Insight into glacier climate interaction: reconstruction of the mass balance field using ice extent data

NASA Astrophysics Data System (ADS)

Visnjevic, Vjeran; Herman, Frédéric; Licul, Aleksandar

2016-04-01

With the end of the Last Glacial Maximum (LGM), about 20 000 years ago, ended the most recent long-lasting cold phase in Earth's history. We recently developed a model that describes large-scale erosion and its response to climate and dynamical changes with the application to the Alps for the LGM period. Here we will present an inverse approach we have recently developed to infer the LGM mass balance from known ice extent data, focusing on a glacier or ice cap. The ice flow model is developed using the shallow ice approximation and the developed codes are accelerated using GPUs capabilities. The mass balance field is the constrained variable defined by the balance rate β and the equilibrium line altitude (ELA), where c is the cutoff value: b = max(βṡ(S(z) - ELA), c) We show that such a mass balance can be constrained from the observed past ice extent and ice thickness. We are also investigating several different geostatistical methods to constrain spatially variable mass balance, and derive uncertainties on each of the mass balance parameters.

Influence of Arctic Sea Ice Extent on Polar Cloud Fraction and Vertical Structure and Implications for Regional Climate

NASA Technical Reports Server (NTRS)

Palm, Stephen P.; Strey, Sara T.; Spinhirne, James; Markus, Thorsten

2010-01-01

Recent satellite lidar measurements of cloud properties spanning a period of 5 years are used to examine a possible connection between Arctic sea ice amount and polar cloud fraction and vertical distribution. We find an anticorrelation between sea ice extent and cloud fraction with maximum cloudiness occurring over areas with little or no sea ice. We also find that over ice!free regions, there is greater low cloud frequency and average optical depth. Most of the optical depth increase is due to the presence of geometrically thicker clouds over water. In addition, our analysis indicates that over the last 5 years, October and March average polar cloud fraction has increased by about 7% and 10%, respectively, as year average sea ice extent has decreased by 5% 7%. The observed cloud changes are likely due to a number of effects including, but not limited to, the observed decrease in sea ice extent and thickness. Increasing cloud amount and changes in vertical distribution and optical properties have the potential to affect the radiative balance of the Arctic region by decreasing both the upwelling terrestrial longwave radiation and the downward shortwave solar radiation. Because longwave radiation dominates in the long polar winter, the overall effect of increasing low cloud cover is likely a warming of the Arctic and thus a positive climate feedback, possibly accelerating the melting of Arctic sea ice.

Estimating the extent of Antarctic summer sea ice during the Heroic Age of Antarctic Exploration

NASA Astrophysics Data System (ADS)

Edinburgh, Tom; Day, Jonathan J.

2016-11-01

In stark contrast to the sharp decline in Arctic sea ice, there has been a steady increase in ice extent around Antarctica during the last three decades, especially in the Weddell and Ross seas. In general, climate models do not to capture this trend and a lack of information about sea ice coverage in the pre-satellite period limits our ability to quantify the sensitivity of sea ice to climate change and robustly validate climate models. However, evidence of the presence and nature of sea ice was often recorded during early Antarctic exploration, though these sources have not previously been explored or exploited until now. We have analysed observations of the summer sea ice edge from the ship logbooks of explorers such as Robert Falcon Scott, Ernest Shackleton and their contemporaries during the Heroic Age of Antarctic Exploration (1897-1917), and in this study we compare these to satellite observations from the period 1989-2014, offering insight into the ice conditions of this period, from direct observations, for the first time. This comparison shows that the summer sea ice edge was between 1.0 and 1.7° further north in the Weddell Sea during this period but that ice conditions were surprisingly comparable to the present day in other sectors.

Predicting the Extent of Summer Sea Ice in the Arctic

NASA Astrophysics Data System (ADS)

Rigor, I. G.; Wallace, J. M.

2003-12-01

The summers of 1998 and 2002 had the least sea ice extent (SIE) in the Arctic. These observations seem to agree with the trends noted by Parkinson, et al. (1999, hereafter P99) for the period 1979-1997, but the spatial pattern of these recent decreases in summer SIE were different. The summer trends shown by P99, exhibit large decreases in SIE primarily in the East Siberian Sea (ESS), while the decreases observed during 1998 and 2002 were much larger in the Beaufort and Chukchi seas (BCS). We now show that the trends for the period 1979 - 2002 are much smaller in the ESS than the trends shown by P99, and the largest decreasing trends have shifted from the ESS to the BCS. Rigor, et al. (2002) showed that the changes in SIE that P99 noted were driven by changes in atmospheric circulation related to the phase of the prior winter Arctic Oscillation (AO, Thompson and Wallace, 1998) index. Given that the latest trends in SIE are different than those shown by P99, one could ask whether the affect of the AO on sea ice noted by Rigor, et al. (2002) has also changed, and whether some large scale climate modes other than the AO has influenced the climate of the Arctic Ocean more? To answer these questions, we applied Empirical Orthogonal Function (EOF) analysis on the September SIE data from microwave satellites, and found that the first two modes SIE were most highly correlated to the prior winter AO, and the AO index of the summer months just prior to each September. These modes explain more than 45% of the variance in SIE, and show that the influence of the winter and summer AO dominates Arctic climate from 1979 - 2002. Using data from the International Arctic Buoy Programme and the National Centers for Environmental Prediction, we will show that the changes in sea ice extent are primarily driven by dynamic changes in sea ice thickness and discuss the implications for predicting summer SIE.

Recalculated Areas for Maximum Ice Extents of the Baltic Sea During Winters 1971-2008

NASA Astrophysics Data System (ADS)

Niskanen, T.; Vainio, J.; Eriksson, P.; Heiler, I.

2009-04-01

Publication of operational ice charts in Finland was started from the Baltic Sea in a year 1915. Until year 1993 all ice charts were hand drawn paper copies but in the year 1993 ice charting software IceMap was introduced. Since then all ice charts were produced digitally. Since the year 1996 IceMap has had an option that user can calculate areas of single ice area polygons in the chart. Using this option the area of the maximum ice extent can be easily solved fully automatically. Before this option was introduced (and in full operation) all maximum extent areas were calculated manually by a planimeter. During recent years it has become clear that some areas calculated before 1996 don't give the same result as IceMap. Differences can come from for example inaccuracy of old coastlines, map projections, the calibration of the planimeter or interpretation of old ice area symbols. Old ice charts since winter 1970-71 have now been scanned, rectified and re-drawn. New maximum ice extent areas for Baltic Sea have now been re-calculated. By these new technological tools it can be concluded that in some cases clear differences can be found.

A Detailed Geophysical Investigation of the Grounding of Henry Ice Rise, with Implications for Holocene Ice-Sheet Extent.

NASA Astrophysics Data System (ADS)

Wearing, M.; Kingslake, J.

2017-12-01

It is generally assumed that since the Last Glacial Maximum the West Antarctic Ice Sheet (WAIS) has experienced monotonic retreat of the grounding line (GL). However, recent studies have cast doubt on this assumption, suggesting that the retreat of the WAIS grounding line may have been followed by a significant advance during the Holocene in the Weddell and Ross Sea sectors. Constraining this evolution is important as reconstructions of past ice-sheet extent are used to spin-up predictive ice-sheet models and correct mass-balance observations for glacial isostatic adjustment. Here we examine in detail the formation of the Henry Ice Rise (HIR), which ice-sheet model simulations suggest played a key role in Holocene ice-mass changes in the Weddell Sea sector. Observations from a high-resolution ground-based, ice-penetrating radar survey are best explained if the ice rise formed when the Ronne Ice Shelf grounded on a submarine high, underwent a period of ice-rumple flow, before the GL migrated outwards to form the present-day ice rise. We constrain the relative chronology of this evolution by comparing the alignment and intersection of isochronal internal layers, relic crevasses, surface features and investigating the dynamic processes leading to their complex structure. We also draw analogies between HIR and the neighbouring Doake Ice Rumples. The date of formation is estimated using vertical velocities derived with a phase-sensitive radio-echo sounder (pRES). Ice-sheet models suggest that the formation of the HIR and other ice rises may have halted and reversed large-scale GL retreat. Hence the small-scale dynamics of these crucial regions could have wide-reaching consequences for future ice-sheet mass changes and constraining their formation and evolution further would be beneficial. One stringent test of our geophysics-based conclusions would be to drill to the bed of HIR to sample the ice for isotopic analysis and the bed for radiocarbon analysis.

Data-adaptive Harmonic Decomposition and Real-time Prediction of Arctic Sea Ice Extent

NASA Astrophysics Data System (ADS)

Kondrashov, Dmitri; Chekroun, Mickael; Ghil, Michael

2017-04-01

Decline in the Arctic sea ice extent (SIE) has profound socio-economic implications and is a focus of active scientific research. Of particular interest is prediction of SIE on subseasonal time scales, i.e. from early summer into fall, when sea ice coverage in Arctic reaches its minimum. However, subseasonal forecasting of SIE is very challenging due to the high variability of ocean and atmosphere over Arctic in summer, as well as shortness of observational data and inadequacies of the physics-based models to simulate sea-ice dynamics. The Sea Ice Outlook (SIO) by Sea Ice Prediction Network (SIPN, http://www.arcus.org/sipn) is a collaborative effort to facilitate and improve subseasonal prediction of September SIE by physics-based and data-driven statistical models. Data-adaptive Harmonic Decomposition (DAH) and Multilayer Stuart-Landau Models (MSLM) techniques [Chekroun and Kondrashov, 2017], have been successfully applied to the nonlinear stochastic modeling, as well as retrospective and real-time forecasting of Multisensor Analyzed Sea Ice Extent (MASIE) dataset in key four Arctic regions. In particular, DAH-MSLM predictions outperformed most statistical models and physics-based models in real-time 2016 SIO submissions. The key success factors are associated with DAH ability to disentangle complex regional dynamics of MASIE by data-adaptive harmonic spatio-temporal patterns that reduce the data-driven modeling effort to elemental MSLMs stacked per frequency with fixed and small number of model coefficients to estimate.

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

NASA Technical Reports Server (NTRS)

Abdalati, Waleed; Steffen, Konrad

2000-01-01

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

The role of declining summer sea ice extent in increasing Arctic winter precipitation

NASA Astrophysics Data System (ADS)

Hamman, J.; Roberts, A.; Cassano, J. J.; Nijssen, B.

2016-12-01

In the past three decades, the Arctic has experienced large declines in summer sea ice cover, permafrost extent, and spring snow cover, and increases in winter precipitation. This study explores the relationship between declining Arctic sea ice extent (IE) and winter precipitation (WP) across the Arctic land masses. The first part of this presentation presents the observed relationship between IE and WP. Using satellite estimates of IE and WP data based on a combination of in-situ observations and global reanalyses, we show that WP is negatively correlated with summer IE and that this relationship is strongest before the year 2000. After 2000, around the time IE minima began to decline most rapidly, the relationship between IE and WP degenerates. This indicates that other processes are driving changes in IE and WP. We hypothesize that positive anomalies in poleward moisture transport have historically driven anomalously low IE and high WP, and that since the significant decline in IE, moisture divergence from the central Arctic has been a larger contributor to WP over land. To better understand the physical mechanisms driving the observed changes in the Arctic climate system and the sensitivity of the Arctic climate system to declining sea ice, we have used the fully-coupled Regional Arctic System Model (RASM) to simulate two distinct sea ice climates. The first climate represents normal IE, while the second includes reduced summer IE. The second portion of this presentation analyzes these two RASM simulations, in conjunction with our observation-based analysis, to understand the coupled relationship between poleward moisture transport, IE, evaporation from the Arctic Ocean, and precipitation. We will present the RASM-simulated Arctic water budget and demonstrate the role of IE in driving WP anomalies. Finally, a spatial correlation analysis identifies characteristic patterns in IE, ocean evaporation, and polar cap convergence that contribute to anomalies in WP.

Developing and Implementing Protocols for Arctic Sea Ice Observations

NASA Astrophysics Data System (ADS)

Perovich, Donald K.; Gerland, Sebastian

2009-05-01

Arctic Surface-Based Sea Ice Observations: Integrated Protocols and Coordinated Data Acquisition; Tromsø, Norway, 26-27 January 2009; The Arctic sea ice cover is diminishing. Over the past several years, not only has ice thinned but the extent of ice at the end of summer, and hence perennial ice, has declined markedly. These changes affect a wide range of issues and are important for a varied group of stakeholders, including Arctic coastal communities, policy makers, industry, the scientific community, and the public. Concerns range from the role of sea ice cover as an indicator and amplifier of climate change to marine transportation, resource extraction, and coastal erosion. To understand and respond to these ongoing changes, it is imperative to develop and implement consistent and robust observational protocols that can be used to describe the current state of the ice cover as well as future changes.

The impact of lower sea-ice extent on Arctic greenhouse-gas exchange

USGS Publications Warehouse

Parmentier, Frans-Jan W.; Christensen, Torben R.; Sørensen, Lise Lotte; Rysgaard, Søren; McGuire, A. David; Miller, Paul A.; Walker, Donald A.

2013-01-01

In September 2012, Arctic sea-ice extent plummeted to a new record low: two times lower than the 1979–2000 average. Often, record lows in sea-ice cover are hailed as an example of climate change impacts in the Arctic. Less apparent, however, are the implications of reduced sea-ice cover in the Arctic Ocean for marine–atmosphere CO2 exchange. Sea-ice decline has been connected to increasing air temperatures at high latitudes. Temperature is a key controlling factor in the terrestrial exchange of CO2 and methane, and therefore the greenhouse-gas balance of the Arctic. Despite the large potential for feedbacks, many studies do not connect the diminishing sea-ice extent with changes in the interaction of the marine and terrestrial Arctic with the atmosphere. In this Review, we assess how current understanding of the Arctic Ocean and high-latitude ecosystems can be used to predict the impact of a lower sea-ice cover on Arctic greenhouse-gas exchange.

Bellingshausen Sea Ice Extent Recorded in an Antarctic Peninsula Ice Core

NASA Technical Reports Server (NTRS)

Porter, Stacy E.; Parkinson, Claire L.; Mosley-Thompson, Ellen

2016-01-01

Annual net accumulation (A(sub n)) from the Bruce Plateau (BP) ice core retrieved from the Antarctic Peninsula exhibits a notable relationship with sea ice extent (SIE) in the Bellingshausen Sea. Over the satellite era, both BP A(sub n) and Bellingshausen SIE are influenced by large-scale climatic factors such as the Amundsen Sea Low, Southern Annular Mode, and Southern Oscillation. In addition to the direct response of BP A(sub n) to Bellingshausen SIE (e.g., more open water as a moisture source), these large-scale climate phenomena also link the BP and the Bellingshausen Sea indirectly such that they exhibit similar responses (e.g., northerly wind anomalies advect warm, moist air to the Antarctic Peninsula and neighboring Bellingshausen Sea, which reduces SIE and increases A(sub n)). Comparison with a time series of fast ice at South Orkney Islands reveals a relationship between BP A(sub n) and sea ice in the northern Weddell Sea that is relatively consistent over the twentieth century, except when it is modulated by atmospheric wave patterns described by the Trans-Polar Index. The trend of increasing accumulation on the Bruce Plateau since approximately 1970 agrees with other climate records and reconstructions in the region and suggests that the current rate of sea ice loss in the Bellingshausen Sea is unrivaled in the twentieth century.

The Influence of Arctic Sea Ice Extent on Polar Cloud Fraction and Vertical Structure and Implications for Regional Climate

NASA Technical Reports Server (NTRS)

Palm, Stephen P.; Strey, Sara T.; Spinhirne, James; Markus, Thorsten

2010-01-01

Recent satellite lidar measurements of cloud properties spanning a period of five years are used to examine a possible connection between Arctic sea ice amount and polar cloud fraction and vertical distribution. We find an anti-correlation between sea ice extent and cloud fraction with maximum cloudiness occurring over areas with little or no sea ice. We also find that over ice free regions, there is greater low cloud frequency and average optical depth. Most of the optical depth increase is due to the presence of geometrically thicker clouds over water. In addition, our analysis indicates that over the last 5 years, October and March average polar cloud fraction has increased by about 7 and 10 percent, respectively, as year average sea ice extent has decreased by 5 to 7 percent. The observed cloud changes are likely due to a number of effects including, but not limited to, the observed decrease in sea ice extent and thickness. Increasing cloud amount and changes in vertical distribution and optical properties have the potential to affect the radiative balance of the Arctic region by decreasing both the upwelling terrestrial longwave radiation and the downward shortwave solar radiation. Since longwave radiation dominates in the long polar winter, the overall effect of increasing low cloud cover is likely a warming of the Arctic and thus a positive climate feedback, possibly accelerating the melting of Arctic sea ice.

Arctic sea ice decline: Projected changes in timing and extent of sea ice in the Bering and Chukchi Seas

USGS Publications Warehouse

Douglas, David C.

2010-01-01

among models. High agreement also accompanies projections that the Chukchi Sea will be completely ice covered during February, March, and April at the end of the century. Large uncertainties, however, are associated with the timing and amount of partial ice cover during the intervening periods of melt and freeze. For the Bering Sea, median March ice extent is projected to be about 25 percent less than the 1979-1988 average by mid-century and 60 percent less by the end of the century. The ice-free season in the Bering Sea is projected to increase from its contemporary average of 5.5 months to a median of about 8.5 months by the end of the century. A 3-month longer ice- free season in the Bering Sea is attained by a 1-month advance in melt and a 2-month delay in freeze, meaning the ice edge typically will pass through the Bering Strait in May and January at the end of the century rather than June and November as presently observed.

Variability and Trends in Sea Ice Extent and Ice Production in the Ross Sea

NASA Technical Reports Server (NTRS)

Comiso, Josefino; Kwok, Ronald; Martin, Seelye; Gordon, Arnold L.

2011-01-01

Salt release during sea ice formation in the Ross Sea coastal regions is regarded as a primary forcing for the regional generation of Antarctic Bottom Water. Passive microwave data from November 1978 through 2008 are used to examine the detailed seasonal and interannual characteristics of the sea ice cover of the Ross Sea and the adjacent Bellingshausen and Amundsen seas. For this period the sea ice extent in the Ross Sea shows the greatest increase of all the Antarctic seas. Variability in the ice cover in these regions is linked to changes in the Southern Annular Mode and secondarily to the Antarctic Circumpolar Wave. Over the Ross Sea shelf, analysis of sea ice drift data from 1992 to 2008 yields a positive rate of increase in the net ice export of about 30,000 sq km/yr. For a characteristic ice thickness of 0.6 m, this yields a volume transport of about 20 cu km/yr, which is almost identical, within error bars, to our estimate of the trend in ice production. The increase in brine rejection in the Ross Shelf Polynya associated with the estimated increase with the ice production, however, is not consistent with the reported Ross Sea salinity decrease. The locally generated sea ice enhancement of Ross Sea salinity may be offset by an increase of relatively low salinity of the water advected into the region from the Amundsen Sea, a consequence of increased precipitation and regional glacial ice melt.

Observed and Modeled Trends in Southern Ocean Sea Ice

NASA Technical Reports Server (NTRS)

Parkinson, Claire L.

2003-01-01

Conceptual models and global climate model (GCM) simulations have both indicated the likelihood of an enhanced sensitivity to climate change in the polar regions, derived from the positive feedbacks brought about by the polar abundance of snow and ice surfaces. Some models further indicate that the changes in the polar regions can have a significant impact globally. For instance, 37% of the temperature sensitivity to a doubling of atmospheric CO2 in simulations with the GCM of the Goddard Institute for Space Studies (GISS) is attributable exclusively to inclusion of sea ice variations in the model calculations. Both sea ice thickness and sea ice extent decrease markedly in the doubled CO, case, thereby allowing the ice feedbacks to occur. Stand-alone sea ice models have shown Southern Ocean hemispherically averaged winter ice-edge retreats of 1.4 deg latitude for each 1 K increase in atmospheric temperatures. Observations, however, show a much more varied Southern Ocean ice cover, both spatially and temporally, than many of the modeled expectations. In fact, the satellite passive-microwave record of Southern Ocean sea ice since late 1978 has revealed overall increases rather than decreases in ice extents, with ice extent trends on the order of 11,000 sq km/year. When broken down spatially, the positive trends are strongest in the Ross Sea, while the trends are negative in the Bellingshausen/Amundsen Seas. Greater spatial detail can be obtained by examining trends in the length of the sea ice season, and those trends show a coherent picture of shortening sea ice seasons throughout almost the entire Bellingshausen and Amundsen Seas to the west of the Antarctic Peninsula and in the far western Weddell Sea immediately to the east of the Peninsula, with lengthening sea ice seasons around much of the rest of the continent. This pattern corresponds well with the spatial pattern of temperature trends, as the Peninsula region is the one region in the Antarctic with a strong

Evidence for smaller extents of the northwestern Greenland Ice Sheet and North Ice Cap during the Holocene

NASA Astrophysics Data System (ADS)

Kelly, M. A.; Osterberg, E. C.; Axford, Y.; Bigl, M.; Birkel, S. D.; Corbett, L. B.; Roy, E. P.; Thompson, J. T.; Whitecloud, S.

2013-12-01

The Greenland Ice Sheet (GrIS) and local glaciers on Greenland are responding dynamically to warming temperatures with widespread retreat. GRACE satellite data (e.g., Kahn et al., 2010) and the Petermann Glacier calving events document the recent expansion of ice loss into northwestern Greenland. To improve the ability to estimate future ice loss in a warming climate, we are developing records of the response of the northwestern Greenlandic cryosphere to Holocene climatic conditions, with a focus on past warm periods. Our ongoing research includes analyses of glacial geology, sub-fossil vegetation, lake sediment cores, chironomid assemblages and ice cores combined with glaciological modeling. To constrain past ice extents that were as small as, or smaller than, at present, we recovered sub-fossil vegetation exposed at the receding margins of the GrIS and North Ice Cap (NIC) in the Nunatarssuaq region (~76.7°N, 67.4°W) and of the GrIS near Thule (~76.5°N, 68.7°W). We present vegetation types and radiocarbon ages of 30 plant samples collected in August 2012. In the Nunatarssuaq region, five ages of in situ (rooted) vegetation including Polytrichum moss, Saxifraga nathorstii and grasses located <5 m outboard of the GrIS margin are ~120-200 cal yr BP (range of medians of the 2-sigma calibrated age ranges). Nine ages of in situ Polytrichum, Saxifraga oppositafolia and grasses from ~1-5 m inboard of the NIC margin (excavated from beneath ice) range from ~50 to 310 cal yr BP. The growth of these plants occurred when the GrIS and NIC were at least as small as at present and their ages suggest that ice advances occurred in the last 50-120 yrs. In addition to the in situ samples, we collected plants from well-preserved ground material exposed along shear planes in the GrIS margins. In Nunatarssuaq, two Polytrichum mosses rooted in ground material and exposed along a shear plane in the GrIS margin date to 4680 and 4730 cal yr BP. Near Thule, three ages of Salix arctica

Bedrock Erosion Surfaces Record Former East Antarctic Ice Sheet Extent

NASA Astrophysics Data System (ADS)

Paxman, Guy J. G.; Jamieson, Stewart S. R.; Ferraccioli, Fausto; Bentley, Michael J.; Ross, Neil; Armadillo, Egidio; Gasson, Edward G. W.; Leitchenkov, German; DeConto, Robert M.

2018-05-01

East Antarctica hosts large subglacial basins into which the East Antarctic Ice Sheet (EAIS) likely retreated during past warmer climates. However, the extent of retreat remains poorly constrained, making quantifying past and predicted future contributions to global sea level rise from these marine basins challenging. Geomorphological analysis and flexural modeling within the Wilkes Subglacial Basin are used to reconstruct the ice margin during warm intervals of the Oligocene-Miocene. Flat-lying bedrock plateaus are indicative of an ice sheet margin positioned >400-500 km inland of the modern grounding zone for extended periods of the Oligocene-Miocene, equivalent to a 2-m rise in global sea level. Our findings imply that if major EAIS retreat occurs in the future, isostatic rebound will enable the plateau surfaces to act as seeding points for extensive ice rises, thus limiting extensive ice margin retreat of the scale seen during the early EAIS.

Revisiting the Potential of Melt Pond Fraction as a Predictor for the Seasonal Arctic Sea Ice Extent Minimum

NASA Technical Reports Server (NTRS)

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

2015-01-01

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

Skillful Spring Forecasts of September Arctic Sea Ice Extent Using Passive Microwave Data

NASA Technical Reports Server (NTRS)

Petty, A. A.; Schroder, D.; Stroeve, J. C.; Markus, Thorsten; Miller, Jeffrey A.; Kurtz, Nathan Timothy; Feltham, D. L.; Flocco, D.

2017-01-01

In this study, we demonstrate skillful spring forecasts of detrended September Arctic sea ice extent using passive microwave observations of sea ice concentration (SIC) and melt onset (MO). We compare these to forecasts produced using data from a sophisticated melt pond model, and find similar to higher skill values, where the forecast skill is calculated relative to linear trend persistence. The MO forecasts shows the highest skill in March-May, while the SIC forecasts produce the highest skill in June-August, especially when the forecasts are evaluated over recent years (since 2008). The high MO forecast skill in early spring appears to be driven primarily by the presence and timing of open water anomalies, while the high SIC forecast skill appears to be driven by both open water and surface melt processes. Spatial maps of detrended anomalies highlight the drivers of the different forecasts, and enable us to understand regions of predictive importance. Correctly capturing sea ice state anomalies, along with changes in open water coverage appear to be key processes in skillfully forecasting summer Arctic sea ice.

Tropically driven and externally forced patterns of Antarctic sea ice change: reconciling observed and modeled trends

NASA Astrophysics Data System (ADS)

Schneider, David P.; Deser, Clara

2018-06-01

Recent work suggests that natural variability has played a significant role in the increase of Antarctic sea ice extent during 1979-2013. The ice extent has responded strongly to atmospheric circulation changes, including a deepened Amundsen Sea Low (ASL), which in part has been driven by tropical variability. Nonetheless, this increase has occurred in the context of externally forced climate change, and it has been difficult to reconcile observed and modeled Antarctic sea ice trends. To understand observed-model disparities, this work defines the internally driven and radiatively forced patterns of Antarctic sea ice change and exposes potential model biases using results from two sets of historical experiments of a coupled climate model compared with observations. One ensemble is constrained only by external factors such as greenhouse gases and stratospheric ozone, while the other explicitly accounts for the influence of tropical variability by specifying observed SST anomalies in the eastern tropical Pacific. The latter experiment reproduces the deepening of the ASL, which drives an increase in regional ice extent due to enhanced ice motion and sea surface cooling. However, the overall sea ice trend in every ensemble member of both experiments is characterized by ice loss and is dominated by the forced pattern, as given by the ensemble-mean of the first experiment. This pervasive ice loss is associated with a strong warming of the ocean mixed layer, suggesting that the ocean model does not locally store or export anomalous heat efficiently enough to maintain a surface environment conducive to sea ice expansion. The pervasive upper-ocean warming, not seen in observations, likely reflects ocean mean-state biases.

Tropically driven and externally forced patterns of Antarctic sea ice change: reconciling observed and modeled trends

NASA Astrophysics Data System (ADS)

Schneider, David P.; Deser, Clara

2017-09-01

Recent work suggests that natural variability has played a significant role in the increase of Antarctic sea ice extent during 1979-2013. The ice extent has responded strongly to atmospheric circulation changes, including a deepened Amundsen Sea Low (ASL), which in part has been driven by tropical variability. Nonetheless, this increase has occurred in the context of externally forced climate change, and it has been difficult to reconcile observed and modeled Antarctic sea ice trends. To understand observed-model disparities, this work defines the internally driven and radiatively forced patterns of Antarctic sea ice change and exposes potential model biases using results from two sets of historical experiments of a coupled climate model compared with observations. One ensemble is constrained only by external factors such as greenhouse gases and stratospheric ozone, while the other explicitly accounts for the influence of tropical variability by specifying observed SST anomalies in the eastern tropical Pacific. The latter experiment reproduces the deepening of the ASL, which drives an increase in regional ice extent due to enhanced ice motion and sea surface cooling. However, the overall sea ice trend in every ensemble member of both experiments is characterized by ice loss and is dominated by the forced pattern, as given by the ensemble-mean of the first experiment. This pervasive ice loss is associated with a strong warming of the ocean mixed layer, suggesting that the ocean model does not locally store or export anomalous heat efficiently enough to maintain a surface environment conducive to sea ice expansion. The pervasive upper-ocean warming, not seen in observations, likely reflects ocean mean-state biases.

Response of Arctic Snow and Sea Ice Extents to Melt Season Atmospheric Forcing Across the Land-Ocean Boundary

NASA Astrophysics Data System (ADS)

Bliss, A. C.; Anderson, M. R.

2011-12-01

Little research has gone into studying the concurrent variations in the annual loss of continental snow cover and sea ice extent across the land-ocean boundary, however, the analysis of these data averaged spatially over three study regions located in North America and Eastern and Western Russia, reveals a distinct difference in the response of anomalous snow and sea ice conditions to the atmospheric forcing. This study compares the monthly continental snow cover and sea ice extent loss in the Arctic, during the melt season months (May-August) for the period 1979-2007, with regional atmospheric conditions known to influence summer melt including: mean sea level pressures, 925 hPa air temperatures, and mean 2 m U and V wind vectors from NCEP/DOE Reanalysis 2. The monthly hemispheric snow cover extent data used are from the Rutgers University Global Snow Lab and sea ice extents for this study are derived from the monthly passive microwave satellite Bootstrap algorithm sea ice concentrations available from the National Snow and Ice Data Center. Three case study years (1985, 1996, and 2007) are used to compare the direct response of monthly anomalous sea ice and snow cover areal extents to monthly mean atmospheric forcing averaged spatially over the extent of each study region. This comparison is then expanded for all summer months over the 29 year study period where the monthly persistence of sea ice and snow cover extent anomalies and changes in the sea ice and snow conditions under differing atmospheric conditions are explored further. The monthly anomalous atmospheric conditions are classified into four categories including: warmer temperatures with higher pressures, warmer temperatures with lower pressures, cooler temperatures with higher pressures, and cooler temperatures with lower pressures. Analysis of the atmospheric conditions surrounding anomalous loss of snow and ice cover over the independent study regions indicates that conditions of warmer temperatures

Correlating Ice Cores from Quelccaya Ice Cap with Chronology from Little Ice Age Glacial Extents

NASA Astrophysics Data System (ADS)

Stroup, J. S.; Kelly, M. A.; Lowell, T. V.

2010-12-01

Proxy records indicate Southern Hemisphere climatic changes during the Little Ice Age (LIA; ~1300-1850 AD). In particular, records of change in and around the tropical latitudes require attention because these areas are sensitive to climatic change and record the dynamic interplay between hemispheres (Oerlemans, 2005). Despite this significance, relatively few records exist for the southern tropics. Here we present a reconstruction of glacial fluctuations of Quelccaya Ice Cap (QIC), Peruvian Andes, from pre-LIA up to the present day. In the Qori Kalis valley, extensive sets of moraines exist beginning with the 1963 AD ice margin (Thompson et al., 2006) and getting progressively older down valley. Several of these older moraines can be traced and are continuous with moraines in the Challpa Cocha valley. These moraines have been dated at <1050-1350-AD (Mercer and Palacios, 1977) and interpreted to have been deposited during the Little Ice Age. We present a new suite of surface exposure and radiocarbon dates collected in 2008 and 2009 that constrain the ages of these moraines. Preliminary 10Be ages of boulder surfaces atop the moraines range from ~350-1370 AD. Maximum and minimum-limiting radiocarbon ages bracketing the moraines are ~0-1800 AD. The chronology of past ice cap extents are correlated with ice core records from QIC which show an accumulation increase during ~1500-1700 AD and an accumulation decrease during ~1720-1860 AD (Thompson et al., 1985; 1986; 2006). In addition, other proxy records from Peru and the tropics are correlated with the records at QIC as a means to understand climate conditions during the LIA. This work forms the basis for future modeling of the glacial system during the LIA at QIC and for modeling of past temperature and precipitation regimes at high altitude in the tropics.

Seasonal and interannual variability of fast ice extent in the southeastern Laptev Sea between 1999 and 2013

NASA Astrophysics Data System (ADS)

Selyuzhenok, V.; Krumpen, T.; Mahoney, A.; Janout, M.; Gerdes, R.

2015-12-01

Along with changes in sea ice extent, thickness, and drift speed, Arctic sea ice regime is characterized by a decrease of fast ice season and reduction of fast ice extent. The most extensive fast ice cover in the Arctic develops in the southeastern Laptev Sea. Using weekly operational sea ice charts produced by Arctic and Antarctic Research Institute (AARI, Russia) from 1999 to 2013, we identified five main key events that characterize the annual evolution of fast ice in the southeastern Laptev Sea. Linking the occurrence of the key events with the atmospheric forcing, bathymetry, freezeup, and melt onset, we examined the processes driving annual fast ice cycle. The analysis revealed that fast ice in the region is sensitive to thermodynamic processes throughout a season, while the wind has a strong influence only on the first stages of fast ice development. The maximal fast ice extent is closely linked to the bathymetry and local topography and is primarily defined by the location of shoals, where fast ice is likely grounded. The annual fast ice cycle shows significant changes over the period of investigation, with tendencies toward later fast ice formation and earlier breakup. These tendencies result in an overall decrease of the fast ice season by 2.8 d/yr, which is significantly higher than previously reported trends.

Antartic sea ice, 1973 - 1976: Satellite passive-microwave observations

NASA Technical Reports Server (NTRS)

Zwally, H. J.; Comiso, J. C.; Parkinson, C. L.; Campbell, W. J.; Carsey, F. D.; Gloersen, P.

1983-01-01

Data from the Electrically Scanning Microwave Radiometer (ESMR) on the Nimbus 5 satellite are used to determine the extent and distribution of Antarctic sea ice. The characteristics of the southern ocean, the mathematical formulas used to obtain quantitative sea ice concentrations, the general characteristics of the seasonal sea ice growth/decay cycle and regional differences, and the observed seasonal growth/decay cycle for individual years and interannual variations of the ice cover are discussed. The sea ice data from the ESMR are presented in the form of color-coded maps of the Antarctic and the southern oceans. The maps show brightness temperatures and concentrations of pack ice averaged for each month, 4-year monthly averages, and month-to-month changes. Graphs summarizing the results, such as areas of sea ice as a function of time in the various sectors of the southern ocean are included. The images demonstrate that satellite microwave data provide unique information on large-scale sea ice conditions for determining climatic conditions in polar regions and possible global climatic changes.

Wind, current and swell influences on the ice extent and flux in the Grand Banks-Labrador sea area as observed in the LIMEX '87 experiment

NASA Technical Reports Server (NTRS)

Argus, Susan Digby; Carsey, Frank; Holt, Benjamin

1988-01-01

This paper presents data collected by airborne and satellite instruments during the Labrador Ice Margin Experiment, that demonstrate the effects of oceanic and atmospheric processes on the ice conditions in the Grand Banks-Labrador sea area. Special consideration is given to the development of algorithms for extracting information from SAR data. It is shown that SAR data can be used to monitor ice extent, determine ice motion, locate shear zones, monitor the penetration of swell into the ice, estimate floe sizes, and establish the dimensions of the ice velocity zones. It is also shown that the complex interaction of the ice cover with winds, currents, swell, and coastlines is similar to the dynamics established for a number of sites in both polar regions.

The Impact of Stratospheric Circulation Extremes on Minimum Arctic Sea Ice Extent

NASA Astrophysics Data System (ADS)

Smith, K. L.; Polvani, L. M.; Tremblay, B.

