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1

Melting Ice  

NSDL National Science Digital Library

Monitor the temperature of a melting ice cube and use temperature probes to electronically plot the data on graphs. Investigate what temperature the ice is as it melts in addition to monitoring the temperature of liquid the ice is submerged in.

2012-07-19

2

Experimental Investigation of Discharge Performance and Temperature Distribution of an External Melt Ice-on-Coil Ice Storage Tank  

Microsoft Academic Search

A 633 MJ (50 ton-h) ice storage tank was built to study the discharge characteristics of an external melt ice-on-coil ice storage tank. Temperature distributions in the tank were measured to analyze the performance of the ice storage tank. Several control parameters, including the entering mode, water flow rate, inlet temperature, load power, initial ice storage quantity, and ice bridging

Baolong Wang; Xianting Li; Maoyong Zhang; Xudong Yang

2003-01-01

3

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

Microsoft Academic Search

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

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

2008-01-01

4

Concord Consortium: Melting Ice  

NSDL National Science Digital Library

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.

5

Melting of Ice under Pressure  

SciTech Connect

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.

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

2008-07-31

6

Melting of ice under pressure  

PubMed Central

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 1050 GPa. Our computed melting temperatures are consistent with existing diamond anvil cell experiments. We find that for pressures between 10 and 40 GPa, ice melts as a molecular solid. For pressures above ?45 Gpa, there is a sharp increase in the slope of the melting curve because of the presence of molecular dissociation and proton diffusion in the solid before 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. PMID:18809909

Schwegler, Eric; Sharma, Manu; Gygi, Franois; Galli, Giulia

2008-01-01

7

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

NASA Astrophysics Data System (ADS)

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.

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

2012-07-01

8

Pressure melting and ice skating  

NASA Astrophysics Data System (ADS)

Pressure melting cannot be responsible for the low friction of ice. The pressure needed to reach the melting temperature is above the compressive failure stress and, if it did occur, high squeeze losses would result in very thin films. Pure liquid water cannot coexist with ice much below -20 C at any pressure and friction does not increase suddenly in that range. If frictional heating and pressure melting contribute equally, the length of the wetted contact could not exceed 15 ?m at a speed of 5 m/s, which seems much too short. If pressure melting is the dominant process, the water films are less than 0.08 ?m thick because of the high pressures.

Colbeck, S. C.

1995-10-01

9

Temperature index melt modelling in mountain areas  

Microsoft Academic Search

Temperature index or degree-day models rest upon a claimed relationship between snow or ice melt and air temperature usually expressed in the form of positive temperatures. Since air temperature generally is the most readily available data, such models have been the most widely used method of ice and snow melt computations for many purposes, such as hydrological modelling, ice dynamic

Regine Hock

2003-01-01

10

How ice shelf morphology controls basal melting  

NASA Astrophysics Data System (ADS)

The response of ice shelf basal melting to climate is a function of ocean temperature, circulation, and mixing in the open ocean and the coupling of this external forcing to the sub-ice shelf circulation. Because slope strongly influences the properties of buoyancy-driven flow near the ice shelf base, ice shelf morphology plays a critical role in linking external, subsurface heat sources to the ice. In this paper, the slope-driven dynamic control of local and area-integrated melting rates is examined under a wide range of ocean temperatures and ice shelf shapes, with an emphasis on smaller, steeper ice shelves. A 3-D numerical ocean model is used to simulate the circulation underneath five idealized ice shelves, forced with subsurface ocean temperatures ranging from -2.0C to 1.5C. In the sub-ice shelf mixed layer, three spatially distinct dynamic regimes are present. Entrainment of heat occurs predominately under deeper sections of the ice shelf; local and area-integrated melting rates are most sensitive to changes in slope in this "initiation" region. Some entrained heat is advected upslope and used to melt ice in the "maintenance" region; however, flow convergence in the "outflow" region limits heat loss in flatter portions of the ice shelf. Heat flux to the ice exhibits (1) a spatially nonuniform, superlinear dependence on slope and (2) a shape- and temperature-dependent, internally controlled efficiency. Because the efficiency of heat flux through the mixed layer decreases with increasing ocean temperature, numerical simulations diverge from a simple quadratic scaling law.

Little, Christopher M.; Gnanadesikan, Anand; Oppenheimer, Michael

2009-12-01

11

Why does salt melt ice?  

NSDL National Science Digital Library

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).

Senese, Fred

12

Climatology of increased temperatures and melt at Swiss Camp, western slope of Greenland ice sheet, 1991-2012  

NASA Astrophysics Data System (ADS)

Climate observations (1991-2012) will be discussed from the Swiss Camp (69deg 33?53?N, 49deg 19?51?W, 1176 m), located at the western slope of the Greenland ice sheet, 60 km inland from Ilulissat. The mean annual temperature of -12 C increased 3.6 C between 1991 and 2012 (1.7 C per decade) with large interannual variability in all seasons. The mean spring temperature increased from -16.0 C to -13.8 C, and the fall temperature increased from -12.4 C to -11.3 C in the same time. The winter temperature showed the largest increase of 6.5 C, whereas summer temperatures increased 3.0 C during the 21 years (1991 - 2012). Radiation has been monitored continuously at Swiss Camp since 1993. Net radiation of 50 W/ m2 was recorded in 2012, the warmest summer month on record. The entire annual snow cover melted at Swiss Camp, reducing the monthly albedo value to 0.4 with bare ice exposed. Interannual variability of snow accumulation ranged between 0.07 and 0.70 m water equivalent, whereas annual snow and ice ablation varied between +0.35 (net gain) and -1.8 m (net loss) for the time period 1991-2012. The equilibrium line altitude (ELA) is no longer located at Swiss Camp (1176 m elevation) with a net surface lowering of 9.5 m since 1991. Increasing summer air temperatures have resulted in an upward migration of both the percolation facies and ablation area of the Greenland ice sheet. The 0C isothermal migrated upward at a rate of 35 m/a over the 1995-2012 period in West Greenland. There is a 50% probability of the mean annual dry snow line migrating above Summit by 2025, at which time Summit will experience routine melt on an annual basis. The surface mass balance observations similarly indicate that the ELA has migrated upwards at a rate of 44 m/a over the 1997-2011 period in West Greenland, resulting in a more than doubling of the ablation zone width during this period. Inter-annual variability of monthly mean albedo at the Swiss Camp (1993 - 2012). Albedo at 0.5 is shown with a yellow contour line. The lowest surface albedo with 0.35 was recorded in summer 2010 and 2012.

Steffen, K.; McGrath, D.

2013-12-01

13

Ice Cream Structural Elements that Affect Melting Rate and Hardness  

Microsoft Academic Search

Statistical models were developed to reveal which structural elements of ice cream affect melting rate and hardness. Ice creams were frozen in a batch freezer with three types of sweetener, three levels of the emulsifier polysorbate 80, and two different draw temperatures to produce ice creams with a range of microstructures. Ice cream mixes were analyzed for viscosity, and finished

M. R. Muse; R. W. Hartel

2004-01-01

14

Mountain of Ice: If the Ice Melts  

NSDL National Science Digital Library

This interactive resource portrays what might happen to world coastlines if entire sections of the Antarctic Ice Sheet were to melt. Viewers can see how much land area might be flooded by a relatively modest 17-foot rise in sea level (represented by the collapse of the Western Antarctic Ice Sheet), or a more severe 170-foot rise, represented by the collapse of the Eastern Antarctic Ice Sheet. By comparing present-day coastline positions with those from the peak glacial advance 20,000 years ago, it is possible to appreciate how much water is contained in glaciers, the importance of monitoring their condition, and the impact accelerated global warming could one day have on sea level. A background essay and list of discussion questions are also provided.

15

Ice-Shelf Melting Around Antarctica  

NASA Astrophysics Data System (ADS)

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.

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

2013-07-01

16

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

E-print Network

C at melting point of ice to 100oC at boiling point of water Also (Kelvin, K) = oC plus 273.15 0 K is absolute be much stronger than it is (ie larger drop of temperature with altitude) without the global water cycle ­ a measure of the amount of invisible (or gaseous) water (vapour) dissolved in the air relative

Allan, Richard P.

17

Ice cream structural elements that affect melting rate and hardness.  

PubMed

Statistical models were developed to reveal which structural elements of ice cream affect melting rate and hardness. Ice creams were frozen in a batch freezer with three types of sweetener, three levels of the emulsifier polysorbate 80, and two different draw temperatures to produce ice creams with a range of microstructures. Ice cream mixes were analyzed for viscosity, and finished ice creams were analyzed for air cell and ice crystal size, overrun, and fat destabilization. The ice phase volume of each ice cream were calculated based on the freezing point of the mix. Melting rate and hardness of each hardened ice cream was measured and correlated with the structural attributes by using analysis of variance and multiple linear regression. Fat destabilization, ice crystal size, and the consistency coefficient of the mix were found to affect the melting rate of ice cream, whereas hardness was influenced by ice phase volume, ice crystal size, overrun, fat destabilization, and the rheological properties of the mix. PMID:14765804

Muse, M R; Hartel, R W

2004-01-01

18

Linking surface energy balance calculations and Temperature Index models of surface melt: Revision of the Positive Degree-Day (PDD) methodology for the Greenland Ice Sheet  

NASA Astrophysics Data System (ADS)

Positive Degree-Day (PDD) methodology (Braithwaite and Olesen, 1989; Reeh, 1991) is widely used in conjunction with observationally-derived Degree-Day Factors (DDFs) for snow and ice in order to simulate ice-sheet wide ablation rates using mean monthly temperature as the only input. Monthly PDD totals are calculated using the assumption that the monthly temperature distribution follows a Gaussian relationship with a spatially and temporally invariable standard deviation (?m), typically in the range of 4-5oC. DDFs for snow and ice used in ice sheet modelling are usually fixed at ~3 and 8 mm w.e. oC-1 day-1 respectively, but field observations show that these can vary by at least a factor of two depending on the albedo characteristics of the glacier surface (Hock, 2003). At odds with the assumption of constant ?m, it has been shown that temperature variability is reduced at temperatures close to or above the melting point, due to thermal (latent heat) buffering and the maximum temperature of 0oC for a melting snow/ice surface (e.g., Marshall and Sharp, 2009). Analysis of hourly temperature data from 22 GC-Net stations (Steffen and Box, 2001) spanning the period 1995-2010 shows that observed ?m follows a quadratic relationship with observed average monthly temperature. Comparisons of calculated and observed monthly PDD totals from GC-Net locations show that current assumptions of ?m = 4-5oC can overestimate monthly PDD totals by 25% on average, compared to ~3% for the new methodology using a spatially varying ?m. In the absence of extensive field measurements, 'theoretical' daily melt rates are calculated at several GC-Net locations using available field data to estimate the components of the daily surface energy budget (Net radiation, sensible and latent heat and subsurface energy flux). Subsequently, 'theoretical' DDFs are evaluated as a function of surface albedo. Our results suggest that future studies should consider DDFs for snow and ice of 3-7 mm w.e. oC-1 day-1 and > 9 mm w.e. oC-1 day-1 respectively, alongside the use of a spatially and temporally variable ?m, which can be parameterized as a function of monthly mean temperature. We demonstrate the impact of our new methodology and previous assumptions of fixed ?m on millennial-scale changes in Greenland Ice Sheet volume and resulting global and local RSL predictions using a 3D thermomechanical ice model where a spatially and temporally variable ?m acts to reduce the magnitude and variability associated with surface melt. These results demonstrate a need for additional empirical derivations of Degree-Day Factors in Greenland and their relationship with surface albedo in order to compliment the purely theoretical approach taken in this study.

Wake, L. M.; Marshall, S. J.; Lecavalier, B.; Milne, G. A.; Huybrechts, P.; Simpson, M. J. R.; Bayou, N.

2012-04-01

19

Getz Ice Shelf melting response to changes in ocean forcing  

NASA Astrophysics Data System (ADS)

The large and complex Getz Ice Shelf extends along nearly half of the West Antarctic coastline in the Amundsen Sea and is exposed to a more variable ocean environment than most other Pacific sector ice shelves. Ocean temperature, salinity, and dissolved oxygen profiles acquired near its sub-ice cavity openings are used here to estimate seawater transports and meltwater fractions. More complete coverage during 2000 and 2007 brackets most of the variability observed from 1994 to 2011, and yearlong records near one ice front support the use of summer profiles to determine annual basal melt rates. We find area average rates of 1.1 and 4.1 m/yr, higher in 2007 when a larger volume of warmer deep water occupied the adjacent continental shelf, and the ocean circulation was stronger. Results are consistent with changes in thermocline depths relative to ice shelf draft and mass transports onto the adjacent continental shelf. We also calculate steady state and actual melting of 2.5 and 4.6 m/yr in 2007-2008 from satellite measurements of ice flux, modeled accumulation, and thinning from 2003 to 2008. This implies a positive mass balance in 2000, but negative in 2007, when the Getz was producing more meltwater than any of the larger, slower melting or smaller, faster-melting ice shelves.

Jacobs, S.; Giulivi, C.; Dutrieux, P.; Rignot, E.; Nitsche, F.; Mouginot, J.

2013-09-01

20

Relationship between the upper ocean and sea ice during the Antarctic melting season  

Microsoft Academic Search

During the Antarctic ice-melting season, high-resolution sea ice data were collected with the video monitoring system aboard the icebreaker Shirase along with the monitoring of temperature and salinity in the upper ocean. On the basis of these data, relationships among sea ice concentration, temperature, and salinity are investigated. In the ice interior region away from the ice-free ocean, ice concentration

Kay I. Ohshima; Kazumasa Yoshida; Haruhito Shimoda; Masaaki Wakatsuchi; Tatsuo Endoh; Mitsuo Fukuchi

1998-01-01

21

Sea-ice melting processes inferred from ice-upper ocean relationships in the Ross Sea, Antarctica  

Microsoft Academic Search

Sea-ice melting processes are inferred from various summer sea-ice and upper ocean data obtained in the Ross Sea in January 1999. Using spatially (30 km) averaged continuous data, an ice concentration-water temperature plot (CT-plot) shows that the temperature at a depth of ~7 m increases as ice concentration decreases in the ice interior region. The CT-plot is explained by a

Sohey Nihashi; Kay I. Ohshima; Martin O. Jeffries; Toshiyuki Kawamura

2005-01-01

22

Regelation: why does ice melt under pressure?  

E-print Network

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.

Sun, Chang Q

2015-01-01

23

Ice, Ice, Baby: Examining the Causes and Effects of Melting Ice Formations in Antarctica  

NSDL National Science Digital Library

In this lesson, students learn about the causes and effects of the melting ice formations in Antarctica. They are directed to examine the causes and effects of melting ice shelves and perform an experiment to learn how melting ice affects water levels. As part of an associated activity, students research different aspects of the topic and create a news special. Objectives, a materials list, procedures, discussion questions, and extension activities are provided. Academic content standards and links to additional information are also included.

24

Causes and Effects of Melting Ice  

NSDL National Science Digital Library

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.

Bell, Elizabeth V.; Marshall, Brittney; Bliss, Angela

2012-11-14

25

Satellite and In Situ Observations of Arctic Sea Ice Floe Breakup and Melt  

NASA Astrophysics Data System (ADS)

During the summer melt season the Arctic sea ice cover undergoes a major transformation. In spring the ice cover consists of large, angular floes covered by snow. By late-summer it is an ensemble of smaller rounded ice floes embedded in a lace of open water, with a surface that is a mix of bare ice and melt ponds. We integrated in situ observations of sea ice mass balance with high resolution, visible satellite imagery from April to October 2013 to follow the evolution of the seasonal marginal ice zone in the Beaufort Sea. The autonomous sea ice mass balance buoy recorded a time series of ice temperature, ice growth, snow depth, ice thickness, and surface and bottom melting. The satellite images were collected by tracking the movement of the buoy as it drifted with the ice cover. Each image covered an area of about 250 km2 with a spatial resolution of just over one meter. From the images we computed ice concentration, pond fraction, floe perimeter, pond fraction, floe and pond size distribution, and the timing of melt and freezeup. Ridges and cracks formed in winter were followed into summer to investigate their effect on the floe size distribution. Measurements from the ice mass balance buoys are scaled up using the imagery to generate area estimates of the evolution of the sea ice mass loss during summer melt. There was an increase in pond coverage starting in mid-June and an increase in floe perimeter as melt proceeded into July and August.

Richter-Menge, J.; Perovich, D. K.

2013-12-01

26

Important role for ocean warming and increased ice-shelf melt in Antarctic sea-ice expansion  

NASA Astrophysics Data System (ADS)

Changes in sea ice significantly modulate climate change because of its high reflective and strong insulating nature. In contrast to Arctic sea ice, sea ice surrounding Antarctica has expanded, with record extent in 2010. This ice expansion has previously been attributed to dynamical atmospheric changes that induce atmospheric cooling. Here we show that accelerated basal melting of Antarctic ice shelves is likely to have contributed significantly to sea-ice expansion. Specifically, we present observations indicating that melt water from Antarctica's ice shelves accumulates in a cool and fresh surface layer that shields the surface ocean from the warmer deeper waters that are melting the ice shelves. Simulating these processes in a coupled climate model we find that cool and fresh surface water from ice-shelf melt indeed leads to expanding sea ice in austral autumn and winter. This powerful negative feedback counteracts Southern Hemispheric atmospheric warming. Although changes in atmospheric dynamics most likely govern regional sea-ice trends, our analyses indicate that the overall sea-ice trend is dominated by increased ice-shelf melt. We suggest that cool sea surface temperatures around Antarctica could offset projected snowfall increases in Antarctica, with implications for estimates of future sea-level rise.

Bintanja, R.; Oldenborgh, G. V.; Drijhout, S.; Wouters, B.; Katsman, C. A.

2013-12-01

27

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

USGS Publications Warehouse

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.

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

2004-01-01

28

Snow melt on sea ice surfaces as determined from passive microwave satellite data  

NASA Technical Reports Server (NTRS)

SMMR data for the year 1979, 1980 and 1984 have been analyzed to determine the variability in the onset of melt for the Arctic seasonal sea ice zone. The results show melt commencing in either the Kara/Barents Seas or Chukchi Sea and progressing zonally towards the central Asian coast (Laptev Sea). Individual regions had interannual variations in melt onset in the 10-20 day range. To determine whether daily changes occur in the sea ice surface melt, the SMMR 18 and 37 GHz brightness temperature data are analyzed at day/night/twilight periods. Brightness temperatures illustrate diurnal variations in most regions during melt. In the East Siberian Sea, however, daily variations are observed in 1979, throughout the analysis period, well before any melt would usually have commenced. Understanding microwave responses to changing surface conditions during melt will perhaps give additional information about energy budgets during the winter to summer transition of sea ice.

Anderson, Mark R.

1987-01-01

29

Melting characteristics of a vertical ice layer immersed in immiscible liquid  

SciTech Connect

Melting of a vertical ice layer immersed in immiscible liquid has been investigated experimentally to determine the interaction of melt flow based on ice melting and free convection induced by buoyancy in the liquid. Oil, which was contained in a rectangular vessel, was utilized as a testing liquid. During the melting process the solid-liquid interface behavior as well as the ambient liquid flow patterns were extensively observed. Three distinct flow regimes were identified for the ambient liquid temperatures of 7.6 to 30.0 C covered. Photographs of flow regimes are presented, and dependence of the flow structure on the melting morphology is discussed. The local/average heat transfer coefficient at the melting interface and the melt fraction were determined as a function of the ambient liquid temperature as well as melting time.

Yamada, M.; Fukusako, S.; Eman-Bellah Sayed, M. [Hokkaido Univ., Sapporo (Japan). Div. of Mechanical Science

1996-12-31

30

Antifreeze protein-induced superheating of ice inside Antarctic notothenioid fishes inhibits melting during summer warming  

PubMed Central

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 (19992012), 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

Cziko, Paul A.; DeVries, Arthur L.; Evans, Clive W.; Cheng, Chi-Hing Christina

2014-01-01

31

High density amorphous ice at room temperature  

PubMed Central

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 H2O 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 dynamicsbut all reported to exist below the crystallization temperature of approximately 150170K below 45GPa. Here, we present the evidence of high density amorphous (HDA) ice formed well above the crystallization temperature at 1GPawell inside the so-called no-mans 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

Chen, Jing-Yin; Yoo, Choong-Shik

2011-01-01

32

In-Situ Biological Decontamination of an Ice Melting Probe  

NASA Astrophysics Data System (ADS)

A major concern in space and even many terrestrial missions is the forward contamination of the alien environment with microbes and biological molecules, transported on spacecraft from Earth. Furthermore, organisms and molecules can be brought to the sampling place from the surface. All this can lead to serious misinterpretations of the obtained data and more impor-tantly, could irreversibly alter the pristine nature of the extraterrestrial environments. These issues were addressed and are constantly updated in COSPAR planetary protection policy (20 October 2002; Amended 24 March 2005; 20 July 2008). The objective of our study was to investigate the efficacy of different in-situ decontamination protocols in the conditions of thermo-mechanical ice-melting. We evaluated survival rate of microorganisms on the melting probe as a function of both time and penetration depth. Special focus was made on deter-mination of the optimal concentration of chemical decontaminants (hydrogen peroxide and sodium hypochlorite) the peculiarities of their antimicrobial action at low temperatures (-80 to 0C) combined with constant dilution with melted ice and mechanical abrasion. Common, non-pathogenic microbial strains belonging to different morphological and metabolic groups (Pseudomonas, Micrococcus, Escherichia, Bacillus and others) were chosen as test objects for this study. The working part of the melting probe was first controllably contaminated by in-cubation in suspension of microbial cells. After appropriate sedimentation of microbial cells had been reached, the drilling-melting process was started using specially prepared sterile ice blocks. Every 2 minutes the samples were taken and analyzed. In the control tests, 1 mL of distilled water was injected into the penetration site at the onset of drilling. In the other tests, 1 mL of hydrogen peroxide (30Collected data suggest high efficacy of both used compounds in respect of all tested microbial groups. Typically, 99.9

Digel, Ilya

33

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

Microsoft Academic Search

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

Chuansi Gao; John Abeysekera; Mikko Hirvonen; Carita Aschan

2003-01-01

34

Transmission of sunlight through melting Arctic sea ice (Invited)  

NASA Astrophysics Data System (ADS)

The transmission of solar radiation through sea ice affects internal warming and melting of the ice cover, contributes heat to the ocean, and determines light availability for primary productivity within and beneath the ice cover. In situ measurements of the spectral extinction of shortwave radiation in sea ice were made for both bare and ponded multiyear ice and bare first-year Arctic sea ice during the SHEBA field experiment. The present analysis results in irradiance extinction coefficients for melting multiyear ice that range from 0.65 to 0.98 m-1 at 600 nm. These values are considerably smaller than the previously accepted value of 1.5 m-1. The effect of this is that more light is predicted to penetrate deep into the ice and into the ocean than was previously accounted for. Together with observations of vertical ice structure profiles, the data were used to develop a model for light transmission through sea ice. The model suggests that transmission through bare summer ice is governed by the thicknesses of each of three layers: a highly scattering surface layer, a drained freeboard layer, and below-freeboard "interior" ice. The vertical profile for ponded ice was found to be considerably simpler: liquid water over melting interior ice. These findings are used in conjunction with compilations of observed ice concentration, and estimated incident shortwave flux, surface albedo, and ice thickness to estimate the flux of shortwave radiation at the base of the ice cover. Estimated fluxes are prepared for monthly gridded maps of the Arctic basin over the period 1979 - 2008. This study indicates that transmitted radiation through summer ice needs to be taken into account to properly understand regional shortwave energy partitioning and resulting ice-radiation feedback processes.

Light, B.; Perovich, D. K.; Grenfell, T. C.; Runciman, K.

2009-12-01

35

Impact of tide-topography interactions on basal melting of Larsen C Ice Shelf, Antarctica  

NASA Astrophysics Data System (ADS)

Basal melting of ice shelves around Antarctica contributes to formation of Antarctic Bottom Water and can affect global sea level by altering the offshore flow of grounded ice streams and glaciers. Tides influence ice shelf basal melt rate (wb) by contributing to ocean mixing and mean circulation as well as thermohaline exchanges with the ice shelf. We use a three-dimensional ocean model, thermodynamically coupled to a nonevolving ice shelf, to investigate the relationship between topography, tides, andwb for Larsen C Ice Shelf (LCIS) in the northwestern Weddell Sea, Antarctica. Using our best estimates of ice shelf thickness and seabed topography, we find that the largest modeled LCIS melt rates occur in the northeast, where our model predicts strong diurnal tidal currents (0.4 m s-1). This distribution is significantly different from models with no tidal forcing, which predict largest melt rates along the deep grounding lines. We compare several model runs to explore melt rate sensitivity to geometry, initial ocean potential temperature (?0), thermodynamic parameterizations of heat and freshwater ice-ocean exchange, and tidal forcing. The resulting range of LCIS-averagedwb is 0.11-0.44 m a-1. The spatial distribution of wb is very sensitive to model geometry and thermodynamic parameterization while the overall magnitude of wb is influenced by ?0. These sensitivities in wbpredictions reinforce a need for high-resolution maps of ice draft and sub-ice-shelf seabed topography together with ocean temperature measurements at the ice shelf front to improve representation of ice shelves in coupled climate system models.

Mueller, R. D.; Padman, L.; Dinniman, M. S.; Erofeeva, S. Y.; Fricker, H. A.; King, M. A.

2012-05-01

36

Thin sectioning and surface replication of ice at low temperature.  

USGS Publications Warehouse

We have developed a new technique for making thin sections and surface replicas of ice at temperatures well below 273d K. The ability to make thin sections without melting sample material is important in textural and microstructural studies of ice deformed at low temperatures because of annealing effects we have observed during conventional section making.-from Author

Daley, M.A.; Kirby, S.H.

1984-01-01

37

Dissociative melting of ice VII at high pressure  

SciTech Connect

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.

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

38

Dissociative melting of ice VII at high pressure.  

PubMed

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 (DeltaH(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. PMID:19334858

Goncharov, Alexander F; Sanloup, Chrystele; Goldman, Nir; Crowhurst, Jonathan C; Bastea, Sorin; Howard, W M; Fried, Laurence E; Guignot, Nicolas; Mezouar, Mohamed; Meng, Yue

2009-03-28

39

The extreme melt across the Greenland ice sheet in 2012  

NASA Astrophysics Data System (ADS)

The discovery of the 2012 extreme melt event across almost the entire surface of the Greenland ice sheet is presented. Data from three different satellite sensors - including the Oceansat-2 scatterometer, the Moderate-resolution Imaging Spectroradiometer, and the Special Sensor Microwave Imager/Sounder - are combined to obtain composite melt maps, representing the most complete melt conditions detectable across the ice sheet. Satellite observations reveal that melt occurred at or near the surface of the Greenland ice sheet across 98.6% of its entire extent on 12 July 2012, including the usually cold polar areas at high altitudes like Summit in the dry snow facies of the ice sheet. This melt event coincided with an anomalous ridge of warm air that became stagnant over Greenland. As seen in melt occurrences from multiple ice core records at Summit reported in the published literature, such a melt event is rare with the last significant one occurring in 1889 and the next previous one around seven centuries earlier in the Medieval Warm Period. Given its rarity, the 2012 extreme melt across Greenland provides an exceptional opportunity for new studies in broad interdisciplinary geophysical research.

Nghiem, S. V.; Hall, D. K.; Mote, T. L.; Tedesco, M.; Albert, M. R.; Keegan, K.; Shuman, C. A.; DiGirolamo, N. E.; Neumann, G.

2012-10-01

40

A box model of circulation and melting in ice shelf caverns  

NASA Astrophysics Data System (ADS)

A simple box model of the circulation into and inside the ocean cavern beneath an ice shelf is used to estimate the melt rates of Antarctic glaciers and ice shelves. The model uses simplified cavern geometries and includes a coarse parameterization of the overturning circulation and vertical mixing. The melting/freezing physics at the ice shelf/ocean interface are those usually implemented in high-resolution circulation models of ice shelf caverns. The model is driven by the thermohaline inflow conditions and coupling to the heat and freshwater exchanges at the sea surface in front of the cavern. We tune the model for Pine Island Glacier and then apply it to six other major caverns. The dependence of the melting rate on thermohaline conditions at the ice shelf front is investigated for this set of caverns, including sensitivity studies, alternative parameterizations, and warming scenarios. An analytical relation between the melting rate and the inflow temperature is derived for a particular model version, showing a quadratic dependence of basal melting on small values of the temperature of the inflow, which changes to a linear dependence for larger values. The model predicts melting at all ice shelf bases in agreement with observations, ranging from below a meter per year for Ronne Ice Shelf to about 25 m/year for the Pine Island Glacier. In a warming scenario with a one-degree increase of the inflow temperature, the latter glacier responds with a 1.4-fold increase of the melting rate. Other caverns respond by more than a tenfold increase, as, e.g., Ronne Ice Shelf. The model is suitable for use as a simple fast module izn coarse large-scale ocean models.

Olbers, Dirk; Hellmer, Hartmut

2010-02-01

41

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

E-print Network

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

Feltham, Daniel

42

Winter sea ice melting in the Atlantic Water subduction area, Svalbard Norway  

NASA Astrophysics Data System (ADS)

we study a small area along the shelf west of Spitsbergen, near Prins Karls Forland, where warm, saline Atlantic Water of the West Spitsbergen Current currently first encounters sea ice. This sea ice is drifting in a coastal current that carries Arctic Water originating from the Barents Sea northward over the shelf. Our aim was to investigate whether melting of sea ice by Atlantic Water in this area might be a significant factor that could contribute to the formation of a cold halocline layer that isolates the sea ice from further melting from below. Observations of temperature and salinity profiles were collected during two winters, via CTD-SRDL instruments deployed on harbor seals (Phoca vitulina), and fed into a heat and freshwater budget box model in order to quantify the importance of melting relative to other processes that could transform the shelf water mass during winter. Cross-frontal exchange of Atlantic Water from the West Spitsbergen Current, driven by buoyancy forcing rather than Ekman upwelling, was determined to be the source of the heat that melted drift ice on the shelf. Some local sea ice formation did take place, but its importance in the total heat and freshwater budgets appeared to be minor. The data suggest that the production of a cold halocline layer was preceded by southerly winds and rapid drift ice melting.

Tverberg, V.; Nst, O. A.; Lydersen, C.; Kovacs, K. M.

2014-09-01

43

Climate change and forest fires synergistically drive widespread melt events of the Greenland Ice Sheet  

PubMed Central

In July 2012, over 97% of the Greenland Ice Sheet experienced surface melt, the first widespread melt during the era of satellite remote sensing. Analysis of six Greenland shallow firn cores from the dry snow region confirms that the most recent prior widespread melt occurred in 1889. A firn core from the center of the ice sheet demonstrated that exceptionally warm temperatures combined with black carbon sediments from Northern Hemisphere forest fires reduced albedo below a critical threshold in the dry snow region, and caused the melting events in both 1889 and 2012. We use these data to project the frequency of widespread melt into the year 2100. Since Arctic temperatures and the frequency of forest fires are both expected to rise with climate change, our results suggest that widespread melt events on the Greenland Ice Sheet may begin to occur almost annually by the end of century. These events are likely to alter the surface mass balance of the ice sheet, leaving the surface susceptible to further melting. PMID:24843158

Keegan, Kaitlin M.; Albert, Mary R.; McConnell, Joseph R.; Baker, Ian

2014-01-01

44

Climate change and forest fires synergistically drive widespread melt events of the Greenland Ice Sheet.  

PubMed

In July 2012, over 97% of the Greenland Ice Sheet experienced surface melt, the first widespread melt during the era of satellite remote sensing. Analysis of six Greenland shallow firn cores from the dry snow region confirms that the most recent prior widespread melt occurred in 1889. A firn core from the center of the ice sheet demonstrated that exceptionally warm temperatures combined with black carbon sediments from Northern Hemisphere forest fires reduced albedo below a critical threshold in the dry snow region, and caused the melting events in both 1889 and 2012. We use these data to project the frequency of widespread melt into the year 2100. Since Arctic temperatures and the frequency of forest fires are both expected to rise with climate change, our results suggest that widespread melt events on the Greenland Ice Sheet may begin to occur almost annually by the end of century. These events are likely to alter the surface mass balance of the ice sheet, leaving the surface susceptible to further melting. PMID:24843158

Keegan, Kaitlin M; Albert, Mary R; McConnell, Joseph R; Baker, Ian

2014-06-01

45

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

The melting temperature (Tm) of ice Ih was determined from constant enthalphy (NPH) Born-Oppenheimer Molecular Dynamics (BOMD) simulations to be 4173 K for the Perdew-Burke-Ernzerhof (PBE) and 4114 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.

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

2009-06-11

46

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

NASA Astrophysics Data System (ADS)

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 1.2C). The Iceland and Svalbard ice caps show weaker positive air temperature anomalies in the same period (0.38 to 0.4C), while the Novaya Zemlya, Severnaya Zemlya and Franz Josef Land ice caps (Russia) display negative anomalies (-0.10 to -0.25C). 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.

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

2011-12-01

47

Control of the width of West Antarctic ice streams by internal melting in the ice sheet near the margins  

NASA Astrophysics Data System (ADS)

Could the 40 to 80 km widths of West Antarctic (Ross Shelf) ice streams be controlled by onset of melting within the ice sheet at the stream margins? The streams are driven by gravity which is resisted by basal drag, inferred to be small, and by shear stress at the lateral margins, assuming longitudinal stress gradients are unimportant [Whilans & van der Veen, JG'93]. Lateral shear stress in the sheet scales with the difference between gravitational stress and basal drag, and increases linearly with the lateral distance X from the center of a stream. With increasing X, that lateral shear stress times the creep strain rate it induces becomes a significant heat source within the ice sheet (proportional to X4 using Glen's law), and must ultimately induce internal melting. We study this possibility using data for a set of 5 ice stream profiles (A, WNar, C, D, E) of Joughin et al. [JGR'02]. They used measured lateral shear strain rates at the margins, and a depth-averaged values of the Glen's law creep parameter, based on a 1-D conduction-advection heat transfer analysis, without internal heating, to estimate the lateral drag. We find that when we incorporate the product of their drag stress and strain rate as a source in a conductive heat transfer model, the predicted margin temperatures are in excess of melting over some depth range for all five profiles. This supports the possibility that internal melting within the ice sheet is indeed related to why the margins are where they are. Next, we reformulated the 1-D vertical heat flux problem allowing some lower depth range of the of ice sheet to be partially melted ice at the melting temperature, with the rest of the sheet frozen and undergoing conductive heat transfer. The sheet was subjected to a uniform lateral shear rate, allowing the Glen's law parameter and local shear stress to be different for the two zones. The predicted fraction of the thickness that is molten, if any, depends on the lateral shear strain rate (or, equivalently, on the thickness-averaged lateral stress). For the profiles (A, WNar, C, D, E), the observed strain rates are respectively (1.2, 2.4, 0.6, 0.9, 1.9) times the levels at which internal melting should begin; with the exception of C (upper tributary of Kamb), the results are compatible with the hypothesis that the margin is undergoing internal melting. Also, the model predicts that a 5% increase in lateral stress, and hence in ice stream width, is enough to go from onset of internal melting to melting half the sheet thickness. The liquid production rate in the melting zone is also predicted. Using the permeability model of Nye and Frank [JG'73], melt rains downward to the bed via a vein system, and a permeability of ~10-16 m2 is reached at the bottom of the sheet, corresponding to a Darcy flux of ~5 m/yr. We expect that the massive drainage to the bed associated with melting causes R-channel development, with channel fluid pressure sufficiently below the ice overburden pressure that the effective normal stress on the bed adjacent to the channel is notably larger than in the central regions of the stream. That is conjectured to lock the ice sheet to the bed outboard of the R-channel and hence create the limit to width of the stream of fast-flowing ice.

Perol, T.; Rice, J. R.

2011-12-01

48

Simulation of melt pond evolution on level ice  

NASA Astrophysics Data System (ADS)

A melt pond model is presented that predicts pond size and depth changes, given an initial ice thickness field and representative surface fluxes. The model is based on the assumption that as sea ice melts, fresh water builds up in the ice pore space and eventually saturates the ice. Under these conditions, a water table is defined equal to the draft of the ice or sea level, and ponds are produced in ice surface depressions, much like lakes in a watershed. Pond evolution is forced by applying fluxes of heat at the pond surface and a radiative transfer model for solar radiation that penetrates the pond. Results from the model using forcing data from the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment and representative pond parameters indicate that the model accurately simulates pond depth and fractional area over the summer melt season, with fractional area increasing linearly. Overall, ice albedo is affected primarily by the increase in pond coverage. Decrease in pond albedo from pond deepening has a much lower influence on the total albedo. Cases with predominately sunny conditions are shown to produce more rapid pond expansion than overcast cases. In both sunny and cloudy cases the fractional area increases linearly.

Skyllingstad, Eric D.; Paulson, Clayton A.; Perovich, Donald K.

2009-12-01

49

Melting and Freezing Under the Ross Ice Shelf: Lessons From an Impacted Cavity  

NASA Astrophysics Data System (ADS)

The dimensions of ice shelves are strongly influenced by the temperature and circulation of the underlying ocean. Inflow temperatures vary by about three degrees, with most ice shelves floating in seawater near the in situ freezing point. Circulation under the ice depends on modifications of the thermohaline field by melting, freezing and tidal mixing, which determine the vertical stratification and heat flux. Observations near ice fronts have previously been used to estimate the amount of meltwater present in outflows from ice shelf cavities. While limited by the seasonality and dynamic range of the measurements, along with discrete sampling methods and uncertain source water assumptions, geochemical data add valuable information to the more commonly utilized temperature and salinity fields. Here we evaluate repeat chlorofluorocarbon and thermohaline sections in a region that has experienced a multidecadal decline in shelf water salinity. Inferences about net basal melting are compared with results from numerical models and bottom-moored instruments. Ice shelf cavities are sinks for much of the high salinity shelf water produced by sea ice formation. Outflows from those cavities reflect the properties of shelf water inflows, and affect the salinity and density of downstream bottom water production. We suggest future work that could help to better understand ocean forcing of ice shelf change in an evolving climate.

Jacobs, S. S.; Smethie, W. M.; Assmann, K. M.; Holland, D. M.; Bergamasco, A.

