properties to shed light on the structural transformations of the melt.

  7. Temperatures in the earth's core from melting-point measurements of iron at high static pressures

    Microsoft Academic Search

    R. Boehler

    1993-01-01

    The most reliable method for determining the temperature gradient at the earth's core is the estimation of Fe and Fe-rich compounds' melting temperature at the pressure of the inner core boundary. Attention is presently given to melting-point measurements on Fe and Fe-O compounds at up to 2 Mbar. An extrapolation of these results to 3.3 Mbar yields an inner core

  8. Excimer laser-induced temperature field in melting and resolidification of silicon thin films

    Microsoft Academic Search

    Mutsuko Hatano; Seungjae Moon; Minghong Lee; Kenkichi Suzuki; Costas P. Grigoropoulos

    2000-01-01

    The liquid\\/solid interface motion and temperature history during excimer laser annealing of 50-nm-thick Si films on fused quartz substrates are investigated by in situ nanosecond time-resolved electrical conductance, optical reflectance, and transmittance at visible and near-IR wavelengths, combined with thermal emission measurements. The temperature response, melt propagation and evolution of the recrystallization process are fundamentally different in the partial-melting and

  9. Sensitivity of Pine Island and Thwaites Glaciers to ocean-induced melt investigated using a new physically-based melt parameterisation

    NASA Astrophysics Data System (ADS)

    Hilmar Gudmundsson, G.; Jenkins, Adrian

    2015-04-01

    Ongoing changes on both Pine Island and Thwaites Glaciers are generally considered to be driven by ocean-induced melt along the undersides of their respective ice shelves. In ice-flow studies to date, melt has usually been prescribed using simple parametrisations that, for example, relate the melt rate directly to the ice draft. Alternatively, ocean circulation models can be used to calculate the melt distribution in a coupled approach. Such coupled ice-ocean model runs are however very time consuming and therefore not suitable for performing large-scale parameter studies. Here we present an alternative methodology that falls in-between these two approaches. We use a new, physically-based parametrisation of melt that has been derived from plume theory to link melt with the geometry of the ice shelf base and the ocean temperature. The sensitivities of Pine Island and Thwaites Glaciers to ocean-induced melting are then estimated using the hybrid flow model Úa.

  10. Vital role of daily temperature variability in surface mass balance parameterizations of the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Rogozhina, I.; Rau, D.

    2014-04-01

    This study aims to demonstrate that the spatial and seasonal effects of daily temperature variability in positive degree-day (PDD) models play a decisive role in shaping the modeled surface mass balance (SMB) of continental-scale ice masses. Here we derive monthly fields of daily temperature standard deviation (SD) across Greenland from the ERA-40 (European Centre for Medium-Range Weather Forecasts 40 yr Reanalysis) reanalysis spanning from 1958 to 2001 and apply these fields to model recent surface responses of the Greenland Ice Sheet (GIS). Neither the climate data set analyzed nor in situ measurements taken in Greenland support the range of commonly used spatially and temporally uniform SD values (~ 5 °C). In this region, the SD distribution is highly inhomogeneous and characterized by low values during summer months (~ 1 to 2.5 °C) in areas where most surface melting occurs. As a result, existing SMB parameterizations using uniform, high SD values fail to capture both the spatial pattern and amplitude of the observed surface responses of the GIS. Using realistic SD values enables significant improvements in the modeled regional and total SMB with respect to existing estimates from recent satellite observations and the results of a high-resolution regional model. In addition, this resolves large uncertainties associated with other major parameters of a PDD model, namely degree-day factors. The model appears to be nearly insensitive to the choice of degree-day factors after adopting the realistic SD distribution.

  11. A decade time series of melt season duration on pan-Arctic land ice

    Microsoft Academic Search

    G. J. Wolken; M. J. Sharp

    2010-01-01

    Inter-annual variability in the surface mass balance of many glaciers in the Arctic is driven mainly by variations in summer melt. Given the paucity of in situ mass balance measurements in the Arctic there is considerable interest in using surface melt characteristics derived from remote sensing methods as proxy indicators of annual surface mass balance. Microwave remote sensing is well-suited

  12. Evaluation of the effectiveness of wet ice, dry ice, and cryogenic packs in reducing skin temperature.

    PubMed

    Belitsky, R B; Odam, S J; Hubley-Kozey, C

    1987-07-01

    The purposes of this study were to evaluate and compare the ability of wet ice (WI), dry ice (DI), and cryogenic packs (CGPs) to reduce and maintain the reduction of skin temperature directly under the cooling agent and to determine whether the cooling effect on skin extended beyond the surface area in contact with the cooling agent. Ten female volunteers participated in the study, and each of the three cold modalities was applied randomly to the skin overlying the right triceps surae muscle. After 15 minutes of cold application, mean skin temperatures recorded under WI, DI, and CGP decreased 12 degrees, 9.9 degrees, and 7.3 degrees C, respectively. The only significant differences in cooling were between WI and DI and between WI and CGP. Fifteen minutes after removal of the cold modalities, no significant differences were found in mean skin temperature between WI, DI, and CGP. The residual mean decrease in skin temperature between the pretreatment rest interval (time 0) and 15 minutes after removal of the cold modality (time 30) was significant for WI only. No cooling was demonstrated 1 cm proximal or distal to any of the cooling agents after 15 minutes of cold application. These findings provide valuable information for the use of cryotherapy in the clinical setting. PMID:3602101

  13. Light reflection from a sea-ice cover during the onset of summer melt

    Microsoft Academic Search

    Donald K. Perovich; John W. Govoni

    1992-01-01

    A knowledge of the reflection of light from a sea ice cover is important for both the interpretation of remote sensing imagery at visible and near-infrared wavelengths and for climatological studies involving the energy balance of the polar regions. Spectral measurements of albedo, bidirectional reflectance function (BDRF), and polarized reflectance were made for sea ice conditions found during the onset

  14. Viscosity-temperature relations and structure in fully polymerized aluminosilicate melts from ion dynamics simulations

    SciTech Connect

    Scamehorn, C.A.; Angell, C.A. (Arizona State Univ., Tempe (United States))

    1991-03-01

    Results of a series of molecular dynamics simulations indicate that the Al:Si ratio present in aluminosilicate melts induces a chemical pressure that significantly influences the temperature dependence of the melt viscosity. The temperature dependence of the T-O bond length and T-O-T angle in the melt has been calculated for albite, anorthite, nepheline, and MgAl{sub 2}Si{sub 2}O{sub 8} (a magnesium analog of anorthite) at their experimental melt densities at atmospheric pressure and for pure silica at two different densities corresponding to V/V{sub 0} = 1.0 (1atm) and V/V{sub 0} = 0.8 ({approximately}4 GPa). These simulations show that melt fragility can be correlated to increasing T-O length and decreasing T-O-T angle, both of which are characteristics of silicate melts under increasing pressure. Framework cations with coordination numbers greater than four are observed in these aluminosilicate melts and are shown to be related to fragile behavior. Finally, for nepheline and anorthite we infer a large contribution to fragility from configurational disordering of Al-O-Si links which are known to be dominant in the glasses but are found to be absent from the simulated melts.

  15. Arctic sea ice melt, the Polar vortex, and mid-latitude weather: Are they connected?

    NASA Astrophysics Data System (ADS)

    Vihma, Timo; Overland, James; Francis, Jennifer; Hall, Richard; Hanna, Edward; Kim, Seong-Joong

    2015-04-01

    The potential of recent Arctic changes to influence broader hemispheric weather is a difficult and controversial topic with considerable skepticism, as time series of potential linkages are short (<10 years) and the signal-to-noise ratio relative to chaotic weather events is small. A way forward is through further understanding of potential atmospheric dynamic mechanisms. Although not definitive of change in a statistical or in a causality sense, the exceptionally warm Arctic winters since 2007 do contain increased variability according to some climate indices, with six negative (and two positive) Arctic Oscillation atmospheric circulation index events that created meridional flow reaching unusually far north and south. High pressure anomalies developed east of the Ural Mountains in Russia in response to sea-ice loss in the Barents/Kara Seas, which initiated eastward-propagating wave trains of high and low pressure that advected cold air over central and eastern Asia. Increased Greenland blocking and greater geopotential thickness related to low-level temperatures increases led to northerly meridional flow into eastern North America, inducing persistent cold periods. Arctic connections in Europe and western North America are less clear. The quantitative impact of potential Arctic change on mid-latitude weather will not be resolved within the foreseeable future, yet new approaches to high-latitude atmospheric dynamics can contribute to improved extended range forecasts as outlined by the WMO/Polar Prediction Program and other international activities.

  16. Molybdenum at high pressure and temperature: melting from another solid phase.

    PubMed

    Belonoshko, A B; Burakovsky, L; Chen, S P; Johansson, B; Mikhaylushkin, A S; Preston, D L; Simak, S I; Swift, D C

    2008-04-01

    The Gibbs free energies of bcc and fcc Mo are calculated from first principles in the quasiharmonic approximation in the pressure range from 350 to 850 GPa at room temperatures up to 7500 K. It is found that Mo, stable in the bcc phase at low temperatures, has lower free energy in the fcc structure than in the bcc phase at elevated temperatures. Our density-functional-theory-based molecular dynamics simulations demonstrate that fcc melts at higher than bcc temperatures above 1.5 Mbar. Our calculated melting temperatures and bcc-fcc boundary are consistent with the Mo Hugoniot sound speed measurements. We find that melting occurs at temperatures significantly above the bcc-fcc boundary. This suggests an explanation of the recent diamond anvil cell experiments, which find a phase boundary in the vicinity of our extrapolated bcc-fcc boundary. PMID:18517968

  17. Mg/Casea surface temperatures during the Marine Isotope Stage 31 collapse of the Ross Ice Shelf

    NASA Astrophysics Data System (ADS)

    Dunbar, G. B.

    2012-04-01

    The recovery of the AND-1b and CRP-1 drill cores from the Southwest Ross Sea highlighted the potential instability in of the Ross Ice Shelf and the West Antarctic Ice Sheet it buttresses. Both cores recovered a few individuals of the planktonic foraminifera Neogloboquadrina pachyderma from marine isotope stage (MIS) 31. This interval is significant because it marks the youngest occurrence of open ocean diatom sediment at AND-1b, which is now situated under the McMurdo Ice Shelf, indicating a substantial retreat of the Ross Ice Shelf occurred during this interglacial. However, sediment deposited after MIS 31 at both sites is represented only by glacial-dominated sediment, suggesting a critical environmental threshold had been crossed enabling the Ross Ice Shelf to form and persist. Numerical modeling by Pollard and DeConto (Nature, 2009) suggested that sub-ice oceanic melting is a critical element in the stability of ice shelves and that "WAIS will begin to collapse when nearby ocean temperatures warm by roughly 5°C." Laser ablation ICPMS measurement of the Mg/Ca content of N. pachyderma shows that although there is considerable heterogeneity in the distribution of Mg in their tests the mean Mg/Ca of a sample population appears proportional to calcification temperature. By empirically calibrating Mg/Ca in CRP-1 N. pachyderma against values measured in modern populations collected from Ross Sea and Southern Ocean sites with SSTs ranging from 1.2°C to 14°C it is concluded that SST during MIS 31 was warmer than today by 5-9°C, consistent with model projections.

  18. Radiolysis of astrophysical ice analogs by energetic ions: the effect of projectile mass and ice temperature.

    PubMed

    Pilling, Sergio; Duarte, Eduardo Seperuelo; Domaracka, Alicja; Rothard, Hermann; Boduch, Philippe; da Silveira, Enio F

    2011-09-21

    An experimental study of the interaction of highly charged, energetic ions (52 MeV (58)Ni(13+) and 15.7 MeV (16)O(5+)) with mixed H(2)O : C(18)O(2) astrophysical ice analogs at two different temperatures is presented. This analysis aims to simulate the chemical and the physicochemical interactions induced by cosmic rays inside dense, cold astrophysical environments, such as molecular clouds or protostellar clouds as well at the surface of outer solar system bodies. The measurements were performed at the heavy ion accelerator GANIL (Grand Accelerateur National d'Ions Lourds) in Caen, France. The gas samples were deposited onto a CsI substrate at 13 K and 80 K. In situ analysis was performed by a Fourier transform infrared (FTIR) spectrometer at different fluences. Radiolysis yields of the produced species were quantified. The dissociation cross section at 13 K of both H(2)O and CO(2) is about 3-4 times smaller when O ions are employed. The ice temperature seems to affect differently each species when the same projectile was employed. The formation cross section at 13 K of molecules such as C(18)O, CO (with oxygen from water), and H(2)O(2) increases when Ni ions are employed. The formation of organic compounds seems to be enhanced by the oxygen projectiles and at lower temperatures. In addition, because the organic production at 13 K is at least 4 times higher than the value at 80 K, we also expect that interstellar ices are more organic-rich than the surfaces of outer solar system bodies. PMID:21647477

  19. Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century

    Microsoft Academic Search

    N. A. Rayner; D. E. Parker; E. B. Horton; C. K. Folland; L. V. Alexander; D. P. Rowell; E. C. Kent; A. Kaplan

    2003-01-01

    We present the Met Office Hadley Centre's sea ice and sea surface temperature (SST) data set, HadISST1, and the nighttime marine air temperature (NMAT) data set, HadMAT1. HadISST1 replaces the global sea ice and sea surface temperature (GISST) data sets and is a unique combination of monthly globally complete fields of SST and sea ice concentration on a 1° latitude-longitude

  20. Arctic Warming, Greenland Melt and Moulins

    NASA Astrophysics Data System (ADS)

    Steffen, K.; Huff, R.; Behar, A.

    2007-12-01

    Air temperatures on the Greenland ice sheet have increased by 4 deg. C since 1991. The ice sheet melt area increased by 30% for the western part between 1979-2006, with record melt years in 1987, 1991, 1998, 2002, 2005, and possibly the most extreme melt year in 2007. The increasing trend in the total area of melting bare ice is unmistakable at 13% per year, significant at a probability of 0.99. Hence, the bare ice region, the wet snow region, and the equilibrium line altitude have moved further inland and resulting in increased melt water flux towards the coast. Warm and extended air temperatures are to blame for 1.5 m water equivalent surface reduction at the long-term equilibrium line altitude, 1100 m elevation at 70 deg. N during summer 2007. Increase in ice velocity in the ablation region and the concurrent increase in melt water suggests that water penetrates to great depth through moulins and cracks, lubricating the bottom of the ice sheet. New insight was gained of subsurface hydrologic channels and cavities using new instrumentation and a video system during the melt peak in August 2007. Volume and geometry of a 100 m deep moulin were mapped with a rotating laser, and photographs with digital cameras. Sub-glacial hydrologic channels were investigated and filmed using a tethered, autonomous system, several hundred meters into the ice. These new results will be discussed in view of the rapid increase in melt area and mass loss of the Greenland ice sheet due to increasing air temperatures.

  1. On detection of the thermophysical state of landfast first-year sea ice using in-situ microwave emission during spring melt

    Microsoft Academic Search

    Byong Jun Hwang; Alexandre Langlois; David G. Barber; Timothy N. Papakyriakou

    2007-01-01

    In this study we examine the critical linkages between thermophysical properties and microwave emissions of landfast snow-covered first-year sea ice during spring melt. For this we analyzed the temporal evolution of radiation fluxes, electro-thermophysical properties and microwave emissions, and perform model simulations to evaluate the observations. The results show five major microwave signature events: brine-rich, blowing snow, melt onset, the

  2. Coincident high resolution optical-SAR image analysis for surface albedo estimation of first-year sea ice during summer melt

    Microsoft Academic Search

    Randall K. Scharien; John J. Yackel; Mats A. Granskog; Brent G. T. Else

    2007-01-01

    The parameterization of sea ice albedo during summer, when fluctuations in the fractional coverage of melt ponds change on a variety of spatial and temporal scales, represents a significant challenge for both the modelling and remote sensing communities. Ubiquitous cloud cover in summer inhibits the use of optical sensors for providing large-scale estimates of sea ice surface albedo. C-band (5.3 GHz)

  3. Spatial and temporal melt variability at Helheim Glacier, East Greenland, and its effect on ice dynamics

    E-print Network

    Anderson, M.L.; Larsen, T.B.; Nettles, M.; Elosegui, P.; van As, D.; Hamilton, Gordon S.; Stearns, Leigh; Davis, J.L.; Ahlstrom, A.P.; de Juan, J.; Ekstrom, G.; Stenseng, L.; Khan, S.A.; Forsberg, R.; Dahl-Jensen, D.

    2010-12-29

    in velocity, with a 1 day delay in velocity relative to melt. Although the velocity changes are small compared to accelerations previously observed following some calving events, our findings suggest that the flow speed of Helheim Glacier is sensitive...

  4. A Climate-Data Record (CDR) of the "Clear Sky" Surface Temperature of the Greenland Ice Sheet

    NASA Technical Reports Server (NTRS)

    Hall, Dorothy K.; Comiso, J. C.; DiGirolamo, N. E.; Shuman, C. A.

    2011-01-01

    To quantify the ice-surface temperature (IST) we are developing a climate-data record (CDR) of monthly IST of the Greenland ice sheet, from 1982 to the present using Advanced Very High Resolution Radiometer (AVHRR) and Moderate-Resolution Imaging Spectroradiometer (MODIS) data at 5-km resolution. "Clear-sky" surface temperature increases have been measured from the early 1980s to the early 2000s in the Arctic using AVHRR data, showing increases ranging from 0.57-0.02 (Wang and Key, 2005) to 0.72 0.10 deg C per decade (Comiso, 2006). Arctic warming has implications for ice-sheet mass balance because much of the periphery of the ice sheet is near 0 deg C in the melt season and is thus vulnerable to more extensive melting (Hanna et al., 2008). The algorithm used for this work has a long history of measuring IST in the Arctic with AVHRR (Key and Haefliger, 1992). The data are currently available from 1981 to 2004 in the AVHRR Polar Pathfinder (APP) dataset (Fowler et al., 2000). J. Key1NOAA modified the AVHRR algorithm for use with MODIS (Hall et al., 2004). The MODIS algorithm is now being processed over Greenland. Issues being addressed in the production of the CDR are: time-series bias caused by cloud cover, and cross-calibration between AVHRR and MODIS instruments. Because of uncertainties, time series of satellite ISTs do not necessarily correspond with actual surface temperatures. The CDR will be validated by comparing results with in-situ (see Koenig and Hall, in press) and automatic-weather station data (e.g., Shuman et al., 2001).

  5. Satellite-derived ice data sets no. 2: Arctic monthly average microwave brightness temperatures and sea ice concentrations, 1973-1976

    NASA Technical Reports Server (NTRS)

    Parkinson, C. L.; Comiso, J. C.; Zwally, H. J.

    1987-01-01

    A summary data set for four years (mid 70's) of Arctic sea ice conditions is available on magnetic tape. The data include monthly and yearly averaged Nimbus 5 electrically scanning microwave radiometer (ESMR) brightness temperatures, an ice concentration parameter derived from the brightness temperatures, monthly climatological surface air temperatures, and monthly climatological sea level pressures. All data matrices are applied to 293 by 293 grids that cover a polar stereographic map enclosing the 50 deg N latitude circle. The grid size varies from about 32 X 32 km at the poles to about 28 X 28 km at 50 deg N. The ice concentration parameter is calculated assuming that the field of view contains only open water and first-year ice with an ice emissivity of 0.92. To account for the presence of multiyear ice, a nomogram is provided relating the ice concentration parameter, the total ice concentration, and the fraction of the ice cover which is multiyear ice.

  6. SEASAT SAR sea-ice imagery: summer melt to autumn freeze-up

    Microsoft Academic Search

    R. D. KETCHUM Jr

    1984-01-01

    Some salient aspects of SEASAT L-band SAR sea-ice imagery are presented. High backscatter attributed to water-saturated surface layers reduces the ability to interpret ice conditions. Slush on water areas produces a strong backscatter which could be misinterpreted as rubble, but sequential imagery and floe sizes and shapes can be used to resolve this ambiguity. The slush effect may enhance the

  7. Effect of Hydrogen and Carbon on the Melting Temperature of the Core

    NASA Astrophysics Data System (ADS)

    Nakajima, Y.; Sakamaki, K.; Takahashi, E.; Fukai, Y.; Suzuki, T.; Funakoshi, K.

    2007-12-01

    The temperature of the Earth's outer core has been discussed based on the melting temperature of Fe- O-S alloys (e.g., Boehler, 1996). Although hydrogen and carbon are the possible candidates of the core component, their effects on the melting temperature of iron at high-pressures are unclear. Using a Kawai-type multi-anvil apparatus at SPring-8 synchrotron, we carried out a series of melting experiments on FeH and Fe3C up to 20 and 28 GPa, respectively. In the experiments on FeH, Fe sponge mixed with MgO was packed into a NaCl container with a hydrogen source, LiAlH4 (e.g., Fukai et al., 1989). During heating under high-pressures, hydrogenation of iron was observed by volume change. The phase boundary between ?'-phase (low-temperature phase) and ?-phase (high-temperature phase) of iron-hydride was determined using both cooling and heating experiments. Hydrogen concentrations in the ?-FeHx and ?'-FeHx were calculated based on the excess volume data from that of pure iron. It is found that ?-FeHx and ?'-FeHx synthesized in our experiments at pressures between 10 and 20 GPa are nearly stoichiometric FeH. Melting temperature of the ?-FeH was determined by the abrupt change in the X-ray diffraction patterns (crystalline to amorphous). The melting temperatures were determined to be 1473, 1473, 1493, 1573 and 1593 K at 10, 11.5, 15, 18 and 20 GPa, respectively. In the experiments using Fe3C, the synthesized Fe3C powder was encapsulated in a MgO container. In the diffraction sequences during heating, the peaks of Fe3C disappeared, and the new peaks identified as those of Fe7C3 were observed with halo caused by liquid. Finally, the Fe7C3 peaks disappeared, and only the halo pattern was observed. Based on these observations, the incongruent melting of Fe3C to Fe7C3 and liquid is estimated to occur at 1823 and 1923 K at 19.7 and 27.0 GPa, respectively. The liquidus temperatures of the Fe3C composition are found to be at 2098 and 2198 K at 19.5 and 26.8 GPa, respectively. The melting temperatures of Fe3C determined by our experiments are >700 K lower than that of the previous estimation based on thermodynamic calculation (Wood, 1993). Our experimental results show a possibility that the hydrogen and carbon lower the melting temperature of iron (outer core) dramatically. The melting temperatures of ?-FeH and Fe3C at 20 GPa are already 500 K lower than that of pure iron estimated by Anderson and Isaak (2000). Extrapolating our experimental melting curves for FeH and Fe3C to core pressures using Lindemann's melting law, we obtained the melting temperatures to be ~2600 and ~2900 K at the core-mantle boundary (CMB), respectively. In the presence of both hydrogen and carbon, melting temperature of the Earth's outer core could be >1500 K lower than that of the previous estimates, implying that the temperature gap at CMB could be much smaller than the current estimates.

  8. Temperature, accumulation, and ice sheet elevation in central Greenland through the last deglacial transition

    Microsoft Academic Search

    Kurt M. Cuffey; Gary D. Clow

    1997-01-01

    We present a combined heat- and ice-flow model, constrained by measurements of temperature in the Greenland Ice Sheet Project 2 (GISP2) borehole and by the GISP2 51so record and depth-age scale, which determines a history of temperature, accumulation rate, and ice sheet elevation for the past 50,000 years in central Greenland. Important results are: that the temperature increase from average

  9. Control of melt pool temperature and deposition height during direct metal deposition process

    Microsoft Academic Search

    Lijun Song; Vijayavel Bagavath-Singh; Bhaskar Dutta; Jyoti Mazumder

    This paper presents a hybrid control system that is able to improve dimensional accuracy of geometrically complex parts manufactured\\u000a by direct metal deposition process. The melt pool height is monitored by three high-speed charged couple device cameras in\\u000a a triangulation setup. The melt pool temperature is monitored by a dual-color pyrometer. A two-input single-output hybrid\\u000a control system including a master

  10. Vapor pressure above ice at temperatures below 170 K

    Microsoft Academic Search

    Konrad Mauersberger; Dieter Krankowsky

    2003-01-01

    Ice clouds in the earth's atmosphere and the presence of ices in comets and on planetary surfaces have raised the interest in the formation and existence of ice particles and of ice in bulk matter. Of special importance are the saturated vapor pressures well below 200 K. Marti and Mauersberger [1993] published a simple, experimentally derived equation that covers the

  11. A 1700-year Record of Tropical Sea Surface Temperatures and High-altitude Andean Climate Derived from the Quelccaya Ice Cap, Peru (Invited)

    NASA Astrophysics Data System (ADS)

    Thompson, L. G.; Mosley-Thompson, E. S.; Davis, M. E.; Lin, P.