2017-12-01

The interannual variability of summertime Arctic sea ice extent (SIE) is anti-correlated with the leading mode of extratropical atmospheric variability in preceding winter, the Arctic Oscillation (AO). Given this relationship and the need for better seasonal predictions of Arctic SIE, we here examine the role of stratospheric circulation extremes and stratosphere-troposphere coupling in linking the AO and Arctic SIE variability. We show that extremes in the stratospheric circulation during the winter season, namely stratospheric sudden warming (SSW) and strong polar vortex (SPV) events, are associated with significant anomalies in sea ice concentration in the Bering Straight and the Sea of Okhotsk in winter, the Barents Sea in spring and along the Eurasian coastline in summer in both observations and a fully-coupled, stratosphere-resolving general circulation model. The accompanying figure shows the composite mean sea ice concentration anomalies from the Whole Atmosphere Community Climate Model (WACCM) for SSWs (N = 126, top row) and SPVs (N = 99, bottom row) for winter (a,d), spring (b,e) and summer (c,f). Consistent with previous work on the AO, we find that SSWs, which are followed by the negative phase of the AO at the surface, result in sea ice growth, whereas SPVs, which are followed by the positive phase of the AO at the surface, result in sea ice loss, although the dynamic and thermodynamic processes driving these sea ice anomalies in the three Arctic regions, noted above, are different. Our analysis suggests that the presence or absence of stratospheric circulation extremes in winter may play a non-trivial role in determining total September Arctic SIE when combined with other factors.

Contribution of Increasing Glacial Freshwater Fluxes to Observed Trends in Antarctic Sea Ice

NASA Astrophysics Data System (ADS)

Le Sommer, J.; Merino, N.; Durand, G.; Jourdain, N.; Goosse, H.; Mathiot, P.; Gurvan, M.

2016-02-01

Southern Ocean sea-ice extent has experienced an overall positive trend over recent decades. While the amplitude of this trend is open to debate, the geographical pattern of regional changes has been clearly identified by observations. Mechanisms driving changes in the Antarctic Sea Ice Extent (SIE) are not fully understood and climate models fail to simulate these trends. Changes in different atmospheric features such as SAM or ENSO seem to explain the observed trend of Antartic sea ice, but only partly, since they can not account for the actual amplitude of the observed signal. The increasing injection of freshwater due to the accelerating ice discharge from Antarctica Ice Sheet (AIS) during the last two decades has been proposed as another candidate to contribute to SIE trend. However, the quantity and the distribution of the extra freshwater injection were not properly constrained. Recent glaciological estimations may improve the way the glacial freshwater is injected in the model. Here, we study the role of the glacial freshwater into the observed SIE trend, using the state-of-the-art Antarctic mass loss estimations. Ocean/sea-ice model simulations have been carried out with two different Antarctic freshwater scenarios corresponding to 20-years of Antarctic Ice Sheet evolution. The combination of an improved iceberg model with the most recent glaciological estimations has been applied to account for the most realistic possible Antarctic freshwater evolution scenarios. Results suggest that Antarctica has contributed to almost a 30% of the observed trend in regions of the South Pacific and South East Indian sectors, but has little impact in the South Atlantic sector. We conclude that the observed SIE trend over the last decades is due to a combination of both an atmospheric forcing and the extra freshwater injection. Our results advocates that the evolution of glacial freshwater needs to be correctly represented in climate models.

Assessing the Extent of Influence Subglacial Hydrology Has on Dynamic Ice Sheet Behavior

NASA Astrophysics Data System (ADS)

Babonis, G. S.; Csatho, B. M.

2012-12-01

Numerous recent studies have done an excellent job capturing and quantifying the complex pattern of dynamic changes of the Greenland Ice Sheet (GrIS) over the past several decades. The timing of changes in ice velocities and mass balance indicate that the mechanisms controlling these behaviors, both external and internal, act over variable spatial and temporal regimes, can change in rapid and complex fashion, and have significant effect on ice sheet behavior as well as sea level rise. With roughly half of the estimated ice loss from the GrIS attributed to dynamic processes, these changes account for about 250 Gt/yr (2003-2008), equivalence to 0.6 mm/yr sea level rise. One of the primary influences of dynamic ice behavior is ice sheet hydrology, including the storage and transport of water from the supraglacial to subglacial environment, and the subsequent development of water transport pathways, thus demonstrating the need for further characterization of the subglacial environment. Enhanced dynamic flow of ice due to the influence of meltwater distribution on the subglacial environment has been reported, including In-SAR observations of large velocity increases over short periods of time, suggesting regions where dynamic changes are likely being caused by changes in hydrology. Additionally, building upon the 1993-2011 laser altimetry record, analyzed by our Surface Elevation Reconstruction And Change detection (SERAC) procedure, we have detected complex patterns of rapid thickening and thinning patterns over several outlet glaciers. This study presents a comprehensive investigation of hydrologic control on dynamic glacier behavior for several key sites in Greenland. We combine a high resolution surface digital elevation model (DEM) derived by fusing space- and airborne laser altimetry observations and SPIRIT SPOT DEMs, with a high resolution, hydrologically-corrected bedrock DEM derived from a combination of CResIS and Operation Icebridge ice penetrating radar data

2015 Arctic Sea Ice Maximum Annual Extent Is Lowest On Record

NASA Image and Video Library

2015-03-19

The sea ice cap of the Arctic appeared to reach its annual maximum winter extent on Feb. 25, according to data from the NASA-supported National Snow and Ice Data Center (NSIDC) at the University of Colorado, Boulder. At 5.61 million square miles (14.54 million square kilometers), this year’s maximum extent was the smallest on the satellite record and also one of the earliest. Read more: 1.usa.gov/1Eyvelz Credit: NASA's Goddard Space Flight Center NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Conditions leading to the unprecedented low Antarctic sea ice extent during the 2016 austral spring season

NASA Astrophysics Data System (ADS)

Stuecker, Malte F.; Bitz, Cecilia M.; Armour, Kyle C.

2017-09-01

The 2016 austral spring was characterized by the lowest Southern Hemisphere (SH) sea ice extent seen in the satellite record (1979 to present) and coincided with anomalously warm surface waters surrounding most of Antarctica. We show that two distinct processes contributed to this event: First, the extreme El Niño event peaking in December-February 2015/2016 contributed to pronounced extratropical SH sea surface temperature and sea ice extent anomalies in the eastern Ross, Amundsen, and Bellingshausen Seas that persisted in part until the following 2016 austral spring. Second, internal unforced atmospheric variability of the Southern Annular Mode promoted the exceptional low sea ice extent in November-December 2016. These results suggest that a combination of tropically forced and internal SH atmospheric variability contributed to the unprecedented sea ice decline during the 2016 austral spring, on top of a background of slow changes expected from greenhouse gas and ozone forcing.

A 21-Year Record of Arctic Sea Ice Extents and Their Regional, Seasonal, and Monthly Variability and Trends

NASA Technical Reports Server (NTRS)

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

2001-01-01

Satellite passive-microwave data have been used to calculate sea ice extents over the period 1979-1999 for the north polar sea ice cover as a whole and for each of nine regions. Over this 21-year time period, the trend in yearly average ice extents for the ice cover as a whole is -32,900 +/- 6,100 sq km/yr (-2.7 +/- 0.5 %/decade), indicating a reduction in sea ice coverage that has decelerated from the earlier reported value of -34,000 +/- 8,300 sq km/yr (-2.8 +/- 0.7 %/decade) for the period 1979-1996. Regionally, the reductions are greatest in the Arctic Ocean, the Kara and Barents Seas, and the Seas of Okhotsk and Japan, whereas seasonally, the reductions are greatest in summer, for which season the 1979-1999 trend in ice extents is -41,600 +/- 12,900 sq km/ yr (-4.9 +/- 1.5 %/decade). On a monthly basis, the reductions are greatest in July and September for the north polar ice cover as a whole, in September for the Arctic Ocean, in June and July for the Kara and Barents Seas, and in April for the Seas of Okhotsk and Japan. Only two of the nine regions show overall ice extent increases, those being the Bering Sea and the Gulf of St. Lawrence.For neither of these two regions is the increase statistically significant, whereas the 1079 - 1999 ice extent decreases are statistically significant at the 99% confidence level for the north polar region as a whole, the Arctic Ocean, the Seas of Okhotsk and Japan, and Hudson Bay.

Critical Mechanisms for the Formation of Extreme Arctic Sea-Ice Extent in the Summers of 2007 and 1996

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dong, Xiquan; Zib, Benjamin J.; Xi, Baike

A warming Arctic climate is undergoing significant e 21 nvironmental change, most evidenced by the reduction of Arctic sea-ice extent during the summer. In this study, we examine two extreme anomalies of September sea-ice extent in 2007 and 1996, and investigate the impacts of cloud fraction (CF), atmospheric precipitable water vapor (PWV), downwelling longwave flux (DLF), surface air temperature (SAT), pressure and winds on the sea-ice variation in 2007 and 1996 using both satellite-derived sea-ice products and MERRA reanalysis. The area of the Laptev, East Siberian and West Chukchi seas (70-90oN, 90-180oE) has experienced the largest variation in sea-ice extentmore » from year-to-year and defined here as the Area Of Focus (AOF). The record low September sea-ice extent in 2007 was associated with positive anomalies 30 of CF, PWV, DLF, and SAT over the AOF. Persistent anti-cyclone positioned over the Beaufort Sea coupled with low pressure over Eurasia induced easterly zonal and southerly meridional winds. In contrast, negative CF, PWV, DLF and SAT anomalies, as well as opposite wind patterns to those in 2007, characterized the 1996 high September sea-ice extent. Through this study, we hypothesize the following positive feedbacks of clouds, water vapor, radiation and atmospheric variables on the sea-ice retreat during the summer 2007. The record low sea-ice extent during the summer 2007 is initially triggered by the atmospheric circulation anomaly. The southerly winds across the Chukchi and East Siberian seas transport warm, moist air from the north Pacific, which is not only enhancing sea-ice melt across the AOF, but also increasing clouds. The positive cloud feedback results in higher SAT and more sea-ice melt. Therefore, 40 more water vapor could be evaporated from open seas and higher SAT to form more clouds, which will enhance positive cloud feedback. This enhanced positive cloud feedback will then further increase SAT and accelerate the sea-ice retreat

Integrating Observations and Models to Better Understand a Changing Arctic Sea Ice Cover

NASA Astrophysics Data System (ADS)

Stroeve, J. C.

2017-12-01

TThe loss of the Arctic sea ice cover has captured the world's attention. While much attention has been paid to the summer ice loss, changes are not limited to summer. The last few winters have seen record low sea ice extents, with 2017 marking the 3rdyear in a row with a new record low for the winter maximum extent. More surprising is the number of consecutive months between January 2016 through April 2017 with ice extent anomalies more than 2 standard deviations below the 1981-2010 mean. Additionally, October 2016 through April 2017 saw 7 consecutive months with record low extents, something that had not happened before in the last 4 decades of satellite observations. As larger parts of the Arctic Ocean become ice-free in summer, regional seas gradually transition from a perennial to a seasonal ice cover. The Barents Sea is already only seasonally ice covered, whereas the Kara Sea has recently lost most of its summer ice and is thereby starting to become a seasonally ice covered region. These changes serve as harbinger for what's to come for other Arctic seas. Given the rapid pace of change, there is an urgent need to improve our understanding of the drivers behind Arctic sea ice loss, the implications of this ice loss and to predict future changes to better inform policy makers. Climate models play a fundamental role in helping us synthesize the complex elements of the Arctic sea ice system yet generally fail to simulate key features of the sea ice system and the pace of sea ice loss. Nevertheless, modeling advances continue to provide better means of diagnosing sea ice change, and new insights are likely to be gained with model output from the 6th phase of the Coupled Model Intercomparison Project (CMIP6). The CMIP6 Sea-Ice Model Intercomparison Project (SIMIP) aim is to better understand biases and errors in sea ice simulations so that we can improve our understanding of the likely future evolution of the sea ice cover and its impacts on global climate. To

Variability of Arctic Sea Ice as Determined from Satellite Observations

NASA Technical Reports Server (NTRS)

Parkinson, Claire L.

1999-01-01

The compiled, quality-controlled satellite multichannel passive-microwave record of polar sea ice now spans over 18 years, from November 1978 through December 1996, and is revealing considerable information about the Arctic sea ice cover and its variability. The information includes data on ice concentrations (percent areal coverages of ice), ice extents, ice melt, ice velocities, the seasonal cycle of the ice, the interannual variability of the ice, the frequency of ice coverage, and the length of the sea ice season. The data reveal marked regional and interannual variabilities, as well as some statistically significant trends. For the north polar ice cover as a whole, maximum ice extents varied over a range of 14,700,000 - 15,900,000 sq km, while individual regions experienced much greater percent variations, for instance, with the Greenland Sea having a range of 740,000 - 1,110,000 sq km in its yearly maximum ice coverage. In spite of the large variations from year to year and region to region, overall the Arctic ice extents showed a statistically significant, 2.80% / decade negative trend over the 18.2-year period. Ice season lengths, which vary from only a few weeks near the ice margins to the full year in the large region of perennial ice coverage, also experienced interannual variability, along with spatially coherent overall trends. Linear least squares trends show the sea ice season to have lengthened in much of the Bering Sea, Baffin Bay, the Davis Strait, and the Labrador Sea, but to have shortened over a much larger area, including the Sea of Okhotsk, the Greenland Sea, the Barents Sea, and the southeastern Arctic.

Additional Arctic observations improve weather and sea-ice forecasts for the Northern Sea Route

PubMed Central

Inoue, Jun; Yamazaki, Akira; Ono, Jun; Dethloff, Klaus; Maturilli, Marion; Neuber, Roland; Edwards, Patti; Yamaguchi, Hajime

2015-01-01

During ice-free periods, the Northern Sea Route (NSR) could be an attractive shipping route. The decline in Arctic sea-ice extent, however, could be associated with an increase in the frequency of the causes of severe weather phenomena, and high wind-driven waves and the advection of sea ice could make ship navigation along the NSR difficult. Accurate forecasts of weather and sea ice are desirable for safe navigation, but large uncertainties exist in current forecasts, partly owing to the sparse observational network over the Arctic Ocean. Here, we show that the incorporation of additional Arctic observations improves the initial analysis and enhances the skill of weather and sea-ice forecasts, the application of which has socioeconomic benefits. Comparison of 63-member ensemble atmospheric forecasts, using different initial data sets, revealed that additional Arctic radiosonde observations were useful for predicting a persistent strong wind event. The sea-ice forecast, initialised by the wind fields that included the effects of the observations, skilfully predicted rapid wind-driven sea-ice advection along the NSR. PMID:26585690

Reconstruction of the extent and variability of late Quaternary ice sheets and Arctic sea ice: Insights from new mineralogical and geochemical proxy records

NASA Astrophysics Data System (ADS)

Stein, R. H.; Niessen, F.; Fahl, K.; Forwick, M.; Kudriavtseva, A.; Ponomarenko, E.; Prim, A. K.; Quatmann-Hense, A.; Spielhagen, R. F.; Zou, H.

2016-12-01

The Arctic Ocean and surrounding continents are key areas within the Earth system and very sensitive to present and past climate change. In this context, the timing and extent of circum-Arctic ice sheets and its interaction with oceanic and sea-ice dynamics are major interest and focus of international research. New sediment cores recovered during the Polarstern Expeditions PS87 (Lomonosov Ridge/2014) and PS93.1 (Fram Strait/2015) together with several sediment cores available from previous Polarstern expeditions allow to carry out a detailed sedimentological and geochemical study that may help to unravel the changes in Arctic sea ice and circum-Arctic ice sheets during late Quaternary times. Our new data include biomarkers indicative for past sea-ice extent, phytoplankton productivity and terrigenous input as well as grain size, physical property, XRD and XRF data indicative for sources and pathways of terrigenous sediments (ice-rafted debris/IRD) related to glaciations in Eurasia, East Siberia, Canada and Greenland. Here, we present examples from selected sediment cores that give new insights into the timing and extent of sea ice and glaciations during MIS 6 to MIS 2. To highlight one example: SE-NW oriented, streamlined landforms have been mapped on top of the southern Lomonosov Ridge (LR) at water depths between 800 and 1000 m over long distances during Polarstern Expedition PS87, interpreted to be glacial lineations that formed beneath grounded ice sheets and ice streams. The orientations of the lineations identified are similar to those on the East Siberian continental margin, suggesting an East Siberian Chukchi Ice Sheet extended far to the north on LR during times of extreme Quaternary glaciations. Based on our new biomarker records from Core PS2757 (located on LR near 81°N) indicating a MIS 6 ice-edge situation with some open-water phytoplankton productivity, the glacial erosional event should have been older than MIS 6 (e.g., MIS 12?).

Statistical Analysis of SSMIS Sea Ice Concentration Threshold at the Arctic Sea Ice Edge during Summer Based on MODIS and Ship-Based Observational Data.

PubMed

Ji, Qing; Li, Fei; Pang, Xiaoping; Luo, Cong

2018-04-05

The threshold of sea ice concentration (SIC) is the basis for accurately calculating sea ice extent based on passive microwave (PM) remote sensing data. However, the PM SIC threshold at the sea ice edge used in previous studies and released sea ice products has not always been consistent. To explore the representable value of the PM SIC threshold corresponding on average to the position of the Arctic sea ice edge during summer in recent years, we extracted sea ice edge boundaries from the Moderate-resolution Imaging Spectroradiometer (MODIS) sea ice product (MOD29 with a spatial resolution of 1 km), MODIS images (250 m), and sea ice ship-based observation points (1 km) during the fifth (CHINARE-2012) and sixth (CHINARE-2014) Chinese National Arctic Research Expeditions, and made an overlay and comparison analysis with PM SIC derived from Special Sensor Microwave Imager Sounder (SSMIS, with a spatial resolution of 25 km) in the summer of 2012 and 2014. Results showed that the average SSMIS SIC threshold at the Arctic sea ice edge based on ice-water boundary lines extracted from MOD29 was 33%, which was higher than that of the commonly used 15% discriminant threshold. The average SIC threshold at sea ice edge based on ice-water boundary lines extracted by visual interpretation from four scenes of the MODIS image was 35% when compared to the average value of 36% from the MOD29 extracted ice edge pixels for the same days. The average SIC of 31% at the sea ice edge points extracted from ship-based observations also confirmed that choosing around 30% as the SIC threshold during summer is recommended for sea ice extent calculations based on SSMIS PM data. These results can provide a reference for further studying the variation of sea ice under the rapidly changing Arctic.

Holocene sea surface temperature and sea ice extent in the Okhotsk and Bering Seas

USGS Publications Warehouse

Harada, Naomi; Katsuki, Kota; Nakagawa, Mitsuhiro; Matsumoto, Akiko; Seki, Osamu; Addison, Jason A.; Finney, Bruce P.; Sato, Miyako

2014-01-01

Accurate prediction of future climate requires an understanding of the mechanisms of the Holocene climate; however, the driving forces, mechanisms, and processes of climate change in the Holocene associated with different time scales remain unclear. We investigated the drivers of Holocene sea surface temperature (SST) and sea ice extent in the North Pacific Ocean, and the Okhotsk and Bering Seas, as inferred from sediment core records, by using the alkenone unsaturation index as a biomarker of SST and abundances of sea ice-related diatoms (F. cylindrus and F. oceanica) as an indicator of sea ice extent to explore controlling mechanisms in the high-latitude Pacific. Temporal changes in alkenone content suggest that alkenone production was relatively high during the middle Holocene in the Okhotsk Sea and the western North Pacific, but highest in the late Holocene in the eastern Bering Sea and the eastern North Pacific. The Holocene variations of alkenone-SSTs at sites near Kamchatka in the Northwest Pacific, as well as in the western and eastern regions of the Bering Sea, and in the eastern North Pacific track the changes of Holocene summer insolation at 50°N, but at other sites in the western North Pacific, in the southern Okhotsk Sea, and the eastern Bering Sea they do not. In addition to insolation, other atmosphere and ocean climate drivers, such as sea ice distribution and changes in the position and activity of the Aleutian Low, may have systematically influenced the timing and magnitude of warming and cooling during the Holocene within the subarctic North Pacific. Periods of high sea ice extent in both the Okhotsk and Bering Seas may correspond to some periods of frequent or strong winter–spring dust storms in the Mongolian Gobi Desert, particularly one centered at ∼4–3 thousand years before present (kyr BP). Variation in storm activity in the Mongolian Gobi Desert region may reflect changes in the strength and positions of the Aleutian Low and Siberian

Sea salt sodium record from Talos Dome (East Antarctica) as a potential proxy of the Antarctic past sea ice extent.

PubMed

Severi, M; Becagli, S; Caiazzo, L; Ciardini, V; Colizza, E; Giardi, F; Mezgec, K; Scarchilli, C; Stenni, B; Thomas, E R; Traversi, R; Udisti, R

2017-06-01

Antarctic sea ice has shown an increasing trend in recent decades, but with strong regional differences from one sector to another of the Southern Ocean. The Ross Sea and the Indian sectors have seen an increase in sea ice during the satellite era (1979 onwards). Here we present a record of ssNa + flux in the Talos Dome region during a 25-year period spanning from 1979 to 2003, showing that this marker could be used as a potential proxy for reconstructing the sea ice extent in the Ross Sea and Western Pacific Ocean at least for recent decades. After finding a positive relationship between the maxima in sea ice extent for a 25-year period, we used this relationship in the TALDICE record in order to reconstruct the sea ice conditions over the 20th century. Our tentative reconstruction highlighted a decline in the sea ice extent (SIE) starting in the 1950s and pointed out a higher variability of SIE starting from the 1960s and that the largest sea ice extents of the last century occurred during the 1990s. Copyright © 2017 Elsevier Ltd. All rights reserved.

Sea-level records from the U.S. mid-Atlantic constrain Laurentide Ice Sheet extent during Marine Isotope Stage 3

PubMed Central

Pico, T; Creveling, J. R.; Mitrovica, J. X.

2017-01-01

The U.S. mid-Atlantic sea-level record is sensitive to the history of the Laurentide Ice Sheet as the coastline lies along the ice sheet's peripheral bulge. However, paleo sea-level markers on the present-day shoreline of Virginia and North Carolina dated to Marine Isotope Stage (MIS) 3, from 50 to 35 ka, are surprisingly high for this glacial interval, and remain unexplained by previous models of ice age adjustment or other local (for example, tectonic) effects. Here, we reconcile this sea-level record using a revised model of glacial isostatic adjustment characterized by a peak global mean sea level during MIS 3 of approximately −40 m, and far less ice volume within the eastern sector of the Laurentide Ice Sheet than traditional reconstructions for this interval. We conclude that the Laurentide Ice Sheet experienced a phase of very rapid growth in the 15 kyr leading into the Last Glacial Maximum, thus highlighting the potential of mid-field sea-level records to constrain areal extent of ice cover during glacial intervals with sparse geological observables. PMID:28555637

Anomalous Variability in Antarctic Sea Ice Extents During the 1960s With the Use of Nimbus Data

NASA Technical Reports Server (NTRS)

Gallaher, David W.; Campbell, G. Garrett; Meier, Walter N.

2014-01-01

The Nimbus I, II, and III satellites provide a new opportunity for climate studies in the 1960s. The rescue of the visible and infrared imager data resulted in the utilization of the early Nimbus data to determine sea ice extent. A qualitative analysis of the early NASA Nimbus missions has revealed Antarctic sea ice extents that are signicant larger and smaller than the historic 1979-2012 passive microwave record. The September 1964 ice mean area is 19.7x10 km +/- 0.3x10 km. This is more the 250,000 km greater than the 19.44x10 km seen in the new 2012 historic maximum. However, in August 1966 the maximum sea ice extent fell to 15.9x10 km +/- 0.3x10 km. This is more than 1.5x10 km below the passive microwave record of 17.5x10 km set in September of 1986. This variation between 1964 and 1966 represents a change of maximum sea ice of over 3x10 km in just two years. These inter-annual variations while large, are small when compared to the Antarctic seasonal cycle.

Ice conditions on the Chesapeake Bay as observed from LANDSAT during the winters of 1977, 1978 and 1979

NASA Technical Reports Server (NTRS)

Foster, J. L.

1980-01-01

The LANDSAT observations during the winters of 1977, 1978 and 1979, which were unusually cold in the northeastern U.S. and in the Chesapeake Bay area, were evaluated. Abnormal atmospheric circulation patterns displaced cold polar air to the south, and as a result, the Chesapeake Bay experienced much greater than normal icing conditions during these 3 years. The LANDSAT observations of the Chesapeake Bay area during these winters demonstrate the satellite's capabilities to monitor ice growth and melt, to detect ice motions, and to measure ice extent.

Atmospheric icing of structures: Observations and simulations

NASA Astrophysics Data System (ADS)

Ágústsson, H.; Elíasson, Á. J.; Thorsteins, E.; Rögnvaldsson, Ó.; Ólafsson, H.

2012-04-01

This study compares observed icing in a test span in complex orography at Hallormsstaðaháls (575 m) in East-Iceland with parameterized icing based on an icing model and dynamically downscaled weather at high horizontal resolution. Four icing events have been selected from an extensive dataset of observed atmospheric icing in Iceland. A total of 86 test-spans have been erected since 1972 at 56 locations in complex terrain with more than 1000 icing events documented. The events used here have peak observed ice load between 4 and 36 kg/m. Most of the ice accretion is in-cloud icing but it may partly be mixed with freezing drizzle and wet snow icing. The calculation of atmospheric icing is made in two steps. First the atmospheric data is created by dynamically downscaling the ECMWF-analysis to high resolution using the non-hydrostatic mesoscale Advanced Research WRF-model. The horizontal resolution of 9, 3, 1 and 0.33 km is necessary to allow the atmospheric model to reproduce correctly local weather in the complex terrain of Iceland. Secondly, the Makkonen-model is used to calculate the ice accretion rate on the conductors based on the simulated temperature, wind, cloud and precipitation variables from the atmospheric data. In general, the atmospheric model correctly simulates the atmospheric variables and icing calculations based on the atmospheric variables correctly identify the observed icing events, but underestimate the load due to too slow ice accretion. This is most obvious when the temperature is slightly below 0°C and the observed icing is most intense. The model results improve significantly when additional observations of weather from an upstream weather station are used to nudge the atmospheric model. However, the large variability in the simulated atmospheric variables results in high temporal and spatial variability in the calculated ice accretion. Furthermore, there is high sensitivity of the icing model to the droplet size and the possibility that

Paleo ice-cap surfaces and extents

NASA Astrophysics Data System (ADS)

Gillespie, A.; Pieri, D.

2008-12-01

The distribution, equilibrium-line altitude (ELA) and timing of Pleistocene alpine glaciers are used to constrain paleoclimatic reconstructions. Attention has largely focused on the geomorphic evidence for the former presence of simple valley glaciers; paleo alpine ice caps and their outlet glaciers have proven to be more problematical. This is especially so in the remote continental interior of Asia, where the research invested in the Alps or Rocky Mountains has yet to be duplicated. Even the putative existence and size of paleo ice caps in Tibet and the Kyrgyz Tien Shan is controversial. Remote sensing offers the opportunity to assess vast tracts of land quickly, with images and co-registered digital elevation models (DEMs) offering the most information for studies of paleoglaciers. We pose several questions: (1) With what confidence can nunataks be identified remotely? (2) What insights do their physiographic characteristics offer? (3) What characteristics of the bed of a paleo ice cap can be used to identify its former presence remotely? and (4) Can the geomorphic signatures of the edges of paleo ice caps be recognized and mapped? Reconstruction of the top surface of a paleo ice cap depends on the recognition of nunataks, typically rougher at 1 m to 100 m scales than their surroundings. Nunataks in southern Siberia are commonly notched by multiple sub- horizontal bedrock terraces. These step terraces appear to originate from freeze-thaw action on the rock-ice interface during periods of stability, and presence of multiple terraces suggests stepwise lowering of ice surfaces during deglaciation. An older generation of step-terraced nunataks, distinguished by degraded and eroded terraces, delineates a larger paleo ice cap in the Sayan Range (Siberian - Mongolian border) that significantly pre-dates the last glacial maximum (LGM). Large ice caps can experience pressure melting at their base and can manifest ice streams within the ice cap. Valleys left behind differ

Sea Ice Summer Camp: Bringing Together Arctic Sea Ice Modelers and Observers

NASA Astrophysics Data System (ADS)

Perovich, D. K.; Holland, M. M.

2016-12-01

The Arctic sea ice has undergone dramatic change and numerical models project this to continue for the foreseeable future. Understanding the mechanisms behind sea ice loss and its consequences for the larger Arctic and global systems is of critical importance if we are to anticipate and plan for the future. One impediment to progress is a disconnect between the observational and modeling communities. A sea ice summer camp was held in Barrow Alaska from 26 May to 1 June 2016 to overcome this impediment and better integrate the sea ice community. The 25 participants were a mix of modelers and observers from 13 different institutions at career stages from graduate student to senior scientist. The summer camp provided an accelerated program on sea ice observations and models and also fostered future collaborative interdisciplinary activities. Each morning was spent in the classroom with a daily lecture on an aspect of modeling or remote sensing followed by practical exercises. Topics included using models to assess sensitivity, to test hypotheses and to explore sources of uncertainty in future Arctic sea ice loss. The afternoons were spent on the ice making observations. There were four observational activities; albedo observations, ice thickness measurements, ice coring and physical properties, and ice morphology surveys. The last field day consisted of a grand challenge where the group formulated a hypothesis, developed an observational and modeling strategy to test the hypothesis, and then integrated the observations and model results. The impacts of changing sea ice are being felt today in Barrow Alaska. We opened a dialog with Barrow community members to further understand these changes. This included an evening discussion with two Barrow sea ice experts and a community presentation of our work in a public lecture at the Inupiat Heritage Center.

Marginal Ice Zone Processes Observed from Unmanned Aerial Systems

NASA Astrophysics Data System (ADS)

Zappa, C. J.

2015-12-01

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 mixing and gas exchange in leads, polynyas and in the presence of ice floes using both field and laboratory measurements. Measurements from unmanned aerial systems (UAS) in the marginal ice zone were made during 2 experiments: 1) North of Oliktok Point AK in the Beaufort Sea were made during the Marginal Ice Zone Ocean and Ice Observations and Processes EXperiment (MIZOPEX) in July-August 2013 and 2) Fram Strait and Greenland Sea northwest of Ny-Ålesund, Svalbard, Norway during the Air-Sea-Ice Physics and Biogeochemistry Experiment (ASIPBEX) April - May 2015. We developed a number of new payloads that include: i) hyperspectral imaging spectrometers to measure VNIR (400-1000 nm) and NIR (900-1700 nm) spectral radiance; ii) net longwave and net shortwave radiation for ice-ocean albedo studies; iii) air-sea-ice turbulent fluxes as well as wave height, ice freeboard, and surface roughness with a LIDAR; and iv) drone-deployed micro-drifters (DDµD) deployed from the UAS that telemeter temperature, pressure, and RH as it descends through the atmosphere and temperature and salinity of the upper meter of the ocean once it lands on the ocean's surface. Visible and IR imagery of melting ice floes 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

Observed microphysical changes in Arctic mixed-phase clouds when transitioning from sea-ice to open ocean

NASA Astrophysics Data System (ADS)

Young, Gillian; Jones, Hazel M.; Crosier, Jonathan; Bower, Keith N.; Darbyshire, Eoghan; Taylor, Jonathan W.; Liu, Dantong; Allan, James D.; Williams, Paul I.; Gallagher, Martin W.; Choularton, Thomas W.

2016-04-01

The Arctic sea-ice is intricately coupled to the atmosphere[1]. The decreasing sea-ice extent with the changing climate raises questions about how Arctic cloud structure will respond. Any effort to answer these questions is hindered by the scarcity of atmospheric observations in this region. Comprehensive cloud and aerosol measurements could allow for an improved understanding of the relationship between surface conditions and cloud structure; knowledge which could be key in validating weather model forecasts. Previous studies[2] have shown via remote sensing that cloudiness increases over the marginal ice zone (MIZ) and ocean with comparison to the sea-ice; however, to our knowledge, detailed in-situ data of this transition have not been previously presented. In 2013, the Aerosol-Cloud Coupling and Climate Interactions in the Arctic (ACCACIA) campaign was carried out in the vicinity of Svalbard, Norway to collect in-situ observations of the Arctic atmosphere and investigate this issue. Fitted with a suite of remote sensing, cloud and aerosol instrumentation, the FAAM BAe-146 aircraft was used during the spring segment of the campaign (Mar-Apr 2013). One case study (23rd Mar 2013) produced excellent coverage of the atmospheric changes when transitioning from sea-ice, through the MIZ, to the open ocean. Clear microphysical changes were observed, with the cloud liquid-water content increasing by almost four times over the transition. Cloud base, depth and droplet number also increased, whilst ice number concentrations decreased slightly. The surface warmed by ~13 K from sea-ice to ocean, with minor differences in aerosol particle number (of sizes corresponding to Cloud Condensation Nuclei or Ice Nucleating Particles) observed, suggesting that the primary driver of these microphysical changes was the increased heat fluxes and induced turbulence from the warm ocean surface as expected. References: [1] Kapsch, M.L., Graversen, R.G. and Tjernström, M. Springtime

Observed platelet ice distributions in Antarctic sea ice: An index for ocean-ice shelf heat flux

NASA Astrophysics Data System (ADS)

Langhorne, P. J.; Hughes, K. G.; Gough, A. J.; Smith, I. J.; Williams, M. J. M.; Robinson, N. J.; Stevens, C. L.; Rack, W.; Price, D.; Leonard, G. H.; Mahoney, A. R.; Haas, C.; Haskell, T. G.

2015-07-01

Antarctic sea ice that has been affected by supercooled Ice Shelf Water (ISW) has a unique crystallographic structure and is called platelet ice. In this paper we synthesize platelet ice observations to construct a continent-wide map of the winter presence of ISW at the ocean surface. The observations demonstrate that, in some regions of coastal Antarctica, supercooled ISW drives a negative oceanic heat flux of -30 Wm-2 that persists for several months during winter, significantly affecting sea ice thickness. In other regions, particularly where the thinning of ice shelves is believed to be greatest, platelet ice is not observed. Our new data set includes the longest ice-ocean record for Antarctica, which dates back to 1902 near the McMurdo Ice Shelf. These historical data indicate that, over the past 100 years, any change in the volume of very cold surface outflow from this ice shelf is less than the uncertainties in the measurements.

Anomalous Variability in Antarctic Sea Ice Extents During the 1960s With the Use of Nimbus Data

NASA Technical Reports Server (NTRS)

Gallaher, David W.; Campbell, G. Garrett; Meier, Walter N.

2013-01-01

The Nimbus I, II, and III satellites provide a new opportunity for climate studies in the 1960s. The rescue of the visible and infrared imager data resulted in the utilization of the early Nimbus data to determine sea ice extent. A qualitative analysis of the early NASA Nimbus missions has revealed Antarctic sea ice extents that are significant larger and smaller than the historic 1979-2012 passive microwave record. The September 1964 ice mean area is 19.7x10(exp 6) sq. km +/- 0.3x10(exp 6) sq. km. This is more the 250,000 sq. km greater than the 19.44x10(exp 6) sq. km seen in the new 2012 historic maximum. However, in August 1966 the maximum sea ice extent fell to 15.9x10(exp 6) sq. km +/- 0.3x10(exp 6) sq. km. This is more than 1.5x10(exp 6) sq. km below the passive microwave record of 17.5x10(exp 6) sq. km set in September of 1986. This variation between 1964 and 1966 represents a change of maximum sea ice of over 3x10(exp 6) sq. km in just two years. These inter-annual variations while large, are small when compared to the Antarctic seasonal cycle.

Seasonal regional forecast of the minimum sea ice extent in the LapteV Sea

NASA Astrophysics Data System (ADS)

Tremblay, B.; Brunette, C.; Newton, R.