2003-12-01

50

Synoptic and mesoscale climate forcing on Antarctic ice shelf surface melt dynamics  

NASA Astrophysics Data System (ADS)

Given that the polar regions, especially the Antarctic Peninsula, have experienced one of the largest temperature increases on Earth over the last few decades, an understanding of Antarctic climate has become more urgent. Ice shelves themselves are located at the intersection of the atmosphere, hydrosphere and the cryosphere---the air-ice-ocean boundary, and are sensitive to changes in any of these media. In addition to being particularly sensitive to changes in climate, ice shelves play an important role in controlling the flow of glaciers into the ocean, which has important implications for sea level changes. In a warming world, an increased understanding of how climate change is affecting Antarctic ice shelves is valuable for assessing vulnerable regions of the Antarctic that may be prone to further instability. This work focuses on determining the underlying climatic processes controlling energy and mass balance responsible for driving melting over ice shelves. A novel melt-magnitude retrieval method is presented that uses Moderate Resolution Imaging Spectroradiometer (MODIS)-derived near-IR reflectance coupled with ice surface temperature as a proxy for surface melt magnitude. This method has a higher spatial resolution than passive microwave melt detection, has the added benefit of retrieving melt magnitude rather than a binary melt occurrence or non-occurrence, but has a lower temporal resolution than either passive-microwave or microwave-scatterometry melt detection. This limitation is a result of the opacity of cloud cover to both visible and IR radiation, requiring more satellite overpasses to obtain spatially contiguous imagery. This work also examines several weather variables associated with a large-extent, long-duration surface melt event on the Ross Ice Shelf. It is shown that cloudy conditions coupled with increased sensible and latent heat flux to the surface were present during the event, and these conditions are consistent with those that induce surface melting. Finally, an analysis of co-occurring climate conditions and surface melting over a recent 15-year time period (1987-2002) is presented. This analysis examines surface melt extent in three regions: Ross Ice Shelf, Larsen Ice Shelf and the Amundsen-Bellingshausen Region. Self-Organizing Maps (SOMs) are used to categorize weather patterns for each December and January day during the study period, and the average surface melt extent for each SOM pattern is computed. These values are compared to average December and January surface melt extents for each region to determine the SOM patterns associated with significantly greater or significantly less melt than the 15-year average. Over the Ross region, increases in sensible and latent heat fluxes are associated with greater surface melt extent, as is the presence of cyclonic circulation in the Ross Sea that drives mild maritime air poleward. In the Larsen and Amundsen-Bellingshausen regions, radiation fluxes appear to be more closely associated with surface melt extent, although the relationship for the geographically heterogeneous Amundsen-Bellingshausen region is less clear. These results can guide future mesoscale modeling studies that will be able to more precisely determine the causative role of each atmospheric variable in generating surface melting on West Antarctic ice shelves.

Karmosky, Christopher

51

Water isotopic ratios from a continuously melted ice core sample  

NASA Astrophysics Data System (ADS)

A new technique for on-line high resolution isotopic analysis of liquid water, tailored for ice core studies is presented. We built an interface between a Wavelength Scanned Cavity Ring Down Spectrometer (WS-CRDS) purchased from Picarro Inc. and a Continuous Flow Analysis (CFA) system. The system offers the possibility to perform simultaneuous water isotopic analysis of ?18O and ?D on a continuous stream of liquid water as generated from a continuously melted ice rod. Injection of sub ?l amounts of liquid water is achieved by pumping sample through a fused silica capillary and instantaneously vaporizing it with 100% efficiency in a~home made oven at a temperature of 170 C. A calibration procedure allows for proper reporting of the data on the VSMOW-SLAP scale. We apply the necessary corrections based on the assessed performance of the system regarding instrumental drifts and dependance on the water concentration in the optical cavity. The melt rates are monitored in order to assign a depth scale to the measured isotopic profiles. Application of spectral methods yields the combined uncertainty of the system at below 0.1 and 0.5 for ?18O and ?D, respectively. This performance is comparable to that achieved with mass spectrometry. Dispersion of the sample in the transfer lines limits the temporal resolution of the technique. In this work we investigate and assess these dispersion effects. By using an optimal filtering method we show how the measured profiles can be corrected for the smoothing effects resulting from the sample dispersion. Considering the significant advantages the technique offers, i.e. simultaneuous measurement of ?18O and ?D, potentially in combination with chemical components that are traditionally measured on CFA systems, notable reduction on analysis time and power consumption, we consider it as an alternative to traditional isotope ratio mass spectrometry with the possibility to be deployed for field ice core studies. We present data acquired in the field during the 2010 season as part of the NEEM deep ice core drilling project in North Greenland.

Gkinis, V.; Popp, T. J.; Blunier, T.; Bigler, M.; Schpbach, S.; Kettner, E.; Johnsen, S. J.

2011-11-01

52

Level-ice melt ponds in the Los Alamos sea ice model, CICE  

NASA Astrophysics Data System (ADS)

A new meltpond parameterization has been developed for the CICE sea ice model, taking advantage of the level ice tracer available in the model. The ponds evolve according to physically based process descriptions, assuming a depth-area ratio for changes in pond volume. A novel aspect of the new scheme is that the ponds are carried as tracers on the level ice area of each thickness category, thus limiting their spatial extent based on the simulated sea ice topography. This limiting is meant to approximate the horizontal drainage of melt water into depressions in ice floes. Simulated melt pond processes include collection of liquid melt water and rain into ponds, drainage through permeable sea ice or over the edges of floes, infiltration of snow by pond water, and refreezing of ponds. Furthermore, snow that falls on top of ponds whose top surface has refrozen blocks radiation from penetrating into the ponds and sea ice below. Along with a control simulation, we present a range of sensitivity tests to parameters related to each subprocess described by the parameterization. With the exception of one parameter that alters the albedo of snow-covered pond ice, results are not highly sensitive to these parameters unless an entire process is removed. The snow simulation itself is critical, because the volume of snow deposition and rate of snow melt largely determine the timing and extent of the simulated melt ponds. Nevertheless, compensating effects moderate the model's sensitivity to precipitation changes. For instance, infiltration of the snow by melt water postpones the appearance of ponds and the subsequent acceleration of melting through albedo feedback, while snow on top of refrozen pond ice also reduces the ponds' effect on the radiation budget. By construction, the model simulation of level and ridged ice is also important for this parameterization. We find that as sea ice thins, either through time or when comparing sensitivity tests, the area of level ice increases. This leads to an enhanced thinning feedback in the model, because a greater ice area may be exposed to ponding and further thinning due to lowered albedo.

Hunke, Elizabeth C.; Hebert, David A.; Lecomte, Olivier

2013-11-01

53

Seasonal melting of surface water ice condensing in martian gullies  

Microsoft Academic Search

In this work we consider when and how much liquid water during present climate is possible within the gullies observed on the surface of Mars. These features are usually found on poleward directed slopes. We analyse the conditions for melting of H2O ice, which seasonally condenses within the gullies. We follow full annual cycle of condensation and sublimation of atmospheric

Konrad J. Kossacki; Wojciech J. Markiewicz

2004-01-01

54

Quantifying signal dispersion in a hybrid ice core melting system.  

PubMed

We describe a microcontroller-based ice core melting and data logging system allowing simultaneous depth coregistration of a continuous flow analysis (CFA) system (for microparticle and conductivity measurement) and a discrete sample analysis system (for geochemistry and microparticles), both supplied from the same melted ice core section. This hybrid melting system employs an ice parcel tracking algorithm which calculates real-time sample transport through all portions of the meltwater handling system, enabling accurate (1 mm) depth coregistration of all measurements. Signal dispersion is analyzed using residence time theory, experimental results of tracer injection tests and antiparallel melting of replicate cores to rigorously quantify the signal dispersion in our system. Our dispersion-limited resolution is 1.0 cm in ice and ~2 cm in firn. We experimentally observe the peak lead phenomenon, where signal dispersion causes the measured CFA peak associated with a given event to be depth assigned ~1 cm shallower than the true event depth. Dispersion effects on resolution and signal depth assignment are discussed in detail. Our results have implications for comparisons of chemistry and physical properties data recorded using multiple instruments and for deconvolution methods of enhancing CFA depth resolution. PMID:23050603

Breton, Daniel J; Koffman, Bess G; Kurbatov, Andrei V; Kreutz, Karl J; Hamilton, Gordon S

2012-11-01

55

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;ABSTRACT - 1 - ABSTRACT Sea-level change is influenced by a wide range of factors, including climate non-eustatic components, and each over their own characteristic time scales. Climate induced sea

56

Did Davy melt Ice by Friction in a Vacuum?  

Microsoft Academic Search

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,

Florian Cajori

1926-01-01

57

Atmospheric and oceanic climate forcing of the exceptional Greenland Ice Sheet surface melt in summer 2012  

NASA Astrophysics Data System (ADS)

The NASA announcement of record surface melting of the Greenland ice sheet in July 2012 led us to examine the atmospheric and oceanic climatic anomalies that are likely to have contributed to these exceptional conditions and also to ask the question of how unusual these anomalies were compared to available records. Our analysis allows us to assess the relative contributions of these two key influences to both the extreme melt event and ongoing climate change. In 2012, as in recent warm summers since 2007, a blocking high pressure feature, associated with negative NAO conditions, was present in the mid-troposphere over Greenland for much of the summer. This circulation pattern advected relatively warm southerly winds over the western flank of the ice sheet, forming a "heat dome" over Greenland that led to the widespread surface melting. Both sea-surface temperature and sea-ice cover anomalies seem to have played a minimal role in this record melt, relative to atmospheric circulation. Two representative coastal climatological station averages and several individual stations in S, W and NW Greenland set new surface air temperature records for May, June, July and the whole (JJA) summer. The unusually warm summer 2012 conditions extended to the top of the ice sheet at Summit, where our reanalysed (1994-2012) DMI Summit weather station summer (JJA) temperature series set new record high mean and extreme temperatures in 2012; 3-hourly instantaneous 2-m temperatures reached an exceptional value of 2.2degC at Summit on 11 July 2012. These conditions translated into the record observed ice-sheet wide melt during summer 2012. However, 2012 seems not to be climatically representative of future "average" summers projected this century.

Hanna, Edward; Fettweis, Xavier; Mernild, Sebastian; Cappelen, John; Ribergaard, Mads; Shuman, Christopher; Steffen, Konrad; Wood, Len; Mote, Thomas

2013-04-01

58

Surface Melt-Induced Acceleration of Greenland Ice-Sheet Flow  

Microsoft Academic Search

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

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

2002-01-01

59

A meteorological experiment in the melting zone of the Greenland ice sheet  

SciTech Connect

Preliminary results are described from a glaciometeorological experiment carried out in the margin (melting zone) of the Greenland ice sheet in the summers of 1990 and 1991. This work was initiated within the framework of a Dutch research program on land ice and sea level change. Seven meteostations were operated along a transect running from the tundra well onto the ice sheet. At the ice edge, humidity, temperature, and wind profiles were obtained with a tethered balloon. On the ice sheet, 90 km from the edge, a boundary-layer research unit, including a sound detecting and ranging system (SODAR) and a radio acoustic sounding system (RASS), was established. Although focusing on the relation between surface energy balance, glacier mass balance, and ice flow, the experiment has also delivered a unique dataset on the dynamics of the atmospheric boundary layer around the warm tundra-cold ice sheet transition. Unexpected behavior was found for the surface albedo during the melt season. Lowest values are not found close to the ice edge, which is usual for glaciers, but higher on the ice sheet. Meltwater accumulation due to inefficient surface drainage was found to be the cause for this. The wind regime is dominated by katabatic flow from the ice sheet. The katabatic layer is typically 100-200 m thick. Close to the ice edge, the flow exhibits a very regular daily rhythm, with maximum wind speed in the afternoon. Farther on the ice sheet, the regime changes, and wind speed reaches maximum values in late night/early morning.

Oerlemans, J. (Utrecht Univ. (Netherlands)); Vugts, H.F. (Free Univ. of Amsterdam (Netherlands))

1993-03-01

60

Enhanced Sea Ice Concentration and Ice Temperature Algorithms for AMSR  

NASA Technical Reports Server (NTRS)

Accurate quantification of sea ice concentration and ice temperature from satellite passive microwave data is important because they provide the only long term, spatially detailed and consistent data set needed to study the climatology of the polar regions. Sea ice concentration data are used to derive large-scale daily ice extents that are utilized in trend analysis of the global sea ice cover. They are also used to quantify the amount of open water and thin ice in polynya and divergence regions which together with ice temperatures are in turn needed to estimate vertical heat and salinity fluxes in these regions. Sea ice concentrations have been derived from the NASA Team and Bootstrap algorithms while a separate technique for deriving ice temperature has been reported. An integrated technique that will utilizes most of the channels of AMSR (Advanced Microwave Scanning Radiometer) has been developed. The technique uses data from the 6 GHz and 37 GHz channels at vertical polarization obtain an initial estimate of sea ice concentration and ice temperature. The derived ice temperature is then utilized to estimate the emissivities for the corresponding observations at all the other channels. A procedure for calculating the ice concentration similar to the Bootstrap technique is then used but with variables being emissivities instead of brightness temperatures to minimizes errors associated with spatial changes in ice temperatures within the ice pack. Comparative studies of ice concentration results with those from other algorithms, including the original Bootstrap algorithm and those from high resolution satellite visible and infrared data will be presented. Also, results from a simulation study that demonstrates the effectiveness of the technique in correcting for spatial variations in ice temperatures will be shown. The ice temperature results are likewise compared with satellite infrared and buoy data with the latter adjusted to account for the effects of the snow cover.

Comiso, Josefino C.; Manning, Will; Gersten, Robert

1998-01-01

61

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

NASA Astrophysics Data System (ADS)

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.

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

2010-12-01

62

Eddy-resolving simulations of the Fimbul Ice Shelf cavity circulation: Basal melting and exchange with open ocean  

NASA Astrophysics Data System (ADS)

Melting at the base of floating ice shelves is a dominant term in the overall Antarctic mass budget. This study applies a high-resolution regional ice shelf/ocean model, constrained by observations, to (i) quantify present basal mass loss at the Fimbul Ice Shelf (FIS); and (ii) investigate the oceanic mechanisms that govern the heat supply to ice shelves in the Eastern Weddell Sea. The simulations confirm the low melt rates suggested by observations and show that melting is primarily determined by the depth of the coastal thermocline, regulating deep ocean heat fluxes towards the ice. Furthermore, the uneven distribution of ice shelf area at different depths modulates the melting response to oceanic forcing, causing the existence of two distinct states of melting at the FIS. In the simulated present-day state, only small amounts of Modified Warm Deep Water enter the continental shelf, and ocean temperatures beneath the ice are close to the surface freezing point. The basal mass loss in this so-called state of shallow melting is mainly controlled by the seasonal inflow of solar-heated surface water affecting large areas of shallow ice in the upper part of the cavity. This is in contrast to a state of deep melting, in which the thermocline rises above the shelf break depth, establishing a continuous inflow of Warm Deep Water towards the deep ice. The transition between the two states is found to be determined by a complex response of the Antarctic Slope Front overturning circulation to varying climate forcings. A proper representation of these frontal dynamics in climate models will therefore be crucial when assessing the evolution of ice shelf basal melting along this sector of Antarctica.

Hattermann, T.; Smedsrud, L. H.; Nst, O. A.; Lilly, J. M.; Galton-Fenzi, B. K.

2014-10-01

63

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

64

Getz Ice Shelf, West Antarctica: Little glacier speed increase despite basal ice shelf melting  

NASA Astrophysics Data System (ADS)

The Getz Ice Shelf, stretching along ~500 km of coastline in the Amundsen Sea Sector of West Antarctica, occupies a region of changing climatic and oceanic conditions. Climatically, the region is influenced by the Amundsen Sea Low, a mean atmospheric circulation feature of West Antarctica that has slowly increased in intensity over the past several decades. Oceanographically, the shelf is affected by intrusions of Antarctic Circumpolar Deep Water, which are currently melting the shelf from below at a rate of 4.3 0.4 meters of water per year. Recent results from gravity-based assessments of mass change in the region indicate significant mass loss for the entire Getz ice drainage area, and altimetry studies of grounded ice in the Getz Ice Shelf catchment area show significant elevation loss since the 1990s. Our study examines the history of ice velocities from 1972-present on the Getz Ice Shelf, with particular attention to the ice shelf edge and the grounding zone area during the last decade. The shelf and grounded ice are characterized by relatively narrow zones of faster outflow and steep grounded ice surface slopes. The fastest outflow speeds are found toward the western edge at DeVicq Glacier, typically 800-1000 ma-1 near the ice edge and 400-800 ma-1 at the grounding line. Slower speeds towards the east are generally 250-500 ma-1 at the ice edge and 150-400 ma-1 near the grounding line. Despite significant basal melt and thinning of grounded ice, the Getz Ice Shelf has exhibited only modest accelerations: ~20% near the grounding line in the DeVicq Glacier region, ~35% at the far eastern edge, and <10% across central sections of the shelf. This contrasts with the nearly 50% flow speed increase of Pine Island Glacier between 1972 and 2012, and >100% for the adjacent Smith Glacier between 1992 and 2008. We postulate that steep slopes in the grounded ice flow just above the grounding line imply high basal shear stresses for the feeder glaciers and therefore relative insensitivity to thinning of the shelf. With steep initial surface slope, the increase in driving stress caused by grounding line melting is minor. We also examine the potential connection between the measured elevation loss of grounded ice feeding the Getz Ice Shelf with changes (decreases) in annual snow accumulation associated with the evolution of the Amundsen Sea Low.

Alley, K. E.; Scambos, T. A.

2013-12-01

65

A simple parameterisation of melting near the grounding lines of ice shelves and tidewater glaciers  

NASA Astrophysics Data System (ADS)

Both the Antarctic and Greenland ice sheets are experiencing rapid change, at least in part as a result of acceleration of some of their larger, marine-terminating outlet glaciers. It is generally assumed that the accelerations have been driven by the ocean, probably through changes in the submarine melt rate. However, the processes that drive melting, particularly in the region close to the grounding line are difficult to observer and quantify. The rapid flow of the outlet glaciers is almost always associated with an active sub-glacial hydrological system, so in the key regions where the glaciers either discharge into ice shelves or terminate in fjords there will be a flow of freshwater draining across the grounding line from the glacier bed. The input of freshwater to the ocean provides a source of buoyancy and drives convective motion alongside the ice-ocean interface. This process is modelled using the theory of buoyant plumes that has previously been applied to the study of the larger-scale circulation beneath ice shelves. The plume grows through entrainment of ocean waters, and the heat brought into the plume as a result drives melting at the ice-ocean interface. The equations are non-dimensionalised using scales appropriate for the region where the sub-glacial drainage, rather than the subsequent addition of meltwater, supplies the majority of the buoyancy forcing. It is found that the melt rate within this region can be approximated reasonably well by a simple expression that is linear in ocean temperature, has a cube root dependence on the flux of sub-glacial meltwater, and a more complex dependency on the slope of the ice-ocean interface. The model is used to investigate variability in melting induced by changes in both ocean temperature and sub-glacial discharge for a number of realistic examples of ice shelves and tidewater glaciers. The results show how warming ocean waters and increasing sub-glacial drainage both generate increases in melting near the grounding line. The model is particularly appropriate for the study of melting at the quasi-vertical calving face of a tidewater glacier, where conventional ocean models struggle to capture the appropriate scales and fundamentally non-hydrostatic dynamics.

Jenkins, A.

2012-04-01

66

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

NASA Astrophysics Data System (ADS)

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.

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

2005-03-01

67

Calving fluxes and basal melt rates of Antarctic ice shelves.  

PubMed

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

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

68

Ross ice shelf cavity circulation, residence time, and melting: Results from a model of oceanic chlorofluorocarbons  

NASA Astrophysics Data System (ADS)

Despite their harmful effects in the upper atmosphere, anthropogenic chlorofluorocarbons dissolved in seawater are extremely useful for studying ocean circulation and ventilation, particularly in remote locations. Because they behave as a passive tracer in seawater, and their atmospheric concentrations are well-mixed, well-known, and have changed over time, they are ideal for gaining insight into the oceanographic characteristics of the isolated cavities found under Antarctic ice shelves, where direct observations are difficult to obtain. Here we present results from a modeling study of air-sea chlorofluorocarbon exchange and ocean circulation in the Ross Sea, Antarctica. We compare our model estimates of oceanic CFC-12 concentrations along an ice shelf edge transect to field data collected during three cruises spanning 16 yr. Our model produces chlorofluorocarbon concentrations that are quite similar to those measured in the field, both in magnitude and distribution, showing high values near the surface, decreasing with depth, and increasing over time. After validating modeled circulation and air-sea gas exchange through comparison of modeled temperature, salinity, and chlorofluorocarbons with field data, we estimate that the residence time of water in the Ross Ice Shelf cavity is approximately 2.2 yr and that basal melt rates for the ice shelf average 10 cm yr -1. The model predicts a seasonal signature to basal melting, with highest melt rates in the spring and also the fall.

Reddy, Tasha E.; Holland, David M.; Arrigo, Kevin R.

2010-04-01

69

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

NASA Technical Reports Server (NTRS)

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.

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

2010-01-01

70

Combining Modis and Quikscat Data to Delineate Surface and Near-Surface Melt on the Greenland Ice Sheet  

NASA Technical Reports Server (NTRS)

Over the last two decades, increasing melt has been measured on the Greenland Ice Sheet, along with mass loss as determined from satellite data, Monitoring the state of the Greenland Ice Sheet becomes critical especially because it is actively losing mass, and the ice sheet has a sea-level rise potential of 7 in. However measurement of the extent of surface melt varies depending on the sensor used, whether it is passive or active microwave or visible or thermal infrared. We have used remote-sensing data products to study surface and near-surface melt characteristics of the Greenland Ice Sheet. We present a blended MODIS-QS melt daily product for 2007 [1]. The products, including Moderate Resolution Imaging Spectroradiometer (MODIS) daily land-surface temperature (LST) and a special daily melt product derived from the QuikSCAT (QS) scatterometer [2,3] show consistency in delineating the melt boundaries on a daily basis in the 2007 melt season [I], though some differences are identified. An assessment of maximum melt area for the 2007 melt shows that the QSCAT product detects a greater amount of melt (862,769 square kilometers) than is detected by the MODIS LST product (766,184 square kilometers). The discrepancy is largely because the QS product can detect both surface and near-surface melt and the QS product captures melt if it occurred anytime during the day while the MODIS product is obtained from a point in time on a given day. However on a daily bases, other factors influence the measurement of melt extent. In this work we employ the digital-elevation model of Bamber et al. [4] along with the National Centers for Environmental Prediction (NCEP) data to study some areas and time periods in detail during the 2007 melt season. We focus on times in which the QS and MODIS LST products do not agree exactly. We use NCEP and elevation data to analyze the atmospheric factors forcing the melt process, to gain an improved understanding of the conditions that lead to melt and melt persistence, and our ability to capture surface melt accurately using MODIS and QS data.

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

2010-01-01

71

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

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

72

Enhanced high-temperature ice nucleation ability of crystallized aerosol particles after preactivation at low temperature  

NASA Astrophysics Data System (ADS)

cloud chamber experiments with crystallized aqueous ammonium sulfate, oxalic acid, and succinic acid solution droplets, we have studied a preactivation mechanism that markedly enhances the particles' heterogeneous ice nucleation ability. First cloud expansion experiments were performed at a high temperature (267-244 K) where the crystallized particles did not promote any heterogeneous ice nucleation. Ice nucleation at this temperature, however, could be triggered by temporarily cooling the crystallized particles to a lower temperature. This is because upon crystallization, residuals of the aqueous solution are trapped within the crystals. These captured liquids can freeze when cooled below their respective homogeneous or heterogeneous freezing temperature, leading to the formation of ice pockets in the crystalline particles. When warmed again to the higher temperature, ice formation by the preactivated particles occurred via depositional and deliquescence-induced ice growth, with ice active fractions ranging from 1 to 4% and from 4 to 20%, respectively. Preactivation disappeared above the eutectic temperature, which for the organic acids are close to the melting point of ice. This mechanism could therefore contribute to the very small fraction of atmospheric aerosol particles that are still ice active well above 263 K.

Wagner, Robert; Mhler, Ottmar; Saathoff, Harald; Schnaiter, Martin

2014-07-01

73

Modelling the impact of ocean warming on melting and water masses of ice shelves in the Eastern Weddell Sea  

Microsoft Academic Search

The Eastern Weddell Ice Shelves (EWIS) are believed to modify the water masses of the coastal current and thus preconditions\\u000a the water mass formation in the southern and western Weddell Sea. We apply various ocean warming scenarios to investigate\\u000a the impact on the temperaturesalinity distribution and the sub-ice shelf melting in the Eastern Weddell Sea. In our numerical\\u000a experiments, the

Malte Thoma; Klaus Grosfeld; Keith Makinson; Manfred A. Lange

2010-01-01

74

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

SciTech Connect

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.

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

2008-11-12

75

Attribution of Recent Arctic Sea Ice Melting to Human Influence  

NASA Astrophysics Data System (ADS)

During recent three decades Arctic sea ice extent (SIE) has been decreasing with its rate accelerating. There have been, however, limited studies which have identified human influence on the Arctic sea ice using a formal detection approach. This study conducts an updated detection analysis of recent Arctic SIE during 1979-2012 by comparing observed changes with those from CMIP5 (Coupled Model Intercomparison Project Phase 5) multi-model simulations. We use the NSIDC (National Snow and Ice Data Center) sea ice index as observations. The simulated Arctic SIEs are calculated from available ensembles of CMIP5 multi-models which have been performed under natural plus anthropogenic forcing (ALL: historical combined with RCP4.5, 112 runs from 40 models), natural forcing only (NAT: historicalNat, 48 runs from 10 models) and greenhouse gas forcing only (GHG: historicalGHG, 35 runs from 9 models). Anthropogenic forcing (ANT) responses are estimated from differences between ALL and NAT. We apply an optimal fingerprinting method where observations are regressed onto model-simulated signals (multi-model means of ALL, NAT, and GHG). Here the internal variability noise is estimated from historical simulations after removing multi-model averages. The observations display decreasing trends across all months with stronger amplitude in summer than other seasons, which is reasonably reproduced by CMIP5 simulations. Results from one-signal analyses show that the ALL, ANT, and GHG signals are all detected when considering four months (Mar, Jun, Sep, and Dec) together and also from September to January when looking at individual months. Results from two-signal analyses show that ANT is separable from NAT and also that GHG is separable from other non-GHG forcings. Scaling factors of the detected ANT and GHG signals include unity, indicating that observed Arctic sea ice melting during the satellite period is largely attributable to human-induced increases in GHGs.

Heo, Joonghyeok; Min, Seung-Ki

2014-05-01

76

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

NASA Technical Reports Server (NTRS)

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.

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

2009-01-01

77

Near-total surface melt detected on the Greenland Ice Sheet  

NASA Astrophysics Data System (ADS)

On 12 July 2012, 98.6% of the surface of the Greenland Ice Sheet melted, an event so expansive that a similar episode had not previously been seen in the satellite era. Ice core records indicate that the most recent melting event of this scale was 123 years ago. The one before that occurred another 7 centuries prior, during the Medieval Warm Period. Just 2 weeks following the near-total melt of the surface of the Greenland Ice Sheet, after the surface ice had refrozen to seasonal levels, a second episode pushed the melt area back up to 79.2%. Compiling measurements from three different satellite systems and from in-the-field observations, Nghiem et al. describe the extent of the melt. The authors suggest that warm air ridges stagnating over Greenland, coincident with the melt episodes, may have underlain the extensive melting.

Schultz, Colin

2013-01-01

78

Documenting Melting Features of the Greenland Ice Sheet  

NASA Astrophysics Data System (ADS)

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.

Tedesco, M.

2011-12-01

79

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 statisti- cally significant mass loss interpreted as inland ice melt-off to the SE and NW, [1]. The EWH data consisting of 281 images with 180 rows and 360 columns each, span the period from

80

ANALYSIS OF ANTARCTIC ICEBERG AND SEA ICE MELTING PATTERNS USING QUIKSCAT  

E-print Network

ANALYSIS OF ANTARCTIC ICEBERG AND SEA ICE MELTING PATTERNS USING QUIKSCAT Keith M. Stuart and David ABSTRACT QuikSCAT tracking of Antarctic icebergs is discussed, and iceberg movement trends are illustrated. Iceberg melting factors are explored and a backscatter time-series is presented. Interactions between ice

Long, David G.

81

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

Threaten Northeast United States, Canada Innovations Report 06/15/2009 Adapting to climate change depends Cause Dramatic Change of Northeast Coasts V1 Magazine 05/29/2009 Greenland ice could fuel severe U07/06/2009 Melting Ice Could Lead to Massive Waves of Climate Refugees Treehugger 06

Hu, Aixue

82

A box model of circulation and melting in ice shelf caverns  

Microsoft Academic Search

A simple box model of the circulation into and inside the ocean cavern beneath an ice shelf is used to estimate the melt rates\\u000a of Antarctic glaciers and ice shelves. The model uses simplified cavern geometries and includes a coarse parameterization\\u000a of the overturning circulation and vertical mixing. The melting\\/freezing physics at the ice shelf\\/ocean interface are those\\u000a usually implemented

Dirk Olbers; Hartmut Hellmer

2010-01-01

83

Variability of Basal Melt Beneath the Pine Island Glacier Ice Shelf, West Antarctica  

NASA Technical Reports Server (NTRS)

Observations from satellite and airborne platforms are combined with model calculations to infer the nature and efficiency of basal melting of the Pine Island Glacier ice shelf, West Antarctica, by ocean waters. Satellite imagery shows surface features that suggest ice-shelf-wide changes to the ocean s influence on the ice shelf as the grounding line retreated. Longitudinal profiles of ice surface and bottom elevations are analyzed to reveal a spatially dependent pattern of basal melt with an annual melt flux of 40.5 Gt/a. One profile captures a persistent set of surface waves that correlates with quasi-annual variations of atmospheric forcing of Amundsen Sea circulation patterns, establishing a direct connection between atmospheric variability and sub-ice-shelf melting. Ice surface troughs are hydrostatically compensated by ice-bottom voids up to 150m deep. Voids form dynamically at the grounding line, triggered by enhanced melting when warmer-than-average water arrives. Subsequent enlargement of the voids is thermally inefficient (4% or less) compared with an overall melting efficiency beneath the ice shelf of 22%. Residual warm water is believed to cause three persistent polynyas at the ice-shelf front seen in Landsat imagery. Landsat thermal imagery confirms the occurrence of warm water at the same locations.

Bindschadler, Robert; Vaughan, David G.; Vornberger, Patricia

2011-01-01

84

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

E-print Network

by melt- water reaching the bedrock from surface melt or supraglacial lake drainages (Lu¨thje and othersSediment plume response to surface melting and supraglacial lake drainages on the Greenland ice Space Center, Technical University of Denmark, ?rsteds Plads Building 348, DK-2800 Kgs. Lyngby, Denmark

Smith, Laurence C.

85

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

NASA Technical Reports Server (NTRS)

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.

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

2004-01-01

86

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

NASA Technical Reports Server (NTRS)

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.

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

2004-01-01

87

The influence of coastal polynyas on the basal melting of ice shelves  

Microsoft Academic Search

The dense water production from coastal polynyas can strongly modify local circulation patterns with implications for both net basal melting of ice shelves and dense water formation. Results are presented from two different ice-shelf\\/ocean models: one of the Amery Ice Shelf\\/Prydz Bay region; and one of the Mertz Glacier Ice Tongue region. The models are based on the Regional Ocean

Benjamin Galton-Fenzi; Simon Marsland; Andrew Meijers; Alex Fraser

2010-01-01

88

A correction factor for positive degree-day modeling of ice sheet surface melt under changing orbital configurations  

NASA Astrophysics Data System (ADS)

Positive degree-day (PDD) models have commonly been used to approximate continental ice sheet surface melt for the last two decades. The approach is advantageous in that it approximates present-day surface melt reasonably well and it is computationally very efficient. However, the empirical coefficients used to translate PDDs into melt are tuned to present-day conditions and thus may not be appropriate for use under other orbital configurations. Here we explore to what extent the current formulation of a PDD melt equation affects melt estimates for different levels of orbital-scale insolation changes. We find that insolation anomalies can cause large discrepancies between melt calculated using PDDs and using a simple energy-balance equation. However, higher temperatures reduce the effect of the insolation anomaly since its relative importance decreases in the energy balance. We introduce a correction factor for the PDD model that accounts for changes in insolation and improves the agreement of melt estimated by the two different methods. A particular feature of this factor is that it is fully consistent with current PDD models for present-day insolation. The new insolation-corrected PDD formulation is further tested with transient simulations of the Greenland ice sheet for the Eemian.

Robinson, Alexander; Goelzer, Heiko; Huybrechts, Philippe

2013-04-01

89

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

NSDL National Science Digital Library

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.

Landis, Carol

90

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

SciTech Connect

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.

Wei, Xing

2000-12-21

91

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

NASA Astrophysics Data System (ADS)

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.

Jin, ZheYan; Jin, SongYue; Yang, ZhiGang

2013-11-01

92

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

NASA Astrophysics Data System (ADS)

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 Mller 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.

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

93

Local Effects of Ice Floes on Skin Sea Surface Temperature in the Marginal Ice Zone from UAVs  

NASA Astrophysics Data System (ADS)

Recent years have seen extreme changes in the Arctic. Particularly striking are changes within the Pacific sector of the Arctic Ocean, and especially in the seas north of the Alaskan coast. These areas have experienced record warming, reduced sea ice extent, and loss of ice in areas that had been ice-covered throughout human memory. Even the oldest and thickest ice types have failed to survive through the summer melt period in areas such as the Beaufort Sea and Canada Basin, and fundamental changes in ocean conditions such as earlier phytoplankton blooms may be underway. Marginal ice zones (MIZ), or areas where the "ice-albedo feedback" driven by solar warming is highest and ice melt is extensive, may provide insights into the extent of these changes. Airborne remote sensing, in particular InfraRed (IR), offers a unique opportunity to observe physical processes at sea-ice margins. It permits monitoring the ice extent and coverage, as well as the ice and ocean temperature variability. It can also be used for derivation of surface flow field allowing investigation of turbulence and mixing at the ice-ocean interface. Here, we present measurements of visible and IR imagery of melting ice floes in the marginal ice zone north of Oliktok Point AK in the Beaufort Sea made during the Marginal Ice Zone Ocean and Ice Observations and Processes EXperiment (MIZOPEX) in July-August 2013. The visible and IR imagery were taken from the unmanned airborne vehicle (UAV) ScanEagle. The visible imagery clearly defines the scale of the ice floes. The IR imagery show distinct cooling of the skin sea surface temperature (SST) as well as a intricate circulation and mixing pattern that depends on the surface current, wind speed, and near-surface vertical temperature/salinity structure. Individual ice floes develop turbulent wakes as they drift and cause transient mixing of an influx of colder surface (fresh) melt water. The upstream side of the ice floe shows the coldest skin SST, and downstream the skin SST is mixed within the turbulent wake over 10s of meters. We compare the structure of circulation and mixing of the influx of cold skin SST driven by surface currents and wind. In-situ temperature measurements provide the context for the vertical structure of the mixing and its impact on the skin SST. Furthermore, comparisons to satellite-derived sea surface temperature of the region are presented. The accuracy of satellite derived SST products and how well the observed skin SSTs represent ocean bulk temperatures in polar regions is not well understood, due in part to lack of observations. Estimated error in the polar seas is relatively high at up to 0.4 deg. C compared to less than 0.2 deg. C for other areas. The goal of these and future analyses of the MIZOPEX data set is to elucidate a basic question that is significant for the entire Earth system. Have these regions passed a tipping point, such that they are now essentially acting as sub-Arctic seas where ice disappears in summer, or instead whether the changes are transient, with the potential for the ice pack to recover?

Zappa, C. J.; Brown, S.; Emery, W. J.; Adler, J.; Wick, G. A.; Steele, M.; Palo, S. E.; Walker, G.; Maslanik, J. A.

2013-12-01

94

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

NASA Astrophysics Data System (ADS)

We investigate the large-scale oceanic features determining the future ice shelf-ocean interaction by analyzing global warming experiments in a coarse resolution climate model with a comprehensive ocean component. Heat and freshwater fluxes from basal ice shelf melting (ISM) are parameterized following Beckmann and Goosse [Ocean Model 5(2):157-170, 2003]. Melting sensitivities to the oceanic temperature outside of the ice shelf cavities are varied from linear to quadratic (Holland et al. in J Clim 21, 2008). In 1% per year CO2-increase experiments the total freshwater flux from ISM triples to 0.09 Sv in the linear case and more than quadruples to 0.15 Sv in the quadratic case after 140 years at which 4 280 ppm = 1,120 ppm was reached. Due to the long response time of subsurface temperature anomalies, ISM thereafter increases drastically, if CO2 concentrations are kept constant at 1,120 ppm. Varying strength of the Antarctic circumpolar current (ACC) is crucial for ISM increase, because southward advection of heat dominates the warming along the Antarctic coast. On centennial timescales the ACC accelerates due to deep ocean warming north of the current, caused by mixing of heat along isopycnals in the Southern Ocean (SO) outcropping regions. In contrast to previous studies we find an initial weakening of the ACC during the first 150 years of warming. This purely baroclinic effect is due to a freshening in the SO which is consistent with present observations. Comparison with simulations with diagnosed ISM but without its influence on the ocean circulation reveal a number of ISM-related feedbacks, of which a negative ISM-feedback, due to the ISM-related local oceanic cooling, is the dominant one.

Hattermann, Tore; Levermann, Anders

2010-10-01

95

Identification of Ancient Feather Fragments Found in Melting Alpine Ice Patches in Southern Yukon  

Microsoft Academic Search

Twelve ancient artifacts or fragmented feather samples recovered from melting alpine ice patches in southern Yukon were analyzed in order to identify the species of birds associated with the ice patches or used on weapons recovered from these sites. The identification of bird species used by ancient hunters as long ago as 4500 BP enhances our insight into the customs,

CARLA J. DOVE; P. GREGORY HARE; MARCY HEACKER

2005-01-01

96

Perception of Melting and Flavor Release of Ice Cream Containing Different Types and Contents of Fat  

Microsoft Academic Search

Temporal effects of dairy and vegetable fats (0 to 18%) on perception of strawberry flavor release and melting of ice cream were studied using the time inten- sity sensory method. Also, aroma and flavor attributes of the ice cream samples were evaluated. Only slight effects of fat on the rate of flavor release and flavor intensity wereperceived. Aslightly fasterflavor release

L. Hyvnen; M. Linna; H. Tuorila; G. Dijksterhuis

2003-01-01

97

Mechanisms of summertime upper Arctic Ocean warming and the effect on sea ice melt  

Microsoft Academic Search

In this study, we use a numerical sea-ice-ocean model to examine what causes summertime upper ocean warming and sea ice melt during the 21st century in the Arctic Ocean. Our first question is, What causes the ocean to warm in the Pacific Sector during the summer? We find that about 80% of total heating over this region comes from ocean

Michael Steele; Jinlun Zhang; Wendy Ermold

2010-01-01

98

Anisotropic elastocreep in glacial ice: A mechanism for intergranular melt and recrystallization  

Microsoft Academic Search

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

Steven M. Jepsen; Edward E. Adams

2008-01-01

99

Efficacy of sanitized ice in reducing bacterial load on fish fillet and in the water collected from the melted ice.  

PubMed

This study investigated the efficacy of sanitized ice for the reduction of bacteria in the water collected from the ice that melted during storage of whole and filleted Tilapia fish. Also, bacterial reductions on the fish fillets were investigated. The sanitized ice was prepared by freezing solutions of PRO-SAN (an organic acid formulation) and neutral electrolyzed water (NEW). For the whole fish study, the survival of the natural microflora was determined from the water of the melted ice prepared with PRO-SAN and tap water. These water samples were collected during an 8 h storage period. For the fish fillet study, samples were inoculated with Escherichia coli K12, Listeria innocua, and Pseudomonas putida then stored on crushed sanitized ice. The efficacies of these were tested by enumerating each bacterial species on the fish fillet and in the water samples at 12 and 24 h intervals for 72 h, respectively. Results showed that each bacterial population was reduced during the test. However, a bacterial reduction of < 1 log CFU was obtained for the fillet samples. A maximum of approximately 2 log CFU and > 3 log CFU reductions were obtained in the waters sampled after the storage of whole fish and the fillets, respectively. These reductions were significantly (P < 0.05) higher in the water from sanitized ice when compared with the water from the unsanitized melted ice. These results showed that the organic acid formulation and NEW considerably reduced the bacterial numbers in the melted ice and thus reduced the potential for cross-contamination. PMID:20546415

Feliciano, Lizanel; Lee, Jaesung; Lopes, John A; Pascall, Melvin A

2010-05-01

100

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

NASA Astrophysics Data System (ADS)

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, 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 perturbations to the surface and sub-shelf mass balance forcing fields from our 2000 yr "reference" model run indicate that both the Institute and Mller 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 Rutford, Carlson or Foundation ice streams, while Evans Ice Stream is found to enter a phase of unstable retreat only after melt at its grounding line has increased by an order-of-magnitude from likely present-day values.