    2010-12-01

    Stable isotopic, aerosol, and physical stratigraphy provided by new ice-core records from the Quelccaya ice cap (5670 masl) in Peru provide annual time series of tropical climatic and environmental variations extending back to 315 AD. These records present an opportunity to extract new information about links between rising temperatures on Andean tropical glaciers and sea surface temperatures (SSTs) in El Niño-Southern Oscillation (ENSO) indicator regions and in the Intertropical Convergence Zone (ITCZ) in the eastern Pacific and western Atlantic Oceans. ENSO is a dominant force for tropical climate variability on interannual time scales. It is linked with the position of the ITCZ and the associated teleconnections affect the strength and direction of air masses and storm tracks, variations in convective activity that control flooding and drought, and modulation of tropical storm intensities. The Quelccaya ice core record may be considered as the “Rosetta Stone” for high resolution climate records extracted from tropical glaciers, relating stable isotopic variations with tropical SSTs and freezing level heights. The ice core histories from Quelccaya also provide the longer term context needed to assess the significance of the magnitude and rate of its current ice loss. The cores provide a detailed description of climate conditions in the tropical Andes during the "Little Ice Age" and "Medieval Climate Anomaly” periods. They show that the recent acceleration of ice retreat in this Andean region is not driven solely by precipitation changes and that over decadal and longer time scales stable isotopic ratios are not significantly correlated with precipitation. The well-documented accelerating ice loss on Quelccaya in the Andes, as well as that on Naimona’nyi in the Himalayas, on Kilimanjaro in eastern Africa, and on ice fields near Puncak Jaya, Papua, Indonesia point to an overarching, larger scale driver. The ongoing melting of these ice fields is consistent with model predictions for a vertical amplification of temperature in the tropics, and has serious implications for the people who live in these areas.

  12. SENSITIVITY OF BRIGHTNESS TEMPERATURES FROM AMSR-E LOW FREQUENCY CHANNELS TO THE SEASONAL EVOLUTION OF LAKE ICE THICKNESS

    Microsoft Academic Search

    Kyung-Kuk Kang; Claude R. Duguay; Stephen E. L. Howell; Chris P. Derksen; Richard E. J. Kelly

    Lake ice growth and decay include: freeze-up in the autumn; a long period of growth and thickening in winter; a short period of ice melting and thinning, and finally, break-up and the complete disappearance of the ice cover in spring. The sensitivity of freeze-up and break-up dates, and therefore ice cover duration, to climate variability and change has been demonstrated

  13. Breakdown of time-temperature superposition in a bead-spring polymer melt near the glass transition temperature

    E-print Network

    Tamio Yamazaki

    2014-10-06

    The breakdown of the time-temperature superposition (TTS) near its glass transition temperature (Tg) in simple bead-spring polymer melts with and without the chain angle potential was numerically investigated. The stress relaxation modulus at different temperatures G(t,T) was calculated by the Green-Kubo relation. The TTS of G(t,T) of bead-spring polymer melts worked well at temperatures sufficiently higher than its Tg. However, when the system temperature is approaching the glass transition regime, the breakdown of TTS is observed. At temperatures near the Tg, the temperature dependence of the shift factor aTB, which is defined at the time scale between the bond relaxation and the chain relaxation regimes of a G(t)-function, is significantly stronger than ones aTA defined by the time scale of the chain relaxation modes. In direct relation to the breakdown of TTS of G(t,T), the decoupling of Stokes-Einstein law of diffusion-viscosity relation also appears in the glass transition regime. The analysis of the van Hove function Gs(r,t) and non-gaussian parameter, a2(t), of the bead motions strongly suggest that the TTS breakdown is concerned with the dynamic heterogeneity. The effect of the chain stiffness on the temperature dependence of the shift factors was also investigated in this study. The stiffer chains melt has a stronger temperature dependence of the shift factors than the ones of the flexible chains melt. However, regardless of the chain stiffness, the stress relaxation modulus functions of the bead-spring polymer melts will begin to breakdown the TTS at a similar Tg-normalized temperature around T/Tg ~ 1.2.

  14. Ice thickness effects on Aquarius brightness temperatures over Antarctica

    NASA Astrophysics Data System (ADS)

    Pablos, Miriam; Piles, María.; González-Gambau, Verónica; Camps, Adriano; Vall-llossera, Mercè

    2015-04-01

    The Dome-C region, in the East Antarctic Plateau, is regarded as an ideal natural laboratory for calibration/validation of space-borne microwave radiometers. At L-band, the thermal stability of this region has been confirmed by several experimental campaigns. However, its use as an independent external calibration target has recently been questioned due to some spatial inhomogeneities and seasonal effects revealed in the brightness temperatures (TB) acquired in this area. This paper shows the observed relationship, from exploratory research, between the Antarctic ice thickness spatial variations and the measured Aquarius TB changes. A 3-months no-daylight period during the Austral winter has been analyzed. Four transects have been defined over East Antarctica covering areas with different ice thickness variations and ranges. The theoretical L-band penetration depth has been estimated to understand the possible contributions to the measured signal. A good agreement has been observed between Aquarius TB and ice thickness variations over the whole Antarctica, with correlations of ˜0.6-0.7. The two variables show a linear trend with slopes of ˜8.3-9.5 K/km. No correlation has been observed with the subglacial bedrock. The maximum L-band penetration depth has been estimated to be ˜1-1.5 km. Results are therefore consistent: the spatial variations found on Aquarius TB are not related to the emissivity of the bedrock, which lies deeper. This study provides evidence that new L-band satellite observations could contribute to further our understanding of Antarctic geophysical processes.

  15. A molecular dynamics simulation of the melting points and glass transition temperatures of myo-and neo-inositol

    E-print Network

    de Gispert, Adrià

    A molecular dynamics simulation of the melting points and glass transition temperatures of myo December 2003; accepted 23 August 2004 The heat of sublimation, density, melting point, and glass of glucose4 as well as the glass transition in a number of glucose hydrates.5 For the melting point and glass

  16. Shear Melting and High Temperature Embrittlement: Theory and Application to Machining Titanium

    NASA Astrophysics Data System (ADS)

    Healy, Con; Koch, Sascha; Siemers, Carsten; Mukherji, Debashis; Ackland, Graeme J.

    2015-04-01

    We describe a dynamical phase transition occurring within a shear band at high temperature and under extremely high shear rates. With increasing temperature, dislocation deformation and grain boundary sliding are supplanted by amorphization in a highly localized nanoscale band, which allows for massive strain and fracture. The mechanism is similar to shear melting and leads to liquid metal embrittlement at high temperature. From simulation, we find that the necessary conditions are lack of dislocation slip systems, low thermal conduction, and temperature near the melting point. The first two are exhibited by bcc titanium alloys, and we show that the final one can be achieved experimentally by adding low-melting-point elements: specifically, we use insoluble rare earth metals (REMs). Under high shear, the REM becomes mixed with the titanium, lowering the melting point within the shear band and triggering the shear-melting transition. This in turn generates heat which remains localized in the shear band due to poor heat conduction. The material fractures along the shear band. We show how to utilize this transition in the creation of new titanium-based alloys with improved machinability.

  17. Shear melting and high temperature embrittlement: theory and application to machining titanium.

    PubMed

    Healy, Con; Koch, Sascha; Siemers, Carsten; Mukherji, Debashis; Ackland, Graeme J

    2015-04-24

    We describe a dynamical phase transition occurring within a shear band at high temperature and under extremely high shear rates. With increasing temperature, dislocation deformation and grain boundary sliding are supplanted by amorphization in a highly localized nanoscale band, which allows for massive strain and fracture. The mechanism is similar to shear melting and leads to liquid metal embrittlement at high temperature. From simulation, we find that the necessary conditions are lack of dislocation slip systems, low thermal conduction, and temperature near the melting point. The first two are exhibited by bcc titanium alloys, and we show that the final one can be achieved experimentally by adding low-melting-point elements: specifically, we use insoluble rare earth metals (REMs). Under high shear, the REM becomes mixed with the titanium, lowering the melting point within the shear band and triggering the shear-melting transition. This in turn generates heat which remains localized in the shear band due to poor heat conduction. The material fractures along the shear band. We show how to utilize this transition in the creation of new titanium-based alloys with improved machinability. PMID:25955055

  18. Trace element analyses of spheres from the melt zone of the Greenland ice cap using synchrotron X ray fluorescence

    NASA Technical Reports Server (NTRS)

    Chevallier, P.; Wang, J.; Jehanno, C.; Maurette, M.; Sutton, S. R.

    1986-01-01

    Synchrotron X-ray fluorescence spectra of unpolished iron and chondritic spheres extracted from sediments collected on the melt zone of the Greenland ice cap allow the analysis of Ni, Cu, Zn, Ga, Ge, Pb, and Se with minimum detection limits on the order of several parts per million. All detected elements are depleted relative to chondritic abundance with the exception of Pb, which shows enrichments up to a factor of 500. An apparent anticorrelation between the Ni-content and trace element concentration was observed in both types of spherules. The fractionation patterns of the iron and chondritic spheres are not complementary and consequently the two iron spheres examined in this study are unlikely to result from ejection of globules of Fe/Ni from parent chondritic micrometeoroids.

  19. NorthNorth Sea ice and glaciers are melting, permafrost is thawing, tundra

    E-print Network

    Sturm, Matthew

    of carbon frozen into the Arctic in the form of peat. As the climate warms and this peat thaws, it could on the Greenland Ice Sheet, Alaskan glaciers retreating at un- precedented rates. Add to this the in- creasing, and the Arctic will become a poorer repository, eventually warming the cli- mate of the entire planet. Figuring

  20. Low temperature biodegradation of airport de-icing fluids.

    PubMed

    Revitt, D M; Worrall, P

    2003-01-01

    The biodegradabilities of glycol- and acetate-based aircraft de-icing fluids on airport surfaces have been investigated at three temperatures between 0 degrees C and 10 degrees C. The aqueous solubilities of these substances can result in high BOD loadings in runoff and pose serious toxicity problems in receiving waters. The measured surface biodegradation rates for de-icing products based on ethylene/diethylene glycol (Konsin), propylene glycol (Kilfrost) and potassium acetate (Clearway) at 4 degrees C were 0.082, 0.073 and 0.033 day(-1). The resulting reductions in the potential BOD loadings, of a single application of a typical mixture of these products, over a 5 day biodegradation period are predicted to be 32.9%, 30.2% and 21.4%, respectively at 8 degrees C, 4 degrees C and 1 degrees C. For consecutive daily applications, the comparable cumulative reductions over 5 days are 20.8%, 18.9% and 13.3%. The subsequent savings in the amount of treatment required for airport runoff prior to safe discharge to receiving waters are discussed and hence the relevance of surface biodegradation processes to the design of stormwater treatment systems involving the wash-off of biodegradable pollutants following retention on urban surfaces. PMID:14703144

  1. Characterization of Superhydrophobic Surfaces for Anti-icing in a Low-Temperature Wind Tunnel

    SciTech Connect

    Swarctz, Christopher [Stevens Institute of Technology, Hoboken, New Jersey; Alijallis, Elias [Stevens Institute of Technology, Hoboken, New Jersey; Hunter, Scott Robert [ORNL; Simpson, John T [ORNL; Choi, Chang-Hwan [Stevens Institute of Technology, Hoboken, New Jersey

    2010-01-01

    In this study, a closed loop low-temperature wind tunnel was custom-built and uniquely used to investigate the anti-icing mechanism of superhydrophobic surfaces in regulated flow velocities, temperatures, humidity, and water moisture particle sizes. Silica nanoparticle-based hydrophobic coatings were tested as superhydrophobic surface models. During tests, images of ice formation were captured by a camera and used for analysis of ice morphology. Prior to and after wind tunnel testing, apparent contact angles of water sessile droplets on samples were measured by a contact angle meter to check degradation of surface superhydrophobicity. A simple peel test was also performed to estimate adhesion of ice on the surfaces. When compared to an untreated sample, superhydrophobic surfaces inhibited initial ice formation. After a period of time, random droplet strikes attached to the superhydrophobic surfaces and started to coalesce with previously deposited ice droplets. These sites appear as mounds of accreted ice across the surface. The appearance of the ice formations on the superhydrophobic samples is white rather than transparent, and is due to trapped air. These ice formations resemble soft rime ice rather than the transparent glaze ice seen on the untreated sample. Compared to untreated surfaces, the icing film formed on superhydrophobic surfaces was easy to peel off by shear flows.

  2. Dual speciation of nitrogen in silicate melts at high pressure and temperature: An experimental study

    NASA Astrophysics Data System (ADS)

    Roskosz, Mathieu; Mysen, Bjorn O.; Cody, George D.

    2006-06-01

    Solubility and speciation of nitrogen in silicate melts have been investigated between 1400 and 1700 °C and at pressures ranging from 10 to 30 kbar for six different binary alkali and alkaline-earth silicate liquids and a Ca-Mg-alumino silicate. Experiments were performed in a piston-cylinder apparatus. The nitrogen source is silver azide, which breaks down to Ag and molecular N 2 below 300 °C. At high pressure and temperature, the nitrogen content may be as high as 0.7 wt% depending on the melt composition, pressure, and temperature. It increases with T, P and the polymerization state of the liquid. Characterization by Raman spectroscopy and 15N solid state MAS NMR indicates that nitrogen is not only physically dissolved as N 2 within the melt structure like noble gases, but a fraction of nitrogen interacts strongly with the silicate network. The most likely nitrogen-bearing species that can account for Raman and NMR results is nitrosyl group. Solubility data follow an apparent Henry's law behavior and are in good agreement with previous studies when the nitrosyl content is low. On the other hand, a significant departure from a Henry's law behavior is observed for highly depolymerized melts, which contain more nitrosyl than polymerized melts. Possible solubility mechanisms are also discussed. Finally, a multi-variant empirical relation is given to predict the relative content of nitrosyl and molecular nitrogen as a function of P, T, and melt composition and structure. This complex speciation of nitrogen in melts under high pressure may have significant implication concerning crystal-melt partitioning of nitrogen as well as for potential elemental and isotopic fractionation of nitrogen in the deep Earth.

  3. Atomistic simulations of melting and solidification using temperature accelerated molecular dynamics

    NASA Astrophysics Data System (ADS)

    Yu, Tang-Qing; Samanta, Amit; E, Weinan; Tuckerman, Mark; vanden-Eijnden, Eric

    2013-03-01

    A detailed understanding of melting/solidification mechanisms in metals remains obscure, though over the years many simulations and experiments have been performed for clarifying it. We have applied the enhanced-sampling method, Temperature-Accelerated Molecular Dynamics, to study the melting/solidification of FCC metals like copper, nickel under the constant temperature and pressure conditions. Free energy surfaces along Steinhardt order parameters and local density are obtained and minimum free energy path (MFEP) between the metastable states are calculated. An analysis of the atomic structure along the MFEP, reveals that an interplay between orientation ordering and positional ordering governs this phase transition.

  4. Adhesion of Polymer Composite Melt to PTFE at Elevated Temperature

    NASA Astrophysics Data System (ADS)

    Pan, David; Debies, Thomas; McVeigh, Dan

    2007-03-01

    A novel technique for measuring the adhesive force between a thin molten polyester composite film and a PTFE surface is presented in the paper. The molten film was prepared by first depositing powdery composite particles on a substrate and then heating the powdery film on the substrate to the test temperature through a heated pressure nip between two conformable rollers comprising a PTFE overcoat at a speed up to 400 mm/s. The adhesive force is measured by wedging a bendable metal knife into the interface between the molten film and PTFE near the exit of the heating nip. Strain gauges were mounted on both sides of the metal knife. The differential strain gauge reading resulting from the degree of the knife bending is calibrated against standard weights. The technique was used to investigate the effects of the substrate, substrate roughness, molten film thickness, temperature and type of wax additive on the adhesion of the molten composite film to PTFE. On the effects of temperature and type of wax, we found that the adhesive force remains relatively constant at low temperature, and then drops significantly, in some instances to zero, as the temperature further increases. A phenomenological model is proposed to explain the effects of main temperature and the wax additive. The model is evidenced by the surface segregation of wax from the polyester composite film as determined by XPS.

  5. Temperature Dependence of Density, Viscosity and Electrical Conductivity for Hg-Based II-VI Semiconductor Melts

    NASA Technical Reports Server (NTRS)

    Li, C.; Ban, H.; Lin, B.; Scripa, R. N.; Su, C.-H.; Lehoczky, S. L.

    2004-01-01

    The relaxation phenomenon of semiconductor melts, or the change of melt structure with time, impacts the crystal growth process and the eventual quality of the crystal. The thermophysical properties of the melt are good indicators of such changes in melt structure. Also, thermophysical properties are essential to the accurate predication of the crystal growth process by computational modeling. Currently, the temperature dependent thermophysical property data for the Hg-based II-VI semiconductor melts are scarce. This paper reports the results on the temperature dependence of melt density, viscosity and electrical conductivity of Hg-based II-VI compounds. The melt density was measured using a pycnometric method, and the viscosity and electrical conductivity were measured by a transient torque method. Results were compared with available published data and showed good agreement. The implication of the structural changes at different temperature ranges was also studied and discussed.

  6. Ocean rises are products of variable mantle composition, temperature and focused melting

    NASA Astrophysics Data System (ADS)

    Dick, Henry J. B.; Zhou, Huaiyang

    2015-01-01

    Ocean ridges, where Earth's tectonic plates are pulled apart, range from more than 5-km depth in the Arctic to 750 m above sea level in Iceland. This huge relief is generally attributed to mantle plumes underlying mantle hotspots--areas of voluminous volcanism marked by ocean islands. The plumes are thought to feed the mantle beneath adjacent ocean ridges. This process results in thickened crust and ridge elevation to form ocean rises. The composition of mid-ocean ridge basalt, a direct function of mantle composition and temperature, varies systematically along ocean rises, but in a unique way for each different rise. Here we use thermodynamic calculations of melt-evolution pathways to show that variations in both mantle temperature and source composition are required to explain the chemical make-up of rise basalts. Thus, lateral gradients in mantle temperature cannot be uniquely determined from basalt chemistry, and ocean rises can be supported by chemically buoyant mantle or by robust mantle plumes. Our calculations also indicate that melt is conserved and focused by percolative flow towards the overlying ridge, progressively interacting with the mantle to shallow depth. We conclude that most mantle melting occurs by an overlooked mechanism, focused melting, whereas fractional melting is a secondary process that is important largely at shallow depth.

  7. Greenland Ice Sheet Surface Air Temperature Variability: 18402007* JASON E. BOX

    E-print Network

    Howat, Ian M.

    Greenland Ice Sheet Surface Air Temperature Variability: 1840­2007* JASON E. BOX Byrd Polar, seasonal, and annual mean Greenland ice sheet near- surface air temperatures. Independent observations Greenland in autumn and southern Greenland in winter. Spring trends marked the 1920s warming onset, while

  8. Little Ice Age cold interval in West Antarctica: Evidence from borehole temperature at the West Antarctic

    E-print Network

    Severinghaus, Jeffrey P.

    Little Ice Age cold interval in West Antarctica: Evidence from borehole temperature at the West, especially in Antarctica. We present temperature data from a 300 m borehole at the West Antarctic Ice Sheet and West Antarctica suggests that the feedbacks amplifying the radiative forcing may not operate

  9. The mechanisms for pressure-induced amorphization of ice Ih

    Microsoft Academic Search

    J. S. Tse; D. D. Klug; C. A. Tulk; I. Swainson; E. C. Svensson; C.-K. Loong; V. Shpakov; V. R. Belosludov; R. V. Belosludov; Y. Kawazoe

    1999-01-01

    There has been considerable interest in the structure of liquid water at low temperatures and high pressure following the discovery of the high-density amorphous (HDA) phase of ice Ih (ref. 1). HDA ice forms at a pressure close to the extrapolated melting curve of ice, leading to the suggestion that it may have structure similar to that of dense water.

  10. Distribution of Temperatures over an Airplane Wing with Reference to the Phenomena of Ice Formation

    NASA Technical Reports Server (NTRS)

    Brun, Edmond

    1938-01-01

    The results obtained from the present study of temperature distribution over an airplane wing afford means for making the following statements as regards the conditions of ice accretion and the use of a thermic anti-icer or de-icer: 1) Ice can form on a wing only when the temperature is below or hovering around zero. 2) The thermic effects produced on contact of the air with the moving wing rather oppose ice accretion. 3) The thermic procedure in the fight against ice accretion on the wing consists in electrical heating of the leading edge. 4) It seems that the formation of ice on the wing ought to be accompanied by a temperature rise which brings the accretion to 0 degrees. 5) If the thermic effects of friction favor the operation of the thermic anti-icer, the functioning of the de-icer is facilitated by the release of heat which accompanies the deposit of ice.

  11. `Melting ice' I at 77 K and 10 kbar: a new method of making amorphous solids

    Microsoft Academic Search

    O. Mishima; L. D. Calvert; E. Whalley

    1984-01-01

    Amorphous solids are made mainly by cooling the liquid below the glass transition without crystallizing it, a method used since before recorded history1, and by depositing the vapour onto a cold plate2, as well as by several other methods3,4. We report here a new way-by `melting' a solid by pressure below the glass transition of the liquid-and apply it to

  12. Melting Temperatures of Extruded Products with Texturized Proteins

    Microsoft Academic Search

    S. Thymi; M. K. Krokida; A. Pappa; D. Marinos-Kouris

    2008-01-01

    Thermal properties of new extruded products with texturized properties were examined using Differential Scanning Calorimetry (DSC). Corn-texturized protein systems were extrusion-cooked in a twin-screw extruder with varying feed rate (0.7–1.9 g\\/s), screw speed (150–250 rpm), extrusion temperature (150 to 260°C), and feed moisture content (13 to 19 g\\/100g wet basis). Four different texturized legume flours, namely bean, chickpea, kidneybean, and

  13. Melt viscosity, temperature and transport processes, Troodos ophiolite, Cyprus

    NASA Astrophysics Data System (ADS)

    Schouten, Hans; Kelemen, Peter B.

    2002-07-01

    The lava section in the Troodos ophiolite, Cyprus, is chemically stratified and divided into a shallow lava sequence with low TiO 2 content and a deeper lava sequence with high TiO 2 content. We calculate the viscosity at magmatic temperature based on major element chemistry of lavas in Cyprus Crustal Study Project (CCSP) Holes CY-1 and 1A. We find that typical shallow low-Ti lavas have a magmatic viscosity that is two to three orders of magnitude lower than that of the deeper high-Ti lavas. This implies that, after eruption on-axis, Troodos low-Ti lavas would have been able to flow down the same slope faster and farther than high-Ti lavas. The calculated lava viscosity increases systematically from the lava-sediment interface to the bottom of the composite Hole CY-1/1A. This suggests that an efficient process of lava segregation by viscosity on the upper flanks of the paleo Troodos rise may have been responsible for the chemical stratification in the Troodos lava pile. Calculated magmatic temperature and molar Mg/(Mg+Fe), or Mg#, decrease systematically down-section, while SiO 2 content increases. Correlation of Mg# in the lavas with Mg# in the underlying, lower crustal plutonic rocks sampled by CCSP Hole CY-4 shows that the shallow lavas came from a high-temperature, lower crustal magma reservoir which is now represented by high-Mg# pyroxenite cumulates, while the deeper lavas were erupted from a lower-temperature, mid-crustal reservoir which is now represented by gabbroic cumulates with lower Mg#.

  14. Velocity of sound in solid methane near melting temperatures 

    E-print Network

    Whitehead, John Martin

    1968-01-01

    crystal. The dewar they employed did not allow visual observation of the crystal, and they apparently had no means of determining the growth rate that produced this single crystal, Thiele, Whitney, and Chase grew clear methane crystals 1 cm 19... Transverse Velocity Measurements Longitudinal Velocity Measurements IV. SUMMARY 23 24 34 REFERENCES 35 LIST OF FIGURES Figure Page 1. Density of Solid and Liquid Methane Versus Temperature . 5 Longitudinal Velocity of Sound in Solid Methane Versus...

  15. Recent Changes in the Arctic Melt Season

    NASA Technical Reports Server (NTRS)

    Stroeve, Julienne; Markus, Thorsten; Meier, Walter N.; Miller, Jeff

    2007-01-01

    Melt-season duration, melt-onset and freeze-up dates are derived from satellite passive microwave data and analyzed from 1979 to 2005 over Arctic sea ice. Results indicate a shift towards a longer melt season, particularly north of Alaska and Siberia, corresponding to large retreats of sea ice observed in these regions. Although there is large interannual and regional variability in the length of the melt season, the Arctic is experiencing an overall lengthening of the melt season at a rate of about 2 weeks decade(sup -1). In fact, all regions in the Arctic (except for the central Arctic) have statistically significant (at the 99% level or higher) longer melt seasons by greater than 1 week decade(sup -1). The central Arctic shows a statistically significant trend (at the 98% level) of 5.4 days decade(sup -1). In 2005 the Arctic experienced its longest melt season, corresponding with the least amount of sea ice since 1979 and the warmest temperatures since the 1880s. Overall, the length of the melt season is inversely correlated with the lack of sea ice seen in September north of Alaska and Siberia, with a mean correlation of -0.8.