2017-12-01

Late winter anomaly of sea ice export from the peripheral seas of the Atctic Ocean was found to be a useful predictor for the minimum sea ice extent (SIE) in the Arctic Ocean (Williams et al., 2017). In the following, we present a proof of concept for a regional seasonal forecast of the min SIE for the Laptev Sea based on late winter coastal divergence quantified using a Lagrangian Ice Tracking System (LITS) forced with satellite derived sea-ice drifts from the Polar Pathfinder. Following Nikolaeva and Sesterikov (1970), we track an imaginary line just offshore of coastal polynyas in the Laptev Sea from December of the previous year to May 1 of the following year using LITS. Results show that coastal divergence in the Laptev Sea between February 1st and May 1st is best correlated (r = -0.61) with the following September minimum SIE in accord with previous results from Krumpen et al. (2013, for the Laptev Sea) and Williams et a. (2017, for the pan-Arctic). This gives a maximum seasonal predictability of Laptev Sea min SIE anomalies from observations of approximately 40%. Coastal ice divergence leads to formation of thinner ice that melts earlier in early summer, hence creating areas of open water that have a lower albedo and trigger an ice-albedo feedback. In the Laptev Sea, we find that anomalies of coastal divergence in late winter are amplified threefold to result in the September SIE. We also find a correlation coefficient r = 0.49 between February-March-April (FMA) anomalies of coastal divergence with the FMA averaged AO index. Interestingly, the correlation is stronger, r = 0.61, when comparing the FMA coastal divergence anomalies to the DJFMA averaged AO index. It is hypothesized that the AO index at the beginning of the winter (and the associated anomalous sea ice export) also contains information that impact the magnitude of coastal divergence opening later in the winter. Our approach differs from previous approaches (e.g. Krumpen et al and Williams et al

ARCTIC SEA ICE EXTENT AND DRIFT, MODELED AS A VISCOUS FLUID.

USGS Publications Warehouse

Ling, Chi-Hai; Parkinson, Claire L.

1986-01-01

A dynamic/thermodynamic numerical model of sea ice has been used to calculate the yearly cycle of sea ice thicknesses, concentrations, and velocities in the Arctic Ocean and surrounding seas. The model combines the formulations of two previous models, taking the thermodynamics and momentum equations from the model of Parkinson and Washington and adding the constitutive equation and equation of state from the model of Ling, Rasmussen, and Campbell. Simulated annually averaged ice drift vectors compare well with observed ice drift from the Arctic Ocean Buoy Program.

Arctic sea ice decline contributes to thinning lake ice trend in northern Alaska

USGS Publications Warehouse

Alexeev, Vladimir; Arp, Christopher D.; Jones, Benjamin M.; Cai, Lei

2016-01-01

Field measurements, satellite observations, and models document a thinning trend in seasonal Arctic lake ice growth, causing a shift from bedfast to floating ice conditions. September sea ice concentrations in the Arctic Ocean since 1991 correlate well (r = +0.69,p < 0.001) to this lake regime shift. To understand how and to what extent sea ice affects lakes, we conducted model experiments to simulate winters with years of high (1991/92) and low (2007/08) sea ice extent for which we also had field measurements and satellite imagery characterizing lake ice conditions. A lake ice growth model forced with Weather Research and Forecasting model output produced a 7% decrease in lake ice growth when 2007/08 sea ice was imposed on 1991/92 climatology and a 9% increase in lake ice growth for the opposing experiment. Here, we clearly link early winter 'ocean-effect' snowfall and warming to reduced lake ice growth. Future reductions in sea ice extent will alter hydrological, biogeochemical, and habitat functioning of Arctic lakes and cause sub-lake permafrost thaw.

Predicting September sea ice: Ensemble skill of the SEARCH Sea Ice Outlook 2008-2013

NASA Astrophysics Data System (ADS)

Stroeve, Julienne; Hamilton, Lawrence C.; Bitz, Cecilia M.; Blanchard-Wrigglesworth, Edward

2014-04-01

Since 2008, the Study of Environmental Arctic Change Sea Ice Outlook has solicited predictions of September sea-ice extent from the Arctic research community. Individuals and teams employ a variety of modeling, statistical, and heuristic approaches to make these predictions. Viewed as monthly ensembles each with one or two dozen individual predictions, they display a bimodal pattern of success. In years when observed ice extent is near its trend, the median predictions tend to be accurate. In years when the observed extent is anomalous, the median and most individual predictions are less accurate. Statistical analysis suggests that year-to-year variability, rather than methods, dominate the variation in ensemble prediction success. Furthermore, ensemble predictions do not improve as the season evolves. We consider the role of initial ice, atmosphere and ocean conditions, and summer storms and weather in contributing to the challenge of sea-ice prediction.

Ice cover extent drives phytoplankton and bacterial community structure in a large north-temperate lake: implications for a warming climate.

PubMed

Beall, B F N; Twiss, M R; Smith, D E; Oyserman, B O; Rozmarynowycz, M J; Binding, C E; Bourbonniere, R A; Bullerjahn, G S; Palmer, M E; Reavie, E D; Waters, Lcdr M K; Woityra, Lcdr W C; McKay, R M L

2016-06-01

Mid-winter limnological surveys of Lake Erie captured extremes in ice extent ranging from expansive ice cover in 2010 and 2011 to nearly ice-free waters in 2012. Consistent with a warming climate, ice cover on the Great Lakes is in decline, thus the ice-free condition encountered may foreshadow the lakes future winter state. Here, we show that pronounced changes in annual ice cover are accompanied by equally important shifts in phytoplankton and bacterial community structure. Expansive ice cover supported phytoplankton blooms of filamentous diatoms. By comparison, ice free conditions promoted the growth of smaller sized cells that attained lower total biomass. We propose that isothermal mixing and elevated turbidity in the absence of ice cover resulted in light limitation of the phytoplankton during winter. Additional insights into microbial community dynamics were gleaned from short 16S rRNA tag (Itag) Illumina sequencing. UniFrac analysis of Itag sequences showed clear separation of microbial communities related to presence or absence of ice cover. Whereas the ecological implications of the changing bacterial community are unclear at this time, it is likely that the observed shift from a phytoplankton community dominated by filamentous diatoms to smaller cells will have far reaching ecosystem effects including food web disruptions. © 2015 Society for Applied Microbiology and John Wiley & Sons Ltd.

Interannual observations and quantification of summertime H2O ice deposition on the Martian CO2 ice south polar cap

USGS Publications Warehouse

Brown, Adrian J.; Piqueux, Sylvain; Titus, Timothy N.

2014-01-01

The spectral signature of water ice was observed on Martian south polar cap in 2004 by the Observatoire pour l'Mineralogie, l'Eau les Glaces et l'Activite (OMEGA) ( Bibring et al., 2004). Three years later, the OMEGA instrument was used to discover water ice deposited during southern summer on the polar cap ( Langevin et al., 2007). However, temporal and spatial variations of these water ice signatures have remained unexplored, and the origins of these water deposits remains an important scientific question. To investigate this question, we have used observations from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on the Mars Reconnaissance Orbiter (MRO) spacecraft of the southern cap during austral summer over four Martian years to search for variations in the amount of water ice. We report below that for each year we have observed the cap, the magnitude of the H2O ice signature on the southern cap has risen steadily throughout summer, particularly on the west end of the cap. The spatial extent of deposition is in disagreement with the current best simulations of deposition of water ice on the south polar cap (Montmessin et al., 2007). This increase in water ice signatures is most likely caused by deposition of atmospheric H2O ice and a set of unusual conditions makes the quantification of this transport flux using CRISM close to ideal. We calculate a ‘minimum apparent‘ amount of deposition corresponding to a thin H2O ice layer of 0.2 mm (with 70% porosity). This amount of H2O ice deposition is 0.6–6% of the total Martian atmospheric water budget. We compare our ‘minimum apparent’ quantification with previous estimates. This deposition process may also have implications for the formation and stability of the southern CO2 ice cap, and therefore play a significant role in the climate budget of modern day Mars.

Observed Hemispheric Asymmetry in Global Sea Ice Changes

NASA Technical Reports Server (NTRS)

Cavalieri, D. J.; Gloersen, P.; Parkinson, C. L.; Comiso, J. C.; Zwally, H. J.

1997-01-01

From November 1978 through December 1996, the areal extent of sea ice decreased by 2.9 +/- 0.4 percent per decade in the Arctic and increased by 1.3 +/- 0.2 percent per decade in the Antarctic. The observed hemispheric asymmetry in these trends is consistent with a modeled response to a carbon dioxide-induced climate warming. The interannual variations, which are 2.3 percent of the annual mean in the Arctic, with a predominant period of about 5 years, and 3.4 percent of the annual mean in the Antarctic, with a predominant period of about 3 years, are uncorrelated.

Earth Observing System (EOS) Snow and Ice Products for Observation and Modeling

NASA Technical Reports Server (NTRS)

Hall, D.; Kaminski, M.; Cavalieri, D.; Dickinson, R.; Marquis, M.; Riggs, G.; Robinson, D.; VanWoert, M.; Wolfe, R.

2005-01-01

Snow and ice are the key components of the Earth's cryosphere, and their influence on the Earth's energy balance is very significant due at least in part to the large areal extent and high albedo characterizing these features. Large changes in the cryosphere have been measured over the last century and especially over the past decade, and remote sensing plays a pivotal role in documenting these changes. Many of NASA's Earth Observing System (EOS) products derived from instruments on the Terra, Aqua, and Ice, Cloud and land Elevation Satellite (ICESat) satellites are useful for measuring changes in features that are associated with climate change. The utility of the products is continually enhanced as the length of the time series increases. To gain a more coherent view of the cryosphere and its historical and recent changes, the EOS products may be employed together, in conjunction with other sources of data, and in models. To further this goal, the first EOS Snow and Ice Products Workshop was convened. The specific goals of the workshop were to provide current and prospective users of EOS snow and ice products up-to-date information on the products, their validation status and future enhancements, to help users utilize the data products through hands-on demonstrations, and to facilitate the integration of EOS products into models. Oral and poster sessions representing a wide variety of snow and ice topics were held; three panels were also convened to discuss workshop themes. Panel discussions focused on data fusion and assimilation of the products into models. Approximately 110 people attended, representing a wide array of interests and organizations in the cryospheric community.

Seasonal and Interannual Variability of the Arctic Sea Ice: A Comparison between AO-FVCOM and Observations

NASA Astrophysics Data System (ADS)

Zhang, Y.; Chen, C.; Beardsley, R. C.; Gao, G.; Qi, J.; Lin, H.

2016-02-01

A high-resolution (up to 2 km), unstructured-grid, fully ice-sea coupled Arctic Ocean Finite-Volume Community Ocean Model (AO-FVCOM) was used to simulate the Arctic sea ice over the period 1978-2014. Good agreements were found between simulated and observed sea ice extent, concentration, drift velocity and thickness, indicating that the AO-FVCOM captured not only the seasonal and interannual variability but also the spatial distribution of the sea ice in the Arctic in the past 37 years. Compared with other six Arctic Ocean models (ECCO2, GSFC, INMOM, ORCA, NAME and UW), the AO-FVCOM-simulated ice thickness showed a higher correlation coefficient and a smaller difference with observations. An effort was also made to examine the physical processes attributing to the model-produced bias in the sea ice simulation. The error in the direction of the ice drift velocity was sensitive to the wind turning angle; smaller when the wind was stronger, but larger when the wind was weaker. This error could lead to the bias in the near-surface current in the fully or partially ice-covered zone where the ice-sea interfacial stress was a major driving force.

Mechanisms influencing seasonal to inter-annual prediction skill of sea ice extent in the Arctic Ocean in MIROC

NASA Astrophysics Data System (ADS)

Ono, Jun; Tatebe, Hiroaki; Komuro, Yoshiki; Nodzu, Masato I.; Ishii, Masayoshi

2018-02-01

To assess the skill of seasonal to inter-annual predictions of the detrended sea ice extent in the Arctic Ocean (SIEAO) and to clarify the underlying physical processes, we conducted ensemble hindcasts, started on 1 January, 1 April, 1 July and 1 October for each year from 1980 to 2011, for lead times up to three years, using the Model for Interdisciplinary Research on Climate (MIROC) version 5 initialised with the observed atmosphere and ocean anomalies and sea ice concentration. Significant skill is found for the winter months: the December SIEAO can be predicted up to 11 months ahead (anomaly correlation coefficient is 0.42). This skill might be attributed to the subsurface ocean heat content originating in the North Atlantic. A plausible mechanism is as follows: the subsurface water flows into the Barents Sea from spring to fall and emerges at the surface in winter by vertical mixing, and eventually affects the sea ice variability there. Meanwhile, the September SIEAO predictions are skillful for lead times of up to two months, due to the persistence of sea ice in the Beaufort, Chukchi, and East Siberian seas initialised in July, as suggested by previous studies.

Observed ices in the Solar System

USGS Publications Warehouse

Clark, Roger N.; Grundy, Will; Carlson, Robert R.; Noll, Keith; Gudipati, Murthy; Castillo-Rogez, Julie C.

2013-01-01

Ices have been detected and mapped on the Earth and all planets and/or their satellites further from the sun. Water ice is the most common frozen volatile observed and is also unambiguously detected or inferred in every planet and/or their moon(s) except Venus. Carbon dioxide is also extensively found in all systems beyond the Earth except Pluto although it sometimes appears to be trapped rather than as an ice on some objects. The largest deposits of carbon dioxide ice is on Mars. Sulfur dioxide ice is found in the Jupiter system. Nitrogen and methane ices are common beyond the Uranian system. Saturn’s moon Titan probably has the most complex active chemistry involving ices, with benzene (C6H6) and many tentative or inferred compounds including ices of Cyanoacetylene (HC3N), Toluene (C7H8), Cyanogen (C2N2), Acetonitrile (CH3CN), H2O, CO2, and NH3. Confirming compounds on Titan is hampered by its thick smoggy atmosphere. Ammonia was predicted on many icy moons but is notably absent among the definitively detected ices with the possible exception of Enceladus. Comets, storehouses of many compounds that could exist as ices in their nuclei, have only had small amounts of water ice definitively detected on their surfaces. Only one asteroid has had a direct detection of surface water ice, although its presence can be inferred in others. This chapter reviews some of the properties of ices that lead to their detection, and surveys the ices that have been observed on solid surfaces throughout the Solar System.

Variability of Antarctic Sea Ice 1979-1998

NASA Technical Reports Server (NTRS)

Zwally, H. Jay; Comiso, Josefino C.; Parkinson, Claire L.; Cavalieri, Donald J.; Gloersen, Per; Koblinsky, Chester J. (Technical Monitor)

2001-01-01

The principal characteristics of the variability of Antarctic sea ice cover as previously described from satellite passive-microwave observations are also evident in a systematically-calibrated and analyzed data set for 20.2 years (1979-1998). The total Antarctic sea ice extent (concentration > 15 %) increased by 13,440 +/- 4180 sq km/year (+1.18 +/- 0.37%/decade). The area of sea ice within the extent boundary increased by 16,960 +/- 3,840 sq km/year (+1.96 +/- 0.44%/decade). Regionally, the trends in extent are positive in the Weddell Sea (1.5 +/- 0.9%/decade), Pacific Ocean (2.4 +/- 1.4%/decade), and Ross (6.9 +/- 1.1 %/decade) sectors, slightly negative in the Indian Ocean (-1.5 +/- 1.8%/decade, and strongly negative in the Bellingshausen-Amundsen Seas sector (-9.5 +/- 1.5%/decade). For the entire ice pack, small ice increases occur in all seasons with the largest increase during autumn. On a regional basis, the trends differ season to season. During summer and fall, the trends are positive or near zero in all sectors except the Bellingshausen-Amundsen Seas sector. During winter and spring, the trends are negative or near zero in all sectors except the Ross Sea, which has positive trends in all seasons. Components of interannual variability with periods of about 3 to 5 years are regionally large, but tend to counterbalance each other in the total ice pack. The interannual variability of the annual mean sea-ice extent is only 1.6% overall, compared to 5% to 9% in each of five regional sectors. Analysis of the relation between regional sea ice extents and spatially-averaged surface temperatures over the ice pack gives an overall sensitivity between winter ice cover and temperature of -0.7% change in sea ice extent per K. For summer, some regional ice extents vary positively with temperature and others negatively. The observed increase in Antarctic sea ice cover is counter to the observed decreases in the Arctic. It is also qualitatively consistent with the

An Examination of the Sea Ice Rheology for Seasonal Ice Zones Based on Ice Drift and Thickness Observations

NASA Astrophysics Data System (ADS)

Toyota, Takenobu; Kimura, Noriaki

2018-02-01

The validity of the sea ice rheological model formulated by Hibler (1979), which is widely used in present numerical sea ice models, is examined for the Sea of Okhotsk as an example of the seasonal ice zone (SIZ), based on satellite-derived sea ice velocity, concentration and thickness. Our focus was the formulation of the yield curve, the shape of which can be estimated from ice drift pattern based on the energy equation of deformation, while the strength of the ice cover that determines its magnitude was evaluated using ice concentration and thickness data. Ice drift was obtained with a grid spacing of 37.5 km from the AMSR-E 89 GHz brightness temperature using a maximum cross-correlation method. The ice thickness was obtained with a spatial resolution of 100 m from a regression of the PALSAR backscatter coefficients with ice thickness. To assess scale dependence, the ice drift data derived from a coastal radar covering a 70 km range in the southernmost Sea of Okhotsk were similarly analyzed. The results obtained were mostly consistent with Hibler's formulation that was based on the Arctic Ocean on both scales with no dependence on a time scale, and justify the treatment of sea ice as a plastic material, with an elliptical shaped yield curve to some extent. However, it also highlights the difficulty in parameterizing sub-grid scale ridging in the model because grid scale ice velocities reduce the deformation magnitude by half due to the large variation of the deformation field in the SIZ.

Sensitivity of Totten Glacier Ice Shelf extent and grounding line to oceanic forcing

NASA Astrophysics Data System (ADS)

Pelle, T.; Morlighem, M.; Choi, Y.

2017-12-01

Totten Glacier is a major outlet glacier of the East Antarctic Ice Sheet and has been shown to be vulnerable to ocean-induced melt in both its past and present states. The intrusion of warm, circumpolar deep water beneath the Totten Glacier Ice Shelf (TGIS) has been observed to accelerate ice shelf thinning and promote iceberg calving, a primary mechanism of mass discharge from Totten. As such, accurately simulating TGIS's ice front dynamics is crucial to the predictive capabilities of ice sheet models in this region. Here, we study the TGIS using the Ice Sheet System Model (ISSM) and test the applicability of three calving laws: Crevasse Formation calving, Eigen calving, and Tensile Stress calving. We simulate the evolution of Totten Glacier through 2100 under enhanced oceanic forcing in order to investigate both future changes in ice front dynamics and possible thresholds of instability. In addition, we artificially retreat Totten's ice front position and allow the model to proceed dynamically in order to analyze the response of the glacier to calving events. Our analyses show that Tensile Stress calving most accurately reproduces Totten Glacier's observed ice front position. Furthermore, unstable grounding line retreat is projected when Totten is simulated under stronger oceanic thermal forcing scenarios and when the calving front is significantly retreated.

Polar Climate: Arctic sea ice

USGS Publications Warehouse

Stone, R.S.; Douglas, David C.; Belchansky, G.I.; Drobot, S.D.

2005-01-01

Recent decreases in snow and sea ice cover in the high northern latitudes are among the most notable indicators of climate change. Northern Hemisphere sea ice extent for the year as a whole was the third lowest on record dating back to 1973, behind 1995 (lowest) and 1990 (second lowest; Hadley Center–NCEP). September sea ice extent, which is at the end of the summer melt season and is typically the month with the lowest sea ice extent of the year, has decreased by about 19% since the late 1970s (Fig. 5.2), with a record minimum observed in 2002 (Serreze et al. 2003). A record low extent also occurred in spring (Chapman 2005, personal communication), and 2004 marked the third consecutive year of anomalously extreme sea ice retreat in the Arctic (Stroeve et al. 2005). Some model simulations indicate that ice-free summers will occur in the Arctic by the year 2070 (ACIA 2004).

Dark ice dynamics of the south-west Greenland Ice Sheet

NASA Astrophysics Data System (ADS)

Tedstone, Andrew J.; Bamber, Jonathan L.; Cook, Joseph M.; Williamson, Christopher J.; Fettweis, Xavier; Hodson, Andrew J.; Tranter, Martyn

2017-11-01

Runoff from the Greenland Ice Sheet (GrIS) has increased in recent years due largely to changes in atmospheric circulation and atmospheric warming. Albedo reductions resulting from these changes have amplified surface melting. Some of the largest declines in GrIS albedo have occurred in the ablation zone of the south-west sector and are associated with the development of dark ice surfaces. Field observations at local scales reveal that a variety of light-absorbing impurities (LAIs) can be present on the surface, ranging from inorganic particulates to cryoconite materials and ice algae. Meanwhile, satellite observations show that the areal extent of dark ice has varied significantly between recent successive melt seasons. However, the processes that drive such large interannual variability in dark ice extent remain essentially unconstrained. At present we are therefore unable to project how the albedo of bare ice sectors of the GrIS will evolve in the future, causing uncertainty in the projected sea level contribution from the GrIS over the coming decades. Here we use MODIS satellite imagery to examine dark ice dynamics on the south-west GrIS each year from 2000 to 2016. We quantify dark ice in terms of its annual extent, duration, intensity and timing of first appearance. Not only does dark ice extent vary significantly between years but so too does its duration (from 0 to > 80 % of June-July-August, JJA), intensity and the timing of its first appearance. Comparison of dark ice dynamics with potential meteorological drivers from the regional climate model MAR reveals that the JJA sensible heat flux, the number of positive minimum-air-temperature days and the timing of bare ice appearance are significant interannual synoptic controls. We use these findings to identify the surface processes which are most likely to explain recent dark ice dynamics. We suggest that whilst the spatial distribution of dark ice is best explained by outcropping of particulates from

Thin Sea-Ice Thickness as Inferred from Passive Microwave and In Situ Observations

NASA Technical Reports Server (NTRS)

Naoki, Kazuhiro; Ukita, Jinro; Nishio, Fumihiko; Nakayama, Masashige; Comiso, Josefino C.; Gasiewski, Al

2007-01-01

Since microwave radiometric signals from sea-ice strongly reflect physical conditions of a layer near the ice surface, a relationship of brightness temperature with thickness is possible especially during the early stages of ice growth. Sea ice is most saline during formation stage and as the salinity decreases with time while at the same time the thickness of the sea ice increases, a corresponding change in the dielectric properties and hence the brightness temperature may occur. This study examines the extent to which the relationships of thickness with brightness temperature (and with emissivity) hold for thin sea-ice, approximately less than 0.2 -0.3 m, using near concurrent measurements of sea-ice thickness in the Sea of Okhotsk from a ship and passive microwave brightness temperature data from an over-flying aircraft. The results show that the brightness temperature and emissivity increase with ice thickness for the frequency range of 10-37 GHz. The relationship is more pronounced at lower frequencies and at the horizontal polarization. We also established an empirical relationship between ice thickness and salinity in the layer near the ice surface from a field experiment, which qualitatively support the idea that changes in the near-surface brine characteristics contribute to the observed thickness-brightness temperature/emissivity relationship. Our results suggest that for thin ice, passive microwave radiometric signals contain, ice thickness information which can be utilized in polar process studies.

Field and Satellite Observations of the Formation and Distribution of Arctic Atmospheric Bromine Above a Rejuvenated Sea Ice Cover

NASA Technical Reports Server (NTRS)

Nghiem, Son V.; Rigor, Ignatius G.; Richter, Andreas; Burrows, John P.; Shepson, Paul B.; Bottenheim, Jan; Barber, David G.; Steffen, Alexandra; Latonas, Jeff; Wang, Feiyue;

Extent of the last ice sheet in northern Scotland tested with cosmogenic 10Be exposure ages

USGS Publications Warehouse

Phillips, W.M.; Hall, A.M.; Ballantyne, C.K.; Binnie, S.; Kubik, P.W.; Freeman, S.

2008-01-01

The extent of the last British-Irish Ice Sheet (BIIS) in northern Scotland is disputed. A restricted ice sheet model holds that at the global Last Glacial Maximum (LGM; ca. 23-19 ka) the BIIS terminated on land in northern Scotland, leaving Buchan, Caithness and the Orkney Islands ice-free. An alternative model implies that these three areas were ice-covered at the LGM, with the BIIS extending offshore onto the adjacent shelves. We test the two models using cosmogenic 10Be surface exposure dating of erratic boulders and glacially eroded bedrock from the three areas. Our results indicate that the last BIIS covered all of northern Scotland during the LGM, but that widespread deglaciation of Caithness and Orkney occurred prior to rapid warming at ca. 14.5 ka. Copyright ?? 2008 John Wiley & Sons, Ltd.

Wave-ice interaction, observed and modelled

NASA Astrophysics Data System (ADS)

Gemmrich, Johannes

2017-04-01

The need for wide-spread, up-to-date sea state predictions and observations in the emerging ice-free Arctic will further increase as the region will open up to marine operations. Wave models for arctic regions have to capture the additional wave physics associated with wave-ice interactions, and different prediction schemes have to be tested against observations. Here we present examples of spatial wave field parameters obtained from TerraSAR-X StripMap swaths in the southern Beaufort Sea taken as part of the "Arctic Sea State and Boundary Layer DRI". Fetch evolution of the significant wave height and length in open waters, and dominant wave lengths and the high frequency cut-off of the wave spectrum in ice are readily extracted from the SAR (synthetic aperture radar) data. A surprising result is that wave evolution in off-ice wind conditions is more rapidly than the fetch evolution in off-land cases, suggesting seeding of the wave field within the ice-covered region.

The role of sea ice in 2 x CO2 climate model sensitivity. Part 1: The total influence of sea ice thickness and extent

NASA Technical Reports Server (NTRS)

Rind, D.; Healy, R.; Parkinson, C.; Martinson, D.

1995-01-01

As a first step in investigating the effects of sea ice changes on the climate sensitivity to doubled atmospheric CO2, the authors use a standard simple sea ice model while varying the sea ice distributions and thicknesses in the control run. Thinner ice amplifies the atmospheric temperature senstivity in these experiments by about 15% (to a warming of 4.8 C), because it is easier for the thinner ice to be removed as the climate warms. Thus, its impact on sensitivity is similar to that of greater sea ice extent in the control run, which provides more opportunity for sea ice reduction. An experiment with sea ice not allowed to change between the control and doubled CO2 simulations illustrates that the total effect of sea ice on surface air temperature changes, including cloud cover and water vapor feedbacks that arise in response to sea ice variations, amounts to 37% of the temperature sensitivity to the CO2 doubling, accounting for 1.56 C of the 4.17 C global warming. This is about four times larger than the sea ice impact when no feedbacks are allowed. The different experiments produce a range of results for southern high latitudes with the hydrologic budget over Antarctica implying sea level increases of varying magnitude or no change. These results highlight the importance of properly constraining the sea ice response to climate perturbations, necessitating the use of more realistic sea ice and ocean models.

Tracking the seasonal cycle of coastal sea ice: Community-based observations and satellite remote sensing in service of societal needs

NASA Astrophysics Data System (ADS)

Eicken, Hajo; Lee, Olivia A.; Johnson, Mark A.; Pulsifer, Peter; Danielsen, Finn

2017-04-01

Break-up and freeze-up of coastal sea ice determine the timing and extent of a number of human activities, ranging from ice use by Indigenous hunters to coastal shipping. Yet, while major reductions in the extent of Arctic summer sea ice have been well studied, changes in its seasonal cycle have received less attention. Here, we discuss decadal scale changes and interannual variability in the timing of spring break-up and fall freeze-up, with a focus on coastal communities in Arctic Alaska. Observations of ice conditions by Indigenous sea-ice experts since 2006 indicate significant interannual variability in both the character and timing of freeze-up and break-up in the region. To aid in the archival and sharing of such observations, we have developed a database for community ice observations (eloka-arctic.org/sizonet). Development of this database addressed key questions ranging from community guidance on different levels of data sharing and access to the development of protocols that may lend themselves for implementation in the context of operational programs such as Global Cryosphere Watch. The lessons learned and tools developed through this effort may help foster the emergence of common observation protocols and sharing practices across the Arctic, as explored jointly with the Greenlandic PISUNA initiative and the European INTAROS project. For the Arctic Alaska region, we developed an algorithm to extract the timing of break-up and freeze-up from passive microwave satellite data, drawing on community-based observations. Data from 1979 to 2013 show break-up start arriving earlier by 5-9 days per decade and freeze-up start arriving later by 7-14 days per decade in the Chukchi and Beaufort Seas. The trends towards a shorter ice season observed over the past several decades point towards a substantial change in the winter ice regime by mid-century with incipient overlap of the end of the freeze-up and start of the break-up season as defined by coastal ice users.

McMurdo Ice Shelf Sounding and Radar Statistical Reconnaissance at 60-MHz: Brine Infiltration Extent and Surface Properties

NASA Astrophysics Data System (ADS)

Grima, C.; Rosales, A.; Blankenship, D. D.; Young, D. A.

2014-12-01

McMurdo Ice Shelf, Antarctica, is characterized by two particular geophysical processes. (1) Marine ice accretion supplies most of the ice shelf material rather than meteoric ice from glacier outflow and snow-falls. (2) A brine layer infiltrates the ice shelf laterally up to 20-km inward. The infiltration mainly initiates at the ice-front from sea water percolation when the firn/snow transition is below sea-level. A better characterization of the McMurdo ice shelf could constrain our knowledges of these mechanisms and assess the stability of the region that hosts numerous human activities from the close McMurdo station (USA) and Scott base (New-Zealand). McMurdo ice shelf is also an analog for the Jovian icy moon Europa where brine pockets are supposed to reside in the ice crust and accretion to occur at the 10-30-km deep ice-ocean interface.The University of Texas Institute for Geophysics (UTIG) acquired two radar survey grids over the McMurdo Ice Shelf during southern summers 2011-2012 and 2012-2013 with the High Capability Radar Sounder (HiCARS) on-board a Basler DC-3 aircraft. HiCARS transmits a chirped signal at 60-MHz central frequency and 15-MHz bandwidth. The corresponding vertical resolution in ice is 5-10 m. An important design goal of the radar was to maintain sufficient dynamic range to correctly measure echo intensities.Here we present the brine infiltration extent and bathymetry derived from its dielectric horizon well distinguishable on the HiCARS radargram. We complement the ice-shelf characterization by classifying its surface thanks to the novel Radar Statistical Reconnaissance (RSR) methodology. The RSR observable is the statistical distribution of the surface echo amplitudes from successive areas defined along-track. The distributions are best-fitted with a theoretical stochastic envelop parameterized with the signal reflectance and scattering. Once those two components are deduced from the fit, they are used in a backscattering model to invert

Satellite remote sensing over ice

NASA Technical Reports Server (NTRS)

Thomas, R. H.

1984-01-01

Satellite remote sensing provides unique opportunities for observing ice-covered terrain. Passive-microwave data give information on snow extent on land, sea-ice extent and type, and zones of summer melting on the polar ice sheets, with the potential for estimating snow-accumulation rates on these ice sheets. All weather, high-resolution imagery of sea ice is obtained using synthetic aperture radars, and ice-movement vectors can be deduced by comparing sequential images of the same region. Radar-altimetry data provide highly detailed information on ice-sheet topography, with the potential for deducing thickening/thinning rates from repeat surveys. The coastline of Antarctica can be mapped accurately using altimetry data, and the size and spatial distribution of icebergs can be monitored. Altimetry data also distinguish open ocean from pack ice and they give an indication of sea-ice characteristics.

Satellite remote sensing over ice

NASA Technical Reports Server (NTRS)

Thomas, R. H.

1986-01-01

Satellite remote sensing provides unique opportunities for observing ice-covered terrain. Passive-microwave data give information on snow extent on land, sea-ice extent and type, and zones of summer melting on the polar ice sheets, with the potential for estimating snow-accumulation rates on these ice sheets. All weather, high-resolution imagery of sea ice is obtained using synthetic aperture radars, and ice-movement vectors can be deduced by comparing sequential images of the same region. Radar-altimetry data provide highly detailed information on ice-sheet topography, with the potential for deducing thickening/thinning rates from repeat surveys. The coastline of Antarctica can be mapped accurately using altimetry data, and the size and spatial distribution of icebergs can be monitored. Altimetry data also distinguish open ocean from pack ice and they give an indication of sea-ice characteristics.

Seasonal and interannual variability of the Arctic sea ice: A comparison between AO-FVCOM and observations

NASA Astrophysics Data System (ADS)

Zhang, Yu; Chen, Changsheng; Beardsley, Robert C.; Gao, Guoping; Qi, Jianhua; Lin, Huichan

2016-11-01

A high-resolution (up to 2 km), unstructured-grid, fully ice-sea coupled Arctic Ocean Finite-Volume Community Ocean Model (AO-FVCOM) was used to simulate the sea ice in the Arctic over the period 1978-2014. The spatial-varying horizontal model resolution was designed to better resolve both topographic and baroclinic dynamics scales over the Arctic slope and narrow straits. The model-simulated sea ice was in good agreement with available observed sea ice extent, concentration, drift velocity and thickness, not only in seasonal and interannual variability but also in spatial distribution. Compared with six other Arctic Ocean models (ECCO2, GSFC, INMOM, ORCA, NAME, and UW), the AO-FVCOM-simulated ice thickness showed a higher mean correlation coefficient of ˜0.63 and a smaller residual with observations. Model-produced ice drift speed and direction errors varied with wind speed: the speed and direction errors increased and decreased as the wind speed increased, respectively. Efforts were made to examine the influences of parameterizations of air-ice external and ice-water interfacial stresses on the model-produced bias. The ice drift direction was more sensitive to air-ice drag coefficients and turning angles than the ice drift speed. Increasing or decreasing either 10% in water-ice drag coefficient or 10° in water-ice turning angle did not show a significant influence on the ice drift velocity simulation results although the sea ice drift speed was more sensitive to these two parameters than the sea ice drift direction. Using the COARE 4.0-derived parameterization of air-water drag coefficient for wind stress did not significantly influence the ice drift velocity simulation.

Arctic sea ice concentration observed with SMOS during summer

NASA Astrophysics Data System (ADS)

Gabarro, Carolina; Martinez, Justino; Turiel, Antonio

2017-04-01

The Arctic Ocean is under profound transformation. Observations and model predictions show dramatic decline in sea ice extent and volume [1]. A retreating Arctic ice cover has a marked impact on regional and global climate, and vice versa, through a large number of feedback mechanisms and interactions with the climate system [2]. The launch of the Soil Moisture and Ocean Salinity (SMOS) mission, in 2009, marked the dawn of a new type of space-based microwave observations. Although the mission was originally conceived for hydrological and oceanographic studies [3,4], SMOS is also making inroads in the cryospheric sciences by measuring the thin ice thickness [5,6]. SMOS carries an L-band (1.4 GHz), passive interferometric radiometer (the so-called MIRAS) that measures the electromagnetic radiation emitted by the Earth's surface, at about 50 km spatial resolution, continuous multi-angle viewing, large wide swath (1200-km), and with a 3-day revisit time at the equator, but more frequently at the poles. A novel radiometric method to determine sea ice concentration (SIC) from SMOS is presented. The method uses the Bayesian-based Maximum Likelihood Estimation (MLE) approach to retrieve SIC. The advantage of this approach with respect to the classical linear inversion is that the former takes into account the uncertainty of the tie-point measured data in addition to the mean value, while the latter only uses a mean value of the tie-point data. When thin ice is present, the SMOS algorithm underestimates the SIC due to the low opacity of the ice at this frequency. However, using a synergistic approach with data from other satellite sensors, it is possible to obtain accurate thin ice thickness estimations with the Bayesian-based method. Despite its lower spatial resolution relative to SSMI or AMSR-E, SMOS-derived SIC products are little affected by the atmosphere and the snow (almost transparent at L-band). Moreover L-band measurements are more robust in front of the

Ice Sheet and Sea Ice Observations from Unmanned Aircraft Systems

NASA Astrophysics Data System (ADS)

Crocker, R. I.; Maslanik, J. A.