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

2013-11-01

101

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

NASA Technical Reports Server (NTRS)

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.

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

2012-01-01

102

Snow Dunes: A Controlling Factor of Melt Pond Distribution on Arctic Sea Ice  

NASA Technical Reports Server (NTRS)

The location of snow dunes over the course of the ice-growth season 2007/08 was mapped on level landfast first-year sea ice near Barrow, Alaska. Landfast ice formed in mid-December and exhibited essentially homogeneous snow depths of 4-6 cm in mid-January; by early February distinct snow dunes were observed. Despite additional snowfall and wind redistribution throughout the season, the location of the dunes was fixed by March, and these locations were highly correlated with the distribution of meltwater ponds at the beginning of June. Our observations, including ground-based light detection and ranging system (lidar) measurements, show that melt ponds initially form in the interstices between snow dunes, and that the outline of the melt ponds is controlled by snow depth contours. The resulting preferential surface ablation of ponded ice creates the surface topography that later determines the melt pond evolution.

Petrich, Chris; Eicken, Hajo; Polashenski, Christopher M.; Sturm, Matthew; Harbeck, Jeremy P.; Perovich, Donald K.; Finnegan, David C.

2012-01-01

103

Regional and temporal variations in the formation of supraglacial melt ponds on the Greenland Ice Sheet  

NASA Astrophysics Data System (ADS)

Surface melt ponds form seasonally in the ablation zone of the Greenland Ice Sheet and they have been shown to provide the sites for the hydrofracture initiation of the moulins required for supraglacial meltwater to reach the bed of the Greenland Ice Sheet (Das et al., 2008). Studies to date have been restricted to a region of large surface lakes surrounding the Jakobshavn Isbrae catchment area (Box and Ski, 2007). However, large surface lakes also develop seasonally in other areas of the ice sheet, especially in the northern regions. We have developed a high temporal resolution dataset of lake evolution and drainage in all of the regions of the Greenland Ice Sheet where large surface lakes develop during summer. This study spans the period 2001-2008 using approximately 200 MODIS scenes per melt season per region. We show that there are significant regional differences in the supraglacial hydrology of the ice sheet, which could cause spatial variations in the role of melt water in ice dynamics across Greenland as it responds to the warming climate. Das, S., Joughin, M., Behn, M., Howat, I., King, M., Lizarralde, D., Bhatia, M., 2008. Fracture propagation to the base of the Greenland Ice Sheet during supra-glacial lake drainage, Science, 5877, p.778-781. Box, J., and Ski, K., 2007. Remote sounding of Greenland supraglacial melt lakes: implications for subglacial hydraulics. J. Glaciol., 53(181), p. 257-265.

Selmes, N.; Murray, T.; James, T. D.

2009-04-01

104

Summer temperature trend over the past two millennia using air content in Himalayan ice  

NASA Astrophysics Data System (ADS)

Two Himalayan ice cores display a factor-two decreasing trend of air content over the past two millennia, in contrast to the relatively stable values in Greenland and Antarctica ice cores over the same period. Because the air content can be related with the relative frequency and intensity of melt phenomena, its variations along the Himalayan ice cores provide an indication of summer temperature trend. Our reconstruction point toward an unprecedented warming trend in the 20th century but does not depict the usual trends associated with "Medieval Warm Period" (MWP), or "Little Ice Age" (LIA).

Hou, S.; Chappellaz, J.; Jouzel, J.; Chu, P. C.; Masson-Delmotte, V.; Qin, D.; Raynaud, D.; Mayewski, P. A.; Lipenkov, V. Y.; Kang, S.

2007-02-01

105

Summer temperature trend over the past two millennia using air content in Himalayan ice  

NASA Astrophysics Data System (ADS)

Two Himalayan ice cores display a factor-two decreasing trend of air content over the past two millennia, in contrast to the relatively stable values in Greenland and Antarctica ice cores over the same period. Because the air content can be related with the relative frequency and intensity of melt phenomena, its variations along the Himalayan ice cores provide an indication of summer temperature trend. Our reconstruction point toward an unprecedented warming trend in the 20th century but does not depict the usual trends associated with "Medieval Warm Period" (MWP), or "Little Ice Age" (LIA).

Hou, S.; Chappellaz, J.; Jouzel, J.; Chu, P. C.; Masson-Delmotte, V.; Qin, D.; Raynaud, D.; Mayewski, P. A.; Lipenkov, V. Y.; Kang, S.

2005-09-01

106

Molecular transport and phase transition of polycrystalline ice doped with HCl and SO2 near its melting point  

NASA Astrophysics Data System (ADS)

HCl and SO2 are major trace gases in atmosphere, which greatly affects chemical properties of atmospheric ice particles. A particular interest to atmospheric science is the effects of impurities on molecular transport and phase transition at grain boundaries in polycrystalline ice. Effects of doped HCl and SO2 on transport and phase transition at grain boundary of 2-4 micrometer polycrystalline ice were studied using a novel technique - Fast Thermal Desorption Spectroscopy (FTDS) [1] in the temperature range from -2 to -20 deg. C. In these experiments, H2O/D2O/H2O sandwich-like polycrystalline ice films doped with HCl and SO2 were vapor- deposited on the surface of a thin filament positioned in a vacuum chamber and maintained initially at cryogenic temperatures. After the deposition, the temperature of the filament was rapidly raised to a value near ice melting point, thus, initiating rapids H/D exchange reaction at the interface of H2O and D2O layers. Diffusion controlled rate of isotopic exchange in the desorbing film was monitored with a sensitive mass-spectrometer making it possible to gain quantitative information of the extent of diffusion of chemical species along the grain boundaries in polycrystalline ice samples. Comparisons of the experimental results in pure and doped polycrystalline ice show that water self diffusivity at the grain boundaries is significantly enhanced (by at least an order of magnitude) in the presence of HCl or SO2. The strong, non- Arrhenius, dependence of the water self-diffusivity on temperature indicates that this is due to grain boundary premelting [2], which may occur at temperatures as low as 10 deg. below ice melting point. We will discuss implication of this and other results of our FTDS experiments to various environmental phenomena. References: 1. Haiping Lu, Stephanie A. McCartney, M. Chonde, D. Smyla, and Vlad Sadtchenko, Fast thermal desorption spectroscopy study of morphology and vaporization kinetics of polycrystalline ice films, J. Chem. Phys., 125, 044709, 2006. 2. Dash, J.G., A.W. Rempel and J.S. Wettlaufer, The physics of premelted ice and its geophysical consequences, Rev. Mod. Phys., 78, 695, 2006.

Lu, H.; McCartney, S.; Sadtchenko, V.

2007-12-01

107

Continuous monitoring of Antarctic sub-ice shelf dynamics and ocean column temperatures  

NASA Astrophysics Data System (ADS)

Monitoring of ice shelf dynamics and sub-ice shelf ocean processes represents an important, but challenging step in understanding the dynamics of ice sheet behavior. In November 2011, a set of moorings through the McMurdo Ice Shelf at Windless Bight were installed to develop new installation and monitoring tools for understanding sub-ice shelf conditions. The mooring consists of fiber optic cables for distributed temperature sensing (DTS) extending from the surface, through 190m of ice shelf and to a depth of ~920m through the water column along with pressure transducer and independent thermistor strings. With DTS, temperature measurements are made every meter along the fiber optic cable. A continuous in time and depth temperature record was collected from late November 2011 through June 2012. A total of 5.5 million data points of temperature have been collected to date. The temperature record for the water column beneath the ice shelf clearly shows the intrusion of warm currents ( > -1.75 C) under the ice shelf starting in late January and remaining present into May. Observed warming continues down through the water column into March, reaching depths of ~200m below the ice-ocean interface. The maximum recorded temperature occurred on March 7th and was -1.09 C, indicating a maximum warming of ~0.8 C. From March through May the water column began to cool back to the early spring isothermal condition of -1.9 C. Temperature profiles within the shelf ice indicate a long-term basal melt rate of ~1 m/yr, preliminary observations from the ocean-ice interface show similar melt rates. The system is currently in a depowered state and will be revisited in the following field season.

Kobs, S.; Tyler, S. W.; Zagorodnov, V.; Holland, D. M.; Stern, A.; Sledek, C.; Bryenton, J.

2012-12-01

108

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

NASA Technical Reports Server (NTRS)

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.

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

2001-01-01

109

Thermohaline circulation below the Ross Ice Shelf - A consequence of tidally induced vertical mixing and basal melting  

NASA Technical Reports Server (NTRS)

The warmest water below parts of the Ross Ice Shelf resides in the lowest portion of the water column because of its high salinity. Vertical mixing caused by tidal stirring can thus induce ablation by lifting the warm but dense water into contact with the ice shelf. A numerical tidal simulation indicates that vertically well-mixed conditions predominate in the southeastern part of the sub-ice shelf cavity, where the water column thickness is small. Basal melting in this region is expected to be between 0.05 and 0.5 m/yr and will drive a thermohaline circulation having the following characteristics: high salinity shelf water (at - 1.8 C), formed by winter sea ice production in the open Ross Sea, flows along the seabed toward the tidal mixing fronts below the ice shelf; and meltwater (at -2.2 C), produced in the well-mixed region, flows out of the sub-ice shelf cavity along the ice shelf bottom. Sensitivity of this ablation process to climatic change is expected to be small because high salinity shelf water is constrained to have the sea surface freezing temperature.

Macayeal, D. R.

1984-01-01

110

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

E-print Network

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

Long, David G.

111

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

SciTech Connect

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?1.5110{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.

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

112

The influence of coastal polynyas on the basal melting of ice shelves.  

NASA Astrophysics Data System (ADS)

The dense water production from coastal polynyas can strongly modify local circulation patterns with implications for both net basal melting of ice shelves and dense water formation. Results are presented from two different ice-shelf/ocean models: one of the Amery Ice Shelf/Prydz Bay region; and one of the Mertz Glacier Ice Tongue region. The models are based on the Regional Ocean Modeling System (ROMS). Two important modifications have been made to improve the simulation of thermodynamic processes beneath ice shelves: the inclusion of direct basal melt/freeze processes; and the inclusion of frazil ice dynamics. The models are forced with tides and with a smoothy varying seasonal cycle of winds. Thermohaline and circulation fields are relaxed to a smoothly varying seasonal climatology at the lateral boundaries. The open ocean surface fluxes are modified by an imposed climatological sea-ice cover that includes the seasonal effect of polynyas. It was found that the Prydz Bay gyre and Mertz gyre are summertime features. Both the strength and direction of the gyres are controlled by the production of dense water from local coastal polynyas. The production of dense water creates a current that blocks the westward flowing coastal current and diverts it northward away from the coast. For the Amery region, the coastal current bypasses the Amery Ice Shelf and flows out of the Prydz Bay channel and westward along the slope front. During summer, when the polynyas in Prydz Bay are inactive, Modified Circumpolar Deep Water (MCDW) is entrained with the eastward flowing coastal current as part of the gyre circulation. Observations of sea-ice confirm the presence of the Prydz Bay gyre under these conditions. The melt rates are higher in winter (~0.8 m ice per year) compared with summer (~0.7 m ice per year). The melting is primarily driven by dense shelf waters, with sufficient negative bouyancy, that drain to the deepest parts of the ice shelf at ~2500m below mean sea level. Preliminary studies of the Mertz region show that times of highest basal melting correspond to the summertime movement of MCDW onto the shelf from the deep ocean. The model shows that the circulation in the Mertz depression is controlled seasonally by the formation of dense water that is formed in the polynya. The Mertz polynya also acts to block the movement of MCDW onto the shelf region and thus leads to lower melt rates during winter. Simulations that include a dynamic sea-ice model, without accounting for the effect of subgrid scale features, such as coastal polynyas, can potentially underestimate the production of dense shelf water, which has consequences for the basal melting of ice shelves. This research contributes to understanding how interaction between ice shelves and various forcing mechanisms can lead to changes in basal melt/freeze and dense water formation, which has major implications for the stability of ice shelves, sea level rise, and the salt budget of the global oceans.

Galton-Fenzi, Benjamin; Marsland, Simon; Meijers, Andrew; Fraser, Alex

2010-05-01

113

New insights into ice growth and melting modifications by  

E-print Network

proteins 1. INTRODUCTION The adaptation of organisms to cold environments has led to the evolution, and sudden, fast ice-growth occurs. Since the first observation of AFGPs in the serum of Antarctic fishes [14

Wettlaufer, John S.

114

Modelling the impact of ocean warming on melting and water masses of ice shelves in the Eastern Weddell Sea  

NASA Astrophysics Data System (ADS)

The Eastern Weddell Ice Shelves (EWIS) are believed to modify the water masses of the coastal current and thus preconditions the water mass formation in the southern and western Weddell Sea. We apply various ocean warming scenarios to investigate the impact on the temperature-salinity distribution and the sub-ice shelf melting in the Eastern Weddell Sea. In our numerical experiments, the warming is imposed homogeneously along the open inflow boundaries of the model domain, leading to a warming of the warm deep water (WDW) further downstream. Our modelling results indicate a weak quadratic dependence of the melt rate at the ice shelf base on the imposed amount of warming, which is consistent with earlier studies. The total melt rate has a strong dependence on the applied ocean warming depth. If the warming is restricted to the upper ocean (above 1,000 m), the water column (aside from the mixed surface layer) in the vicinity of the ice shelves stabilises. Hence, reduced vertical mixing will reduce the potential of Antarctic Bottom Water formation further downstream with consequences on the global thermohaline circulation. If the warming extends to the abyss, the WDW core moves significantly closer to the continental shelf break. This sharpens the Antarctic Slope Front and leads to a reduced density stratification. In contrast to the narrow shelf bathymetry in the EWIS region, a wider continental shelf (like in the southern Weddell Sea) partly protects ice shelves from remote ocean warming. Hence, the freshwater production rate of, e.g., the Filchner-Ronne Ice Shelf increases much less compared with the EWIS for identical warming scenarios. Our study therefore indicates that the ice-ocean interaction has a significant impact on the temperature-salinity distribution and the water column stability in the vicinity of ice shelves located along a narrow continental shelf. The effects of ocean warming and the impact of increased freshwater fluxes on the circulation are of the same order of magnitude and superimposed. Therefore, a consideration of this interaction in large-scale climate studies is essential.

Thoma, Malte; Grosfeld, Klaus; Makinson, Keith; Lange, Manfred A.

2010-06-01

115

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

NASA Technical Reports Server (NTRS)

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.

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

2004-01-01

116

Thermal equivalence of DNA duplexes without calculation of melting temperature  

E-print Network

DNA is the hybridization and melting of the double helix: from transmission of genetic information very intensive and may require sophisticated searching algorithms6 . On the other hand, many of melting/hybridization temperatures. Instead of calculating the temperature, we investigate the question

Loss, Daniel

117

Massively parallel molecular-dynamics simulation of ice crystallisation and melting: the roles of system size, ensemble, and electrostatics.  

PubMed

Ice crystallisation and melting was studied via massively parallel molecular dynamics under periodic boundary conditions, using approximately spherical ice nano-particles (both "isolated" and as a series of heterogeneous "seeds") of varying size, surrounded by liquid water and at a variety of temperatures. These studies were performed for a series of systems ranging in size from ?1 10(6) to 8.6 10(6) molecules, in order to establish system-size effects upon the nano-clusters" crystallisation and dissociation kinetics. Both "traditional" four-site and "single-site" and water models were used, with and without formal point charges, dipoles, and electrostatics, respectively. Simulations were carried out in the microcanonical and isothermal-isobaric ensembles, to assess the influence of "artificial" thermo- and baro-statting, and important disparities were observed, which declined upon using larger systems. It was found that there was a dependence upon system size for both ice growth and dissociation, in that larger systems favoured slower growth and more rapid melting, given the lower extent of "communication" of ice nano-crystallites with their periodic replicae in neighbouring boxes. Although the single-site model exhibited less variation with system size vis--vis the multiple-site representation with explicit electrostatics, its crystallisation-dissociation kinetics was artificially fast. PMID:25527942

English, Niall J

2014-12-21

118

Massively parallel molecular-dynamics simulation of ice crystallisation and melting: The roles of system size, ensemble, and electrostatics  

NASA Astrophysics Data System (ADS)

Ice crystallisation and melting was studied via massively parallel molecular dynamics under periodic boundary conditions, using approximately spherical ice nano-particles (both "isolated" and as a series of heterogeneous "seeds") of varying size, surrounded by liquid water and at a variety of temperatures. These studies were performed for a series of systems ranging in size from 1 106 to 8.6 106 molecules, in order to establish system-size effects upon the nano-clusters" crystallisation and dissociation kinetics. Both "traditional" four-site and "single-site" and water models were used, with and without formal point charges, dipoles, and electrostatics, respectively. Simulations were carried out in the microcanonical and isothermal-isobaric ensembles, to assess the influence of "artificial" thermo- and baro-statting, and important disparities were observed, which declined upon using larger systems. It was found that there was a dependence upon system size for both ice growth and dissociation, in that larger systems favoured slower growth and more rapid melting, given the lower extent of "communication" of ice nano-crystallites with their periodic replicae in neighbouring boxes. Although the single-site model exhibited less variation with system size vis--vis the multiple-site representation with explicit electrostatics, its crystallisation-dissociation kinetics was artificially fast.

English, Niall J.

2014-12-01

119

Melt anomalies on the Greenland Ice Sheet and large scale modes of atmospheric circulation  

NASA Astrophysics Data System (ADS)

The relationships between inter annual melt variability in Greenland and large scale atmospheric circulation are explored based on an empirical orthogonal function (EOF) analysis of melt in Greenland derived from passive microwave satellite observations. The first EOF of the melt anomalies was found to be highly representative of the spatial and temporal distribution of melt anomalies accounting for over 34% of the variability and the principal component (PC) time series is 98% correlated with the annual total melt extent time series. The leading melt PC is highly correlated with key features of the large scale atmospheric circulation both in the vicinity of Greenland and regions that are well removed. Some aspects of the atmospheric pressure anomaly fields related to melt in Greenland are congruent with the summer expression of the AO/NAO including the main center of action east of Greenland, however there are features of the melt related anomaly field that are not. During peak melt years there is a decrease in the pressure gradient between the Bearing Sea and more southerly latitudes resulting in a redistribution of the central Arctic low pressure toward the Pacific side of the Arctic basin. This pattern is expressed as a 50% correlation between melt in Greenland and the phase of planetary pressure wave #1 and #2 north of 50 N. The storm tracks related to increased melt in Greenland result in increased summer storm activity to the south and west of Greenland balanced by decreased cyclonic activity to the east and north. Comparison with the NAO related storm track highlights key differences relative to the melt related atmospheric circulation that lead to increased southerly flow directly into Greenland during years with increased melt. The pattern of summer sea ice concentration anomalies linked to the melt PC is remarkably similar to the spatial pattern of recent sea ice decline. The pattern of circulation anomalies associated with increased melt in Greenland likely accounts for some of the continued decline in sea ice concentrations in recent years particularly in the Beaufort Sea.

Huff, Russell

120

Effect of Salts on the Properties of Aqueous Sugar Systems, in Relation to Biomaterial Stabilization. 1. Water Sorption Behavior and Ice Crystallization\\/Melting  

Microsoft Academic Search

Trehalose and sucrose, two sugars that are involved in the protection of living organisms under extreme conditions, and their mixtures with salts were employed to prepare supercooled or freeze-dried glassy systems. The objective of the present work was to explore the effects of different salts on water sorption, glass transition temperature (Tg), and formation and melting of ice in aqueous

M. F. Mazzobre; M. P. Longinotti; H. R. Corti; M. P. Buera

2001-01-01

121

Empirical Retrieval of Surface Melt Magnitude from Coupled MODIS Optical and Thermal Measurements over the Greenland Ice Sheet during the 2001 Ablation Season  

PubMed Central

Accelerated ice flow near the equilibrium line of west-central Greenland Ice Sheet (GIS) has been attributed to an increase in infiltrated surface melt water as a response to climate warming. The assessment of surface melting events must be more than the detection of melt onset or extent. Retrieval of surface melt magnitude is necessary to improve understanding of ice sheet flow and surface melt coupling. In this paper, we report on a new technique to quantify the magnitude of surface melt. Cloud-free dates of June 10, July 5, 7, 9, and 11, 2001 Moderate Resolution Imaging Spectroradiometer (MODIS) daily reflectance Band 5 (1.230-1.250?m) and surface temperature images rescaled to 1km over western Greenland were used in the retrieval algorithm. An optical-thermal feature space partitioned as a function of melt magnitude was derived using a one-dimensional thermal snowmelt model (SNTHERM89). SNTHERM89 was forced by hourly meteorological data from the Greenland Climate Network (GC-Net) at reference sites spanning dry snow, percolation, and wet snow zones in the Jakobshavn drainage basin in western GIS. Melt magnitude or effective melt (E-melt) was derived for satellite composite periods covering May, June, and July displaying low fractions (0-1%) at elevations greater than 2500m and fractions at or greater than 15% at elevations lower than 1000m assessed for only the upper 5 cm of the snow surface. Validation of E-melt involved comparison of intensity to dry and wet zones determined from QSCAT backscatter. Higher intensities (> 8%) were distributed in wet snow zones, while lower intensities were grouped in dry zones at a first order accuracy of ? 2%.

Lampkin, Derrick; Peng, Rui

2008-01-01

122

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

Microsoft Academic Search

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

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

2010-01-01

123

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

NASA Astrophysics Data System (ADS)

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.

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

2014-09-01

124

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

PubMed

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

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

2014-01-01

125

Aragonite Undersaturation in the Arctic Ocean: Effects of Ocean Acidification and Sea Ice Melt  

Microsoft Academic Search

The increase in anthropogenic carbon dioxide emissions and attendant increase in ocean acidification and sea ice melt act together to decrease the saturation state of calcium carbonate in the Canada Basin of the Arctic Ocean. In 2008, surface waters were undersaturated with respect to aragonite, a relatively soluble form of calcium carbonate found in plankton and invertebrates. Undersaturation was found

Michiyo Yamamoto-Kawai; Fiona A. McLaughlin; Eddy C. Carmack; Shigeto Nishino; Koji Shimada

2009-01-01

126

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

Microsoft Academic Search

Vegetation structure was surveyed in gullies developed by the melting of ice wedges along the Kolyma River, northern Siberia, using 7250 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

Shiro Tsuyuzaki; Takeshi Ishizaki; Toshiyuki Sato

1999-01-01

127

Surface melting on antarctic peninsula ice shelves detected by passive microwave sensors  

Microsoft Academic Search

A 13 year time series of spaceborne passive microwave radiance measurements over the Antarctic Peninsula ice shelves, reveals a systematic increase in the duration of the summer melt season. Combined with data from meteorological stations on the Antarctic Peninsula, the annual motion and long-term trends of the 0 C isotherm can be monitored.

Jeff Ridley

1993-01-01

128

Simulation of ice speedup events in Greenland from seasonal surface melt signals via explicit modelling of basal water pressure  

NASA Astrophysics Data System (ADS)

We model the glacial dynamic response of Greenland to seasonal patterns of surface melt. Our aim is to produce a model that can explain a number of aspects of observed speed-up behaviour in Greenland. These include: a seasonal acceleration of ice, differing speed-up of outlet and land terminating ice, and inter-annual variability of sliding velocity. The model is based on an ice-sheet scale model of basal water pressure HYDRO, originally developed to consider basal melt inputs to the subglacial environment. This is coupled to the community ice sheet model GLIMMER, via two principle mechanisms. First, the basal water pressure is incorporated into a function to describe a basal drag coefficient. This in turn is used in a sliding law which has a linear dependence on shear stress. Second, the model also defines a friction coefficient which explicitly defines basal heating rates as a function of basal ice velocity and water pressure. Water pressure distribution is predicted by resolving large-scale water production and flow over the ice sheet domain driven by hydraulic pressure gradients. This is based on a simple Darcian expression, but the model has the capacity to represent areas of efficient and inefficient flow by modifying the overall basal hydraulic conductivity as a function of water flux. Thus with high water throughput, the model can switch to an efficient mode, serving as a simple large-scale proxy to the development of basal water conduits without explicit specification of the system. The bed becomes impermeable where it is frozen. The surface system is coupled to the basal model by, a) developing a simple expression to pond any surface melt locally on the ice sheet surface (surface flow is omitted for simplicity) b) developing a simple proxy mechanism to hydrofracturing by allowing ponded water to reach the bed instantaneously once its depth is greater than a specific threshold, but controlled probabilistically c) such water is then included as if it were instantaneous basal melt. d) any further melt in the same season goes directly to the bed. An approximation to present Greenland is first modelled assuming quasi-equilibrium with present climate. This provides an ice temperature field and initial basal pressure regime. The model is then run for a further period using monthly time steps and surface water inputs. In doing so we can demonstrate a variety of speed-up behaviour at the margin linked to seasonal melt patterns. Given there is no explicit description of longitudinal stresses in the model we show a) a small response inland from where water reaches the bed, b) seasonal speed-up in some margins, but less so in those which already experience low effective pressures (e.g. Ilulissat), c) multi-seasonal pressure build-up and speed-up in some areas, d) a relative insensitivity to the overall magnitude of surface melt input fluxes but complex behaviour resulting from the triggered inclusion of surface water into the basal system.

Karatay, Mehmet; Hulton, Nick

2010-05-01

129

Cenozoic ice volume and temperature simulations with a 1-D ice-sheet model  

Microsoft Academic Search

Ice volume and temperature for the past 35 Million years is investigated with a 1-D ice-sheet model, simulating ice-sheets on both hemispheres. The simulations include two continental Northern Hemisphere (NH) ice-sheets representative for glaciation on the two major continents, i.e. Eurasia (EAZ) and North America (NAM). Antarctic glaciation is simulated with two separate ice-sheets, respectively for West and East Antarctica.

B. de Boer; R. Bintanja; L. J. Lourens; E. Tuenter

2009-01-01

130

Aragonite Undersaturation in the Arctic Ocean: Effects of Ocean Acidification and Sea Ice Melt  

NASA Astrophysics Data System (ADS)

The increase in anthropogenic carbon dioxide emissions and attendant increase in ocean acidification and sea ice melt act together to decrease the saturation state of calcium carbonate in the Canada Basin of the Arctic Ocean. In 2008, surface waters were undersaturated with respect to aragonite, a relatively soluble form of calcium carbonate found in plankton and invertebrates. Undersaturation was found to be a direct consequence of the recent extensive melting of sea ice in the Canada Basin. In addition, the retreat of the ice edge well past the shelf-break has produced conditions favorable to enhanced upwelling of subsurface, aragonite-undersaturated water onto the Arctic continental shelf. Undersaturation will affect both planktonic and benthic calcifying biota and therefore the composition of the Arctic ecosystem.

Yamamoto-Kawai, Michiyo; McLaughlin, Fiona A.; Carmack, Eddy C.; Nishino, Shigeto; Shimada, Koji

2009-11-01

131

Method For Synthesizing Extremely High-Temperature Melting Materials  

DOEpatents

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.

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

2005-11-22

132

Method for synthesizing extremely high-temperature melting materials  

DOEpatents

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.

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

2007-11-06

133

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

USGS Publications Warehouse

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.

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

2004-01-01

134

Velocity of sound in solid methane near melting temperatures  

E-print Network

VELOCITY OF SOUND IN SOLID METHANE NEAR MELTING TEMPERATURES A Thesis By JOHN MARTIN WHITEHEAD Submitted to the Graduate College of the Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE May... 1968 Ma)or Sub)ect: Physics VELOCITY OF SOVND IN SOLID METHANE NEAR MELTING TEMPERATURES A Thesis By JOHN MARTIN WHITEHEAD Approved as to style and content by& (Chairman of Committee) (Head of Departsmnt) (Mem er (Member) May 1968...

Whitehead, John Martin

2012-06-07

135

Local effects of ice floes and leads on skin sea surface temperature, mixing and gas transfer in the marginal ice zone  

NASA Astrophysics Data System (ADS)

Recent years have seen extreme changes in the Arctic. Marginal ice zones (MIZ), or areas where the "ice-albedo feedback" driven by solar warming is highest and ice melt is extensive, may provide insights into the extent of these changes. Furthermore, MIZ play a central role in setting the air-sea CO2 balance making them a critical component of the global carbon cycle. Incomplete understanding of how the sea-ice modulates gas fluxes renders it difficult to estimate the carbon budget in MIZ. Here, we investigate the turbulent mechanisms driving gas exchange in leads, polynyas and in the presence of ice floes using both field and laboratory measurements. Here, we present measurements of visible and IR imagery of melting ice floes in the marginal ice zone north of Oliktok Point AK in the Beaufort Sea made during the Marginal Ice Zone Ocean and Ice Observations and Processes EXperiment (MIZOPEX) in July-August 2013. The visible and IR imagery were taken from the unmanned airborne vehicle (UAV) ScanEagle. The visible imagery clearly defines the scale of the ice floes. The IR imagery show distinct cooling of the skin sea surface temperature (SST) as well as an intricate circulation and mixing pattern that depends on the surface current, wind speed, and near-surface vertical temperature/salinity structure. Individual ice floes develop turbulent wakes as they drift and cause transient mixing of an influx of colder surface (fresh) melt water. We capture a melting and mixing event that explains the changing pattern observed in skin SST and is substantiated using laboratory experiments. The Gas Transfer through Polar Sea Ice experiment was performed at the US Army Cold Regions Research and Engineering Laboratory (Hanover, NH) under varying ice coverage, winds speed, fetch and currents. Supporting measurements were made of air and water temperature, humidity, salinity and wave height. Air-side profiling provided momentum, heat, and CO2 fluxes. Transfer velocities are also estimated via the active controlled flux technique. Surface turbulence statistics derived from PIV and optical flow applied to infrared imagery are linked to subsurface turbulence and used to investigate how turbulent mechanisms at the ice-water boundary including shear and buoyancy contribute to the magnitude of the transfer. Gas exchange variability with lead size and enhancement near floes will be examined. Thanks are due to the entire MIZOPEX Team.

Zappa, Christopher; Brumer, Sophia; Brown, Scott; LeBel, Deborah; McGillis, Wade; Schlosser, Peter; Loose, Brice

2014-05-01

136

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

NASA Astrophysics Data System (ADS)

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.

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

137

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

NASA Technical Reports Server (NTRS)

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.

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

1997-01-01

138

Arctic warming: nonlinear impacts of sea-ice and glacier melt on seabird foraging.  

PubMed

Arctic climate change has profound impacts on the cryosphere, notably via shrinking sea-ice cover and retreating glaciers, and it is essential to evaluate and forecast the ecological consequences of such changes. We studied zooplankton-feeding little auks (Alle alle), a key sentinel species of the Arctic, at their northernmost breeding site in Franz-Josef Land (80N), Russian Arctic. We tested the hypothesis that little auks still benefit from pristine arctic environmental conditions in this remote area. To this end, we analysed remote sensing data on sea-ice and coastal glacier dynamics collected in our study area across 1979-2013. Further, we recorded little auk foraging behaviour using miniature electronic tags attached to the birds in the summer of 2013, and compared it with similar data collected at three localities across the Atlantic Arctic. We also compared current and historical data on Franz-Josef Land little auk diet, morphometrics and chick growth curves. Our analyses reveal that summer sea-ice retreated markedly during the last decade, leaving the Franz-Josef Land archipelago virtually sea-ice free each summer since 2005. This had a profound impact on little auk foraging, which lost their sea-ice-associated prey. Concomitantly, large coastal glaciers retreated rapidly, releasing large volumes of melt water. Zooplankton is stunned by cold and osmotic shock at the boundary between glacier melt and coastal waters, creating new foraging hotspots for little auks. Birds therefore switched from foraging at distant ice-edge localities, to highly profitable feeding at glacier melt-water fronts within <5km of their breeding site. Through this behavioural plasticity, little auks maintained their chick growth rates, but showed a 4% decrease in adult body mass. Our study demonstrates that arctic cryosphere changes may have antagonistic ecological consequences on coastal trophic flow. Such nonlinear responses complicate modelling exercises of current and future polar ecosystem dynamics. PMID:25639886

Grmillet, David; Fort, Jrme; Amlineau, Franoise; Zakharova, Elena; Le Bot, Tangi; Sala, Enric; Gavrilo, Maria

2015-03-01

139

Modelling the impact of submarine frontal melting and ice mlange on glacier dynamics  

NASA Astrophysics Data System (ADS)

Two mechanisms are generally proposed to explain seasonal variations in the calving front of tidewater glaciers: submarine melting of the calving face and the mechanical back-force applied by the ice mlange. However, the way these processes affect the calving rate and the glacier dynamics remains uncertain. In this study, we used the finite element model Elmer/Ice to simulate the impact of these forcings on more than 200 two dimensional theoretical flowline glacier configurations. The model, which includes calving processes, suggests that frontal melting affects the position of the terminus only slightly (< a few hundred meters) and does not affect the pluriannual glacier mass balance at all. However, the ice mlange has a greater impact on the advance and retreat cycles of the glacier front (more than several 1000 m) and its consequences for the mass balance are not completely negligible, stressing the need for better characterization of forcing properties. We also show that ice mlange forcing against the calving face can mechanically prevent crevasse propagation at sea level and hence prevent calving. Results also revealed different behaviors in grounded and floating glaciers: in the case of a floating extension, the heaviest forcings can disrupt the glacier equilibrium by modifying its buttressing and ice flux at the grounding line.

Krug, J.; Durand, G.; Gagliardini, O.; Weiss, J.

2015-01-01

140

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)

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.

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

1990-01-01

141

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

USGS Publications Warehouse

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.

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

2004-01-01

142

Water solubility in phonolite melts: Influence of melt composition and temperature  

Microsoft Academic Search

The water solubility in various phonolite melts was determined experimentally at pressures between 50 and 395MPa and at temperatures between 850 and 1200C. The aim of this study was to elucidate to which extent chemical and physical parameters such as relative amounts of alkali and alkaline earth elements or temperature affect the water solubility. For this purpose a total of

Burkhard C. Schmidt; Harald Behrens

2008-01-01

143

Significant melting of ice-wedges and formation of thermocirques on hill-slopes of thermokarst lakes in Central Yakutia (Siberia)  

NASA Astrophysics Data System (ADS)

On Earth, permafrost containing a high ice volume (referred as ice-rich) are sensible to climate change, they have been regionally degraded (thermokarst) during the early Holocene climatic optimum forming numerous thermokarst lakes in Central Yakutia (eastern Siberia). Recent temperature increases in the Arctic and Subarctic have been significantly greater than global averages. The frequency and magnitude of terrain disturbances associated with thawing permafrost are increasing in these regions and are thought to intensify in the future. Therefore, understand how is the current development of thermokarst is a critical question. Here, we describe the significant melting of ice-wedges on slopes of thermokarst lakes that leads to formation of amphitheatrical hollows referred as thermocirques. The evolution of thermocirques in Central Yakutia has been little studied and analyzing their formation could help to understand the recent thermokarst in relation to climate change in Central Yakutia. We studied the thermocirques at two scales: (i) field surveys of different thermocirques in July 2009-2010 and October 2012 to examine the processes and origin of melting of ice-wedges and; (ii) photo-interpretation of time series of satellite images (KH-9 Hexagon images of 6-9 m/pixel and GeoEye images of 50 cm/pixel) to study the temporal evolution of thermocirques. The melting of ground-ice on the scarp of thermocirque triggers falls and small mud-flows that induce the retreat of the scarp parallel to itself. Based on field studies and on GeoEye image comparison, we show that their rate of retrogressive growth is 1-2 m/year. On the hill-slopes of lakes, the thermokarst could be initiated by different processes that lead to the uncover and then melting of ice-wedges: thermal erosion by the waves of the ice-rich bluff; active-layer detachment (a form of slope failure linked to detachment of the seasonally thawed upper ground); flowing of water on the slope (precipitation) or; increase of near-surface temperature (insolation, summer temperature). We suggest that the preferential occurrence of thermocirques on south-facing slopes of lakes could emphasize the role of insolation as a factor controlling the preferential melting of ice-wedges. The air temperatures are shown to have increased in Central Yakutia over years and deciphering if ongoing climate warming could lead to an increased development of thermocirques along lake slopes in Central Yakutia is a question that we will address in future study.

Sjourn, Antoine; Costard, Franois; Gargani, Julien; Fedorov, Alexander; Skorve, Johnny

2013-04-01

144

Basal Melt and Thickness Change of the Antarctic Ice Shelves Revealed by the Lagrangian Elevation Measurement from Satellite Laser Altimetry  

NASA Astrophysics Data System (ADS)

We present a novel method for estimating the elevation change on the Antarctic ice shelves using laser altimetry data from the Ice Cloud and land Elevation Satellite (ICESat; 2003-2009). Unlike the conventional crossover or repeat-track analysis fixed on the geodetic position, we estimate the elevation change rate at points fixed on the surface of moving ice, i.e. in the Lagrangian coordinate system. The ICESat ground tracks are relocated into the Lagrangian coordinate system based on the velocity field from the interferometric synthetic aperture radar (InSAR) and then the elevation change rate is measured from their crossover differences. The thickness change rates converted from the elevation change rates through a hydrostatic formula are applied to the mass conservation equation in the Lagrangian coordinate system, in order to derive the basal melt rate. In Lagrangian approach, the crossover difference is less affected by the small-scale surface relief on the moving ice, which causes the large uncertainty of elevation change rate in the conventional (Eulerian) crossover analysis. The basal melt derived from the mass conservation equation is also less sensitive to the noises of gridded ice thicknesses in the Largrangian approach than in the Eulerian approach. Our analysis provides a reliable map of basal melt rate and thickness change rate in the Antarctic ice shelves, which is a snapshot for the ICESat period. The highest ice thinning rates, accompanying strongest basal melts, are observed in the small ice shelves along the Amundsen Sea coast. In the Ross Ice Shelf, the ice thickness change is mainly controlled by the shutdown of Kamb Ice Stream. The ice thinning is dominant in the Filchner-Ronne Ice Shelf and strong within 150 km from the ice front.

Lee, C.; Seo, K.; Scambos, T.

2012-12-01

145

Quantum Melting of Charge Ice and Non-Fermi-Liquid Behavior: An Exact Solution for the Extended Falicov-Kimball Model in the Ice-Rule Limit  

NASA Astrophysics Data System (ADS)

An exact solution is obtained for a model of itinerant electrons coupled to ice-rule variables on the tetrahedron Husimi cactus, an analogue of the Bethe lattice of corner-sharing tetrahedra. It reveals a quantum critical point with the emergence of non-Fermi-liquid behavior in melting of the charge ice insulator. The electronic structure is compared with the numerical results for the pyrochlore-lattice model to elucidate the physics of electron systems interacting with the tetrahedron ice rule.

Udagawa, Masafumi; Ishizuka, Hiroaki; Motome, Yukitoshi

2010-06-01

146

Effect of Sweetener, Stabilizer, and Storage Temperature on Ice Recrystallization in Ice Cream  

Microsoft Academic Search

ABSTRACT In ice cream manufacturing, control of ice crystal growth,through,proper formulation,and storage tem- perature is important,for stability during storage. The objective of this study was,to investigate the influence of sweetener (sucrose, 20 dextrose equivalent corn syrup, 42 dextrose equivalent corn syrup, and 42 high fructose corn syrup), with and without stabilizer, on ice recrystallization in ice cream,at three storage temperatures.