  16. Temperature-dependent thermal expansivities of silicate melts: The system anorthite-diopside

    Microsoft Academic Search

    R. Knoche; D. B. Dingwell; S. L. Webb

    1992-01-01

    The temperature-dependent thermal expansivities of melts along the join anorthite-diopside have been determined on glassy and liquid samples using a combination of calorimetry, dilatometry, and Pt double bob Archimedean densitometry. Supercooled liquid volumes and molar thermal expansivities were determined using scanning calorimetric and dilatometric measurements of properties in the glass region and their behavior at the glass transition. The extraction

  17. PUBLISHED ONLINE: 8 NOVEMBER 2009 | DOI: 10.1038/NPHYS1438 Melting temperature of diamond at

    E-print Network

    Loss, Daniel

    LETTERS PUBLISHED ONLINE: 8 NOVEMBER 2009 | DOI: 10.1038/NPHYS1438 Melting temperature of diamond be `diamonds in the sky' in 1981 (ref. 1), the idea of significant quantities of pure carbon existing in giant the evolution and structure of such planets4 . Still, one of the most defining of thermal properties for diamond

  18. Meltwater migration in temperate ice

    NASA Astrophysics Data System (ADS)

    Schoof, C.; Hewitt, I.

    2014-12-01

    Frictional heating in the fast deforming ice of an ice stream potentially warms the ice to the melting point and there is evidence that a substantial region of temperate ice may exist near the base of the ice-stream margins. The production of meltwater in such a region alters the heat balance and the usual temperature equation solved in ice-sheet models must be modified to take account of this. In some cases, simply capping the temperature at the melting point and assuming excess heating produces meltwater can give the correct dynamics. But in general this is too simplistic an approach. Meltwater drains under gravity and dynamic pressure gradients, and the resulting transport of heat must be accounted for in order to correctly locate the boundaries between temperate and subtemperate ice. In this study, we look in detail at the dynamics of the temperate ice, focussing on the movement of meltwater in a compacting, viscous matrix of ice and the way in which meltwater transport influences the subtemperate-temperate transition. Four canonical cases can be considered: when the ice flows into or out of the temperate region, and when the meltwater flows towards or away from the interface. We examine the possible formation of boundary layers near these regions, and discuss how these may be responsible for channeling meltwater to the ice bed. We also discuss the use of numerical enthalpy and enthalpy-gradient methods, and the conditions under which these can correctly describe the dynamics.

  19. A Climate-Data Record of the "Clear-Sky" Surface Temperature of the Greenland Ice Sheet

    NASA Technical Reports Server (NTRS)

    Hall, D. K.; Comiso, J. C.; Digirolamo, N. E.; Stock, L. V.; Riggs, G. A.; Shuman, C. A.

    2009-01-01

    We are developing a climate-data record (CDR of daily "clear-sky" ice-surface temperature (IST) of the Greenland Ice Sheet, from 1982 to the present using Advanced Very High Resolution Radiometer (AVHRR) (1982 - present) and Moderate-Resolution Imaging Spectroradiometer (MODIS) data (2000 - present) at a resolution of approximately 5 km. The CDR will be continued in the National Polar-orbiting Operational Environmental Satellite System Visible/Infrared Imager Radiometer Suite era. Two algorithms remain under consideration. One algorithm under consideration is based on the split-window technique used in the Polar Pathfinder dataset (Fowler et al., 2000 & 21007). Another algorithm under consideration, developed by Comiso (2006), uses a single channel of AVHRR data (channel 4) in conjunction with meteorological-station data to account for atmospheric effects and drift between AVHRR instruments. Known issues being addressed in the production of the CDR are: tune-series bias caused by cloud cover (surface temperatures can be different under clouds vs. clear areas) and cross-calibration in the overlap period between AVHRR instruments, and between AVHRR and MODIS instruments. Because of uncertainties, mainly due to clouds (Stroeve & Steffen, 1998; Wang and Key, 2005; Hall et al., 2008 and Koenig and Hall, submitted), time-series of satellite 1S'1" do not necessarily correspond to actual surface temperatures. The CDR will be validated by comparing results with automatic-,",eather station (AWS) data and with satellite-derived surface-temperature products. Regional "clear-sky" surface temperature increases in the Arctic, measured from AVHRR infrared data, range from 0.57+/-0.02 deg C (Wang and Key, 2005) to 0.72+/-0.10 deg C (Comiso, 2006) per decade since the early 1980s. Arctic warming has important implications for ice-sheet mass balance because much of the periphery of the Greenland Ice Sheet is already near 0 deg C during the melt season, and is thus vulnerable to rapid melting if temperatures continue to increase. References

  20. An Ice Storage System using Supercooled Water

    NASA Astrophysics Data System (ADS)

    Moriya, Mitsuru; Tanino, Masayuki; Kikuchi, Sakae; Hayashi, Toshio; Okonogi, Tokio; Kozawa, Yoshiyuki

    The storage and melting characteristics of slurry-ice mixtures in several tanks were investigated exprimentally. For ice storage processes, three different kinds ofice-feeding methods were tested in connection with the fluidizable water-ice two-phase mixture produced in the system. It was confirmed that the achievable bulk IPF in any tank and using any of these methods was 30-40% under stable operational conditions. For ice melting processes, two different kinds of methods were considered and tested. Both were advantageous in that almost all ice stored in a tank could be consumed, thereby maintaining high system performance. By a modeling analysis of ice melting processes in the tank, it was possible to predict accurately the time history of tank outlet water temperatures.

  1. Resolving Histories of Magmatic Volatiles in Fluids and Silicate Melts as a Function of Pressure, Temperature, and Melt Composition through Apatite Geochemistry

    NASA Astrophysics Data System (ADS)

    Webster, J. D.; Piccoli, P. M.; Goldoff, B. A.

    2012-12-01

    Fluids including aqueous or aqueous-carbonic vapor, aqueous liquid, and hydrosaline liquid, if present in magma, influence magmatic and volcanic processes, and the exsolution of fluids from magma sequesters and buffers volatile components from melt thus impacting the textural and chemical evolution of melts and phenocrysts. Establishing the timing of initial magmatic fluid saturation and monitoring changes in fluid chemistry through textural interpretations are often challenging because primary magmatic fluid inclusions are uncommon to most plutonic systems and are extremely rare in phenocrysts of eruptive magmas. Moreover, miarolitic cavities, often interpreted to be a priori evidence of fluid exsolution, are rarely observed in igneous systems. Geochemical tools used to resolve magmatic volatile histories include the analysis and interpretation of melt inclusion compositions and those of hydrous minerals including micas, amphiboles, and apatite. We have conducted more than 50 new hydrothermal experiments involving apatite+rhyodacite melt±fluids at 28, 50, 100, 200, and 400 MPa, and have combined these new data with published results for apatite-saturated melts at 200 MPa. This integrated body of data supports determination of a broadly applicable geochemical relationship that correlates the mole fractions of H2O and Cl in apatite with mole fractions of H2O and Cl in coexisting silicate melt as a function of pressure, temperature, and melt composition (for felsic to basaltic melts). The mathematical expression of this relationship is useful for a wide variety of applications: constraining H2O, Cl, and F concentrations in silicate melts and hence verifying concentrations of magmatic volatiles determined from silicate melt inclusions; establishing pressures or temperatures of apatite crystallization or last equilibration with melt ± fluids (if temperature and pressure, respectively, are constrained from other geothermobarometers); determining concentrations of volatiles in magmatic fluids; and interpreting magmatic degassing based on concentrations and zonation patterns of halogens and hydroxyl in apatite. We have applied this relationship to eruptive units of Augustine volcano, Alaska, to interpret magma evolution and to highlight the behavior of volatiles in melt and fluid(s); Augustine melt inclusion data are limited largely to felsic compositions. For geologically reasonable ranges in temperature and using compositions of rhyodacitic to rhyolitic melt inclusions and coexisting apatite for these units, we derive apparent pressures of apatite crystallization (or of subsequent equilibration of apatite with melt and fluid) that are generally higher than apparent pressures of melt inclusion entrapment (many differ by a factor of two). Thus, inclusions of apatite, trapped in other phenocrysts, provide a record of melt and fluid compositions for magmas located deeper and formed potentially earlier during differentiation than that of felsic melt inclusions from the same rock samples. We will also apply this geochemical relationship to apatites from high-silica rhyolitic and other subduction-related volcanic systems to provide new constraints on the behavior of volatiles in eruptive magma and fluid(s) and compare these results to those determined from coexisting melt inclusions in such systems.

  2. Flavor dependence of baryon melting temperature in effective models of QCD

    E-print Network

    Torres-Rincon, Juan M; Aichelin, Joerg

    2015-01-01

    We apply the three-flavor (Polyakov-)Nambu-Jona-Lasinio model to generate baryons as quark-diquark bound states using many-body techniques at finite temperature. All the baryonic states belonging to the octet and decuplet flavor representations are generated in the isospin-symmetric case. For each state we extract the melting temperature at which the baryon may decay into a quark-diquark pair. We seek for an evidence of the strangeness dependence of the baryon melting temperature as suggested by the statistical thermal models and supported by lattice-QCD results. A clear and robust signal for this claim is found, pointing to a flavor dependence of the hadronic deconfinement temperature.

  3. Flavor dependence of baryon melting temperature in effective models of QCD

    E-print Network

    Juan M. Torres-Rincon; Benjamin Sintes; Joerg Aichelin

    2015-02-11

    We apply the three-flavor (Polyakov-)Nambu-Jona-Lasinio model to generate baryons as quark-diquark bound states using many-body techniques at finite temperature. All the baryonic states belonging to the octet and decuplet flavor representations are generated in the isospin-symmetric case. For each state we extract the melting temperature at which the baryon may decay into a quark-diquark pair. We seek for an evidence of the strangeness dependence of the baryon melting temperature as suggested by the statistical thermal models and supported by lattice-QCD results. A clear and robust signal for this claim is found, pointing to a flavor dependence of the hadronic deconfinement temperature.

  4. Flavor dependence of baryon melting temperature in effective models of QCD

    NASA Astrophysics Data System (ADS)

    Torres-Rincon, Juan M.; Sintes, Benjamin; Aichelin, Joerg

    2015-06-01

    We apply the three-flavor (Polyakov-)Nambu-Jona-Lasinio model to generate baryons as quark-diquark bound states using many-body techniques at finite temperature. All the baryonic states belonging to the octet and decuplet flavor representations are generated in the isospin-symmetric case. For each state we extract the melting temperature at which the baryon may decay into a quark-diquark pair. We seek for an evidence of the strangeness dependence of the baryon melting temperature as suggested by the statistical thermal models and supported by lattice quantum chromodynamics results. A clear and robust signal for this claim is found, pointing to a flavor dependence of the hadronic deconfinement temperature.

  5. Properties of Silicate Melts at High Pressure and Temperature from Ab Initio Calculations

    NASA Astrophysics Data System (ADS)

    Seclaman, A. C.; Caracas, R.

    2014-12-01

    The evolution of planetary interiors is intrinsically connected to the behavior and properties of silicate melts at high pressures and temperatures. Our work comes as a complement to existing data expanding the pressure, temperature, and compositional ranges. We used the V.A.S.P. code to perform NVT Molecular Dynamics simulations on two basic compositions: Mg2SiO4 and MgSiO3. All calculations are done within augmented planar wave formalism of the Density Functional Theory. Supercells of 160 atoms clino-enstatite and 112 atoms forsterite were melted at 5000K and then cooled and thermalized, using the Nose-Hoover thermostat, at temperatures more representative of Earth's interior (3000 and 4000K). The pressure range of our investigations spans from 0 to approximately 160GPa. Since important properties, density and magnetism, are dependent on the presence of iron we also created (Fex-1,Mgx)SiO3 and (Fex-1,Mgx)2SiO4melts from the thermalized pure compositions by replacing the desired amount of magnesium atoms with iron. Because other transitional elements present similar behavior as iron, and nickel is an important element in the core, compositions containing different amounts of nickel were also created by adding extra Ni atoms in the system. We analyze in detail the behavior with pressure of the density, clustering and coordination, total magnetization, and thermodynamical parameters of the melts. Our results indicate that changes in the structure and magnetic moment of the Forsterite melt begin at relatively low pressure. As an application of our data to the Earth's present deep interior we analyzed in great detail various possible mixtures of Fe bearing melt and solid mantle in an attempt to fit the density estimated for the Ultra Low Velocity Zones.

  6. Diffusive motion in alkali silicate melts: an NMR study at high temperature

    Microsoft Academic Search

    S. B. Liu; J. F. Stebbins; E. Schneider; A. Pines

    1988-01-01

    Nuclear magnetic resonance (NMR) spectroscopy at high temperature is an excellent tool for studying the atomic scale diffusive processes in molten silicates which control their transport and thermodynamic properties. The authors present here ²³Na and ²⁹Si NMR data on lineshapes, spin-lattice, and spin-spin relaxation times in a series of alkali silicate and aluminosilicate melts from room temperature to about 1200°C.

  7. In situ observation of partial melting in superplastic aluminum alloy composites at high temperatures

    Microsoft Academic Search

    J. Koike; M. Mabuchi; K. Higashi

    1995-01-01

    The possibility of partial melting and its relations to the superplasticity at high strain rates were studied with transmission electron microscopy and differential scanning calorimetry in Al?Cu?Mg (2124), Al?Mg (5052), and Al?Mg?Si (6061) alloys reinforced with Si3N4 particles. Calorimetry measurements of all three composites showed a sharp endothermic peak at an optimum superplastic temperature. At the same temperature, transmission electron

  8. Experimental Evidence for a Crossover between Two Distinct Mechanisms of Amorphization in Ice Ih under Pressure

    Microsoft Academic Search

    Thierry Strässle; Stefan Klotz; Gérard Hamel; Michael M. Koza; Helmut Schober

    2007-01-01

    We report neutron scattering data which reveal the central role of phonon softening leading to a negative melting line, solid-state amorphization, and negative thermal expansion of ice. We find that pressure-induced amorphization is due to mechanical melting at low temperatures, while at higher temperatures amorphization is governed by thermal melting (violations of Born's and Lindemann's criteria, respectively). This confirms earlier

  9. Dynamic-Type Ice Thermal Storage Systems

    NASA Astrophysics Data System (ADS)

    Ohira, Akiyoshi

    This paper deals with reviews for research and development of a dynamic-type ice thermal storage system. This system has three main features. First, the ice thermal storage tank and the ice generator are separate. Second, ice is transported to the tank from the ice generator by water or air. Third, the ice making and melting processes are operated at the same time. Outlet water temperature from the dynamic-type ice thermal storage tank remains low for a longer time. In this paper, dynamic-Type ice thermal storage systems are divided into three parts: the ice making part, the ice transport part, and the cold energy release part. Each part is reviewed separately.

  10. Non-melting and self-wetting of alkali halide surfaces at high temperatures

    NASA Astrophysics Data System (ADS)

    Ceresoli, Davide; Zykova-Timan, Tania; Tartaglino, Ugo; Sekkal, Wassila; Jagla, Edoardo; Tosatti, Erio

    2004-03-01

    We investigated theoretically the high temperature thermodynamic properties and the (lack of) self-wetting of ionic crystal surfaces, with NaCl(100) as a prototype case. We found by classical molecular dynamics simulations that NaCl(100) is a non-melting crystal surface and can be overheated to a spinodal temperature TS 150 K above the bulk melting temperature (T_M). While surface non-melting is in itself well known, and is observed on semiconductors as well as on close packed metal surfaces, the basic mechanism for NaCl appears to be different from either of them. Moreover, there appear to be two distinct metastability regimes of solid NaCl(100) above T_M. The first regime TM < T < T_1, (T1 - TM = 60 K) the metastable solid surface is strongly protected by a nucleation barrier of large thickness. This thickness decreases with temperature, until it drops to a lattice spacing a at T_1. In the second regime T1 < T < TS is characterized by a ``fragile'' metastability, with a nucleation barrier one lattice spacing thick. Here, the smallest seed is able to cause melting, i.e., it is enough to melt the first monolayer for the liquid to break through and melt the whole system. A basic explanation of these facts and of the two regimes is given, based on a short-range oscillatory interaction between the solid-liquid and the liquid-vapor interfaces. In addition, we also simulated a liquid NaCl nanodroplet, deposited on a solid NaCl surface in the vicinity of the bulk melting point. The anomalously large contact angle measured long ago by Mutaftschiev [1] is well reproduced by this realistic molecular dynamics droplet simulation. Based on these results, and on independent determinations of the liquid-vapor (?_LV) and the solid-vapor interface free energy (?_SV) an estimate of the solid-liquid interface free energy (?_SL) is extracted. The solid-vapor surface free energy turns out to be anomalously small and similar to the liquid-vapor one, providing a direct thermodynamic explanation of the reduced wetting ability of the ionic melt. G. Grange and B. Mutaftschiev, Surf. Sci. 47, 723 (1975).

  11. An experimental study on the effect of temperature and melt composition on the partitioning of nickel between olivine and silicate melt

    Microsoft Academic Search

    R. J. Kinzler; T. L. Grove; S. I. Recca

    1990-01-01

    Experiments in the simple system CaO-MgO-AlâOâ-SiOâNaâO-FeO were carried out to investigate the control of temperature and melt composition on the partitioning of nickel between olivine and silicate melt (D{sup oliv\\/liq}{sub Ni}). Eleven experiments determine the influence of changing forsterite (Of) content on D{sup oliv\\/liq}{sub Ni} in this simple system. The equation of Hart and Davis (1978) that accounts for the

  12. An experimental study on the effect of temperature and melt composition on the partitioning of nickel between olivine and silicate melt

    Microsoft Academic Search

    Rosamond J. Kinzler; Timothy L. Grove; Steven I. Recca

    1990-01-01

    Experiments in the simple system CaO-MgO-Al 2 O 3 -SiO 2 -Na 2 O-FeO were carried out to investigate the control of temperature and melt composition on the partitioning of nickel between olivine and silicate melt ( D oliv \\/ liq Ni ). Eleven experiments determine the influence of changing forsterite (Fo) content on D oliv \\/ liq Ni in

  13. Sea ice-albedo climate feedback mechanism

    SciTech Connect

    Schramm, J.L.; Curry, J.A. [Univ. of Colorado, Boulder, CO (United States); Ebert, E.E. [Bureau of Meterology Research Center, Melbourne (Australia)

    1995-02-01

    The sea ice-albedo feedback mechanism over the Arctic Ocean multiyear sea ice is investigated by conducting a series of experiments using several one-dimensional models of the coupled sea ice-atmosphere system. In its simplest form, ice-albedo feedback is thought to be associated with a decrease in the areal cover of snow and ice and a corresponding increase in the surface temperature, further decreasing the area cover of snow and ice. It is shown that the sea ice-albedo feedback can operate even in multiyear pack ice, without the disappearance of this ice, associated with internal processes occurring within the multiyear ice pack (e.g., duration of the snow cover, ice thickness, ice distribution, lead fraction, and melt pond characteristics). The strength of the ice-albedo feedback mechanism is compared for several different thermodynamic sea ice models: a new model that includes ice thickness distribution., the Ebert and Curry model, the Mayjut and Untersteiner model, and the Semtner level-3 and level-0 models. The climate forcing is chosen to be a perturbation of the surface heat flux, and cloud and water vapor feedbacks are inoperative so that the effects of the sea ice-albedo feedback mechanism can be isolated. The inclusion of melt ponds significantly strengthens the ice-albedo feedback, while the ice thickness distribution decreases the strength of the modeled sea ice-albedo feedback. It is emphasized that accurately modeling present-day sea ice thickness is not adequate for a sea ice parameterization; the correct physical processes must be included so that the sea ice parameterization yields correct sensitivities to external forcing. 22 refs., 6 figs., 1 tab.

  14. 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

  15. Sensitivity of AMSR-E Brightness Temperatures to the Seasonal Evolution of Lake Ice Thickness

    Microsoft Academic Search

    Kyung-Kuk Kang; Claude R. Duguay; Stephen E. L. Howell; Chris P. Derksen; Richard E. J. Kelly

    2010-01-01

    The sensitivity of brightness temperature (TB) at 6.9, 10.7, and 18.7 GHz from Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) observations is investigated over five winter seasons (2002-2007) on Great Bear Lake and Great Slave Lake, Northwest Territories, Canada. The TB measurements are compared to ice thicknesses obtained with a previously validated thermodynamic lake ice model. Lake ice thickness is

  16. Thermal diffusivity of rhyolitic glasses and melts: effects of temperature, crystals and dissolved water

    NASA Astrophysics Data System (ADS)

    Romine, William L.; Whittington, Alan G.; Nabelek, Peter I.; Hofmeister, Anne M.

    2012-12-01

    Thermal diffusivity ( D) was measured using laser-flash analysis on pristine and remelted obsidian samples from Mono Craters, California. These high-silica rhyolites contain between 0.013 and 1.10 wt% H2O and 0 to 2 vol% crystallites. At room temperature, D glass varies from 0.63 to 0.68 mm2 s-1, with more crystalline samples having higher D. As T increases, D glass decreases, approaching a constant value of ˜0.55 mm2 s-1 near 700 K. The glass data are fit with a simple model as an exponential function of temperature and a linear function of crystallinity. Dissolved water contents up to 1.1 wt% have no statistically significant effect on the thermal diffusivity of the glass. Upon crossing the glass transition, D decreases rapidly near ˜1,000 K for the hydrous melts and ˜1,200 K for anhydrous melts. Rhyolitic melts have a D melt of ˜0.51 mm2 s-1. Thermal conductivity ( k = D· ?· C P) of rhyolitic glass and melt increases slightly with T because heat capacity ( C P) increases with T more strongly than density ( ?) and D decrease. The thermal conductivity of rhyolitic melts is ˜1.5 W m-1 K-1, and should vary little over the likely range of magmatic temperatures and water contents. These values of D and k are similar to those of major crustal rock types and granitic protoliths at magmatic temperatures, suggesting that changes in thermal properties accompanying partial melting of the crust should be relatively minor. Numerical models of shallow rhyolite intrusions indicate that the key difference in thermal history between bodies that quench to obsidian, and those that crystallize, results from the release of latent heat of crystallization. Latent heat release enables bodies that crystallize to remain at high temperatures for much longer times and cool more slowly than glassy bodies. The time to solidification is similar in both cases, however, because solidification requires cooling through the glass transition in the first case, and cooling only to the solidus in the second.

  17. Improvements to the Total Temperature Calibration of the NASA Glenn Icing Research Tunnel

    NASA Technical Reports Server (NTRS)

    Arrington, E. Allen; Gonsalez, Jose C.

    2005-01-01

    The ability to accurately set repeatable total temperature conditions is critical for collecting quality icing condition data, particularly near freezing conditions. As part of efforts to continually improve data quality in the NASA Glenn Icing Research Tunnel (IRT), new facility instrumentation and new calibration hardware for total temperature measurement were installed and new operational techniques were developed and implemented. This paper focuses on the improvements made in the calibration of total temperature in the IRT.

  18. Measurements and modelling of snow particle size and shortwave infrared albedo over a melting Antarctic ice sheet

    NASA Astrophysics Data System (ADS)

    Pirazzini, R.; Räisänen, P.; Vihma, T.; Johansson, M.; Tastula, E.-M.

    2015-06-01

    The albedo of a snowpack depends on the single-scattering properties of individual snow crystals, which have a variety of shapes and sizes, and are often bounded in clusters. From the point of view of optical modelling, it is essential to identify the geometric dimensions of the population of snow particles that synthetize the scattering properties of the snowpack surface. This involves challenges related to the complexity of modelling the radiative transfer in such an irregular medium, and to the difficulty of measuring microphysical snow properties. In this paper, we illustrate a method to measure the size distribution of a snow particle parameter, which roughly corresponds to the smallest snow particle dimension, from two-dimensional macro-photos of snow particles taken in Antarctica at the surface layer of a melting ice sheet. We demonstrate that this snow particle metric corresponds well to the optically equivalent effective radius utilized in radiative transfer modelling, in particular when snow particles are modelled with the droxtal shape. The surface albedo modelled on the basis of the measured snow particle metric showed an excellent match with the observed albedo when there was fresh or drifted snow at the surface. In the other cases, a good match was present only for wavelengths longer than 1.4 ?m. For shorter wavelengths, our modelled albedo generally overestimated the observations, in particular when surface hoar and faceted polycrystals were present at the surface and surface roughness was increased by millimetre-scale cavities generated during melting. Our results indicate that more than just one particle metric distribution is needed to characterize the snow scattering properties at all optical wavelengths, and suggest an impact of millimetre-scale surface roughness on the shortwave infrared albedo.

  19. Passive ice freezing-releasing heat pipe

    DOEpatents

    Gorski, Anthony J. (Lemont, IL); Schertz, William W. (Batavia, IL)

    1982-01-01

    A heat pipe device has been developed which permits completely passive ice formation and periodic release of ice without requiring the ambient temperature to rise above the melting point of water. This passive design enables the maximum amount of cooling capacity to be stored in the tank.