2011-12-01

A suite of sensors has been assembled to map ice sheet and sea ice surface topography with fine-resolution from small unmanned aircraft systems (UAS). This payload is optimized to provide coincident surface elevation and imagery data, and with its low cost and ease of reproduction, it has the potential to become a widely-distributed observational resource to complement polar manned-aircraft and satellite missions. To date, it has been deployed to map ice sheet elevations near Jakobshavn Isbræ in Greenland, and to measure sea ice freeboard and roughness in Fram Strait off the coast of Svalbard. Data collected during these campaigns have facilitate a detailed assessment of the system's surface elevation measurement accuracy, and provide a glimpse of the summer 2009 Fram Strait sea ice conditions. These findings are presented, along with a brief overview of our future Arctic UAS operations.

An observational search for CO2 ice clouds on Mars

NASA Technical Reports Server (NTRS)

Bell, James F., III; Calvin, Wendy M.; Pollack, James B.; Crisp, David

1993-01-01

CO2 ice clouds were first directly identified on Mars by the Mariner 6 and 7 infrared spectrometer limb scans. These observations provided support for early theoretical modeling efforts of CO2 condensation. Mariner 9 IRIS temperature profiles of north polar hood clouds were interpreted as indicating that these clouds were composed of H2O ice at lower latitudes and CO2 ice at higher latitudes. The role of CO2 condensation on Mars has recently received increased attention because (1) Kasting's model results indicated that CO2 cloud condensation limits the magnitude of the proposed early Mars CO2/H2O greenhouse, and (2) Pollack el al.'s GCM results indicated that the formation of CO2 ice clouds is favorable at all polar latitudes during the fall and winter seasons. These latter authors have shown that CO2 clouds play an important role in the polar energy balance, as the amount of CO2 contained in the polar caps is constrained by a balance between latent heat release, heat advected from lower latitudes, and thermal emission to space. The polar hood clouds reduce the amount of CO2 condensation on the polar caps because they reduce the net emission to space. There have been many extensive laboratory spectroscopic studies of H2O and CO2 ices and frosts. In this study, we use results from these and other sources to search for the occurrence of diagnostic CO2 (and H2O) ice and/or frost absorption features in ground based near-infrared imaging spectroscopic data of Mars. Our primary goals are (1) to try to confirm the previous direct observations of CO2 clouds on Mars; (2) to determine the spatial extent, temporal variability, and composition (H2O/CO2 ratio) of any clouds detected; and (3) through radiative transfer modeling, to try to determine the mean particle size and optical depth of polar hood clouds, thus, assessing their role in the polar heat budget.

Water ice clouds observations with PFS on Mars Express

NASA Astrophysics Data System (ADS)

Moroz, V. I.; Zasova, L. V.; Formisano, V.; Grassi, D.; Ignatiev, N. I.; Giuranna, M.; Maturilli, A.; Pfs Team

The water ice cloud observation is one of the scientific goals of PFS. Presence and properties of the ice particles are identified from absorption features, observed in both spectral ranges of PFS. Being in the near perihelion condition, the temperature of the Martian atmosphere is pretty high and ice clouds exist only in some places, for example, related to topography or at north high latitudes et etc. The ice clouds are observed often above the tops of the volcanoes. We have found the ice clouds above Olympus (orbit 37) and Ascraeus Mons (orbit 68). Effective radius of particles according to the thermal IR is preliminary estimated of 1 μ m, which leads to the visual opacity of 0.2 -0.3 above Olympus and of maximum of 0.6 above Ascraeus Mons. In the case of Ascraeus Mons the ice clouds are observed on the south slope near the top of the volcano. The maximum surface temperature, observed there, results in the upward flux of warm air, which, cooling, provides the condensation of H2O. We will present a detailed analysis of the ice clouds, observed over the planet in the IR spectral range.

Observing Ice in Clouds from Space

NASA Technical Reports Server (NTRS)

Ackerman, S.; Star, D. O'C.; Skofronick-Jackson, G.; Evans, F.; Wang, J. R.; Norris, P.; daSilva, A.; Soden, B.

2006-01-01

There are many satellite observations of cloud top properties and the liquid and rain content of clouds, however, we do not yet quantitatively understand the processes that control the water budget of the upper troposphere where ice is the predominant phase, and how these processes are linked to precipitation processes and the radiative energy budget. The ice in clouds in the upper troposphere either melts into rain or is detrained, and persists, as cirrus clouds affecting the hydrological and energy cycle, respectively. Fully modeling the Earth's climate and improving weather and climate forecasts requires accurate satellite measurements of various cloud properties at the temporal and spatial scales of cloud processes. These properties include cloud horizontal and vertical structure, cloud water content and some measure of particle sizes and shapes. The uncertainty in knowledge of these ice characteristics is reflected in the large discrepancies in model simulations of the upper tropospheric water budget. Model simulations are sensitive to the partition of ice between precipitation and outflow processes, i.e., to the parameterization of ice clouds and ice processes. One barrier to achieving accurate global ice cloud properties is the lack of adequate observations at millimeter and submillimeter wavelengths (183-874 GHz). Recent advances in instrumentation have allowed for the development and implementation of an airborne submillimeter-wave radiometer. The brightness temperatures at these frequencies are especially sensitive to cirrus ice particle sizes (because they are comparable to the wavelength). This allows for more accurate ice water path estimates when multiple channels are used to probe into the cloud layers. Further, submillimeter wavelengths offer simplicity in the retrieval algorithms because they do not probe into the liquid and near surface portions of clouds, thus requiring only one term of the radiative transfer equation (ice scattering) to relate

STS-48 ESC Earth observation of ice pack, Antarctic Ice Shelf

NASA Technical Reports Server (NTRS)

1991-01-01

STS-48 Earth observation taken aboard Discovery, Orbiter Vehicle (OV) 103, is of the breakup of pack ice along the periphery of the Antarctic Ice Shelf. Strong offshore winds, probably associated with katabatic downdrafts from the interior of the continent, are seen peeling off the edges of the ice shelf into long filaments of sea ice, icebergs, bergy bits, and growlers to flow northward into the South Atlantic Ocean. These photos are used to study ocean wind, tide and current patterns. Similar views photographed during previous missions, when analyzed with these recent views may yield information about regional ice drift and breakup of ice packs. The image was captured using an electronic still camera (ESC), was stored on a removable hard disk or small optical disk, and was converted to a format suitable for downlink transmission. The ESC documentation was part of Development Test Objective (DTO) 648, Electronic Still Photography.

The Antarctic Ice Sheet, Sea Ice, and the Ozone Hole: Satellite Observations of how they are Changing

NASA Technical Reports Server (NTRS)

Parkinson, Claire L.

2012-01-01

Antarctica is the Earth's coldest and highest continent and has major impacts on the climate and life of the south polar vicinity. It is covered almost entirely by the Earth's largest ice sheet by far, with a volume of ice so great that if all the Antarctic ice were to go into the ocean (as ice or liquid water), this would produce a global sea level rise of about 60 meters (197 feet). The continent is surrounded by sea ice that in the wintertime is even more expansive than the continent itself and in the summertime reduces to only about a sixth of its wintertime extent. Like the continent, the expansive sea ice cover has major impacts, reflecting the sun's radiation back to space, blocking exchanges between the ocean and the atmosphere, and providing a platform for some animal species while impeding other species. Far above the continent, the Antarctic ozone hole is a major atmospheric phenomenon recognized as human-caused and potentially quite serious to many different life forms. Satellites are providing us with remarkable information about the ice sheet, the sea ice, and the ozone hole. Satellite visible and radar imagery are providing views of the large scale structure of the ice sheet never seen before; satellite laser altimetry has produced detailed maps of the topography of the ice sheet; and an innovative gravity-measuring two-part satellite has allowed mapping of regions of mass loss and mass gain on the ice sheet. The surrounding sea ice cover has a satellite record that goes back to the 1970s, allowing trend studies that show a decreasing sea ice presence in the region of the Bellingshausen and Amundsen seas, to the west of the prominent Antarctic Peninsula, but increasing sea ice presence around much of the rest of the continent. Overall, sea ice extent around Antarctica has increased at an average rate of about 17,000 square kilometers per year since the late 1970s, as determined from satellite microwave data that can be collected under both light and

The frequency and extent of sub-ice phytoplankton blooms in the Arctic Ocean

PubMed Central

Horvat, Christopher; Jones, David Rees; Iams, Sarah; Schroeder, David; Flocco, Daniela; Feltham, Daniel

2017-01-01

In July 2011, the observation of a massive phytoplankton bloom underneath a sea ice–covered region of the Chukchi Sea shifted the scientific consensus that regions of the Arctic Ocean covered by sea ice were inhospitable to photosynthetic life. Although the impact of widespread phytoplankton blooms under sea ice on Arctic Ocean ecology and carbon fixation is potentially marked, the prevalence of these events in the modern Arctic and in the recent past is, to date, unknown. We investigate the timing, frequency, and evolution of these events over the past 30 years. Although sea ice strongly attenuates solar radiation, it has thinned significantly over the past 30 years. The thinner summertime Arctic sea ice is increasingly covered in melt ponds, which permit more light penetration than bare or snow-covered ice. Our model results indicate that the recent thinning of Arctic sea ice is the main cause of a marked increase in the prevalence of light conditions conducive to sub-ice blooms. We find that as little as 20 years ago, the conditions required for sub-ice blooms may have been uncommon, but their frequency has increased to the point that nearly 30% of the ice-covered Arctic Ocean in July permits sub-ice blooms. Recent climate change may have markedly altered the ecology of the Arctic Ocean. PMID:28435859

Aircraft Surveys of the Beaufort Sea Seasonal Ice Zone

NASA Astrophysics Data System (ADS)

Morison, J.

2016-02-01

The Seasonal Ice Zone Reconnaissance Surveys (SIZRS) is a program of repeated ocean, ice, and atmospheric measurements across the Beaufort-Chukchi sea seasonal sea ice zone (SIZ) utilizing US Coast Guard Arctic Domain Awareness (ADA) flights of opportunity. The SIZ is the region between maximum winter sea ice extent and minimum summer sea ice extent. As such, it contains the full range of positions of the marginal ice zone (MIZ) where sea ice interacts with open water. The increasing size and changing air-ice-ocean properties of the SIZ are central to recent reductions in Arctic sea ice extent. The changes in the interplay among the atmosphere, ice, and ocean require a systematic SIZ observational effort of coordinated atmosphere, ice, and ocean observations covering up to interannual time-scales, Therefore, every year beginning in late Spring and continuing to early Fall, SIZRS makes monthly flights across the Beaufort Sea SIZ aboard Coast Guard C-130H aircraft from USCG Air Station Kodiak dropping Aircraft eXpendable CTDs (AXCTD) and Aircraft eXpendable Current Profilers (AXCP) for profiles of ocean temperature, salinity and shear, dropsondes for atmospheric temperature, humidity, and velocity profiles, and buoys for atmosphere and upper ocean time series. Enroute measurements include IR imaging, radiometer and lidar measurements of the sea surface and cloud tops. SIZRS also cooperates with the International Arctic Buoy Program for buoy deployments and with the NOAA Earth System Research Laboratory atmospheric chemistry sampling program on board the aircraft. Since 2012, SIZRS has found that even as SIZ extent, ice character, and atmospheric forcing varies year-to-year, the pattern of ocean freshening and radiative warming south of the ice edge is consistent. The experimental approach, observations and extensions to other projects will be discussed.

On the relationship between atmospheric circulation and the fluctuations in the sea ice extents of the Bering and Okhotsk Seas

NASA Technical Reports Server (NTRS)

Cavalieri, D. J.; Parkinson, C. L.

1987-01-01

The influence of the hemispheric atmospheric circulation on the sea ice covers of the Bering Sea and the Sea of Okhotsk is examined using data obtained with the Nimbus 5 electrically scanning microwave radiometer for the four winters of the 1973-1976 period. The 3-day averaged sea ice extent data were used to establish periods for which there is an out-of-phase relationship between fluctuations of the two ice covers. A comparison of the sea-level atmospheric pressure field with the seasonal, interannual, and short-term sea ice fluctuations reveal an association between changes in the phase and the amplitude of the long waves in the atmosphere and advance and retreat of Arctic ice covers.

Antarctic Sea-Ice Freeboard and Estimated Thickness from NASA's ICESat and IceBridge Observations

NASA Technical Reports Server (NTRS)

Yi, Donghui; Kurtz, Nathan; Harbeck, Jeremy; Manizade, Serdar; Hofton, Michelle; Cornejo, Helen G.; Zwally, H. Jay; Robbins, John

2016-01-01

ICESat completed 18 observational campaigns during its lifetime from 2003 to 2009. Data from all of the 18 campaign periods are used in this study. Most of the operational periods were between 34 and 38 days long. Because of laser failure and orbit transition from 8-day to 91-day orbit, there were four periods lasting 57, 16, 23, and 12 days. IceBridge data from 2009, 2010, and 2011 are used in this study. Since 2009, there are 19 Airborne Topographic Mapper (ATM) campaigns, and eight Land, Vegetation, and Ice Sensor (LVIS) campaigns over the Antarctic sea ice. Freeboard heights are derived from ICESat, ATM and LVIS elevation and waveform data. With nominal densities of snow, water, and sea ice, combined with snow depth data from AMSR-E/AMSR2 passive microwave observation over the southern ocean, sea-ice thickness is derived from the freeboard. Combined with AMSR-E/AMSR2 ice concentration, sea-ice area and volume are also calculated. During the 2003-2009 period, sea-ice freeboard and thickness distributions show clear seasonal variations that reflect the yearly cycle of the growth and decay of the Antarctic pack ice. We found no significant trend of thickness or area for the Antarctic sea ice during the ICESat period. IceBridge sea ice freeboard and thickness data from 2009 to 2011 over the Weddell Sea and Amundsen and Bellingshausen Seas are compared with the ICESat results.

Observations of the Sea Ice Cover Using Satellite Radar Interferometry

NASA Technical Reports Server (NTRS)

Kwok, Ronald

1995-01-01

The fringes observed in repeat pass interferograms are expressions of surface relief and relative displacements. The limiting condition in the application of spaceborne radar interferometry to the remote sensing of the sea ice cover is the large magnitude of motion between repeat passes. The translation and rotation of ice floes tend to decorrelate the observations rendering radar interferometry ineffective. In our study, we have located three images in the high Arctic during a period when there was negligible motion between repeat observations. The fringes obtained from these images show a wealth of information about the sea ice cover which is important in atmosphere-ice interactions and sea ice mechanics. These measurements provide the first detailed remote sensing view of the sea ice cover. Ridges can be observed and their heights estimated if the interferometric baseline allows. We have observed ridges with heights greater than 4m. The variability in the phase measurements over an area provides an indication of the large scale roughness. Relative centimetric displacements between rigid ice floes have been observed. We illustrate these observations with examples extracted from the interferograms formed from this set of ERS-1 SAR images.

30-Year Satellite Record Reveals Accelerated Arctic Sea Ice Loss, Antarctic Sea Ice Trend Reversal

NASA Technical Reports Server (NTRS)

Cavalieri, Donald J.; Parkinson, C. L.; Vinnikov, K. Y.

2003-01-01

Arctic sea ice extent decreased by 0.30 plus or minus 0.03 x 10(exp 6) square kilometers per decade from 1972 through 2002, but decreased by 0.36 plus or minus 0.05 x 10(exp 6) square kilometers per decade from 1979 through 2002, indicating an acceleration of 20% in the rate of decrease. In contrast to the Arctic, the Antarctic sea ice extent decreased dramatically over the period 1973-1977, then gradually increased, with an overall 30-year trend of -0.15 plus or minus 0.08 x 10(exp 6) square kilometers per 10yr. The trend reversal is attributed to a large positive anomaly in Antarctic sea ice extent observed in the early 1970's.

Surface exposure chronology of the Waimakariri glacial sequence in the Southern Alps of New Zealand: Implications for MIS-2 ice extent and LGM glacial mass balance

NASA Astrophysics Data System (ADS)

Rother, Henrik; Shulmeister, James; Fink, David; Alexander, David; Bell, David

2015-11-01

During the late Quaternary, the Southern Alps of New Zealand experienced multiple episodes of glaciation with large piedmont glaciers reaching the coastal plains in the west and expanding into the eastern alpine forelands. Here, we present a new 10Be exposure age chronology for a moraine sequence in the Waimakariri Valley (N-Canterbury), which has long been used as a reference record for correlating glacial events across New Zealand and the wider Southern Hemisphere. Our data indicate that the Waimakariri glacier reached its maximum last glaciation extent prior to ∼26 ka well before the global last glaciation maximum (LGM). This was followed by a gradual reduction in ice volume and the abandonment of the innermost LGM moraines at about 17.5 ka. Significantly, we find that during its maximum extent, the Waimakariri glacier overflowed the Avoca Plateau, previously believed to represent a mid-Pleistocene glacial surface (i.e. MIS 8). At the same time, the glacier extended to a position downstream of the Waimakariri Gorge, some 15 km beyond the previously mapped LGM ice limit. We use a simple steady-state mass balance model to test the sensitivity of past glacial accumulation to various climatic parameters, and to evaluate possible climate scenarios capable of generating the ice volume required to reach the full local-LGM extent. Model outcomes indicate that under New Zealand's oceanic setting, a cooling of 5 °C, assuming modern precipitation levels, or a cooling of 6.5 °C, assuming a one third reduction in precipitation, would suffice to drive the Waimakariri glacier to the eastern alpine forelands (Canterbury Plains). Our findings demonstrate that the scale of LGM glaciation in the Waimakariri Valley and adjacent major catchments, both in terms of ice volume and downvalley ice extent, has been significantly underestimated. Our observation that high-lying glacial surfaces, so far believed to represent much older glacial episodes, were glaciated during the LGM

Extent and relevance of stacking disorder in “ice Ic”

PubMed Central

Kuhs, Werner F.; Sippel, Christian; Falenty, Andrzej; Hansen, Thomas C.

2012-01-01

A solid water phase commonly known as “cubic ice” or “ice Ic” is frequently encountered in various transitions between the solid, liquid, and gaseous phases of the water substance. It may form, e.g., by water freezing or vapor deposition in the Earth’s atmosphere or in extraterrestrial environments, and plays a central role in various cryopreservation techniques; its formation is observed over a wide temperature range from about 120 K up to the melting point of ice. There was multiple and compelling evidence in the past that this phase is not truly cubic but composed of disordered cubic and hexagonal stacking sequences. The complexity of the stacking disorder, however, appears to have been largely overlooked in most of the literature. By analyzing neutron diffraction data with our stacking-disorder model, we show that correlations between next-nearest layers are clearly developed, leading to marked deviations from a simple random stacking in almost all investigated cases. We follow the evolution of the stacking disorder as a function of time and temperature at conditions relevant to atmospheric processes; a continuous transformation toward normal hexagonal ice is observed. We establish a quantitative link between the crystallite size established by diffraction and electron microscopic images of the material; the crystallite size evolves from several nanometers into the micrometer range with progressive annealing. The crystallites are isometric with markedly rough surfaces parallel to the stacking direction, which has implications for atmospheric sciences. PMID:23236184

Ocean Wave-to-Ice Energy Transfer Determined from Seafloor Pressure and Ice Shelf Seismic Observations

NASA Astrophysics Data System (ADS)

Chen, Z.; Bromirski, P. D.; Gerstoft, P.; Stephen, R. A.; Wiens, D.; Aster, R. C.; Nyblade, A.

2017-12-01

Ice shelves play an important role in buttressing land ice from reaching the sea, thus restraining the rate of sea level rise. Long-period gravity wave impacts excite vibrations in ice shelves that may trigger tabular iceberg calving and/or ice shelf collapse events. Three kinds of seismic plate waves were continuously observed by broadband seismic arrays on the Ross Ice Shelf (RIS) and on the Pine Island Glacier (PIG) ice shelf: (1) flexural-gravity waves, (2) flexural waves, and (3) extensional Lamb waves, suggesting that all West Antarctic ice shelves are subjected to similar gravity wave excitation. Ocean gravity wave heights were estimated from pressure perturbations recorded by an ocean bottom differential pressure gauge at the RIS front, water depth 741 m, about 8 km north of an on-ice seismic station that is 2 km from the shelf front. Combining the plate wave spectrum, the frequency-dependent energy transmission and reflection at the ice-water interface were determined. In addition, Young's modulus and Poisson's ratio of the RIS are estimated from the plate wave motions, and compared with the widely used values. Quantifying these ice shelf parameters from observations will improve modeling of ice shelf response to ocean forcing, and ice shelf evolution.

Observations of brine plumes below melting Arctic sea ice

NASA Astrophysics Data System (ADS)

Peterson, Algot K.

2018-02-01

In sea ice, interconnected pockets and channels of brine are surrounded by fresh ice. Over time, brine is lost by gravity drainage and flushing. The timing of salt release and its interaction with the underlying water can impact subsequent sea ice melt. Turbulence measurements 1 m below melting sea ice north of Svalbard reveal anticorrelated heat and salt fluxes. From the observations, 131 salty plumes descending from the warm sea ice are identified, confirming previous observations from a Svalbard fjord. The plumes are likely triggered by oceanic heat through bottom melt. Calculated over a composite plume, oceanic heat and salt fluxes during the plumes account for 6 and 9 % of the total fluxes, respectively, while only lasting in total 0.5 % of the time. The observed salt flux accumulates to 7.6 kg m-2, indicating nearly full desalination of the ice. Bulk salinity reduction between two nearby ice cores agrees with accumulated salt fluxes to within a factor of 2. The increasing fraction of younger, more saline ice in the Arctic suggests an increase in desalination processes with the transition to the new Arctic.

Sea-ice anomalies observed in the Greenland and Labrador seas during 1901 1984 and their relation to an interdecadal Arctic climate cycle

NASA Astrophysics Data System (ADS)

Mysak, L. A.; Manak, D. K.; Marsden, R. F.

1990-12-01

Two independent ice data sets from the Greenland and Labrador Seas have been analyzed for the purpose of characterizing interannual and decadal time scale sea-ice extent anomalies during this century. Sea-ice concentration data for the 1953 1984 period revealed the presence of a large positive anomaly in the Greenland Sea during the 1960s which coincided with the “great salinity anomaly”, an upper-ocean low-salinity water mass that was observed to travel cyclonically around the northern North Atlantic during 1968 1982. This ice anomaly as well as several smaller ones propagated into the Labrador Sea and then across to the Labrador and east Newfoundland coast, over a period of 3 to 5 years. A complex empirical orthogonal function analysis of the same data also confirmed this propagation phenomenon. An inverse relation between sea-ice and salinity anomalies in the Greenland-Labrador Sea region was also generally found. An analysis of spring and summer ice-limit data obtained from Danish Meteorological Institute charts for the period 1901 1956 indicated the presence of heavy ice conditions (i.e., positive ice anomalies) in the Greenland Sea during 1902 1920 and in the late 1940s, and generally negative ice anomalies during the 1920s and 1930s. Only limited evidence of the propagation of Greenland Sea ice anomalies into the Labrador Sea was observed, however, probably because the data were from the ice-melt seasons. On the other hand, several large ice anomalies in the Greenland Sea occurred 2 3 years after large runoffs (in the early 1930s and the late 1940s) from northern Canada into the western Arctic Ocean. Similarly, a large runoff into the Arctic during 1964 1966 preceded the large Greenland Sea ice anomaly of the 1960s. These facts, together with recent evidence of ‘climatic jumps’ in the Northern Hemisphere tropospheric circulation, suggest the existence of an interdecadal self-sustained climate cycle in the Arctic. In the Greenland Sea, this cycle is

The Last Arctic Sea Ice Refuge

NASA Astrophysics Data System (ADS)

Pfirman, S. L.; Tremblay, B.; Newton, R.; Fowler, C.

2010-12-01

Summer sea ice may persist along the northern flank of Canada and Greenland for decades longer than the rest of the Arctic, raising the possibility of a naturally formed refugium for ice-associated species. Observations and models indicate that some ice in this region forms locally, while some is transported to the area by winds and ocean currents. Depending on future changes in melt patterns and sea ice transport rates, both the central Arctic and Siberian shelf seas may be sources of ice to the region. An international system of monitoring and management of the sea ice refuge, along with the ice source regions, has the potential to maintain viable habitat for ice-associated species, including polar bears, for decades into the future. Issues to consider in developing a strategy include: + the likely duration and extent of summer sea ice in this region based on observations, models and paleoenvironmental information + the extent and characteristics of the “ice shed” contributing sea ice to the refuge, including its dynamics, physical and biological characteristics as well as potential for contamination from local or long-range sources + likely assemblages of ice-associated species and their habitats + potential stressors such as transportation, tourism, resource extraction, contamination + policy, governance, and development issues including management strategies that could maintain the viability of the refuge.

Timing and regional patterns of snowmelt on Antarctic sea ice from passive microwave satellite observations

NASA Astrophysics Data System (ADS)

Arndt, Stefanie; Willmes, Sascha; Dierking, Wolfgang; Nicolaus, Marcel

2016-04-01

The better understanding of temporal variability and regional distribution of surface melt on Antarctic sea ice is crucial for the understanding of atmosphere-ocean interactions and the determination of mass and energy budgets of sea ice. Since large regions of Antarctic sea ice are covered with snow during most of the year, observed inter-annual and regional variations of surface melt mainly represents melt processes in the snow. It is therefore important to understand the mechanisms that drive snowmelt, both at different times of the year and in different regions around Antarctica. In this study we combine two approaches for observing both surface and volume snowmelt by means of passive microwave satellite data. The former is achieved by measuring diurnal differences of the brightness temperature TB at 37 GHz, the latter by analyzing the ratio TB(19GHz)/TB(37GHz). Moreover, we use both melt onset proxies to divide the Antarctic sea ice cover into characteristic surface melt patterns from 1988/89 to 2014/15. Our results indicate four characteristic melt types. On average, 43% of the ice-covered ocean shows diurnal freeze-thaw cycles in the surface snow layer, resulting in temporary melt (Type A), less than 1% shows continuous snowmelt throughout the snowpack, resulting in strong melt over a period of several days (Type B), 19% shows Type A and B taking place consecutively (Type C), and for 37% no melt is observed at all (Type D). Continuous melt is primarily observed in the outflow of the Weddell Gyre and in the northern Ross Sea, usually 20 days after the onset of temporary melt. Considering the entire data set, snowmelt processes and onset do not show significant temporal trends. Instead, areas of increasing (decreasing) sea-ice extent have longer (shorter) periods of continuous snowmelt.

Observational Evidence of a Hemispheric-wide Ice-ocean Albedo Feedback Effect on Antarctic Sea-ice Decay

NASA Technical Reports Server (NTRS)

Nihashi, Sohey; Cavalieri, Donald J.

2007-01-01

The effect of ice-ocean albedo feedback (a kind of ice-albedo feedback) on sea-ice decay is demonstrated over the Antarctic sea-ice zone from an analysis of satellite-derived hemispheric sea ice concentration and European Centre for Medium-Range Weather Forecasts (ERA-40) atmospheric data for the period 1979-2001. Sea ice concentration in December (time of most active melt) correlates better with the meridional component of the wind-forced ice drift (MID) in November (beginning of the melt season) than the MID in December. This 1 month lagged correlation is observed in most of the Antarctic sea-ice covered ocean. Daily time series of ice , concentration show that the ice concentration anomaly increases toward the time of maximum sea-ice melt. These findings can be explained by the following positive feedback effect: once ice concentration decreases (increases) at the beginning of the melt season, solar heating of the upper ocean through the increased (decreased) open water fraction is enhanced (reduced), leading to (suppressing) a further decrease in ice concentration by the oceanic heat. Results obtained fi-om a simple ice-ocean coupled model also support our interpretation of the observational results. This positive feedback mechanism explains in part the large interannual variability of the sea-ice cover in summer.

Improving Arctic Sea Ice Observations and Data Access to Support Advances in Sea Ice Forecasting

NASA Astrophysics Data System (ADS)

Farrell, S. L.

2017-12-01

The economic and strategic importance of the Arctic region is becoming apparent. One of the most striking and widely publicized changes underway is the declining sea ice cover. Since sea ice is a key component of the climate system, its ongoing loss has serious, and wide-ranging, socio-economic implications. Increasing year-to-year variability in the geographic location, concentration, and thickness of the Arctic ice cover will pose both challenges and opportunities. The sea ice research community must be engaged in sustained Arctic Observing Network (AON) initiatives so as to deliver fit-for-purpose remote sensing data products to a variety of stakeholders including Arctic communities, the weather forecasting and climate modeling communities, industry, local, regional and national governments, and policy makers. An example of engagement is the work currently underway to improve research collaborations between scientists engaged in obtaining and assessing sea ice observational data and those conducting numerical modeling studies and forecasting ice conditions. As part of the US AON, in collaboration with the Interagency Arctic Research Policy Committee (IARPC), we are developing a strategic framework within which observers and modelers can work towards the common goal of improved sea ice forecasting. Here, we focus on sea ice thickness, a key varaible of the Arctic ice cover. We describe multi-sensor, and blended, sea ice thickness data products under development that can be leveraged to improve model initialization and validation, as well as support data assimilation exercises. We will also present the new PolarWatch initiative (polarwatch.noaa.gov) and discuss efforts to advance access to remote sensing satellite observations and improve communication with Arctic stakeholders, so as to deliver data products that best address societal needs.

Gypsum crystals observed in experimental and natural sea ice

NASA Astrophysics Data System (ADS)

Geilfus, N.-X.; Galley, R. J.; Cooper, M.; Halden, N.; Hare, A.; Wang, F.; Søgaard, D. H.; Rysgaard, S.

2013-12-01

gypsum has been predicted to precipitate in sea ice, it has never been observed. Here we provide the first report on gypsum precipitation in both experimental and natural sea ice. Crystals were identified by X-ray diffraction analysis. Based on their apparent distinguishing characteristics, the gypsum crystals were identified as being authigenic. The FREeZing CHEMistry (FREZCHEM) model results support our observations of both gypsum and ikaite precipitation at typical in situ sea ice temperatures and confirms the "Gitterman pathway" where gypsum is predicted to precipitate. The occurrence of authigenic gypsum in sea ice during its formation represents a new observation of precipitate formation and potential marine deposition in polar seas.

Dynamics of landfast sea ice near Jangbogo Antarctic Research Station observed by SAR interferometry

NASA Astrophysics Data System (ADS)

Lee, H.; Han, H.

2015-12-01

Landfast sea ice is a type of sea ice adjacent to the coast and immobile for a certain period of time. It is important to analyze the temporal and spatial variation of landfast ice because it has significant influences on marine ecosystem and the safe operation of icebreaker vessels. However, it has been a difficult task for both remote sensing and in situ observation to discriminate landfast ice from other types of sea ice, such as pack ice, and also to understand the dynamics and internal strss-strain of fast ice. In this study, we identify landfast ice and its annual variation in Terra Nova Bay (74° 37' 4"S, 164° 13' 7"E), East Antarctica, where Jangbogo Antarctic Research Station has recently been constructed in 2014, by using Interferometric Synthetic Aperture Radar (InSAR) technology. We generated 38 interferograms having temporal baselines of 1-9 days out of 62 COSMO-SkyMed SAR images over Terra Nova Bay obtained from December 2010 to January 2012. Landfast ice began to melt in November 2011 when air temperature raised above freezing point but lasted more than two month to the end of the study period in January 2012. No meaningful relationship was found between sea ice extent and wind and current. Glacial strain (~67cm/day) is similar to tidal strain (~40 cm) so that they appear similar in one-day InSAR. As glacial stress is cumulative while tidal stress is oscillatory, InSAR images with weekly temporal baseline (7~9 days) revealed that a consistent motion of Campbell Glacier Tongue (CGT) is pushing the sea ice continuously to make interferometric fringes parallel to the glacier-sea ice contacts. Glacial interferometric fringe is parallel to the glacier-sea ice contact lines while tidal strain should be parallel to the coastlines defined by sea shore and glacier tongue. DDInSAR operation removed the consistent glacial strain leaving tidal strain alone so that the response of fast ice to tide can be used to deduce physical properties of sea ice in various

Observing Arctic Sea Ice from Bow to Screen: Introducing Ice Watch, the Data Network of Near Real-Time and Historic Observations from the Arctic Shipborne Sea Ice Standardization Tool (ASSIST)

NASA Astrophysics Data System (ADS)

Orlich, A.; Hutchings, J. K.; Green, T. M.

2013-12-01

The Ice Watch Program is an open source forum to access in situ Arctic sea ice conditions. It provides the research community and additional stakeholders a convenient resource to monitor sea ice and its role in understanding the Arctic as a system by implementing a standardized observation protocol and hosting a multi-service data portal. International vessels use the Arctic Shipborne Sea Ice Standardization Tool (ASSIST) software to report near-real time sea ice conditions while underway. Essential observations of total ice concentration, distribution of multi-year ice and other ice types, as well as their respective stage of melt are reported. These current and historic sea ice conditions are visualized on interactive maps and in a variety of statistical analyses, and with all data sets available to download for further investigation. The summer of 2012 was the debut of the ASSIST software and the Ice Watch campaign, with research vessels from six nations reporting from a wide spatio-temporal scale spanning from the Beaufort Sea, across the North Pole and Arctic Basin, the coast of Greenland and into the Kara and Barents Seas during mid-season melt and into the first stages of freeze-up. The 2013 summer field season sustained the observation and data archiving record, with participation from some of the same cruises as well as other geographic and seasonal realms covered by new users. These results are presented to illustrate the evolution of the program, increased participation and critical statistics of ice regime change and record of melt and freeze processes revealed by the data. As an ongoing effort, Ice Watch/ASSIST aims to standardize observations of Arctic-specific sea ice features and conditions while utilizing nomenclature and coding based on the World Meteorological Organization (WMO) standards and the Antarctic Sea Ice and Processes & Climate (ASPeCt) protocol. Instigated by members of the CliC Sea Ice Working Group, the program has evolved with

A 100-year Reconstruction of Regional Sea Ice Extent in the Ross and Amundsen-Bellingshausen Seas as Derived from the RICE Ice Core, Coastal West Antarctica

NASA Astrophysics Data System (ADS)

Emanuelsson, D. B.; Bertler, N. A. N.; Baisden, W. T.; Keller, E. D.

2014-12-01

Antarctic sea ice increased over the past decades. This increase is the result of an increase in the Ross Sea (RS) and along the coast of East Antarctica, whereas the Amundsen-Bellingshausen Seas (ABS) and the Antarctic Peninsula has seen a general decline. Several mechanisms have been suggested as drivers for the regional, complex sea ice pattern, which include changes in ocean currents, wind pattern, as well as ocean and atmospheric temperature. As part of the Roosevelt Island Climate Evolution (RICE) project, a 763 m deep ice core was retrieved from Roosevelt Island (RI; W161° 21', S79°41', 560 m a.s.l.), West Antarctica. The new record provides a unique opportunity to investigate mechanism driving sea ice variability in the RS and ABS sectors. Here we present the water stable isotope record (δD) from the upper part of the RICE core 0-40 m, spanning the time period from 1894 to 2011 (Fig. 1a). Annual δD are correlated with Sea Ice Concentration (SIC). A significant negative (r= -0.45, p≤ 0.05) correlation was found between annual δD and SIC in the eastern RS sector (boxed region in Fig. 1b) for the following months NDJFMA (austral summer and fall). During NDJFMA, RI receives local moisture input from the RS, while during the rest of the year a large extent of this local moisture source area will be covered with sea ice with the exception of the RS Polynya. Concurrently, we observe positive δD and SIC correlations in the ABS, showing a dipole pattern with the eastern RS. For this reason, we suggest that the RICE δD might be used as a proxy for past SIC for the RS and ABS region. There is no overall trend in δD over 100 years (r= -0.08 ‰ dec-1, p= 0.81, 1894-2011). However, we observe a strong increase from 2000-2011 of 17.7 ‰ dec-1(p≤ 0.1), yet the recent δD values and trend of the last decade are not unprecedented (Fig. 1a). We investigate changes in sea surface temperature, atmospheric temperature, inferred surface ocean currents and

Observations of Recent Arctic Sea Ice Volume Loss and Its Impact on Ocean-Atmosphere Energy Exchange and Ice Production

NASA Technical Reports Server (NTRS)

Kurtz, N. T.; Markus, T.; Farrell, S. L.; Worthen, D. L.; Boisvert, L. N.