Tadashi Hagiwara; Richard W. Hartelt

1996-01-01

147

Mixing of the Immiscible: Hydrocarbons in Water-Ice near the Ice Crystallization Temperature.  

PubMed

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

Lignell, Antti; Gudipati, Murthy S

2014-10-27

148

Low melting temperature alloy deployment mechanism and recent experiments  

NASA Technical Reports Server (NTRS)

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.

Madden, M. J.

1993-01-01

149

Effect of ice melting on bacterial carbon fluxes channelled by viruses and protists in the Arctic Ocean  

Microsoft Academic Search

During the last few years, extensive sea ice melting in the Arctic due to climate change has been detected, which could potentially\\u000a modify the organic carbon fluxes in these waters. In this study, the effect of sea ice melting on bacterial carbon channelling\\u000a by phages and protists has been evaluated in the northern Greenland Sea and Arctic Ocean. Grazing on

Julia A. BorasM; M. Montserrat Sala; Jesus M. Arrieta; Elisabet L. S; Jorge Felipe; Susana Agust; Carlos M. Duarte; Dolors Vaqu

2010-01-01

150

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

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

151

Pressure dependence of the melting temperature of metals  

NASA Technical Reports Server (NTRS)

A new method for the analysis of the experimental data for the pressure dependence of the melting temperature of metals is presented. The method combines Lindemann's law, the Debye model, and a first-order equation of state with the experimental observation that the Grueneisen parameter divided by the volume is constant. It is observed that, based on these assumptions, in the absence of phase transitions, plots of the logarithm of the normalized melting temperature versus the logarithm of the normalized pressure are straight lines. It is found that the normalized-melting--temperature versus normalized-pressure curves accurately satisfy the linear relationship for Al, Ag, Au, Cs, Cu, K, Na, Pt, and Rb. In addition, this technique provides a sensitive tool for detecting phase transitions.

Schlosser, Herbert; Vinet, Pascal; Ferrante, John

1989-01-01

152

Polarimetric C-/X-band Synthetic Aperture Radar Observations of Melting Sea Ice in the Canadian Arctic Archipelago  

NASA Astrophysics Data System (ADS)

Operational ice information services rely heavily on space-borne synthetic aperture radar (SAR) data for the production of ice charts to meet their mandate of providing timely and accurate sea ice information to support safe and efficient marine operations. During the summer melt period, the usefulness of SAR data for sea ice monitoring is limited by the presence of wet snow and melt ponds on the ice surface, which can mask the signature of the underlying ice. This is a critical concern for ice services whose clients (e.g. commercial shipping, cruise tourism, resource exploration and extraction) are most active at this time of year when sea ice is at its minimum extent, concentration and thickness. As a result, there is a need to further quantify the loss of ice information in SAR data during the melt season and to identify what information can still be retrieved about ice surface conditions and melt pond evolution at this time of year. To date the majority of studies have been limited to analysis of single-polarization C-band SAR data. This study will investigate the potential complimentary and unique sea ice information that polarimetric C- and X-band SAR data can provide to supplement the information available from traditional single co-polarized C-band SAR data. A time-series of polarimetric C- and X-band SAR data was acquired over Jones Sound in the Canadian Arctic Archipelago, in the vicinity of the Grise Fiord, Nunavut. Five RADARSAT-2 Wide Fine Quad-pol images and 11 TerraSAR-X StripMap dual-pol (HH/VV) images were acquired. The time-series begins at the onset of melt in early June and extends through advanced melt conditions in late July. Over this period several ponding and drainage events and two snowfall events occurred. Field observations of sea ice properties were collected using an Ice Mass Balance (IMB) buoy, hourly photos from a time-lapse camera deployed on a coastal cliff, and manual in situ measurements of snow thickness and melt pond depth. Where available, clear-sky data from optical sensors (MODIS, Landsat-8, and WorldView) are also used to provide supplementary information on melt pond coverage and evolution. Meteorological data are available from an Environment Canada weather station in Grise Fiord. In this presentation we will discuss the sea ice information provided by each polarization and frequency and evaluate the impact of melt pond evolution on SAR backscatter. Results to date indicate that C- and X-band provide predominantly redundant information, and cross-polarized backscatter (only acquired at C-band) is often very low and near the system noise floor. Early in the melt season a thick wet snow pack is present and both frequencies provide very little ice information. This is attributed to the strong attenuation of the microwave signal by the wet snow. At this time the underlying ice is effectively obscured. During heavily ponded periods backscatter is highly variable, attributed to changing winds and thus variable melt pond surface roughness. In the final week of observations the fast ice in the region is breaking up and open water is present in some images. In these images C-band appears to provide greater contrast between the melting ice and open water than X-band. Analysis of polarimetric parameters is ongoing.

Casey, J. A.; Beckers, J. F.; Brossier, E.; Haas, C.

2013-12-01

153

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

NASA Astrophysics Data System (ADS)

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.

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

2010-12-01

154

Sea Ice Temperature with Regions of No Data Indicated (WMS)  

NSDL National Science Digital Library

This animation shows the daily sea ice surface temperature over the northern hemisphere from September 2002 through May 2003. The sea ice surface temperature was measured by the MODIS instrument on the Aqua satellite. Since this instrument cannot take measurements through clouds, in cloud-covered regions or areas with suspect data quality, the prior days value is retained until a valid data reading is obtained. The satellite instruments are also unable to collect data in the dark, so the region around the pole is shown here with a grey cap that grows and shrinks, indicating the region in polar darkness. The color of the sea ice indicates the sea ice surface temperature.

Starr, Cindy; Sokolowsky, Eric; Hall, Dorothy

2005-01-11

155

Deformation-induced melting in the margin of Whillans ice stream (B2), Siple Coast, Antarctica, and implications for ice-stream dynamics  

NASA Astrophysics Data System (ADS)

The mass balance of the West Antarctic ice sheet depends primarily on the location and flow speed of arterial drainage routes called ice streams, which represent localized zones of rapid ice flow separated by ridges of comparatively stagnant ice. One main challenge in current models of ice streams is the treatment of the shear margin, which plays an important role in the force balance. The goal of this study is to shed new light on the interplay between mechanical deformation and deformation-induced melting in ice-stream margins and explore to what degree the processes in the shear margins affect ice-stream dynamics. To compare our modeling results with observational data, we specifically address the margin of Whillans ice stream B2, but argue that our insights may apply to ice streams more generally. We propose a 2D anti-plane-strain model representing a cross-section through the ice-stream margin perpendicular to the downstream flow direction. Our approximation neglects small components of non-anti-plane deformation that must accompany the marginal melting and drainage that we infer. By coupling heat and mass flow and taking into account that ice deforms through Glen's law, we are able to show that a temperate zone is likely to form above the margin, where the heat production from lateral shear is most intense. We study the properties of the temperate zone through a conjunction of analytical and numerical techniques. Mathematically, the transition from a slipping ice stream to a locked ridge takes the form of a crack problem, for which the near-tip field is amenable to analytical solutions, yielding an estimate for the dissipation and melt production in the vicinity of the margin singularity. We complement these analytical results with a numerical solution of the problem, which provides less accuracy in the immediate vicinity of the singularity, but allows to capture and study the effect of strain-heating throughout the full depth-extent of the deformation zone at the margin. Our numerical results, based on the Glen's-law parameterization recommended by Cuffey and Paterson (2010), are in excellent agreement with available observational data for the transverse profile of surface velocities across Whillans ice stream B2 measured by Echelmeyer et al., 1994. The numerical solution also enables us to test how the extent of the temperate zone and the amount of melt water produced depends on the assumed model parameters, in particular the latent heat of melting, the vertical advection of cold surface ice, and the ice-stream width. Based on our modeling we conclude that deformation-induced melting produces a significant amount of melt water in the margin of Whillans ice stream B2. Assuming a simplistic percolation of melt water based on Darcy's law, we find that the amount of water produced would be sufficient to create a channelized drainage of Rthlisberger type (like in Perol and Rice, submitted, 2012). This result suggests that the width of ice streams might be controlled by the width necessary to create sufficient lateral shearing and thereby sufficient internal melting to create a channel, which generates reduced nearby pore pressures in the temperate ice and till which are expected to increase locking to the bed.

Suckale, J.; Perol, T.; Platt, J. D.; Rice, J. R.

2012-12-01

156

Snow Cover Effects on Glacier Ice Surface Temperature Margherita Maggioni*{  

E-print Network

Snow Cover Effects on Glacier Ice Surface Temperature Margherita Maggioni*{ Michele Freppaz* Paolo.maggioni@unito.it Abstract Snowpack evolution and glacier ice surface temperatures were studied on the Indren glacier of an artificial increase in the snow density was evaluated. During the season rich in snow there was a prevalence

Williams, Mark W.

157

Ultrasonic absorption in liquid metals at the melting temperature  

NASA Astrophysics Data System (ADS)

The Stokes-Kirchhoff theory is used to study the ultrasound absorption coefficient in 33 liquid metals (25 metals are analyzed for the first time) at the melting temperature. A relation between the absorption coefficient and the conduction electron concentration is found. The ratio of the absorption coefficient caused by heat conduction to the absorption coefficient caused by viscosity is estimated.

Tekuchev, V. V.; Svezhintsev, E. N.; Ivanova, I. V.

2014-03-01

158

Modeling Regolith Temperatures and Volatile Ice Processes (Invited)  

NASA Astrophysics Data System (ADS)

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.

Mellon, M. T.

2013-12-01

159

Determination of the bulk melting temperature of nickel using Monte Carlo simulations: Inaccuracy of extrapolation from cluster melting temperatures  

NASA Astrophysics Data System (ADS)

We have determined the bulk melting temperature Tm of nickel according to a recent interatomic interaction model via Monte Carlo simulation by two methods: extrapolation from cluster melting temperatures based on the Pavlov model (a variant of the Gibbs-Thompson model) and by calculation of the liquid and solid Gibbs free energies via thermodynamic integration. The result of the latter, which is the most reliable method, gives Tm=201035K , to be compared to the experimental value of 1726 K. The cluster extrapolation method, however, gives a 325 higher value of Tm=2335K . This remarkable result is shown to be due to a barrier for melting, which is associated with a nonwetting behavior.

Los, J. H.; Pellenq, R. J. M.

2010-02-01

160

Sea ice concentration, ice temperature, and snow depth using AMSR-E data  

Microsoft Academic Search

A summary of the theoretical basis and initial performance of the algorithms that are used to derive sea ice concentration, ice temperature, and snow depth on sea ice from newly acquired Earth Observing System-Aqua\\/Advanced Microwave Scanning Radiometer-EOS (AMSR-E) radiances is presented. The algorithms have been developed and tested using historical satellite passive microwave data and are expected to provide more

Josefino C. Comiso; Donald J. Cavalieri; Thorsten Markus

2003-01-01

161

Skin Temperature Processes in the Presence of Sea Ice  

NASA Astrophysics Data System (ADS)

Monitoring the sea-ice margins of polar oceans and understanding the physical processes at play at the ice-ocean-air interface is essential in the perspective of a changing climate in which we face an accelerated decline of ice caps and sea ice. Remote sensing and in particular InfraRed (IR) imaging offer a unique opportunity not only to observe physical processes at sea-ice margins, but also to measure air-sea exchanges near ice. It permits monitoring ice and ocean temperature variability, and can be used for derivation of surface flow field allowing investigating turbulence and shearing at the ice-ocean interface as well as ocean-atmosphere gas transfer. Here we present experiments conducted with the aim of gaining an insight on how the presence of sea ice affects the momentum exchange between the atmosphere and ocean and investigate turbulence production in the interplay of ice-water shear, convection, waves and wind. A set of over 200 high resolution IR imagery records was taken at the US Army Cold Regions Research and Engineering Laboratory (CRREL, Hanover NH) under varying ice coverage, fan and pump settings. In situ instruments provided air and water temperature, salinity, subsurface currents and wave height. Air side profiling provided environmental parameters such as wind speed, humidity and heat fluxes. The study aims to investigate what can be gained from small-scale high-resolution IR imaging of the ice-ocean-air interface; in particular how sea ice modulates local physics and gas transfer. The relationship between water and ice temperatures with current and wind will be addressed looking at the ocean and ice temperature variance. Various skin temperature and gas transfer parameterizations will be evaluated at ice margins under varying environmental conditions. Furthermore the accuracy of various techniques used to determine surface flow will be assessed from which turbulence statistics will be determined. This will give an insight on how ice presence may affect the dissipation of turbulent kinetic energy.

Brumer, S. E.; Zappa, C. J.; Brown, S.; McGillis, W. R.; Loose, B.

2013-12-01

162

Measuring Surface Deformations Induced by Present-Day Ice Melting in Svalbard  

NASA Astrophysics Data System (ADS)

The vertical movement of the Earth's surface is the result of a number of internal processes in the solid Earth, tidal forces, and mass redistribution in the atmosphere, oceans, terrestrial hydrosphere, and cryosphere. Close to ice sheets and glaciers, the changes in the ice loads can induce large vertical motions at intra-seasonal to secular time scales. The GPS and VLBI antennas in Ny-AAlesund, Svalbard, which started observations in 1991 and 1994, respectively, observe vertical uplift rates on the order of 7 mm/yr and even higher for some geodetic solutions, which are considerably larger than those predicted by post-glacial rebound models (order 2 mm/yr). Despite the differences in secular uplift determined for the different sites and solutions, the inter- annual signal appears to be rather consistent across the different solutions. The time series exhibit a significant nonlinear behavior, with increased uplift rates starting some time in 2000. A local GPS campaign network, which has been reoccupied annually since 1998, reveals a tilting away from the neighboring ice sheet. The Svalbard ice sheets exhibit large melting during the last century and increased melting since about 2000. We compare the observed vertical motion to the motion predicted by loading models using a detailed ice model with annual time resolution as forcing. The model predictions correlate well with the observations both with respect to the inter-annual variations and the spatial pattern of long-term trends. The regression coefficients for predicted and observed inter-annual variations in height is 1.030.36, while the regression coefficient for the predicted and observed spatial pattern turns out to be 1.120.38. Estimates of the predicted secular trend in height due to post-glacial rebound and present-day melting are on the order of 5.5 mm/yr and thus smaller than the observed secular trend in height. This difference between predicted and observed secular trends may be due to reference frame effects or model biases.

Kierulf, H.; Plag, H.; Kohler, J.

2008-12-01

163

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

SciTech Connect

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.

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

2010-07-19

164

Melting of Temperature-Sensitive 3D Colloidal Crystals  

NASA Astrophysics Data System (ADS)

We employ thermally responsive monodisperse microgel colloidal spheres to study the melting mechanisms of colloidal crystals [1]. The particle diameter decreases with increasing temperature and leads to volume fraction changes that drive phase-transitions. We will describe observations of a variety of phenomena. Premelting, the localized loss of crystalline order near defects (e.g. grain boundaries) at volume fractions above the bulk melting transition, is directly observed by video microscopy, and is characterized by monitoring the first peak position of the particle pair correlation function. We find the position of the first peak shifts toward smaller particle separations at the onset of premelting. After Delaunay triangulation, mean square rotational and translational fluctuations of bonds were measured close to and away from defects. The behavior of all such quantities exhibits increased disorder near the defects. By locally heating the material within a crystal domain, we also studied the superheating and melting of a perfect 3D crystal. Finally, the introduction of weak attractions between spheres reveals free-floating 3D crystal `blobs' which can be made to melt and recrystallize by tuning the temperature. [1] A. M. Alsayed, M. F. Islam, J. Zhang, P. J. Collings, A. G. Yodh, Science 309, 1207 (2005). This work was supported by grants from NSF (DMR-0505048 and MRSEC DMR05-20020) and NASA (NAG8-2172).

Alsayed, Ahmed; Han, Yilong; Yodh, Arjun

2006-03-01

165

Low melt rates with seasonal variability at the base of Fimbul Ice Shelf, East Antarctica, revealed by in situ interferometric radar measurements  

NASA Astrophysics Data System (ADS)

melt is a major cause of ice shelf thinning affecting the stability of the ice shelf and reducing its buttressing effect on the inland ice. The Fimbul ice shelf (FIS) in Dronning Maud Land (DML), East Antarctica, is fed by the fast-flowing Jutulstraumen glacier, responsible for 10% of ice discharge from the DML sector of the ice sheet. Current estimates of the basal melt rates of the FIS come from regional ocean models, autosub measurements, and satellite observations, which vary considerably. This discrepancy hampers evaluation of the stability of the Jutulstraumen catchment. Here, we present estimates of basal melt rates of the FIS using ground-based interferometric radar. We find a low average basal melt rate on the order of 1 m/yr, with the highest rates located at the ice shelf front, which extends beyond the continental shelf break. Furthermore, our results provide evidence for a significant seasonal variability.

Langley, Kirsty; Kohler, Jack; Sinisalo, Anna; yan, Mats Jrgen; Hamran, Svein Erik; Hattermann, Tore; Matsuoka, Kenichi; Nst, Ole Anders; Isaksson, Elisabeth

2014-11-01

166

Al20(+) does melt, albeit above the bulk melting temperature of aluminium.  

PubMed

Employing first principles parallel tempering molecular dynamics in the microcanonical ensemble, we report the presence of a clear solid-liquid-like melting transition in Al20(+) clusters, not found in experiments. The phase transition temperature obtained from the multiple histogram method is 993 K, 60 K above the melting point of aluminium. Root mean squared bond length fluctuation, the velocity auto-correlation function and the corresponding power spectrum further confirm the phase transition from a solid-like to liquid-like phase. Atoms-In-Molecules analysis shows a strong charge segregation between the internal and surface atoms, with negatively charged internal atoms and positive charge at the surface. Analysis of the calculated diffusion coefficients indicates different mobilities of the internal and surface atoms in the solid-like phase, and the differences between the environment of the internal atoms in these clusters with that of the bulk atoms suggest a physical picture for the origin of greater-than-bulk melting temperatures. PMID:25556528

Ojha, Udbhav; Steenbergen, Krista G; Gaston, Nicola

2015-02-01

167

Measurement of convective temperature fluctuations in free silicon melt zones  

NASA Astrophysics Data System (ADS)

Growing silicon crystals form free melt zones, the flow regime is usually dominated by time-dependent convection, resulting in temperature fluctuations in the melt and subsequently in irregular dopant distributions in the crystal. The contribution of buoyancy and thermocapillary convection can be separated and their specific characteristics determined by taking advantage of microgravity conditions. For quantification of convective temperature fluctuations, temperature measurements have been performed in liquid silicon zones. Both half zone and full zone and full zone arrangements have been investigated. In case of the latter one, temperature measurements have been performed during the growth process to analyze the relation between the temperature fluctuations and the dopant distribution. All experiments have been carried out in monoellipsoid mirror furnaces. For temperature measurements, sheathed thermocouples or graphite-coated blackbody sensors have been used. The maximum temperature fluctuations were up to 7K in the half-zone case and 0.7K in the full-zone one. In both cases the main frequencies are in the range of 0.05 to 0.5Hz but they are slightly shifted to higher values with increasing Marangoni number. For the half-zone configuration, four thermocouples and up to two black-body sensor were inserted into the melt. Between certain pairs of thermocouples and sensors, a well developed phase correlation or 180 degrees anti-phase correlation has been detected indicating a pulsating flow regime. In the case of the floating zone experiments, a very good agreement is found between the frequency characteristics of the temperature signal and the frequency distribution of dopant irregularities.

Dold, Peter W.; Croll, A.; Schweizer, M.; Nakamura, Shinya; Hibiya, Taketoshi; Benz, Klaus-Werner

1999-07-01

168

Shock temperatures and melting in CsI  

SciTech Connect

Shock-temperature measurements have been made on CsI up to 10 800 K and 0.9 Mbar. Melting has been observed to occur at 0.25 Mbar and 3500 K. A simple model for melting based on the packing of soft spheres is shown to adequately describe the data. The results suggest that in the liquid along the freezing line there is a gradual pressure-induced change from an open NaCl-like structure to one in which atoms are arranged as in a close-packed monatomic fluid. Above 5000 K, electronic excitation is observed to occur due to the high shock temperatures generated and the narrowing of the CsI band gap under pressure.

Radousky, H.B.; Ross, M.; Mitchell, A.C.; Nellis, W.J.

1985-02-01

169

Parameterization and testing of a surface melt and water routing model for the Greenland Ice Sheet  

NASA Astrophysics Data System (ADS)

Rapid supraglacial lake drainages are thought to cause temporary spikes in subglacial water pressure, reductions in basal friction and transient ice sheet accelerations. In order to model potential lake drainage events of the correct magnitude and timing, it is necessary to accurately model: i) the temporal and spatial variability of surface melt; and ii) the surface routing of this water to lakes / moulins. This study is focussed on the Paakitsoq region of western Greenland and is composed of two key components. First, we parameterize a high resolution surface energy / mass balance model by comparing modelled accumulation, melt and albedo against measurements made at the GC-NET stations JAR 1, JAR 2 and Swiss Camp; and modelled snowline position against measurements derived from Landsat 7 ETM+ imagery. Snowline position is obtained from the satellite imagery using a combination of Normalised Difference Snow Index (NDSI) calculations and image thresholding. Second, we parameterize a surface routing and lake filling model using field data collected in June 2011. We focus on the filling of two supraglacial lakes in the Paakitsoq region: 'Lake Ponting' and 'Lake Half Moon'. Using the parameterized distributed surface energy balance model we generate hourly melt output per DEM cell for a 100 km2 area containing these two lakes. Using the Darcian equation for flow at the bottom of a saturated snow pack and the Manning Strickler equation for flow over a bare ice surface, hourly discharge hydrographs into each lake are calculated. These are used in conjunction with the DEM to calculate the temporal changes in lake depths and compared to pressure sensor data from both lakes.

Banwell, A. F.; Willis, I. C.; Arnold, N. S.; Tedesco, M.; Messerli, A.; Ahlstrom, A. P.

2011-12-01

170

Thermohaline Circulation Below the Ross Ice Shelf: A Consequence of Tidally Induced Vertical Mixing and Basal Melting  

Microsoft Academic Search

warm but dense water into contact with the ice shelf. A numerical tidal simulation indicates that vertically well-mixed conditions predominate in the southeastern part of the sub-ice-shelf cavity where the water column thickness is small. Basal melting in this region is expected to be between 0.05 and 0.5 m\\/yr and will drive a thermohaline circulation having the following characteristics: high

Douglas Reed MacAyeal

1984-01-01

171

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

NASA Technical Reports Server (NTRS)

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.

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

2010-01-01

172

Anomalous Proton Dynamics in Ice at Low Temperatures  

SciTech Connect

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.

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

173

BINARY: an optical freezing array for assessing temperature and time dependence of heterogeneous ice nucleation  

NASA Astrophysics Data System (ADS)

A new optical freezing array for the study of heterogeneous ice nucleation in microliter-sized droplets is introduced, tested and applied to the study of immersion freezing in aqueous Snomax suspensions. In the Bielefeld Ice Nucleation ARraY (BINARY) ice nucleation can be studied simultaneously in 36 droplets at temperatures down to -40 C (233 K) and at cooling rates between 0.1 K min-1 and 10 K min-1. The droplets are separated from each other in individual compartments, thus preventing a Wegener-Bergeron-Findeisen type water vapor transfer between droplets as well as avoiding the seeding of neighboring droplets by formation and surface growth of frost halos. Analysis of freezing and melting occurs via an automated real time image analysis of the optical brightness of each individual droplet. As an application ice nucleation in water droplets containing Snomax at concentrations from 1 ng mL-1 to 1 mg mL-1 was investigated. Using different cooling rates a minute time dependence of ice nucleation induced by Class A and Class C ice nucleators contained in Snomax was detected. For the Class A IN a very strong increase of the heterogeneous ice nucleation rate coefficient with decreasing temperature of ? ≡ -dln(jhet)/dT = 8.7 K-1 was observed emphasizing the capability of the BINARY device. This value is larger than those of other types of IN reported in the literature, suggesting that the BINARY setup is suitable for quantifying time dependence for most other IN of atmospheric interest, making it a useful tool for future investigations.

Budke, C.; Koop, T.

2014-09-01

174

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

E-print Network

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

Golden, Kenneth M.

175

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

E-print Network

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) ...

Woskov, Paul P.

176

Understanding changes in the Arctic basin sea ice mass budget as simulated by CCSM4: Implications from melt season characteristics and the surface albedo feedback  

Microsoft Academic Search

Observations reveal alarming drops in Arctic sea ice extent, and climate models project that further changes will occur that could have global repercussions. An important aspect of this change is the surface albedo feedback, driven by the contrast between the albedos of snow\\/ice and the open ocean. In response to warming, this feedback enhances ice melt and amplifies surface warming

D. A. Pollak; M. M. Holland; D. A. Bailey

2010-01-01

177

Measurements of restitution coefficients of ice at low temperatures  

Microsoft Academic Search

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

M. Higa; M. Arakawa; N. Maeno

1996-01-01

178

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

NASA Technical Reports Server (NTRS)

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.

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

2004-01-01

179

Isotopic probes of ice microphysics at cold temperatures  

NASA Astrophysics Data System (ADS)

Measurements of the isotopic composition of water can provide a valuable probe of cirrus microphysics because the parameters relevant for ice nucleation and growth -- for example, temperature, supersaturation, ice habit, and gas exchange -- all affect isotopic fractionation during ice growth. In particular, isotopic measurements can discriminate between some of the mechanisms proposed to explain apparent persistent supersaturation at very cold temperatures (< 200 K). Proposed mechanisms fall into two broad categories, those that involve partial inhibition of homogeneous ice nucleation and those that involve inhibition of growth of ice particles via some surface effect. The former category results in diffusion limitation of vapor reaching ice particles and a characteristic kinetic fractionation signature; the latter category results in ordinary equilibrium fractionation. We discuss the relevant isotopic physics in relation to potential factors such as aerosol glassification, accommodation coefficient uncertainty, and surface effects of organic or other coatings. We show the magnitudes of the expected effects for different cirrus scenarios, and describe a new measurement program aimed at their diagnosis. ISOCLOUD is a measurement campaign to take place at the AIDA aerosol and cloud simulation chamber during 2012-2014, aimed at obtaining simultaneous isotopic measurements of water vapor in the chamber during cold-temperature cirrus formation experiments.

Moyer, E. J.; Aho, S.; Sarkozy, L.; Saathoff, H.; Mhler, O.; Ebert, V.

2011-12-01

180

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

PubMed

The melting temperature (T(m)) 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 I(h)-liquid coexisting system. Dispersion corrections to BLYP lower T(m) to about 360 K, a large improvement over the value of T(m) > 400 K previously obtained with the original BLYP functional under the same simulation conditions. For TTM3-F, T(m) = 248 K from classical molecular dynamics simulations. PMID:21456638

Yoo, Soohaeng; Xantheas, Sotiris S

2011-03-28

181

Evaluation of methods for characterizing the melting curves of a high temperature cobalt-carbon fixed point to define and determine its melting temperature  

NASA Astrophysics Data System (ADS)

The future mise en pratique for the realization of the kelvin will be founded on the melting temperatures of particular metal-carbon eutectic alloys as thermodynamic temperature references. However, at the moment there is no consensus on what should be taken as the melting temperature. An ideal melting or freezing curve should be a completely flat plateau at a specific temperature. Any departure from the ideal is due to shortcomings in the realization and should be accommodated within the uncertainty budget. However, for the proposed alloy-based fixed points, melting takes place over typically some hundreds of millikelvins. Including the entire melting range within the uncertainties would lead to an unnecessarily pessimistic view of the utility of these as reference standards. Therefore, detailed analysis of the shape of the melting curve is needed to give a value associated with some identifiable aspect of the phase transition. A range of approaches are or could be used; some purely practical, determining the point of inflection (POI) of the melting curve, some attempting to extrapolate to the liquidus temperature just at the end of melting, and a method that claims to give the liquidus temperature and an impurity correction based on the analytical Scheil model of solidification that has not previously been applied to eutectic melting. The different methods have been applied to cobalt-carbon melting curves that were obtained under conditions for which the Scheil model might be valid. In the light of the findings of this study it is recommended that the POI continue to be used as a pragmatic measure of temperature but where required a specified limits approach should be used to define and determine the melting temperature.

Lowe, David; Machin, Graham

2012-06-01

182

Past temperatures directly from the greenland ice sheet  

PubMed

A Monte Carlo inverse method has been used on the temperature profiles measured down through the Greenland Ice Core Project (GRIP) borehole, at the summit of the Greenland Ice Sheet, and the Dye 3 borehole 865 kilometers farther south. The result is a 50, 000-year-long temperature history at GRIP and a 7000-year history at Dye 3. The Last Glacial Maximum, the Climatic Optimum, the Medieval Warmth, the Little Ice Age, and a warm period at 1930 A.D. are resolved from the GRIP reconstruction with the amplitudes -23 kelvin, +2.5 kelvin, +1 kelvin, -1 kelvin, and +0.5 kelvin, respectively. The Dye 3 temperature is similar to the GRIP history but has an amplitude 1.5 times larger, indicating higher climatic variability there. The calculated terrestrial heat flow density from the GRIP inversion is 51.3 milliwatts per square meter. PMID:9765146

Dahl-Jensen; Mosegaard; Gundestrup; Clow; Johnsen; Hansen; Balling

1998-10-01

183

Recrystallization of ice in ice cream during controlled accelerated storage  

Microsoft Academic Search

Accelerated ice recrystallization in a thin film of vanilla ice cream was studied on a cold stage microscope, housed in a refrigerated glove box. Sample temperature was held constant (within 0.01 C) or sinusoidally oscillated for 5 days. Changes in ice crystal size distribution were monitored using an image analysis technique. Several recrystallization mechanisms were observed. Melt-refreeze recrystallization was important

Daniel P. Donhowe; Richard W. Hartel

1996-01-01

184

Distribution of REE between clinopyroxene and basaltic melt along a mantle adiabat: Effects of major element composition, water, and temperature  

Microsoft Academic Search

The distribution of REE between clinopyroxene (cpx) and basaltic melt is important in deciphering the processes of mantle melting. Most models for mantle melting assume constant mineral-melt partition coefficient (D) for trace elements, even though partitioning experiments have demonstrated that D depends on pressure (P), temperature (T), and compositions of mineral and melt. In general, DREE from a given cpx-melt

C. Sun; Y. Liang

2010-01-01

185

On the melting temperatures of low-temperature phases of polymorphic metals  

NASA Technical Reports Server (NTRS)

An improved analytical formula for determining the melting temperatures of the low-temperature phases of polymorphic metals is proposed which uses the specific heat differences at the equilibrium transition temperatures. The formula is solved by an iterative method, with no more than one iteration necessary to converge. The results obtained using the formula proposed here are generally in good agreement with the analytical solution.

Ohsaka, K.; Trinh, E. H.

1992-01-01

186

Impact experiments in low-temperature ice  

NASA Astrophysics Data System (ADS)

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.

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

1987-03-01

187

The Holocene thermal maximum in the Nordic Seas: the impact of Greenland Ice Sheet melt and other forcings in a coupled atmosphere-sea-ice-ocean model  

NASA Astrophysics Data System (ADS)

The relatively warm early Holocene climate in the Nordic Seas, known as the Holocene thermal maximum (HTM), is often associated with an orbitally forced summer insolation maximum at 10 ka BP. The spatial and temporal response recorded in proxy data in the North Atlantic and the Nordic Seas reveals a complex interaction of mechanisms active in the HTM. Previous studies have investigated the impact of the Laurentide Ice Sheet (LIS), as a remnant from the previous glacial period, altering climate conditions with a continuous supply of melt water to the Labrador Sea and adjacent seas and with a downwind cooling effect from the remnant LIS. In our present work we extend this approach by investigating the impact of the Greenland Ice Sheet (GIS) on the early Holocene climate and the HTM. Reconstructions suggest melt rates of 13 mSv for 9 ka BP, which result in our model in an ocean surface cooling of up to 2 K near Greenland. Reconstructed summer SST gradients agree best with our simulation including GIS melt, confirming that the impact of the early Holocene GIS is crucial for understanding the HTM characteristics in the Nordic Seas area. This implies that modern and near-future GIS melt can be expected to play an active role in the climate system in the centuries to come.

Blaschek, M.; Renssen, H.

2013-07-01

188

Antarctic Glaciological Data at NSIDC: field data, temperature, and ice velocity  

NASA Astrophysics Data System (ADS)

An extensive collection of many Antarctic glaciological parameters is available for the polar science community upon request. The National Science Foundation's Office of Polar Programs funds the Antarctic Glaciological Data Center (AGDC) at the National Snow and Ice Data Center (NSIDC) to archive and distribute Antarctic glaciological and cryospheric system data collected by the U.S. Antarctic Program. AGDC facilitates data exchange among Principal Investigators, preserves recently collected data useful to future research, gathers data sets from past research, and compiles continent-wide information useful for modeling and field work planning. Data sets are available via our web site, http://nsidc.org/agdc/. From here, users can access extensive documentation, citation information, locator maps, derived images and references, and the numerical data. More than 50 Antarctic scientists have contributed data to the archive. Among the compiled products distributed by AGDC are VELMAP and THERMAP. THERMAP is a compilation of over 600 shallow firn temperature measurements ('10-meter temperatures') collected since 1950. These data provide a record of mean annual temperature, and potentially hold a record of climate change on the continent. The data are represented with maps showing the traverse route, and include data sources, measurement technique, and additional measurements made at each site, i.e., snow density and accumulation. VELMAP is an archive of surface ice velocity measurements for the Antarctic Ice Sheet. The primary objective of VELMAP is to assemble a historic record of outlet glaciers and ice shelf ice motion over the Antarctic. The collection includes both PI-contributed measurements and data generated at NSIDC using Landsat and SPOT satellite imagery. Tabular data contain position, speed, bearing, and data quality information, and related references. Two new VELMAP data sets are highlighted: the Mertz Glacier and the Institute Ice Stream. Mertz Glacier ice velocity provides an upper limit for change in velocity for this glacier over the past decade. Two pairs of Landsat images were used to compare velocities from 2000-2001 to 1989-2000. No significant change in velocity is observed. A new ice discharge flux of 17.8 km3a-1 was determined, and basal melting at the grounding line was re-calculated at 11 m per year (Berthier et al., 2003, in press). Velocity data for the Institute Ice Stream was compiled at NSIDC using a Landsat images from 1986, 1989, and 1997. The data were recently used in a study outlining the velocity, mass balance, and morphology of the Institute ice stream and nearby Ronne ice shelf area. (Scambos et al., 2003, in review). The study indicates the Institute has regions with flow and morphology characteristics similar to the Ross Embayment ice streams. Ice velocity research contributes to understanding the mass balance and overall stability of the Antarctic Ice Sheet. The archiving of velocity data has proven to be a useful tool to the Antarctic science community, and VELMAP continues to grow as a valuable resource through PI contributions. If you have velocity data that you would like to contribute to the VELMAP archive please contact agdc@nsidc.org. The velocity data used in the two studies presented here can be accessed on the VELMAP web site at http://nsidc.org/data/velmap.

Bauer, R.; Bohlander, J.; Scambos, T.; Berthier, E.; Raup, B.; Scharfen, G.

2003-12-01

189

Evidence for Past Melting at the Base of the GISP2 Ice Core from Uranium-Thorium Disequilibrium Measurements  

NASA Astrophysics Data System (ADS)

We measured 238U-234U-230Th disequilibria by mass spectrometric methods for silty ice samples from the base of the GISP2 Greenland ice core, at a depth of 3040-3052 m. The expected age of these samples is >150 kyr based on counting ice layers. We separated the samples into several fractions by filtration and analyzed the <50 nm (truly dissolved + particulate) and >200 nm (particulate) filtered fractions. In the <50 nm fractions, low Th/U mass ratios of 0.51-0.65 indicate that a large portion (86-89%) of U is truly dissolved and not associated with particles. In addition, 230Th/234U activity ratios are quite low (0.18-0.24), suggesting either recent 230Th loss and/or 234U addition to the samples. This Th/U fractionation is not consistent with an age >150 kyr. Since liquid water is characterized by 230Th/234U activity ratios <<1, these results suggest that recent melting/freezing event(s) have occurred at the base of the GISP2 core. The particulate (>200 nm) fraction is characterized by Th/U ratios of ~4.4-4.9, 234U/238U activity ratios of 1.049-1.056, and 230Th/234U activity ratios of 1.12-1.23. The U-Th disequilibrium in the particles is consistent with recent (<350 kyr) fractionation of U-Th in these ice samples. We have modeled these results using a two component mass balance calculation, with dissolved and particulate pools for each radionuclide. The main assumption is that all of the 232Th in the <50 nm fraction is due to particles, due to the low aqueous solubility of 232Th. By mass balance, 230Th/234U activity ratios for the truly dissolved fraction are 0.031-0.062, and dates for when the samples were last frozen are 3.5-6.9 kyr. These results are consistent with the notion of ice melting at the base of large continental ice sheets, with recent evidence of large sub-glacial lakes in Antarctica and active melting at the base of the nearby N-GRIP Greenland ice core. There also appears to be a significant difference in age for the deepest ice sample (3.5 kyr; 3052 m) and the other samples (5.2-6.9 kyr; 3040-3048 m), suggesting that the deepest part of the ice core adjacent to bedrock at 3053.3 m depth may have existed as liquid water for at least several hundred - few thousand years.

Goldstein, S. J.; Lee, V. E.; Nishiizumi, K.; Murrell, M. T.; Amato, R. S.; Nunn, A. J.

2011-12-01

190

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

NASA Technical Reports Server (NTRS)

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.

Schlosser, Herbert; Ferrante, John

1991-01-01

191

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)

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.

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

2014-12-01

192

46 CFR 153.908 - Cargo viscosity and melting point information; measuring cargo temperature during discharge...  

Code of Federal Regulations, 2012 CFR

...melting point information; measuring cargo temperature during discharge: Categories A, B...melting point information; measuring cargo temperature during discharge: Categories A, B...exceeds 25 mPa.s at 20 C, the temperature at which the viscosity is 25...

2012-10-01

193

46 CFR 153.908 - Cargo viscosity and melting point information; measuring cargo temperature during discharge...  

...melting point information; measuring cargo temperature during discharge: Categories A, B...melting point information; measuring cargo temperature during discharge: Categories A, B...exceeds 25 mPa.s at 20 C, the temperature at which the viscosity is 25...

2014-10-01

194

46 CFR 153.908 - Cargo viscosity and melting point information; measuring cargo temperature during discharge...  

Code of Federal Regulations, 2013 CFR

...melting point information; measuring cargo temperature during discharge: Categories A, B...melting point information; measuring cargo temperature during discharge: Categories A, B...exceeds 25 mPa.s at 20 C, the temperature at which the viscosity is 25...

2013-10-01

195

46 CFR 153.908 - Cargo viscosity and melting point information; measuring cargo temperature during discharge...  

Code of Federal Regulations, 2011 CFR

...melting point information; measuring cargo temperature during discharge: Categories A, B...melting point information; measuring cargo temperature during discharge: Categories A, B...exceeds 25 mPa.s at 20 C, the temperature at which the viscosity is 25...