  20. Oxygen adsorption and the magnetic susceptibility of ice at low temperatures

    USGS Publications Warehouse

    Senftle, F.E.; Thorpe, A.

    1962-01-01

    WHEN dealing with the magnetic susceptibility of tumour tissue1, we reported the magnetic susceptibility of ice at various temperatures from 273??K. down to 77??K. Since this publication, the authors have made many susceptibility measurements of ice, using the same equipment, and have obtained similar results, that is, a relatively large increase in diamagnetism below 150??K. Normal diamagnetism is not dependent on temperature, and hence further experiments were made of the magnetic susceptibility of ice at low temperatures in an attempt to determine some extraneous cause of the increased diamagnetism. ?? 1962 Nature Publishing Group.

  1. Untangling the formation of the cyclic carbon trioxide isomer in low temperature carbon dioxide ices

    E-print Network

    Kaiser, Ralf I.

    Untangling the formation of the cyclic carbon trioxide isomer in low temperature carbon dioxide of the cyclic carbon trioxide isomer, CO3(X 1 A1), in carbon-dioxide-rich extraterrestrial ices and in the atmospheres of Earth and Mars were investigated experimentally and theoretically. Carbon dioxide ices were

  2. Holocene temperature history at the western Greenland Ice Sheet margin reconstructed from lake sediments

    E-print Network

    Briner, Jason P.

    Holocene temperature history at the western Greenland Ice Sheet margin reconstructed from lake form 15 October 2012 Accepted 19 October 2012 Available online 29 November 2012 Keywords: Greenland t Predicting the response of the Greenland Ice Sheet to future climate change presents a major challenge

  3. Late Noachian and early Hesperian ridge systems in the south circumpolar Dorsa Argentea Formation, Mars: Evidence for two stages of melting of an extensive late Noachian ice sheet

    NASA Astrophysics Data System (ADS)

    Kress, Ailish M.; Head, James W.

    2015-05-01

    The Dorsa Argentea Formation (DAF), extending from 270°-100° E and 70°-90° S, is a huge circumpolar deposit surrounding and underlying the Late Amazonian South Polar Layered Deposits (SPLD) of Mars. Currently mapped as Early-Late Hesperian in age, the Dorsa Argentea Formation has been interpreted as volatile-rich, possibly representing the remnants of an ancient polar ice cap. Uncertain are its age (due to the possibility of poor crater retention in ice-related deposits), its mode of origin, the origin of the distinctive sinuous ridges and cavi that characterize the unit, and its significance in the climate history of Mars. In order to assess the age of activity associated with the DAF, we examined the ridge populations within the Dorsa Argentea Formation, mapping and characterizing seven different ridge systems (composed of nearly 4,000 ridges covering a total area of ~300,000 km2, with a cumulative length of ridges of ~51,000 km) and performing crater counts on them using the method of buffered crater counting to determine crater retention ages of the ridge populations. We examined the major characteristics of the ridge systems and found that the majority of them were consistent with an origin as eskers, sediment-filled subglacial drainage channels. Ridge morphologies reflect both distributed and channelized esker systems, and evidence is also seen that some ridges form looping moraine-like termini distal to some distributed systems. The ridge populations fall into two age groups: ridge systems between 270° and 0° E date to the Early Hesperian, but to the east, the Promethei Planum and the Chasmata ridge systems date to the Late Noachian. Thus, these ages, and esker and moraine-like morphologies, support the interpretation that the DAF is a remnant ice sheet deposit, and that the esker systems represent evidence of significant melting and drainage of meltwater from portions of this ice sheet, thus indicating at least some regions and/or periods of wet-based glaciation. The Late Noachian and Early Hesperian ages of the ridge systems closely correspond to the ages of valley network/open basin lake systems, representing runoff, drainage and storage of liquid water in non-polar regions of the surface of Mars. Potential causes of such wet-based conditions in the DAF include: 1) top-down melting due to atmospheric warming, 2) enhanced snow and ice accumulation and raising of the melting isotherm to the base of the ice sheet, or 3) basal melting associated with intrusive volcanism (volcano-ice interactions). The early phase of melting is closely correlated in time with valley network formation and thus may be due to global atmospheric warming, while the later phase of melting may be linked to Early Hesperian global volcanism and specific volcano-ice interactions (table mountains) in the DAF. Crater ages indicate that these wet-based conditions ceased by the Late Hesperian, and that further retreat of the DAF to its present configuration occurred largely through sublimation, not melting, thus preserving the extensive ridge systems. MARSIS radar data suggest that significant areas of layered, potentially ice-rich parts of the Dorsa Argentea Formation remain today.

  4. Some fundamental properties and reactions of ice surfaces at low temperatures.

    PubMed

    Park, Seong-Chan; Moon, Eui-Seong; Kang, Heon

    2010-10-14

    Ice surfaces offer a unique chemical environment in which reactions occur quite differently from those in liquid water or gas phases. In this article, we examine the basic properties of ice surfaces below the surface premelting temperature and discuss some of the recent investigations carried out on reactions at the ice surfaces. The static and dynamic properties of an ice surface as a reaction medium, such as its structure, molecule diffusion and proton transfer dynamics, and the surface preference of hydronium and hydroxide ions, are discussed in relation to the reactivity of the surface. PMID:20683515

  5. Climate scenarios of sea level rise for the northeast Atlantic Ocean: a study including the effects of ocean dynamics and gravity changes induced by ice melt

    Microsoft Academic Search

    Caroline A. Katsman; Wilco Hazeleger; Sybren S. Drijfhout; Geert Jan van Oldenborgh; Gerrit J. H. Burgers

    2008-01-01

    Here we present a set of regional climate scenarios of sea level rise for the northeast Atlantic Ocean. In this study, the\\u000a latest observations and results obtained with state-of-the-art climate models are combined. In addition, regional effects\\u000a due to ocean dynamics and changes in the Earth’s gravity field induced by melting of land-based ice masses have been taken\\u000a into account.

  6. 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.

  7. 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.

  8. Chlorophyll fluorescence imaging analysis of the responses of Antarctic bottom-ice algae to light and salinity during melting

    Microsoft Academic Search

    K. G. Ryan; M. L. Tay; A. Martin; A. McMinn; S. K. Davy

    2011-01-01

    Bottom-ice algae within Antarctic sea ice were examined using chlorophyll fluorescence imaging. The detailed structure of the bottom-ice algal community growing in the platelet and congelation layers of solid pieces of sea ice was evident for the first time in chlorophyll imaging mode. Strands of fluorescence representing algal cells were clearly visible growing upward into brine channels in a fine

  9. 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.

  10. The Importance of Insolation Changes for Paleo Ice Sheet Modeling

    NASA Astrophysics Data System (ADS)

    Goelzer, H.; Robinson, A.

    2014-12-01

    The growth and retreat of continental ice sheets in the past has largely been a response to changing climatic forcing. Since ablation is the principal component of mass loss for land-based ice sheets, the calculation of surface melt is an important aspect of paleo ice sheet modeling. Changes in insolation are often not accounted for in calculations of surface melt, under the assumption that the near-surface temperature transmits the majority of the climatic forcing to the ice sheet. To assess how this could affect paleo simulations, here we investigate the importance of different orbital configurations for estimating melt on the Greenland ice sheet. We find that during peak Eemian conditions, increased insolation contributes 20-50% to the surface melt anomaly. However, this percentage depends strongly on the temperature anomaly at the time. For higher temperature anomalies, the role of insolation changes is less important. This relationship is not homogenous over the ice sheet, since the contribution of insolation to melt is modulated by the local surface albedo. In coupled simulations, the additional insolation-induced melt translates into up to threefold more ice volume loss, compared to output using a model that does not account for insolation changes. We also introduce a simple correction factor that allows reduced-complexity melt models to account for changes in insolation.

  11. Modeling englacial radar attenuation at Siple Dome, West Antarctica, using ice chemistry and temperature data

    USGS Publications Warehouse

    MacGregor, J.A.; Winebrenner, D.P.; Conway, H.; Matsuoka, K.; Mayewski, P.A.; Clow, G.D.

    2007-01-01

    The radar reflectivity of an ice-sheet bed is a primary measurement for discriminating between thawed and frozen beds. Uncertainty in englacial radar attenuation and its spatial variation introduces corresponding uncertainty in estimates of basal reflectivity. Radar attenuation is proportional to ice conductivity, which depends on the concentrations of acid and sea-salt chloride and the temperature of the ice. We synthesize published conductivity measurements to specify an ice-conductivity model and find that some of the dielectric properties of ice at radar frequencies are not yet well constrained. Using depth profiles of ice-core chemistry and borehole temperature and an average of the experimental values for the dielectric properties, we calculate an attenuation rate profile for Siple Dome, West Antarctica. The depth-averaged modeled attenuation rate at Siple Dome (20.0 ?? 5.7 dB km-1) is somewhat lower than the value derived from radar profiles (25.3 ?? 1.1 dB km-1). Pending more experimental data on the dielectric properties of ice, we can match the modeled and radar-derived attenuation rates by an adjustment to the value for the pure ice conductivity that is within the range of reported values. Alternatively, using the pure ice dielectric properties derived from the most extensive single data set, the modeled depth-averaged attenuation rate is 24.0 ?? 2.2 dB km-1. This work shows how to calculate englacial radar attenuation using ice chemistry and temperature data and establishes a basis for mapping spatial variations in radar attenuation across an ice sheet. Copyright 2007 by the American Geophysical Union.

  12. Gallium melts under high-pressure and temperature conditions: Synchrotron x-ray tomography and diffraction studies

    NASA Astrophysics Data System (ADS)

    Liu, L. L.; Liu, H.

    2014-12-01

    Gallium has a rare water-ice type P-V-T phase diagram in which the density of Ga melt exceeds by about 3 % that of the stable solid Ga phase I at ambient pressure. Liquid gallium, which is easily supercooled, can remain in a metastable liquid state for several months at ambient pressure. A rich polymorphism and metastable modifications of Ga have been discovered in P-T domain. There are a number of studies of liquid gallium under high pressure conditions, but some fundamental properties, such as the equation of state (EoS) of liquid Ga under extreme conditions remain unclear. Very recently, the advanced pair distribution function (PDF) method in which synchrotron high-energy x-ray total scattering data, combined with reverse Monte Carlo simulation, was used to study the microstructure and EoS of liquid gallium under high pressure conditions. However, the application of PDF method for amorphous or liquid samples under pressure conditions normally required a priori knowledge of their EoS. The density estimation from the reverse Monte Carlo simulation with the best mathematical fit to the measured structure factor data could cause big errors if it is calculated without knowing the EoS. In the paper, the volume change of liquid and solid gallium have been studied as a function of pressure and temperature up to 3.63 GPa using synchrotron x-ray microtomography combined with energy dispersive x-ray diffraction (EDXRD) techniques. Two sets of directly measured P-V data at 300 K and 330 K were obtained from 3D tomography reconstruction data. The existence of a liquid-liquid phase transition region is proposed based on the abnormal compressibility of Ga melt at about 2.44 GPa and 330 K conditions.

  13. Upper Ocean Temperature, Salinity, and Turbulence Across the Marginal Ice Zone from Autonomous Seaglider Surveys

    NASA Astrophysics Data System (ADS)

    Rainville, L.; Lee, C.

    2014-12-01

    We present initial results from several autonomous Seaglider deployments during summer 2014 in the ice-free region, under ice, and in the marginal ice zone (MIZ) of the Beaufort Sea. Measuring temperature and salinity of the upper ocean on scales of 2-3 km, these surveys resolve the short temporal and spatial scales associated with key upper ocean processes in the MIZ.Gliders also carry temperature and shear microstructure sensors, providing direct direct estimates of turbulent dissipation rates at the base of the surface mixed layer and in the halocline. The objective of this work to understand the balance and interplay of processes that supply freshwater and heat to the ice ocean boundary layer and their variations as a function of ice cover.

  14. Enzymic hydrolysis of animal fats in organic solvents at temperatures below their melting points

    Microsoft Academic Search

    M. D. Virto; Jose Miguel Lascaray; Rodolfo Solozabal; Mertxe de Renobales

    1991-01-01

    Lipase fromCandida rugosa catalyzed the hydrolysis of inedible beef tallow and pork lard (edible and inedible) in the presence of organic solvents\\u000a at temperatures below the melting point of the fat. Reactions were carried out at 50% substrate with 180 lipase units per\\u000a gram of fat in a two-liter reactor. In the presence of isooctane (5-10%) beef tallow yielded 94%

  15. Collective dynamics in liquid aluminum near the melting temperature: Theory and computer simulation

    Microsoft Academic Search

    A. V. Mokshin; R. M. Yulmetyev; R. M. Khusnutdinov; P. Haenggi

    2006-01-01

    The microscopic collective dynamics of liquid aluminum near the melting temperature has been studied using two independent\\u000a methods: first, using a theoretical approach developed in terms of the Zwanzig-Mori formalism and based on Bogolyubov’s idea\\u000a of reduced description of relaxation processes in liquids; second, using molecular dynamics simulation. The X-ray inelastic\\u000a scattering spectra obtained with the theoretical approach and computer

  16. Molding of temperature field for the induction skull melting process of Ti47Ni9Nb

    Microsoft Academic Search

    Yanqing Su; Yuan Liu; Guizhong Liu; JingJie Guo; Daming Xu; Jun Jia

    2001-01-01

    Based on the direct finite-difference method, a numerical model for simulating the temperature field in the charge during\\u000a the induction skull melting (ISM) process has been developed in this article. The related factors, including water-cooling\\u000a boundaries, the induction-heating electromagnetic stirring hump, and the power distribution in the charge, had been analyzed.\\u000a The interfaces between the charge and crucible were treated

  17. Low Temperature Air Distribution with Ice Storage System: A Case Study 

    E-print Network

    Ash, A.

    1990-01-01

    This paper discusses the performance of an off peak ice storage air conditioning system installed on an office warehouse building in Dallas, Texas. The system also incorporates a low temperature (45 degree) air distribution system utilized...

  18. Sessile droplet freezing and ice adhesion on aluminum with different surface wettability and surface temperature

    NASA Astrophysics Data System (ADS)

    Ou, JunFei; Shi, QingWen; Wang, ZhiLe; Wang, FaJun; Xue, MingShan; Li, Wen; Yan, GuiLong

    2015-07-01

    This paper focused on the sessile droplet freezing and ice adhesion on aluminum with different wettability (hydrophilic, common hydrophobic, and superhydrophobic surfaces, coded as HIS, CHS, SHS, respectively) over a surface temperature range of -9°C to -19°C. It was found that SHS could retard the sessile droplet freezing and lower the ice adhesion probably due to the interfacial air pockets (IAPs) on water/SHS interface. However, as surface temperature decreasing, some IAPs were squeezed out and such freezing retarding and adhesion lowering effect for SHS was reduced greatly. For a surface temperature of -19°C, ice adhesion on SHS was even greater than that on CHS. To discover the reason for the squeezing out of IAPs, forces applied to the suspended water on IAPs were analyzed and it was found that the stability of IAPs was associated with surface micro-structures and surface temperature. These findings might be helpful to designing of SHS with good anti-icing properties.

  19. Very low temperature formaldehyde reactions and the build-up of organic molecules in comets and interstellar ices

    NASA Technical Reports Server (NTRS)

    Schutte, W. A.; Allamandola, L. J.; Sandford, S. A.

    1995-01-01

    We have investigated thermally promoted reactions of formaldehyde (H2CO) in very low temperature ices. No such reactions occurred in ices of pure formaldehyde. However, addition of trace amounts of ammonia (NH3) were sufficient to catalyze reactions at temperatures as low as 40 K. Similar reactions could take place in interstellar ices and in Comets and produce considerable amounts of organic molecules.

  20. Study on Ice Formation in Still Supercooled Water with Ice Nucleating Substance

    NASA Astrophysics Data System (ADS)

    Inaba, Hideo; Takeya, Kengo; Asano, Takaya

    Relating to the problem of supercooling phenomenon for ice storage system, the effect of ice nucleating substances (Xanthan gum, Silver iodide, Copper sulfide, Cholesterole and Ice nucleating bacteria) in still bulk supercooled water was investigated. In the experiment, the test water sample containing the ice nucleating substance was cooled below the equilibrium freezing point temperature in low-temperature room maintained at -40 °C, and its freezing temperature was measured for various mass ratios of ice nucleating substance to water. The supercooling degree for the test water sample decreased with an increase in the mass ratio. It was found that the supercooling degree for the test sample with the insoluble ice nucleating substance was smaller than that for the soluble one. Among test ice nucleating substances, Cholesterole had a pronounced effect on the ice nucleation of supercooled water. However, it was clarified that the supercooling degree for each test sample increased by repeating the process of freezing and melting.

  1. A calorimetric study on the low temperature dynamics of doped ice V and its reversible phase transition to hydrogen ordered ice XIII.

    PubMed

    Salzmann, Christoph G; Radaelli, Paolo G; Finney, John L; Mayer, Erwin

    2008-11-01

    Doped ice V samples made from solutions containing 0.01 M HCl (DCl), HF (DF), or KOH (KOD) in H(2)O (D(2)O) were slow-cooled from 250 to 77 K at 0.5 GPa. The effect of the dopant on the hydrogen disorder --> order transition and formation of hydrogen ordered ice XIII was studied by differential scanning calorimetry (DSC) with samples recovered at 77 K. DSC scans of acid-doped samples are consistent with a reversible ice XIII <--> ice V phase transition at ambient pressure, showing an endothermic peak on heating due to the hydrogen ordered ice XIII --> disordered ice V phase transition, and an exothermic peak on subsequent cooling due to the ice V --> ice XIII phase transition. The equilibrium temperature (T(o)) for the ice V <--> ice XIII phase transition is 112 K for both HCl doped H(2)O and DCl doped D(2)O. From the maximal enthalpy change of 250 J mol(-1) on the ice XIII --> ice V phase transition and T(o) of 112 K, the change in configurational entropy for the ice XIII --> ice V transition is calculated as 2.23 J mol(-1) K(-1) which is 66% of the Pauling entropy. For HCl, the most effective dopant, the influence of HCl concentration on the formation of ice XIII was determined: on decreasing the concentration of HCl from 0.01 to 0.001 M, its effectiveness is only slightly lowered. However, further HCl decrease to 0.0001 M drastically lowered its effectiveness. HF (DF) doping is less effective in inducing formation of ice XIII than HCl (DCl) doping. On heating at a rate of 5 K min(-1), kinetic unfreezing starts in pure ice V at approximately 132 K, whereas in acid doped ice XIII it starts at about 105 K due to acceleration of reorientation of water molecules. KOH doping does not lead to formation of hydrogen ordered ice XIII, a result which is consistent with our powder neutron diffraction study (C. G. Salzmann, P. G. Radaelli, A. Hallbrucker, E. Mayer, J. L. Finney, Science, 2006, 311, 1758). We further conjecture whether or not ice XIII has a stable region in the water/ice phase diagram, and on a metastable triple point where ice XIII, ice V and ice II are in equilibrium. PMID:18936855

  2. UV-induced protonation of molecules adsorbed on ice surfaces at low temperature

    SciTech Connect

    Moon, Eui-Seong; Lee, Chang-Woo; Kim, Joon-Ki; Park, Seong-Chan; Kang, Heon [Department of Chemistry, Seoul National University, Gwanak-gu, Seoul 151-747 (Korea, Republic of)

    2008-05-21

    UV irradiation of ice films adsorbed with methylamine molecules induces protonation of the adsorbate molecules at low temperature (50-130 K). The observation indicates that long-lived protonic defects are created in the ice film by UV light, and they transfer protons to the adsorbate molecules via tunneling mechanism at low temperature. The methylammonium ion formed by proton transfer remains to be stable at the ice surface. It is suggested that this solid-phase protonation might play a significant role in the production of molecular ions in interstellar clouds.

  3. A late glacial record of ice-sheet dynamics and melt supply recovered in the sediments of IODP Expedition 347 in the Baltic Sea

    NASA Astrophysics Data System (ADS)

    Passchier, Sandra; Jensen, Jørn Bo; Kenzler, Michael; Johnson, Sean; Andrén, Thomas; Barker Jørgensen, Bo

    2015-04-01

    Modern observations of increased surface ablation, meltwater routing to the bed, and increases in glacial speeds point to feedbacks between ice-sheet dynamics, melt supply, and subglacial discharge. Paleorecords have the potential to explore the decadal to centennial variability of these systems, but until recently such records were short and discontinuous in ice-proximal settings and underutilized for this specific purpose. The Integrated Ocean Drilling Program Expedition 347 in the Baltic Sea recovered annually laminated sediments that document the dynamics of the Scandinavian Ice Sheet. Hydraulic piston cores recovered from Sites M0060, M0063, M0064, and M0065 allow us to reconstruct a nearly complete record of ca. 6000 years in ice retreat history at annual to decadal resolution between ca. 17 and 11ka. The late glacial successions of these four IODP drillsites comprise of a till or proglacial fluvioglacial sediment overlain by variable thicknesses of well-laminated deglacial successions within several high-recovery holes. As the Scandinavian Ice Sheet retreated from the western Baltic Sea, and to the North, the ice-sheet's grounding line migrated across the four sites and deposited overlapping sections of high-resolution ice-proximal to ice-distal successions. Laser particle size results from Sites M0060 and M0063, and inspection of line-scan images, show shifts in sedimentary facies and lithologies that were not recognized during initial visual core description. For example, at Site M0060 in the Kattegat, ice-rafting fluxes in silty clays decrease upward and are negligible in the overlying varved succession. These characteristics are interpreted as ice retreat within a calving bay environment from ca. 17ka onward, followed by distal glacial marine deposition from sediment plumes governed by meltwater discharge. Moreover, at Site M0063 in the Baltic Sea, laser particle size distributions record an abrupt shift from interlaminated clayey silt to laminated clay within deglacial Baltic Ice Lake strata (ca. 13-11ka), marking a shift from rhythmic hyperpycnites to distal varves. The excellent recovery of both proximal and distal rhythmites at multiple drillsites provides a unique opportunity to study feedbacks between Scandinavian Ice Sheet dynamics and its hydrological system on decadal to millennial timescales.

  4. 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.

  5. Surface melting observations in Antarctica by microwave radiometers: Correcting 26-year time series from changes in acquisition hours

    Microsoft Academic Search

    G. Picard; M. Fily

    2006-01-01

    Surface melting duration and extent of the Antarctic coasts and ice-shelves is a climatic indicator related to the summer temperature and radiative budget. Surface melting is easily detectable by remote sensing using passive microwave observations. The preliminary goal of this study is to extend to 26 years an existing data set of surface melting [Torinesi, O., Fily, M., Genthon, C. (2003),

  6. The temperature of primary melts and mantle sources of komatiites, OIBs, MORBs and LIPs

    NASA Astrophysics Data System (ADS)

    Sobolev, Alexander

    2015-04-01

    There is general agreement that the convecting mantle, although mostly peridotitic in composition, is compositionally and thermally heterogeneous on different spatial scales. The amount, sizes, temperatures and compositions of these heterogeneities significantly affect mantle dynamics because they may diverge greatly from dominant peridotites in their density and fusibility. Differences in potential temperature and composition of mantle domains affect magma production and cannot be easily distinguished from each other. This has led to radically different interpretations of the melting anomalies that produce ocean-island basalts, large igneous provinces and komatiites: most scientists believe that they originate as hot, deep-sourced mantle plumes; but a small though influential group (e.g. Anderson 2005, Foulger, 2010) propose that they derive from high proportions of easily fusible recycled or delaminated crust, or in the case of komatiites contain large amount of H2O (e.g. Grove & Parman, 2004). The way to resolve this ambiguity is an independent estimation of temperature and composition of mantle sources of various types of magma. In this paper I report application of newly developed olivine-spinel-melt geothermometers based on partition of Al, Cr, Sc and Y for different primitive lavas from mid-ocean ridges, ocean-island basalts, large igneous provinces and komatiites. The results suggest significant variations of crystallization temperature for the same Fo of high magnesium olivines of different types of mantle-derived magmas: from the lowest (down to 1220 degree C) for MORB to the highest (up to over 1500 degree C) for komatiites and Siberian meimechites. These results match predictions from Fe-Mg olivine-melt equilibrium and confirm the relatively low temperature of the mantle source of MORB and higher temperatures in the mantle plumes that produce the OIB of Iceland, Hawaii, Gorgona, Archean komatiites and several LIPs (e.g Siberian and NAMP). The established liquidus temperatures and compositions of primary melts allow estimating potential temperatures and compositions of their mantle sources. The results strongly confirm mantle plume theory and presence of variable amounts of recycled crustal material in the mantle sources. This study has been founded by Russian Science Foundation grant 14-17-00491.

  7. A Possible Correlation between the Surface Temperature and Thickness of Arctic Sea Ice

    NASA Astrophysics Data System (ADS)

    Roadcap, C.; Herman, R. B.; Eagle, J. L.; Montgomery, S. B.; Baumgardner, C.; Brett, M. C.; Blake, D.