2011-01-01

Using recently developed techniques we estimate snow and sea ice thickness distributions for the Arctic basin through the combination of freeboard data from the Ice, Cloud, and land Elevation Satellite (ICESat) and a snow depth model. These data are used with meteorological data and a thermodynamic sea ice model to calculate ocean-atmosphere heat exchange and ice volume production during the 2003-2008 fall and winter seasons. The calculated heat fluxes and ice growth rates are in agreement with previous observations over multiyear ice. In this study, we calculate heat fluxes and ice growth rates for the full distribution of ice thicknesses covering the Arctic basin and determine the impact of ice thickness change on the calculated values. Thinning of the sea ice is observed which greatly increases the 2005-2007 fall period ocean-atmosphere heat fluxes compared to those observed in 2003. Although there was also a decline in sea ice thickness for the winter periods, the winter time heat flux was found to be less impacted by the observed changes in ice thickness. A large increase in the net Arctic ocean-atmosphere heat output is also observed in the fall periods due to changes in the areal coverage of sea ice. The anomalously low sea ice coverage in 2007 led to a net ocean-atmosphere heat output approximately 3 times greater than was observed in previous years and suggests that sea ice losses are now playing a role in increasing surface air temperatures in the Arctic.

Collaborative, International Efforts at Estimating Arctic Sea Ice Processes During IPY (Invited)

NASA Astrophysics Data System (ADS)

Overland, J. E.; Eicken, H.; Wiggins, H. V.

2009-12-01

Planning for the fourth IPY was conducted during a time of moderate decadal change in the Arctic. However, after this initial planning was completed, further rapid changes were seen, including a 39 % reduction in summer sea ice extent in 2007 and 2008 relative to the 1980s-1990s, loss of multi-year sea ice, and increased sea ice mobility. The SEARCH and DAMOCLES Programs endeavored to increase communication within the research community to promote observations and understanding of rapidly changing Arctic sea ice conditions during IPY. In May 2008 a web-based Sea Ice Outlook was initiated, an international collaborative effort that synthesizes, on a monthly basis throughout the summer, the community’s projections for September arctic sea ice extent. Each month, participating investigators provided a projection for the mean September sea ice extent based on spring and early summer data, along with a rationale for their estimates. The Outlook continued in summer of 2009. The Outlook is a method of rapidly synthesizing a broad range of remote sensing and field observations collected at the peak of the IPY, with analysis methods ranging from heuristic to statistical to ice-ocean model ensemble runs. The 2008 Outlook was a success with 20 groups participating and providing a median sea ice extent projection from June 2008 data of 4.4 million square kilometers (MSQK)—near the observed extent in September 2008 of 4.7 MSQK, and well below the 1979-2007 climatological extent of 6.7 MSQK. More importantly, the contrast of sea ice conditions and atmospheric forcing in 2008 compared to 2007 provided clues to the future fate of arctic sea ice. The question was whether the previous loss of multi-year ice and delay in autumn freeze-up in 2007 would allow sufficient winter thickening of sea ice to last through the summer 2008, promoting recovery from the 2007 minimum, or whether most first-year sea ice would melt out as in 2005 and 2007, resulting in a new record minimum extent

Satellite microwave and in situ observations of the Weddell Sea ice cover and its marginal ice zone

NASA Technical Reports Server (NTRS)

Comiso, J. C.; Sullivan, C. W.

1986-01-01

The radiative and physical characteristics of the Weddell Sea ice cover and its marginal ice zone are analyzed using multichannel satellite passive microwave data and ship and helicopter observations obtained during the 1983 Antarctic Marine Ecosystem Research. Winter and spring brightness temperatures are examined; spatial variability in the brightness temperatures of consolidated ice in winter and spring cyclic increases and decrease in brightness temperatures of consolidated ice with an amplitude of 50 K at 37 GHz and 20 K at 18 GHz are observed. The roles of variations in air temperature and surface characteristics in the variability of spring brightness temperatures are investigated. Ice concentrations are derived using the frequency and polarization techniques, and the data are compared with the helicopter and ship observations. Temporal changes in the ice margin structure and the mass balance of fresh water and of biological features of the marginal ice zone are studied.

Canadian Arctic sea ice reconstructed from bromine in the Greenland NEEM ice core.

PubMed

Spolaor, Andrea; Vallelonga, Paul; Turetta, Clara; Maffezzoli, Niccolò; Cozzi, Giulio; Gabrieli, Jacopo; Barbante, Carlo; Goto-Azuma, Kumiko; Saiz-Lopez, Alfonso; Cuevas, Carlos A; Dahl-Jensen, Dorthe

2016-09-21

Reconstructing the past variability of Arctic sea ice provides an essential context for recent multi-year sea ice decline, although few quantitative reconstructions cover the Holocene period prior to the earliest historical records 1,200 years ago. Photochemical recycling of bromine is observed over first-year, or seasonal, sea ice in so-called "bromine explosions" and we employ a 1-D chemistry transport model to quantify processes of bromine enrichment over first-year sea ice and depositional transport over multi-year sea ice and land ice. We report bromine enrichment in the Northwest Greenland Eemian NEEM ice core since the end of the Eemian interglacial 120,000 years ago, finding the maximum extension of first-year sea ice occurred approximately 9,000 years ago during the Holocene climate optimum, when Greenland temperatures were 2 to 3 °C above present values. First-year sea ice extent was lowest during the glacial stadials suggesting complete coverage of the Arctic Ocean by multi-year sea ice. These findings demonstrate a clear relationship between temperature and first-year sea ice extent in the Arctic and suggest multi-year sea ice will continue to decline as polar amplification drives Arctic temperatures beyond the 2 °C global average warming target of the recent COP21 Paris climate agreement.

30-Year Satellite Record Reveals Contrasting Arctic and Antarctic Decadal Sea Ice Variability

NASA Technical Reports Server (NTRS)

Cavalieri, D. J.; Parkinson, C. L.; Vinnikov, K. Y.

2003-01-01

A 30-year satellite record of sea ice extents derived mostly from satellite microwave radiometer observations reveals that the Arctic sea ice extent decreased by 0.30+0.03 x 10(exp 6) square kilometers per 10 yr from 1972 through 2002, but by 0.36 plus or minus 0.05 x 10(exp 6) square kilometers per 10yr from 1979 through 2002, indicating an acceleration of 20% in the rate of decrease. In contrast, the Antarctic sea ice extent decreased dramatically over the period 1973-1977, then gradually increased. Over the full 30-year period, the Antarctic ice extent decreased by 0.15 plus or minus 0.08 x 10(exp 6) square kilometers per 10 yr. The trend reversal is attributed to a large positive anomaly in Antarctic sea ice extent in the early 1970's, an anomaly that apparently began in the late 1960's, as observed in early visible and infrared satellite images.

Sea Ice

NASA Technical Reports Server (NTRS)

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

2013-01-01

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

Observations of sea ice and icebergs from satellite radar altimeters

NASA Technical Reports Server (NTRS)

Rapley, C. G.

1984-01-01

Satellite radar altimeters can make useful contributions to the study of sea ice both by enhancing observations from other instruments and by providing a unique probe of ocean-ice interaction in the Marginal Ice Zone (MIZ). The problems, results and future potential of such observations are discussed.

Seafloor Control on Sea Ice

NASA Technical Reports Server (NTRS)

Nghiem, S. V.; Clemente-Colon, P.; Rigor, I. G.; Hall, D. K.; Neumann, G.

2011-01-01

The seafloor has a profound role in Arctic sea ice formation and seasonal evolution. Ocean bathymetry controls the distribution and mixing of warm and cold waters, which may originate from different sources, thereby dictating the pattern of sea ice on the ocean surface. Sea ice dynamics, forced by surface winds, are also guided by seafloor features in preferential directions. Here, satellite mapping of sea ice together with buoy measurements are used to reveal the bathymetric control on sea ice growth and dynamics. Bathymetric effects on sea ice formation are clearly observed in the conformation between sea ice patterns and bathymetric characteristics in the peripheral seas. Beyond local features, bathymetric control appears over extensive ice-prone regions across the Arctic Ocean. The large-scale conformation between bathymetry and patterns of different synoptic sea ice classes, including seasonal and perennial sea ice, is identified. An implication of the bathymetric influence is that the maximum extent of the total sea ice cover is relatively stable, as observed by scatterometer data in the decade of the 2000s, while the minimum ice extent has decreased drastically. Because of the geologic control, the sea ice cover can expand only as far as it reaches the seashore, the continental shelf break, or other pronounced bathymetric features in the peripheral seas. Since the seafloor does not change significantly for decades or centuries, sea ice patterns can be recurrent around certain bathymetric features, which, once identified, may help improve short-term forecast and seasonal outlook of the sea ice cover. Moreover, the seafloor can indirectly influence cloud cover by its control on sea ice distribution, which differentially modulates the latent heat flux through ice covered and open water areas.

Will Arctic sea ice thickness initialization improve seasonal forecast skill?

NASA Astrophysics Data System (ADS)

Day, J. J.; Hawkins, E.; Tietsche, S.

2014-11-01

Arctic sea ice thickness is thought to be an important predictor of Arctic sea ice extent. However, coupled seasonal forecast systems do not generally use sea ice thickness observations in their initialization and are therefore missing a potentially important source of additional skill. To investigate how large this source is, a set of ensemble potential predictability experiments with a global climate model, initialized with and without knowledge of the sea ice thickness initial state, have been run. These experiments show that accurate knowledge of the sea ice thickness field is crucially important for sea ice concentration and extent forecasts up to 8 months ahead, especially in summer. Perturbing sea ice thickness also has a significant impact on the forecast error in Arctic 2 m temperature a few months ahead. These results suggest that advancing capabilities to observe and assimilate sea ice thickness into coupled forecast systems could significantly increase skill.

Observational Simulation of Icing in Extreme Weather Conditions

NASA Astrophysics Data System (ADS)

Gultepe, Ismail; Heymsfield, Andrew; Agelin-Chaab, Martin; Komar, John; Elfstrom, Garry; Baumgardner, Darrel

2017-04-01

Observations and prediction of icing in extreme weather conditions are important for aviation, transportation, and shipping applications, and icing adversely affects the economy. Icing environments can be studied either in the outdoor atmosphere or in the laboratory. There have been several aircraft based in-situ studies related to weather conditions affecting aviation operations, transportation, and marine shipping that includes icing, wind, and turbulence. However, studying severe weather conditions from aircraft observations are limited due to safety and sampling issues, instrumental uncertainties, and even the possibility of aircraft producing its own physical and dynamical effects. Remote sensing based techniques (e.g. retrieval techniques) for studying severe weather conditions represent usually a volume that cannot characterize the important scales and also represents indirect observations. Therefore, laboratory simulations of atmospheric processes can help us better understand the interactions among microphysical and dynamical processes. The Climatic Wind Tunnel (CWT) in ACE at the University of Ontario Institute of Technology (UOIT) has a large semi-open jet test chamber with flow area 7-13 m2 that can precisely control temperatures down to -40°C, and up to 250 km hr-1 wind speeds, for heavy or dry snow conditions with low visibility, similar to ones observed in the Arctic and cold climate regions, or at high altitude aeronautical conditions. In this study, the ACE CWT employed a spray nozzle array suspended in its settling chamber and fed by pressurized water, creating various particle sizes from a few microns up to mm size range. This array, together with cold temperature and high wind speed, enabled simulation of severe weather conditions, including icing, visibility, strong wind and turbulence, ice fog and frost, freezing fog, heavy snow and blizzard conditions. In this study, the test results will be summarized, and their application to aircraft

Arctic Sea Ice Decline: Observations, Projections, Mechanisms, and Implications

NASA Astrophysics Data System (ADS)

DeWeaver, Eric T.; Bitz, Cecilia M.; Tremblay, L.-Bruno

This volume addresses the rapid decline of Arctic sea ice, placing recent sea ice decline in the context of past observations, climate model simulations and projections, and simple models of the climate sensitivity of sea ice. Highlights of the work presented here include • An appraisal of the role played by wind forcing in driving the decline; • A reconstruction of Arctic sea ice conditions prior to human observations, based on proxy data from sediments; • A modeling approach for assessing the impact of sea ice decline on polar bears, used as input to the U.S. Fish and Wildlife Service's decision to list the polar bear as a threatened species under the Endangered Species Act; • Contrasting studies on the existence of a "tipping point," beyond which Arctic sea ice decline will become (or has already become) irreversible, including an examination of the role of the small ice cap instability in global warming simulations; • A significant summertime atmospheric response to sea ice reduction in an atmospheric general circulation model, suggesting a positive feedback and the potential for short-term climate prediction. The book will be of interest to researchers attempting to understand the recent behavior of Arctic sea ice, model projections of future sea ice loss, and the consequences of sea ice loss for the natural and human systems of the Arctic.

Multi-resolution Changes in the Spatial Extent of Perennial Arctic Alpine Snow and Ice Fields with Potential Archaeological Significance in the Central Brooks Range, Alaska

NASA Astrophysics Data System (ADS)

Tedesche, M. E.; Freeburg, A. K.; Rasic, J. T.; Ciancibelli, C.; Fassnacht, S. R.

2015-12-01

Perennial snow and ice fields could be an important archaeological and paleoecological resource for Gates of the Arctic National Park and Preserve in the central Brooks Range mountains of Arctic Alaska. These features may have cultural significance, as prehistoric artifacts may be frozen within the snow and ice. Globally significant discoveries have been made recently as ancient artifacts and animal dung have been found in melting alpine snow and ice patches in the Southern Yukon and Northwest Territories in Canada, the Wrangell mountains in Alaska, as well as in other areas. These sites are melting rapidly, which results in quick decay of biological materials. The summer of 2015 saw historic lows in year round snow cover extent for most of Alaska. Twenty mid to high elevation sites, including eighteen perennial snow and ice fields, and two glaciers, were surveyed in July 2015 to quantify their areal extent. This survey was accomplished by using both low flying aircraft (helicopter), as well as with on the ground in-situ (by foot) measurements. By helicopter, visual surveys were conducted within tens of meters of the surface. Sites visited by foot were surveyed for extent of snow and ice coverage, melt water hydrologic parameters and chemistry, and initial estimates of depths and delineations between snow, firn, and ice. Imagery from both historic aerial photography and from 5m resolution IKONOS satellite information were correlated with the field data. Initial results indicate good agreement in permanent snow and ice cover between field surveyed data and the 1985 to 2011 Landsat imagery-based Northwest Alaska snow persistence map created by Macander et al. (2015). The most deviation between the Macander et al. model and the field surveyed results typically occurred as an overestimate of perennial extent on the steepest aspects. These differences are either a function of image classification or due to accelerated ablation rates in perennial snow and ice coverage

Regional Changes in the Sea Ice Cover and Ice Production in the Antarctic

NASA Technical Reports Server (NTRS)

Comiso, Josefino C.

2011-01-01

Coastal polynyas around the Antarctic continent have been regarded as sea ice factories because of high ice production rates in these regions. The observation of a positive trend in the extent of Antarctic sea ice during the satellite era has been intriguing in light of the observed rapid decline of the ice extent in the Arctic. The results of analysis of the time series of passive microwave data indicate large regional variability with the trends being strongly positive in the Ross Sea, strongly negative in the Bellingshausen/Amundsen Seas and close to zero in the other regions. The atmospheric circulation in the Antarctic is controlled mainly by the Southern Annular Mode (SAM) and the marginal ice zone around the continent shows an alternating pattern of advance and retreat suggesting the presence of a propagating wave (called Antarctic Circumpolar Wave) around the circumpolar region. The results of analysis of the passive microwave data suggest that the positive trend in the Antarctic sea ice cover could be caused primarily by enhanced ice production in the Ross Sea that may be associated with more persistent and larger coastal polynyas in the region. Over the Ross Sea shelf, analysis of sea ice drift data from 1992 to 2008 yields a positive rate-of-increase in the net ice export of about 30,000 km2 per year. For a characteristic ice thickness of 0.6 m, this yields a volume transport of about 20 km3/year, which is almost identical, within error bars, to our estimate of the trend in ice production. In addition to the possibility of changes in SAM, modeling studies have also indicated that the ozone hole may have a role in that it causes the deepening of the lows in the western Antarctic region thereby causing strong winds to occur offthe Ross-ice shelf.

Thin Sea Ice, Thick Snow, and Widespread Negative Freeboard Observed During N-ICE2015 North of Svalbard

NASA Astrophysics Data System (ADS)

Rösel, Anja; Itkin, Polona; King, Jennifer; Divine, Dmitry; Wang, Caixin; Granskog, Mats A.; Krumpen, Thomas; Gerland, Sebastian

2018-02-01

In recent years, sea-ice conditions in the Arctic Ocean changed substantially toward a younger and thinner sea-ice cover. To capture the scope of these changes and identify the differences between individual regions, in situ observations from expeditions are a valuable data source. We present a continuous time series of in situ measurements from the N-ICE2015 expedition from January to June 2015 in the Arctic Basin north of Svalbard, comprising snow buoy and ice mass balance buoy data and local and regional data gained from electromagnetic induction (EM) surveys and snow probe measurements from four distinct drifts. The observed mean snow depth of 0.53 m for April to early June is 73% above the average value of 0.30 m from historical and recent observations in this region, covering the years 1955-2017. The modal total ice and snow thicknesses, of 1.6 and 1.7 m measured with ground-based EM and airborne EM measurements in April, May, and June 2015, respectively, lie below the values ranging from 1.8 to 2.7 m, reported in historical observations from the same region and time of year. The thick snow cover slows thermodynamic growth of the underlying sea ice. In combination with a thin sea-ice cover this leads to an imbalance between snow and ice thickness, which causes widespread negative freeboard with subsequent flooding and a potential for snow-ice formation. With certainty, 29% of randomly located drill holes on level ice had negative freeboard.

ASPECTS OF ARCTIC SEA ICE OBSERVABLE BY SEQUENTIAL PASSIVE MICROWAVE OBSERVATIONS FROM THE NIMBUS-5 SATELLITE.

USGS Publications Warehouse

Campbell, William J.; Gloersen, Per; Zwally, H. Jay; ,

1984-01-01

Observations made from 1972 to 1976 with the Electrically Scanning Microwave Radiometer on board the Nimbus-5 satellite provide sequential synoptic information of the Arctic sea ice cover. This four-year data set was used to construct a fairly continuous series of three-day average 19-GHz passive microwave images which has become a valuable source of polar information, yielding many anticipated and unanticipated discoveries of the sea ice canopy observed in its entirety through the clouds and during the polar night. Short-term, seasonal, and annual variations of key sea ice parameters, such as ice edge position, ice types, mixtures of ice types, ice concentrations, and snow melt on the ice, are presented for various parts of the Arctic.

Developing A Model for Lake Ice Phenology Using Satellite Remote Sensing Observations

NASA Astrophysics Data System (ADS)

Skoglund, S. K.; Weathers, K. C.; Norouzi, H.; Prakash, S.; Ewing, H. A.

2017-12-01

Many northern temperate freshwater lakes are freezing over later and thawing earlier. This shift in timing, and the resulting shorter duration of seasonal ice cover, is expected to impact ecological processes, negatively affecting aquatic species and the quality of water we drink. Long-term, direct observations have been used to analyze changes in ice phenology, but those data are sparse relative to the number of lakes affected. Here we develop a model to utilize remote sensing data in approximating the dates of ice-on and ice-off for many years over a variety of lakes. Day and night surface temperatures from MODIS (Moderate Resolution Imaging Spectroradiometer) Aqua and Terra (MYD11A1 and MOD11A1 data products) for 2002-2017 were utilized in combination with observed ice-on and ice-off dates of Lake Auburn, Maine, to determine the ability of MODIS data to match ground-based observations. A moving average served to interpolate MODIS temperature data to fill data gaps from cloudy days. The nighttime data were used for ice-off, and the daytime measurements were used for ice-on predictions to avoid fluctuations between day and night ice/water status. The 0˚C intercepts of those data were used to mark approximate days of ice-on or ice-off. This revealed that approximations for ice-off dates were satisfactory (average ±8.2 days) for Lake Auburn as well as for Lake Sunapee, New Hampshire (average ±8.1 days), while approximations for Lake Auburn ice-on were less accurate and showed consistently earlier-than-observed ice-on dates (average -33.8 days). The comparison of observed and remotely sensed Lake Auburn ice cover duration showed relative agreement with a correlation coefficient of 0.46. Other remote sensing observations, such as the new GOES-R satellite, and further exploration of the ice formation process can improve ice-on approximation methods. The model shows promise for estimating ice-on, ice-off, and ice cover duration for northern temperate lakes.

Statistical Analyses of High-Resolution Aircraft and Satellite Observations of Sea Ice: Applications for Improving Model Simulations

NASA Astrophysics Data System (ADS)

Farrell, S. L.; Kurtz, N. T.; Richter-Menge, J.; Harbeck, J. P.; Onana, V.

2012-12-01

Satellite-derived estimates of ice thickness and observations of ice extent over the last decade point to a downward trend in the basin-scale ice volume of the Arctic Ocean. This loss has broad-ranging impacts on the regional climate and ecosystems, as well as implications for regional infrastructure, marine navigation, national security, and resource exploration. New observational datasets at small spatial and temporal scales are now required to improve our understanding of physical processes occurring within the ice pack and advance parameterizations in the next generation of numerical sea-ice models. High-resolution airborne and satellite observations of the sea ice are now available at meter-scale resolution or better that provide new details on the properties and morphology of the ice pack across basin scales. For example the NASA IceBridge airborne campaign routinely surveys the sea ice of the Arctic and Southern Oceans with an advanced sensor suite including laser and radar altimeters and digital cameras that together provide high-resolution measurements of sea ice freeboard, thickness, snow depth and lead distribution. Here we present statistical analyses of the ice pack primarily derived from the following IceBridge instruments: the Digital Mapping System (DMS), a nadir-looking, high-resolution digital camera; the Airborne Topographic Mapper, a scanning lidar; and the University of Kansas snow radar, a novel instrument designed to estimate snow depth on sea ice. Together these instruments provide data from which a wide range of sea ice properties may be derived. We provide statistics on lead distribution and spacing, lead width and area, floe size and distance between floes, as well as ridge height, frequency and distribution. The goals of this study are to (i) identify unique statistics that can be used to describe the characteristics of specific ice regions, for example first-year/multi-year ice, diffuse ice edge/consolidated ice pack, and convergent

Satellite Observations of Antarctic Sea Ice Thickness and Volume

NASA Technical Reports Server (NTRS)

Kurtz, Nathan; Markus, Thorsten

2012-01-01

We utilize satellite laser altimetry data from ICESat combined with passive microwave measurements to analyze basin-wide changes in Antarctic sea ice thickness and volume over a 5 year period from 2003-2008. Sea ice thickness exhibits a small negative trend while area increases in the summer and fall balanced losses in thickness leading to small overall volume changes. Using a five year time-series, we show that only small ice thickness changes of less than -0.03 m/yr and volume changes of -266 cu km/yr and 160 cu km/yr occurred for the spring and summer periods, respectively. The calculated thickness and volume trends are small compared to the observational time period and interannual variability which masks the determination of long-term trend or cyclical variability in the sea ice cover. These results are in stark contrast to the much greater observed losses in Arctic sea ice volume and illustrate the different hemispheric changes of the polar sea ice covers in recent years.

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

NASA Technical Reports Server (NTRS)

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

2004-01-01

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

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

NASA Technical Reports Server (NTRS)

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

2004-01-01

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

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

USGS Publications Warehouse

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

2004-01-01

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

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

USGS Publications Warehouse

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

2004-01-01

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

Operationally Monitoring Sea Ice at the Canadian Ice Service

NASA Astrophysics Data System (ADS)

de Abreu, R.; Flett, D.; Carrieres, T.; Falkingham, J.

2004-05-01

The Canadian Ice Service (CIS) of the Meteorological Service of Canada promotes safe and efficient maritime operations and protects Canada's environment by providing reliable and timely information about ice and iceberg conditions in Canadian waters. Daily and seasonal charts describing the extent, type and concentration of sea ice and icebergs are provided to support navigation and other activities (e.g. oil and gas) in coastal waters. The CIS relies on a suite of spaceborne visible, infrared and microwave sensors to operationally monitor ice conditions in Canadian coastal and inland waterways. These efforts are complemented by operational sea ice models that are customized and run at the CIS. The archive of these data represent a 35 year archive of ice conditions and have proven to be a valuable dataset for historical sea ice analysis. This presentation will describe the daily integration of remote sensing observations and modelled ice conditions used to produce ice and iceberg products. A review of the decadal evolution of this process will be presented, as well as a glimpse into the future of ice and iceberg monitoring. Examples of the utility of the CIS digital sea ice archive for climate studies will also be presented.

Sea-ice evaluation of NEMO-Nordic 1.0: a NEMO-LIM3.6-based ocean-sea-ice model setup for the North Sea and Baltic Sea

NASA Astrophysics Data System (ADS)

Pemberton, Per; Löptien, Ulrike; Hordoir, Robinson; Höglund, Anders; Schimanke, Semjon; Axell, Lars; Haapala, Jari

2017-08-01

The Baltic Sea is a seasonally ice-covered marginal sea in northern Europe with intense wintertime ship traffic and a sensitive ecosystem. Understanding and modeling the evolution of the sea-ice pack is important for climate effect studies and forecasting purposes. Here we present and evaluate the sea-ice component of a new NEMO-LIM3.6-based ocean-sea-ice setup for the North Sea and Baltic Sea region (NEMO-Nordic). The setup includes a new depth-based fast-ice parametrization for the Baltic Sea. The evaluation focuses on long-term statistics, from a 45-year long hindcast, although short-term daily performance is also briefly evaluated. We show that NEMO-Nordic is well suited for simulating the mean sea-ice extent, concentration, and thickness as compared to the best available observational data set. The variability of the annual maximum Baltic Sea ice extent is well in line with the observations, but the 1961-2006 trend is underestimated. Capturing the correct ice thickness distribution is more challenging. Based on the simulated ice thickness distribution we estimate the undeformed and deformed ice thickness and concentration in the Baltic Sea, which compares reasonably well with observations.

The Effect of Recent Decreases in Sea Ice Extent and Increases in SST on the Seasonal Availability of Arctic Cod (Boreogadus saida) to Seabirds in the Beaufort Sea

NASA Astrophysics Data System (ADS)

Divoky, G.; Druckenmiller, M. L.

2016-02-01

With major decreases in pan-Arctic summer sea ice extent steadily underway, the Beaufort Sea has been nearly ice-free in five of the last eight summers. This loss of a critical arctic marine habitat and the concurrent warming of the recently ice-free waters could potentially cause major changes in the biological oceanography of the Beaufort Sea and alter the distribution, abundance and condition of the region's upper trophic level predators that formerly relied on prey associated with sea ice or cold (<2°C) surface waters. Arctic cod (Boreogadus saida), the primary forage fish for seabirds in the Beaufort Sea, is part of the cryopelagic fauna associated with sea ice and is also found in adjacent ice-free waters. In the extreme western Beaufort Sea near Cooper Island, Arctic cod availability to breeding Black Guillemots (Cepphus grylle), a diving seabird, has declined since 2002. Guillemots are a good indicator of Arctic cod availability in surface waters and the upper water column as they feed at depths of 1-20m. Currently, when sea ice is absent from the nearshore and SST exceeds 4°C, guillemots are observed to seasonally shift from Arctic cod to nearshore demersal prey, with a resulting decrease in nestling survival and quality. Arctic cod is the primary prey for many of the seabirds utilizing the Beaufort Sea as a post-breeding staging area and migratory corridor in late summer and early fall. The loss of approximately 200-300 thousand sq km of summer sea ice habitat in recent years could be expected to affect the distribution, abundance, and movements of these species as there are few alternative fish resources in the region. We examine temporal and spatial variation in August sea ice extent and SST in the Beaufort Sea to determine the regions, periods and bird species that are potentially most affected as the Beaufort Sea transitions to becoming regularly ice-free in late summer.

Understanding the Sea Ice Zone: Scientists and Communities Partnering to Archive, Analyze and Disseminate Local Ice Observations

NASA Astrophysics Data System (ADS)

Collins, J. A.; Oldenburg, J.; Liu, M.; Pulsifer, P. L.; Kaufman, M.; Eicken, H.; Parsons, M. A.

2012-12-01

Knowledge of sea ice is critical to the hunting, whaling, and cultural activities of many Indigenous communities in Northern and Western Alaska. Experienced hunters have monitored seasonal changes of the sea ice over many years, giving them a unique expertise in assessing the current state of the sea ice as well as any anomalies in seasonal sea ice conditions. The Seasonal Ice Zone Observing Network (SIZONet), in collaboration with the Exchange for Local Observations and Knowledge of the Arctic (ELOKA), has developed an online application for collecting, storing, and analyzing sea ice observations contributed by local experts from coastal Alaskan communities. Here we present the current iteration of the application, outline future plans and discuss how the development process and resulting system have improved our collective understanding of sea ice processes and changes. The SIZONet application design is based on the needs of the research scientists responsible for entering observation data into the database, the needs of local sea ice experts contributing their observations and knowledge, and the information needs of Alaska coastal communities. Entry forms provide a variety of input methods, including menus, check boxes, and free text input. Input options strive to balance flexibility in capturing concepts and details with the need for analytical consistency. Currently, research staff at the University of Alaska Fairbanks use the application to enter observations received via written or electronic communications from local sea ice experts. Observation data include current weather conditions, snow and ice quantity and quality, and wildlife sighted or taken. Future plans call for direct use of the SIZONet interface by local sea ice experts as well as students, both as contributors to the data collection and as users seeking meaning in the data. This functionality is currently available to a limited number of community members as we extend the application to support

The influence of sea ice on Antarctic ice core sulfur chemistry and on the future evolution of Arctic snow depth: Investigations using global models

NASA Astrophysics Data System (ADS)

Hezel, Paul J.

Observational studies have examined the relationship between methanesulfonic acid (MSA) measured in Antarctic ice cores and sea ice extent measured by satellites with the aim of producing a proxy for past sea ice extent. MSA is an oxidation product of dimethylsulfide (DMS) and is potentially linked to sea ice based on observations of very high surface seawater DMS in the sea ice zone. Using a global chemical transport model, we present the first modeling study that specifically examines this relationship on interannual and on glacial-interglacial time scales. On interannual time scales, the model shows no robust relationship between MSA deposited in Antarctica and sea ice extent. We show that lifetimes of MSA and DMS are longer in the high latitudes than in the global mean, interannual variability of sea ice is small (<25%) as a fraction of sea ice area, and sea ice determines only a fraction of the variability (<30%) of DMS emissions from the ocean surface. A potentially larger fraction of the variability in DMS emissions is determined by surface wind speed (up to 46%) via the parameterization for ocean-to-atmosphere gas exchange. Furthermore, we find that a significant fraction (up to 74%) of MSA deposited in Antarctica originates from north of 60°S, north of the seasonal sea ice zone. We then examine the deposition of MSA and non-sea-salt sulfate (nss SO2-4 ) on glacial-interglacial time scales. Ice core observations on the East Antarctic Plateau suggest that MSA increases much more than nss SO2-4 during the last glacial maximum (LGM) compared to the modern period. It has been suggested that high MSA during the LGM is indicative of higher primary productivity and DMS emissions in the LGM compared to the modern day. Studies have also shown that MSA is subject to post-depositional volatilization, especially during the modern period. Using the same chemical transport model driven by meteorology from a global climate model, we examine the sensitivity of MSA and nss

On the discrepancy between observed and CMIP5 multi-model simulated Barents Sea winter sea ice decline

NASA Astrophysics Data System (ADS)

Li, Dawei; Zhang, Rong; Knutson, Thomas R.

2017-04-01

This study aims to understand the relative roles of external forcing versus internal climate variability in causing the observed Barents Sea winter sea ice extent (SIE) decline since 1979. We identify major discrepancies in the spatial patterns of winter Northern Hemisphere sea ice concentration trends over the satellite period between observations and CMIP5 multi-model mean externally forced response. The CMIP5 externally forced decline in Barents Sea winter SIE is much weaker than that observed. Across CMIP5 ensemble members, March Barents Sea SIE trends have little correlation with global mean surface air temperature trends, but are strongly anti-correlated with trends in Atlantic heat transport across the Barents Sea Opening (BSO). Further comparison with control simulations from coupled climate models suggests that enhanced Atlantic heat transport across the BSO associated with regional internal variability may have played a leading role in the observed decline in winter Barents Sea SIE since 1979.

Oceans Melting Greenland (OMG): 2017 Observations and the First Look at Yearly Ocean/Ice Changes

NASA Astrophysics Data System (ADS)

Willis, J. K.; Rignot, E. J.; Fenty, I. G.; Khazendar, A.; Moller, D.; Tinto, K. J.; Morison, J.; Schodlok, M.; Thompson, A. F.; Fukumori, I.; Holland, D.; Forsberg, R.; Jakobsson, M.; Dinardo, S. J.

2017-12-01

Oceans Melting Greenland (OMG) is an airborne NASA Mission to investigate the role of the oceans in ice loss around the margins of the Greenland Ice Sheet. A five-year campaign, OMG will directly measure ocean warming and glacier retreat around all of Greenland. By relating these two, we will explore one of the most pressing open questions about how climate change drives sea level rise: How quickly are the warming oceans melting the Greenland Ice Sheet from the edges? This year, OMG collected its second set of both elevation maps of marine terminating glaciers and ocean temperature and salinity profiles around all of Greenland. This give us our first look at year-to-year changes in both ice volume at the margins, as well as the volume and extent of warm, salty Atlantic water present on the continental shelf. In addition, we will compare recent data in east Greenland waters with historical ocean observations that suggest a long-term warming trend there. Finally, we will briefly review the multi-beam sonar and airborne gravity campaigns—both of which were completed last year—and the dramatic improvement they had on bathymetry maps over the continental shelf around Greenland.

Observation of Sea Ice Surface Thermal States Under Cloud Cover

NASA Technical Reports Server (NTRS)

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

2001-01-01

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

Sparse ice: Geophysical, biological and Indigenous knowledge perspectives on a habitat for ice-associated fauna

NASA Astrophysics Data System (ADS)

Lee, O. A.; Eicken, H.; Weyapuk, W., Jr.; Adams, B.; Mohoney, A. R.

2015-12-01

The significance of highly dispersed, remnant Arctic sea ice as a platform for marine mammals and indigenous hunters in spring and summer may have increased disproportionately with changes in the ice cover. As dispersed remnant ice becomes more common in the future it will be increasingly important to understand its ecological role for upper trophic levels such as marine mammals and its role for supporting primary productivity of ice-associated algae. Potential sparse ice habitat at sea ice concentrations below 15% is difficult to detect using remote sensing data alone. A combination of high resolution satellite imagery (including Synthetic Aperture Radar), data from the Barrow sea ice radar, and local observations from indigenous sea ice experts was used to detect sparse sea ice in the Alaska Arctic. Traditional knowledge on sea ice use by marine mammals was used to delimit the scales where sparse ice could still be used as habitat for seals and walrus. Potential sparse ice habitat was quantified with respect to overall spatial extent, size of ice floes, and density of floes. Sparse ice persistence offshore did not prevent the occurrence of large coastal walrus haul outs, but the lack of sparse ice and early sea ice retreat coincided with local observations of ringed seal pup mortality. Observations from indigenous hunters will continue to be an important source of information for validating remote sensing detections of sparse ice, and improving understanding of marine mammal adaptations to sea ice change.