2011-10-01

196

Temperature effects on atomic pair distribution functions of melts  

SciTech Connect

Using molecular dynamics simulations, we investigate the temperature-dependent evolution of the first peak position/shape in pair distribution functions of liquids. For metallic liquids, the peak skews towards the left (shorter distance side) with increasing temperature, similar to the previously reported anomalous peak shift. Making use of constant-volume simulations in the absence of thermal expansion and change in inherent structure, we demonstrate that the apparent shift of the peak maximum can be a result of the asymmetric shape of the peak, as the asymmetry increases with temperature-induced spreading of neighboring atoms to shorter and longer distances due to the anharmonic nature of the interatomic interaction potential. These findings shed light on the first-shell expansion/contraction paradox for metallic liquids, aside from possible changes in local topological or chemical short-range ordering. The melts of covalent materials are found to exhibit an opposite trend of peak shift, which is attributed to an effect of the directionality of the interatomic bonds.

Ding, J., E-mail: ding@jhu.edu; Ma, E. [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States)] [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Xu, M. [I. Physikalisches Institut IA, RWTH Aachen University, Aachen 52056 (Germany)] [I. Physikalisches Institut IA, RWTH Aachen University, Aachen 52056 (Germany); Guan, P. F. [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States) [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Beijing Computational Science Research Center, Beijing 100086 (China); Deng, S. W. [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States) [Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Department of Chemistry, East China University of Science and Technology, Shanghai 200237 (China); Cheng, Y. Q. [Chemical and Engineering Materials Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)] [Chemical and Engineering Materials Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

2014-02-14

197

Retrieval of the floe size and melt pond statistics of Arctic sea ice using high-resolution SAR  

NASA Astrophysics Data System (ADS)

In this paper we present the recent works on retrieving sea ice floe size distribution and melt pond statistics (pond size and shape) by using high-resolution SAR. The results contains the image analysis from TerraSAR-X data as well as airborne-SAR system deployed on a helicopter in the Chukchi Sea of the Arctic Ocean. Our study highlights promising results in retrieving these important but difficult parameters, as well as discussing limitations we have for the retrieval.

Hwang, B.; Kim, D. J.; Chung, K. H.; Lee, S. H.; Jung, H. S.; Moon, W. M.

2012-04-01

198

Snow and Ice Melt Flow Features on Devon Island, Nunavut, Arctic Canada as Possible Analogs for Recent Slope Flow Features on Mars  

NASA Astrophysics Data System (ADS)

Based on morphologic and contextual analogs from Devon Island, Arctic Canada, the recent martian slope flow features reported by Malin and Edgett are reinterpreted as being due not necessarily to groundwater seepage but possibly to snow or ice melt.

Lee, P.; Cockell, C. S.; Marinova, M. M.; McKay, C. P.; Rice, J. W., Jr.

2001-03-01

199

Femtosecond laser melting and resolidifying of high-temperature powder materials  

NASA Astrophysics Data System (ADS)

Though the development of laser additive manufacturing has achieved great success and has been widely used for various materials, it still has limited applications for materials with high melting temperature. In this report, we explore the feasibility of using femtosecond lasers to melt and resolidify these materials, as femtosecond lasers can generate MW-level peak power and create high local temperature. Tungsten, which has the highest melting point (3,422 ) among all the elements, and several other materials with melting temperature higher than 3,000 are chosen for the proof of concept. For the first time, femtosecond laser melting and resolidification of these high-temperature powder materials is achieved. Fabricated samples are characterized by scanning electron microscope and energy-dispersive X-ray spectroscopy. The results manifest that femtosecond laser melting can be an ideal solution for laser additive manufacturing of high-temperature materials.

Nie, Bai; Huang, Huan; Bai, Shuang; Liu, Jian

2015-01-01

200

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

USGS Publications Warehouse

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.

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

2001-01-01

201

Sea surface temperature control on the distribution of far-traveled Southern Ocean ice-rafted detritus during the Pliocene  

NASA Astrophysics Data System (ADS)

flux and provenance of ice-rafted detritus (IRD) deposited in the Southern Ocean can reveal information about the past instability of Antarctica's ice sheets during different climatic conditions. Here we present a Pliocene IRD provenance record based on the 40Ar/39Ar ages of ice-rafted hornblende grains from Ocean Drilling Program Site 1165, located near Prydz Bay in the Indian Ocean sector of the Southern Ocean, along with the results of modeled sensitivity tests of iceberg trajectories and their spatial melting patterns under a range of sea surface temperatures (SSTs). Our provenance results reveal that IRD and hence icebergs in the Prydz Bay area were mainly sourced from (i) the local Prydz Bay region and (ii) the remote Wilkes Land margin located at the mouth of the low-lying Aurora Subglacial Basin. A series of IRD pulses, reaching up to 10 times background IRD flux levels, were previously identified at Site 1165 between 3.3 and 3.0 Ma. Our new results reveal that the average proportion of IRD sourced from distal Wilkes Land margin doubles after 3.3 Ma. Our iceberg trajectory-melting models show that slower iceberg melting under cooling SSTs over this middle Pliocene interval allowed Wilkes Land icebergs to travel farther before melting. Hence, declining SSTs can account for a large part of the observed IRD provenance record at Site 1165. In early Pliocene IRD layers, sampled at suborbital resolution around 4.6 Ma, we find evidence for significant increases in icebergs derived from Wilkes Land during very warm interglacials. This is suggestive of large-scale destabilization of the East Antarctic Ice Sheet in the Aurora Subglacial Basin, as far-traveled icebergs would have to overcome enhanced melting in warmer SSTs. Our results highlight the importance of considering SSTs when interpreting IRD flux and provenance records in distal locations.

Cook, C. P.; Hill, D. J.; Flierdt, Tina; Williams, T.; Hemming, S. R.; Dolan, A. M.; Pierce, E. L.; Escutia, C.; Harwood, D.; Cortese, G.; Gonzales, J. J.

2014-06-01

202

High temperature ultrasonic sensor for the simultaneous measurement of viscosity and temperature of melts  

SciTech Connect

An ultrasonic sensor that simultaneously measures temperature and viscosity of molten materials at very high temperature is described. This sensor has applications as a process monitor in melters. The sensor is based on ultrasonic shear reflectance at the solid-melt interface. A delay line probe is constructed using refractory materials. A change in the time of flight within the delay line is used to measure the temperature. The results obtained from this sensor on various calibration glass samples demonstrate a measurement range of 100-20 000 P for the viscosity and 25-1500 degree sign C for the temperature. (c) 1999 American Institute of Physics.

Balasubramaniam, Krishnan [Department of Aerospace Engineering and Mechanics, Mississippi State University, Mississippi State, Mississippi 39762 (United States)] [Department of Aerospace Engineering and Mechanics, Mississippi State University, Mississippi State, Mississippi 39762 (United States); Shah, Vimal V. [Diagnostic Instrumentation and Analysis Laboratory, Mississippi State University, Mississippi State, Mississippi 39762 (United States)] [Diagnostic Instrumentation and Analysis Laboratory, Mississippi State University, Mississippi State, Mississippi 39762 (United States); Costley, R. Daniel [Miltec Incorporated, National Center for Physical Acoustics, University, Mississippi 38677 (United States)] [Miltec Incorporated, National Center for Physical Acoustics, University, Mississippi 38677 (United States); Boudreaux, Gary [Diagnostic Instrumentation and Analysis Laboratory, Mississippi State University, Mississippi State, Mississippi 39762 (United States)] [Diagnostic Instrumentation and Analysis Laboratory, Mississippi State University, Mississippi State, Mississippi 39762 (United States); Singh, Jagdish P. [Diagnostic Instrumentation and Analysis Laboratory, Mississippi State University, Mississippi State, Mississippi 39762 (United States)] [Diagnostic Instrumentation and Analysis Laboratory, Mississippi State University, Mississippi State, Mississippi 39762 (United States)

1999-12-01

203

Thirty-seven year mass balance of Devon Ice Cap, Nunavut, Canada, determined by shallow ice coring and melt modeling  

Microsoft Academic Search

In AprilMay 2000, eight boreholes were drilled to ?1520 m depth on the Devon Ice Cap. 137Cs ? activity profiles of each borehole showed a peak count rate at depth that is associated with fallout from atmospheric thermonuclear weapons testing in 1963. Snow, firn, and ice densities were measured at each core site and were used to estimate the average

Douglas Mair; David Burgess; Martin Sharp

2005-01-01

204

Unlabeled Oligonucleotides as Internal Temperature Controls for Genotyping by Amplicon Melting  

PubMed Central

Amplicon melting is a closed-tube method for genotyping that does not require probes, real-time analysis, or allele-specific polymerase chain reaction. However, correct differentiation of homozygous mutant and wild-type samples by melting temperature (Tm) requires high-resolution melting and closely controlled reaction conditions. When three different DNA extraction methods were used to isolate DNA from whole blood, amplicon Tm differences of 0.03 to 0.39C attributable to the extractions were observed. To correct for solution chemistry differences between samples, complementary unlabeled oligonucleotides were included as internal temperature controls to shift and scale the temperature axis of derivative melting plots. This adjustment was applied to a duplex amplicon melting assay for the methylenetetrahydrofolate reductase variants 1298A>C and 677C>T. High- and low-temperature controls bracketing the amplicon melting region decreased the Tm SD within homozygous genotypes by 47 to 82%. The amplicon melting assay was 100% concordant to an adjacent hybridization probe (HybProbe) melting assay when temperature controls were included, whereas a 3% error rate was observed without temperature correction. In conclusion, internal temperature controls increase the accuracy of genotyping by high-resolution amplicon melting and should also improve results on lower resolution instruments. PMID:17591926

Seipp, Michael T.; Durtschi, Jacob D.; Liew, Michael A.; Williams, Jamie; Damjanovich, Kristy; Pont-Kingdon, Genevieve; Lyon, Elaine; Voelkerding, Karl V.; Wittwer, Carl T.

2007-01-01

205

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

NASA Astrophysics Data System (ADS)

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 model forced with four sets of measured surface parameters. Modeled backscatter signatures are compared to coincident surface-based C band scatterometer signatures in order to elucidate the signature controlling properties of the ice. Results show that 50 MHz impedance probe dielectric measurements of desalinated upper ice layers exhibit statistically significant diurnal variations due to the link between solar forcing and the availability of free water in brine-free upper ice layers. Enhanced downwelling longwave radiation to the surface from low-level stratus clouds is positively linearly associated (r = 0.709) with volumetric moisture mv detected in upper ice layers. Model results show that desalinated upper ice layers contribute volume scattering from smooth, snow-free FYI under the observed surface mv range. Sustained cloud-free periods result in the formation of a 0.5-2.5 cm granular surface layer, composed of 5.2 mm ice grains, which enhances backscatter under relatively dry conditions. Sensitivity analyses show that layer thickness plays a significant role in scattering due to the increased number density of inclusions which act as discrete scatterers, and sufficient energy may penetrate to, and scatter from, the saline columnar ice layer under relatively dry conditions only (mv < 2%).

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

2010-12-01

206

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

Microsoft Academic Search

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 5wt% dissolved water were decompressed at temperatures\\u000a that ranged from 775 to 1,085C. Decompressions were also carried out using dacite melts with 4.3wt% dissolved water at 1,150C.\\u000a Water bubbles

James E. GardnerRichard; Richard A. Ketcham

207

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

NASA Astrophysics Data System (ADS)

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.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. Electronic supplementary information (ESI) available: Experimental details and additional DSC data on nanocomposites and pure PI resin. See DOI: 10.1039/c3nr02842a

Liu, Minglu; Wang, Robert Y.

2013-07-01

208

Dependence of Eemian Greenland temperature reconstructions on the ice sheet topography  

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

209

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

Microsoft Academic Search

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

James Marti; Konrad Mauersberger

1993-01-01

210

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

E-print Network

indicate a frequent occurrence of abrupt climate change events in the last glacial period, e). For future climates, without the inclusion of the potential Greenland melting flux, the increaseEffect of the potential melting of the Greenland Ice Sheet on the Meridional Overturning

Han, Weiqing

211

Melting Temperature of High-Temperature Fixed Points for Thermocouple Calibrations  

NASA Astrophysics Data System (ADS)

Thermocouples can be calibrated at pure metal ingot-based fixed points at temperatures up to the freezing point of copper (1084.62 C). For Pt/Pd thermocouples, the deviation from the accepted reference function very often takes an approximately linear form up to the copper fixed point. The calibration of Pt/Pd thermocouples may therefore be more amenable to extrapolation than that of Pt/Pt-Rh thermocouples. Here, the melting temperatures of a Co-C and a Pd-C eutectic fixed point are determined by extrapolating the deviation functions of several Pt/Pd thermocouples, after the fashion of Edler et al. The results are compared with the melting temperatures measured using non-contact radiation thermometry. The expanded uncertainty ( k = 2) of the melting temperatures determined by extrapolation of the Pt/Pd thermocouple calibrations is 0.32 C for the Co-C fixed point, and 0.49 C for the Pd-C fixed point. For both fixed points, these uncertainties are comparable to those of non-contact radiation thermometry measurements. While a number of assumptions are made in performing the extrapolation of the calibrations, the method does appear to offer a useful complement to non-contact radiation thermometry measurements.

Pearce, J. V.; Montag, V.; Lowe, D.; Dong, W.

2011-01-01

212

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

E-print Network

CO2 isotopes as tracers of firn air diffusion and age in an Arctic ice cap with summer melting zone from 50 to 60 m depth. A firn-ice age profile was produced from density measurements of 54.9 (+6.0/?12.0) years for firn air at 60 m depth in 140-year-old ice. Thus CO2 has a mean age 85

Chappellaz, Jérôme

213

High-temperature chlorine corrosion of technical carbons Part II. Anodic corrosion in chloride melt  

Microsoft Academic Search

Medium (200 to 400C) to high (600 to 800C) temperature corrosion of technical carbons (Acheson graphites) have been investigated in alkali chloride melts at chlorine evolving anodes. At low temperature in chloride melts containing free Lewis acid (AlCl3) no chlorine is evolved even at high current densities because chlorine, together with aluminium chloride, instantaneously form intercalation compounds with

H. Wendt; A. Khalil; C. E. Padberg

1991-01-01

214

Melt temperature field measurement in single screw extrusion using thermocouple meshes  

Microsoft Academic Search

The development and validation of a sensor for extrusion melt temperature field measurement is described. A grid of opposing thermocouple wires was constructed and held in position by a supporting frame. Wires were joined together at crossing points to form thermocouple junctions, which were computer monitored. The mesh was used to monitor melt temperature fields during single screw extrusion at

E. C. Brown; A. L. Kelly; P. D. Coates

2004-01-01

215

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)

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.

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

2013-12-01

216

Diffractometer for synchrotron radiation structural studies of high temperature melts  

NASA Astrophysics Data System (ADS)

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.

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

1989-07-01

217

Investigating Crevasse Structure Impact on Glacial Sub-Surface Ice Temperature Distribution with Implications for Moulin Formation  

NASA Astrophysics Data System (ADS)

Ice flow acceleration in the ablation zone of outlet glaciers in Greenland has been linked to an increase in infiltration of surface melt through moulins. In order to understand the potential for moulin formation within cracks and crevasses in glacial ice and their impact on melt infiltration rates it is important to gain knowledge about how crevasse structure influences sub-surface ice cold content. A tower of seven wireless sensors was deployed in a moulin at the base of a crevasse in Svinasfellsjokull, glacier in Iceland as an analog to those in Greenland to measure temperature and incoming solar radiation at depth. Seven Crossbow Environmental Motes (MEP410 Models) measuring temperature and irradiance (integrated from 0.4- 0.6?m) were deployed and inserted in a moulin at a depth of 156.8 cm for three days. Temperature measurements indicate greater diurnal fluctuations near the surface of 0.39 C from the near surface mote, while sub-surface temperature remain stable near mean temperature of -0.05 C at a depth of 139.8 cm. Incoming solar radiation measurements showed diurnal variation as expected near the surface at 5.30 W/m2 in the top of the sensor tower, whereas no variation occurred at other depths as the average was 0 W/m2. A computational fluid dynamic model has been calibrated by measured mote temperatures. The model was run accounting for diffusion and convective processes and forced with meteorological data to explore how crevasse density, depth, and geometry influence sub-surface ice temperature distribution.

Hurley, A.; Lampkin, D.

2008-12-01

218

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

PubMed

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

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

219

Daily Snow and Sea Ice Temperature over Asia  

NSDL National Science Digital Library

This animation shows the global advance and retreat of daily snow cover along with daily sea ice surface temperature over Asia from September 2002 through May 2003. The snow cover was measured by the MODIS instrument on the Terra satellite, while the sea ice surface temperature was measured by the MODIS instrument on the Aqua satellite. Since these instruments cannot take measurements through clouds, in cloud-covered regions or areas with suspect data quality, the prior days value is retained until a valid data reading is obtained. This visualization designates an area as covered by snow when the instrument takes a valid measurement showing greater than ~50% snow coverage in that area. This area is assumed to be snow covered until the instrument takes a valid measurement showing less than 40% snow coverage in that same area. A color bar indicates the sea ice surface temperature values. The satellite instruments are unable to collect data through darkness. The region in polar darkness is shown as a grey cap over the pole that grows and shrinks seasonally. A date slider indicates the progression of time. SeaWiFS Land Reflectance shows the seasonal changes in landcover.

Starr, Cindy; Shirah, Greg; Newcombe, Marte; Hall, Dorothy

2004-09-25

220

Daily Snow and Sea Ice Temperature over Europe  

NSDL National Science Digital Library

This animation shows the global advance and retreat of daily snow cover along with daily sea ice surface temperature over Europe from September 2002 through May 2003. The snow cover was measured by the MODIS instrument on the Terra satellite, while the sea ice surface temperature was measured by the MODIS instrument on the Aqua satellite. Since these instruments cannot take measurements through clouds, in cloud-covered regions or areas with suspect data quality, the prior days value is retained until a valid data reading is obtained. This visualization designates an area as covered by snow when the instrument takes a valid measurement showing greater than ~50% snow coverage in that area. This area is assumed to be snow covered until the instrument takes a valid measurement showing less than 40% snow coverage in that same area. A color bar indicates the sea ice surface temperature values. The satellite instruments are unable to collect data through darkness. The region in polar darkness is shown as a grey cap over the pole that grows and shrinks seasonally. A date slider indicates the progression of time. SeaWiFS Land Reflectance shows the seasonal changes in landcover.

Starr, Cindy; Shirah, Greg; Newcombe, Marte; Hall, Dorothy

2004-09-25

221

Daily Snow and Sea Ice Temperature over North America  

NSDL National Science Digital Library

This animation shows the global advance and retreat of daily snow cover along with daily sea ice surface temperature over North America from September 2002 through May 2003. The snow cover was measured by the MODIS instrument on the Terra satellite, while the sea ice surface temperature was measured by the MODIS instrument on the Aqua satellite. Since these instruments cannot take measurements through clouds, in cloud-covered regions or areas with suspect data quality, the prior days value is retained until a valid data reading is obtained. This visualization designates an area as covered by snow when the instrument takes a valid measurement showing greater than ~50% snow coverage in that area. This area is assumed to be snow covered until the instrument takes a valid measurement showing less than 40% snow coverage in that same area. A color bar indicates the sea ice surface temperature values. The satellite instruments are unable to collect data through darkness. The region in polar darkness is shown as a grey cap over the pole that grows and shrinks seasonally. A date slider indicates the progression of time. SeaWiFS Land Reflectance shows the seasonal changes in landcover.

Starr, Cindy; Shirah, Greg; Newcombe, Marte; Hall, Dorothy

2004-09-25

222

Global Daily Snow and Sea Ice Surface Temperature  

NSDL National Science Digital Library

This animation shows the global advance and retreat of daily snow cover along with daily sea ice surface temperature over the Northern Hemisphere from September 2002 through May 2003. The snow cover was measured by the MODIS instrument on the Terra satellite, while the sea ice surface temperature was measured by the MODIS instrument on the Aqua satellite. Since these instruments cannot take measurements through clouds, in cloud-covered regions or areas with suspect data quality, the prior days value is retained until a valid data reading is obtained. This visualization designates an area as covered by snow when the instrument takes a valid measurement showing greater than ~50% snow coverage in that area. This area is assumed to be snow covered until the instrument takes a valid measurement showing less than 40% snow coverage in that same area. A color bar indicates the sea ice surface temperature values. The satellite instruments are unable to collect data through darkness. The region in polar darkness is shown as a grey cap over the pole that grows and shrinks seasonally. A date slider indicates the progression of time. SeaWiFS Land Reflectance shows the seasonal changes in landcover.

Starr, Cindy; Shirah, Greg; Newcombe, Marte; Hall, Dorothy

2004-09-25

223

Daily Snow and Sea Ice Temperature over the North Pole  

NSDL National Science Digital Library

This animation shows the global advance and retreat of daily snow cover along with daily sea ice surface temperature over the Northern Hemisphere from September 2002 through May 2003. The snow cover was measured by the MODIS instrument on the Terra satellite, while the sea ice surface temperature was measured by the MODIS instrument on the Aqua satellite. Since these instruments cannot take measurements through clouds, in cloud-covered regions or areas with suspect data quality, the prior days value is retained until a valid data reading is obtained. This visualization designates an area as covered by snow when the instrument takes a valid measurement showing greater than ~50% snow coverage in that area. This area is assumed to be snow covered until the instrument takes a valid measurement showing less than 40% snow coverage in that same area. A color bar indicates the sea ice surface temperature values. The satellite instruments are unable to collect data through darkness. The region in polar darkness is shown as a grey cap over the pole that grows and shrinks seasonally. A date slider indicates the progression of time. SeaWiFS Land Reflectance shows the seasonal changes in landcover.

Starr, Cindy; Shirah, Greg; Newcombe, Marte; Hall, Dorothy

2004-09-25

224

In situ observation of partial melting in superplastic aluminum alloy composites at high temperature  

SciTech Connect

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 Si[sub 3]N[sub 4] particles. Calorimetry measurements of all three composites showed a sharp endothermic peak at an optimum superplastic temperature. At the same temperature, transmission electron microscopy showed the melting of grain boundaries and interfaces, suggesting direct correlations between partial melting and the superplasticity. Solute segregation was also observed at boundaries and interfaces, and was discussed as causes for partial melting.

Koike, J. (Oregon State Univ., Corvallis, OR (United States). Dept. of Mechanical Engineering); Mabuchi, M. (Government Industrial Research Inst., Nagoya (Japan)); Higashi, K. (Univ. of Osaka Prefecture (Japan). Dept. of Mechanical Systems Engineering)

1995-01-01

225

Arctic sea ice freeboard heights from satellite altimetry  

Microsoft Academic Search

The Arctic sea ice cover is most sensitive to climate change and variability, mainly due to the ice-albedo feedback effect. With an increase in the average temperature across the Arctic during the past few decades, sea ice has been melting rapidly. The decline in the sea ice extent was estimated as 10% per decade since satellite observations began in 1979.

Vidyavathy Renganathan

2010-01-01

226

Constraining the equation of state of fluid H2O to 60 GPa using the melting curve of Ice VII and the formation of Mg(OH)2 in the MgO-H2O system.  

NASA Astrophysics Data System (ADS)

The physical properties of fluid H2O are important geologically over a large range of pressure and temperature. Shock-wave data have served as the main resource for the derivations of many equations of state for fluid H2O. Direct measurements of the specific volume of water are required to test the validity of these models; however, direct measurements at elevated pressures and temperatures are difficult and, as a result, rare. The study presented here sought to determine the PVT properties of Ice VII along the melting curve at pressures > 20 GPa using the a Mao-Bell type diamond anvil cell with an external Mo-wire resistance heater. Small grains of MgO, gold and a relatively large volume of H2O were loaded in a sample chamber drilled in a pre-indented Re-gasket. The temperature of the experiment was determined by placing a thermocouple between the diamond anvil and Re-gasket, directly against the surface of the diamond. The experiments were conducted on beam line X17C at the Brookhaven National Synchrotron Light Source using the Energy Dispersive X-ray Diffraction (EDXD) technique. The unit cells of Ice VII, MgO, and gold were monitored during the experiment with gold being used as an internal pressure calibrant. The methodology was to use the disappearance of the diffraction pattern of Ice VII with the production of brucite following the reaction of fluid H2O with MgO. Generally, experiments would follow the following sequence as temperature was increased: 1.) slight drop in pressure, 2.) the appearance of diffraction lines indicative of brucite, and 3.) total disappearance of Ice VII diffraction lines and noticeable drop in pressure (up to ~2 GPa at the highest pressures). The appearance of brucite would always proceed the disappearance of Ice VII diffraction lines. The data suggest that brucite formed as soon as fluid H2O became available whereas Ice VII melted over a small range over temperature (<50 K). The melting curve for Ice VII from 3-60 GPa can be related by: P(GPa)=10.448 - 0.02375*(T)- 4.1826x10-5*(T2) + 1.3114x10-7*(T3) where T is temperature in Kelvin. The molar volume of Ice VII along the melting curve was found to be related by: P (GPa) = -0.1791 + 2017.7*exp(-0.5912*V) where V is the molar volume (cm3/mol). We used the melting curve of Ice VII to constrain the density of fluid H2O along the melting curve by taking the pressure derivative of the Gibbs Free Energy difference between Ice VII and fluid H2O. Comparison of these results suggests that the previously stated equations of state of fluid H2O overestimate the molar volume of water at pressures > 45 GPa.

Frank, M. R.; Fei, Y.

2002-12-01

227

Dependence of Eemian Greenland temperature reconstructions on the ice sheet topography  

NASA Astrophysics Data System (ADS)

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.

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

2014-06-01

228

Dependence of Eemian Greenland temperature reconstructions on the ice sheet topography  

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

229

Melting Temperature and Partial Melt Chemistry of H2O-Saturated Mantle Peridotite to 11 Gigapascals  

PubMed

The H2O-saturated solidus of a model mantle composition (Kilborne Hole peridotite nodule, KLB-1) was determined to be just above 1000C from 5 to 11 gigapascals. Given reasonable H2O abundances in Earth's mantle, an H2O-rich fluid could exist only in a region defined by the wet solidus and thermal stability limits of hydrous minerals, at depths between 90 and 330 kilometers. The experimental partial melts monotonously became more mafic with increasing pressure from andesitic composition at 1 gigapascal to more mafic than the starting peridotite at 10 gigapascals. Because the chemistry of the experimental partial melts is similar to that of kimberlites, it is suggested that kimberlites may be derived by low-temperature melting of an H2O-rich mantle at depths of 150 to 300 kilometers. PMID:9092469

Kawamoto; Holloway

1997-04-11

230

Measurement of the Melting Point Temperature of Several Lithium-Sodium-Beryllium Fluoride Salt (Flinabe) Mixtures  

SciTech Connect

The molten salt Flibe, a combination of lithium and beryllium fluorides studied for molten salt fission reactors, has been proposed as a breeder and coolant for fusion applications. The melting points of 2LiF-BeF{sub 2} and LiF-BeF{sub 2} are 460 deg. C and 363 deg. C, but LiF-BeF{sub 2} is rather viscous and has less lithium for breeding. In the Advanced Power Extraction (APEX) Program, concepts with a free flowing liquid for the first wall and blanket were investigated. Flinabe (a mixture of LiF, BeF{sub 2} and NaF) was selected for a molten salt design because a melting temperature below 350 deg. C appeared possible and this provided an attractive operating temperature window for a reactor. To confirm that a ternary salt with a low melting temperature existed, several combinations of the fluoride salts, LiF, NaF and BeF{sub 2}, were melted in a stainless steel crucible under vacuum. One had an apparent melting temperature of 305 deg. C. The test system, preparation of the mixtures, melting procedures and temperature curves for the melting and cooling are presented along with the apparent melting points. Thermal modeling of the salt pool and crucible is reported in an accompanying paper.

McDonald, J.M; Nygren, R.E.; Lutz, T.J.; Tanaka, T.J; Ulrickson, M.A.; Boyle, T.J.; Troncosa, K.P. [Sandia National Laboratories (United States)

2005-04-15

231

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

SciTech Connect

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.

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

2010-01-28

232

Effects of Fat Replacers on the Sensory Properties, Color, Melting, and Hardness of Ice Cream1  

Microsoft Academic Search

We examined the effects of individual fat replacers on the physical and sensory properties of fat-free ice cream. Ice creams (? 0.5% milk fat) were formulated with maltodextrin, milk protein concentrate, or poly- dextrose. Lactose-reduced, freeze-concentrated skim milk was used to prepare a 1.6% fat ice cream mix. Experimental mixes were formulated to maintain the sweetness intensity and freezing characteristics

Ann M. Roland; Lance G. Phillips; Kathryn J. Boor

1999-01-01

233

In-situ temperature measurement of the McMurdo Ice Shelf and ice shelf cavity using fiber-optic distributed temperature sensing  

NASA Astrophysics Data System (ADS)

Ocean-ice interactions in ice shelf cavities have great potential to affect ice shelf mass balance and stability. In-situ temperature of the ice shelf and ocean water column at Windless Bight, Antarctica, was remotely monitored using fiber-optic distributed temperature sensing (DTS). Fiber-optic cables were installed in two boreholes completed using a combination of electromechanical and hot point drilling. Between November 2011 and January 2013 a set of moorings, comprising of fiber-optic cables for distributed temperature sensing, an independent thermistor string and pressure-temperature transducers were monitored. Data presented summarizes the field deployment of the system between November 2011 and January 2013. Heat serves as natural tracer in environmental systems and is useful for identifying fluxes across boundaries. The heat flux near the ice-ocean interface is estimated from the temperature gradient in the lower ice shelf. Variation in the ice shelf temperature near the ice-ocean interface can be seen. Finally, these new data show the intrusion of warm water under the ice shelf previously observed in 2012.

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

2013-12-01

234

Temperature Temperature is the physical property of a  

E-print Network

interval between melting ice and boiling water under 1 atm pressure shall be 100. @ melting ice temperature temperature scale; boiling water to 373.15 degrees. The scale is named after Lord Kelvine, 1 degree Kelvine 1 atm presure @ saturated water vapor temp, 1 atm pressure p0 V0=RT 0 p1V 1=RT1= RT0100 #12;AbsoluteTemperature

Alexeenko, Alina

235

Sudden sea-level change from melting Antarctic ice: How likely?  

SciTech Connect

There has been concern that the West Antarctic marine ice sheet could collapse catastrophically, leading to a 5-meter rise in sea level in a single century. However, that idea was based on a modeled instability at the grounding line that reflected a discontinuity between the mathematical models used for the grounded and floating parts of the ice sheet, respectively. Improved knowledge about ice streams, the active portions of the marine ice sheet, reveals that in the Ross Sea sector, at least, there is in reality a broad, gradual transition zone, rather than a discontinuity, between the inland ice and the ice shelf. Consequently, there probably is no instability; total disappearance of the ice sheet would take a millenium or more. The resulting average contribution to sea-level rise thus would be only a few millimeters per year, comparable to the present rate of rise (from all sources). Furthermore, dynamic response to present-day climate change would not even begin in less than a century. It is still uncertain whether the Antarctic ice sheet is making a positive or negative contribution to sea-level rise now. Whichever the case, however, during the next century or two the effect of climatic warming almost surely will be to increase the mass input to the ice sheet, thus yielding a negative contribution to sea-level rise of the order of a millimeter per year.

Bentley, C.R. [Univ. of Wisconsin, Madison, WI (United States)

1995-12-31

236

Experiments on melting of slush ice in a horizontal cylindrical capsule  

Microsoft Academic Search

Melting phenomena are related to a wide variety of engineering fields: purification of metals, welding, electroslag melting, thawing of moist soil, and latent heat-of-fusion thermal-energy storage are a few of important applications which have motivated research in this area.Melting is a phase transformation process that is accompanied by absorption of thermal energy. The essential feature of the systems that exhibit

Tsuyoshi Kawanami; Shoichiro Fukusako; Masahiko Yamada; Kenji Itoh

1999-01-01

237

Analysis of Temperature Gradients during Simultaneous Laser Beam Melting of Polymers  

NASA Astrophysics Data System (ADS)

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.

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

238

Melting temperature and explosive crystallization of amorphous silicon during pulsed laser irradiation  

Microsoft Academic Search

Measurements during pulsed laser irradiation indicate that amorphous Si melts at a temperature 200 +- 50 K below the crystalline value. Below energy densities required to melt the amorphous layer fully , the data are interpreted in terms of an explosive crystallization. The initial liquid layer solidifies to form coarse grained polycrystalline Si. A thin, self-propagating liquid layer travels through

Michael Thompson; G. J. Galvin; J. W. Mayer; P. S. Peercy; J. M. Poate; D. C. Jacobson; A. G. Cullis; N. G. Chew

1984-01-01

239

First-year sea ice melt pond fraction estimation from dual-polarisation C-band SAR - Part 1: In situ observations  

NASA Astrophysics Data System (ADS)

Understanding the evolution of melt ponds on Arctic sea ice is important for climate model parameterisations, weather forecast models and process studies involving mass, energy and biogeochemical exchanges across the ocean-sea ice-atmosphere interface. A field campaign was conducted in a region of level first-year sea ice (FYI) in the central Canadian Arctic Archipelago (CAA), during the summer of 2012, to examine the potential for estimating melt pond fraction (fp) from satellite synthetic aperture radar (SAR). In this study, 5.5 GHz (C-band) dual co- (HH + VV - horizontal transmit and horizontal receive + vertical transmit and vertical receive) and cross-polarisation (HV + HH - horizontal transmit and vertical receive + horizontal transmit and horizontal receive) radar scatterometer measurements of melt-pond-covered FYI are combined with ice and pond properties to analyse the effects of in situ physical and morphological changes on backscatter parameters. Surface roughness statistics of ice and ponds are characterised and compared to the validity domains of the Bragg and integral equation model (IEM) scattering models. Experimental and model results are used to outline the potential and limitations of the co-polarisation ratio (VV / HH) for retrieving melt pond information, including fp, at large incidence angles (?35). Despite high variability in cross-polarisation ratio (HV / HH) magnitudes, increases at small incidence angles (<30) are attributed to the formation of ice lids on ponds. Implications of the results for pond information retrievals from satellite C-, L- and P-band SARs are discussed.

Scharien, R. K.; Landy, J.; Barber, D. G.

2014-11-01

240

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

PubMed

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

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

2011-09-21

241

Arctic sea ice conditions in spring 2009-2013 prior to melt  

NASA Astrophysics Data System (ADS)

from NASA IceBridge airborne surveys in March/April 2009-2013 over the western Arctic Ocean are presented in the context of previous observations to assess changes in the characteristics of the sea ice cover during the last decade, taking into account spatial and temporal limitations in the available data. Following a precipitous drop in the amount and thickness of multiyear (MY) ice in 2007-2008, the characteristics of the ice cover have remained largely consistent through March 2013. The central Arctic continues to be dominated by MY ice with mean and modal thicknesses of 3.2 m and 2.4 m, respectively. The southern Beaufort and Chukchi Sea region is a complex mixture of ~75% first-year ice and 25% MY ice. IceBridge observations indicate that the mean thickness in the Beaufort and Chukchi Seas may have decreased from ~2.5 m to as low as 1.6 m over the 5 year period.

Richter-Menge, Jacqueline A.; Farrell, Sinead L.

2013-11-01

242

Temperature dependence of the grain boundary migration in ice bicrystals  

NASA Astrophysics Data System (ADS)

The grain boundary (GB) migration plays a very important role in the texture and fabrics in the glacier and polar ice (Gow A. et al 1997). The study of the GB migration in bicrystalline samples permits the investigation of this complex phenomenon with more details. In this work, the GB movement under the influence of surface was studied in pure bicrystalline ice samples. The bicrystals having a <1010>/600 crystalline misorientation were annealed at -50C, -100C, -150C, -200C in a silicone oil bath for 170 days. The results obtained were analyzed using the GB movement equation with the Sun and Bauer configuration (Sun and Bauer 1972), driven by capillarity under the retarding effect produced by a diffusion-generated groove at the GB-surface intersection (Di Prinzio y Nasello 1998). Different temperatures GB mobility and the activation energy of the migration process were determined. The results were compared with the results obtained in grain growth in glacier ice.

Nasello, O. B.; Guzman, P. G.

2003-12-01

243

Effects of pressure and temperature on the melt density and the melt flow rate of LDEP and glass bead-filled LDPE composite  

Microsoft Academic Search

The effects of pressure and temperature on the melt density (?m) and the melt flow rate (MFR) of the low-density polyethylene (LDPE) and a glass bead-filled LDPE composite (LDPE\\/GB) have been investigated using a capillary plastometer. It was discovered that the MFR of the melts increased as an exponential law function with a rise in temperatures and increased as a

J. Z. Liang; R. K. Y. Li; S. C. Tjong

1999-01-01

244

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

SciTech Connect

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.

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 Lon Brillouin CEA/Saclay, 91191 Gif-Sur-Yvette Cedex (France)] [Laboratoire Lon Brillouin CEA/Saclay, 91191 Gif-Sur-Yvette Cedex (France)

2014-03-07

245

Thermal Diffusivity for III-VI Semiconductor Melts at Different Temperatures  

NASA Technical Reports Server (NTRS)

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.

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

2004-01-01

246

Melting temperature of metal polycrystalline nanowires electrochemically deposited into the pores of anodic aluminum oxide.  

PubMed

The arrays of metallic nanowires are considered as promising precursors for 1D semiconductor nanostructures after appropriate treatment at temperatures close to the melting point. Therefore the melting behaviour of the metallic structures in oxide templates is a key parameter for the subsequent conversion process. The present paper focuses on understanding of the effect of mechanical stress generated during heating on the melting point of the metal nanowires deposited into the pores of anodic alumina. Extremely high local compressive stress appears due to the difference in the thermal coefficients of the oxide template and nanowires inside the pores. The effect of the composite structural parameter that may be related to the concentration of nanowires on the melting temperature has been investigated. A numerical model predicting the melting point has been developed for composites with indium, tin, and zinc nanowires. The simulation results obtained using the suggested model were compared with the experimental data. PMID:25101924

Shilyaeva, Yu I; Bardushkin, V V; Gavrilov, S A; Silibin, M V; Yakovlev, V B; Borgardt, N I; Volkov, R L; Smirnov, D I; Zheludkevich, M L

2014-09-28

247

Defects Can Increase the Melting Temperature of DNA-Nanoparticle Assemblies  

E-print Network

DNA-gold nanoparticle assemblies have shown promise as an alternative technology to DNA microarrays for DNA detection and RNA profiling. Understanding the effect of DNA sequences on the melting temperature of the system is central to developing reliable detection technology. We studied the effects of DNA base-pairing defects, such as mismatches and deletions, on the melting temperature of DNA-nanoparticle assemblies. We found that, contrary to the general assumption that defects lower the melting temperature of DNA, some defects increase the melting temperature of DNA-linked nanoparticle assemblies. The effects of mismatches and deletions were found to depend on the specific base pair, the sequence, and the location of the defects. Our results demonstrate that the surface-bound DNA exhibit hybridization behavior different from that of free DNA. Such findings indicate that a detailed understanding of DNA-nanoparticle assembly phase behavior is required for quantitative interpretation of DNA-nanoparticle aggreg...

Harris, Nolan C

2006-01-01

248

The Met Office Hadley Centre sea ice and sea surface temperature data set, version 2: 1. Sea ice concentrations  

NASA Astrophysics Data System (ADS)

present a new version of the sea ice concentration component of the Met Office Hadley Centre sea ice and sea surface temperature data set, HadISST.2.1.0.0. Passive microwave data are combined with historical sources, such as sea ice charts, to create global analyses on a 1 grid from 1850 to 2007. Climatology was used when no information about the sea ice was available. Our main aim was to create a homogenous data set by calculating and applying bias adjustments using periods of overlaps between the different data sources used. National Ice Center charts from 1995 to 2007 have been used as a reference to achieve this. In particular, large bias adjustments have been applied to the passive microwave data in both the Antarctic and Arctic summers. Overall, HadISST.2.1.0.0 contains more ice than HadISST1.1, with higher concentrations, shorter marginal ice zones, and larger extents and areas in some regions and periods. A new method for estimating the concentrations within the ice pack using the distance from the ice edge has been developed and evaluated. This was used when only the extents were known or the original concentration fields were heterogeneous. A number of discontinuities in the HadISST1.1 record are no longer found in HadISST.2.1.0.0.