    2014-12-01

    A geophysical survey of the Chukchi Sea ice was conducted just offshore from the Naval Arctic Research Laboratory in Barrow, Alaska. Multiple surveys were conducted along 200-meter lines using a capacitively coupled resistivity array, a thermal sensor array, and an ice drill. A custom thermal sensor array based on the Arduino platform was constructed for this work. This array included an infrared sensor with a 35° field of view. This gave an average surface temperature reading over a spot of ?25cm diameter with an accuracy of ±0.1°C . An ambient temperature sensor with an accuracy of ±1°C was positioned 25cm above the ice. Both of these were mounted on a repurposed GPR cart with a custom-built odometer wheel. Sets of 30 data points were collected every 17cm along the survey lines. Most data were collected during daylight hours. Some thermal data were collected in the morning twilight to study the effects of shadows cast by snow mounds. Resistivity data were obtained at 8 to 10 vertical depths as determined by the length of the array using 2.5m dipoles. This depended on the ice thickness along a survey line as well as the equipment's susceptibility to ambient temperature variations. The data points were obtained approximately 35cm apart horizontally. The resistivity data were inverted using software with a number of parameters to be set by the user. Adjusting these parameters caused the modeled depth to the ice/water boundary to vary significantly. The parameters have been refined through ice drill data obtained at 10-meter intervals. The ice drill was deployed only after resistivity and thermal data were obtained for each survey line. The resistivity and ice drill data showed an average ice depth of 1.2-1.7 meters, significantly thinner than in previous years' surveys. The modeled locations of the ice/water boundaries from the resistivity and ice drill data were compared to the surface temperatures along the survey lines. An analysis of the correlation of the temperature and ice thickness will be presented. Possible extensions of this method to further ice thickness studies will be discussed.

  8. High -Temperature melting in intra-continental settings - insight from numerical modelling

    NASA Astrophysics Data System (ADS)

    Gorczyk, Weronika; Hobbs, Bruce; Gonzalez, Christopher; Smithies, Hugh

    2015-04-01

    Most of intra-continental melting is associated with interaction of deep mantle plume with mantle lithosphere. Vast amount of mafic/felsic intra-plate intrusions are located along post-collisional lines, where for longer periods of time regional tectonic conditions are more likely to be (weakly) compressional to transpressional, and more rarely extensional. Arrival of the asthenosphere-derived plume would suggest initiation of extension along the weak/post-collision zone. Alternatively, in compressional regime a surprisingly large range of instabilities can develop that lead to melting of the lower crust and mantle lithosphere. Unexpected structural complexity arises which is quite sensitive to the geometry and rheological properties. This has dramatic effects on melting and devolatilisation within the lithosphere and hence in the localisation of and melt emplacement. Melts extracted in theses circumstances lead to emplacement of all variety of magmas: mafic, intermediate and felsic, from wide range of PT conditions. In order to investigate theses intra-plate sites of deformation, melt production and crustal growth in relation to pre-worked lithospheric crust we performed a series of 2D numerical experiments by using a coupled petrological - thermomechanical numerical model. The model includes, stable mineralogy, aqueous fluid transport, partial melting, melt extraction and melt emplacement in form of extrusive volcanics and intrusive plutons. As a case study we will present Musgrave Orogeny in Central Australia. The Musgrave Province developed at the nexus of the North, West and South Australian cratons and its Mesoproterozoic evolution incorporates a 100 Ma period of ultra-high temperature (UHT) metamorphism from ca. 1220 to ca. 1120 Ma. This was accompanied by high-temperature A-type granitic magmatism over an 80 Ma period, sourced in part from mantle-derived components and emplaced as a series of pulsed events that also coincide with peaks in UHT metamorphism. The initial constraint for each model setup is that reasonable geological and physical parameters (e.g., physical rock properties, far field stresses) must account for the most significant geological features of the Musgrave Orogeny, including: (1) an assumed architecture comprising a recently thinned Proterozoic belt between two (in a 2D scenario) thicker cratonic masses; (2) the c. 100 Ma total duration of the UHT event, punctuated into c. 10-20 Ma cycles; (3) the more or less continuous production of charnockitic A-type granites which, based on geochemical and thermal arguments formed from a source that homogenized roughly equal proportions of mantle and residual crustal material. The three case studies (Model I, Model II and Model III) presented here show an overall similar tectonic/magmatic evolution within the area of interest. Each numerical model replicates parts of the inferred evolution of the Musgrave Orogeny. The results indicate that the most plausible process that introduces ultra-high temperatures >1000°C is mechanical removal of the mantle lithosphere by asymmetric delamination which can be induced by (multiple) episodes of compressional tectonics.

  9. Density and structure of jadeite melt at high pressure and high temperature

    NASA Astrophysics Data System (ADS)

    Sakamaki, T.; Yu, T.; Jing, Z.; Park, C.; Shen, G.; Wang, Y.

    2011-12-01

    Knowledge of density of magma is important for understanding magma-related processes such as volcanic activity and differentiation in the Earth's early history. Since these processes take place in Earth's interior, we need to measure the density of magma in situ at high pressures. It is also necessary to relate the density with the structure of silicate melts at high pressure and temperature and further understand the densification mechanism of magma with pressure. Here we report the density and structural data for jadeite melt up to 7 GPa,. The density measurements were carried out using a DIA-type cubic press at the 13-BM-D beamline at APS using monochromatic radiation tuned to the desired energy (~20 keV) with a Si (111) double-crystal monochromator. Intensities of the incident and transmitted X-rays were measured by two ion chambers placed before and after the press for X-ray absorption measurements. Incident and transmitted X-ray intensities were obtained by moving the incident slits perpendicular to the X-ray beam direction at 0.010 mm steps crosses the sample. Lambert-Beer law was then applied to the normalized intensities as a function of the sample position across the assembly. Density of jadeite melt was determined up to 7 GPa and 2300 K. For structural determination, high-pressure and high-temperature energy-dispersive XRD experiments were carried out by using a Paris-Edinburgh press installed at the 16-BM-B of APS. Incident X-rays were collimated by a vertical slit (0.5 mm) and a horizontal slit (0.1 mm) to irradiate the sample. Diffracted X-rays were detected by a Ge solid state detector with a 4k multi-channel analyzer, through a collimator and 5.0mm (V) by and 0.1mm (H) receiving slits. Diffraction patterns were collected until the highest intensity reached 2000 counts, at 12 angles (2theta=3, 4, 5, 7, 9, 11, 15, 20, 25, 30, 35, 39.5 degrees). The structural measurements were carried out in the pressure range from 1 to 5 GPa and at 1600 to 2000 K. Pressure and temperature dependence of density of jadeite melt will be presented, along with structure factor S(Q) and radial distribution function G(r) of jadeite melt at high pressure and high temperature. The density-structure relationships will be discussed.

  10. The Melting Temperature of Bulk Silicon from ab initio Molecular Dynamics Simulations

    SciTech Connect

    Yoo, Soohaeng; Xantheas, Sotiris S.; Zeng, Xiao Cheng

    2009-10-19

    We estimated a melting temperature of Tm ~ 1540 ± 90 K at zero pressure for silicon from constant enthalpy and constant pressure (NPH) Born-Oppenheimer Molecular Dynamics (BOMD) simulations of a coexisting crystalline-liquid phase. The computed Tm is below the experimental melting point of 1685 K, but it is consistent with a previously predicted first-order liquid-liquid phase transition (LLPT) at a critical point Tc ~ 1232 K and Pc ~ - 12kB [Ganesh and Widom, Phys. Rev. Lett. 102, 075701 (2009)], which is in a highly supercooled state. This work was supported by the US Department of Energy, Office of Basic Energy Sciences, Chemical Sciences program. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

  11. The Temperature of Intracellular Ice Formation in Mouse Oocytes vs. the Unfrozen Fraction at that Temperature ?

    PubMed Central

    Mazur, Peter; Pinn, Irina L.; Kleinhans, F.W.

    2009-01-01

    We have previously reported [11] that intracellular ice formation (IIF) in mouse oocytes suspended in various concentrations of glycerol and ethylene glycol (EG) occurs at temperatures where the percentage of unfrozen water is about 6% and 12% respectively even though the IIF temperatures varied from ?14° to ?41°C. However, because of the way the solutions were prepared, the concentrations of salt and glycerol or EG in that unfrozen fraction at IIF were also rather tightly grouped. The experiments reported in the present paper were designed to separate the effects of the unfrozen fraction at IIF from that of the solute concentration in the unfrozen fraction. This separation makes use of two facts. One is that the concentration of solutes in the residual liquid at a given subzero temperature is fixed regardless of their concentration in the initial unfrozen solution. However, second, the fraction unfrozen at a given temperature is dependent on the initial solute concentration. Experimentally, oocytes were suspended in solutions of glycerol/buffered saline and EG/buffered saline of varying total solute concentration with the restriction that the mass ratio of glycerol and EG to salts are held constant. The oocytes were then cooled rapidly enough (20°C/min) to avoid significant osmotic shrinkage, and the temperature at which IIF occurred as noted. When this is done, we find, as previously that the fraction of water remaining unfrozen at the temperature of IIF remains nearly constant at 5 to 8% for both glycerol and EG even though the IIF temperatures vary from ?14°C to ?50°C. But unlike the previous results, the salt and CPA concentrations in the unfrozen fraction vary by a factor of three. The present procedure for preparing the solutions produces a potentially complicating factor; namely, the cell volumes vary substantially prior to freezing: Substantially greater than isotonic in some solution; substantially smaller in others. However, the data in toto demonstrate that cell volume is not a determining factor in the IIF temperature. PMID:17379206

  12. A study of the evolution of the under-ice water layer during summer melt phase in an Arctic bay

    Microsoft Academic Search

    Subramaniam D. Rajan; Henry Laible; Walter B. Tucker

    1997-01-01

    An acoustic ice tomography experiment which extended over a 12-month period was conducted in the Sabine Bay area of the Canadian Archipelago. Acoustic transmitter and receiver arrays were deployed in the ice for this experiment. The vertical arrays penetrated through the ice and extended into the water column. The acoustic data collected from the transmitter\\/receiver pairs in the water column

  13. A study of the influence of isotopic substitution on the melting point and temperature of maximum density of water by means of path integral simulations of rigid models

    E-print Network

    McBride, Carl; Noya, Eva G; Vega, Carlos; 10.1039/C2CP42393F

    2012-01-01

    The melting point of ice Ih, as well as the temperature of maximum density (TMD) in the liquid phase, has been computed using the path integral Monte Carlo method. Two new models are introduced; TIP4PQ_D2O and TIP4PQ_T2O which are specifically designed to study D2O and T2O respectively. We have also used these models to study the "competing quantum effects" proposal of Habershon, Markland and Manolopoulos; the TIP4PQ/2005, TIP4PQ/2005 (D2O) and TIP4PQ/2005 (T2O) models are able to study the isotopic substitution of hydrogen for deuterium or tritium whilst constraining the geometry, while the TIP4PQ_D2O and TIP4PQ_T2O models, where the O-H bond lengths are progressively shortened, permit the study of the influence of geometry (and thus dipole moment) on the isotopic effects. For TIP4PQ_D2O - TIP4PQ/2005 we found a melting point shift of 4.9 K (experimentally the value is 3.68K) and a TMD shift of 6K (experimentally 7.2K). For TIP4PQ_T2O - TIP4PQ/2005 we found a melting point shift of 5.2 K (experimentally the ...

  14. Sea ice melt pond fraction estimation from dual-polarisation C-band SAR - Part 2: Scaling in situ to Radarsat-2

    NASA Astrophysics Data System (ADS)

    Scharien, R. K.; Hochheim, K.; Landy, J.; Barber, D. G.

    2014-01-01

    Observed changes in the Arctic have motivated efforts to understand and model its components as an integrated and adaptive system at increasingly finer scales. Sea ice melt pond fraction, an important summer sea ice component affecting surface albedo and light transmittance across the ocean-sea ice-atmosphere interface, is inadequately parameterized in models due to a lack of large scale observations. In this paper, results from a multi-scale remote sensing program dedicated to the retrieval of pond fraction from satellite C-band synthetic aperture radar (SAR) are detailed. The study was conducted on first-year sea (FY) ice in the Canadian Arctic Archipelago during the summer melt period in June 2012. Approaches to retrieve the subscale FY ice pond fraction from mixed pixels in RADARSAT-2 imagery, using in situ, surface scattering theory, and image data are assessed. Each algorithm exploits the dominant effect of high dielectric free-water ponds on the VV/HH polarisation ratio (PR) at moderate to high incidence angles (about 40° and above). Algorithms are applied to four images corresponding to discrete stages of the seasonal pond evolutionary cycle, and model performance is assessed using coincident pond fraction measurements from partitioned aerial photos. A RMSE of 0.07, across a pond fraction range of 0.10 to 0.70, is achieved during intermediate and late seasonal stages. Weak model performance is attributed to wet snow (pond formation) and synoptically driven pond freezing events (all stages), though PR has utility for identification of these events when considered in time series context. Results demonstrate the potential of wide-swath, dual-polarisation, SAR for large-scale observations of pond fraction with temporal frequency suitable for process-scale studies and improvements to model parameterizations.

  15. Entropy dependence of viscosity and the glass-transition temperature of melts in the system diopside-anorthite

    Microsoft Academic Search

    H. Taniguchi

    1992-01-01

    Viscosities of diopside-anorthite melts were measured over the wide range of temperature (near the glass-transition temperature-1580°C\\/1bar) and pressure (5–20 kb\\/above the liquidus temperature). The measurements were carried out by the fibre-elongation method for low temperature and the counter-balanced sphere method for high temperature at 1 bar, and the sinking and floating spheres method for high temperature at high pressure. Some

  16. Deformation, warming and softening of Greenland’s ice by refreezing meltwater

    NASA Astrophysics Data System (ADS)

    Bell, Robin E.; Tinto, Kirsteen; Das, Indrani; Wolovick, Michael; Chu, Winnie; Creyts, Timothy T.; Frearson, Nicholas; Abdi, Abdulhakim; Paden, John D.

    2014-07-01

    Meltwater beneath the large ice sheets can influence ice flow by lubrication at the base or by softening when meltwater refreezes to form relatively warm ice. Refreezing has produced large basal ice units in East Antarctica. Bubble-free basal ice units also outcrop at the edge of the Greenland ice sheet, but the extent of refreezing and its influence on Greenland’s ice flow dynamics are unknown. Here we demonstrate that refreezing of meltwater produces distinct basal ice units throughout northern Greenland with thicknesses of up to 1,100 m. We compare airborne gravity data with modelled gravity anomalies to show that these basal units are ice. Using radar data we determine the extent of the units, which significantly disrupt the overlying ice sheet stratigraphy. The units consist of refrozen basal water commonly surrounded by heavily deformed meteoric ice derived from snowfall. We map these units along the ice sheet margins where surface melt is the largest source of water, as well as in the interior where basal melting is the only source of water. Beneath Petermann Glacier, basal units coincide with the onset of fast flow and channels in the floating ice tongue. We suggest that refreezing of meltwater and the resulting deformation of the surrounding basal ice warms the Greenland ice sheet, modifying the temperature structure of the ice column and influencing ice flow and grounding line melting.

  17. Temperature-dependent thermal expansivities of silicate melts: The system anorthite-diopside

    SciTech Connect

    Knoche, R.; Dingwell, D.B.; Webb, S.L. (Univ. Bayreuth (West Germany))

    1992-02-01

    The temperature-dependent thermal expansivities of melts along the join anorthite-diopside have been determined on glassy and liquid samples using a combination of calorimetry, dilatometry, and Pt double bob Archimedean densitometry. Supercooled liquid volumes and molar thermal expansivities were determined using scanning calorimetric and dilatometric measurements of properties in the glass region and their behavior at the glass transition. The extraction of low-temperature liquid molar expansivities from dilatometry/calorimetry is based on an assumed equivalence of the relaxation of volume and enthalpy at the glass transition using a method developed and tested by Webb et al. (1992). This method corrects for transient effects at the glass transition which can lead to serious overestimates of liquid thermal expansivity from peak' values. Superliquidus volumes were determined using double Pt bob Archimedean densitometry at temperatures up to 1,650C. The resulting data for liquid volumes near glass transition temperatures (810-920C) and at superliquidus temperatures (1,400-1,650C) are combined to yield thermal expansivities over the entire supercooled and stable liquid range. The molar expansivities are, in general, temperature dependent. The temperature-dependence of thermal expansivity increases from anorthite to diopside composition. The thermal expansivity of anorthite is essentially temperature independent, whereas that of diopside decreases by {congruent} 50% between 800 and 1,500C, with the consequence that the thermal expansivities of the liquids in the anorthite-diopside system converge at high temperature.

  18. Snow Cover Effects on Glacier Ice Surface Temperature Margherita Maggioni*{

    E-print Network

    Williams, Mark W.

    of rounded crystals originated by melt-freeze metamorphism, while in the season poor in snow depth hoar), Italy {Institute of Arctic and Alpine Research and Department of Geography, University of Colorado at Boulder, UCB 450, Boulder, Colorado 80309, U.S.A. {Corresponding author: margherita

  19. Temperature variability beneath Ronne Ice Shelf, Antarctica, from thermistor cables

    Microsoft Academic Search

    Keith W. Nicholls

    1996-01-01

    Thermistor cables have been deployed at two sites beneath Ronne Ice Shelf, Antarctica. One site is to the east of a submarine ridge that delineates the eastern boundary of the Ronne Depression, and the other is 100 km to the north, above the eastern slope of the depression. Long records from the cables (up to 22 months) indicate a large

  20. 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,

  1. Dependence of Glass Transition Temperature on the Oxidation State of Ferrosilicate Melts

    NASA Astrophysics Data System (ADS)

    Nichols, A. R.; Potuzak, M.; Dingwell, D. B.

    2005-12-01

    Global models suggest that iron is one of the major fabric element of the terrestrial planet interiors and probably the most abundant transition metal at all. The presence of volcanic rocks containing iron has been confirmed on Earth, Moon, Mars and Venus. Based on our study we suggest that the oxidation state of iron is probably second only to volatiles in its influence on the physical properties of natural silicic magma. This is shown by examining the effect of the oxidation state on the glass transition temperature. The heat capacity of ferrosilicate melts has been measured using differential scanning calorimetry (DSC). Two different simple Fe-bearing systems have been studied: (i) anorthite-diopside eutectic composition (AnDi) with 10 wt% of Fe as a basalt analogue and (ii) sodium disilicate (NS2) with variable amount of Fe (up to 30 wt% Fe). Samples with different oxidation state of Fe have been prepared using the concentric cylinder method. The melt was reduced stepwise by flowing CO2 or a mixture of CO2-CO through the alumina muffle tube. A drop of liquid was quenched in water after each redox equilibrium step. The resulting glasses were analyzed by electron microprobe, and volumetric titration was employed to determine FeO. The high temperature viscosities rapidly decrease with increasing ferrous iron content. This decrease is non-linear function of iron reduction. Fragments of glass were analyzed by differential scanning calorimetry (DSC). Glasses were placed in a platinum crucible and heated through a range of temperatures from 298 to 1050 K, approximately 50 K above the glass transition. After initial heating at 5 K.min-1, the samples were cooled and heated at matched rates of 20, 15, 10 and 5 K.min-1. Glass transition temperatures (Tg) have been defined as a peak of the heat capacity curve (Cp). Tg decreases steadily with increasing ferrous content, the strongest affect is during the initial reduction of Fe. Reducing Fe by about 66% causes a drop in Tg of about 60 K. These changes are independent of heating/cooling rate. The equivalence of the activation energy of the melts obtained from DSC and low-T viscometry allow to predict viscosities of melts at temperature close to the Tg. The low-T viscosities are strongly ferric/ferrous dependent. These effects are similar to those of water. Therefore, like with the addition of water, the reduction of Fe can strongly influence the magma's physical properties and thus magma behaviour during crystallization, degassing, foaming and fragmentation.

  2. Formation of hexagonal and cubic ice during low-temperature growth

    PubMed Central

    Thürmer, Konrad; Nie, Shu

    2013-01-01

    From our daily life we are familiar with hexagonal ice, but at very low temperature ice can exist in a different structure––that of cubic ice. Seeking to unravel the enigmatic relationship between these two low-pressure phases, we examined their formation on a Pt(111) substrate at low temperatures with scanning tunneling microscopy and atomic force microscopy. After completion of the one-molecule-thick wetting layer, 3D clusters of hexagonal ice grow via layer nucleation. The coalescence of these clusters creates a rich scenario of domain-boundary and screw-dislocation formation. We discovered that during subsequent growth, domain boundaries are replaced by growth spirals around screw dislocations, and that the nature of these spirals determines whether ice adopts the cubic or the hexagonal structure. Initially, most of these spirals are single, i.e., they host a screw dislocation with a Burgers vector connecting neighboring molecular planes, and produce cubic ice. Films thicker than ?20 nm, however, are dominated by double spirals. Their abundance is surprising because they require a Burgers vector spanning two molecular-layer spacings, distorting the crystal lattice to a larger extent. We propose that these double spirals grow at the expense of the initially more common single spirals for an energetic reason: they produce hexagonal ice. PMID:23818592

  3. A temperature-dependent, structural-optical model of first-year sea ice

    NASA Astrophysics Data System (ADS)

    Light, B.; Maykut, G. A.; Grenfell, T. C.

    2004-06-01

    A model has been developed that relates the structural properties of first-year sea ice to its inherent optical properties, quantities needed by detailed radiative transfer models. The structural-optical model makes it possible to calculate absorption coefficients, scattering coefficients, and phase functions for the ice from information about its physical properties. The model takes into account scattering by brine inclusions in the ice, gas bubbles in both brine and ice, and precipitated salt crystals. The model was developed using concurrent laboratory measurements of the microstructure and apparent optical properties of first-year, interior sea ice between temperatures of -33°C and -1°C. Results show that the structural-optical properties of sea ice can be divided into three distinct thermal regimes: cold (T < -23°C), moderate (-23°C < T < -8°C), and warm (T > -8°C). Relationships between structural and optical properties in each regime involve different sets of physical processes, of which most are strongly tied to freezing equilibrium of the brine and ice. Volume scattering in cold ice is dominated by the size and number distribution of precipitated hydrohalite crystals. Scattering at intermediate temperatures is controlled by changes in the distribution of brine inclusions, gas bubbles, and mirabilite crystals. Total volume scattering in this regime is approximately independent of temperature because of a balance between increasing and decreasing scattering related to the thermal evolution of these inclusions and scattering by drained inclusions. In warm ice, scattering is controlled principally by temperature-dependent changes in the real refractive index of brine and by the escape of gas bubbles from the ice. Model predictions indicate that scattering coefficients can exceed 3000 m-1 for cold ice, averaging ˜450 m-1 for moderate and warm ice and reaching a minimum of ˜340 m-1 at -8°C. Scattering in all three regimes is very strongly forward peaked, with values of the asymmetry parameter g generally falling between 0.975 (T = -8°C) and 0.995 (T = -33°C).

  4. 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

  5. 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.

  6. 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

  7. Effect of Hofmeister and alkylcarboxylate anionic counterions on the Krafft temperature and melting temperature of cationic gemini surfactants.