Will sea ice thickness initialisation improve Arctic seasonal-to-interannual forecast skill?

NASA Astrophysics Data System (ADS)

Day, J. J.; Hawkins, E.; Tietsche, S.

2014-12-01

A number of recent studies have suggested that Arctic sea ice thickness is an important predictor of Arctic sea ice extent. However, coupled forecast systems do not currently use sea ice thickness observations in their initialization and are therefore missing a potentially important source of additional skill. A set of ensemble potential predictability experiments, with a global climate model, initialized with and without knowledge of the sea ice thickness initial state, have been run to investigate this. These experiments show that accurate knowledge of the sea ice thickness field is crucially important for sea ice concentration and extent forecasts up to eight months ahead. Perturbing sea ice thickness also has a significant impact on the forecast error in the 2m temperature and surface pressure fields a few months ahead. These results show that advancing capabilities to observe and assimilate sea ice thickness into coupled forecast systems could significantly increase skill.

Observationally constrained projections of Antarctic ice sheet instability

NASA Astrophysics Data System (ADS)

Edwards, Tamsin; Ritz, Catherine; Durand, Gael; Payne, Anthony; Peyaud, Vincent; Hindmarsh, Richard

2015-04-01

Large parts of the Antarctic ice sheet lie on bedrock below sea level and may be vulnerable to a positive feedback known as Marine Ice Sheet Instability (MISI), a self-sustaining retreat of the grounding line triggered by oceanic or atmospheric changes. There is growing evidence MISI may be underway throughout the Amundsen Sea Embayment (ASE) of West Antarctica, induced by circulation of warm Circumpolar Deep Water. If this retreat is sustained the region could contribute up to 1-2 m to global mean sea level, and if triggered in other areas the potential contribution to sea level on centennial to millennial timescales could be two to three times greater. However, physically plausible projections of Antarctic MISI are challenging: numerical ice sheet models are too low in spatial resolution to resolve grounding line processes or else too computationally expensive to assess modelling uncertainties, and no dynamical models exist of the ocean-atmosphere-ice sheet system. Furthermore, previous numerical ice sheet model projections for Antarctica have not been calibrated with observations, which can reduce uncertainties. Here we estimate the probability of dynamic mass loss in the event of MISI under a medium climate scenario, assessing 16 modelling uncertainties and calibrating the projections with observed mass losses in the ASE from 1992-2011. We project losses of up to 30 cm sea level equivalent (SLE) by 2100 and 72 cm SLE by 2200 (95% credibility interval: CI). Our results are substantially lower than previous estimates. The ASE sustains substantial losses, 83% of the continental total by 2100 and 67% by 2200 (95% CI), but in other regions losses are limited by ice dynamical theory, observations, or a lack of projected triggers.

Overview of Sea-Ice Properties, Distribution and Temporal Variations, for Application to Ice-Atmosphere Chemical Processes.

NASA Astrophysics Data System (ADS)

Moritz, R. E.

2005-12-01

The properties, distribution and temporal variation of sea-ice are reviewed for application to problems of ice-atmosphere chemical processes. Typical vertical structure of sea-ice is presented for different ice types, including young ice, first-year ice and multi-year ice, emphasizing factors relevant to surface chemistry and gas exchange. Time average annual cycles of large scale variables are presented, including ice concentration, ice extent, ice thickness and ice age. Spatial and temporal variability of these large scale quantities is considered on time scales of 1-50 years, emphasizing recent and projected changes in the Arctic pack ice. The amount and time evolution of open water and thin ice are important factors that influence ocean-ice-atmosphere chemical processes. Observations and modeling of the sea-ice thickness distribution function are presented to characterize the range of variability in open water and thin ice.

Arctic Sea ice thickness loss determined using subsurface, aircraft, and satellite observations

NASA Astrophysics Data System (ADS)

Lindsay, R. W.; Schweiger, A. J. B.

2014-12-01

Sea ice thickness is a fundamental climate state variable. However, observations of ice thickness have been sparse in time and space making the construction of observation-based time series difficult. Moreover, different groups use a variety of methods and processing procedures to measure ice thickness and each observational source likely has different and poorly characterized measurement and sampling biases. Observational sources include upward looking sonars mounted on submarines or moorings, electromagnetic sensors on helicopters or aircraft, and lidar or radar altimeters on airplanes or satellites. Are these data sources now adequate so that we can construct time series of the mean sea ice thickness with meaningful information about thickness changes? How do the different measurement systems compare in the mean? Are there systematic differences? Very few of the observations provide overlapping measurements of ice of a variety of thickness classes or types for direct comparisons. Error characteristics may vary considerably depending on the presence or thickness of the ridged ice. Here we use a curve-fitting approach to evaluate the systematic differences between eight different observation systems in the Arctic Basin, including ICESat and IceBridge measurements. The approach determines the large-scale spatial and temporal variability of the ice thickness as well as the mean differences between the observation systems using over 3000 estimates of the ice thickness. The thickness estimates are measured over spatial scales of approximately 50 km or time scales of 1 month and the primary time period analyzed is 2000-2013 when the modern mix of observations is available. Good agreement is found between five of the systems, within 0.15 m, while systematic differences of up to 0.5 m are found for three others compare to the five. The annual mean ice thickness for the central Arctic Basin based on observations only has decreased from 3.45 m in 1975 to 1.11 m in 2013, a

Observing Radiative Properties of a Thinner, Seasonal Arctic Ice Pack

NASA Astrophysics Data System (ADS)

Hudson, S. R.; Nicolaus, M.; Granskog, M.; Gerland, S.; Wang, C.

2011-12-01

The Arctic is coming to be dominated by young ice, much of it seasonal. Many of our observations of the radiative properties of sea ice come from drifting stations on thick, multi-year ice. To better understand the Arctic climate system in a warmer world, we need more data about the radiative properties and their seasonal and spatial variability on thinner, younger ice. Since this younger ice is not always thick enough to support lengthy drifting stations, there is a need for new technologies to help us get optical measurements on seasonal ice. One challenge is obtaining seasonal data on ice that is too weak to support even a ship-based camp, and especially to have these observations extend well into the melt season. For these situations, we have developed a spectral radiation monitoring buoy that can be deployed during a one-day ice station, and that can then autonomously observe the spectral albedo and transmittance of the sea ice, transmitting all data in near real time by satellite, until the buoy melts out. Similar installations at manned or regularly visited sites have provided good data, with surprisingly few data-quality problems due to frost, precipitation, or tilting. The buoys consist of 3 spectral radiometers, covering wavelengths 350 to 800 nm, and a datalogger with an Irridium modem. The datalogger and necessary batteries are inside a sealed housing which is frozen into a hole drilled in the ice. Arms extend from both the top and bottom of the housing, holding sensors that measure incident, reflected, and transmitted spectra. The under-ice radiometer is equipped with a bioshutter to avoid algal growth on the sensor. They will be deployed alongside ice mass balance buoys, providing data about the physical development of the ice and snow, as well as position. While the buoys provide an excellent record of diurnal, synoptic, and seasonal variability, they are fixed to one location in the ice, so other methods are still needed for measuring the spatial

Progress on wave-ice interactions: satellite observations and model parameterizations

NASA Astrophysics Data System (ADS)

Ardhuin, Fabrice; Boutin, Guillaume; Dumont, Dany; Stopa, Justin; Girard-Ardhuin, Fanny; Accensi, Mickael

2017-04-01

In the open ocean, numerical wave models have their largest errors near sea ice, and, until recently, virtually no wave data was available in the sea ice to. Further, wave-ice interaction processes may play an important role in the Earth system. In particular, waves may break up an ice layer into floes, with significant impact on air-sea fluxes. With thinner Arctic ice, this process may contribut to the growing similarity between Arctic and Antarctic sea ice. In return, the ice has a strong damping impact on the waves that is highly variable and not understood. Here we report progress on parameterizations of waves interacting with a single ice layer, as implemented in the WAVEWATCH III model (WW3 Development Group, 2016), and based on few in situ observations, but extensive data derived from Synthetic Aperture Radars (SARs). Our parameterizations combine three processes. First a parameterization for the energy-conserving scattering of waves by ice floes (assuming isotropic back-scatter), which has very little effect on dominant waves of periods larger than 7 s, consistent with the observed narrow directional spectra and short travel times. Second, we implemented a basal friction below the ice layer (Stopa et al. The Cryosphere, 2016). Third, we use a secondary creep associated with ice flexure (Cole et al. 1998) adapted to random waves. These three processes (scattering, friction and creep) are strongly dependent on the maximum floe size. We have thus included an estimation of the potential floe size based on an ice flexure failure estimation adapted from Williams et al. (2013). This combination of dissipation and scattering is tested against measured patterns of wave height and directional spreading, and evidence of ice break-up, all obtained from SAR imagery (Ardhuin et al. 2017), and some in situ data (Collins et al. 2015). The combination of creep and friction is required to reproduce a strong reduction in wave attenuation in broken ice as observed by Collins

Precipitation Impacts of a Shrinking Arctic Sea Ice Cover

NASA Astrophysics Data System (ADS)

Stroeve, J. C.; Frei, A.; Gong, G.; Ghatak, D.; Robinson, D. A.; Kindig, D.

2009-12-01

Since the beginning of the modern satellite record in October 1978, the extent of Arctic sea ice has declined in all months, with the strongest downward trend at the end of the melt season in September. Recently the September trends have accelerated. Through 2001, the extent of September sea ice was decreasing at a rate of -7 per cent per decade. By 2006, the rate of decrease had risen to -8.9 per cent per decade. In September 2007, Arctic sea ice extent fell to its lowest level recorded, 23 per cent below the previous record set in 2005, boosting the downward trend to -10.7 per cent per decade. Ice extent in September 2008 was the second lowest in the satellite record. Including 2008, the trend in September sea ice extent stands at -11.8 percent per decade. Compared to the 1970s, September ice extent has retreated by 40 per cent. Summer 2009 looks to repeat the anomalously low ice conditions that characterized the last couple of years. Scientists have long expected that a shrinking Arctic sea ice cover will lead to strong warming of the overlying atmosphere, and as a result, affect atmospheric circulation and precipitation patterns. Recent results show clear evidence of Arctic warming linked to declining ice extent, yet observational evidence for responses of atmospheric circulation and precipitation patterns is just beginning to emerge. Rising air temperatures should lead to an increase in the moisture holding capacity of the atmosphere, with the potential to impact autumn precipitation. Although climate models predict a hemispheric wide decrease in snow cover as atmospheric concentrations of GHGs increase, increased precipitation, particular in autumn and winter may result as the Arctic transitions towards a seasonally ice free state. In this study we use atmospheric reanalysis data and a cyclone tracking algorithm to investigate the influence of recent extreme ice loss years on precipitation patterns in the Arctic and the Northern Hemisphere. Results show

Arctic Sea Ice in Transformation: A Review of Recent Observed Changes and Impacts on Biology and Human Activity

NASA Technical Reports Server (NTRS)

Meier, Walter N.; Hovelsrud, Greta K.; van Oort, Bob E. H.; Key, Jeffrey R.; Kovacs, Kit M.; Michel, Christine; Haas, Christian; Granskog, Mats A.; Gerland, Sebastian; Perovich, Donald K.;

Deglaciation-induced uplift of the Petermann glacier ice margin observed with InSAR

NASA Astrophysics Data System (ADS)

Lu, Q.; Amelung, F.; Wdowinski, S.

2016-12-01

The Greenland ice sheet is rapidly shrinking with the fastest retreat and thinning occurring at the ice sheet margin and near the outlet glaciers. The changes of the ice mass cause an elastic response of the bedrock. Ice mass loss during the summer months is associated with uplift, whereas ice mass increase during the winter months is associated with subsidence.The German TerraSAR-X and TanDEM-X satellites have systematically observed selected sites along the Greenland Petermann ice sheet margin since summer 2012. Here we present ground deformation observations obtained using an InSAR time-series approach based on small baseline interferograms. We observed rapid deglaciation-induced uplift on naked bedrock near the Petermann glacier ice margin Deformation observed by InSAR is consistent with GPS vertical observations. The time series displacement data reveal not only net uplift but also the seasonal variations. There is no strong relative between displacement changes and SMB ice mass change. The seasonal variations in local area may caused by both nearby SMB changes and ice dynamic changes.

The influence of the hydrologic cycle on the extent of sea ice with climatic implications

NASA Technical Reports Server (NTRS)

Dean, Kenneson G.; Stringer, William J.; Searcy, Craig

1993-01-01

Multi-temporal satellite images, field observations, and field measurements were used to investigate the mechanisms by which sea ice melts offshore from the Mackenzie River delta. Advanced Very High Resolution Radiometer (AVHRR) satellite data recorded in 1986 were analyzed. The satellite data were geometrically corrected and radiometrically calibrated so that albedo and temperature values could be extracted. The investigation revealed that sea ice melted approximately 2 weeks earlier offshore from the Mackenzie River delta than along coasts where river discharge is minimal or non-existent. There is significant intra-delta variability in the timing and patterns of ice melt. An estimation of energy flux indicates that 30 percent more of the visible wavelength energy and 25 percent more of the near-infrared wavelength energy is absorbed by water offshore of the delta compared to coastal areas with minimal river discharge. The analysis also revealed that the removal of sea ice involves the following: over-ice-flooding along the coast offshore from river delta channels; under-ice flow of 'warm' river water; melting and calving of the fast ice; and, the formation of a bight in the pack ice edge. Two stages in the melting of sea ice were identified: (1) an early stage where heat is supplied to overflows largely by solar radiation, and (2) a later stage where heat is supplied by river discharge in addition to solar radiation. A simple thermodynamic model of the thaw process in the fast ice zone was developed and parameterized based on events recorded by the satellite images. The model treats river discharge as the source of sensible heat at the base of the ice cover. The results of a series of sensitivity tests to assess the influence of river discharge on the near shore ice are presented.

Assessment of Arctic and Antarctic Sea Ice Predictability in CMIP5 Decadal Hindcasts

NASA Technical Reports Server (NTRS)

Yang, Chao-Yuan; Liu, Jiping (Inventor); Hu, Yongyun; Horton, Radley M.; Chen, Liqi; Cheng, Xiao

2016-01-01

This paper examines the ability of coupled global climate models to predict decadal variability of Arctic and Antarctic sea ice. We analyze decadal hindcasts/predictions of 11 Coupled Model Intercomparison Project Phase 5 (CMIP5) models. Decadal hindcasts exhibit a large multimodel spread in the simulated sea ice extent, with some models deviating significantly from the observations as the predicted ice extent quickly drifts away from the initial constraint. The anomaly correlation analysis between the decadal hindcast and observed sea ice suggests that in the Arctic, for most models, the areas showing significant predictive skill become broader associated with increasing lead times. This area expansion is largely because nearly all the models are capable of predicting the observed decreasing Arctic sea ice cover. Sea ice extent in the North Pacific has better predictive skill than that in the North Atlantic (particularly at a lead time of 3-7 years), but there is a reemerging predictive skill in the North Atlantic at a lead time of 6-8 years. In contrast to the Arctic, Antarctic sea ice decadal hindcasts do not show broad predictive skill at any timescales, and there is no obvious improvement linking the areal extent of significant predictive skill to lead time increase. This might be because nearly all the models predict a retreating Antarctic sea ice cover, opposite to the observations. For the Arctic, the predictive skill of the multi-model ensemble mean outperforms most models and the persistence prediction at longer timescales, which is not the case for the Antarctic. Overall, for the Arctic, initialized decadal hindcasts show improved predictive skill compared to uninitialized simulations, although this improvement is not present in the Antarctic.

Arctic Ice-Ocean Coupling and Gyre Equilibration Observed With Remote Sensing

NASA Astrophysics Data System (ADS)

Dewey, Sarah; Morison, James; Kwok, Ronald; Dickinson, Suzanne; Morison, David; Andersen, Roger

2018-02-01

Model and observational evidence has shown that ocean current speeds in the Beaufort Gyre have increased and recently stabilized. Because these currents rival ice drift speeds, we examine the potential for the Beaufort Gyre's shift from a system in which the wind drives the ice and the ice drives a passive ocean to one in which the ocean often, in the absence of high winds, drives the ice. The resultant stress exerted on the ocean by the ice and the resultant Ekman pumping are reversed, without any change in average wind stress curl. Through these curl reversals, the ice-ocean stress provides a key feedback in Beaufort Gyre stabilization. This manuscript constitutes one of the first observational studies of ice-ocean stress inclusive of geostrophic ocean currents, by making use of recently available remote sensing data.

Characterization of Arctic ice cloud properties observed during ISDAC

NASA Astrophysics Data System (ADS)

Jouan, Caroline; Girard, Eric; Pelon, Jacques; Gultepe, Ismail; Delanoë, Julien; Blanchet, Jean-Pierre

2012-12-01

Extensive measurements from ground-based sites and satellite remote sensing (CloudSat and CALIPSO) reveal the existence of two types of ice clouds (TICs) in the Arctic during the polar night and early spring. The first type (TIC-2A), being topped by a cover of nonprecipitating very small (radar unseen) ice crystals (TIC-1), is found more frequently in pristine environment, whereas the second type (TIC-2B), detected by both sensors, is associated preferentially with a high concentration of aerosols. To further investigate the microphysical properties of TIC-1/2A and TIC-2B, airborne in situ and satellite measurements of specific cases observed during Indirect and Semi-Direct Aerosol Campaign (ISDAC) have been analyzed. For the first time, Arctic TIC-1/2A and TIC-2B microstructures are compared using in situ cloud observations. Results show that the differences between them are confined in the upper part of the clouds where ice nucleation occurs. TIC-2B clouds are characterized by fewer (by more than 1 order of magnitude) and larger (by a factor of 2 to 3) ice crystals and a larger ice supersaturation (of 15-20%) compared to TIC-1/2A. Ice crystal growth in TIC-2B clouds seems explosive, whereas it seems more gradual in TIC-1/2A. It is hypothesized that these differences are linked to the number concentration and the chemical composition of aerosols. The ice crystal growth rate in very cold conditions impinges on the precipitation efficiency, dehydration and radiation balance. These results represent an essential and important first step to relate previous modeling, remote sensing and laboratory studies with TICs cloud in situ observations.

Ice shelf basal melt rates around Antarctica from simulations and observations

NASA Astrophysics Data System (ADS)

Schodlok, M. P.; Menemenlis, D.; Rignot, E. J.

2016-02-01

We introduce an explicit representation of Antarctic ice shelf cavities in the Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2) ocean retrospective analysis; and compare resulting basal melt rates and patterns to independent estimates from satellite observations. Two simulations are carried out: the first is based on the original ECCO2 vertical discretization; the second has higher vertical resolution particularly at the depth range of ice shelf cavities. The original ECCO2 vertical discretization produces higher than observed melt rates and leads to a misrepresentation of Southern Ocean water mass properties and transports. In general, thicker levels at the base of the ice shelves lead to increased melting because of their larger heat capacity. This strengthens horizontal gradients and circulation within and outside the cavities and, in turn, warm water transports from the shelf break to the ice shelves. The simulation with more vertical levels produces basal melt rates (1735 ± 164 Gt/a) and patterns that are in better agreement with observations. Thinner levels in the sub-ice-shelf cavities improve the representation of a fresh/cold layer at the ice shelf base and of warm/salty water near the bottom, leading to a sharper pycnocline and reduced vertical mixing underneath the ice shelf. Improved water column properties lead to more accurate melt rates and patterns, especially for melt/freeze patterns under large cold-water ice shelves. At the 18 km grid spacing of the ECCO2 model configuration, the smaller, warm-water ice shelves cannot be properly represented, with higher than observed melt rates in both simulations.

Potential sea-level rise from Antarctic ice-sheet instability constrained by observations.

PubMed

Ritz, Catherine; Edwards, Tamsin L; Durand, Gaël; Payne, Antony J; Peyaud, Vincent; Hindmarsh, Richard C A

2015-12-03

Large parts of the Antarctic ice sheet lying on bedrock below sea level may be vulnerable to marine-ice-sheet instability (MISI), a self-sustaining retreat of the grounding line triggered by oceanic or atmospheric changes. There is growing evidence that MISI may be underway throughout the Amundsen Sea embayment (ASE), which contains ice equivalent to more than a metre of global sea-level rise. If triggered in other regions, the centennial to millennial contribution could be several metres. Physically plausible projections are challenging: numerical models with sufficient spatial resolution to simulate grounding-line processes have been too computationally expensive to generate large ensembles for uncertainty assessment, and lower-resolution model projections rely on parameterizations that are only loosely constrained by present day changes. Here we project that the Antarctic ice sheet will contribute up to 30 cm sea-level equivalent by 2100 and 72 cm by 2200 (95% quantiles) where the ASE dominates. Our process-based, statistical approach gives skewed and complex probability distributions (single mode, 10 cm, at 2100; two modes, 49 cm and 6 cm, at 2200). The dependence of sliding on basal friction is a key unknown: nonlinear relationships favour higher contributions. Results are conditional on assessments of MISI risk on the basis of projected triggers under the climate scenario A1B (ref. 9), although sensitivity to these is limited by theoretical and topographical constraints on the rate and extent of ice loss. We find that contributions are restricted by a combination of these constraints, calibration with success in simulating observed ASE losses, and low assessed risk in some basins. Our assessment suggests that upper-bound estimates from low-resolution models and physical arguments (up to a metre by 2100 and around one and a half by 2200) are implausible under current understanding of physical mechanisms and potential triggers.

Potential sea-level rise from Antarctic ice-sheet instability constrained by observations

NASA Astrophysics Data System (ADS)

Ritz, Catherine; Edwards, Tamsin L.; Durand, Gaël; Payne, Antony J.; Peyaud, Vincent; Hindmarsh, Richard C. A.

2015-12-01

Large parts of the Antarctic ice sheet lying on bedrock below sea level may be vulnerable to marine-ice-sheet instability (MISI), a self-sustaining retreat of the grounding line triggered by oceanic or atmospheric changes. There is growing evidence that MISI may be underway throughout the Amundsen Sea embayment (ASE), which contains ice equivalent to more than a metre of global sea-level rise. If triggered in other regions, the centennial to millennial contribution could be several metres. Physically plausible projections are challenging: numerical models with sufficient spatial resolution to simulate grounding-line processes have been too computationally expensive to generate large ensembles for uncertainty assessment, and lower-resolution model projections rely on parameterizations that are only loosely constrained by present day changes. Here we project that the Antarctic ice sheet will contribute up to 30 cm sea-level equivalent by 2100 and 72 cm by 2200 (95% quantiles) where the ASE dominates. Our process-based, statistical approach gives skewed and complex probability distributions (single mode, 10 cm, at 2100; two modes, 49 cm and 6 cm, at 2200). The dependence of sliding on basal friction is a key unknown: nonlinear relationships favour higher contributions. Results are conditional on assessments of MISI risk on the basis of projected triggers under the climate scenario A1B (ref. 9), although sensitivity to these is limited by theoretical and topographical constraints on the rate and extent of ice loss. We find that contributions are restricted by a combination of these constraints, calibration with success in simulating observed ASE losses, and low assessed risk in some basins. Our assessment suggests that upper-bound estimates from low-resolution models and physical arguments (up to a metre by 2100 and around one and a half by 2200) are implausible under current understanding of physical mechanisms and potential triggers.

HiRISE observations of new impact craters exposing Martian ground ice

USGS Publications Warehouse

Dundas, Colin M.; Byrne, Shane; McEwen, Alfred S.; Mellon, Michael T.; Kennedy, Megan R.; Daubar, Ingrid J.; Saper, Lee

2014-01-01

Twenty small new impact craters or clusters have been observed to excavate bright material inferred to be ice at mid and high latitudes on Mars. In the northern hemisphere, the craters are widely distributed geographically and occur at latitudes as low as 39°N. Stability modeling suggests that this ice distribution requires a long-term average atmospheric water vapor content around 25 precipitable microns, more than double the present value, which is consistent with the expected effect of recent orbital variations. Alternatively, near-surface humidity could be higher than expected for current column abundances if water vapor is not well-mixed with atmospheric CO2, or the vapor pressure at the ice table could be lower due to salts. Ice in and around the craters remains visibly bright for months to years, indicating that it is clean ice rather than ice-cemented regolith. Although some clean ice may be produced by the impact process, it is likely that the original ground ice was excess ice (exceeding dry soil pore space) in many cases. Observations of the craters suggest small-scale heterogeneities in this excess ice. The origin of such ice is uncertain. Ice lens formation by migration of thin films of liquid is most consistent with local heterogeneity in ice content and common surface boulders, but in some cases nearby thermokarst landforms suggest large amounts of excess ice that may be best explained by a degraded ice sheet.

Observed Arctic sea-ice loss directly follows anthropogenic CO2 emission.

PubMed

Notz, Dirk; Stroeve, Julienne

2016-11-11

Arctic sea ice is retreating rapidly, raising prospects of a future ice-free Arctic Ocean during summer. Because climate-model simulations of the sea-ice loss differ substantially, we used a robust linear relationship between monthly-mean September sea-ice area and cumulative carbon dioxide (CO 2 ) emissions to infer the future evolution of Arctic summer sea ice directly from the observational record. The observed linear relationship implies a sustained loss of 3 ± 0.3 square meters of September sea-ice area per metric ton of CO 2 emission. On the basis of this sensitivity, Arctic sea ice will be lost throughout September for an additional 1000 gigatons of CO 2 emissions. Most models show a lower sensitivity, which is possibly linked to an underestimation of the modeled increase in incoming longwave radiation and of the modeled transient climate response. Copyright © 2016, American Association for the Advancement of Science.

The role of summer surface wind anomalies in the summer Arctic sea ice extent in 2010 and 2011

NASA Astrophysics Data System (ADS)

Ogi, M.; Wallace, J. M.

2012-12-01

Masayo Ogi 1 and John M. Wallace 2 masayo.ogi@jamstec.go.jp wallace@atmos.washington.edu 1Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan 2 Department of Atmospheric Sciences, University of Washington, Seattle, Washington The seasonal evolutions of Arctic sea ice extent (SIE) during the summers of 2010 and 2011 are contrasted with that in 2007. The June SIE in 2010 was lower than that in 2007 and was the lowest for that calendar month in the 32-year (1979-2010) record. The September SIE in 2010 would have set a new record low had it not been for the fact that the ice retreated more slowly during the summer months in that year than it did in 2007. Hence from early July onward, the SIE in 2010 remained at levels above those observed in 2007. The SIE minimum in September 2010 proved to be the third lowest on record, eclipsed by values in both 2007 and 2008. In spring and summer of 2011, the Arctic SIE was as low as it was in 2007, but the SIE in September 2011 did not reach record low levels. The SIE minimum in 2011 proved to be the second lowest on record for the period of 1979-2011. Summertime atmospheric conditions play an important role in controlling the variations in Arctic SIE. In a previous study based on statistical analysis of data collected prior to 2007, we showed that anticyclonic summertime circulation anomalies over the Arctic Ocean during the summer months favor low September SIE. We also found that the record-low ice summer year 2007 was characterized by a strong anticyclonic circulation anomaly, accompanied by an Ekman drift of ice out of the marginal seas toward the central Arctic and eventually toward the Fram Strait, as evidenced by the tracks of drifting buoys. Here we assess the extent to which year-to-year differences in summer winds over the Arctic might have contributed to the differing rates of retreat of ice during the summers of 2007, 2010, and 2011. Our results show that the May-June (MJ) pattern in 2010 is

Ice Shelf-Ocean Interactions Near Ice Rises and Ice Rumples

NASA Astrophysics Data System (ADS)

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

2013-12-01

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

A Mission to Observe Ice in Clouds from Space

NASA Technical Reports Server (NTRS)

Ackerman, S.; O'CStarr, D.; Skofronick-Jackson, G.; Evans, F.; Wang, J. R.; Racette, P.; Norris, P.; daSilva, A.; Soden, B.

2006-01-01

To date there have been multiple satellite missions to observe and retrieve cloud top properties and the liquid in, and precipitation from, clouds. There are currently a few missions that attempt to measure cloud ice properties as a byproduct of other observations. However, we do not yet quantitatively understand the processes that control the water budget of the upper troposphere where ice is the predominant phase, and how these processes are linked to precipitation processes and the radiative energy budget. The ice in clouds either melts into rain or is detrained, and persists, as cirrus clouds affecting the hydrological and energy cycle, respectively. Fully modeling the Earth's climate and improving weather and climate forecasts requires accurate satellite measurements of various cloud properties at the temporal and spatial scales of cloud processes. The uncertainty in knowledge of these ice characteristics is reflected in the large discrepancies in model simulations of the upper tropospheric water budget. Model simulations are sensitive to the partition of ice between precipitation and outflow processes, i.e., to the parameterization of ice clouds and ice processes. This presentation will describe the Submillimeter-wave InfraRed Ice Cloud Experiment (SIRICE) concept, a satellite mission designed to acquire global Earth radiance measurements in the infrared and submillimeter-wave region (183-874 GHz). If successful, this mission will bridge the measurement gap between microwave sounders and shorter-wavelength infrared and visible sensors. The brightness temperatures at submillimeter-wave frequencies are especially sensitive to cirrus ice particle sizes (because they are comparable to the wavelength). This allows for more accurate ice water path estimates when multiple channels are used to probe into the cloud layers. Further, submillimeter wavelengths offer simplicity in the retrieval algorithms because they do not probe into the liquid and near surface portions

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

NASA Astrophysics Data System (ADS)

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

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

NASA's Observes Effects of Summer Melt on Greenland Ice Sheet

NASA Image and Video Library

2017-12-08

NASA's IceBridge, an airborne survey of polar ice, flew over the Helheim/Kangerdlugssuaq region of Greenland on Sept. 11, 2016. This photograph from the flight captures Greenland's Steenstrup Glacier, with the midmorning sun glinting off of the Denmark Strait in the background. IceBridge completed the final flight of the summer campaign to observe the impact of the summer melt season on the ice sheet on Sept. 16. The IceBridge flights, which began on Aug. 27, are mostly repeats of lines that the team flew in early May, so that scientists can observe changes in ice elevation between the spring and late summer. For this short, end-of-summer campaign, the IceBridge scientists flew aboard an HU-25A Guardian aircraft from NASA's Langley Research Center in Hampton, Virginia. Credit: NASA/John Sonntag NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

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

NASA Technical Reports Server (NTRS)

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

2001-01-01

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

CIRS-Observed Titan’s Stratospheric Ice Clouds Studied in the Laboratory

NASA Astrophysics Data System (ADS)

Nna-Mvondo, Delphine; Anderson, Carrie; Samuelson, Robert E.

2018-06-01

Stratospheric ice clouds have been repeatedly observed in Titan’s atmosphere by the Cassini Composite InfraRed Spectrometer (CIRS) since the Cassini spacecraft entered into orbit around Saturn in 2004. Most of these stratospheric ice clouds form as a result of vapor condensation, composed of a combination of pure and mixed nitriles and hydrocarbons. So far, the crystalline cyanoacetylene (HC3N) ν6 band at 506 cm‑1 and a co-condensed nitrile ice feature at 160 cm‑1, dominated by a mixture of HCN and HC3N ices, have been identified in the CIRS limb spectra. However, the presence of other observed stratospheric ice emission features, such as the ν8 band of dicyanoacetylene (C4N2) at 478 cm‑1 and the Haystack emission feature at 220 cm‑1, are puzzling since they have no associated observed vapor emission features. As well, recently, a massive stratospheric ice cloud system, the High-Altitude South Polar (HASP) cloud, was discovered in Titan’s early southern winter stratosphere with an emission feature near 210 cm‑1. We are investigating in laboratory these perplexing stratospheric ices to better understand their formation mechanisms, identify their chemical compositions, and determine their optical properties. We perform transmission spectroscopy of thin films of pure and mixed nitrile ices, as well as ices combined with hydrocarbons, from 50 cm‑1 to 11700 cm‑1, at deposition temperature 30 K - 150 K, using the SPECTRAL high-vacuum chamber at NASA GSFC. The spectral evolution with time and temperature is studied, the ice phase formation identified, and optical constants computed. The first surprising yet significant result reveals that the libration mode of HCN is drastically altered by the surrounding molecules when mixing occurs in a co-condensed phase. For propionitrile ice, we observe peculiar temperature and time-driven ice phase transitions, revealed by significant spectral changes until a stable crystalline phase is achieved. Comparing our

Arctic ice cover, ice thickness and tipping points.

PubMed

Wadhams, Peter

2012-02-01

We summarize the latest results on the rapid changes that are occurring to Arctic sea ice thickness and extent, the reasons for them, and the methods being used to monitor the changing ice thickness. Arctic sea ice extent had been shrinking at a relatively modest rate of 3-4% per decade (annually averaged) but after 1996 this speeded up to 10% per decade and in summer 2007 there was a massive collapse of ice extent to a new record minimum of only 4.1 million km(2). Thickness has been falling at a more rapid rate (43% in the 25 years from the early 1970s to late 1990s) with a specially rapid loss of mass from pressure ridges. The summer 2007 event may have arisen from an interaction between the long-term retreat and more rapid thinning rates. We review thickness monitoring techniques that show the greatest promise on different spatial and temporal scales, and for different purposes. We show results from some recent work from submarines, and speculate that the trends towards retreat and thinning will inevitably lead to an eventual loss of all ice in summer, which can be described as a 'tipping point' in that the former situation, of an Arctic covered with mainly multi-year ice, cannot be retrieved.

Observation of wave refraction at an ice edge by synthetic aperture radar

NASA Technical Reports Server (NTRS)

Liu, Antony K.; Vachon, Paris W.; Peng, Chih Y.

1991-01-01

In this note the refraction of waves at the ice edge is studied by using aircraft synthesis aperture radar (SAR). Penetration of a dominant swell from open ocean into the ice cover was observed by SAR during the Labrador Ice Margin Experiment (LIMEX), conducted on the marginal ice zone (MIZ) off the east coast of Newfoundland, Canada, in March 1987. At an ice edge with a large curvature, the dominant swell component disappeared locally in the SAR imagery. Six subscenes of waves in the MIZ from the SAR image have been processed, revealing total reflection, refraction, and energy reduction of the ocean waves by the ice cover. The observed variations of wave spectra from SAR near the ice edge are consistent with the model prediction of wave refraction at the ice edge due to the change of wave dispersion relation in ice developed by Liu and Mollo-Christensen (1988).

Preliminary Flight Deck Observations During Flight in High Ice Water Content Conditions

NASA Technical Reports Server (NTRS)

Ratvasky, Thomas; Duchanoy, Dominque; Bourdinot, Jean-Francois; Harrah, Steven; Strapp, Walter; Schwarzenboeck, Alfons; Dezitter, Fabien; Grandin, Alice

2015-01-01

In 2006, Mason et al. identified common observations that occurred in engine power-loss events attributed to flight in high concentrations of ice crystals. Observations included light to moderate turbulence, precipitation on the windscreen (often reported as rain), aircraft total temperature anomalies, lack of significant airframe icing, and no flight radar echoes at the location and altitude of the engine event. Since 2006, Mason et al. and others have collected information from pilots who experienced engine power-loss events via interviews and questionnaires to substantiate earlier observations and support event analyses. In 2011, Mason and Grzych reported that vertical acceleration data showed increases in turbulence prior to engine events, although the turbulence was usually light to moderate and not unique to high ice water content (HIWC) clouds. Mason concluded that the observation of rain on the windscreen was due to melting of ice high concentrations of ice crystals on the windscreen, coalescing into drops. Mason also reported that these pilot observations of rain on the windscreen were varied. Many pilots indicated no rain was observed, while others observed moderate rain with unique impact sounds. Mason concluded that the variation in the reports may be due to variation in the ice concentration, particle size, and temperature.