Titchner, Holly A.; Rayner, Nick A.

2014-03-01

249

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

NASA Technical Reports Server (NTRS)

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.

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

1987-01-01

250

Vapor pressure above ice at temperatures below 170 K  

Microsoft Academic Search

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

Konrad Mauersberger; Dieter Krankowsky

2003-01-01

251

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

Microsoft Academic Search

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

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

2000-01-01

252

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

Microsoft Academic Search

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

R. Boehler

1993-01-01

253

Surface-melt driven Laurentide Ice Sheet retreat during the early Holocene  

Microsoft Academic Search

To better understand mechanisms of ice-sheet decay, we investigate the surface mass balance of the Laurentide Ice Sheet (LIS) during the early Holocene, a period of known rapid LIS retreat. We use a surface energy-mass balance model (EMBM) driven with conditions derived from an equilibrium atmosphere-ocean general circulation model 9 kilo-years ago simulation. Our EMBM indicates a net LIS surface

A. E. Carlson; F. S. Anslow; E. A. Obbink; A. N. LeGrande; D. J. Ullman; J. M. Licciardi

2009-01-01

254

Evidence for Recent Melting at the Base of the GISP2 Ice Core From Uranium-Thorium Disequilibrium Measurements  

NASA Astrophysics Data System (ADS)

We measured 238U-234U-230Th disequilibria by mass spectrometric methods for a set of dusty ice samples from the base of the GISP2 Greenland ice core, at a depth of 3040-3052 m. The goal of this work was to further test the Fireman (1986) recoil-based model for producing uranium-series disequilibria in dusty ice on samples thought to be > 150 ka in age based on layer counting. However, the base of the GISP2 core is greatly disturbed in chemistry and dustiness relative to upper portions of the core. Samples consisted of 11 cm sections of ice core with sample weights of 340-430 g. We separated the samples into several fractions by filtration and analyzed the < 0.05 um fraction. This fraction had exceedingly high U and Th concentrations (2.5- 5 ppb U; 1.4-2.7 ppb Th). These U and Th concentrations are a factor of 1000 higher than measured for ice at Allan Hills, Antarctica. Low Th/U ratios of 0.51-0.65 indicate that a large portion of the uranium present in the samples is dissolved and not associated with particles, which are expected to have Th/U ratios around 3. However, 234U/238U activity ratios range from 0.972-0.992 (+/- 0.001), indicating a depletion of 234U relative to secular equilibrium of 1-3%. In addition, 230Th/234U activity ratios are quite low (0.18-0.24), suggesting either recent Th loss and/or U addition to the samples. This recent Th/U fractionation is not consistent with an age > 150 ka. Since liquid water would be characterized by 230Th/234U activity ratios ?1, the low 230Th/234U activity ratios likely indicate that recent melting/freezing event(s) have occurred at the base of the GISP2 core. We can model these results with a two component mass balance calculation, with dissolved and particulate pools for each radionuclide. Although several assumptions are required to calculate ages, preliminary results of these calculations suggest that the melting events may be as young as <10 ka.

Goldstein, S. J.; Murrell, M. T.; Nunn, A. J.; Nishiizumi, K.

2007-12-01

255

The Agulhas Current is said to attenuate the effect of melting ice  

E-print Network

, could in return be offsetting the effects of glacial melting on thermohaline circulation2 and the global helping to maintain worldwide thermohaline circulation. The phenomenon could be partly offsetting

256

Measurement of the melting point temperature of several lithium-sodium-beryllium fluoride salt (FLINABE) mixtures.  

SciTech Connect

The molten salt Flibe, a combination of lithium and beryllium flourides, was studied for molten salt fission reactors and has been proposed as a breeder and coolant for the fusion applications. 2LiF-BeF{sub 2} melts at 460 C. LiF-BeF{sub 2} melts at a lower temperature, 363 C, but is rather viscous and has less lithium breeder. In the Advanced Power Extraction (APEX) Program, concepts with a free flowing ternary molten salt for the first wall surface and blanket were investigated. The molten salt (FLiNaBe, a ternary mixture of LiF, BeF2 and NaF) salt was selected because a melting temperature below 350 C that would provide an attractive operating temperature window for a reactor application appeared possible. This information came from a Russian binary phase diagram and a US ternary phase diagram in the 1960's that were not wholly consistent. To confirm that a ternary salt with a low melting temperature existed, several combinations of the fluoride salts, LiF, NaF and, BeF{sub 2}, were melted in a small stainless steel crucible under vacuum. The proportions of the three salts were selected to yield conglomerate salts with as low a melting temperature as possible. The temperature of the salts and the crucible were recorded during the melting and subsequent re-solidification using a thermocouple directly in the salt pool and two thermocouples embedded in the crucible. One mixture had an apparent melting temperature of 305 C. Particular attention was paid to the cooling curve of the salt temperature to observe evidence of any mixed intermediate phases between the fully liquid and fully solid states. The clarity, texture, and thickness were observed and noted as well. The test system, preparation of the mixtures, and the melting procedure are described. The temperature curves for the melting and cooling of each of the mixtures are presented along with the apparent melting points. Thermal modeling of the salt pool and crucible was also done and is reported in a separate paper.

Boyle, Timothy J.; Troncosa, Kenneth P.; Nygren, Richard Einar; Lutz, Thomas Joseph; McDonald, Jimmie M.; Tanaka, Tina Joan; Ulrickson, Michael Andrew

2004-09-01

257

Molybdenum at High Pressure and Temperature: Melting from Another Solid Phase  

NASA Astrophysics Data System (ADS)

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.

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

258

Ice nucleation in the upper troposphere: Sensitivity to aerosol number density, temperature, and cooling rate  

SciTech Connect

We have investigated the processes that control ice crystal nucleation in the upper troposphere using a numerical model. Nucleation of ice resulting from cooling was simulated for a range of aerosol number densities, initial temperatures, and cooling rates. In contrast to observations of stratus clouds, we find that the number of ice crystals that nucleate in cirrus is relatively insensitive to the number of aerosols present. The ice crystal size distribution at the end of the nucleation process is unaffected by the assumed initial aerosol number density. Essentially, nucleation continues until enough ice crystals are present such that their deposition growth rapidly depletes the vapor and shuts off any further nucleation. However, the number of ice crystals nucleated increases rapidly with decreasing initial temperature and increasing cooling rate. This temperature dependence alone could explain the large ice crystal number density observed in very cold tropical cirrus.

Jensen, E.J.; Toon, O.B. [NASA, Ames Research Center, Moffett Field, CA (United States)] [NASA, Ames Research Center, Moffett Field, CA (United States)

1994-09-01

259

Quantum melting of a two-dimensional vortex lattice at zero temperature A. Rozhkov and D. Stroud  

E-print Network

Quantum melting of a two-dimensional vortex lattice at zero temperature A. Rozhkov and D. Stroud simple models for estimat- ing the conditions for quantum melting of a 2D vortex lattice at T 0 the quantum melting of a two-dimensional flux lattice at temperature T 0 in the ``superclean limit

Stroud, David

260

Laser induced breakdown spectroscopy of soils, rocks and ice at subzero temperatures in simulated martian conditions  

NASA Astrophysics Data System (ADS)

We applied Laser Induced Breakdown Spectroscopy (LIBS) on moist soil/rock samples in simulated Martian conditions. The signal behavior as a function of the surface temperature in the range from + 25 C to - 60 C was studied at pressure of 7 mbar. We observed the strong signal oscillations below 0 C with different negative peaks, whose position, width and magnitude depend on the surface roughness. In some cases, the signal was reduced for one order of magnitude with consequences for the LIBS analytical capability. We attribute such a signal behavior to the presence of supercooled water inside the surface pores, which freezing point depends on the pore size. On a same rock samples with different grades of the surface polishing, the signal has different temperature dependence. Its decrease was always registered close to 0 C, corresponding to the freezing/melting of normal disordered ice, which can be present inside larger pores and scratching. An amount of the signal reduction at the phase transition temperatures does not seem to change with the laser energy density in the examined range. Comparative measurements were performed on a frozen water solution. A large depression, for two orders of magnitude, of the LIBS intensity was observed close to - 50 C. The same negative peak, but with a smaller magnitude, was also registered on some rock/soil samples. Ablation rates and plasma parameters as a function of the sample temperature are also discussed, and their consequences for in-situ analyses.

Lazic, V.; Rauschenbach, I.; Jovicevic, S.; Jessberger, E. K.; Fantoni, R.; Di Fino, M.

2007-12-01

261

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

Microsoft Academic Search

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

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

262

Meteorological factors controlling year-to-year variations in the spring onset of snow melt over the Arctic sea ice  

NASA Astrophysics Data System (ADS)

The spring onset of snow melt on the Arctic sea ice shows large inter-annual variability. Surface melt triggers positive feedback mechanisms between the albedo, snow properties and thickness, as well as sea ice thickness. Hence, it is important to quantify the factors contributing to inter-annual variability of the melt onset (MO) in various parts of the Arctic Ocean. Meteorological factors controlling surface heat budget and surface melting/freezing are the shortwave and longwave radiative fluxes and the turbulent fluxes of sensible and latent heat. These fluxes depend on the weather conditions, including the radiative impact of clouds, heat advection and wind speed. We make use of SSM/I-based MO time series (Markus, Miller and Stroeve) and the ECMWF ERA Interim reanalysis on the meteorological conditions and surface fluxes, both data sets spanning the period 1989-2008 and covering recent years with a rapid sea ice decline. The advantage is that SSM/I-based MO time series are independent of the ERA-Interim data. Our objective is to investigate if there exists a physically consistent and statistically significant relationship between MO timing and corresponding meteorological conditions. Results based on the regression analysis between the MO timing and seasonal anomalies of surface longwave radiative fluxes reveal strong relationships. Synoptic scale (3-14 days) anomalies in downward longwave radiation are essential in the Western Arctic. Regarding the longer history (20-60 days) the distinct contribution from the downward longwave radiative fluxes is captured within the whole study region. Positive anomalies in the downward longwave radiation dominate over the simultaneous negative anomalies in the downward shortwave radiation. The anomalies in downward radiative fluxes are consistent with the total column water vapor, sea level pressure and 10-m wind direction. Sensible and latent heat fluxes affect surface melt timing in the Beaufort Sea and in the Atlantic sector of the Arctic Basin. Stronger winds strengthen the relationship between the turbulent fluxes and the MO timing. The turbulent surface fluxes in spring are relatively weak, of the order of 1-10W/m2, compared to the downward shortwave and longwave radiative fluxes, which are of the order of 100-150W/m2. As soon as data uncertainties are comparable to the anomaly in turbulent fluxes, statistical relationships found between MO timing and preceding anomaly in turbulent fluxes do not necessarily prove their reasonal-causal relationship. This joint study of SSM/I-based MO record and the ERA-Interim meteorological fields region-wide with a focus on the seasonal transition demonstrates their consistency in time and space. Such result could be regarded as an important indicator that both data sets have the appropriate performance of the surface state in the Arctic Ocean. Nevertheless, an important additional effort is needed for to resolve better the cloud radiative and boundary layer turbulent processes over the sea ice.

Maksimovich, E.

2010-09-01

263

Dependence of the time scale of the Greenland Ice Sheet's response to imposed temperature change  

NASA Astrophysics Data System (ADS)

An ensemble of ice sheet model simulations shows that the time scale of the Greenland Ice Sheet's response to climate warming depends strongly on temperature increase. The Greenland Ice Sheet is believed to be sensitive to temperature. Previous modeling studies suggest that the ice sheet will inevitably disintegrate for global mean temperature changes of 1-3 K above preindustrial values, and that this disintegration could take as little as 300 yr. However, few studies have systematically examined the ice sheet's equilibration properties. Here, we perform simulations with the three-dimensional ice sheet model SICOPOLIS (http://sicopolis.greveweb.net/), in which we impose instantaneous Greenland annual mean temperature increases up to 12 K on the simulated modern ice sheet. The modeled curves of ice volume as a function of time resemble decaying exponential functions, allowing us to extract the equilibrium ice volume change and e-folding time of ice volume decline for different temperature changes. The e-folding time is the time required for the ice sheet to lose 1/e (about a third) of its equilibrium volume change. Consistent with earlier studies, we find that the ice sheet eventually disappears for temperature changes of more than a few degrees. However, we also observe a consistent decline in the e-folding time of ice volume loss, from millennia for small temperature increases to a century or less for large ones. Climate model simulations from the CMIP5 archive show that the larger Greenland temperature anomalies imposed in our experiments could plausibly be achieved by the end of the century. Our simulations examine the response of the ice sheet to instantaneous temperature increases, whereas the real climate response to greenhouse gas increases is lagged; thus, our estimated time scales can be considered as lower bounds for the real ice sheet's response time. SICOPOLIS is a shallow-ice model, meaning that it neglects some stress components within the ice body. We examine how this simplification affects our results using a higher-order profile model. We further comment on the mechanisms involved in producing this decline in time scale with temperature anomaly and the implications of our results for projecting the future of the ice sheet.

Applegate, P. J.; Parizek, B. R.; Nicholas, R. E.; Keller, K.

2013-12-01

264

The melting curve of iron to 250 gigapascals - A constraint on the temperature at earth's center  

NASA Technical Reports Server (NTRS)

The melting curve of iron, the primary constituent of earth's core, has been measured to pressures of 250 gigapascals with a combination of static and dynamic techniques. The melting temperature of iron at the pressure of the core-mantle boundary (136 GPa) is 4800 + or - 200 K, whereas at the inner core-outer core boundary (330 GPa), it is 7600 + or - 500 K. A melting temperature for iron-rich alloy of 6600 K at the inner core-outer core boundary and a maximum temperature of 6900 K at earth's center are inferred. This latter value is the first experimental upper bound on the temperature at earth's center, and these results imply that the temperature of the lower mantle is significantly less than that of the outer core.

Williams, Quentin; Jeanloz, Raymond; Bass, Jay; Svendsen, Bob; Ahrens, Thomas J.

1987-01-01

265

Freezing and melting water in lamellar structures.  

PubMed Central

The manner in which ice forms in lamellar suspensions of dielaidoylphosphatidylethanolamine, dielaidoylphosphatidylcholine, and dioleoylphosphatidylcholine in water depends strongly on the water fraction. For weight fractions between 15 and 9%, the freezing and melting temperatures are significantly depressed below 0 degree C. The ice exhibits a continuous melting transition spanning as much as 20 degrees C. When the water weight fraction is below 9%, ice never forms at temperatures as low as -40 degrees C. We show that when water contained in a lamellar lipid suspension freezes, the ice is not found between the bilayers; it exists as pools of crystalline ice in equilibrium with the bound water associated with the polar lipid headgroups. We have used this effect, together with the known chemical potential of ice, to measure hydration forces between lipid bilayers. We find exponentially decaying hydration repulsion when the bilayers are less than about 7 A apart. For larger separations, we find significant deviations from single exponential decay. PMID:7948683

Gleeson, J T; Erramilli, S; Gruner, S M

1994-01-01

266

Cold ice in the ablation zone: Its relation to glacier hydrology and ice water content  

NASA Astrophysics Data System (ADS)

ice within a polythermal ice body controls its flow dynamics through the temperature dependence of viscosity, and affects glacier hydrology by blocking water flow paths. Lakes on the surface, linked by persistent, deeply incised meltwater streams, are hallmark features of cold ice in the ablation zone of a glacier or ice sheet. Ice radar is a convenient method to map scattering from internal water bodies present in ice at the pressure melting temperature (PMT). Consequently, lack of internal scatters is indicative of cold ice. We use a helicopter-borne 30 MHz ice radar to delineate the extent of cold ice within Grenzgletscher (Zermatt, Swiss Alps). The inferred thermal structure is validated with temperature measurements in 15 deep boreholes, showing excellent agreement. The cold ice occupies 80-90 % of the total ice thickness in a 400 m wide flow band along the central flow line. Quantitative interpretation of ice radar scattering power indicates a decrease of ice water content between PMT and 0.5 K below PMT, as predicted by theory, and observed in the laboratory. The cold ice which emerges at the surface in the lower ablation zone is impermeable to water, and is thus devoid of moulins if not crevassed. The surface water from melt and rain is routed through deeply incised, persistent streams and lakes, and cryoconite holes are frequent, in stark contrast to the adjacent temperate ice from other tributaries. The cold ice thus has a strong control on glacier hydrology, but is likely to change due to continued warming.

Ryser, C.; Lthi, M.; Blindow, N.; Suckro, S.; Funk, M.; Bauder, A.

2013-06-01

267

Low temperature biodegradation of airport de-icing fluids.  

PubMed

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

Revitt, D M; Worrall, P

2003-01-01

268

Early spring turbulent mixing in an ice-covered Arctic fjord during transition to melting  

NASA Astrophysics Data System (ADS)

Observations are presented of currents, hydrography and turbulence in a jet-type tidally forced fjord in Svalbard. The fjord was ice covered at the time of the experiment in early spring 2004. Turbulence measurements were conducted by both moored instruments within the uppermost 5 m below the ice and a microstructure profiler covering 3-60 m at 75 m depth. Tidal choking at the mouth of the fjord induces a tidal jet advecting relatively warmer water past the measurement site and dominating the variability in hydrography. While there was no strong correlation with the observed hydrography or mixing and the phase of the semidiurnal tidal cycle, the mean structure in dissipation of turbulent kinetic energy, work done under the ice and the mixing in the water column correlated with the current when conditionally sampled for tidal jet events. Observed levels of dissipation of turbulent kinetic energy per unit mass, 1.110 -7 W kg -1, and eddy diffusivity, 7.310 -4 m 2 s -1, were comparable to direct measurements at other coastal sites and shelves with rough topography and strong forcing. During spring tides, an average upward heat flux of 5 W m -2 in the under-ice boundary layer was observed. Instantaneous (1 h averaged) large heat flux events were correlated with periods of large inflow, hence elevated heat fluxes were associated with the tidal jet and its heat content. Vertical heat fluxes are derived from shear-probe measurements by employing a novel model for eddy diffusivity [Shih et al., 2005. Parameterization of turbulent fluxes and scales using homogeneous sheared stably stratified turbulence simulations. Journal of Fluid Mechanics 525, 193-214]. When compared to the direct heat flux measurements using the eddy correlation method at 5 m below the ice, the upper 4-6 m averaged heat flux estimates from the microstructure profiler agreed with the direct measurements to within 10%. During the experiment water column was stably, but weakly, stratified. Destabilizing buoyancy fluxes recorded close to the ice were absent at 5 m below the ice, and overall, turbulence production was dominated by shear. A scaling for dissipation employing production by both stress and buoyancy [Lombardo and Gregg, 1989. Similarity scaling of viscous and thermal dissipation in a convecting boundary layer. Journal of Geophysical Research 94, 6273-6284] was found to be appropriate for the under-ice boundary layer.

Fer, Ilker; Widell, Karolina

2007-09-01

269

Characterization of Superhydrophobic Surfaces for Anti-icing in a Low-Temperature Wind Tunnel  

SciTech Connect

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.

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

270

Ocean interactions with the base of Amery Ice Shelf, Antarctica  

NASA Astrophysics Data System (ADS)

Using a two-dimensional ocean thermohaline 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 seafloor 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. A freshwater flux across the grounding line, derived from melting beneath the grounded ice sheet, would have to be anomalously large to produce the basal marine ice layer and account for the Ice Shelf Water outflow. 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.

Hellmer, Hartmut H.; Jacobs, Stanley S.

1992-12-01

271

Calculating melting temperatures and pressures of peridotite protoliths: Implications for the origin of cratonic mantle  

NASA Astrophysics Data System (ADS)

The old, stable cores of continents - cratons - are underlain by thick and cold mantle keels, composed of melt-depleted and low density peridotite residues. The origins of these thick keels are debated. Were these thick keels formed in situ, by orogenic thickening, or by underplating of buoyant residual mantle? Key to this debate is determining the temperature and pressure at which the protoliths of cratonic peridotites melted (igneous protolith conditions) and comparing to their metamorphic (subsolidus) temperatures and pressures within the keel. This paper presents a method for explicit calculation of the temperatures and pressures at which the peridotite protoliths melted. The approach relies only on the bulk FeO and MgO of residual peridotites. A system of equations consisting of mass balance and new calibrations of Mg peridotite/melt partitioning and melt productivity is then solved simultaneously. The igneous protoliths of abyssal peridotites are found to have melted at effective pressures of 1-2 GPa and temperatures of 1300-1400 C, within error of the magmatic temperatures and pressures of melt extraction inferred independently from the SiO2 and MgO contents of mid-ocean ridge basalts. Archean cratonic peridotites, after filtering for the secondary effects of refertilization and orthopyroxene-metasomatism, give igneous protolith pressures and temperatures of 1-5 GPa (30-150 km) and 1400-1750 C, similar to magmatic temperatures and pressures determined for Archean basalts thought to be representative of the thermal state of the Archean ambient mantle. Most importantly, cratonic peridotite protolith pressures and temperatures are shallower and hotter than their subsolidus equilibration pressures (3-7.5 GPa; 90-200 km) and temperatures (900-1300 C), which reflects the recent thermal state of the cratonic lithosphere. Specifically, for individual samples with both melting and subsolidus thermobarometric constraints, we find that subsolidus pressures are 1-2 GPa (30-60 km) higher than their igneous protolith pressures although some of the deepest samples experienced minor increases in pressure. Collectively, these results support the suggestion that the building blocks of cratons were generated by hot shallow melting with a mantle potential temperature 200-300 C warmer than the present. This shallowly generated mantle was subsequently thickened during orogenic episodes, culminating in the formation of a thick, stable craton. Whether such thickening has any modern analogs cannot be answered from this work alone.

Lee, Cin-Ty A.; Chin, Emily J.

2014-10-01

272

Correlation and Trend Studies of the Sea Ice Cover and Surface Temperatures in the Arctic  

NASA Technical Reports Server (NTRS)

Co-registered and continuous satellite data of sea ice concentrations and surface ice temperatures from 1981 to 1999 are analyzed to evaluate relationships between these two critical climate parameters and what they reveal in tandem about the changing Arctic environment. During the 18-year period, the actual Arctic ice area is shown to be declining at a rate of 3.1 +/- 0.4 % /decade while the surface ice temperature has been increasing at 0.4 +/- 0.2 K /decade. Yearly anomaly maps also show that the ice concentration anomalies are predominantly positive in the 1980s and negative in the 1990s while surface temperature anomalies were mainly negative in the 1980s and positive in the 1990s. The yearly ice concentration and surface temperature anomalies are shown to be highly correlated indicating a strong link especially in the seasonal region and around the periphery of the perennial ice cover. The surface temperature data are also especially useful in providing the real spatial scope of each warming (or cooling) phenomenon that usually extends beyond the boundaries of the sea ice cover. Studies of the temporal variability of the summer ice minimum also reveal that the perennial ice cover has been declining at the rate of 6.6% /decade while the summer surface ice temperature has been increasing at the rate of 1.3 K /decade. Moreover, high year-to-year fluctuations in the minimum ice cover in the 1990s may have caused reductions in average thickness of the Arctic sea ice cover.

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

2001-01-01

273

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

NASA Astrophysics Data System (ADS)

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.

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

2007-12-01

274

THE JOURNAL OF CHEMICAL PHYSICS 138, 124707 (2013) Grain boundary melting in ice  

E-print Network

crystals a light scattering apparatus was constructed to nucleate ice bicrystals, control their growth; accepted 10 March 2013; published online 28 March 2013) We describe an optical scattering study of grain should be addressed. Electronic mail: erik.thomson@chem.gu.se modynamic parameters are varied, laser

Wettlaufer, John S.

275

Effects of Fat Content on the Sensory Properties, Melting, Color, and Hardness of Ice Cream1  

Microsoft Academic Search

Ice creams were prepared that varied only in the percentage of milk fat (0.1, 3, 7, or 10%) and the corresponding total solids. All mixes were formulated to have similar freezing points and percentages of water frozen. Quantitative descriptive analysis was used to develop a ballot, which was then used by a trained sensory panel to assess the appearance, flavor,

Ann M. Roland; Lance G. Phillips; Kathryn J. Boor

1999-01-01

276

Quantum melting of a two-dimensional vortex lattice at zero temperature  

Microsoft Academic Search

We consider the quantum melting of a two-dimensional flux lattice at temperature T = 0 in the ``superclean limit.'' In this regime, we find that vortex motion is dominated by the Magnus force. A Lindemann criterion predicts melting when nv\\/np>=beta, where nv and np are the areal number densities of vortex pancakes and Cooper pairs, and beta~=0.1. A second criterion

A. Rozhkov; D. Stroud

1996-01-01

277

Measurement of the melting point temperature of several lithium-sodium-beryllium fluoride salt (FLINABE) mixtures  

Microsoft Academic Search

The molten salt Flibe, a combination of lithium and beryllium flourides, was studied for molten salt fission reactors and has been proposed as a breeder and coolant for the fusion applications. 2LiF-BeF melts at 460 C. LiF-BeF melts at a lower temperature, 363 C, but is rather viscous and has less lithium breeder. In the Advanced Power Extraction (APEX) Program,

Timothy J. Boyle; Kenneth P. Troncosa; Richard Einar Nygren; Thomas Joseph Lutz; Jimmie M. McDonald; Tina Joan Tanaka; Michael Andrew Ulrickson

2004-01-01

278

Snow and Ice Melt Flow Features on Devon Island, Nunavut, Arctic Canada as Possible Analogs for Recent Slope Flow Features on Mars  

NASA Technical Reports Server (NTRS)

Based on morphologic and contextual analogs from Devon Island, Arctic Canada, the recent martian slope flow features reported by Malin and Edgett are reinterpreted as being due not necessarily to groundwater seepage but possibly to snow or ice melt. Additional information is contained in the original extended abstract.

Lee, Pascal; Cockell, Charles S.; Marinova, Margarita M.; McKay, Christopher P.; Rice, James W., Jr.

2001-01-01

279

Reply to ``Comment on `Determination of the bulk melting temperature of nickel using Monte Carlo simulations: Inaccuracy of extrapolation from cluster melting temperatures' ''  

NASA Astrophysics Data System (ADS)

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 pressure) are usually rather close, small shifts in the free energy curves can lead to a large change in the calculated melting temperature. In this Reply to a Comment by Harvey and Gheribi [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.84.096102 84, 096102 (2011)] on our paper [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.81.064112 81, 064112 (2010)], we show that the error in the calculated melting temperature of nickel induced by some technical imperfections in our application of the TI method, as noticed and described in the Comment, is small compared to the error bar given in our paper. We also clarify supposed doubts about the accuracy of the TI method based on Johnson's free energy expression and parametrization [Johnson , Mol. Phys.MOPHAM0026-897610.1080/00268979300100411 78, 591 (1993)] of the Lennard-Jones fluid.

Los, J. H.; Pellenq, R. J. M.

2011-09-01

280

Effect of pressure, temperature, and bulk composition on the structure and species distribution in depolymerized alkali aluminosilicate melts and quenched melts  

Microsoft Academic Search

Influence of pressure, temperature, and bulk composition on the structure of di- and tetra-aluminosilicate melts and quenched melts have been studied with Raman spectroscopy. The melt polymerization and Al(Al+Si) ranges represented are those typically found in quartz-normative basaltic magmatic liquids. The reaction describing the equilibrium among coexisting units in the melts is T2O5(2Q3)0\\/00TO3(Q4), where T=Si+Al, and the superscripts on the

Bjorn O. Mysen

1990-01-01

281

Effective Temperature in an Interacting Vertex System: Theory and Experiment on Artificial Spin Ice  

E-print Network

Effective Temperature in an Interacting Vertex System: Theory and Experiment on Artificial Spin Ice temperature [1­3] (often in the context of glassy transitions, jamming, and rheology [4­7]) on the grounds introduced nanometer-scale metamaterial, ``artificial spin ice'' [12­17], which is controlled by nontrivial

282

Development of a Climate-Data Record of the Surface Temperature of the Greenland Ice Sheet (Invited)  

NASA Astrophysics Data System (ADS)

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 0.570.02 (Wang and Key, 2005) to 0.720.10 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. Key/NOAA 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). References Comiso, J. C., 2006: Arctic warming signals from satellite observations, Weather, 61(3): 70- 76. Fowler, C. et al., 2000: updated 2007. AVHRR Polar Pathfinder Twice-daily 5 km EASE-Grid Composites V003, [used dates from 2000 - 2004], Boulder, CO: NSIDC. Digital media. Hall, D.K., J.Key, K.A. Casey, G.A. Riggs and D. J. Cavalieri, 2004: Sea ice surface temperature product from the Moderate-Resolution Imaging Spectroradiometer (MODIS), IEEE TGRS, 42(5):1076-1087. Hanna, E., P. Huybrechts, K. Steffen, J. Cappelen, R. Huff, C.A. Shuman, T. Irvine-Fynn and S. Wise, 2008: Increased runoff from melt from the Greenland Ice Sheet: a response to global warming? J. Climate, vol. 21(2):331-341. Key, J., and M. Haefliger, 1992: Arctic ice surface temperature retrieval from AVHRR thermal channels, JGR, 97:5885-5893. Koenig, L.S. and D.K. Hall, in press: Comparison of satellite, thermochron and station temperatures at Summit, Greenland, during the winter of 2008-09, J. Glaciol. Shuman, C.A., K. Steffen, J.E. Box and C.R. Stearns, 2001: A dozen years of temperature observations at the Summit: Central Greenland automatic weather stations 1987-1999, JAM, 40(4):741-752. Wang, X., and J. Key, 2005: Arctic surface, cloud, and radiation properties based on the AVHRR Polar Pathfinder data set. Part II: Recent trends, J. Climate, 18, 2575- 2593.

Hall, D. K.; Comiso, J. C.; Digirolamo, N. E.; Shuman, C. A.

2010-12-01

283

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

E-print Network

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.

Tamio Yamazaki

2014-04-03

284

A climate-data record of the clear-sky surface temperature of the Greenland Ice Sheet (Invited)  

NASA Astrophysics Data System (ADS)

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 & 2007). 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: 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 (Stroeve & Steffen, 1998; Wang and Key, 2005; Hall et al., 2008 and Koenig and Hall, submitted), time-series of satellite IST do not necessarily correspond to actual surface temperatures. The CDR will be validated by comparing results with automatic-weather 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 0.570.02 deg C (Wang and Key, 2005) to 0.720.10 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 Comiso, J.C., 2006: Arctic warming signals from satellite observations, Weather, 61(3):70-76. Fowler, Chuck, James Maslanik, Terry Haran, Ted Scambos, Jeffrey Key, and William Emery, 2000, updated 2007: AVHRR Polar Pathfinder Twice-daily 5 km EASE-Grid Composites V003, Boulder, Colorado, USA: NSIDC, digital media. Hall, D.K., R.S. Williams, S.B. Luthcke and N.E. Digirolamo, 2008: Greenland ice sheet surface temperature, melt and mass loss: 2000-06, J. Glaciol., 54(184):81-93. Koenig, L.S. and D.K. Hall, submitted: Comparison of satellite, thermochron and station temperatures at Summit, Greenland during the winter of 2008-09 with implications for global-change monitoring, J. Glaciol. (under review). Stroeve, J. and K. Steffen, 1998: Variability of AVHRR-derived clear-sky surface temperature over the Greenland ice sheet, JAM, 37(1):23-31. Wang, X.J. and J.R. Key, 2005: Arctic surface, cloud, and radiation properties based on the AVHRR Polar Pathfinder dataset. Part II: Recent trends, J. Climate, 18(14):2575-2593.

Hall, D. K.; Comiso, J. C.; Digirolamo, N. E.; Stock, L. V.; Riggs, G. A.; Shuman, C. A.

2009-12-01

285

`Melting ice' I at 77 K and 10 kbar: a new method of making amorphous solids  

Microsoft Academic Search

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

O. Mishima; L. D. Calvert; E. Whalley

1984-01-01

286

Water-melt interaction in hydrous magmatic systems at high temperature and pressure  

NASA Astrophysics Data System (ADS)

Experimental data on the structure and properties of melts and fluids relevant to water-melt interaction in hydrous magmatic systems in the Earth's interior have been reviewed. Complex relationships between water solubility in melts and their bulk composition [Al/Si-ratio, metal oxide/(Al + Si) and electron properties of metal cations] explain why water solubility in felsic magmas such as those of rhyolite and andesite composition is significantly greater than the water solubility in basalt melts. The silicate solubility in aqueous fluid is also significantly dependent on composition with metal oxide/(Al + Si) and electron properties of the metal cations, the dominant variables. Hydrogen bonding is not important in hydrous fluids and melts at temperatures above 500C to 550C and does not, therefore, play a role in hydrous magmatic systems. The properties of hydrous melts and aqueous solutions are governed by how the silicate speciation ( Q n species, where n is the number of bridging oxygen in an individual species) varies with bulk composition, silicate composition, temperature, and pressure. The reactions that describe the interactions are similar in melts, fluids, and supercritical fluids. The degree of melt polymerization caused by dissolved water varies with melt composition and total water content. Silicate- and alkali-rich felsic magmatic melts are more sensitive to water content than more mafic magmas. Transport and configurational properties of hydrous magmatic melts can be modeled with the aid of the Q n speciation variations. Liquidus and melting phase relations of hydrous systems also can be described in such terms, as can minor and trace element partition coefficients. Stable isotope fractionation (e.g., D/H) can also be rationalized in this manner. Critical to these latter observations is the high silicate concentration in aqueous fluids. These components can enhance solubility of minor and trace elements by orders of magnitude and change the speciation of H and D complexes so that their fractionation factors change quite significantly. Data from pure silicate-H2O systems cannot be employed for these purposes.

Mysen, Bjorn

2014-12-01

287

Quantum melting of a two-dimensional vortex lattice at zero temperature  

NASA Astrophysics Data System (ADS)

We consider the quantum melting of a two-dimensional flux lattice at temperature T = 0 in the ``superclean limit.'' In this regime, we find that vortex motion is dominated by the Magnus force. A Lindemann criterion predicts melting when nv/np>=?, where nv and np are the areal number densities of vortex pancakes and Cooper pairs, and ?~=0.1. A second criterion is derived by using Wigner-crystal and Laughlin wave functions for the solid and liquid phases respectively, and setting the two energies equal. This gives a melting value similar to the Lindemann result. We discuss the numerical value of the T=0 melting field for thin layers of a low-Tc superconductor, such as a-MoGe, and single layers of high-Tc materials.

Rozhkov, A.; Stroud, D.

1996-11-01

288

Tools made of ice facilitate forming of soft, sticky materials  

NASA Technical Reports Server (NTRS)

Tools made of ice facilitate the forming or shaping of materials that are soft and sticky in the uncured state. The low-temperature of the ice slows the curing of the material, extending the working time available before setup. Handling problems are eliminated because the material does not adhere to the tool, and the melting ice serves as a lubricant.

Harris, J. E.; Ramsey, J. G., Jr.; Schinbeckler, K. D.

1969-01-01

289

Melt temperature field measurement in single screw extrusion using thermocouple meshes  

NASA Astrophysics Data System (ADS)

The development and validation of a sensor for extrusion melt temperature field measurement is described. A grid of opposing thermocouple wires was constructed and held in position by a supporting frame. Wires were joined together at crossing points to form thermocouple junctions, which were computer monitored. The mesh was used to monitor melt temperature fields during single screw extrusion at the die entrance. Design and construction of the mesh is described in addition to experimental optimization of wire diameter and junction forming. Calibration of the sensor and potential measurement errors including shear heating effects are discussed. Initial results from single screw extrusion are presented for a commercial grade of low density polyethylene using five- and seven-junction thermocouple meshes. The dependence of melt temperature profile on screw speed is illustrated. At low screw speeds melt temperature profiles were flat in shape and higher than set wall temperatures. At higher screw speeds the profiles became more pointed in shape. Use of higher resolution sensors exposed more complex temperature profiles with shoulder regions.

Brown, E. C.; Kelly, A. L.; Coates, P. D.

2004-11-01

290

Ocean rises are products of variable mantle composition, temperature and focused melting  

NASA Astrophysics Data System (ADS)

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.

Dick, Henry J. B.; Zhou, Huaiyang

2015-01-01

291

Temperature Dependence of Density, Viscosity and Electrical Conductivity for Hg-Based II-VI Semiconductor Melts  

NASA Technical Reports Server (NTRS)

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.

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

2004-01-01

292

Decadal variations in Labrador Sea ice cover and North Atlantic sea surface temperatures  

Microsoft Academic Search

The spatial and temporal evolution of winter sea ice anomalies in the Labrador Sea and associated sea surface temperature (SST) variations in the North Atlantic are documented for three periods of above-normal ice cover: 1972-1974, 1983-1985, and 1990-1992. These events are notable for their winter-to-winter persistence, despite the fact that the ice margin retreats to northern Baffin Bay each summer,

Clara Deser; Marika Holland; Gilles Reverdin; Michael Timlin

2002-01-01

293

Sensitivity of AMSR-E Brightness Temperatures to the Seasonal Evolution of Lake Ice Thickness  

Microsoft Academic Search

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

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

2010-01-01

294

A High Temporal-Resolution Dataset of ERS Scatterometer Radar Backscatter and its Application to Detecting Melt Onset on Small Arctic Ice Caps  

NASA Astrophysics Data System (ADS)

Radar backscatter in Arctic and sub-Arctic regions is temporally dynamic and reflects changes in sea ice, glacier facies, soil thaw state, vegetation cover and moisture content. Wind scatterometers on the ERS-1 and ERS-2 satellites have amassed a global archive of C-band radar backscatter data since 1991. We derive three high temporal resolution data products in polar stereographic projection from this archive that are designed to facilitate scatterometer research in high latitude environments. Radar backscatter data have a grid spacing of 25 km and are mapped northwards from 60N latitude over intervals of one, three and seven days for the period between August 1991 and December 2000. Data are corrected to a normalized incident angle of 40. Animations and full-resolution data products are freely available for scientific use at http://merced.gis.ucla.edu/scatterometer/index.htm. We use the daily product of nine years (1992-2000) to detect melt onset of 15 small ice caps scattered in Arctic and sub-Arctic regions. A melt event exhibits a sharp drop on the time series backscatter profile of the site. A computer algorithm was developed to detect melt onset from backscatter time-series. The algorithm successfully detects about 85% of the onset dates for the 15 sites. Regional differences in the timing of melt onset are found between ice caps of the Canadian Archipelago, North Atlantic and Russian sectors. >http://merced.gis.ucla.edu/scatterometer/index.htm

Sheng, Y.; Smith, L. C.; Frey, K. E.; Alsdorf, D. E.

2001-12-01

295

Melting analysis on microbeads in rapid temperature-gradient inside microchannels for single nucleotide polymorphisms detection.  