    PubMed

    Manet, Sabine; Karpichev, Yevgen; Dedovets, Dmytro; Oda, Reiko

    2013-03-19

    The effect of counterions was investigated to probe the principal ionic effects on the solubility in water and melting behavior of cationic gemini surfactants. We focused on two types of counterions: (1) small inorganic counterions that are typically taken from the Hofmeister series were studied to focus on the effect of ion type and (2) n-alkylcarboxylate counterions were studied to focus on the effect of the hydrophobicity of counterions. The Krafft temperature (Tk) and melting temperature (Tm) were obtained by conductivity measurements, calorimetric measurements, and optical microscopy observation. The results clearly indicate that Tk, which represents the solubility of surfactants, is not determined by a single parameter of ions such as the hydration free energy, as is too often assumed, but rather by the combined effects between the hydrophobicity of anions associated with other effects such as the polarizability, dehydrated ion size, and ionic morphology. In parallel, our observation demonstrated that all of the surfactants showed a transition from a crystalline phase to a thermotropic liquid-crystalline phase at around ca. 70 °C, which transformed to an isotropic liquid phase at around ca. 150 °C, and that the transition temperatures depended strongly on the counterion type. The counterion effects on the solubilization and melting behaviors were then compared with micellization properties that have been reported previously. These results provide new insight into understanding the effect of ions on the delicate balance of forces controlling the solution properties and aggregate morphology of charged amphiphilic molecules. Specifically, the solubilization properties of these cationic surfactants with various counterions were determined mainly by the subtle interplay between the hydration of counterions and the dissociation energies (stability of crystallinity) of the ion pair. PMID:23346886

  8. Effect of temperature on dielectric properties of ice in the range 5-39 GHz

    Microsoft Academic Search

    Takeshi Matsuoka; Shuji Fujita; Shinji Mae

    1996-01-01

    The relative complex dielectric permittivity, &egr;*=&egr;??i&egr;?, of ice has been measured in the frequency range 5–39 GHz and in the temperature range 190–265 K. The cavity resonator method at 5 and 10 GHz and the open resonator method at 33 and 39 GHz were used to determine the low dielectric loss of ice. The real part of permittivity &egr;? was

  9. Arctic climate change: observed and modelled temperature and sea-ice variability

    Microsoft Academic Search

    Ola M. Johannessen; Lennart Bengtsson; Martin W. Miles; Svetlana I. Kuzmina; Vladimir A. Semenov; Genrikh V. Alekseev; Andrei P. Nagurnyi; Victor F. Zakharov; Leonid P. Bobylev; Lasse H. Pettersson; Klaus Hasselmann; Howard P. Cattle

    2004-01-01

    Changes apparent in the arctic climate system in recent years require evaluation in a century-scale perspective in order to assess the Arctic's response to increasing anthropogenic greenhouse-gas forcing. Here, a new set of century- and multidecadal-scale observational data of surface air temperature (SAT) and sea ice is used in combination with ECHAM4 and HadCM3 coupled atmosphere ice ocean global model

  10. Investigating the Thermophysical Properties of the Ice-Snow Interface Under a Controlled Temperature Gradient

    NASA Astrophysics Data System (ADS)

    Hammonds, Kevin; Lieb-Lappen, Ross; Baker, Ian; Wang, Xuan; Courville, Zoe

    2015-04-01

    Of critical importance for avalanche forecasting, is the ability to draw meaningful conclusions from a handful of field observations. To this end, it is common for avalanche forecasters to not only have to rely on these sparse data, but also to use their own intuitive understanding of how these observations are correlated with the complex physical processes that produce mechanical instabilities within a snowpack. One such example of this is the long-held notion that kinetic snow metamorphism does not occur at bulk temperature gradients of less than -10°C/m. Although this may be true for the homogeneous case, it has become a point of contention as to whether or not this guideline should be applied to the more representative case of a heavily stratified and anisotropic snowpack. As an idealized case for our initial laboratory investigations, we have studied how an artificially created ice layer or "lens" would affect the thermophysical state of the snow layers adjacent to the ice lens and the ice lens itself, while being held under a controlled temperature gradient. Our findings have shown, via in-situ micro-thermocouple measurements, that a super-temperature gradient many times greater than the imposed bulk temperature gradient can exist within a millimeter above and below the surface of the ice lens. Furthermore, microstructural analysis via time-lapse X-ray Micro-Computed Tomography and environmental SEM imaging has been performed. Results from this analysis show new ice crystal growth and kinetic snow metamorphism occurring simultaneously on or near the ice lens itself with the connectivity density at the ice-snow interface increasing markedly more below the ice lens than above.

  11. Long-Term High-Latitude Sea and Ice Surface Temperature Record from AVHRR GAC Data

    NASA Astrophysics Data System (ADS)

    Luis, C. S.; Dybkjær, G.; Eastwood, S.; Tonboe, R. T.; Høyer, J. L.

    2014-12-01

    Surface temperature is among the most important variables in the surface energy balance equation and it significantly affects the atmospheric boundary layer structure, the turbulent heat exchange and, over ice, the ice growth rate. Here we measure the surface temperature using thermal infrared sensors from 10-12 ?m wavelength, a method whose primary limitation over sea ice is the detection of clouds. However, in the Arctic and around Antarctica there are very few conventional observations of surface temperature from buoys, and it is sometimes difficult to determine if the temperature is measured at the surface or within the snowpack, the latter of which often results in a warm bias. To reduce this bias, much interest is being paid to alternative remote sensing methods for monitoring high latitude surface temperature. We used Advanced Very High Resolution Radiometer (AVHRR) global area coverage (GAC) data to produce a high latitude sea surface temperature (SST), ice surface temperature (IST) and ice cap skin temperature dataset spanning 27 years (1982-2009). This long-term climate record is the first of its kind for IST. In this project we used brightness temperatures from the infrared channels of AVHRR sensors aboard NOAA and Metop polar-orbiting satellites. Surface temperatures were calculated using separate split window algorithms for day SST, night SST, and IST. The snow surface emissivity across all angles of the swath were simulated specifically for all sensors using an emission model. Additionally, all algorithms were tuned to the Arctic using simulated brightness temperatures from a radiative transfer model with atmospheric profiles and skin temperatures from European Centre for Medium-Range Forecasts (ECMWF) re-analysis data (ERA-Interim). Here we present the results of product quality as compared to in situ measurements from buoys and infrared radiometers, as well as a preliminary analysis of climate trends revealed by the record.

  12. Structure of high-temperature nickel alloys after time heat treatment of the melt

    SciTech Connect

    Kolotukhin, E.V.; Kuleshova, E.A.; Baryshev, E.E. [and others

    1995-11-01

    The strict requirements imposed on articles made of high-temperature nickel alloys require improvement of their composition and technology in all stages of metallurgical production. However, at present the degree of their alloying has become practically maximum. The service characteristics of high-temperature alloys can hardly be improved further by correcting their chemical composition. The problem is solved most successfully by developing new technological regimes of melting and casting. It is economically expedient to use new technological approaches to the already well investigated and tested compositions. The present work is concerned with the effect of the so-called time heat treatment (THT) of liquid metal on the macro- and microstructure of high-temperature nickel alloys used in the production of equiaxial and single-crystal castings.

  13. The Retrieval of Ice Water Content from Radar Reflectivity Factor and Temperature and Its Use in Evaluating a Mesoscale Model

    E-print Network

    Hogan, Robin

    The Retrieval of Ice Water Content from Radar Reflectivity Factor and Temperature and Its Use form 11 June 2005) ABSTRACT Ice clouds are an important yet largely unvalidated component of weather, demonstrating that, for stratiform midlatitude ice clouds, radar reflectivity in the Rayleigh-scattering regime

  14. 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

  15. Spectrum of temperature pulsations of the melt in gas-assisted cutting with fiber laser

    NASA Astrophysics Data System (ADS)

    Dubrov, Alexander V.; Zavalov, Yury N.; Dubrov, Vladimir D.; Grezev, Anatoly N.; Grezev, Nikolay V.; Makarova, Elena S.; Dubrovin, Nickolay G.

    2012-09-01

    Measurements of the temperature behavior in the zone of action of the laser-radiation on the molten metal have been performed using multichannel pyrometer. Measurements were carried out for test cutting of a 3-mm mild-steel plate with several values of cutting speed and pressure of assist gas (oxygen), using an 1800-watt Ytterbium fiber laser. It is shown that fluctuations of temperature are related to local melt's surface deformations due to unequal radiation absorption; thus the noise spectrum of temperature fluctuations reflects turbulent surface deformation caused by gas jet and capillary waves. The maximum density of turbulent energy dissipation ? depends on cutting conditions: its value rises with increasing cutting velocity and oxygen pressure in a described range of parameters. The maximum of ? is localized near depth of (1.2…1.5) mm along the cutting front. We can distinguish the specific radiation pulsation spectrum of laser cutting from other processes of radiation affection to the sample, including unwanted degrading of the quality of technological operations. The spectrum of capillary waves on the melt's surface is formed under the effect of assisted gas jet and has a function of ?-3, ? is cycle frequency. The results of this investigation can be useful for the development of monitoring and quality-control systems for the laser-cutting process.

  16. Attenuation and Velocity Structure in Spain and Morocco: Distinguishing Between Water, Temperature, and Partial Melt

    NASA Astrophysics Data System (ADS)

    Bezada, M. J.; Humphreys, E.

    2014-12-01

    Temperature, melt fraction, and water content affect seismic velocity and attenuation differently. Both are sensitive to temperature, but velocity is more sensitive to melt fraction and attenuation is thought to be more sensitive to water content. For these reasons, combining attenuation measurements with tomographic imaging of velocity structure can help untangle these fields and better resolve lithospheric structure and physical state. We map variations in attenuation beneath Spain and northern Morocco using teleseismic data generated by more than a dozen teleseismic deep-focus earthquakes recorded on a dense array of stations. For each event, we first estimate the source from the best quality recordings. We then apply an attenuation operator to the source estimate, using a range of t* values, to match the record at each station. We invert for a smooth map of t* from the ensemble of measurements. The spatial patterns in t* correlate very well with the tectonic domains in Spain and Morocco. In particular, areas in Spain that resisted deformation during the Variscan and Alpine orogenies produce very little attenuation. Comparing the attenuation map with seismic velocity structure we find that, in Morocco, some areas with strong low-velocity anomalies and recent volcanism do not cause high attenuation. These observations suggest that water content is a more likely cause for seismic attenuation in the study area than temperature, and that the non-attenuative low-velocity anomalies in Morocco are produced by partial mel.

  17. Structure and dynamical intra-molecular heterogeneity of star polymer melts above glass transition temperature.

    PubMed

    Chremos, Alexandros; Glynos, Emmanouil; Green, Peter F

    2015-01-28

    Structural and dynamical properties of star melts have been investigated with molecular dynamics simulations of a bead-spring model. Star polymers are known to be heterogeneous, but a systematic simulation study of their properties in melt conditions near the glass transition temperature was lacking. To probe their properties, we have expanded from linear to star polymers the applicability of Dobkowski's chain-length dependence correlation function [Z. Dobkowski, Eur. Polym. J. 18, 563 (1982)]. The density and the isokinetic temperature, based on the canonical definition of the laboratory glass-transition, can be described well by the correlation function and a subtle behavior manifests as the architecture becomes more complex. For linear polymer chains and low functionality star polymers, we find that an increase of the arm length would result in an increase of the density and the isokinetic temperature, but high functionality star polymers have the opposite behavior. The effect between low and high functionalities is more pronounced for short arm lengths. Complementary results such as the specific volume and number of neighbors in contact provide further insights on the subtle relation between structure and dynamics. The findings would be valuable to polymer, colloidal, and nanocomposites fields for the design of materials in absence of solution with the desired properties. PMID:25638003

  18. MELT WIRE SENSORS AVAILABLE TO DETERMINE PEAK TEMPERATURES IN ATR IRRADIATION TESTING

    SciTech Connect

    K. L. Davis; D. Knudson; J. Daw; J. Palmer; J. L. Rempe

    2012-07-01

    In April 2007, the Department of Energy (DOE) designated the Advanced Test Reactor (ATR) a National Scientific User Facility (NSUF) to advance US leadership in nuclear science and technology. By attracting new users from universities, laboratories, and industry, the ATR will support basic and applied nuclear research and development and help address the nation's energy security needs. In support of this new program, the Idaho National Laboratory (INL) has developed in-house capabilities to fabricate, test, and qualify new and enhanced temperature sensors for irradiation testing. Although most efforts emphasize sensors capable of providing real-time data, selected tasks have been completed to enhance sensors provided in irradiation locations where instrumentation leads cannot be included, such as drop-in capsule and Hydraulic Shuttle Irradiation System (HSIS) or 'rabbit' locations. To meet the need for these locations, the INL has developed melt wire temperature sensors for use in ATR irradiation testing. Differential scanning calorimetry and environmental testing of prototypical sensors was used to develop a library of 28 melt wire materials, capable of detecting peak irradiation temperatures ranging from 85 to 1500°C. This paper will discuss the development work and present test results.

  19. Structure and dynamical intra-molecular heterogeneity of star polymer melts above glass transition temperature

    NASA Astrophysics Data System (ADS)

    Chremos, Alexandros; Glynos, Emmanouil; Green, Peter F.

    2015-01-01

    Structural and dynamical properties of star melts have been investigated with molecular dynamics simulations of a bead-spring model. Star polymers are known to be heterogeneous, but a systematic simulation study of their properties in melt conditions near the glass transition temperature was lacking. To probe their properties, we have expanded from linear to star polymers the applicability of Dobkowski's chain-length dependence correlation function [Z. Dobkowski, Eur. Polym. J. 18, 563 (1982)]. The density and the isokinetic temperature, based on the canonical definition of the laboratory glass-transition, can be described well by the correlation function and a subtle behavior manifests as the architecture becomes more complex. For linear polymer chains and low functionality star polymers, we find that an increase of the arm length would result in an increase of the density and the isokinetic temperature, but high functionality star polymers have the opposite behavior. The effect between low and high functionalities is more pronounced for short arm lengths. Complementary results such as the specific volume and number of neighbors in contact provide further insights on the subtle relation between structure and dynamics. The findings would be valuable to polymer, colloidal, and nanocomposites fields for the design of materials in absence of solution with the desired properties.

  20. Sea Ice Brightness Temperature as a Function of Ice Thickness: Computed curves for AMSR-E and SMOS (frequencies from 1.4 to 89 GHz)

    E-print Network

    Mills, Peter

    2012-01-01

    The relationship between sea ice thickness and microwave brightness temperature is explored. Parameterized ice profiles are fed to a radiative-transfer-based sea ice emissivity model (Microwave Emmission of Layered Snowpack, MEMLS). Complex permittivities, required as input for the simulation, are determined using a semi-empirical mixture model. Since the thickness-radiance relation is not fixed but can vary significantly depending upon past and current weather conditions, we determine a range of brightness temperature values for each thickness. This is done using a bootstrap model in which the salinities are varied based on variances supplied with the thickness-salinity curve and the complex permittivities are varied based on variance supplied by the mixture model. The results suggest that scattering is one of the most important parameters determining sea ice brightness temperature, especially for new and forming ice. Further work must be done to accurately model both scattering and complex permittivities in...

  1. Is it possible to decrease skin temperature with ice packs under casts and bandages?

    Microsoft Academic Search

    Guvenir Okcu; H. S. Yercan

    2006-01-01

    Introduction  There is a general belief that the presence of a cast or a bandage eliminates the lowering effects of skin temperature when local cold therapy applied on the surface of the cast or bandage. The purpose of this study is to determine the magnitude of temperature changes at the skin of the ankle after the application of frozen ice packs

  2. Experimental study of mass recovery adsorption cycles for ice making at low generation temperature

    Microsoft Academic Search

    R. G. Oliveira; V SILVEIRAJR; R. Z. Wang

    2006-01-01

    This paper presents the experimental results of an adsorption icemaker operating without refrigerant mass recovery and under two kinds of mass recovery cycles. The generation temperatures used in the experiments were 85 and 115°C. At the lower generation temperature, the cycle with mass recovery in double stage produced the highest cycled mass, rate of ice production, cooling capacity and its

  3. How deep, how hot: comparing pressure and temperature estimates from amphibole and rhyolite-MELTS thermobarometry

    NASA Astrophysics Data System (ADS)

    Pamukcu, A. S.; Gualda, G. A.

    2013-12-01

    Accurately constraining the pressure and temperature of magma residence is problematic, but it is key to understanding the structure and evolution of magmatic systems. Various thermometers exist (Fe-Ti oxides, Ti-in-zircon, Zr-in-sphene, etc.), but there are fewer barometers that can be applied to volcanic rocks. Most barometers capitalize on amphibole, a relatively common mineral whose composition is sensitive to pressure and temperature changes. Glass composition is a function of pressure for magmas saturated in quartz and feldspar, and a new thermobarometer based on rhyolite-MELTS simulations using glass (matrix glass and crystal-hosted glass inclusions) compositions has been recently proposed. We compare results from amphibole and matrix glass thermobarometry. We focus on outflow high-silica rhyolite pumice from the Peach Spring Tuff (CA-NV-AZ, USA), which are characterized by sanidine+plagioclase×quartz+amphibole+sphene in a high-silica rhyolite glass matrix. Compositional variations in amphibole are slight and described by edenite and Ti-Tschermak substitution, with little Al-Tschermak substitution, suggesting small changes in temperature but not in pressure. Plagioclase compositions are also nearly homogeneous. Thus, we expect thermobarometry results to cluster around a single pressure and temperature, making these samples excellent candidates for comparing thermobarometers. Amphibole×plagioclase thermobarometry reveals: - Amphibole-plagioclase: results vary widely depending on the calibration (e.g. 150-420 MPa, 520-730 °C); combined Anderson & Smith (1995) barometer with Holland & Blundy (1990) thermometer is most consistent, suggesting crystallization at 230 MPa, 680 °C. - Amphibole-only: calibrations give significantly different results (75-115 MPa, 770-960 °C [Ridolfi et al. 2010]; 400-950 MPa, 800-950°C [Ridolfi & Renzulli 2012]). Results suggest the recent re-calibration is particularly unreliable for these rocks, and the earlier calibration is unreliable for constraining temperature, if not also pressure. Thermobarometry with matrix glass compositions shows: - Rhyolite-MELTS thermobarometry: 190-260 MPa, 780-800 (×40 °C). Many glass compositions used for these simulations did not yield estimates, only low Na, high K analyses were successful. Thus, rhyolite-MELTS also served to pare down analyses affected by alteration or analytical problems. - Glass SiO2 contents (~76.9 wt.% SiO2): 200-250 MPa. - Projection on haplogranitic ternary: 250 (×50) MPa. We find poor agreement between the many calibrations of amphibole and amphibole-plagioclase thermobarometers. These thermobarometers may be useful for broadly identifying where magmas reside in the Earth's crust (lower, middle, upper), but they are likely not accurate enough to resolve pressure differences within the upper crust, where we expect many eruptible magmas to be stored. Results from glass barometry are more consistent and suggest that the Anderson & Smith (1995) calibration is the most accurate for amphibole. Temperatures from the rhyolite-MELTS thermometer are slight overestimates relative to Zr-in-sphene and Ti-in-zircon temperatures of 750 °C. Overall, rhyolite-MELTS thermobarometry shows great promise for determining crystallization conditions of glass-bearing rocks stored in the upper crust.

  4. Continuous Measurements of Electrical Conductivity and Viscosity of Lherzorite Analogue Samples during Slow Increases and Decreases in Temperature: Melting and Pre-melting Effects

    NASA Astrophysics Data System (ADS)

    Sueyoshi, K.; Hiraga, T.

    2014-12-01

    It has been considered that transport properties of the mantle (ex. electrical conductivity, viscosity, seismic attenuation) changes dramatically during ascend of the mantle especially at around the mantle solidus. To understand the mechanism of such changes, we measured the electrical conductivity and viscosity of the lherzorite analogues during slow increases and decreases in temperature reproducing the mantle crossing its solidus. Two types of samples, one was forsterite plus 20% diopside and the other was 50% forsterite, 40% enstatite and 10% diopside with addition of 0.5% spinel, were synthesized from Mg(OH)2, SiO2, CaCO3 and MgAl2O4 (spinel) powders with particle size of <50 nm. Samples were expected to exhibit different manners in initiation of partial melt and amount of melt during the temperature change. We continuously measured electrical conductivity of these samples at every temperature during gradual temperature change, which crosses the sample solidus (~1380? and 1230? for forsterite + diopside sample and spinel-added samples, respectively). Sample viscosity were also measured under constant loads of 0.5~50 MPa. The electrical conductivity and viscosity at well below (>150?) the sample solidus exhibited linear distributions in their Arrhenius plots indicating that a single mechanism controls for each transport property within the experimental temperature ranges. Such linear relationship especially in the electrical conductivity was no longer observed at higher temperature regime exhibiting its exponential increase until the temperature reached the sample solidus. Such dramatic change with changing temperature has not been detected for the sample viscosity. Monotonic increase of electrical conductivity in accordance with increasing melt fraction was observed above the sample solidus.

  5. An isotopic perspective on the correlation of surface ocean carbon dynamics and sea ice melting in Prydz Bay (Antarctica) during austral summer

    NASA Astrophysics Data System (ADS)

    Zhang, Run; Zheng, Minfang; Chen, Min; Ma, Qiang; Cao, Jianping; Qiu, Yusheng

    2014-01-01

    The stable carbon isotope composition of particulate organic carbon (?13CPOC) and naturally occurring long-lived radionuclide 226Ra (T1/2=1600 a) were applied to study the variations of upper ocean (<100 m) carbon dynamics in response to sea ice melting in Prydz Bay, East Antarctica during austral summer 2006. Surface ?13CPOC values ranged from -27.4‰ to -19.0‰ and generally decreased from inner bay (south of 67°S) toward the Antarctic Divergence. Surface water 226Ra activity concentration ranged from 0.92 to 2.09 Bq/m3 (average 1.65±0.32 Bq/m3, n=20) and increased toward the Antarctic Divergence, probably reflecting the influence of 226Ra-depleted meltwater and upwelled 226Ra-replete deep water. The fraction of meltwater, fi, was estimated from 226Ra activity concentration and salinity using a three-component (along with Antarctic Summer Surface Water, and Prydz Bay Deep Water) mixing model. Although the fraction of meltwater is relatively minor (1.6-11.9%, average 4.1±2.7%, n=20) for the surface waters (sampled at ~6 m), a positive correlation between surface ?13CPOC and fi (?13CPOC=0.94×fi-28.44, n=20, r2=0.66, p<0.0001) was found, implying that sea ice melting may have contributed to elevated ?13CPOC values in the inner Prydz Bay compared to the open oceanic waters. This is the first time for a relationship between ?13CPOC and meltwater fraction to be reported in polar oceans to our knowledge. We propose that sea ice melting may have affected surface ocean ?13CPOC by enhancing water column stability and providing a more favorable light environment for phytoplankton photosynthesis, resulting in drawdown of seawater CO2 availability, likely reducing the magnitude of isotope fractionation during biological carbon fixation. Our results highlight the linkage of ice melting and ?13CPOC, providing insights into understanding the carbon cycling in the highly productive Antarctic waters.

  6. Ocean interactions with the base of Amery Ice Shelf, Antarctica

    NASA Technical Reports Server (NTRS)

    Hellmer, Hartmut H.; Jacobs, Stanley S.

    1992-01-01

    Using a two-dimensional ocean themohaline circulation model, we varied the cavity shape beneath Amery Ice Shelf in an attempt to reproduce the 150-m-thick marine ice layer observed at the 'G1' ice core site. Most simulations caused melting rates which decrease the ice thickness by as much as 400 m between grounding line and G1, but produce only minor accumulation at the ice core site and closer to the ice front. Changes in the sea floor and ice topographies revealed a high sensitivity of the basal mass balance to water column thickness near the grounding line, to submarine sills, and to discontinuities in ice thickness. Model results showed temperature/salinity gradients similar to observations from beneath other ice shelves where ice is melting into seawater. Modeled outflow characteristics at the ice front are in general agreement with oceanographic data from Prydz Bay. We concur with Morgan's inference that the G1 core may have been taken in a basal crevasse filled with marine ice. This ice is formed from water cooled by ocean/ice shelf interactions along the interior ice shelf base.

  7. Summer basal melt rate at the Larsen-C ice shelf, Antarctic Peninsula, measured by phase sensitive radar

    Microsoft Academic Search

    N. Gourmelen; A. Shepherd; M. McMillan; A. Jenkins; M. King

    2010-01-01

    During the past decade, the Larsen Ice Shelf (LIS) has progressively thinned and two large sections have collapsed, catastrophically, leading to increased ice discharge into the oceans and a global sea level rise of about 0.07 mm yr-1. If similar events are to occur at the remaining Larsen-C section, the fate of a tenfold greater ice reservoir hangs in the

  8. Validation of MODIS Terra and Aqua Ice Surface Temperatures at Summit, Greenland

    NASA Astrophysics Data System (ADS)

    Hall, D. K.; Shuman, C. A.; Xiong, X.; Wenny, B. N.; DiGirolamo, N. E.

    2014-12-01

    Ice-surface temperature (IST) is used in many studies, for example for validation of model output and for detection of leads and thin ice in sea ice. The MODerate-resolution Imaging Spectroradiometer (MODIS) instruments on the Terra and Aqua satellites are useful for mapping IST of sea ice and the Greenland ice sheet (Hall et al., 2012), and validation of the ISTs derived from MODIS has been an ongoing effort (e.g., Koenig & Hall, 2010; Shuman et al., 2014). Recent results call into question the calibration of the MODIS-derived ISTs at very cold temperatures that are characteristic of the Greenland ice sheet high interior during winter (Shuman et al., 2014). In the present work, we investigate the calibration of MODIS IR bands 31 (10.780 - 11.280 µm) and 32 (11.770 - 12.270 µm) under very cold conditions. MODIS IR bands are calibrated using a quadratic algorithm. In Collection 6 (C6), the offset and nonlinear calibration coefficients are computed from data collected during the blackbody cool-down vs the warm-up data used in Collection 5 (C5). To improve the calibration accuracy for low-temperature scenes, the offset terms are set to 0. In general, Aqua MODIS bands 31 and 32 perform better than Terra MODIS bands 31 and 32. One of the reasons is that the Aqua bands have a lower saturation temperature (~340 K) than the Terra (~380 K) bands, and lower saturation or smaller dynamic range means better resolution. As compared to ~2-m NOAA air temperatures (TA) at Summit, Greenland, Shuman et al. (2014) show a small (~0.5°C) offset in Terra MODIS-derived IST vs TA near 0°C, and an increasingly larger offset (up to ~5°C) as TA drops to -60°C. To investigate this further, we compare Terra and Aqua C5 and C6 ISTs with TA data from Summit. This work will document the calibration of bands 31 and 32 at very low temperatures in C5 and C6. Hall, D.K., et al., 2012: Satellite-Derived Climate-Quality Data Record of the Clear-Sky Surface Temperature of the Greenland Ice Sheet, Jour. Clim., 25(14):4785-4798.Koenig, L.S. and D.K. Hall, 2010: Comparison of satellite, thermochron and station temperatures at Summit, Greenland, during the winter of 2008/09, Jour. Glaciol., 56(198):735-741. Shuman, C.A., et al., 2014: Comparison of near-surface air temperatures and MODIS ice-surface temperatures at Summit, Greenland (2008-2013), JAMC, in press.