Seasonal Changes of Arctic Sea Ice Physical Properties Observed During N-ICE2015: An Overview

NASA Astrophysics Data System (ADS)

Gerland, S.; Spreen, G.; Granskog, M. A.; Divine, D.; Ehn, J. K.; Eltoft, T.; Gallet, J. C.; Haapala, J. J.; Hudson, S. R.; Hughes, N. E.; Itkin, P.; King, J.; Krumpen, T.; Kustov, V. Y.; Liston, G. E.; Mundy, C. J.; Nicolaus, M.; Pavlov, A.; Polashenski, C.; Provost, C.; Richter-Menge, J.; Rösel, A.; Sennechael, N.; Shestov, A.; Taskjelle, T.; Wilkinson, J.; Steen, H.

2015-12-01

Arctic sea ice is changing, and for improving the understanding of the cryosphere, data is needed to describe the status and processes controlling current seasonal sea ice growth, change and decay. We present preliminary results from in-situ observations on sea ice in the Arctic Basin north of Svalbard from January to June 2015. Over that time, the Norwegian research vessel «Lance» was moored to in total four ice floes, drifting with the sea ice and allowing an international group of scientists to conduct detailed research. Each drift lasted until the ship reached the marginal ice zone and ice started to break up, before moving further north and starting the next drift. The ship stayed within the area approximately 80°-83° N and 5°-25° E. While the expedition covered measurements in the atmosphere, the snow and sea ice system, and in the ocean, as well as biological studies, in this presentation we focus on physics of snow and sea ice. Different ice types could be investigated: young ice in refrozen leads, first year ice, and old ice. Snow surveys included regular snow pits with standardized measurements of physical properties and sampling. Snow and ice thickness were measured at stake fields, along transects with electromagnetics, and in drillholes. For quantifying ice physical properties and texture, ice cores were obtained regularly and analyzed. Optical properties of snow and ice were measured both with fixed installed radiometers, and from mobile systems, a sledge and an ROV. For six weeks, the surface topography was scanned with a ground LIDAR system. Spatial scales of surveys ranged from spot measurements to regional surveys from helicopter (ice thickness, photography) during two months of the expedition, and by means of an array of autonomous buoys in the region. Other regional information was obtained from SAR satellite imagery and from satellite based radar altimetry. The analysis of the data collected has started, and first results will be

Landfast ice thickness in the Canadian Arctic Archipelago from observations and models

NASA Astrophysics Data System (ADS)

Howell, Stephen E. L.; Laliberté, Frédéric; Kwok, Ron; Derksen, Chris; King, Joshua

2016-07-01

Observed and modelled landfast ice thickness variability and trends spanning more than 5 decades within the Canadian Arctic Archipelago (CAA) are summarized. The observed sites (Cambridge Bay, Resolute, Eureka and Alert) represent some of the Arctic's longest records of landfast ice thickness. Observed end-of-winter (maximum) trends of landfast ice thickness (1957-2014) were statistically significant at Cambridge Bay (-4.31 ± 1.4 cm decade-1), Eureka (-4.65 ± 1.7 cm decade-1) and Alert (-4.44 ± 1.6 cm -1) but not at Resolute. Over the 50+-year record, the ice thinned by ˜ 0.24-0.26 m at Cambridge Bay, Eureka and Alert with essentially negligible change at Resolute. Although statistically significant warming in spring and fall was present at all sites, only low correlations between temperature and maximum ice thickness were present; snow depth was found to be more strongly associated with the negative ice thickness trends. Comparison with multi-model simulations from Coupled Model Intercomparison project phase 5 (CMIP5), Ocean Reanalysis Intercomparison (ORA-IP) and Pan-Arctic Ice-Ocean Modeling and Assimilation System (PIOMAS) show that although a subset of current generation models have a "reasonable" climatological representation of landfast ice thickness and distribution within the CAA, trends are unrealistic and far exceed observations by up to 2 orders of magnitude. ORA-IP models were found to have positive correlations between temperature and ice thickness over the CAA, a feature that is inconsistent with both observations and coupled models from CMIP5.

Arctic sea-ice diffusion from observed and simulated Lagrangian trajectories

NASA Astrophysics Data System (ADS)

Rampal, Pierre; Bouillon, Sylvain; Bergh, Jon; Ólason, Einar

2016-07-01

We characterize sea-ice drift by applying a Lagrangian diffusion analysis to buoy trajectories from the International Arctic Buoy Programme (IABP) dataset and from two different models: the standalone Lagrangian sea-ice model neXtSIM and the Eulerian coupled ice-ocean model used for the TOPAZ reanalysis. By applying the diffusion analysis to the IABP buoy trajectories over the period 1979-2011, we confirm that sea-ice diffusion follows two distinct regimes (ballistic and Brownian) and we provide accurate values for the diffusivity and integral timescale that could be used in Eulerian or Lagrangian passive tracers models to simulate the transport and diffusion of particles moving with the ice. We discuss how these values are linked to the evolution of the fluctuating displacements variance and how this information could be used to define the size of the search area around the position predicted by the mean drift. By comparing observed and simulated sea-ice trajectories for three consecutive winter seasons (2007-2011), we show how the characteristics of the simulated motion may differ from or agree well with observations. This comparison illustrates the usefulness of first applying a diffusion analysis to evaluate the output of modeling systems that include a sea-ice model before using these in, e.g., oil spill trajectory models or, more generally, to simulate the transport of passive tracers in sea ice.

Ice Cloud Properties And Their Radiative Effects: Global Observations And Modeling

NASA Astrophysics Data System (ADS)

Hong, Yulan

Ice clouds are crucial to the Earth's radiation balance. They cool the Earth-atmosphere system by reflecting solar radiation back to space and warm it by blocking outgoing thermal radiation. However, there is a lack of an observation-based climatology of ice cloud properties and their radiative effects. Two active sensors, the CloudSat radar and the CALIPSO lidar, for the first time provide vertically resolved ice cloud data on a global scale. Using synergistic signals of these two sensors, it is possible to obtain both optically thin and thick ice clouds as the radar excels in probing thick clouds while the lidar is better to detect the thin ones. First, based on the CloudSat radar and CALIPSO lidar measurements, we have derived a climatology of ice cloud properties. Ice clouds cover around 50% of the Earth surface, and their global-mean optical depth, ice water path, and effective radius are approximately 2 (unitless), 109 g m. {-2} and 48 \\mum, respectively. Ice cloud occurrence frequency not only depends on regions and seasons, but also on the types of ice clouds as defined by optical depth (tau) values. Optically thin ice clouds (tau < 3) are most frequently observed in the tropics around 15 km and in the midlatitudes below 5 km, while the thicker clouds (tau > 3) occur frequently in the tropical convective areas and along the midlatitude storm tracks. Using ice retrievals derived from combined radar-lidar measurements, we conducted radiative transfer modeling to study ice cloud radiative effects. The combined effects of ice clouds warm the earth-atmosphere system by approximately 5 W m-2, contributed by a longwave warming effect of about 21.8 W m-2 and a shortwave cooling effect of approximately -16.7 W m-2. Seasonal variations of ice cloud radiative effects are evident in the midlatitudes where the net effect changes from warming during winter to cooling during summer, and the net warming effect occurs year-round in the tropics (˜ 10 W m-2). Ice cloud

Arctic sea ice thickness loss determined using subsurface, aircraft, and satellite observations

NASA Astrophysics Data System (ADS)

Lindsay, R.; Schweiger, A.

2014-08-01

Sea ice thickness is a fundamental climate state variable that provides an integrated measure of changes in the high-latitude energy balance. However, observations of ice thickness have been sparse in time and space making the construction of observation-based time series difficult. Moreover, different groups use a variety of methods and processing procedures to measure ice thickness and each observational source likely has different and poorly characterized measurement and sampling biases. Observational sources include upward looking sonars mounted on submarines or moorings, electromagnetic sensors on helicopters or aircraft, and lidar or radar altimeters on airplanes or satellites. Here we use a curve-fitting approach to evaluate the systematic differences between eight different observation systems in the Arctic Basin. The approach determines the large-scale spatial and temporal variability of the ice thickness as well as the mean differences between the observation systems using over 3000 estimates of the ice thickness. The thickness estimates are measured over spatial scales of approximately 50 km or time scales of 1 month and the primary time period analyzed is 2000-2013 when the modern mix of observations is available. Good agreement is found between five of the systems, within 0.15 m, while systematic differences of up to 0.5 m are found for three others compared to the five. The trend in annual mean ice thickness over the Arctic Basin is -0.58 ± 0.07 m decade-1 over the period 2000-2013, while the annual mean ice thickness for the central Arctic Basin alone (the SCICEX Box) has decreased from 3.45 m in 1975 to 1.11 m in 2013, a 68% reduction. This is nearly double the 36% decline reported by an earlier study. These results provide additional direct observational confirmation of substantial sea ice losses found in model analyses.

The future of ice sheets and sea ice: between reversible retreat and unstoppable loss.

PubMed

Notz, Dirk

2009-12-08

We discuss the existence of cryospheric "tipping points" in the Earth's climate system. Such critical thresholds have been suggested to exist for the disappearance of Arctic sea ice and the retreat of ice sheets: Once these ice masses have shrunk below an anticipated critical extent, the ice-albedo feedback might lead to the irreversible and unstoppable loss of the remaining ice. We here give an overview of our current understanding of such threshold behavior. By using conceptual arguments, we review the recent findings that such a tipping point probably does not exist for the loss of Arctic summer sea ice. Hence, in a cooler climate, sea ice could recover rapidly from the loss it has experienced in recent years. In addition, we discuss why this recent rapid retreat of Arctic summer sea ice might largely be a consequence of a slow shift in ice-thickness distribution, which will lead to strongly increased year-to-year variability of the Arctic summer sea-ice extent. This variability will render seasonal forecasts of the Arctic summer sea-ice extent increasingly difficult. We also discuss why, in contrast to Arctic summer sea ice, a tipping point is more likely to exist for the loss of the Greenland ice sheet and the West Antarctic ice sheet.

Formation of melt channels on ice shelves

NASA Astrophysics Data System (ADS)

Sergienko, Olga

2013-04-01

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

Reaching and abandoning the furthest ice extent during the Last Glacial Maximum in the Alps

NASA Astrophysics Data System (ADS)

Ivy-Ochs, Susan; Wirsig, Christian; Zasadni, Jerzy; Hippe, Kristina; Christl, Marcus; Akçar, Naki; Schluechter, Christian

2016-04-01

During the Last Glacial Maximum (LGM) in the European Alps (late Würm) local ice caps and extensive ice fields in the high Alps fed huge outlet glaciers that occupied the main valleys and extended onto the forelands as piedmont lobes. Records from numerous sites suggest advance of glaciers beyond the mountain front by around 30 ka (Ivy-Ochs 2015 and references therein). Reaching of the maximum extent occurred by about 27-26 ka, as exemplified by dates from the Rhein glacier area (Keller and Krayss, 2005). Abandonment of the outermost moraines at sites north and south of the Alps was underway by about 24 ka. In the high Alps, systems of transection glaciers with transfluences over many of the Alpine passes dominated, for example, at Grimsel Pass in the Central Alps (Switzerland). 10Be exposure ages of 23 ± 1 ka for glacially sculpted bedrock located just a few meters below the LGM trimline in the Haslital near Grimsel Pass suggest a pulse of ice surface lowering at about the same time that the foreland moraines were being abandoned (Wirsig et al., 2016). Widespread ice surface lowering in the high Alps was underway by no later than 18 ka. Thereafter, glaciers oscillated at stillstand and minor re-advance positions on the northern forelands for several thousand years forming the LGM stadial moraines. Final recession back within the mountain front took place by 19-18 ka. Recalculation to a common basis of all published 10Be exposure dates for boulders situated on LGM moraines suggests a strong degree of synchrony for the timing of onset of ice decay both north and south of the Alps. Ivy-Ochs, S., 2015, Cuadernos de investigación geográfica 41: 295-315. Keller, O., Krayss, E., 2005, Vierteljahrschr. Naturforsch. Gesell. Zürich 150: 69-85. Wirsig, C. et al., 2016, J. Quat. Sci. 31: 46-59.

Ku band airborne radar altimeter observations of marginal sea ice during the 1984 Marginal Ice Zone Experiment

NASA Technical Reports Server (NTRS)

Drinkwater, Mark R.

1991-01-01

Pulse-limited, airborne radar data taken in June and July 1984 with a 13.8-GHz altimeter over the Fram Strait marginal ice zone are analyzed with the aid of large-format aerial photography, airborne synthetic aperture radar data, and surface observations. Variations in the radar return pulse waveforms are quantified and correlated with ice properties recorded during the Marginal Ice Zone Experiment. Results indicate that the wide-beam altimeter is a flexible instrument, capable of identifying the ice edge with a high degree of accuracy, calculating the ice concentration, and discriminating a number of different ice classes. This suggests that microwave radar altimeters have a sensitivity to sea ice which has not yet been fully exploited. When fused with SSM/I, AVHRR and ERS-1 synthetic aperture radar imagery, future ERS-1 altimeter data are expected to provide some missing pieces to the sea ice geophysics puzzle.

MODIS Snow and Sea Ice Products

NASA Technical Reports Server (NTRS)

Hall, Dorothy K.; Riggs, George A.; Salomonson, Vincent V.

2004-01-01

In this chapter, we describe the suite of Earth Observing System (EOS) Moderate-Resolution Imaging Spectroradiometer (MODIS) Terra and Aqua snow and sea ice products. Global, daily products, developed at Goddard Space Flight Center, are archived and distributed through the National Snow and Ice Data Center at various resolutions and on different grids useful for different communities Snow products include binary snow cover, snow albedo, and in the near future, fraction of snow in a 5OO-m pixel. Sea ice products include ice extent determined with two different algorithms, and sea ice surface temperature. The algorithms used to develop these products are described. Both the snow and sea ice products, available since February 24,2000, are useful for modelers. Validation of the products is also discussed.

ICESat-2, its retrievals of ice sheet elevation change and sea ice freeboard, and potential synergies with CryoSat-2

NASA Astrophysics Data System (ADS)

Neumann, Thomas; Markus, Thorsten; Smith, Benjamin; Kwok, Ron

2017-04-01

Understanding the causes and magnitudes of changes in the cryosphere remains a priority for Earth science research. Over the past decade, NASA's and ESA's Earth-observing satellites have documented a decrease in both the areal extent and thickness of Arctic sea ice, and an ongoing loss of grounded ice from the Greenland and Antarctic ice sheets. Understanding the pace and mechanisms of these changes requires long-term observations of ice-sheet mass, sea-ice thickness, and sea-ice extent. NASA's ICESat-2 mission is the next-generation space-borne laser altimeter mission and will use three pairs of beams, each pair separated by about 3 km across-track with a pair spacing of 90 m. The spot size is 17 m with an along-track sampling interval of 0.7 m. This measurement concept is a result of the lessons learned from the original ICESat mission. The multi-beam approach is critical for removing the effects of ice sheet surface slope from the elevation change measurements of most interest. For sea ice, the dense spatial sampling (eliminating along-track gaps) and the small footprint size are especially useful for sea surface height measurements in the, often narrow, leads needed for sea ice freeboard and ice thickness retrievals. Currently, algorithms are being developed to calculate ice sheet elevation change and sea ice freeboard from ICESat-2 data. The orbits of ICESat-2 and Cryosat-2 both converge at 88 degrees of latitude, though the orbit altitude differences result in different ground track patterns between the two missions. This presentation will present an overview of algorithm approaches and how ICESat-2 and Cryosat-2 data may augment each other.

Evaluation of the Simulation of Arctic and Antarctic Sea Ice Coverages by Eleven Major Global Climate Models

NASA Technical Reports Server (NTRS)

Parksinson, Claire; Vinnikov, Konstantin Y.; Cavalieri, Donald J.

2005-01-01

Comparison of polar sea ice results from 11 major global climate models and satellite-derived observations for 1979-2004 reveals that each of the models is simulating seasonal cycles that are phased at least approximately correctly in both hemispheres. Each is also simulating various key aspects of the observed ice cover distributions, such as winter ice not only throughout the central Arctic basin but also throughout Hudson Bay, despite its relatively low latitudes. However, some of the models simulate too much ice, others too little ice (in some cases varying depending on hemisphere and/or season), and some match the observations better in one season versus another. Several models do noticeably better in the Northern Hemisphere than in the Southern Hemisphere, and one does noticeably better in the Southern Hemisphere. In the Northern Hemisphere all simulate monthly average ice extents to within +/-5.1 x 10(exp 6)sq km of the observed ice extent throughout the year; and in the Southern Hemisphere all except one simulate the monthly averages to within +/-6.3 x 10(exp 6) sq km of the observed values. All the models properly simulate a lack of winter ice to the west of Norway; however, most do not obtain as much absence of ice immediately north of Norway as the observations show, suggesting an under simulation of the North Atlantic Current. The spread in monthly averaged ice extents amongst the 11 model simulations is greater in the Southern Hemisphere than in the Northern Hemisphere and greatest in the Southern Hemisphere winter and spring.

Arctic sea ice thickness loss determined using subsurface, aircraft, and satellite observations

NASA Astrophysics Data System (ADS)

Lindsay, R.; Schweiger, A.

2015-02-01

Sea ice thickness is a fundamental climate state variable that provides an integrated measure of changes in the high-latitude energy balance. However, observations of mean ice thickness have been sparse in time and space, making the construction of observation-based time series difficult. Moreover, different groups use a variety of methods and processing procedures to measure ice thickness, and each observational source likely has different and poorly characterized measurement and sampling errors. Observational sources used in this study include upward-looking sonars mounted on submarines or moorings, electromagnetic sensors on helicopters or aircraft, and lidar or radar altimeters on airplanes or satellites. Here we use a curve-fitting approach to determine the large-scale spatial and temporal variability of the ice thickness as well as the mean differences between the observation systems, using over 3000 estimates of the ice thickness. The thickness estimates are measured over spatial scales of approximately 50 km or time scales of 1 month, and the primary time period analyzed is 2000-2012 when the modern mix of observations is available. Good agreement is found between five of the systems, within 0.15 m, while systematic differences of up to 0.5 m are found for three others compared to the five. The trend in annual mean ice thickness over the Arctic Basin is -0.58 ± 0.07 m decade-1 over the period 2000-2012. Applying our method to the period 1975-2012 for the central Arctic Basin where we have sufficient data (the SCICEX box), we find that the annual mean ice thickness has decreased from 3.59 m in 1975 to 1.25 m in 2012, a 65% reduction. This is nearly double the 36% decline reported by an earlier study. These results provide additional direct observational evidence of substantial sea ice losses found in model analyses.

Arctic sea ice trends, variability and implications for seasonal ice forecasting

PubMed Central

Serreze, Mark C.; Stroeve, Julienne

2015-01-01

September Arctic sea ice extent over the period of satellite observations has a strong downward trend, accompanied by pronounced interannual variability with a detrended 1 year lag autocorrelation of essentially zero. We argue that through a combination of thinning and associated processes related to a warming climate (a stronger albedo feedback, a longer melt season, the lack of especially cold winters) the downward trend itself is steepening. The lack of autocorrelation manifests both the inherent large variability in summer atmospheric circulation patterns and that oceanic heat loss in winter acts as a negative (stabilizing) feedback, albeit insufficient to counter the steepening trend. These findings have implications for seasonal ice forecasting. In particular, while advances in observing sea ice thickness and assimilating thickness into coupled forecast systems have improved forecast skill, there remains an inherent limit to predictability owing to the largely chaotic nature of atmospheric variability. PMID:26032315

Exploring changes in vertical ice extent along the margin of the East Antarctic Ice Sheet in western Dronning Maud Land - initial results of the MAGIC-DML collaboration

NASA Astrophysics Data System (ADS)

Lifton, N. A.; Newall, J. C.; Fredin, O.; Glasser, N. F.; Fabel, D.; Rogozhina, I.; Bernales, J.; Prange, M.; Sams, S.; Eisen, O.; Hättestrand, C.; Harbor, J.; Stroeven, A. P.

2017-12-01

Numerical ice sheet models constrained by theory and refined by comparisons with observational data are a central component of work to address the interactions between the cryosphere and changing climate, at a wide range of scales. Such models are tested and refined by comparing model predictions of past ice geometries with field-based reconstructions from geological, geomorphological, and ice core data. However, on the East Antarctic Ice sheet, there are few empirical data with which to reconstruct changes in ice sheet geometry in the Dronning Maud Land (DML) region. In addition, there is poor control on the regional climate history of the ice sheet margin, because ice core locations, where detailed reconstructions of climate history exist, are located on high inland domes. This leaves numerical models of regional glaciation history in this near-coastal area largely unconstrained. MAGIC-DML is an ongoing Swedish-US-Norwegian-German-UK collaboration with a focus on improving ice sheet models by combining advances in numerical modeling with filling critical data gaps that exist in our knowledge of the timing and pattern of ice surface changes on the western Dronning Maud Land margin. A combination of geomorphological mapping using remote sensing data, field investigations, cosmogenic nuclide surface exposure dating, and numerical ice-sheet modeling are being used in an iterative manner to produce a comprehensive reconstruction of the glacial history of western Dronning Maud Land. We will present an overview of the project, as well as field observations and preliminary in situ cosmogenic nuclide measurements from the 2016/17 expedition.

The future of ice sheets and sea ice: Between reversible retreat and unstoppable loss

PubMed Central

Notz, Dirk

2009-01-01

We discuss the existence of cryospheric “tipping points” in the Earth's climate system. Such critical thresholds have been suggested to exist for the disappearance of Arctic sea ice and the retreat of ice sheets: Once these ice masses have shrunk below an anticipated critical extent, the ice–albedo feedback might lead to the irreversible and unstoppable loss of the remaining ice. We here give an overview of our current understanding of such threshold behavior. By using conceptual arguments, we review the recent findings that such a tipping point probably does not exist for the loss of Arctic summer sea ice. Hence, in a cooler climate, sea ice could recover rapidly from the loss it has experienced in recent years. In addition, we discuss why this recent rapid retreat of Arctic summer sea ice might largely be a consequence of a slow shift in ice-thickness distribution, which will lead to strongly increased year-to-year variability of the Arctic summer sea-ice extent. This variability will render seasonal forecasts of the Arctic summer sea-ice extent increasingly difficult. We also discuss why, in contrast to Arctic summer sea ice, a tipping point is more likely to exist for the loss of the Greenland ice sheet and the West Antarctic ice sheet. PMID:19884496

In situ observations of Arctic cloud properties across the Beaufort Sea marginal ice zone

NASA Astrophysics Data System (ADS)

Corr, C.; Moore, R.; Winstead, E.; Thornhill, K. L., II; Crosbie, E.; Ziemba, L. D.; Beyersdorf, A. J.; Chen, G.; Martin, R.; Shook, M.; Corbett, J.; Smith, W. L., Jr.; Anderson, B. E.

2016-12-01

Clouds play an important role in Arctic climate. This is particularly true over the Arctic Ocean where feedbacks between clouds and sea-ice impact the surface radiation budget through modifications of sea-ice extent, ice thickness, cloud base height, and cloud cover. This work summarizes measurements of Arctic cloud properties made aboard the NASA C-130 aircraft over the Beaufort Sea during ARISE (Arctic Radiation - IceBridge Sea&Ice Experiment) in September 2014. The influence of surface-type on cloud properties is also investigated. Specifically, liquid water content (LWC), droplet concentrations, and droplet size distributions are compared for clouds sampled over three distinct regimes in the Beaufort Sea: 1) open water, 2) the marginal ice zone, and 3) sea-ice. Regardless of surface type, nearly all clouds intercepted during ARISE were liquid-phase clouds. However, differences in droplet size distributions and concentrations were evident for the surface types; clouds over the MIZ and sea-ice generally had fewer and larger droplets compared to those over open water. The potential implication these results have for understanding cloud-surface albedo climate feedbacks in Arctic are discussed.

Greenland ice sheet retreat since the Little Ice Age

NASA Astrophysics Data System (ADS)

Beitch, Marci J.

Late 20th century and 21st century satellite imagery of the perimeter of the Greenland Ice Sheet (GrIS) provide high resolution observations of the ice sheet margins. Examining changes in ice margin positions over time yield measurements of GrIS area change and rates of margin retreat. However, longer records of ice sheet margin change are needed to establish more accurate predictions of the ice sheet's future response to global conditions. In this study, the trimzone, the area of deglaciated terrain along the ice sheet edge that lacks mature vegetation cover, is used as a marker of the maximum extent of the ice from its most recent major advance during the Little Ice Age. We compile recently acquired Landsat ETM+ scenes covering the perimeter of the GrIS on which we map area loss on land-, lake-, and marine-terminating margins. We measure an area loss of 13,327 +/- 830 km2, which corresponds to 0.8% shrinkage of the ice sheet. This equates to an averaged horizontal retreat of 363 +/- 69 m across the entire GrIS margin. Mapping the areas exposed since the Little Ice Age maximum, circa 1900 C.E., yields a century-scale rate of change. On average the ice sheet lost an area of 120 +/- 16 km 2/yr, or retreated at a rate of 3.3 +/- 0.7 m/yr since the LIA maximum.

Airborne geophysics for mesoscale observations of polar sea ice in a changing climate

NASA Astrophysics Data System (ADS)

Hendricks, S.; Haas, C.; Krumpen, T.; Eicken, H.; Mahoney, A. R.

2016-12-01

Sea ice thickness is an important geophysical parameter with a significant impact on various processes of the polar energy balance. It is classified as Essential Climate Variable (ECV), however the direct observations of the large ice-covered oceans are limited due to the harsh environmental conditions and logistical constraints. Sea-ice thickness retrieval by the means of satellite remote sensing is an active field of research, but current observational capabilities are not able to capture the small scale variability of sea ice thickness and its evolution in the presence of surface melt. We present an airborne observation system based on a towed electromagnetic induction sensor that delivers long range measurements of sea ice thickness for a wide range of sea ice conditions. The purpose-built sensor equipment can be utilized from helicopters and polar research aircraft in multi-role science missions. While airborne EM induction sounding is used in sea ice research for decades, the future challenge is the development of unmanned aerial vehicle (UAV) platform that meet the requirements for low-level EM sea ice surveys in terms of range and altitude of operations. The use of UAV's could enable repeated sea ice surveys during the the polar night, when manned operations are too dangerous and the observational data base is presently very sparse.

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

NASA Technical Reports Server (NTRS)

Abdalati, Waleed (Technical Monitor); Scambos, Ted

2004-01-01

Ice shelves respond quickly and profoundly to a warming climate. Within a decade after mean summertime temperature reaches approximately 0 deg C and persistent melt ponding is observed, a rapid retreat and disintegration begins. This link was documented for ice shelves in the Antarctic Peninsula region (the Larsen 'A', B', and Wilkins Ice shelves) in the results of a previous grant under ADRO-1. Modeling of shelf ice flow and the effects of meltwater indicated that melt ponding accelerates shelf breakup by increasing fracturing. The ADRO-2 funding (topic of this report) supported further inquiry into the evolution of ice shelves under warming conditions, and the post-breakup effects on their feeder glaciers. Also, this grant considered fast ice and sea ice characteristics, to the extent that they provide information regarding shelf stability. A major component of this work was in the form of NSIDC image data support and in situ sea ice research on the Aurora Australis 'ARISE' cruise of September 9 2003 through October 28 2003.

In situ observations of a high-pressure phase of H2O ice

USGS Publications Warehouse

Chou, I.-Ming; Blank, J.G.; Goncharov, A.F.; Mao, Ho-kwang; Hemley, R.J.

1998-01-01

A previously unknown solid phase of H2O has been identified by its peculiar growth patterns, distinct pressure-temperature melting relations, and vibrational Raman spectra. Morphologies of ice crystals and their pressure-temperature melting relations were directly observed in a hydrothermal diamond-anvil cell for H2O bulk densities between 1203 and 1257 kilograms per cubic meter at temperatures between -10??and 50??C. Under these conditions, four different ice forms were observed to melt: two stable phases, ice V and ice VI, and two metastable phases, ice IV and the new ice phase. The Raman spectra and crystal morphology are consistent with a disordered anisotropic structure with some similarities to ice VI.

Evaluating Antarctic sea ice predictability at seasonal to interannual timescales in global climate models

NASA Astrophysics Data System (ADS)

Marchi, Sylvain; Fichefet, Thierry; Goosse, Hugues; Zunz, Violette; Tietsche, Steffen; Day, Jonny; Hawkins, Ed

2016-04-01

Unlike the rapid sea ice losses reported in the Arctic, satellite observations show an overall increase in Antarctic sea ice extent over recent decades. Although many processes have already been suggested to explain this positive trend, it remains the subject of current investigations. Understanding the evolution of the Antarctic sea ice turns out to be more complicated than for the Arctic for two reasons: the lack of observations and the well-known biases of climate models in the Southern Ocean. Irrespective of those issues, another one is to determine whether the positive trend in sea ice extent would have been predictable if adequate observations and models were available some decades ago. This study of Antarctic sea ice predictability is carried out using 6 global climate models (HadGEM1.2, MPI-ESM-LR, GFDL CM3, EC-Earth V2, MIROC 5.2 and ECHAM 6-FESOM) which are all part of the APPOSITE project. These models are used to perform hindcast simulations in a perfect model approach. The predictive skill is estimated thanks to the PPP (Potential Prognostic Predictability) and the ACC (Anomaly Correlation Coefficient). The former is a measure of the uncertainty of the ensemble while the latter assesses the accuracy of the prediction. These two indicators are applied to different variables related to sea ice, in particular the total sea ice extent and the ice edge location. This first model intercomparison study about sea ice predictability in the Southern Ocean aims at giving a general overview of Antarctic sea ice predictability in current global climate models.

Optimizing Observations of Sea Ice Thickness and Snow Depth in the Arctic

DTIC Science & Technology

2014-09-30

changes in the thickness of sea ice, glaciers , and ice sheets. These observations are critical for predicting the response of Earth’s polar ice to...Arctic Sea Ice Conditions in Spring 2009 - 2013 Prior to Melt , Geophys. Res. Lett., 40, 5888-5893, doi: 10.1002/2013GL058011. [published, refereed

Arctic Sea ice studies with passive microwave satellite observations

NASA Technical Reports Server (NTRS)

Cavalieri, D. J.

1988-01-01

The objectives of this research are: (1) to improve sea ice concentration determinations from passive microwave space observations; (2) to study the role of Arctic polynyas in the production of sea ice and the associated salinization of Arctic shelf water; and (3) to study large scale sea ice variability in the polar oceans. The strategy is to analyze existing data sets and data acquired from both the DMSP SSM/I and recently completed aircraft underflights. Special attention will be given the high resolution 85.5 GHz SSM/I channels for application to thin ice algorithms and processes studies. Analysis of aircraft and satellite data sets is expected to provide a basis for determining the potential of the SSM/I high frequency channels for improving sea ice algorithms and for investigating oceanic processes. Improved sea ice algorithms will aid the study of Arctic coastal polynyas which in turn will provide a better understanding of the role of these polynyas in maintaining the Arctic watermass structure. Analysis of satellite and archived meteorological data sets will provide improved estimates of annual, seasonal and shorter-term sea ice variability.

Observations of banding in first-year Arctic sea ice

NASA Astrophysics Data System (ADS)

Cole, David M.; Eicken, Hajo; Frey, Karoline; Shapiro, Lewis H.

2004-08-01

Horizontal banding features, alternating dark and bright horizontal bands apparent in ice cores and stratigraphic cross sections have long been observed in first-year sea ice and are frequently associated with bands of high and low brine or gas porosity. Observations on the land-fast ice near Barrow, Alaska, in recent years have revealed particularly striking banding patterns and prompted a study of their macroscopic and microscopic characteristics. The banding patterns are quantified from photographs of full-depth sections of the ice, and examples are presented from the Chukchi Sea and Elson Lagoon. Statistics on band spacing are presented, and the growth records for three seasons are employed to estimate their time of formation. These data provide insight into the periodicity of the underlying phenomena. Micrographs are used to examine the microstructural variations associated with various banding features and to quantify the geometry of the constituent brine inclusions associated with high- and low-porosity bands. The micrography revealed that the area fraction of brine inclusions varied by a factor of nearly 3 through the more pronounced high- and low-porosity bands. Vertical micrographs obtained shortly after the materials' removal from the ice sheet showed that significantly larger inclusions form abruptly at the start of the high-porosity bands and frequently terminate abruptly at the end of the band. Crystallographic observations indicated that the high-porosity bands supported the nucleation and growth of crystals having substantially different orientations from the very well aligned columnar structure that characterized the bulk of the sheet.

New aerogeophysical data reveal the extent of the Weddell Sea Rift beneath the Institute and Möller ice streams

NASA Astrophysics Data System (ADS)

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

2011-12-01

Significant continental rifting associated with Gondwana breakup has been widely recognised in the Weddell Sea region. However, plate reconstructions and the extent of this rift system onshore beneath the West Antarctic Ice Sheet (WAIS) are ambiguous, due to the paucity of modern geophysical data across the Institute and Möller ice stream catchments. Understanding this region is key to unravelling Gondwana breakup and the possible kinematic links between the Weddell Sea and the West Antarctic Rift System. The nature of the underlying tectonic structure is also critical, as it provides the template for ice-flow draining ~20% of the West Antarctic Ice Sheet (WAIS). During the 2010/11 Antarctic field season ~25,000 km of new airborne radar, aerogravity and aeromagnetic data were collected to help unveil the crustal structure and geological boundary conditions beneath the Institute and Möller ice streams. Our new potential field maps delineate varied subglacial geology beneath the glacial catchments, including Jurassic intrusive rocks, sedimentary basins, and Precambrian basement rocks of the Ellsworth Mountains. Inversion of airborne gravity data reveal significant crustal thinning directly beneath the faster flowing coastal parts of the Institute and Möller ice streams. We suggest that continental rifting focussed along the Weddell Sea margin of the Ellsworth-Whitmore Mountains block, providing geological controls for the fast flowing ice streams of the Weddell Sea Embayment. Further to the south we suggest that strike-slip motion between the East Antarctica and the Ellsworth-Whitmore Mountains block may provide a kinematic link between Cretaceous-Cenozoic extension in the West Antarctic Rift System and deformation in the Weddell Sea Embayment.

Holocene ice marginal fluctuations of the Qassimiut lobe in South Greenland

PubMed Central

Larsen, Nicolaj K.; Find, Jesper; Kristensen, Anders; Bjørk, Anders A.; Kjeldsen, Kristian K.; Odgaard, Bent V.; Olsen, Jesper; Kjær, Kurt H.

2016-01-01

Knowledge about the Holocene evolution of the Greenland ice sheet (GrIS) is important to put the recent observations of ice loss into a longer-term perspective. In this study, we use six new threshold lake records supplemented with two existing lake records to reconstruct the Holocene ice marginal fluctuations of the Qassimiut lobe (QL) – one of the most dynamic parts of the GrIS in South Greenland. Times when the ice margin was close to present extent are characterized by clastic input from the glacier meltwater, whereas periods when the ice margin was behind its present day extent comprise organic-rich sediments. We find that the overall pattern suggests that the central part of the ice lobe in low-lying areas experienced the most prolonged ice retreat from ~9–0.4 cal. ka BP, whereas the more distal parts of the ice lobe at higher elevation re-advanced and remained close to the present extent during the Neoglacial between ~4.4 and 1.8 cal. ka BP. These results demonstrate that the QL was primarily driven by Holocene climate changes, but also emphasises the role of local topography on the ice marginal fluctuations. PMID:26940998

Isolating the Liquid Cloud Response to Recent Arctic Sea Ice Variability Using Spaceborne Lidar Observations

NASA Astrophysics Data System (ADS)

Morrison, A. L.; Kay, J. E.; Chepfer, H.; Guzman, R.; Yettella, V.