PubMed

A continuous-flow microchip with a temperature gradient in microchannels was utilized to demonstrate spatial melting analysis on microbeads for clinical Single Nucleotide Polymorphisms (SNPs) genotyping on animal genomic DNA. The chip had embedded heaters and thermometers, which created a rapid and yet stable temperature gradient between 60?C and 85?C in a short distance as the detection region. The microbeads, which served as mobile supports carrying the target DNA and fluorescent dye, were transported across the temperature gradient. As the surrounding temperature increased, the fluorescence signals of the microbeads decayed with this relationship being acquired as the melting curve. Fast DNA denaturation, as a result of the improved heat transfer and thermal stability due to scaling, was also confirmed. Further, each individual microbead could potentially bear different sequences and pass through the detection region, one by one, for a series of melting analysis, with multiplex, high-throughput capability being possible. A prototype was tested with target DNA samples in different genotypes (i.e., wild and mutant types) with a SNP location from Landrace sows. The melting temperatures were obtained and compared to the ones using a traditional tube-based approach. The results showed similar levels of SNP discrimination, validating our proposed technique for scanning homozygotes and heterozygotes to distinguish single base changes for disease research, drug development, medical diagnostics, agriculture, and animal production. PMID:25553186

Li, Kan-Chien; Ding, Shih-Torng; Lin, En-Chung; Wang, Lon Alex; Lu, Yen-Wen

2014-11-01

296

Combined influence of temperature forcing and lapse rate on empirical melt-model performance  

NASA Astrophysics Data System (ADS)

Temperature-index models are popular tools for glacier melt-modeling at a variety of scales and are widely used in projections of glacier mass change. Though minimal input data are required to drive these models, the necessary data may only exist distal from the area of interest. Here we explore the combined effects of temperature forcing provenance and surface lapse rate on the performance of an empirical melt model. The model is applied to a polythermal glacier in the St. Elias Mountains of northwestern Canada over five melt seasons. Air temperature records come from three different environments: (1) glacier surfaces, (2) glacier-proximal locations, and (3) low elevation valleys, and are combined with constant lapse rates spanning the range of measured values from the temperature stations to the study site. Model performance is assessed by comparing measured and modeled cumulative summer ablation at a network of stakes and by evaluating the transferability of the model to a second site. We find that the temperature forcings and lapse rates have a modest impact on model performance, relative to the inter-annual variability of model performance due to melt-season conditions and calibration data quality. Despite < 30% variation in estimated summer ablation arising from the combined influences of temperature forcing and lapse rate, the resulting variations in estimated annual mass balance are >100% in some cases. We hypothesize that the quality and quantity of mass-balance data available for model calibration may play a larger role than the combined temperature forcing and lapse rate in dictating empirical melt-model performance.

Flowers, G. E.; Wheler, B.; MacDougall, A. H.; Petersen, E. I.; Whitfield, P. H.; Kohfeld, K. E.

2013-12-01

297

Hydrohalite in cold sea ice: Laboratory observations of single crystals, surface accumulations, and migration rates under a temperature  

E-print Network

the fractional volumes of ice, gas, brine, and precipitated salt. [3] Temperatures within sea ice exhibit a wide and desiccation. Sublimation of a sea ice surface at low temperature leaves a lag deposit of hydrohalite, which depend strongly on temperature, because of freezing-equilibrium relationships which dictate

Warren, Stephen

298

Evolution of Temperature-Driven Stability of Ice on the Moon  

NASA Astrophysics Data System (ADS)

Temperature is the dominant control of ice stability on the Moon. In order to examine the spatial, quantitative, and temporal variability of lunar ice, in this study I develop components of a comprehensive thermal-diffusion model of ice migration. The lunar environment varies dramatically in temperature, from roughly 400 K at the equator, to as low as 20 K in shadowed polar regions. As the sublimation of water ice is exponentially dependent on temperature, this causes an even larger variation in ice stability. However, the lunar thermal environment is a dynamic system. In this work, I model orbital interactions with the Earth and Sun that brought about huge changes in lunar polar illumination. The most dramatic event in this orbital evolution was a high obliquity spin-orbit transition, during which surface temperatures of currently shadowed regions would have exceeded 390 K. Therefore, all lunar ice should have deposited after this event. In order to examine the effects of the evolution of the lunar orbit on the subsurface temperatures and ice migration, I also examine variations in thermal properties and global variation in geothermal heat production. Both of these quantities are important controls over the depth at which ice could be emplaced and are examined here using Apollo era and recent data from the Lunar Reconnaissance Orbiter's Diviner Lunar Radiometer. Additionally, using laboratory data taken under Martian conditions, I examine the likely effects of diffusively emplaced ice on regolith thermal properties. The geometry of vapor-emplaced ice results in a linear variation in thermal conductivity with ice content which differs from previous theory. These components are then compiled together in a preliminary thermal-diffusion model, which will allow for examination of spatial and quantitative prediction of subsurface ice. This model shows that retention of supplied ice is highly temperature dependent, favoring efficient migration of ice into the subsurface between roughly 95 and 145 K, depending on local temperature amplitudes. This causes a favored period in the evolution of the lunar orbit for ice deposition at a given location. Therefore, variations in the spatial distribution of polar volatiles may mark a specific period of enhanced supply, most likely in the form of cometary impacts. I briefly examine how this might play a role in volatile deposition and loss on other solar system bodies.

Siegler, Matthew Adam

299

Recent variations of sea ice and air temperature in high latitudes  

SciTech Connect

Feedbacks resulting from the retreat of sea ice and snow contribute to the polar amplification of the greenhouse warming projected by global climate models. A gridded sea-ice database, for which the record length is now approaching four decades for the Arctic and two decades for the Antarctic, is summarized here. The sea-ice fluctuations derived from the data set are characterized by (1) temporal scales of several seasons to several years and (2) spatial scales of 30[degrees]-180[degrees] of longitude. The ice data are examined in conjunction with air temperature data for evidence of recent climate change in the polar regions. The arctic sea-ice variations over the past several decades are compatible with the corresponding air temperatures, which show a distinct warming that is strongest over northern land areas during the winter and spring. The temperature trends over the sub arctic seas are smaller and even negative in the southern Greenland region. Statistically significant decreases of the summer extent of arctic ice are apparent in the sea-ice data, and new summer minima have been achieved three times in the past 15 years. There is no significant trend of ice extent in the Arctic during winter or in the Antarctic during any season. The seasonal and geographical changes of sea-ice coverage are consistent with the more recent greenhouse experiments performed with coupled atmosphere-ocean models.

Chapman, W.L.; Walsh, J.E. (Univ. of Illinois, Urbana (United States))

1993-01-01

300

Ice crystal number concentration versus temperature for climate studies  

Microsoft Academic Search

ABSTRACT Ice crystal number concentration (Ni) is an important parameter, having a strong influence on the calculation of cloud ,optical and ,microphysical ,parameters. Cloud and ,precipitation parameterizations within climate and weather forecasting models, affecting the heat and moisture budget of the atmosphere, cannot be determined accurately if Ni is not estimated correctly. Previous studies of ice ,crystal number ,concentration versus

I. Gultepe; G. A. Isaac; S. G. Cober

2001-01-01

301

Cenozoic global ice-volume and temperature simulations with 1-D ice-sheet models forced by benthic delta O-18 records  

Microsoft Academic Search

Variations in global ice volume and temperature over the Cenozoic era have been\\u000ainvestigated with a set of one-dimensional (1-D) ice-sheet models. Simulations include three ice sheets\\u000arepresenting glaciation in the Northern Hemisphere, i.e. in Eurasia, North America and Greenland, and\\u000atwo separate ice sheets for Antarctic glaciation. The continental mean Northern Hemisphere surface-air\\u000atemperature has been derived through an

B. de Boer; R. Bintanja; L. J. Lourens; E. Tuenter

2010-01-01

302

Ice  

NSDL National Science Digital Library

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.

Harris, Kathryn L.

303

Laboratory investigations of the temperature dependence of hypervelocity impact cratering in ice  

Microsoft Academic Search

Laboratory investigations by hypervelocity impact cratering in water ices are usually carried out at temperatures of approximate 250-265 K. However, icy surfaces in the Solar System are typically at lower temperatures. Accordingly a study of the temperature dependence of cratering in water ice has been carried out using a two-stage light gas gun firing mm-sized projectile at 5 - 6

I. D. S. Grey; M. J. Burchell; N. R. G. Shrine

2001-01-01

304

Laboratory investigations of the temperature dependence of hypervelocity impact cratering in ice  

Microsoft Academic Search

Laboratory investigations by hypervelocity impact cratering in water ices are usually carried out at temperatures of approximate 250265 K. However, icy surfaces in the Solar System are typically at lower temperatures. Accordingly a study of the temperature dependence of cratering in water ice has been carried out using a two-stage light gas gun firing mm-sized projectile at 5 6

I. D. S. Grey; M. J. Burchell; N. R. G. Shrine

2001-01-01

305

Improvements to the Total Temperature Calibration of the NASA Glenn Icing Research Tunnel  

NASA Technical Reports Server (NTRS)

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.

Arrington, E. Allen; Gonsalez, Jose C.

2005-01-01

306

The temperature-dependent near-infrared absorption spectrum of hexagonal H2O ice  

Microsoft Academic Search

Transmission spectra were measured between 1.0 and 2.7 mum for monocrystalline samples of hexagonal water ice at temperatures between 20 and 270 K. Samples were crystallized from liquid water within closed cells, with thicknesses ranging from 100 mum to 1.0 cm. The absorption spectrum of ice changes with temperature in several ways. With higher temperature, the shapes of absorption bands

W. M. Grundy; B. Schmitt

1998-01-01

307

Pre-heated MgO Shock Temperature Experiments Require a Hot Melting Curve  

NASA Astrophysics Data System (ADS)

MgO is a critical end member for lower mantle phase relations, yet its melting curve is highly controversial. Experimental studies are divergent: a very cold curve from laser-heated DAC [1], a very hot curve from large-volume press study of the MgO-FeO binary loop [2]. Both must be extrapolated upwards to lower mantle pressure (P). Also, despite ab initio and molecular dynamics studies [3-7] span the range between experimental extremes (Figure 1). The melting temperature (T) of MgO helps determine whether lower mantle minimum melts are silicate- or oxide-rich, whether ferropericlase is a liquidus mineral in a magma ocean, and how strongly FeO partitions into melts during crystallization or melting. Shock wave methods can resolve this issue, but compression of MgO from room T requires extreme compression to reach candidate melting curves; this requires laser-based shocks and such results must be extrapolated downwards to lower mantle P. Our approach is to pre-heat single-crystal MgO samples before light gas gun impact, to bring expected melting point crossings into the 100-200 GPa range. Our diagnostic for melting is shock T; melting manifests as a drop in shock T with increasing P and shock T lower than expected for solid periclase. We calibrate against a standard irradiance lamp and the known shock T of NaCl and MgO shocked from 300 K and correct for shock-front reflectivity. A series of experiments from initial T=1850 K reach 9000 K at 250 GPa and remain solid in the shock state. This rules out the melting curve of [1] and probably [3], but gives only a lower bound on the melting curve. Experiments with initial T up to 2350 K are in progress; these are challenging due to material compatibility issues, e.g., evaporation of MgO into vacuum above 2100 K. 1. Zerr & Boehler. Nature, 1994. 371:506-508. 2. Zhang & Fei. Geophys. Res. Lett., 2008. 35(13): L13302. 3. Strachan et al. Phys. Rev. B, 1999. 60:15084-15093. 4. Belonoshko & Dubrovinksy. Geochim. Cosmochim. Acta, 1996. 60(10):1645-1656. 5. Cohen & Gong. Phys. Rev. B, 1994. 50(17): 12301-12311. 6. Cohen & Weitz, in AGU Geophysical Monograph 101, M.H. Manghnani and T. Yagi, Editors. 1998. p. 185-196. 7. Liu et al.. Phys. Lett. A, 2006. 353(2-3):221-225.

Asimow, P. D.; Fat'yanov, O. V.

2011-12-01

308

A reconstruction of temperature, ice volume and atmospheric CO2 over the past 40 million years  

Microsoft Academic Search

Knowledge on past climate change largely emerges from sediment records drilled from the ocean floor and ice-core records from the Antarctic and Greenland ice sheets. From these records proxy data is obtained indicating changes in, for example, temperature, sea level and greenhouse gas concentrations. A key parameter that emerges from the sediment records is the oxygen isotope ratio, ?18O, from

B. de Boer

2012-01-01

309

Equilibrium concentration of interstitials in aluminum just below the melting temperature  

NASA Astrophysics Data System (ADS)

The Interstitialcy Theory offers a unified description of the solid, liquid, and amorphous states of condensed matter, including a direct criterion for the onset of melting. A major prediction of the theory is that the equilibrium concentration of interstitial defects should be only about an order of magnitude less than the vacancy concentration near the melting temperature. Of the various properties affected by the presence of interstitials, the shear modulus is known to be particularly sensitive. A non-contact EMAT technique of ultrasonic generation and detection was used to make high temperature measurements of the C44 and C' shear elastic moduli in aluminum. The results show a large C44 deviation just below the melting temperature and a much smaller effect for C', which is to be expected for interstitials in FCC crystals. The results are analyzed to give a detected interstitial concentration of 1.7 +/- 0.6 x 10-4 just below the melting temperature of 933 K. This corresponds to a reasonable range for the interstitial formation enthalpy and entropy, and supports the prediction of the Interstitialcy Theory.

Gordon, Craig Alan

2000-10-01

310

PUBLISHED ONLINE: 8 NOVEMBER 2009 | DOI: 10.1038/NPHYS1438 Melting temperature of diamond at  

E-print Network

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

Loss, Daniel

311

Evidence for low-temperature melting of mercury owing to relativity.  

PubMed

An old problem solved: Monte Carlo simulations using the diatomic-in-molecule method derived from accurate ground- and excited-state relativistic calculations for Hg2 show that the melting temperature for bulk mercury is lowered by 105?K, which is due to relativistic effects. PMID:23780699

Calvo, Florent; Pahl, Elke; Wormit, Michael; Schwerdtfeger, Peter

2013-07-15

312

Vertical and horizontal surface displacements near Jakobshavn Isbr driven by melt-induced and dynamic ice loss  

NASA Astrophysics Data System (ADS)

We analyze Global Positioning System (GPS) time series of relative vertical and horizontal displacements from 2009-2011, at four GPS sites located between 5 and 150 km from the front of Jakobshavn Isbr (JI). The horizontal displacements at KAGA, ILUL, and QEQE, relative to the site AASI, are directed towards east-north-east, suggesting that the main mass loss signal is south-east of these sites. The directions of the observed displacements are supported by modelled displacements, derived from NASA's Airborne Topographic Mapper (ATM) surveys of surface elevations from 2006 to 2011. The agreement between the observed and modelled relative displacements is 0.8 mm or better, which suggests that the mass loss estimate of JI is well captured. In 2010, we observe a rapid increase in the uplift at all four sites. This uplift anomaly, defined as the deviation at 2010.75 from the 2006-2009.75 trend is estimated to 8.8 +/- 2.4 mm (KAGA), 9.3 +/- 2.2 mm (ILUL), 5.1 +/- 2.0 mm (QEQE), and 6.1 +/- 2.3 mm (AASI). The relative large anomalies at the sites QEQE and AASI, located ~150 km from the front of JI, suggests that the uplift anomalies are caused by a large wide-spread melt-induced ice loss. The relatively low uplift anomaly at KAGA, located only 5 km from the front, indicates that there has been a dramatic decrease in dynamic-induced ice loss near the front of JI. This is supported by elevation changes derived from ATM measurements between 2010 and 2011, where we observe an elevation increase in the flow direction of up to 10 m at the frontal part of JI.

Khan, S. A.; Nielsen, K.; Wahr, J. M.; Bevis, M. G.; Liu, L.; Spada, G.; van Dam, T. M.

2012-12-01

313

PLS Road surface temperature forecast for susceptibility of ice occurrence  

NASA Astrophysics Data System (ADS)

Winter maintenance relies on many operational tools consisting in monitoring atmospheric and pavement physical parameters. Among them, road weather information systems (RWIS) and thermal mapping are mostly used by service in charge of managing infrastructure networks. The Data from RWIS and thermal mapping are considered as inputs for forecasting physical numerical models, commonly in place since the 80s. These numerical models do need an accurate description of the infrastructure, such as pavement layers and sub-layers, along with many meteorological parameters, such as air temperature and global and infrared radiation. The description is sometimes partially known, and meteorological data is only monitored on specific spot. On the other hand, thermal mapping is now an easy, reliable and cost effective way to monitor road surface temperature (RST), and many meteorological parameters all along routes of infrastructure networks, including with a whole fleet of vehicles in the specific cases of roads, or airports. The technique uses infrared thermometry to measure RST and an atmospheric probes for air temperature, relative humidity, wind speed and global radiation, both at a high resolution interval, to identify sections of the road network prone to ice occurrence. However, measurements are time-consuming, and the data from thermal mapping is one input among others to establish the forecast. The idea was to build a reliable forecast on the sole data from thermal mapping. Previous work has established the interest to use principal component analysis (PCA) on the basis of a reduced number of thermal fingerprints. The work presented here is a focus on the use of partial least-square regression (PLS) to build a RST forecast with air temperature measurements. Roads with various environments, weather conditions (clear, cloudy mainly) and seasons were monitored over several months to generate an appropriate number of samples. The study was conducted to determine the minimum number of samples to get a reliable forecast, considering inputs for numerical models do not exceed five thermal fingerprints. Results of PLS have shown that the PLS model could have a R of 0.9562, a RMSEP of 1.34 and a bias of -0.66. The same model applied to establish a forecast on past event indicates an average difference between measurements and forecasts of 0.20 C. The advantage of such approach is its potential application not only to winter events, but also the extreme summer ones for urban heat island.

Marchetti, Mario; Khalifa, Abderrhamen; Bues, Michel

2014-05-01

314

Non-melting and self-wetting of alkali halide surfaces at high temperatures  

NASA Astrophysics Data System (ADS)

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).

Ceresoli, Davide; Zykova-Timan, Tania; Tartaglino, Ugo; Sekkal, Wassila; Jagla, Edoardo; Tosatti, Erio

2004-03-01

315

Dehydration-melting of amphibolite at 10 kbar: the effects of temperature and time  

Microsoft Academic Search

We have simulated the dehydration-melting of a natural, low-K, calcic amphibolite (67.4% hornblende, 32.5% anorthite) in piston-cylinder experiments at 10 kbar and 7501000C, for 19 days. The solidus temperature is lower than 750C; garnet appears at 850C. The overall reaction is: Hb+P?L+Cpx+Al-Hb+Ca-Hb+Ga+Opx. Three stages of reaction are: (1) melting dominated by the growth of clinopyroxene and garnet, with little change

Michael B. Wolf; Peter J. Wyllie

1994-01-01

316

500,000-year temperature record challenges ice age theory  

USGS Publications Warehouse

Just outside the searing heat of Death Valley lies Devils Hole (fig. 1), a fault-created cave that harbors two remnants of the Earth's great ice ages. The endangered desert pupfish (Cyprinodon diabolis) has long made its home in the cave. A 500,000-year record of the planet's climate that challenges a widely accepted theory explaining the ice ages also has been preserved in Devils Hole.

Snow, K. Mitchell

1994-01-01

317

Wetting by simple room-temperature polymer melts: deviations from Newtonian behavior.  

PubMed

The hydrodynamics near moving contact lines of two room-temperature polymer melts, polyisobutylene (PIB) and polystyrene (PS), are different from those of a third polymer melt, polydimethylsiloxane (PDMS). While all three fluids exhibit Newtonian behavior in rotational rheological measurements, a model of the hydrodynamics near moving contact lines which assumes Newtonian behavior of the fluid accurately describes the interface shape of a variety of PDMS fluids but fails to describe the interface deformation by viscous forces in PIB and PS. The magnitude of the deviations from the model and the distance along the liquid-vapor interface over which they are seen increase with increasing capillary number. We conclude that the wetting behaviors of PIB and PS are influenced by weak elasticity in these low molecular weight melts and that dynamic wetting is more sensitive to this elasticity than standard rheometric techniques. PMID:15752812

Seevaratnam, G K; Walker, L M; Ram, E; Garoff, S

2005-04-01

318

Sulfide saturation of basalt and andesite melts at high pressures and temperatures  

NASA Technical Reports Server (NTRS)

When the sulfur content of an Fe-bearing magma exceeds the saturation limit for the bulk composition, an immiscible iron sulfide melt fraction separates. For an understanding of the geochemistry of sulfur-bearing magmatic systems, more information is needed regarding the solubility of metal sulfide in silicate melt at its source and the solubility changes as a function of changing intensive and extensive variables. In the present investigation, the sulfur saturation surface is determined for the pressure range from 12.5 to 30 kbar and the temperature range from 1300 to 1460 C for three silicate melt compositions representing a range of SiO2 and FeO compositions.

Wendlandt, R. F.

1982-01-01

319

Ch.5 Global Temperatures Temperature Concepts  

E-print Network

and Heat #12; Fahrenheit (ºF) ice melting point at 32ºF, boiling point of water at 212ºF Celsius (ºC) ice melting point at 0ºC, boiling point of water at sea level at 100 ºC Kelvin (K) Absolute zero cover Land-water heating differences Principal Temperature Controls #12;Latitude and Temperature From

Pan, Feifei

320

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

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 Earths gravity field induced by melting of land-based ice masses have been taken\\u000a into account.

Caroline A. Katsman; Wilco Hazeleger; Sybren S. Drijfhout; Geert Jan van Oldenborgh; Gerrit J. H. Burgers

2008-01-01

321

Low Temperature Air Distribution with Ice Storage System: A Case Study  

E-print Network

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...

Ash, A.

1990-01-01

322

Thermal diffusivity of rhyolitic glasses and melts: effects of temperature, crystals and dissolved water  

NASA Astrophysics Data System (ADS)

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.

Romine, William L.; Whittington, Alan G.; Nabelek, Peter I.; Hofmeister, Anne M.

2012-12-01

323

A calorimetric study on the low temperature dynamics of doped ice V and its reversible phase transition to hydrogen ordered ice XIII.  

PubMed

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

Salzmann, Christoph G; Radaelli, Paolo G; Finney, John L; Mayer, Erwin

2008-11-01

324

Evaluation of Ice Water Content Retrievals from Cloud Radar Reflectivity and Temperature Using a Large Airborne In Situ Microphysical Database  

E-print Network

Evaluation 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 larger IWCs) different sets of relationships would have to be used for midlatitude and tropical ice

Protat, Alain

325

Temperature and methane records over the last 2 ka in Dasuopu ice core  

Microsoft Academic Search

High resolution ?18O and methane records over the last 2ka have been reconstructed from Dasuopu ice core recovered from the Himalayas. Analysis\\u000a shows that the ?18O record correlates well with the Northern Hemispheric temperature, Dunde ice core record, and with temperature record in\\u000a eastern China. The warming trend detected in ?18O record from the last century is similar to that

Tandong Yao; L. G. Thompson; Keqin Duan; Baiqing Xu; Ninglian Wang; Jianchen Pu; Lide Tian; Weizhen Sun; Shichang Kang; Xiang Qin

2002-01-01

326

Melting Temperatures of Eutectic Fixed-Point Cells Usable for the Calibration of Contact Thermometers  

NASA Astrophysics Data System (ADS)

The objective of the present investigation was the determination of the melting temperatures of the eutectic compounds Fe C, Co C, and Ni C. Six eutectic fixed-point cells of the Physikalisch-Technische Bundesanstalt (PTB) (Fe C1, Fe C2, Co C1, Co C2, Ni C1, and Ni C2) and two cells of the Brazilian National Metrological Institute (Inmetro) (Fe C1V and Ni C1V), useable for the calibration of contact thermometers, were investigated. Their melting temperatures were calculated by extrapolation of the emf-temperature characteristics of four stable Pt/Pd thermocouples, which were calibrated at the eutectic fixed points and at conventional fixed points of the International Temperature Scale of 1990 (ITS-90). On the basis of the eight eutectic fixed-point cells and seven independent calibration runs, the melting temperatures of the Fe C, Co C, and Ni C eutectics resulted in 1153.67 0.15C, 1323.81 0.27C, and 1328.48 0.20C, respectively, with expanded uncertainties corresponding to a coverage factor of k = 2.

Edler, F.; Ederer, P.; Baratto, A. C.; Vieira, H. D.

2007-12-01

327

Influence of Crucible Materials on High-temperature Properties of Vacuum-melted Nickel-chromium-cobalt Alloy  

NASA Technical Reports Server (NTRS)

A study of the effect of induction-vacuum-melting procedure on the high-temperature properties of a titanium-and-aluminum-hardened nickel-base alloy revealed that a major variable was the type of ceramic used as a crucible. Reactions between the melt and magnesia or zirconia crucibles apparently increased high-temperature properties by introducing small amounts of boron or zirconium into the melts. Heats melted in alumina crucibles had relatively low rupture life and ductility at 1,600 F and cracked during hot-working as a result of deriving no boron or zirconium from the crucible.

Decker, R F; Rowe, John P; Freeman, J W

1957-01-01

328

Sea-level rise in the Mediterranean Sea by 2050: Roles of terrestrial ice melt, steric effects and glacial isostatic adjustment  

NASA Astrophysics Data System (ADS)

To assess the regional pattern of future low-frequency sea-level variations in the Mediterranean Sea, we combine the terrestrial ice melt, the glacio-isostatic and the steric sea-level components. The first is obtained from global scenarios for the future mass balance of the Greenland and Antarctica ice sheets, glaciers and ice caps. The second is based on modeling, using different assumptions about the Earth's rheology and the chronology of deglaciation since the Last Glacial Maximum. The third is obtained from published simulations based on regional atmosphere-ocean coupled models. From a minimum and a maximum scenario by 2040-2050, we find that the total, basin averaged sea-level rise will be 9.8 and 25.6 cm. The terrestrial ice melt component will exceed the steric contribution, which however will show the strongest regional imprint. Glacial isostatic adjustment will have comparatively minor effects. According to our estimates, at the Mediterranean Sea tide gauges, the rate of sea-level change will increase, by 2050, by a factor of ~ 1-6 relative to the observed long-term rates.

Galassi, Gaia; Spada, Giorgio

2014-12-01

329

Superheating of ice crystals in antifreeze protein solutions.  

PubMed

It has been argued that for antifreeze proteins (AFPs) to stop ice crystal growth, they must irreversibly bind to the ice surface. Surface-adsorbed AFPs should also prevent ice from melting, but to date this has been demonstrated only in a qualitative manner. Here we present the first quantitative measurements of superheating of ice in AFP solutions. Superheated ice crystals were stable for hours above their equilibrium melting point, and the maximum superheating obtained was 0.44 degrees C. When melting commenced in this superheated regime, rapid melting of the crystals from a point on the surface was observed. This increase in melting temperature was more appreciable for hyperactive AFPs compared to the AFPs with moderate antifreeze activity. For each of the AFP solutions that exhibited superheating, the enhancement of the melting temperature was far smaller than the depression of the freezing temperature. The present findings clearly show that AFPs adsorb to ice surfaces as part of their mechanism of action, and this absorption leads to protection of ice against melting as well as freezing. PMID:20215465

Celik, Yeliz; Graham, Laurie A; Mok, Yee-Foong; Bar, Maya; Davies, Peter L; Braslavsky, Ido

2010-03-23

330

The importance of insolation changes for paleo ice sheet modeling  

NASA Astrophysics Data System (ADS)

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.

Robinson, A.; Goelzer, H.

2014-08-01

331

The role of sea ice in the temperature-precipitation feedback of glacial cycles  

NASA Astrophysics Data System (ADS)

The response of the hydrological cycle to climate variability and change is a critical open question, where model reliability is still unsatisfactory, yet upon which past climate history can shed some light. Sea ice is a key player in the climate system and in the hydrological cycle, due to its strong albedo effect and its insulating effect on local evaporation and air-sea heat flux. Using an atmospheric general circulation model with specified sea surface temperature and sea-ice distribution, the role of sea ice in the hydrological cycle is investigated under last glacial maximum (LGM) and present day conditions, and by studying its contribution to the "temperature-precipitation feedback". By conducting a set of sensitivity experiments in which the albedo and thickness of the sea ice are varied, the various effects of sea ice in the hydrological cycle are isolated. It is demonstrated that for a cold LGM like state, a warmer climate (as a result of reduced sea-ice cover) leads to an increase in snow precipitation over the ice sheets. The insulating effect of the sea ice on the hydrological cycle is found to be larger than the albedo effect. These two effects interact in a nonlinear way and their total effect is not equal to summing their separate contribution.

Gildor, Hezi; Ashkenazy, Yosef; Tziperman, Eli; Lev, Ilit

2014-08-01

332

Melting temperature and thermal conductivity of irradiated (U,Pu)O[sub 2] fuel  

SciTech Connect

Both melting temperature and thermal conductivity are important physical properties to evaluate the thermal behavior of fast breeder reactor (FBR) fuel. Core design for commercialization of the FBR has to realize high burnup, a long refueling interval, and high power density conditions. This means that the internal conversion ratio of the core fuel becomes high and depression of the linear heat generation rate becomes small. Therefore, evaluation of fuel temperature at the end of fuel life is essential to the design of a large FBR core. It is generally accepted that the melting temperature and thermal conductivity of irradiated (U,Pu)O[sub 2] fuel decrease with increasing burnup because of the buildup of fission products in a fuel matrix. However, because of large uncertainties of measured values, little postirradiation examination data are available on irradiation effects. In this study, the effect of irradiation on melting temperature and thermal conductivity with small measurement uncertainties is investigated by modified measurement system on (U,Pu)O[sub 2] fuels irradiated in the JOYO fast reactor and other foreign reactors.

Yamamoto, Kazuya; Hirosawa, Takashi; Yoshikawa, Katsunori; Morozumi, Katsuhumi; Nomura; Shigeo (Power Reactor and Nuclear Fuels Development Corp., Ibaraki-ken (Japan))

1992-01-01

333

Greenland palaeotemperatures derived from GRIP bore hole temperature and ice core isotope profiles  

Microsoft Academic Search

Modelling the temperature profile along the GRIP deep bore at the summit of the Greenland ice sheet leads to conversion factors that allow interpretation of the dated stable isotope profile as a climatic temperature record spanning the last 113,000 years. When corrected for surface elevation changes, the late glacial to Boreal temperature shift appears to have been 22C in central

Sigfus J. Johnsen; Dorthe Dahl-Jensen; Willi Dansgaard; Niels Gundestrup

1995-01-01

334

CO2 & global temperature: Analysis of ice core and marine sediment data in  

E-print Network

CO2 & global temperature: Analysis of ice core and marine sediment data in combination proxy EOF Analysis: temperature pattern & time series #12;Global warming Indian Ocean warming (10%) 3°C;#12;Deglaciation: Data and Models CO2 leads global temperature Marine reservoir ages Deglacial Warming leads

Sengun, Mehmet Haluk

335

Satellite Remote Sensing: Passive-Microwave Measurements of Sea Ice  

NASA Technical Reports Server (NTRS)

Satellite passive-microwave measurements of sea ice have provided global or near-global sea ice data for most of the period since the launch of the Nimbus 5 satellite in December 1972, and have done so with horizontal resolutions on the order of 25-50 km and a frequency of every few days. These data have been used to calculate sea ice concentrations (percent areal coverages), sea ice extents, the length of the sea ice season, sea ice temperatures, and sea ice velocities, and to determine the timing of the seasonal onset of melt as well as aspects of the ice-type composition of the sea ice cover. In each case, the calculations are based on the microwave emission characteristics of sea ice and the important contrasts between the microwave emissions of sea ice and those of the surrounding liquid-water medium.

Parkinson, Claire L.; Zukor, Dorothy J. (Technical Monitor)

2001-01-01

336

Simulation of the temperature distribution in the selective beam melting process for polymer material  

NASA Astrophysics Data System (ADS)

In the present contribution the temperature distribution in the selective beam melting process for polymer materials is simulated to better understand the influence of process parameters on the properties of the produced part. The basis for the developed simulation tool is the nonlinear heat equation including temperature dependent functions for the heat capacity and the heat conduction which were obtained by experimental measurements. The effect of latent heat occurring in the process is also taken into account. The heat equation is discretized in time and space where a Runge-Kutta method of Radau IIA type is used for time integration. An adaptive finite element method is applied for the discretization in space and the model is implemented into the finite element library deal.II. The heat and cooling rate as important process parameters are simulated for different beam velocities. The ability for computing these process parameters makes the simulation tool suited for optimizing the process management of selective beam melting plants.

Riedlbauer, D.; Mergheim, J.; Steinmann, P.

2014-05-01

337

Simulation of the temperature distribution in the selective beam melting process for polymer material  

SciTech Connect

In the present contribution the temperature distribution in the selective beam melting process for polymer materials is simulated to better understand the influence of process parameters on the properties of the produced part. The basis for the developed simulation tool is the nonlinear heat equation including temperature dependent functions for the heat capacity and the heat conduction which were obtained by experimental measurements. The effect of latent heat occurring in the process is also taken into account. The heat equation is discretized in time and space where a Runge-Kutta method of Radau IIA type is used for time integration. An adaptive finite element method is applied for the discretization in space and the model is implemented into the finite element library deal.II. The heat and cooling rate as important process parameters are simulated for different beam velocities. The ability for computing these process parameters makes the simulation tool suited for optimizing the process management of selective beam melting plants.

Riedlbauer, D., E-mail: daniel.riedlbauer@ltm.uni-erlangen.de, E-mail: julia.mergheim@ltm.uni-erlangen.de, E-mail: paul.steinmann@ltm.uni-erlangen.de; Mergheim, J., E-mail: daniel.riedlbauer@ltm.uni-erlangen.de, E-mail: julia.mergheim@ltm.uni-erlangen.de, E-mail: paul.steinmann@ltm.uni-erlangen.de; Steinmann, P., E-mail: daniel.riedlbauer@ltm.uni-erlangen.de, E-mail: julia.mergheim@ltm.uni-erlangen.de, E-mail: paul.steinmann@ltm.uni-erlangen.de [Chair of Applied Mechanics, Friedrich-Alexander-Universitt Erlangen-Nrnberg (Germany)

2014-05-15

338

Revisiting the melting temperature of NpO2 and the challenges associated with high temperature actinide compound measurements  

NASA Astrophysics Data System (ADS)

This work revisits the melting behaviour of neptunium dioxide, an actinide compound which can be produced in the nuclear fuel during operation, and which has an important impact on the nuclear fuel and waste radioactivity especially on the very long term. The present experimental approach employs remote laser heating under controlled atmosphere and fast pyrometry. This technique circumvents problems encountered by more traditional heating techniques, in particular, the reaction between sample and containment at temperatures beyond 2500 K. In addition, only a small amount of sample material is required, which is an advantage with respect to the radioactivity and limited availability of neptunium. The NpO2 melting/freezing temperature has been measured to be 3070 K 62 K, much higher than previous values (around 2830 K) obtained by more traditional thermal analysis methods. The large amount of experimental data collected allowed a consistent statistical analysis. It seems likely, although not fully evident from the present results, that the high oxygen potential at temperatures around melting leads to a slightly hypo-stoichiometric congruent melting composition, as already observed in other actinide (ThO2, PuO2) and lanthanide oxides (e.g., CeO2). Finally, a recently developed phase-field model was used for the simulation of the observed thermograms, allowing a deeper insight in material properties that are difficult to directly measure. For example, a polaron contribution to the high-temperature thermal conductivity, well accepted for the commonly studied actinide oxide UO2, is shown here to likely be present in NpO2.

Bhler, R.; Welland, M. J.; Bruycker, F. De; Boboridis, K.; Janssen, A.; Eloirdi, R.; Konings, R. J. M.; Manara, D.

2012-06-01

339

Enzymic hydrolysis of animal fats in organic solvents at temperatures below their melting points  

Microsoft Academic Search

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%

M. D. Virto; Jose Miguel Lascaray; Rodolfo Solozabal; Mertxe de Renobales

1991-01-01

340

Shifts in chain-melting transition temperature of liposomal membranes by polymer-grafted lipids  

Microsoft Academic Search

The chain-melting transition temperature of dipalmitoyl phosphatidylcholine (DPPC) bilayer membranes containing poly(ethylene glycol)-grafted dipalmitoyl phosphatidylethanolamine (PEG-DPPE) was determined by optical turbidity measurements. The dependence on content, Xp, of PEG-DPPE lipid was studied for different polar headgroup sizes, np, of the polymer lipid, throughout the lamellar phase of the mixtures with DPPC. Mean-field theory for the polymer brush regime predicts that

Manuela Pantusa; Rosa Bartucci; Derek Marsh; Luigi Sportelli

2003-01-01

341

Deformation mechanisms in granodiorite at effective pressures to 100 MPa and temperatures to partial melting  

Microsoft Academic Search

Deformation mechanisms in room-dry and water-saturated specimens of Charcoal Granodiorite, shortened at 10⁻⁴s⁻¹, at effective pressures (Pe) to 100 MPa and temperatures to partial melting (less than or equal to 1050°C) are documented with a view toward providing criteria to recognize and characterize the deformation for geological and engienering applications. Above 800°C strength decreases dramatically at effective pressures greater than

M. Friedman; J. Handin; S. J. Bauer

1981-01-01

342

Reduction of melting temperature and enthalpy of drug crystals: theoretical aspects.  

PubMed

This review deals with the mathematical models describing the reduction of melting temperature and enthalpy of solids in the nano-size range. In particular, the attention focuses on the thermodynamic based models that are theoretically solid and can be suitably used in the case of organic drugs. Indeed, while much effort has been put in the past to study the melting of metal nano-crystals, little work has been done for organic drug nano-crystals. However, due to the high potential of drug nano-crystals (their solubility increases with size reduction), this theme has become more and more important in the pharmaceutical field. Accordingly, this review, after illustrating the physical frame of drug melting, focuses on the thermodynamic aspects required to describe the melting of spherical and not spherical nano-crystals. Finally, the reliability of some models is tested against the results coming from X-rays analysis in the case of two organic drugs (griseofulvin and nifedipine). This test proved models strength. PMID:23567466

Hasa, Dritan; Voinovich, Dario; Perissutti, Beatrice; Grassi, Gabriele; Fiorentino, Simona; Farra, Rossella; Abrami, Michela; Colombo, Italo; Grassi, Mario

2013-09-27

343

Quantum melting of a two-dimensional vortex lattice at zero temperature  

SciTech Connect

We consider the quantum melting of a two-dimensional flux lattice at temperature {ital T} = 0 in the {open_quote}{open_quote}superclean limit.{close_quote}{close_quote} In this regime, we find that vortex motion is dominated by the Magnus force. A Lindemann criterion predicts melting when {ital n}{sub {ital v}}/{ital n}{sub {ital p}}{ge}{beta}, where {ital n}{sub {ital v}} and {ital n}{sub {ital p}} are the areal number densities of vortex pancakes and Cooper pairs, and {beta}{approx_equal}0.1. A second criterion is derived by using Wigner-crystal and Laughlin wave functions for the solid and liquid phases respectively, and setting the two energies equal. This gives a melting value similar to the Lindemann result. We discuss the numerical value of the {ital T}=0 melting field for thin layers of a low-{ital T}{sub {ital c}} superconductor, such as {ital a}-MoGe, and single layers of high-{ital T}{sub {ital c}} materials. {copyright} {ital 1996 The American Physical Society.}

Rozhkov, A.; Stroud, D. [Department of Physics, Ohio State University, Columbus, Ohio 43210 (United States)] [Department of Physics, Ohio State University, Columbus, Ohio 43210 (United States)

1996-11-01

344

A new temperature and humidity dependent surface site density approach for deposition ice nucleation  

NASA Astrophysics Data System (ADS)

Deposition nucleation experiments with Arizona Test Dust (ATD) as a surrogate for mineral dusts were conducted at the AIDA cloud chamber at temperatures between 220 and 250 K. The influence of the aerosol size distribution and the cooling rate on the ice nucleation efficiencies was investigated. Ice nucleation active surface site (INAS) densities were calculated to quantify the ice nucleation efficiency as a function of temperature, humidity and the aerosol surface area concentration. Additionally, a contact angle parameterization according to classical nucleation theory was fitted to the experimental data in order to relate the ice nucleation efficiencies to contact angle distributions. From this study it can be concluded that the INAS density formulation is a very useful tool to decribe the temperature and humidity dependent ice nucleation efficiency of ATD particles. Deposition nucleation on ATD particles can be described by a temperature and relative humidity dependent INAS density function ns(T, Sice) with ns(xtherm) = 1.88 105 \\centerdot exp(0.2659 \\centerdot xtherm) [m-2] (1) where the thermodynamic variable xtherm is defined as xtherm = -(T - 273.2) + (Sice-1) 100 (2) with Sice>1 and within a temperature range between 226 and 250 K. For lower temperatures, xtherm deviates from a linear behavior with temperature and relative humidity over ice. Two different approaches for describing the time dependence of deposition nucleation initiated by ATD particles are proposed. Box model estimates suggest that the time dependent contribution is only relevant for small cooling rates and low number fractions of ice-active particles.