  9. High-load, high-temperature deformation apparatus for synthetic and natural silicate melts

    NASA Astrophysics Data System (ADS)

    Hess, K.-U.; Cordonnier, B.; Lavallée, Y.; Dingwell, D. B.

    2007-07-01

    A unique high-load, high-temperature uniaxial press was developed to measure the rheology of silicate melts and magmatic suspensions at temperature up to 1050°C. This new apparatus is designed to operate at constant stresses (up to 300kN) or constant strain rates (˜10-7 to 100s-1) and further allows us to carry on experiments on samples with high viscosities (˜108 to 1012Pas). The rheological instrument represents an advance in that it accommodates homogeneously heated samples (±2°C) of voluminous sizes (up to 790cm3) which permit the insertion of thermocouples to monitor temperature distribution evolutions during measurements. At last this setup allows for accurate measurements of viscosity of natural multiphase materials at strain rates and temperatures common to natural systems. The apparatus aspires to precisely (1) describe the onset of non-Newtonian behavior and its evolution with increasing strain rate until the point of rupture in the brittle regime, (2) constrain the effect of crystals and bubbles on the viscosity, and (3) record heating dissipated through viscous deformation. Here, we present a series of measurements on NIST standard material SRM 717a to calibrate the instrument. We couple the viscosity determined via Gent's equation with certified viscosity data of the standard material to calibrate this state-of-the-art apparatus. This work shows that we can resolve the viscosity of voluminous melt sample within 0.06 logarithmic unit and furthermore present the detection of minor viscous dissipation for a high-temperature, high strain rate experiment.

  10. On the reduced sensitivity of the Atlantic overturning to Greenland ice sheet melting in projections: a multi-model assessment

    NASA Astrophysics Data System (ADS)

    Swingedouw, Didier; Rodehacke, Christian B.; Olsen, Steffen M.; Menary, Matthew; Gao, Yongqi; Mikolajewicz, Uwe; Mignot, Juliette

    2014-08-01

    Large uncertainties exist concerning the impact of Greenland ice sheet melting on the Atlantic meridional overturning circulation (AMOC) in the future, partly due to different sensitivity of the AMOC to freshwater input in the North Atlantic among climate models. Here we analyse five projections from different coupled ocean-atmosphere models with an additional 0.1 Sv (1 Sv = 106 m3/s) of freshwater released around Greenland between 2050 and 2089. We find on average a further weakening of the AMOC at 26°N of 1.1 ± 0.6 Sv representing a 27 ± 14 % supplementary weakening in 2080-2089, as compared to the weakening relative to 2006-2015 due to the effect of the external forcing only. This weakening is lower than what has been found with the same ensemble of models in an identical experimental set-up but under recent historical climate conditions. This lower sensitivity in a warmer world is explained by two main factors. First, a tendency of decoupling is detected between the surface and the deep ocean caused by an increased thermal stratification in the North Atlantic under the effect of global warming. This induces a shoaling of ocean deep ventilation through convection hence ventilating only intermediate levels. The second important effect concerns the so-called Canary Current freshwater leakage; a process by which additionally released freshwater in the North Atlantic leaks along the Canary Current and escapes the convection zones towards the subtropical area. This leakage is increasing in a warming climate, which is a consequence of decreasing gyres asymmetry due to changes in Ekman pumping. We suggest that these modifications are related with the northward shift of the jet stream in a warmer world. For these two reasons the AMOC is less susceptible to freshwater perturbations (near the deep water formation sides) in the North Atlantic as compared to the recent historical climate conditions. Finally, we propose a bilinear model that accounts for the two former processes to give a conceptual explanation about the decreasing AMOC sensitivity due to freshwater input. Within the limit of this bilinear model, we find that 62 ± 8 % of the reduction in sensitivity is related with the changes in gyre asymmetry and freshwater leakage and 38 ± 8 % is due to the reduction in deep ocean ventilation associated with the increased stratification in the North Atlantic.

  11. On the reduced sensitivity of the Atlantic overturning to Greenland ice sheet melting in projections: a multi-model assessment

    NASA Astrophysics Data System (ADS)

    Swingedouw, Didier; Rodehacke, Christian; Olsen, Steffen; Menary, Matthew; Gao, Yongqi; Mikolajewicz, Uwe; Mignot, Juliette

    2014-05-01

    Large uncertainties exist concerning the impact of Greenland ice sheet melting on the Atlantic meridional overturning circulation (AMOC) in the future, partly due to different sensitivity of the AMOC to freshwater input in the North Atlantic among climate models. Here we analyse five projections from different coupled ocean-atmosphere models with an additional 0.1 Sv of freshwater released around Greenland between 2050 and 2089. We find on average a further weakening of the AMOC at 26°N of 1.1 ± 0.6 Sv representing a 27 ± 14% supplementary weakening in 2080-2089, as compared to the weakening relative to 2006-2015 due to the effect of the external forcing only. This weakening is lower than what has been found with the same ensemble of models in an identical experimental set-up but under recent historical conditions. This lower sensitivity in a warmer world is explained by two main factors. First, a tendency of decoupling is observed between the surface and the deep ocean caused by an increased thermal stratification in the North Atlantic under the effect of global warming. This induces a shoaling of ocean deep ventilation through convection hence ventilating only intermediate levels. The second important effect concerns the so-called Canary Current freshwater leakage; a process by which additionally released freshwater in the North Atlantic leaks along the Canary Current and escapes the convection zones towards the subtropical area. This leakage is increasing in a warming climate, which is a consequence of decreasing gyres asymmetry due to changes in Ekman pumping. We propose that these changes are related with the northward shift of the jet stream in a warmer world. For these two reasons the AMOC is less susceptible to freshwater perturbations (near the deep water formation sides) in the North Atlantic as compared to the recent historical climate conditions. Finally, we propose a bilinear model that accounts for the two former processes to explain the decrease in AMOC sensitivity to freshwater input. From this model, we find that 60% of the reduction in sensitivity of the AMOC is related with the change in gyre asymmetry and freshwater leakage and 40% is due to the reduction in deep ocean ventilation associated with the increased stratification in the North Atlantic.

  12. Ice Shelves and Landfast Ice on the Antarctic Perimeter: Revised Scope of Work

    NASA Technical Reports Server (NTRS)

    Scambos, Ted

    2002-01-01

    Ice shelves respond quickly and profoundly to a warming climate. Within a decade after mean summertime temperature reaches approx. O C and persistent melt pending is observed, a rapid retreat and disintegration occurs. This link was documented for ice shelves in the Antarctic Peninsula region (the Larsen 'A', 'B' and Wilkins Ice shelves) by the results of a previous grant under ADRO-1. Modeling of ice flow and the effects of meltwater indicated that melt pending accelerates shelf breakup by increasing fracture penetration. SAR data supplemented an AVHRR- and SSM/I-based image analysis of extent and surface characteristic changes. This funded grant is a revised, scaled-down version of an earlier proposal under the ADRO-2 NRA. The overall objective remains the same: we propose to build on the previous study by examining other ice shelves of the Antarctic and incorporate an examination of the climate-related characteristics of landfast ice. The study now considers just a few shelf and fast ice areas for study, and is funded for two years. The study regions are the northeastern Ross Ice Shelf, the Larsen 'B' and 'C' shelves, fast ice and floating shelf ice in the Pine Island Glacier area, and fast ice along the Wilkes Land coast. Further, rather than investigating a host of shelf and fast ice processes, we will home in on developing a series of characteristics associated with climate change over shelf and fast ice areas. Melt pending and break-up are the end stages of a response to a warming climate that may begin with increased melt event frequency (which changes both albedo and emissivity temporarily), changing firn backscatter (due to percolation features), and possibly increased rifting of the shelf surface. Fast ice may show some of these same processes on a seasonal timescale, providing insight into shelf evolution.

  13. ??????????????????????????????????????????????????????????? ??????????????????????????????????????????????????????????????? A Numerical Prediction of the Effect of Refrigerant Saturation Temperature on the Specific Energy Consumption of a Tubular-Ice Making Process

    Microsoft Academic Search

    Chittin Tangthieng

    One of the important industries for a tropical country is an ice-making industry. In particular, the tubular ice is a form of ice for consuming, which is available in many grocery stores. This research is a numerical study of the effect of the refrigerant saturation temperatures on the ice thickness, energy consumption, and specific energy consumption of a tubular-ice making

  14. An experimental study on the effect of temperature and melt composition on the partitioning of nickel between olivine and silicate melt

    SciTech Connect

    Kinzler, R.J.; Grove, T.L.; Recca, S.I. (Massachusetts Institute of Technology, Cambridge (USA))

    1990-05-01

    Experiments in the simple system CaO-MgO-Al{sub 2}O{sub 3}-SiO{sub 2}Na{sub 2}O-FeO were carried out to investigate the control of temperature and melt composition on the partitioning of nickel between olivine and silicate melt (D{sup oliv/liq}{sub Ni}). Eleven experiments determine the influence of changing forsterite (Of) content on D{sup oliv/liq}{sub Ni} in this simple system. The equation of Hart and Davis (1978) that accounts for the variation of D{sup oliv/liq}{sub Ni} in terms of MgO content of the silicate liquid is tested using experimental data from iron-bearing simple and natural systems and found to be inadequate to explain the observed variation of D{sup oliv/liq}{sub Ni}. Two different equations are formulated to describe the partitioning behavior of Ni between olivine and silicate melt. The first is similar to that of Hart and Davis (1978) and uses an expression for Ni-Mg exchange between olivine and silicate melt. The second uses an expression for the Ni-olivine formation reaction. The Ni-Mg exchange equation for D{sup oliv/liq}{sub Ni} depends on the forsterite content of the olivine and the mole fraction MgO{sup liq}, and predicts the experimentally determined values within {plus minus}13% relative average error. The Ni-olivine formation reaction equation for D{sup oliv/liq}{sub Ni} depends on temperature, mole fraction SiO{sup liq}{sub 2}, and melt compositional terms that arise from a symmetric, binary, Margules formulation of the activity coefficients for NiO{sup liq} and SiO{sup liq}{sub 2}. This equation predicts the experimentally determined values within {plus minus}9% relative average error.

  15. Temperature measurements of the low-attenuation radiographic ice ball during CT-guided renal cryoablation.

    PubMed

    Permpongkosol, Sompol; Link, Richard E; Kavoussi, Louis R; Solomon, Stephen B

    2008-01-01

    During renal cryoablation a low-attenuation area on CT develops around the cryoprobe. Knowledge of the temperature of the growing low-attenuation area can guide therapy and ensure lethal temperatures. Herein, we report thermocouple results and correlating CT images during the development of the low-attenuation "radiographic ice ball." Five patients who underwent percutaneous CT-guided renal cryoablation were identified who had thermocouples inserted and serial intraprocedural CT images that included images with thermocouple measurements of 0 degrees and sub-0 degrees C. Thermocouples had been percutaneously placed just beyond the edge of the tumors either to ensure adequate cooling or to ensure safety to adjacent critical structures. Renal cryotherapy under CT guidance produced a growing low-attenuation area corresponding to the radiographic ice ball. When the thermocouple measured 0 degrees C, CT images showed the thermocouple tip at the edge of the low-attenuation ice ball. At lower temperatures the tip was within the low-attenuation ice ball. We conclude that knowledge of the temperature at the ice ball edge during cryoablation can be used to predict the extent of tissue necrosis and thus provide an estimate of cryotherapy effectiveness during the procedure. Further work is necessary to establish a firm relationship between the thermal conditions and the zone of damage. PMID:17987248

  16. Tribology of high-speed metal-on-metal sliding at near-melt and fully-melt interfacial temperatures

    Microsoft Academic Search

    Makoto Okada; Nai-Shang Liou; Vikas Prakash; Kazuhisa Miyoshi

    2001-01-01

    The present paper describes results of plate-impact friction experiments conducted to study time-resolved frictional characteristics of sliding interfaces under extreme conditions. By employing pressure–shear impact of tribo–pair materials comprising hard tool-steels against low melt-point metals such as 7075-T6 Al alloys, interfacial normal pressures ranging from 1 to 2GPa and slip-speeds of approximately 100m\\/s have been obtained. The resulting relatively large

  17. Vapor deposition of water on graphitic surfaces: Formation of amorphous ice, bilayer ice, ice I, and liquid water

    SciTech Connect

    Lupi, Laura; Kastelowitz, Noah; Molinero, Valeria, E-mail: Valeria.Molinero@utah.edu [Department of Chemistry, The University of Utah, 315 South 1400 East, Salt Lake City, Utah 84112-0850 (United States)

    2014-11-14

    Carbonaceous surfaces are a major source of atmospheric particles and could play an important role in the formation of ice. Here we investigate through molecular simulations the stability, metastability, and molecular pathways of deposition of amorphous ice, bilayer ice, and ice I from water vapor on graphitic and atomless Lennard-Jones surfaces as a function of temperature. We find that bilayer ice is the most stable ice polymorph for small cluster sizes, nevertheless it can grow metastable well above its region of thermodynamic stability. In agreement with experiments, the simulations predict that on increasing temperature the outcome of water deposition is amorphous ice, bilayer ice, ice I, and liquid water. The deposition nucleation of bilayer ice and ice I is preceded by the formation of small liquid clusters, which have two wetting states: bilayer pancake-like (wetting) at small cluster size and droplet-like (non-wetting) at larger cluster size. The wetting state of liquid clusters determines which ice polymorph is nucleated: bilayer ice nucleates from wetting bilayer liquid clusters and ice I from non-wetting liquid clusters. The maximum temperature for nucleation of bilayer ice on flat surfaces, T{sub B}{sup max} is given by the maximum temperature for which liquid water clusters reach the equilibrium melting line of bilayer ice as wetting bilayer clusters. Increasing water-surface attraction stabilizes the pancake-like wetting state of liquid clusters leading to larger T{sub B}{sup max} for the flat non-hydrogen bonding surfaces of this study. The findings of this study should be of relevance for the understanding of ice formation by deposition mode on carbonaceous atmospheric particles, including soot.

  18. Vapor deposition of water on graphitic surfaces: Formation of amorphous ice, bilayer ice, ice I, and liquid water

    NASA Astrophysics Data System (ADS)

    Lupi, Laura; Kastelowitz, Noah; Molinero, Valeria

    2014-11-01

    Carbonaceous surfaces are a major source of atmospheric particles and could play an important role in the formation of ice. Here we investigate through molecular simulations the stability, metastability, and molecular pathways of deposition of amorphous ice, bilayer ice, and ice I from water vapor on graphitic and atomless Lennard-Jones surfaces as a function of temperature. We find that bilayer ice is the most stable ice polymorph for small cluster sizes, nevertheless it can grow metastable well above its region of thermodynamic stability. In agreement with experiments, the simulations predict that on increasing temperature the outcome of water deposition is amorphous ice, bilayer ice, ice I, and liquid water. The deposition nucleation of bilayer ice and ice I is preceded by the formation of small liquid clusters, which have two wetting states: bilayer pancake-like (wetting) at small cluster size and droplet-like (non-wetting) at larger cluster size. The wetting state of liquid clusters determines which ice polymorph is nucleated: bilayer ice nucleates from wetting bilayer liquid clusters and ice I from non-wetting liquid clusters. The maximum temperature for nucleation of bilayer ice on flat surfaces, TBmax is given by the maximum temperature for which liquid water clusters reach the equilibrium melting line of bilayer ice as wetting bilayer clusters. Increasing water-surface attraction stabilizes the pancake-like wetting state of liquid clusters leading to larger TBmax for the flat non-hydrogen bonding surfaces of this study. The findings of this study should be of relevance for the understanding of ice formation by deposition mode on carbonaceous atmospheric particles, including soot.

  19. Vapor deposition of water on graphitic surfaces: formation of amorphous ice, bilayer ice, ice I, and liquid water.

    PubMed

    Lupi, Laura; Kastelowitz, Noah; Molinero, Valeria

    2014-11-14

    Carbonaceous surfaces are a major source of atmospheric particles and could play an important role in the formation of ice. Here we investigate through molecular simulations the stability, metastability, and molecular pathways of deposition of amorphous ice, bilayer ice, and ice I from water vapor on graphitic and atomless Lennard-Jones surfaces as a function of temperature. We find that bilayer ice is the most stable ice polymorph for small cluster sizes, nevertheless it can grow metastable well above its region of thermodynamic stability. In agreement with experiments, the simulations predict that on increasing temperature the outcome of water deposition is amorphous ice, bilayer ice, ice I, and liquid water. The deposition nucleation of bilayer ice and ice I is preceded by the formation of small liquid clusters, which have two wetting states: bilayer pancake-like (wetting) at small cluster size and droplet-like (non-wetting) at larger cluster size. The wetting state of liquid clusters determines which ice polymorph is nucleated: bilayer ice nucleates from wetting bilayer liquid clusters and ice I from non-wetting liquid clusters. The maximum temperature for nucleation of bilayer ice on flat surfaces, T(B)(max) is given by the maximum temperature for which liquid water clusters reach the equilibrium melting line of bilayer ice as wetting bilayer clusters. Increasing water-surface attraction stabilizes the pancake-like wetting state of liquid clusters leading to larger T(B)(max) for the flat non-hydrogen bonding surfaces of this study. The findings of this study should be of relevance for the understanding of ice formation by deposition mode on carbonaceous atmospheric particles, including soot. PMID:25399173

  20. Near-Surface Temperatures on Mercury and the Moon and the Stability of Polar Ice Deposits

    NASA Astrophysics Data System (ADS)

    Vasavada, Ashwin R.; Paige, David A.; Wood, Stephen E.

    1999-10-01

    In order to assess the thermal stability of polar ice deposits, we present model calculated temperatures of flat surfaces and surfaces within bowl-shaped and flat-floored polar impact craters on Mercury and the Moon. Our model includes appropriate insolation cycles, realistic crater shapes, multiple scattering of sunlight and infrared radiation, and depth- and temperature-dependent regolith thermophysical properties. Unshaded water ice deposits on the surface of either body are rapidly lost to thermal sublimation. A subsurface water ice deposit is stable within 2° latitude of the Moon's poles. Meter-thick water ice deposits require billions of years to sublime if located in the permanently shaded portions of flat-floored craters within 10° latitude of the poles of Mercury and 13° latitude of the poles of the Moon. Results for craters associated with radar features on Mercury are consistent with the presence of stable water ice deposits if a thin regolith layer thermally insulates deposits at lower latitudes and within smaller craters. A regolith cover would also reduce losses from diffusion, ion sputtering, impact vaporization, and H Ly? and is implied independently by the radar observations. Permanently shaded areas near the Moon's poles are generally colder than those near Mercury's poles, but the Moon's obliquity history, its orbit through Earth's magnetospheric tail, and its radar-opaque regolith may limit the volume and radar detectability of ice deposits there.

  1. The Metastable Persistence of Vapor-Deposited Amorphous Ice at Anomalously High Temperatures

    NASA Technical Reports Server (NTRS)

    Blake, David F.; Jenniskens, Peter; DeVincenzi, Donald L. (Technical Monitor)

    1995-01-01

    Studies of the gas release, vaporization behavior and infrared (IR) spectral properties of amorphous and crystalline water ice have direct application to cometary and planetary outgassing phenomena and contribute to an understanding of the physical properties of astrophysical ices. Several investigators report anomalous phenomena related to the warming of vapor-deposited astrophysical ice analogs. However gas release, ice volatilization and IR spectral features are secondary or tertiary manifestations of ice structure or morphology. These observations are useful in mimicking the bulk physical and chemical phenomena taking place in cometary and other extraterrestrial ices but do not directly reveal the structural changes which are their root cause. The phenomenological interpretation of spectral and gas release data is probably the cause of somewhat contradictory explanations invoked to account for differences in water ice behavior in similar temperature regimes. It is the microstructure, micromorphology and microchemical heterogeneity of astrophysical ices which must be characterized if the mechanisms underlying the observed phenomena are to be understood. We have been using a modified Transmission Electron Microscope to characterize the structure of vapor-deposited astrophysical ice analogs as a function of their deposition, temperature history and composition. For the present experiments, pure water vapor is deposited at high vacuum onto a 15 K amorphous carbon film inside an Hitachi H-500H TEM. The resulting ice film (approx. 0.05 micrometers thick) is warmed at the rate of 1 K per minute and diffraction patterns are collected at 1 K intervals. These patterns are converted into radial intensity distributions which are calibrated using patterns of crystalline gold deposited on a small part of the carbon substrate. The small intensity contributed by the amorphous substrate is removed by background subtraction. The proportions of amorphous and crystalline material in each pattern are determined by subtracting a percentage of crystalline component relative to amorphous and pure crystalline endmembers. Vapor-deposited water ice undergoes two amorphous to amorphous structural transformations in the temperature range 15-130 K with important astrophysical implications. The onset of cubic crystallization occurs at 142-160 K (at 1K per minute heating rates) during which the 220 and 311 diffraction maxima appear and 0.1 micrometer crystallites can be seen in bright field images. This transition is time dependent.

  2. Self-heating probe instrument and method for measuring high temperature melting volume change rate of material

    NASA Astrophysics Data System (ADS)

    Wang, Junwei; Wang, Zhiping; Lu, Yang; Cheng, Bo

    2013-03-01

    The castings defects are affected by the melting volume change rate of material. The change rate has an important effect on running safety of the high temperature thermal storage chamber, too. But the characteristics of existing measuring installations are complex structure, troublesome operation and low precision. In order to measure the melting volume change rate of material accurately and conveniently, a self-designed measuring instrument, self-heating probe instrument, and measuring method are described. Temperature in heating cavity is controlled by PID temperature controller; melting volume change rate ? and molten density are calculated based on the melt volume which is measured by the instrument. Positive and negative ? represent expansion and shrinkage of the sample volume after melting, respectively. Taking eutectic LiF+CaF2 for example, its melting volume change rate and melting density at 1 123 K are -20.6% and 2 651 kg·m-3 measured by this instrument, which is only 0.71% smaller than literature value. Density and melting volume change rate of industry pure aluminum at 973 K and analysis pure NaCl at 1 123 K are detected by the instrument too. The measure results are agreed with report values. Measuring error sources are analyzed and several improving measures are proposed. In theory, the measuring errors of the change rate and molten density which are measured by the self-designed instrument is nearly 1/20-1/50 of that measured by the refitted mandril thermal expansion instrument. The self-designed instrument and method have the advantages of simple structure, being easy to operate, extensive applicability for material, relatively high accuracy, and most importantly, temperature and sample vapor pressure have little effect on the measurement accuracy. The presented instrument and method solve the problems of complicated structure and procedures, and large measuring errors for the samples with high vapor pressure by existing installations.

  3. Passive ice freezing-releasing heat pipe. [Patent application

    DOEpatents

    Gorski, A.J.; Schertz, W.W.

    1980-09-29

    A heat pipe device has been developed which permits completely passive ice formation and periodic release of ice without requiring the ambient temperature to rise above the melting point of water. This passive design enables the maximum amount of cooling capacity to be stored in the tank.

  4. A New Approach to Determining the Melt-Area Extent Over the Greenland Ice Sheet Using MODIS Data

    Microsoft Academic Search

    M. F. McCabe; P. Chylek; M. K. Dubey

    2006-01-01

    Polar regions are predicted to warm at a rate exceeding the global mean due to anthropogenic greenhouse gas forcing, creating the potential for serious impacts on future Earth system states. There has been considerable interest in the degree of change over the Greenland ice sheet, with parallel studies focusing on regions in Alaska and Antarctica. Observations of decreasing ice sheet

  5. Evidence for a little ice age and recent warming from a borehole temperature data inversion procedure

    SciTech Connect

    Fivez, J.; Thoen, J. [Laboratorium voor Akoestiek en Thermische Fysica, Department Natuurkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven (Belgium)

    2004-11-15

    In this article, we apply our analytical theory, published earlier in this journal, to obtain information on the earth surface temperature history from some borehole temperature data. Compared to the results of the five different methods applied to the same temperature data, our method seems to be easier, assumption-free, and yields internally consistent results. The results suggest a cooling a few centuries ago, followed by a continuing warming up to these days, in agreement with a little ice age scenario.

  6. Electrical detection of the temperature induced melting transition of a DNA hairpin covalently attached to gold interdigitated microelectrodes.

    PubMed

    Brewood, Greg P; Rangineni, Yaswanth; Fish, Daniel J; Bhandiwad, Ashwini S; Evans, David R; Solanki, Raj; Benight, Albert S

    2008-09-01

    The temperature induced melting transition of a self-complementary DNA strand covalently attached at the 5' end to the surface of a gold interdigitated microelectrode (GIME) was monitored in a novel, label-free, manner. The structural state of the hairpin was assessed by measuring four different electronic properties of the GIME (capacitance, impedance, dissipation factor and phase angle) as a function of temperature from 25 degrees C to 80 degrees C. Consistent changes in all four electronic properties of the GIME were observed over this temperature range, and attributed to the transition of the attached single-stranded DNA (ssDNA) from an intramolecular, folded hairpin structure to a melted ssDNA. The melting curve of the self-complementary single strand was also measured in solution using differential scanning calorimetry (DSC) and UV absorbance spectroscopy. Temperature dependent electronic measurements on the surface and absorbance versus temperature values measured in solution experiments were analyzed assuming a two-state process. The model analysis provided estimates of the thermodynamic transition parameters of the hairpin on the surface. Two-state analyses of optical melting data and DSC measurements provided evaluations of the thermodynamic transition parameters of the hairpin in solution. Comparison of surface and solution measurements provided quantitative evaluation of the effect of the surface on the thermodynamics of the melting transition of the DNA hairpin. PMID:18628294

  7. Electrical detection of the temperature induced melting transition of a DNA hairpin covalently attached to gold interdigitated microelectrodes

    PubMed Central

    Brewood, Greg P.; Rangineni, Yaswanth; Fish, Daniel J.; Bhandiwad, Ashwini S.; Evans, David R.; Solanki, Raj; Benight, Albert S.

    2008-01-01

    The temperature induced melting transition of a self-complementary DNA strand covalently attached at the 5? end to the surface of a gold interdigitated microelectrode (GIME) was monitored in a novel, label-free, manner. The structural state of the hairpin was assessed by measuring four different electronic properties of the GIME (capacitance, impedance, dissipation factor and phase angle) as a function of temperature from 25°C to 80°C. Consistent changes in all four electronic properties of the GIME were observed over this temperature range, and attributed to the transition of the attached single-stranded DNA (ssDNA) from an intramolecular, folded hairpin structure to a melted ssDNA. The melting curve of the self-complementary single strand was also measured in solution using differential scanning calorimetry (DSC) and UV absorbance spectroscopy. Temperature dependent electronic measurements on the surface and absorbance versus temperature values measured in solution experiments were analyzed assuming a two-state process. The model analysis provided estimates of the thermodynamic transition parameters of the hairpin on the surface. Two-state analyses of optical melting data and DSC measurements provided evaluations of the thermodynamic transition parameters of the hairpin in solution. Comparison of surface and solution measurements provided quantitative evaluation of the effect of the surface on the thermodynamics of the melting transition of the DNA hairpin. PMID:18628294

  8. Temperature dependences of structure and coercivity for melt-spun MnBi compound

    NASA Astrophysics Data System (ADS)

    Yang, Y. B.; Chen, X. G.; Guo, S.; Yan, A. R.; Huang, Q. Z.; Wu, M. M.; Chen, D. F.; Yang, Y. C.; Yang, J. B.

    2013-03-01

    Low temperature phase MnBi compound was prepared by annealing the melt-spun amorphous MnBi ribbons. Temperature dependences of structure, magnetization and coercivity were investigated using neutron/X-ray powder diffraction and magnetic measurements. It is found that the lattice parameter c/a ratio of the MnBi increases with the increasing temperature and finally reaches a maximum of 1.433 around 600 K. No structural phase transition is observed at 633 K. Especially, the lattice constants of MnBi at 700 K are a=b=4.30919 Å, and c=6.17521 Å, which are not in accordance with the previous data for bulk MnBi. Magnetic moment of Mn atom tends to lie in the ab-plane at 10 K, and turns to align along c-axis around 90 K. The growth of LTP MnBi grains is observed above 500 K, which increases the content of MnBi. The coercivity of MnBi shows a positive temperature coefficient, reaches a maximum of 2.5 T at 540 K, and decreases to 1.8 T at 610 K. The temperature dependence of the coercivity is related to the change of magnetocrystalline anisotropy, and shows strong dependence on the sizes of MnBi particles.

  9. Borehole temperature response for competing models of Laurentide ice sheet dynamics

    NASA Astrophysics Data System (ADS)

    Rath, Volker; Alvarez-Solas, Jorge; Robinson, Alex; Montoya-Redondo, Marisa

    2013-04-01

    Borehole temperature profiles (BTP) are not only the source for estimates of the background geothermal heat flow, but also allow the reconstruction of past surface temperature changes. Though shallow boreholes (e. g. less than 500 m) are abundant in most continental areas, their use is inhibited by the necessity of extracting the paleoclimatic signal present in the borehole temperature at any depth. However, assuming a long-term ground surface temperature history (GSTH), a generalized reduced temperature may be used for the interpretation of the shallow observations. To derive or test the required assumptions, very deep boreholes (say, > 2000 m) are highly important also for the investigation of shallow measurements. In areas which were influenced by the Last Glacial Period (LGP), the existence of the large scale ice sheets (e.g. the Laurentide or Weichselian), the spatial distribution of basal conditions, and the timing of their retreat have a major influence on the subsurface temperature regime. Though for parts of its history no longer directly related to atmospheric temperature, deep BTPs carry information on basal conditions, oceanic transgressions, and retreat histories, and can thus contribute to the confirmation/rejection, or even calibration of ice sheet models. From this it follows that a meaningful interpretation of the paleoclimatic signal can only proceed with a reasonable understanding of the regional ice sheet behavior, and, in order to quantify the effects, a calibrated numerical ice sheet model. From such a model, synthetic long term GSTHs may be generated, which can subsequently be used to derive the generalized reduced temperatures for the shallow BTPs. This approach is challenging in several aspects: (1) high-resolution, high-order/hybrid ice sheet models are only now emerging, and the physics at the base (e.g. ice streams) needs improvement; (2) a calibration in the sense of a Bayesian inverse problem are rare, and (3) appropriate sets of borehole data (including the corresponding metadata) still have to be collected and need to undergo strict quality control before being used. In addition, a methodological concept fora regional interpretation is missing. In this contribution we will compare the borehole temperature response for two ice sheet models of the Laurentide glaciation, differing in their dynamics. Both were realized by running the hybrid SIA/SSA code GRISLI in different modes. The subsurface temperature anomalies thus generated are significant. Unfortunately the existing deep boreholes in the area are not placed in areas of high sensitivity (e.g., Northern Quebec, Canadian Archipelago). Notwithstanding these difficulties, we will present results for some of these available boreholes in central and northern Canada and Alaska.

  10. Time dependent bio-optical and temperature measurements beneath Arctic pack ice

    NASA Astrophysics Data System (ADS)

    Hill, V. J.; Steele, M.; Light, B.

    2014-12-01

    As part of the Arctic Observing Network, a new ice-tethered buoy has been developed for monitoring under-ice light and temperature fields. A 20 to 50 m string supports sensors both within and below the ice for the collection of hourly estimates of vertically resolved downwelling irradiance (412, 443, 555 nm and PAR), temperature, chlorophyll a (Chl a) backscatter, and colored dissolved organic material (CDOM) fluorescence. Two buoys are currently operating. Buoy 1 was deployed in the Beaufort Sea in March 2014 and buoy 2 was deployed at the Barneo ice camp in collaboration with the North Pole Environmental observatory in April 2014. At both locations, attenuation of light in the uppermost 20 - 50 m of the water column was dominated by CDOM in the early spring. Buoy 1 drifted into the Chukchi Sea in June and experienced a switch from CDOM to phytoplankton dominated absorption. Buoy 2 has continued to drift south, but remains in the central basin. It has moved into water with reduced light attenuation properties, indicating low CDOM and low Chl a concentrations. Both buoys have observed water column temperature increases without associated increases in absorbed energy, indicating proximal open water. These buoys offer a unique opportunity to observe the seasonal evolution of the light field and associated warming of the upper water column in ice-covered seas.

  11. Study on Continuous Ice Slurry Formation Using Functional Fluid for Ice Storage

    NASA Astrophysics Data System (ADS)

    Matsumoto, Koji; Namiki, Yoshiharu; Okada, Masashi; Nakagawa, Shinji; Kawagoe, Tetsuo; Kang, Chaedong

    The functional fluid, which consists of oil. water mixture with additive, is changed into an ice slurry by cooling with stirring. This paper describes a new continuous ice slurry formation system. Experiments were carried out under various conditions of the supply time of solution, the stirrer torque, brine temperature and supercooling degree. As a result, the characteristics of ice recovery and ice formation process were clarified. And it was found that the sizes of formed ice particles gradually became uniform and spherical with time, and then, they could grow up to 3.5mm for about 10 hours. Moreover, the factors influencing the sizes of formed ice particles were discussed because the larger ice particles were expected to increase their melting rate. It was found that the sizes of ice particles became larger with decreases of the supercooling degree and cooling rate, and with increase of the stirrer wing diameter.

  12. Temperature and precipitation signal in two Alpine ice cores over the period 1961-2001

    NASA Astrophysics Data System (ADS)

    Mariani, I.; Eichler, A.; Jenk, T. M.; Brönnimann, S.; Auchmann, R.; Leuenberger, M. C.; Schwikowski, M.

    2014-06-01

    Water stable isotope ratios and net snow accumulation in ice cores are commonly interpreted as temperature or precipitation proxies. However, only in a few cases has a direct calibration with instrumental data been attempted. In this study we took advantage of the dense network of observations in the European Alpine region to rigorously test the relationship of the annual and seasonal resolved proxy data from two highly resolved ice cores with local temperature and precipitation. We focused on the time period 1961-2001 with the highest amount and quality of meteorological data and the minimal uncertainty in ice core dating (±1 year). The two ice cores were retrieved from the Fiescherhorn glacier (northern Alps, 3900 m a.s.l.), and Grenzgletscher (southern Alps, 4200 m a.s.l.). A parallel core from the Fiescherhorn glacier allowed assessing the reproducibility of the ice core proxy data. Due to the orographic barrier, the two flanks of the Alpine chain are affected by distinct patterns of precipitation. The different location of the two glaciers therefore offers a unique opportunity to test whether such a specific setting is reflected in the proxy data. On a seasonal scale a high fraction of ?18O variability was explained by the seasonal cycle of temperature (~60% for the ice cores, ~70% for the nearby stations of the Global Network of Isotopes in Precipitation - GNIP). When the seasonality is removed, the correlations decrease for all sites, indicating that factors other than temperature such as changing moisture sources and/or precipitation regimes affect the isotopic signal on this timescale. Post-depositional phenomena may additionally modify the ice core data. On an annual scale, the ?18O/temperature relationship was significant at the Fiescherhorn, whereas for Grenzgletscher this was the case only when weighting the temperature with precipitation. In both cases the fraction of interannual temperature variability explained was ~20%, comparable to the values obtained from the GNIP stations data. Consistently with previous studies, we found an altitude effect for the ?18O of -0.17‰/100 m for an extended elevation range combining data of the two ice core sites and four GNIP stations. Significant correlations between net accumulation and precipitation were observed for Grenzgletscher during the entire period of investigation, whereas for Fiescherhorn this was the case only for the less recent period (1961-1977). Local phenomena, probably related to wind, seem to partly disturb the Fiescherhorn accumulation record. Spatial correlation analysis shows the two glaciers to be influenced by different precipitation regimes, with the Grenzgletscher reflecting the characteristic precipitation regime south of the Alps and the Fiescherhorn accumulation showing a pattern more closely linked to northern Alpine stations.

  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. Comparison of Near-Surface Air Temperatures and MODIS Ice-Surface Temperatures at Summit, Greenland (2008-2013)

    NASA Technical Reports Server (NTRS)

    Shuman, Christopher A.; Hall, Dorothy K.; DiGirolamo, Nicolo E.; Mefford, Thomas K.; Schnaubelt, Michael J.

    2014-01-01

    We have investigated the stability of the MODerate resolution Imaging Spectroradiometer (MODIS) infrared-derived ice surface temperature (IST) data from Terra for use as a climate quality data record. The availability of climate quality air temperature data (TA) from a NOAA Global Monitoring Division observatory at Greenlands Summit station has enabled this high temporal resolution study of MODIS ISTs. During a 5 year period (July 2008 to August 2013), more than 2500 IST values were compared with 3-minute average TA values derived from the 1-minute data from NOAAs primary 2 m air temperature sensor. These data enabled an expected small offset between air and surface temperatures at this the ice sheet location to be investigated over multiple annual cycles.

  15. Satellite-derived ice data sets no. 1: Antarctic monthly average microwave brightness temperatures and sea-ice concentrations, 1973 - 1976

    NASA Technical Reports Server (NTRS)

    Zwally, H. J.

    1981-01-01

    A summary data set concerning 4 years of Antarctic sea-ice conditions was created and is available on magnetic tape. The data were derived from electrically scanning microwave radiometer brightness temperatures and were mapped into a polar stereographic grid enclosing the 50 deg S latitude circle. The grid size varies from about 32 by 32 sq km at the poles to about 28 by 28 sq km at 50 deg S. The microwave brightness temperatures of Antarctic sea ice are predominantly characteristic of first-year ice with an emissivity of 0.92 at 19 GHz frequency. Sea ice concentrations were calculated from the brightness temperature data for each grid element with an algorithm that uses an emissivity value of 0.92 and an ice physical temperature estimate from climatological surface air temperatures. Monthly, multiyear monthly, and yearly maps of brightness temperatures and sea ice concentrations were created for the 4 years, except for 7 months for which useable data were insufficient.

  16. Evolution of Melt Pond Cover in the Beaufort\\/Chukchi Sea Region During Summer 2004

    Microsoft Academic Search

    M. A. Tschudi; J. A. Maslanik; D. K. Perovich

    2005-01-01

    Melt ponds appear during the onset of summer melt on Arctic sea ice, and their coverage evolves through the course of the melt season. Ponds play a critical role in the absorption of solar radiation by the ice pack, and hence the ice melt rate. The fractional coverage of melt ponds on sea ice is thus an important parameter when

  17. Structure classification and melting temperature prediction in octet AB solids via machine learning

    NASA Astrophysics Data System (ADS)

    Pilania, G.; Gubernatis, J. E.; Lookman, T.

    2015-06-01

    Machine learning methods are being increasingly used in condensed matter physics and materials science to classify crystals structures and predict material properties. However, the reliability of these methods for a given problem, especially when large data sets are unavailable, has not been well studied. By addressing the tasks of classifying crystal structure and predicting melting temperatures of the octet subset of AB solids, we performed such a study and found potential problems with using machine learning methods on relatively small data sets. At the same time, however, we can reaffirm the potential power of such methods for these tasks. In particular, we uncovered an important new material feature, the excess Born effective charge, that significantly increased the accuracy of the predictions for the classification problem we defined. This discovery leads us to propose a new scale for the degree of ionicity and covalency in these solids. More specifically, we partitioned the crystal structures of a set of 75 octet solids into those that are ionic and covalent bonded and thus performed a binary classification task. We found that using the standard indices (r?,r?) , suggested by St. John and Bloch several decades ago, enabled an average success in classification of 92 % . Using just r? and the excess Born effective charge ? ZA of the A atom enabled an average success of 97 % , but we also found relatively large variations about these averages that were dependent on how certain machine learning methods were used and for which a standard deviation was not a proper measure of the degree of confidence we can place in either average. Instead, we calculated and report with 95 % confidence that the traditional classification pair predicts an accuracy in the interval [89 %,95 %] and the accuracy of the new pair lies in the interval [96 %,99 %] . For melting temperature predictions, the size of our data set was 46. We estimate the root-mean-squared error of our resulting model to be 11 % of the mean melting temperature of the data, but we note that if the accuracy of this predicted error is itself measured, our estimated fitting error itself has a root-mean-square error of 50 % . In short, what we illustrate is that classification and regression predictions can vary significantly, depending on the details of how machine learning methods are applied to small data sets. This variation makes it important, if not essential, to average the predictions and compute confidence intervals about these averages to report results meaningfully. However, when properly used, these statistical methods can advance our understanding and improve predictions of material properties even for small data sets.

  18. Entropy dependence of viscosity and the glass-transition temperature of melts in the system diopside-anorthite

    NASA Astrophysics Data System (ADS)

    Taniguchi, H.

    1992-01-01

    Viscosities of diopside-anorthite melts were measured over the wide range of temperature (near the glass-transition temperature-1580°C/1bar) and pressure (5 20 kb/above the liquidus temperature). The measurements were carried out by the fibre-elongation method for low temperature and the counter-balanced sphere method for high temperature at 1 bar, and the sinking and floating spheres method for high temperature at high pressure. Some of the values obtained deviated slightly from those in the literature. The data on viscosity and the glasstransition temperature have been interpreted on the basis of the configurational entropy theory, by which temperature and compositional effects on viscosity were explained well. The configurational entropies at the glasstransition temperature of magmatic silicate melts are almost constant if we use an average molecular weight (amw) or “bead” as a unit; 8.0±1.2 J/K·amw, 1.1 ±0.2cal/K·bead. The latter value coincides well with the value from the literature for organic polymers. The negative deviation from linearity of the glass-transition temperature of intermediate melts may be interpreted as the effect of the mixing entropy. The calculated glasstransition temperature-composition curve using the mixing entropy agreed well with the experimental values.

  19. Tribo-induced melting and temperature gradients at sliding asperity contacts

    NASA Astrophysics Data System (ADS)

    Krim, J.; Pan, L.; Lichtenwalner, D. J.; Kingon, A. I.

    2012-02-01

    Tribo-induced nanoscale surface melting mechanisms have been investigated by means of a combined QCM-STM technique [1] for a range of Au and Au-Ni alloys with varying compositional percentages and phases. The QCM-STM setup allows studies to be performed at sliding speeds of up to m/s, and also reveals valuable information concerning tip-substrate temperature gradients.[3] A transition from solid-solid to solid-``liquid like'' contact was observed for each sample at sufficiently high asperity sliding speeds. Pure gold, solid-solution and two-phase Au-Ni (20 at.% Ni) alloys were compared, which are materials of great relevance to MEMS RF switch technology.[2] The transition points agree favorably with theoretical predictions for their surface melting characteristics. We acknowledge NSF and AFOSR support for this research. [4pt] [1] B. D. Dawson, S. M. Lee, and J. Krim, Phys. Rev. Lett. 103, 205502 (2009) [0pt] [2] Zhenyin Yang; Lichtenwalner, D.J.; Morris, A.S.; Krim, J.; Kingon, A.I, Journal of Microelectromechanical Systems, April 2009, Volume: 18 Issue:2, 287-295 [0pt] [3] C.G. Dunkle, I.B. Altfeder, A.A. Voevodin, J. Jones, J. Krim and P.Taborek, J. Appl. Phys., 107, art#114903, (2010)

  20. Deformation mechanisms in granodiorite at effective pressures to 100 MPa and temperatures to partial melting

    SciTech Connect

    Friedman, M.; Handin, J.; Bauer, S.J.

    1981-01-01

    Deformation mechanisms in room-dry and water-saturated specimens of Charcoal Granodiorite, shortened at 10/sup -4/s/sup -1/, at effective pressures (Pe) to 100 MPa and temperatures to partial melting (less than or equal to 1050/sup 0/C) are documented with a view toward providing criteria to recognize and characterize the deformation for geological and engienering applications. Above 800/sup 0/C strength decreases dramatically at effective pressures greater than or equal to 50 MPa and water-weakening reduces strength an additional 30 to 40% at Pe = 100 MPa. Strains at failure are only 0.1 to 2.2% with macroscopic ductility (within this range) increasing as the effective pressures are increased and in wet versus dry tests. Shattering (multiple faulting) gives way to faulting along a single zone to failure without macroscopic faulting as ductility increases. Microscopically, cataclasis (extension microfracturing and thermal cracking with rigid-body motions) predominates at all conditions. Dislocation gliding contributes little to the strain. Precursive extension microfractures coalesce to produce the throughgoing faults with gouge zones exhibiting possible Riedel shears. Incipient melting, particularly in wet tests, produces a distinctive texture along feldspar grain boundaries that suggests a grain-boundary-softening effect contributes to the weakening. In addition, it is demonstrated that the presence of water does not lead to more microfractures, but to a reduction in the stresses required to initiate and propagate them.

  1. Connections of Yenisei River discharge to sea surface temperatures, sea ice, and atmospheric circulation

    NASA Astrophysics Data System (ADS)

    Ye, Hengchun; Yang, Daqing; Zhang, Xuebin; Zhang, Tingjun

    2003-12-01

    This study examines the connections of Yenisei River discharge to sea surface temperatures (SSTs), atmospheric circulation, and Arctic sea ice coverage using historical records for the time period of 1936-1995. We found that Yenisei River discharge is negatively associated with SSTs over the northern North Atlantic and is positively correlated with SSTs over the tropical South Atlantic and Indian Oceans. This connection is bridged by atmospheric circulation anomalies over the North Atlantic (a pattern similar to the North Atlantic Oscillation) and central Siberia. Sea ice coverage over the eastern Arctic Ocean, specifically over the eastern Siberian Sea, the Kara Sea, and the Greenland Sea, is negatively associated with Yenisei River discharge one season after the annual discharge; the abnormal ice coverage extent persists throughout the year until the next winter season. The persistent negative relationships between discharge and regional sea ice may be a result of the combined effects of the thermal and dynamic contribution of fresh water to sea ice and persistent atmospheric circulation anomalies coupled with sea ice cover over the Arctic Ocean.

  2. Evaluation of Ice Water Content Retrievals from Cloud Radar Reflectivity and Temperature Using a Large Airborne In Situ Microphysical Database

    E-print Network

    Protat, Alain

    of the forthcoming CloudSat spaceborne radar, and of the European CloudNET and U.S. Atmospheric Radiation MeasurementEvaluation of Ice Water Content Retrievals from Cloud Radar Reflectivity and Temperature Using the performances of the proposed ice water content (IWC)­radar reflectivity Z and IWC­Z­temperature T relationships

  3. Strong Alpine glacier melt in the 1940s due to enhanced solar radiation

    Microsoft Academic Search

    M. Huss; M. Funk; A. Ohmura

    2009-01-01

    A 94-year time series of annual glacier melt at four high elevation sites in the European Alps is used to investigate the effect of global dimming and brightening of solar radiation on glacier mass balance. Snow and ice melt was stronger in the 1940s than in recent years, in spite of significantly higher air temperatures in the present decade. An

  4. Equation of state of ice

    SciTech Connect

    Not Available

    1986-01-01

    From July through December 1987, Ktech provided support to Los Alamos National Laboratory in the area of the equation of state of ice. This work consisted of attendance at the International Symposium on the Physics and Chemistry of Ice, timely transmittal of equation of state information obtained there, and modelling to the temperature dependence of the specific heat of ice I/sub h/. The key findings reported at the symposium were acoustic velocities at high pressure of ices I/sub h/, II, III, V and VI. The specific heat modeling demonstrated the importance of anharmonic effects, especially at temperatures above about two thirds of the melting temperature. 20 refs., 1 fig., 2 tab.

  5. Sound velocity, equation of state, temperature and melting of LiF single crystals under shock compression

    NASA Astrophysics Data System (ADS)

    Liu, Qiancheng; Zhou, Xianming; Zeng, Xiaolong; Luo, S. N.

    2015-01-01

    Internal particle velocity history measurements are performed on [100] LiF single crystals under plate impact to 2-152 GPa, to investigate the Gruneisen equation of state and shock-induced melting. Hugoniot and sound velocities of LiF are obtained via the Lagrangian analysis. The drop in the longitudinal sound velocity to bulk sound velocity between 134 and 152 GPa, suggests that shock-induced melting initiates at 134-152 GPa. The Gruneisen parameter as a function of shock-state density is determined. Given high-pressure Gruneisen parameters, shock temperature and melting curve of B1 phase LiF are calculated, and consistent with previous molecular dynamics and ab initio calculations, as well as diamond-anvil cell and shock wave measurements. Our calculation suggests that shock-induced melting initiates at 142 GPa, in agreement with our sound velocity measurements.

  6. Dual luminescence imaging applied for capturing the temperature distribution of a super-cooled droplet in collision icing

    NASA Astrophysics Data System (ADS)

    Morita, Katsuaki; Okamoto, Koji; Sakaue, Hirotaka

    2011-11-01

    Dual luminescence image is applied to capture the temperature distribution of a super-cooled droplet in icing when the droplet collides onto a plate. The imaging technique captures the temperature-sensitive luminescence and the temperature-insensitive luminescence, which are spectrally separated. These images are captured by a hi-speed color camera. The icing process from super-cooled condition to ice gives insight into further understandings of the icing in flights, power cables, architectures, etc. The icing formation is shown by time steps by using the hi-speed camera. The formation is discussed from the images captured. The plates are coated with icephobic coatings to understand their effects on the collision icing.