Steinke, I.; Hoose, C.; Mhler, O.; Connolly, P.; Leisner, T.

2014-07-01

345

Formation of hexagonal and cubic ice during low-temperature growth  

PubMed Central

From our daily life we are familiar with hexagonal ice, but at very low temperature ice can exist in a different structurethat 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

Thrmer, Konrad; Nie, Shu

2013-01-01

346

Recent variations of sea ice and air temperature in high latitudes  

NASA Technical Reports Server (NTRS)

A gridded sea-ice database, for which the record length is now approaching four decades for the Arctic and two decades for the Antarctic, is summarized here. The sea-ice fluctuations derived from the dataset are characterized by temporal scales of several seasons to several years and spatial scales of 30-180 deg of longitude. The ice data are examined in conjunction with air temperature data for evidence of recent climate change in the polar regions. The arctic sea-ice variations over the past several decades are compatible with the corresponding air temperatures, which show a distinct warming that is strongest over northern land areas during the winter and spring. Statistically significant decreases of the summer extent of arctic ice are apparent in the sea-ice data, and new summer minima have been achieved three times in the past 15 years. There is no significant trend if ice extent in the Arctic during winter or in the Antarctic during any season.

Chapman, William L.; Walsh, John E.

1993-01-01

347

Shock-induced incongruent crystallization from forsterite melt at extreme pressure and temperature conditions  

NASA Astrophysics Data System (ADS)

We have measured the Hugoniot of forsterite melt under laser-driven shock compression at pressures of 300-1000 GPa and sample temperatures of 6000-9000 K under shock at 300-400 GPa. We employed VISAR and SOP methods that become poluar in the laser-shock community recently, to monitor velocity and temperature simultaneously. The shock velocity-particle velocity relation displays a kink around 350-400 GPa. The slope increase beyond the kink is associated with heating and volume expansion. This has been discussed in the Huginot of antigorite which also displays a similar change. This can be explained as an exothermic reaction by incongruent crystallization of MgO and the residual melt composition becomes MgSiO3. The MgO will be a B2 structure based on the current proposed phase diagram of MgO. Further increasing of shock pressure follows complete melting above ~400 GPa. Laser-driven shock continues to decay with time but the measured temperature profile has indicated an abrupt increase around 250 GPa with decaying pressure. This state is on a linear extension of the phase transition of liquid-liquid on MgSiO3 that was reported recently. Shock-induced incongruent crystallization at extreme conditions has been recognized for the first time in this study, and it plays an important role in the process of planetary formation and giant impacts to change the melt composition abruptly. This research was performed at ILE as collaboration work.

Sekine, T.; Ozaki, N.; Asami, Y.; Miyanishi, K.; Uranishi, H.; Kodama, R.; Sano, T.; Sawaka, Y.

2012-12-01

348

Strain Hardening in Uniaxial Elongation vs. Temperature for Random Copolymer Melts with High Comonomer Content  

NASA Astrophysics Data System (ADS)

Two metallocene-catalyzed random copolymers with a polyethylene backbone and octene comonomer content of 20 wt% and 38 wt% were tested in uniaxial extensional flow at different temperatures. Sparse LCB was detected in both melts with these measurements. The strain hardening parameter at the lowest strain rate was found to be greater for EO3, the material with the smaller degree of LCB. The temperature dependence of the strain hardening parameter was also greater for EO3 than for EO1. These trends may be related to the two model parameters used by Wagner and coworkers representing branch content and the maximum tube diameter contraction.

Mills, John E.; Jayaraman, Krishnamurthy; Patham, Bhaskar; Dong, Dinshong; Wolkowicz, Michael

2008-07-01

349

Deep water temperature, carbonate ion, and ice volume changes across the Eocene-Oligocene climate transition  

Microsoft Academic Search

Paired benthic foraminiferal stable isotope and Mg\\/Ca data are used to estimate bottom water temperature (BWT) and ice volume changes associated with the Eocene-Oligocene Transition (EOT), the largest global climate event of the past 50 Myr. We utilized ODP Sites 1090 and 1265 in the South Atlantic to assess seawater delta18O (deltaw), Antarctic ice volume, and sea level changes across

A. E. Pusz; R. C. Thunell; K. G. Miller

2011-01-01

350

An ice lithography instrument  

PubMed Central

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

Han, Anpan; Chervinsky, John; Branton, Daniel; Golovchenko, J. A.

2011-01-01

351

Melting and phase transitions of nitrogen under high pressures and temperatures.  

PubMed

Dense nitrogen exhibits fascinating molecular and extended polymorphs as well as an anomalous melt maximum at high temperatures. However, the exact solid-liquid phase boundary is still the subject of debate, as both creating and probing hot dense nitrogen, solid and fluid alike, poses unique experimental challenges. Raman studies of nitrogen were performed to investigate the melting curve and solid-solid phase transitions in the pressure-temperature range of 25 to 103 GPa and 300 to 2000 K. The solid-liquid phase boundary has been probed with time-resolved Raman spectroscopy on ramp heated nitrogen in diamond anvil cell (DAC), showing a melting maximum at 73 GPa and 1690 K. The solid-solid phase boundaries have been measured with spatially resolved micro-confocal Raman spectroscopy on resistively heated DAC, probing the ?-? phase line to 47 GPa and 914 K. At higher pressures the ?-phase was produced upon a repeated thermal heating of the ?-phase, yet no evidence was found for the ?-phase. Hence, the present results signify the path dependence of dense nitrogen phases and provide new constraints for the phase diagram. PMID:24985657

Tomasino, Dane; Jenei, Zsolt; Evans, William; Yoo, Choong-Shik

2014-06-28

352

Ice formation in PEM fuel cells operated isothermally at sub-freezing temperatures  

SciTech Connect

The effect of MEA and GDL structure and composition on the performance of single-PEM fuel cells operated isothermally at subfreezing temperatures is presented. The cell performance and durability are not only dependent on the MEA/GDL materials used but also on their interfaces. When a cell is operated isothermally at sub-freezing temperatures in constant current mode, the water formation due to the current density initially hydrates the membrane/ionomer and then forms ice in the catalyst layer/GDL. An increase in high frequency resistance was also observed in certain MEAs where there is a possibility of ice formation between the catalyst layer and GDL leading to a loss in contact area. The total water/ice holding capacity for any MEA was lower at lower temperatures and higher current densities. The durability of MEAs subjected to multiple isothermal starts was better for LANL prepared MEAs as compared to commercial MEAs, and cloth GDLs when compared to paper GDLs. The ice formation was monitored using high-resolution neutron radiography and was found to be concentrated near the cathode catalyst layer. However, there was significant ice formation in the GDLs especially at the higher temperature ({approx} -10 C) and lower current density (0.02 A/cm{sup 2}) operations. These results are consistent with the longer-term durability observations that show more severe degradation at the lower temperatures.

Mukundan, Rangachary [Los Alamos National Laboratory; Luhan, Roger W [Los Alamos National Laboratory; Davey, John R [Los Alamos National Laboratory; Spendelow, Jacob S [Los Alamos National Laboratory; Borup, Rodney L [Los Alamos National Laboratory; Hussey, Daniel S [NIST; Jacobson, David L [NIST; Arif, Muhammad [NIST

2009-01-01

353

Influence of emulsifiers on ice cream produced by conventional freezing and low-temperature extrusion processing  

Microsoft Academic Search

Ice cream at six different levels of emulsification was produced by freezing in a conventional scraped surface freezer and with a serial configuration of a conventional freezer followed by a low-temperature extruder. The aim was to examine the influence of emulsifiers on the process, since both emulsifier addition and low-temperature extrusion may have similar effects on promotion of colloidal structure

S. Bolliger; B. Kornbrust; H. D. Goff; B. W. Tharp; E. J. Windhab

2000-01-01

354

Effects of melt ageing on the density, elastic modulus and glass transition temperature of bismuth borate glasses  

NASA Astrophysics Data System (ADS)

Disc shaped samples of the glass composition: 0.40Bi2O3-0.60B2O3 were prepared by a melt quenching technique by keeping the quenching rate constant but gradually increasing the melt annealing or ageing time from 15 to 220 min at a temperature of 850 C. A total of five glass samples were prepared. Density, ultrasonic velocity and glass transition temperature measurements showed significant changes in the final glass properties. X-ray fluorescence studies confirmed that the glass composition does not change with the heat treatment of the melt. Our findings challenge the conventional theories of liquids and glass formation which predict that structural changes in a low viscosity melt occur almost instantaneously and a liquid is in its internal equilibrium state above the melting point. We report some unusually slow structural relaxations in bismuth borate glass melts even at elevated temperatures of 850 C, due to which the melt transforms from a thermodynamically fragile, high density amorphous state to a low density amorphous state which is kinetically stronger. Our findings indicate that bismuth borate melts are metastable liquids and strong candidates for the phenomenon of liquid state polyamorphism.

Khanna, Atul; Sawhney, K. J. S.; Tiwari, M. K.; Bhardwaj, Suresh; Awasthi, A. M.

2003-10-01

355

Changing spring air-temperature gradients along large northern rivers: Implications for severity of river-ice floods  

NASA Astrophysics Data System (ADS)

Concern exists about future changes to air-temperature gradients along large northward-flowing Arctic rivers having the potential to affect the timing and severity of spring river-ice breakup, and associated flooding events. To evaluate the significance of this concern, an analysis was conducted of temporal and spatial changes to the spring 0C air-temperature isotherm (I0C), which is also known to be a good index for the timing of spring melt/breakup conditions. Changes in I0C were analyzed for the downstream 2000-km main-stem reaches of four large Arctic rivers: the Lena, Mackenzie, Ob and Yenisey. Current climatic conditions (1979-2008) were compared to those of two future climatic periods (2041-2070 and 2071-2100) projected by an ensemble of four Global Climate Models. Future projections show I0C chronology patterns along the rivers that closely parallel current conditions, but with earlier dates varying from an ensemble mean of 7.5 (13.6) to 16.5 (25.5) days for the 2050s (2080s). Results also reveal a progressive downstream increase in warming under future climates. At the time when headwater temperatures reach 0C, river mouth to headwater temperature differences for the four rivers decrease by an average of 0.8C (2.4C) to 2.1C (3.7C) for the 2050s (2080s). The implications of such decreases on the severity of spring ice-jam floods are discussed.

Prowse, Terry; Shrestha, Rajesh; Bonsal, Barrie; Dibike, Yonas

2010-10-01

356

Ice Shelf-Ocean Interactions Near Ice Rises and Ice Rumples  

NASA Astrophysics Data System (ADS)

The stability of ice shelves depends on the existence of embayments and is largely influenced by ice rises and ice rumples, which act as 'pinning-points' for ice shelf movement. Of additional critical importance are interactions between ice shelves and the water masses underlying them in ice shelf cavities, particularly melting and refreezing processes. The present study aims to elucidate the role of ice rises and ice rumples in the context of climate change impacts on Antarctic ice shelves. However, due to their smaller spatial extent, ice rumples react more sensitively to climate change than ice rises. Different forcings are at work and need to be considered separately as well as synergistically. In order to address these issues, we have decided to deal with the following three issues explicitly: oceanographic-, cryospheric and general topics. In so doing, we paid particular attention to possible interrelationships and feedbacks in a coupled ice-shelf-ocean system. With regard to oceanographic issues, we have applied the ocean circulation model ROMBAX to ocean water masses adjacent to and underneath a number of idealized ice shelf configurations: wide and narrow as well as laterally restrained and unrestrained ice shelves. Simulations were performed with and without small ice rises located close to the calving front. For larger configurations, the impact of the ice rises on melt rates at the ice shelf base is negligible, while for smaller configurations net melting rates at the ice-shelf base differ by a factor of up to eight depending on whether ice rises are considered or not. We employed the thermo-coupled ice flow model TIM-FD3 to simulate the effects of several ice rises and one ice rumple on the dynamics of ice shelf flow. We considered the complete un-grounding of the ice shelf in order to investigate the effect of pinning points of different characteristics (interior or near calving front, small and medium sized) on the resulting flow and stress fields, focusing on the floating ice parts of the Brunt and Riiser-Larsen ice shelves. The major response of the ice is observed instantaneously and is caused by the time independent nature of the Stokes equations and the used Glen-type rheology. The influence of ice temperatures and therefore the time-dependent effect on the flow-rate are small, given a 100 year time frame and applying a fixed-geometry setting.. A particularly important result of the current project lies in the fact that we have numerically simulated the three-dimensional stress fields in an ice shelf. Common numerical models that utilize a vertically integrated Shallow Shelf Approximation (SSA-models), do not provide that information. Due to the detailed horizontal resolution of 1km in our models, we were able to also model the observed heavily fractured areas in the vicinity of McDonald Ice Rise, a region that is characterized by simulated tensile stresses reaching maximum vertical extension in the ice column.

Lange, M. A.; Rckamp, M.; Kleiner, T.

2013-12-01

357

Distribution of REE between clinopyroxene and basaltic melt along a mantle adiabat: Effects of major element composition, water, and temperature  

NASA Astrophysics Data System (ADS)

The distribution of REE between clinopyroxene (cpx) and basaltic melt is important in deciphering the processes of mantle melting. Most models for mantle melting assume constant mineral-melt partition coefficient (D) for trace elements, even though partitioning experiments have demonstrated that D depends on pressure (P), temperature (T), and compositions of mineral and melt. In general, DREE from a given cpx-melt partitioning experiment can be quantitatively described by the lattice strain model [1]. Attempts have been made to parameterize DREE between cpx and melt as a function of P, T, cpx and melt compositions [1]. However, the previous model [1] was based on limited partitioning data, many of which were determined by electron microprobe and some of the experiments might not approach equilibrium, and therefore may not provide accurate prediction. Here, we analyze published REE partitioning data between cpx and basaltic melts, and focus on data obtained by ion probe and LA-ICP-MS and experiments close to equilibrium. We use the nonlinear regression method to parameterize key partitioning parameters in the lattice strain model (D0, r0 and E) as functions of P, T and compositions of cpx and melt. We find that D0 positively correlates with AlIV and MgM2 in cpx, negatively correlates with H2O in the melt and T. Hence variations in DREE are determined by cpx composition, T and H2O in the melt. r0 negative correlates with AlVI and MgM2 in cpx, whereas E and r0 positively correlate with each other. As an application, we examine REE fractionation along a mantle adiabat. We calculate the cpx compositions and H2O contents in the melt during near-fractional melting along the mantle adiabat using pHMELTS [2-3] and for several choices of mantle source composition (DMM, PM and EM) and mantle potential temperature (Tp = 1300oC and 1400oC). As cpx has low Al and Mg abundances at high temperatures during melting in the garnet stability field, REEs are more incompatible in cpx. Melting of a hydrous mantle occurs deeper (in garnet stability field), and produces small-degree melts enriched in H2O. Consequently, REE would be highly incompatible in cpx at the beginning of melting, and become less incompatible as the hydrous melt segregated from the residual mantle. Our model calculations show that DREE in cpx display very small variations during melting in spinel lherzolite regime at a given Tp. This is due to the competing effect between T and cpx composition. Melting in spinel lherzolite regime at higher Tp could generate D values slightly lower than those at lower Tp because the effect of cpx composition is overwhelmed by the temperature effect. At a given Tp, a set of constant D could be used to accurately model adiabatic mantle melting in spinel lherzolite regime, if the major element compositions of residual cpx from pHMELTS [2-3] can be taken as exact. [1] Wood and Blundy (1997) CMP 129, 166-181. [2] Ghiorso et al. (2002) G3, doi:10.1029/2001GC000217. [3] Asimow et al. (2004) G3, doi:10.1029/2003GC000568.

Sun, C.; Liang, Y.

2010-12-01

358

Entropy dependence of viscosity and the glass-transition temperature of melts in the system diopside-anorthite  

Microsoft Academic Search

Viscosities of diopside-anorthite melts were measured over the wide range of temperature (near the glass-transition temperature-1580C\\/1bar) and pressure (520 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

H. Taniguchi

1992-01-01

359

The temperature of intracellular ice formation in mouse oocytes vs. the unfrozen fraction at that temperature.  

PubMed

We have previously reported [Cryobiology 51 (2005) 29-53] 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 degrees 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 ratios of glycerol and EG to salts are held constant. The oocytes were then cooled rapidly enough (20 degrees C/min) to avoid significant osmotic shrinkage, and the temperature at which IIF occurred was 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 5-8% for both glycerol and EG even though the IIF temperatures vary from -14 to -50 degrees 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 solutions; substantially smaller in others. However, the data in toto demonstrate that cell volume is not a determining factor in the IIF temperature. PMID:17379206

Mazur, Peter; Pinn, Irina L; Kleinhans, F W

2007-04-01

360

Are seasonal calving dynamics forced by buttressing from ice mlange or undercutting by melting? Outcomes from full-Stokes simulations of Store Glacier, West Greenland  

NASA Astrophysics Data System (ADS)

We use a full-Stokes 2-D model (Elmer/Ice) to investigate the flow and calving dynamics of Store Glacier, a fast-flowing outlet glacier in West Greenland. Based on a new, subgrid-scale implementation of the crevasse depth calving criterion, we perform two sets of simulations: one to identify the primary forcing mechanisms and another to constrain future stability. We find that the mixture of icebergs and sea ice, known as ice mlange or sikussak, is principally responsible for the observed seasonal advance of the ice front. On the other hand, the effect of submarine melting on the calving rate of Store Glacier appears to be limited. Sensitivity analysis demonstrates that the glacier's calving dynamics are sensitive to seasonal perturbation, but are stable on interannual timescales due to the strong topographic control on the flow regime. Our results shed light on the dynamics of calving glaciers and may help explain why neighbouring glaciers do not necessarily respond synchronously to changes in atmospheric and oceanic forcing.

Todd, J.; Christoffersen, P.

2014-12-01

361

On the reduced sensitivity of the Atlantic overturning to Greenland ice sheet melting in projections: a multi-model assessment  

NASA Astrophysics Data System (ADS)

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 26N 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.

Swingedouw, Didier; Rodehacke, Christian B.; Olsen, Steffen M.; Menary, Matthew; Gao, Yongqi; Mikolajewicz, Uwe; Mignot, Juliette

2014-08-01

362

Modeling of submarine melting in Petermann Fjord, Northwestern Greenland using an ocean general circulation model  

NASA Astrophysics Data System (ADS)

Basal melting of the floating tongue of Petermann Glacier, in northwestern Greenland is by far the largest process of mass ablation. Melting of the floating tongue is controlled by the buoyancy of the melt water plume, the pressure-dependence of the melting point of sea ice, and the mixing of warm subsurface water with fresh buoyant subglacial discharge. In prior simulations of this melting process, the role of subglacial discharge has been neglected because in similar configurations (floating ice shelves) in the Antarctic, surface runoff is negligible; this is however not true in Greenland. Here, we use the Mass Institute of Technology general circulation model (MITgcm) at a high spatial resolution (10 m x 10 m) to simulate the melting process of the ice shelf in 2-D. the model is constrained by ice shelf bathymetry and ice thickness from NASA Operation IceBridge, ocean temperature/salinity data from Johnson et al. (2011), and subglacial discharge estimated from output products of the Regional Atmospheric Climate Model (RACMO). We compare the results obtained in winter (no runoff) with summer, and the sensitivity of the results to thermal forcing from the ocean, and to the magnitude of subglacial runoff. We conclude on the impact of the ocean and surface melting on the melting regime of the floating ice tongue of Petermann. This work is performed under a contract with NASA Cryosphere Program.

Cai, C.; Rignot, E. J.; Xu, Y.; An, L.

2013-12-01

363

Ice Shelves and Landfast Ice on the Antarctic Perimeter: Revised Scope of Work  

NASA Technical Reports Server (NTRS)

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.

Scambos, Ted

2002-01-01

364

Modeling Antarctic ice shelf responses to future climate changes and impacts on the ocean  

NASA Astrophysics Data System (ADS)

We investigate basal melting of all Antarctic ice shelves by a circumpolar ice shelf-sea ice-ocean coupled model and estimate the total basal melting of 770-944 Gt/yr under present-day climate conditions. We present a comparison of the basal melting with previous observational and modeling estimates for each ice shelf. Heat sources for basal melting are largely different among the ice shelves. Sensitivities of the basal melting to surface air warming and to enhanced westerly winds over the Antarctic Circumpolar Current are investigated from a series of numerical experiments. In this model the total basal melting strongly depends on the surface air warming but is hardly affected by the change of westerly winds. The magnitude of the basal melting response to the warming varies widely from one ice shelf to another. The largest response is found at ice shelves in the Bellingshausen Sea, followed by those in the Eastern Weddell Sea and the Indian sector. These increases of basal melting are caused by increases of Circumpolar Deep Water and/or Antarctic Surface Water into ice shelf cavities. By contrast, basal melting of ice shelves in the Ross and Weddell Seas is insensitive to the surface air warming, because even in the warming experiments there is high sea ice production at the front of the ice shelves that keeps the water temperature to the surface freezing point. Weakening of the thermohaline circulation driven by Antarctic dense water formation under warming climate conditions is enhanced by basal melting of ice shelves. This article was originally published online on 14 May 2013. An error was subsequently identified. Figure 5 in the original version of this article was incorrect and has been updated on 18 May 2013.

Kusahara, Kazuya; Hasumi, Hiroyasu

2013-05-01

365

Melting and dissociation of ammonia at high pressure and high temperature  

SciTech Connect

Raman spectroscopy and synchrotron x-ray diffraction measurements of ammonia (NH{sub 3}) in laser-heated diamond anvil cells, at pressures up to 60 GPa and temperatures up to 2500 K, reveal that the melting line exhibits a maximum near 37 GPa and intermolecular proton fluctuations substantially increase in the fluid with pressure. We find that NH{sub 3} is chemically unstable at high pressures, partially dissociating into N{sub 2} and H{sub 2}. Ab initio calculations performed in this work show that this process is thermodynamically driven. The chemical reactivity dramatically increases at high temperature (in the fluid phase at T > 1700 K) almost independent of pressure. Quenched from these high temperature conditions, NH{sub 3} exhibits structural differences from known solid phases. We argue that chemical reactivity of NH{sub 3} competes with the theoretically predicted dynamic dissociation and ionization.

Ojwang, J.G.O.; McWilliams, R. Stewart; Ke, Xuezhi; Goncharov, Alexander F. (Wake Forest); (ECNU); (CIW)

2012-12-10

366

Melting and dissociation of ammonia at high pressure and high temperature  

NASA Astrophysics Data System (ADS)

Raman spectroscopy and synchrotron x-ray diffraction measurements of ammonia (NH3) in laser-heated diamond anvil cells, at pressures up to 60 GPa and temperatures up to 2500 K, reveal that the melting line exhibits a maximum near 37 GPa and intermolecular proton fluctuations substantially increase in the fluid with pressure. We find that NH3 is chemically unstable at high pressures, partially dissociating into N2 and H2. Ab initio calculations performed in this work show that this process is thermodynamically driven. The chemical reactivity dramatically increases at high temperature (in the fluid phase at T > 1700 K) almost independent of pressure. Quenched from these high temperature conditions, NH3 exhibits structural differences from known solid phases. We argue that chemical reactivity of NH3 competes with the theoretically predicted dynamic dissociation and ionization.

Ojwang, J. G. O.; Stewart McWilliams, R.; Ke, Xuezhi; Goncharov, Alexander F.

2012-08-01

367

Microwave brightness temperatures of laboratory-grown undeformed first-year ice with an evolving snow cover  

SciTech Connect

A laboratory experiment was performed to study a case in which a snow cover introduced on an established saline ice sheet resulted in physical processes that significantly affected the microwave brightness temperature over a period of a few weeks. Saline ice was grown to a thickness of 240 mm in an outdoor pool at ambient air temperatures. Precipitation was allowed by use of a movable roof. Brightness temperatures were measured at 10 and 85 GHz before and for several weeks after one snowfall. During the same period, the vertical temperature profile and crystallography of the snow column, as well as ice structure and salinity at the original ice surface, were monitored. The 10-GHz brightness temperature dropped by as much as 100 K from bare ice values during the first few days after the snow fell, because of a saline slush layer which formed at the bottom of the snow. The saline water in the slush layer apparently was forced up through the unbroken ice by the added snow load. The slush layer eventually froze into an added highly emissive frazil ice layer which raised the 10-GHz brightness temperature to above its bare ice values. The frazil ice layer was similar to superimposed frazil ice observed on freezing leads in high-latitude ice packs. The 85-GHz brightness temperature did not change from bare ice values soon after the snowfall but dropped by about 40 K over the following 20 days. We use a simple dielectric model to qualitatively test the dependence of 10-GHz brightness temperature on relevant physical conditions at the bottom of the snow. At 85 GHz the snow layer was optically thick, and the brightness temperature drop was probably the result of increased volume scatter from the growing snow grains. 24 refs., 7 figs.

Lohanick, A.W. (Naval Research Lab., Hanover, NH (United States))

1993-03-15

368

Structure and dynamical intra-molecular heterogeneity of star polymer melts above glass transition temperature.  

PubMed

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

Chremos, Alexandros; Glynos, Emmanouil; Green, Peter F

2015-01-28

369

MELT WIRE SENSORS AVAILABLE TO DETERMINE PEAK TEMPERATURES IN ATR IRRADIATION TESTING  

SciTech Connect

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 1500C. This paper will discuss the development work and present test results.

K. L. Davis; D. Knudson; J. Daw; J. Palmer; J. L. Rempe

2012-07-01

370

Spectrum of temperature pulsations of the melt in gas-assisted cutting with fiber laser  

NASA Astrophysics Data System (ADS)

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 (1.21.5) 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.

Dubrov, Alexander V.; Zavalov, Yury N.; Dubrov, Vladimir D.; Grezev, Anatoly N.; Grezev, Nikolay V.; Makarova, Elena S.; Dubrovin, Nickolay G.

2012-09-01

371

Pressure and temperature effects on oxide melt structure: progress and prognoses (Bunsen Medal Lecture)  

NASA Astrophysics Data System (ADS)

Thanks to decades of study by diffraction and spectroscopy, many aspects of the short-range structure of oxide glasses, and the effects of composition on them, are relatively well known. In most cases, these results represent (at best) the structure of the liquid at the glass transition, which is often far below the magmatic conditions of greatest interest for geological processes. At the same time, detailed thermodynamic and calorimetric studies at ambient pressure, and a few pioneering in-situ, high-pressure melt property measurements, have documented the fact that melt structure must change considerably as temperature and pressure are increased. Closing the gap between magma properties and our atomic-scale view thus requires much better information about temperature and pressure effects on melt structure. Recent progress on temperature effects has been made both by in-situ studies, and by work at ambient conditions on glass samples prepared with different cooling rates and thus capturing the melt structure at different fictive temperatures. The former type has the advantage of a greater accessible range of temperatures but can be limited by the inherent difficulties of high temperature experiments; for the latter, any structural tool may be applied but changes over the accessible range (typically Tg to Tg+200 K or less) can be subtle. We now know, for example, that in some systems local structural changes can be detected for network cations such as B, Al, and even Si, but that these can lead to either coordination decreases with T (e.g. B), correlated with thermal expansion, or to increases with T (e.g. Al in Ca aluminosilicates), correlated with entropic effects. In some systems, increases in the disorder of the network with T can be measured and correlated with heats of reaction among various bridging oxygen species. In a few cases, network modifier environments (e.g. Ni, Mg, Na) can be seen to change with T as well. But in general, extrapolating results from one system to another must be done with caution, as there are clearly compositional effects on the response of the structure to temperature. Structural methods that can yield useful information on high temperature, high pressure melts are even more limited, and future progress in this area will be critical to understanding deep-Earth magmatic processes. Most of our (very limited) understanding of pressure effects on melt structure comes from in situ studies of glasses at ambient temperatures and high P, and from spectroscopy of glasses quenched from high P,T melts. The latter have the advantage of at least having started in a fully relaxed, equilibrium state at P and T, but questions of possible structural relaxation during decompression are not fully resolved. Nonetheless, recent studies of such high pressure glasses, with enough complexity to begin to emulate natural magmas, have begun to reveal trends with composition and P, and correlations between quenched-in density increases and structure, that must have bearing on the high T, P systems. Most obviously, higher field-strength modifier cations (e.g. Mg > Ca > Na > K) lead to more rapid increase with P in both density and Al coordination (Al-27 NMR), which seems to delay increases in Si coordination. Corresponding changes in the types of oxygen species present (i.e. decreases in non-bridging oxygens) are also clearly measurable by O-17 NMR. However, much of the recovered density change must be related to compression of the modifier cation sites through decreases in network bond angles. Depending on the cation, this can lead to shorter M-O bonds distances (e.g. Na), or to coordination increase and longer distances (e.g. La). Finally, we note that important insights for high-pressure silicate systems may be gleaned from other oxide melts in which the network cations undergo large changes in coordination with composition. As a modifier such as Na2O is added to pure B2O3 or GeO2, for example, the B or Ge coordination increases significantly, then decreases. This suggests that in aluminosilicate melt

Stebbins, J. F.

2009-04-01

372

Evidence for a little ice age and recent warming from a borehole temperature data inversion procedure  

SciTech Connect

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.

Fivez, J.; Thoen, J. [Laboratorium voor Akoestiek en Thermische Fysica, Department Natuurkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven (Belgium)

2004-11-15

373

Electronic desorption from low temperature ices and analogs of outer solar system surfaces  

NASA Astrophysics Data System (ADS)

Low energy electron induced radiolysis of ices and surrogates of outer solar system bodies such as icy moons and comets have been investigated. Low energy electrons are effective simulants of high energy charged particle irradiation. Molecular hydrogen emission from comets is used to gain information about the formation temperature and isotopic branching in these primordial solar system objects. Long term storage of comets in the Kuiper belt and Oort cloud can subject these objects to space weathering due to galactic cosmic rays and other radiation. Stimulated desorption of atomic and molecular hydrogen and oxygen occur from these ices as well as water group ions. Yields and internal energy distributions of H2 and D2 from laboratory ices have been measured. Ortho-para hydrogen spin isomers have been observed and their equilibration temperatures determined. These spin isomers carry information about the formation temperature of the ice as well as the mechanisms of space weathering that can influence interpretation of the origin and evolution of ice covered bodies.

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

2009-12-01

374

The D/H Ratio of Water Ice at Low Temperatures  

NASA Astrophysics Data System (ADS)

We present the modeling results of deuterium fractionation of water ice, H2, and the primary deuterium isotopologues of H_3^+ adopting physical conditions associated with the star and planet formation process. We calculated the deuterium chemistry for a range of gas temperatures (T gas ~ 10-30 K), molecular hydrogen density (n(H2) ~ 104-107), and ortho/para ratio (opr) of H2 based on state-to-state reaction rates and explore the resulting fractionation including the formation of a water ice mantle coating grain surfaces. We find that the deuterium fractionation exhibits the expected temperature dependence of large enrichments at low gas temperature. More significantly, the inclusion of water ice formation leads to large D/H ratios in water ice (gsim 102 at 10 K) but also alters the overall deuterium chemistry. For T < 20 K, the implantation of deuterium into ices lowers the overall abundance of HD which reduces the efficiency of deuterium fractionation at high density. In agreement with an earlier study, under these conditions HD may not be the primary deuterium reservoir in the cold dense interstellar medium and H_3^+ will be the main charge carrier in the dense centers of pre-stellar cores and the protoplanetary disk midplane.

Lee, Jeong-Eun; Bergin, Edwin A.

2015-01-01

375

Snowmelt timing (onset and melt-refreeze) trends in the Yukon River basin determined from passive microwave brightness temperatures  

NASA Astrophysics Data System (ADS)

High latitude drainage basins are experiencing increases in temperature higher than the global average with snowmelt dominated basins most sensitive to effects in winter due to snowpack's integration of these changes over the season. This may influence the timing of snowmelt onset and the occurrence of any preceding (early) melt events, resulting in changes in spring runoff and associated flooding, often the most significant hydrologic events of the year. It is therefore critical to be able to understand and model these processes, especially for ungauged basins with little meteorological data. For such basins, passive microwave remote sensing can be utilized; an approach tested in the Yukon River Basin draining more than 850,000 km2 of Alaska and the Yukon Territory. Brightness temperature (Tb) data from the Advanced Microwave Scanning Radiometer for EOS (AMSR-E) 36.5 V-GHz frequency and the Special Sensor Microwave Imager (SSM/I) 37 V-GHz frequency together form a time series from 1988 to 2010, enabling us to detect trends in snowmelt onset timing and the end of melt-refreeze period. Tb encompasses both physical temperature and emissivity with wet snow easily detected by an abrupt increase in emissivity. Tb and diurnal amplitude variation (DAV) thresholds determine dates of melt onset and melt-freeze end (end of high DAV), defined as where thresholds are met for more than three of five consecutive days. Melt that is detected before melt onset and is not sustained for more than three out of five days is classified as an early melt event. Preliminary results of trends in snowmelt onset and occurrence of early melt events suggest sub-basin differences occur with varying landcover, permafrost, and elevation. Of the thirteen sub-basins that comprise the Yukon River basin, five have significant trends toward later melt onset dates, while the northernmost (the Chandalar and Porcupine) have earlier melt onset. The majority of basins with later onset show increasing trends of early melt events, while those with earlier onset have decreasing trends, suggesting winter melt dynamics may affect melt onset later in the year. Significant variability, however, requires further analysis to more definitively determine trends and relationships between the melt parameters.

Semmens, K. A.; Ramage, J. M.

2011-12-01

376

Absorption of crystalline water ice in the far infrared at different temperatures  

NASA Astrophysics Data System (ADS)

The optical properties of ice in the far infrared are important for models of protoplanetary and debris disks. In this report, we derive a new set of data for the absorption (represented by the imaginary part of the refractive index ?) of crystalline water ice in this spectral range. The study includes a detailed inspection of the temperature dependence, which has not been conducted in such detail before. We measured the transmission of three ice layers with different thicknesses at temperatures ? = 10...250 K and present data at wavelengths ? = 80...625 ?m. We found a change in the spectral dependence of ? at a wavelength of 175 6 ?m. At shorter wavelengths, ? exhibits a constant flat slope and no significant temperature dependence. Long-ward of that wavelength, the slope gets steeper and has a clear, approximately linear temperature dependence. This change in behaviour is probably caused by a characteristic absorption band of water ice. The measured data were fitted by a power-law model that analytically describes the absorption behaviour at an arbitrary temperature. This model can readily be applied to any object of interest, for instance a protoplanetary or debris disk. To illustrate how the model works, we simulated the spectral energy distribution (SED) of the resolved, large debris disk around the nearby solar-type star HD 207129. Replacing our ice model by another, commonly used data set for water ice results in a different SED slope at longer wavelengths. This leads to changes in the characteristic model parameters of the disk, such as the inferred particle size distribution, and affects the interpretation of the underlying collisional physics of the disk.

Reinert, C.; Mutschke, H.; Krivov, A. V.; Lhne, T.; Mohr, P.

2015-01-01

377

Borehole temperature response for competing models of Laurentide ice sheet dynamics  

NASA Astrophysics Data System (ADS)

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.

Rath, Volker; Alvarez-Solas, Jorge; Robinson, Alex; Montoya-Redondo, Marisa

2013-04-01

378

Extraction of temperature dependent electrical resistivity and thermal conductivity from silicon microwires self-heated to melting temperature  

NASA Astrophysics Data System (ADS)

Temperature-dependent electrical resistivity, ?(T), and thermal conductivity, k(T), of nanocrystalline silicon microwires self-heated to melt are extracted by matching simulated current-voltage (I-V) characteristics to experimental I-V characteristics. Electrical resistivity is extracted from highly doped p-type wires on silicon dioxide in which the heat losses are predominantly to the substrate and the self-heating depends mainly on ?(T) of the wires. The extracted ?(T) decreases from 11.8 m? cm at room-temperature to 5.2 m? cm at 1690 K, in reasonable agreement with the values measured up to 650 K. Electrical resistivity and thermal conductivity are extracted from suspended highly doped n-type silicon wires in which the heat losses are predominantly through the wires. In this case, measured ?(T) (decreasing from 20.5 m? cm at room temperature to 12 m? cm at 620 K) is used to extract ?(T) at higher temperatures (decreasing to 1 m? cm at 1690 K) and k(T) (decreasing from 30 W m-1 K-1 at room temperature to 20 W m-1 K-1 at 1690 K). The method is tested by using the extracted parameters to model wires with different dimensions. The experimental and simulated I-V curves for these wires show good agreement up to high voltage and temperature levels. This technique allows extraction of the electrical resistivity and thermal conductivity up to very high temperatures from self-heated microstructures.

Bakan, Gokhan; Adnane, Lhacene; Gokirmak, Ali; Silva, Helena

2012-09-01

379

Satellite-derived ice data sets no. 1: Antarctic monthly average microwave brightness temperatures and sea-ice concentrations, 1973 - 1976  

NASA Technical Reports Server (NTRS)

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.

Zwally, H. J.

1981-01-01

380

Stable Isotopes of N and Ar as Tracers to Retrieve Past Air Temperature from Air Trapped in Ice Cores  

Microsoft Academic Search

\\u000a Ice cores are paleoclimatic archives that permit the reconstruction of past local precipitation temperature (from the measurements\\u000a of water isotopes) and past atmospheric gas concentration (from the analysis of the air trapped in the ice) over the past\\u000a 800,000 years. However, water isotopes are not a quantitative tracer for past temperature in Greenland ice cores. Moreover,\\u000a because of the entrapment

A. Landais

381

Ice structure monitoring with an optical fiber sensing system  

Microsoft Academic Search

Ice has been used as an effective and economical material for constructions of roads and platforms in cold regions. However, the practical applications of this brittle material are limited by the fact that ice structures can suddenly crack due to low tensile strength, be crushed due to excessive compression, melt and become soften as temperature elevates. In this paper, an

Zhi Zhou; Minghua Huang; Jianping He; Genda Chen; Jinping Ou

2010-01-01

382

Comparison of Near-Surface Air Temperatures and MODIS Ice-Surface Temperatures at Summit, Greenland (2008-2013)  

NASA Technical Reports Server (NTRS)

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.

Shuman, Christopher A.; Hall, Dorothy K.; DiGirolamo, Nicolo E.; Mefford, Thomas K.; Schnaubelt, Michael J.

2014-01-01