2018-01-01

While the radiative influence of clouds on Arctic sea ice is known, the influence of sea ice cover on Arctic clouds is challenging to detect, separate from atmospheric circulation, and attribute to human activities. Providing observational constraints on the two-way relationship between sea ice cover and Arctic clouds is important for predicting the rate of future sea ice loss. Here we use 8 years of CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) spaceborne lidar observations from 2008 to 2015 to analyze Arctic cloud profiles over sea ice and over open water. Using a novel surface mask to restrict our analysis to where sea ice concentration varies, we isolate the influence of sea ice cover on Arctic Ocean clouds. The study focuses on clouds containing liquid water because liquid-containing clouds are the most important cloud type for radiative fluxes and therefore for sea ice melt and growth. Summer is the only season with no observed cloud response to sea ice cover variability: liquid cloud profiles are nearly identical over sea ice and over open water. These results suggest that shortwave summer cloud feedbacks do not slow long-term summer sea ice loss. In contrast, more liquid clouds are observed over open water than over sea ice in the winter, spring, and fall in the 8 year mean and in each individual year. Observed fall sea ice loss cannot be explained by natural variability alone, which suggests that observed increases in fall Arctic cloud cover over newly open water are linked to human activities.

Scaling properties of Arctic sea ice deformation in high-resolution viscous-plastic sea ice models and satellite observations

NASA Astrophysics Data System (ADS)

Hutter, Nils; Losch, Martin; Menemenlis, Dimitris

2017-04-01

Sea ice models with the traditional viscous-plastic (VP) rheology and very high grid resolution can resolve leads and deformation rates that are localised along Linear Kinematic Features (LKF). In a 1-km pan-Arctic sea ice-ocean simulation, the small scale sea-ice deformations in the Central Arctic are evaluated with a scaling analysis in relation to satellite observations of the Envisat Geophysical Processor System (EGPS). A new coupled scaling analysis for data on Eulerian grids determines the spatial and the temporal scaling as well as the coupling between temporal and spatial scales. The spatial scaling of the modelled sea ice deformation implies multi-fractality. The spatial scaling is also coupled to temporal scales and varies realistically by region and season. The agreement of the spatial scaling and its coupling to temporal scales with satellite observations and models with the modern elasto-brittle rheology challenges previous results with VP models at coarse resolution where no such scaling was found. The temporal scaling analysis, however, shows that the VP model does not fully resolve the intermittency of sea ice deformation that is observed in satellite data.

Extent of Low-accumulation 'Wind Glaze' Areas on the East Antarctic Plateau: Implications for Continental Ice Mass Balance

NASA Technical Reports Server (NTRS)

Scambos, Theodore A.; Frezzotti, Massimo; Haran, T.; Bohlander, J.; Lenaerts, J. T. M.; Van Den Broeke, M. R.; Jezek, K.; Long, D.; Urbini, S.; Farness, K.;

Direct Comparisons of Ice Cloud Microphysical Properties Simulated by the Community Atmosphere Model CAM5 with ARM SPartICus Observations

NASA Astrophysics Data System (ADS)

Wu, C.; Liu, X.; Zhang, K.; Diao, M.; Gettelman, A.

2016-12-01

Cirrus clouds in the upper troposphere play a key role in the Earth radiation budget, and their radiative forcing depends strongly on number concentration and size distribution of ice particles. In this study we evaluate the cloud microphysical properties simulated by the Community Atmosphere Model version 5.4 (CAM5) against the Small Particles in Cirrus (SPartICus) observations over the ARM South Great Plain (SGP) site between January and June 2010. Model simulation is performed using specific dynamics to preserve prognostic meteorology (U, V, and T) close to GEOS-5 analysis. Model results collocated with SPartICus flight tracks spatially and temporally are directly compared with the observations. We compare CAM5 simulated ice crystal number concentration (Ni), ice particle size distribution, ice water content (IWC), and Ni co-variances with temperature and vertical velocity with the statistics from SPartICus observations. All analyses are restricted to T ≤ -40°C and in a 6°×6° area centered at SGP. Model sensitivity tests are performed with different ice nucleation mechanisms and with the effects of pre-existing ice crystals to reflect the uncertainties in cirrus parameterizations. In addition, different threshold size for autoconversion of cloud ice to snow (Dcs) is also tested. We find that (1) a distinctly high Ni (100-1000 L-1) often occurred in the observations but is significantly underestimated in the model, which may be due to the smaller relative humidity with respect to ice (RHi) in the simulation that could suppress the homogeneous nucleation, (2) a positive correlation exists between Ni and vertical velocity variance (σw) at horizontal scales up to 50 km in the observation, and the model can reproduce this relationship but tends to underestimate Ni when σw is relatively small, (3) simulated Ni differs greatly among the sensitive experiments, and simulated IWC is also sensitive to the cirrus parameterizations but to a lesser extent. Moreover

Abrupt shift in the observed runoff from the southwestern Greenland ice sheet

PubMed Central

Ahlstrøm, Andreas P.; Petersen, Dorthe; Langen, Peter L.; Citterio, Michele; Box, Jason E.

2017-01-01

The recent decades of accelerating mass loss of the Greenland ice sheet have arisen from an increase in both surface meltwater runoff and ice flow discharge from tidewater glaciers. Despite the role of the Greenland ice sheet as the dominant individual cryospheric contributor to sea level rise in recent decades, no observational record of its mass loss spans the 30-year period needed to assess its climatological state. We present for the first time a 40-year (1975–2014) time series of observed meltwater discharge from a >6500-km2 catchment of the southwestern Greenland ice sheet. We find that an abrupt 80% increase in runoff occurring between the 1976–2002 and 2003–2014 periods is due to a shift in atmospheric circulation, with meridional exchange events occurring more frequently over Greenland, establishing the first observation-based connection between ice sheet runoff and climate change. PMID:29242827

Arctic sea ice trends, variability and implications for seasonal ice forecasting.

PubMed

Serreze, Mark C; Stroeve, Julienne

2015-07-13

September Arctic sea ice extent over the period of satellite observations has a strong downward trend, accompanied by pronounced interannual variability with a detrended 1 year lag autocorrelation of essentially zero. We argue that through a combination of thinning and associated processes related to a warming climate (a stronger albedo feedback, a longer melt season, the lack of especially cold winters) the downward trend itself is steepening. The lack of autocorrelation manifests both the inherent large variability in summer atmospheric circulation patterns and that oceanic heat loss in winter acts as a negative (stabilizing) feedback, albeit insufficient to counter the steepening trend. These findings have implications for seasonal ice forecasting. In particular, while advances in observing sea ice thickness and assimilating thickness into coupled forecast systems have improved forecast skill, there remains an inherent limit to predictability owing to the largely chaotic nature of atmospheric variability. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

Coordinated Mapping of Sea Ice Deformation Features with Autonomous Vehicles

NASA Astrophysics Data System (ADS)

Maksym, T.; Williams, G. D.; Singh, H.; Weissling, B.; Anderson, J.; Maki, T.; Ackley, S. F.

2016-12-01

Decreases in summer sea ice extent in the Beaufort and Chukchi Seas has lead to a transition from a largely perennial ice cover, to a seasonal ice cover. This drives shifts in sea ice production, dynamics, ice types, and thickness distribution. To examine how the processes driving ice advance might also impact the morphology of the ice cover, a coordinated ice mapping effort was undertaken during a field campaign in the Beaufort Sea in October, 2015. Here, we present observations of sea ice draft topography from six missions of an Autonomous Underwater Vehicle run under different ice types and deformation features observed during autumn freeze-up. Ice surface features were also mapped during coordinated drone photogrammetric missions over each site. We present preliminary results of a comparison between sea ice surface topography and ice underside morphology for a range of sample ice types, including hummocked multiyear ice, rubble fields, young ice ridges and rafts, and consolidated pancake ice. These data are compared to prior observations of ice morphological features from deformed Antarctic sea ice. Such data will be useful for improving parameterizations of sea ice redistribution during deformation, and for better constraining estimates of airborne or satellite sea ice thickness.

Scaling Properties of Arctic Sea Ice Deformation in a High-Resolution Viscous-Plastic Sea Ice Model and in Satellite Observations

NASA Astrophysics Data System (ADS)

Hutter, Nils; Losch, Martin; Menemenlis, Dimitris

2018-01-01

Sea ice models with the traditional viscous-plastic (VP) rheology and very small horizontal grid spacing can resolve leads and deformation rates localized along Linear Kinematic Features (LKF). In a 1 km pan-Arctic sea ice-ocean simulation, the small-scale sea ice deformations are evaluated with a scaling analysis in relation to satellite observations of the Envisat Geophysical Processor System (EGPS) in the Central Arctic. A new coupled scaling analysis for data on Eulerian grids is used to determine the spatial and temporal scaling and the coupling between temporal and spatial scales. The spatial scaling of the modeled sea ice deformation implies multifractality. It is also coupled to temporal scales and varies realistically by region and season. The agreement of the spatial scaling with satellite observations challenges previous results with VP models at coarser resolution, which did not reproduce the observed scaling. The temporal scaling analysis shows that the VP model, as configured in this 1 km simulation, does not fully resolve the intermittency of sea ice deformation that is observed in satellite data.

Scaling Properties of Arctic Sea Ice Deformation in a High-Resolution Viscous-Plastic Sea Ice Model and in Satellite Observations.

PubMed

Hutter, Nils; Losch, Martin; Menemenlis, Dimitris

2018-01-01

Sea ice models with the traditional viscous-plastic (VP) rheology and very small horizontal grid spacing can resolve leads and deformation rates localized along Linear Kinematic Features (LKF). In a 1 km pan-Arctic sea ice-ocean simulation, the small-scale sea ice deformations are evaluated with a scaling analysis in relation to satellite observations of the Envisat Geophysical Processor System (EGPS) in the Central Arctic. A new coupled scaling analysis for data on Eulerian grids is used to determine the spatial and temporal scaling and the coupling between temporal and spatial scales. The spatial scaling of the modeled sea ice deformation implies multifractality. It is also coupled to temporal scales and varies realistically by region and season. The agreement of the spatial scaling with satellite observations challenges previous results with VP models at coarser resolution, which did not reproduce the observed scaling. The temporal scaling analysis shows that the VP model, as configured in this 1 km simulation, does not fully resolve the intermittency of sea ice deformation that is observed in satellite data.

ICESat Observations of Seasonal and Interannual Variations of Sea-Ice Freeboard and Estimated Thickness in the Weddell Sea, Antarctica (2003-2009)

NASA Technical Reports Server (NTRS)

Yi, Donghui; Robbins, John W.

2010-01-01

Sea-ice freeboard heights for 17 ICESat campaign periods from 2003 to 2009 are derived from ICESat data. Freeboard is combined with snow depth from Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) data and nominal densities of snow, water and sea ice, to estimate sea-ice thickness. Sea-ice freeboard and thickness distributions show clear seasonal variations that reflect the yearly cycle of growth and decay of the Weddell Sea (Antarctica) pack ice. During October-November, sea ice grows to its seasonal maximum both in area and thickness; the mean freeboards are 0.33-0.41 m and the mean thicknesses are 2.10-2.59 m. During February-March, thinner sea ice melts away and the sea-ice pack is mainly distributed in the west Weddell Sea; the mean freeboards are 0.35-0.46 m and the mean thicknesses are 1.48-1.94 m. During May-June, the mean freeboards and thicknesses are 0.26-0.29 m and 1.32-1.37 m, respectively. The 6 year trends in sea-ice extent and volume are (0.023+/-0.051) x 10(exp 6)sq km/a (0.45%/a) and (0.007+/-1.0.092) x 10(exp 3)cu km/a (0.08%/a); however, the large standard deviations indicate that these positive trends are not statistically significant.

Loss of sea ice in the Arctic.

PubMed

Perovich, Donald K; Richter-Menge, Jacqueline A

2009-01-01

The Arctic sea ice cover is in decline. The areal extent of the ice cover has been decreasing for the past few decades at an accelerating rate. Evidence also points to a decrease in sea ice thickness and a reduction in the amount of thicker perennial sea ice. A general global warming trend has made the ice cover more vulnerable to natural fluctuations in atmospheric and oceanic forcing. The observed reduction in Arctic sea ice is a consequence of both thermodynamic and dynamic processes, including such factors as preconditioning of the ice cover, overall warming trends, changes in cloud coverage, shifts in atmospheric circulation patterns, increased export of older ice out of the Arctic, advection of ocean heat from the Pacific and North Atlantic, enhanced solar heating of the ocean, and the ice-albedo feedback. The diminishing Arctic sea ice is creating social, political, economic, and ecological challenges.

Direct observations of evolving subglacial drainage beneath the Greenland Ice Sheet.

PubMed

Andrews, Lauren C; Catania, Ginny A; Hoffman, Matthew J; Gulley, Jason D; Lüthi, Martin P; Ryser, Claudia; Hawley, Robert L; Neumann, Thomas A

2014-10-02

Seasonal acceleration of the Greenland Ice Sheet is influenced by the dynamic response of the subglacial hydrologic system to variability in meltwater delivery to the bed via crevasses and moulins (vertical conduits connecting supraglacial water to the bed of the ice sheet). As the melt season progresses, the subglacial hydrologic system drains supraglacial meltwater more efficiently, decreasing basal water pressure and moderating the ice velocity response to surface melting. However, limited direct observations of subglacial water pressure mean that the spatiotemporal evolution of the subglacial hydrologic system remains poorly understood. Here we show that ice velocity is well correlated with moulin hydraulic head but is out of phase with that of nearby (0.3-2 kilometres away) boreholes, indicating that moulins connect to an efficient, channelized component of the subglacial hydrologic system, which exerts the primary control on diurnal and multi-day changes in ice velocity. Our simultaneous measurements of moulin and borehole hydraulic head and ice velocity in the Paakitsoq region of western Greenland show that decreasing trends in ice velocity during the latter part of the melt season cannot be explained by changes in the ability of moulin-connected channels to convey supraglacial melt. Instead, these observations suggest that decreasing late-season ice velocity may be caused by changes in connectivity in unchannelized regions of the subglacial hydrologic system. Understanding this spatiotemporal variability in subglacial pressures is increasingly important because melt-season dynamics affect ice velocity beyond the conclusion of the melt season.

Comparing elevation and freeboard from IceBridge and four different CryoSat-2 retrackers for coincident sea ice observations

NASA Astrophysics Data System (ADS)

Yi, D.; Kurtz, N. T.; Harbeck, J.

2017-12-01

The airborne IceBridge and spaceborne Cryosat-2 missions observe polar sea ice at different altitudes with different footprint sizes and often at different time and locations. Many studies use different retrackers to derive Cryosat-2 surface elevation, which we find causes large differences in the elevation and freeboard comparisons of IceBridge and Cryosat-2. In this study, we compare sea ice surface elevation and freeboard using 8 coincident CryoSat-2, ATM, and LVIS observations with IceBridge airplanes under flying the Cryosat-2 ground tracks. We apply identical ellipsoid, geoid model, tide model, and atmospheric correction to CryoSat-2 and IceBridge data to reduce elevation bias due to their differences. IceBridge's ATM and LVIS elevation and freeboard and Snow Radar snow depth are averaged at each CryoSat-2 footprint for comparison. The four different Cryosat-2 retrackers (ESA, GSFC, AWI, and JPL) show distinct differences in mean elevation up to 0.35 meters over leads and over floes, which suggests that systematic elevation bias exists between the retrackers. The mean IceBridge elevation over leads is within the mean elevation distribution of the four Cryosat-2 retrackers. The mean IceBridge elevation over floes is above the mean elevation distribution of the four Cryosat-2 retrackers. After removing the snow depth from IceBridge elevation, over floe, the mean elevation of IceBridge is within the mean elevation distribution of the four Cryosat-2 retrackers. By identifying the strengths and weaknesses of the retrackers, this study provides a mechanism to improve freeboard retrievals from existing methods.

Ice formation and development in aged, wintertime cumulus over the UK : observations and modelling

NASA Astrophysics Data System (ADS)

Crawford, I.; Bower, K. N.; Choularton, T. W.; Dearden, C.; Crosier, J.; Westbrook, C.; Capes, G.; Coe, H.; Connolly, P.; Dorsey, J. R.; Gallagher, M. W.; Williams, P.; Trembath, J.; Cui, Z.; Blyth, A.

2011-11-01

In-situ high resolution aircraft measurements of cloud microphysical properties were made in coordination with ground based remote sensing observations of Radar and Lidar as part of the Aerosol Properties, PRocesses And InfluenceS on the Earth's climate (APPRAISE) project. A narrow but extensive line (~100 km long) of shallow convective clouds over the southern UK was studied. Cloud top temperatures were observed to be higher than ~-8 °C, but the clouds were seen to consist of supercooled droplets and varying concentrations of ice particles. No ice particles were observed to be falling into the cloud tops from above. Current parameterisations of ice nuclei (IN) numbers predict too few particles will be active as ice nuclei to account for ice particle concentrations at the observed near cloud top temperatures (~-7 °C). The role of biological particles, consistent with concentrations observed near the surface, acting as potential efficient high temperature IN is considered important in this case. It was found that very high concentrations of ice particles (up to 100 L-1) could be produced by powerful secondary ice particle production emphasising the importance of understanding primary ice formation in slightly supercooled clouds. Aircraft penetrations at -3.5 °C, showed peak ice crystal concentrations of up to 100 L-1 which together with the characteristic ice crystal habits observed (generally rimed ice particles and columns) suggested secondary ice production had occurred. To investigate whether the Hallett-Mossop (HM) secondary ice production process could account for these observations, ice splinter production rates were calculated. These calculated rates and observations could only be reconciled provided the constraint that only droplets >24 μm in diameter could lead to splinter production, was relaxed slightly by 2 μm. Model simulations of the case study were also performed with the WRF (Weather, Research and Forecasting) model and ACPIM (Aerosol Cloud and

Chacterization of Teleseismic Earthquakes Observed on an Ice Shelf

NASA Astrophysics Data System (ADS)

Baker, M. G.; Aster, R. C.; Anthony, R. E.; Wiens, D.; Nyblade, A.; Bromirski, P. D.; Stephen, R. A.; Gerstoft, P.

2016-12-01

Broadband seismographs deployed atop large tabular icebergs and ice shelves record a rich superposition of atmospheric, oceanic, and solid earth signals. We characterize these signals, including body and surface wave arrivals from approximately 200 global earthquakes, using a 34-station broadband array spanning the Ross Ice Shelf, Antarctica. Teleseismic earthquake arrivals are essential for constructing models of crustal and upper mantle structure, and observations on the ice shelf are key to resolving the structure of the underlying West Antarctic Rift System. To test the plausibility of passive imaging in this unique environment, we examine seasonal and spatial dependence of signal-to-noise ratios of body wave arrivals and the impact of ice shelf dynamics on surface wave dispersion. We also note unusual phase mechanics arising from the floating platform geometry.

Degree of Ice Particle Surface Roughness Inferred from Polarimetric Observations

NASA Technical Reports Server (NTRS)

Hioki, Souichiro; Yang, Ping; Baum, Bryan A.; Platnick, Steven; Meyer, Kerry G.; King, Michael D.; Riedi, Jerome

2016-01-01

The degree of surface roughness of ice particles within thick, cold ice clouds is inferred from multidirectional, multi-spectral satellite polarimetric observations over oceans, assuming a column-aggregate particle habit. An improved roughness inference scheme is employed that provides a more noise-resilient roughness estimate than the conventional best-fit approach. The improvements include the introduction of a quantitative roughness parameter based on empirical orthogonal function analysis and proper treatment of polarization due to atmospheric scattering above clouds. A global 1-month data sample supports the use of a severely roughened ice habit to simulate the polarized reflectivity associated with ice clouds over ocean. The density distribution of the roughness parameter inferred from the global 1- month data sample and further analyses of a few case studies demonstrate the significant variability of ice cloud single-scattering properties. However, the present theoretical results do not agree with observations in the tropics. In the extra-tropics, the roughness parameter is inferred but 74% of the sample is out of the expected parameter range. Potential improvements are discussed to enhance the depiction of the natural variability on a global scale.

Iceberg severity off eastern North America: Its relationship to sea ice variability and climate change

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marko, J.R.; Fissel, D.B.; Wadhams, P.

1994-09-01

Iceberg trajectory, deterioration (mass loss), and sea ice data are reviewed to identify the sources of observed interannual and seasonal variations in the numbers of icebergs passing south of 48[degrees]N off eastern North America. The results show the dominant role of sea ice in the observed variations. Important mechanisms involved include both seasonal modulation of the southerly iceberg flow by ice cover control of probabilities for entrapment and decay in shallow water, and the suppression of iceberg melt/deterioration rates by high concentrations of sea ice. The Labrador spring ice extent, shown to be the critical parameter in interannual iceberg numbermore » variability, was found to be either determined by or closely correlated with midwinter Davis Strait ice extents. Agreement obtained between observed year-to-year and seasonal number variations with computations based upon a simple iceberg dissipation model suggests that downstream iceberg numbers are relatively insensitive to iceberg production rates and to fluctuations in southerly iceberg fluxes in areas north of Baffin Island. Past variations in the Davis Strait ice index and annual ice extents are studied to identify trends and relationships between regional and larger-scale global climate parameters. It was found that, on decadal timescales in the post-1960 period of reasonable data quality, regional climate parameters have varied, roughly, out of phase with corresponding global and hemispheric changes. These observations are compared with expectations in terms of model results to evaluate current GCM-based capabilities for simulating recent regional behavior. 64 refs., 11 figs., 3 tabs.« less

Mars Global Surveyor TES Results: Observations of Water Ice Clouds

NASA Technical Reports Server (NTRS)

Pearl, John C.; Smith, M. D.; Conrath, B. J.; Bandfield, J. L.; Christensen, P. R.

1999-01-01

On July 31, 1999, Mars Global Surveyor completed its first martian year in orbit. During this time, the Thermal Emission Spectrometer (TES) experiment gathered extensive data on water ice clouds. We report here on three types of martian clouds. 1) Martian southern summer has long been characterized as the season when the most severe dust storms occur. It is now apparent that northern spring/summer is characterized as a time of substantial low latitude ice clouds [1]. TES observations beginning in the northern summer (Lsubs=107) show a well developed cloud belt between 10S and 30N latitude; 12 micron opacities were typically 0.15. This system decreased dramatically after Lsubs= 130. Thereafter, remnants were most persistent over the Tharsis ridge. 2) Clouds associated with major orographic features follow a different pattern [2]. Clouds of this type were present prior to the regional Noachis dust storm of 1997. They disappeared with the onset of the storm, but reappeared rather quickly following its decay. Typical infrared opacities were near 0.5. 3) Extensive, very thin clouds are also widespread [3]. Found at high altitudes (above 35 km), their opacities are typically a few hundredths. At times, such as in northern spring, these clouds are limited in their northern extent only by the southern edge of the polar vortex. We describe the distribution, infrared optical properties, and seasonal trends of these systems during the first martian year of TES operations.

Arctic Sea Ice Parameters from AMSR-E Data using Two Techniques, and Comparisons with Sea Ice from SSM

NASA Technical Reports Server (NTRS)

Comiso, Josefino C.; Parkinson, Claire L.

2007-01-01

We use two algorithms to process AMSR-E data in order to determine algorithm dependence, if any, on the estimates of sea ice concentration, ice extent and area, and trends and to evaluate how AMSR-E data compare with historical SSM/I data. The monthly ice concentrations derived from the two algorithms from AMSR-E data (the AMSR-E Bootstrap Algorithm, or ABA, and the enhanced NASA Team algorithm, or NT2) differ on average by about 1 to 3%, with data from the consolidated ice region being generally comparable for ABA and NT2 retrievals while data in the marginal ice zones and thin ice regions show higher values when the NT2 algorithm is used. The ice extents and areas derived separately from AMSR-E using these two algorithms are, however, in good agreement, with the differences (ABA-NT2) being about 6.6 x 10(exp 4) square kilometers on average for ice extents and -6.6 x 10(exp 4) square kilometers for ice area which are small compared to mean seasonal values of 10.5 x 10(exp 6) and 9.8 x 10(exp 6) for ice extent and area: respectively. Likewise, extents and areas derived from the same algorithm but from AMSR-E and SSM/I data are consistent but differ by about -24.4 x 10(exp 4) square kilometers and -13.9 x 10(exp 4) square kilometers, respectively. The discrepancies are larger with the estimates of extents than area mainly because of differences in channel selection and sensor resolutions. Trends in extent during the AMSR-E era were also estimated and results from all three data sets are shown to be in good agreement (within errors).

Interactions Between Ice Thickness, Bottom Ice Algae, and Transmitted Spectral Irradiance in the Chukchi Sea

NASA Astrophysics Data System (ADS)

Arntsen, A. E.; Perovich, D. K.; Polashenski, C.; Stwertka, C.

2015-12-01

The amount of light that penetrates the Arctic sea ice cover impacts sea-ice mass balance as well as ecological processes in the upper ocean. The seasonally evolving macro and micro spatial variability of transmitted spectral irradiance observed in the Chukchi Sea from May 18 to June 17, 2014 can be primarily attributed to variations in snow depth, ice thickness, and bottom ice algae concentrations. This study characterizes the interactions among these dominant variables using observed optical properties at each sampling site. We employ a normalized difference index to compute estimates of Chlorophyll a concentrations and analyze the increased attenuation of incident irradiance due to absorption by biomass. On a kilometer spatial scale, the presence of bottom ice algae reduced the maximum transmitted irradiance by about 1.5 orders of magnitude when comparing floes of similar snow and ice thicknesses. On a meter spatial scale, the combined effects of disparities in the depth and distribution of the overlying snow cover along with algae concentrations caused maximum transmittances to vary between 0.0577 and 0.282 at a single site. Temporal variability was also observed as the average integrated transmitted photosynthetically active radiation increased by one order of magnitude to 3.4% for the last eight measurement days compared to the first nine. Results provide insight on how interrelated physical and ecological parameters of sea ice in varying time and space may impact new trends in Arctic sea ice extent and the progression of melt.

The Arctic sea ice cover of 2016: a year of record-low highs and higher-than-expected lows

NASA Astrophysics Data System (ADS)

Petty, Alek A.; Stroeve, Julienne C.; Holland, Paul R.; Boisvert, Linette N.; Bliss, Angela C.; Kimura, Noriaki; Meier, Walter N.

2018-02-01

The Arctic sea ice cover of 2016 was highly noteworthy, as it featured record low monthly sea ice extents at the start of the year but a summer (September) extent that was higher than expected by most seasonal forecasts. Here we explore the 2016 Arctic sea ice state in terms of its monthly sea ice cover, placing this in the context of the sea ice conditions observed since 2000. We demonstrate the sensitivity of monthly Arctic sea ice extent and area estimates, in terms of their magnitude and annual rankings, to the ice concentration input data (using two widely used datasets) and to the averaging methodology used to convert concentration to extent (daily or monthly extent calculations). We use estimates of sea ice area over sea ice extent to analyse the relative "compactness" of the Arctic sea ice cover, highlighting anomalously low compactness in the summer of 2016 which contributed to the higher-than-expected September ice extent. Two cyclones that entered the Arctic Ocean during August appear to have driven this low-concentration/compactness ice cover but were not sufficient to cause more widespread melt-out and a new record-low September ice extent. We use concentration budgets to explore the regions and processes (thermodynamics/dynamics) contributing to the monthly 2016 extent/area estimates highlighting, amongst other things, rapid ice intensification across the central eastern Arctic through September. Two different products show significant early melt onset across the Arctic Ocean in 2016, including record-early melt onset in the North Atlantic sector of the Arctic. Our results also show record-late 2016 freeze-up in the central Arctic, North Atlantic and the Alaskan Arctic sector in particular, associated with strong sea surface temperature anomalies that appeared shortly after the 2016 minimum (October onwards). We explore the implications of this low summer ice compactness for seasonal forecasting, suggesting that sea ice area could be a more reliable

NASA IceBridge: Scientific Insights from Airborne Surveys of the Polar Sea Ice Covers

NASA Astrophysics Data System (ADS)

Richter-Menge, J.; Farrell, S. L.

2015-12-01

The NASA Operation IceBridge (OIB) airborne sea ice surveys are designed to continue a valuable series of sea ice thickness measurements by bridging the gap between NASA's Ice, Cloud and Land Elevation Satellite (ICESat), which operated from 2003 to 2009, and ICESat-2, which is scheduled for launch in 2017. Initiated in 2009, OIB has conducted campaigns over the western Arctic Ocean (March/April) and Southern Oceans (October/November) on an annual basis when the thickness of sea ice cover is nearing its maximum. More recently, a series of Arctic surveys have also collected observations in the late summer, at the end of the melt season. The Airborne Topographic Mapper (ATM) laser altimeter is one of OIB's primary sensors, in combination with the Digital Mapping System digital camera, a Ku-band radar altimeter, a frequency-modulated continuous-wave (FMCW) snow radar, and a KT-19 infrared radiation pyrometer. Data from the campaigns are available to the research community at: http://nsidc.org/data/icebridge/. This presentation will summarize the spatial and temporal extent of the OIB campaigns and their complementary role in linking in situ and satellite measurements, advancing observations of sea ice processes across all length scales. Key scientific insights gained on the state of the sea ice cover will be highlighted, including snow depth, ice thickness, surface roughness and morphology, and melt pond evolution.

Sea Ice

NASA Technical Reports Server (NTRS)

Parkinson, Claire L.; Cavalieri, Donald J.

2005-01-01

Sea ice covers vast areas of the polar oceans, with ice extent in the Northern Hemisphere ranging from approximately 7 x 10(exp 6) sq km in September to approximately 15 x 10(exp 6) sq km in March and ice extent in the Southern Hemisphere ranging from approximately 3 x 10(exp 6) sq km in February to approximately 18 x 10(exp 6) sq km in September. These ice covers have major impacts on the atmosphere, oceans, and ecosystems of the polar regions, and so as changes occur in them there are potential widespread consequences. Satellite data reveal considerable interannual variability in both polar sea ice covers, and many studies suggest possible connections between the ice and various oscillations within the climate system, such as the Arctic Oscillation, North Atlantic Oscillation, and Antarctic Oscillation, or Southern Annular Mode. Nonetheless, statistically significant long-term trends are also apparent, including overall trends of decreased ice coverage in the Arctic and increased ice coverage in the Antarctic from late 1978 through the end of 2003, with the Antarctic ice increases following marked decreases in the Antarctic ice during the 1970s. For a detailed picture of the seasonally varying ice cover at the start of the 21st century, this chapter includes ice concentration maps for each month of 2001 for both the Arctic and the Antarctic, as well as an overview of what the satellite record has revealed about the two polar ice covers from the 1970s through 2003.

The Arctic's sea ice cover: trends, variability, predictability, and comparisons to the Antarctic.

PubMed

Serreze, Mark C; Meier, Walter N

2018-05-28

As assessed over the period of satellite observations, October 1978 to present, there are downward linear trends in Arctic sea ice extent for all months, largest at the end of the melt season in September. The ice cover is also thinning. Downward trends in extent and thickness have been accompanied by pronounced interannual and multiyear variability, forced by both the atmosphere and ocean. As the ice thins, its response to atmospheric and oceanic forcing may be changing. In support of a busier Arctic, there is a growing need to predict ice conditions on a variety of time and space scales. A major challenge to providing seasonal scale predictions is the 7-10 days limit of numerical weather prediction. While a seasonally ice-free Arctic Ocean is likely well within this century, there is much uncertainty in the timing. This reflects differences in climate model structure, the unknown evolution of anthropogenic forcing, and natural climate variability. In sharp contrast to the Arctic, Antarctic sea ice extent, while highly variable, has increased slightly over the period of satellite observations. The reasons for this different behavior remain to be resolved, but responses to changing atmospheric circulation patterns appear to play a strong role. © 2018 New York Academy of Sciences.

Observation of sea-ice dynamics using synthetic aperture radar images: Automated analysis

NASA Technical Reports Server (NTRS)

Vesecky, John F.; Samadani, Ramin; Smith, Martha P.; Daida, Jason M.; Bracewell, Ronald N.

1988-01-01

The European Space Agency's ERS-1 satellite, as well as others planned to follow, is expected to carry synthetic-aperture radars (SARs) over the polar regions beginning in 1989. A key component in utilization of these SAR data is an automated scheme for extracting the sea-ice velocity field from a time sequence of SAR images of the same geographical region. Two techniques for automated sea-ice tracking, image pyramid area correlation (hierarchical correlation) and feature tracking, are described. Each technique is applied to a pair of Seasat SAR sea-ice images. The results compare well with each other and with manually tracked estimates of the ice velocity. The advantages and disadvantages of these automated methods are pointed out. Using these ice velocity field estimates it is possible to construct one sea-ice image from the other member of the pair. Comparing the reconstructed image with the observed image, errors in the estimated velocity field can be recognized and a useful probable error display created automatically to accompany ice velocity estimates. It is suggested that this error display may be useful in segmenting the sea ice observed into regions that move as rigid plates of significant ice velocity shear and distortion.

The influence of the hydrologic cycle on the extent of sea ice with climatic implications

NASA Technical Reports Server (NTRS)

Dean, Ken; Gosink, Joan

1991-01-01

The role was analyzed of the hydrologic cycle on the distribution of sea ice, and its influence on forcings and fluxes between the marine environment and the atmosphere. River discharge plays a significant role in degrading the sea ice before any melting occurs elsewhere along the coast. The influence is considered of river discharge on the albedo, thermal balance, and distribution of sea ice. Quantitative atmospheric-hydrologic models are being developed to describe these processes in the coastal zone. Input for the models will come from satellite images, hydrologic data, and field observations. The resulting analysis provides a basis for the study of the significance of the hydrologic cycle throughout the Arctic Basin and its influence on the regional climate as a result of possible climatic scenarios. The area offshore from the Mackenzie River delta was selected as the study area.

Predictability of the Arctic sea ice edge

NASA Astrophysics Data System (ADS)

Goessling, H. F.; Tietsche, S.; Day, J. J.; Hawkins, E.; Jung, T.

2016-02-01

Skillful sea ice forecasts from days to years ahead are becoming increasingly important for the operation and planning of human activities in the Arctic. Here we analyze the potential predictability of the Arctic sea ice edge in six climate models. We introduce the integrated ice-edge error (IIEE), a user-relevant verification metric defined as the area where the forecast and the "truth" disagree on the ice concentration being above or below 15%. The IIEE lends itself to decomposition into an absolute extent error, corresponding to the common sea ice extent error, and a misplacement error. We find that the often-neglected misplacement error makes up more than half of the climatological IIEE. In idealized forecast ensembles initialized on 1 July, the IIEE grows faster than the absolute extent error. This means that the Arctic sea ice edge is less predictable than sea ice extent, particularly in September, with implications for the potential skill of end-user relevant forecasts.

Variability and Anomalous Trends in the Global Sea Ice Cover

NASA Technical Reports Server (NTRS)

Comiso, Josefino C.

2012-01-01

The advent of satellite data came fortuitously at a time when the global sea ice cover has been changing rapidly and new techniques are needed to accurately assess the true state and characteristics of the global sea ice cover. The extent of the sea ice in the Northern Hemisphere has been declining by about -4% per decade for the period 1979 to 2011 but for the period from 1996 to 2010, the rate of decline became even more negative at -8% per decade, indicating an acceleration in the decline. More intriguing is the drastically declining perennial sea ice area, which is the ice that survives the summer melt and observed to be retreating at the rate of -14% per decade during the 1979 to 2012 period. Although a slight recovery occurred in the last three years from an abrupt decline in 2007, the perennial ice extent was almost as low as in 2007 in 2011. The multiyear ice, which is the thick component of the perennial ice and regarded as the mainstay of the Arctic sea ice cover is declining at an even higher rate of -19% per decade. The more rapid decline of the extent of this thicker ice type means that the volume of the ice is also declining making the survival of the Arctic ice in summer highly questionable. The slight recovery in 2008, 2009 and 2010 for the perennial ice in summer was likely associated with an apparent cycle in the time series with a period of about 8 years. Results of analysis of concurrent MODIS and AMSR-E data in summer also provide some evidence of more extensive summer melt and meltponding in 2007 and 2011 than in other years. Meanwhile, the Antarctic sea ice cover, as observed by the same set of satellite data, is showing an unexpected and counter intuitive increase of about 1 % per decade over the same period. Although a strong decline in ice extent is apparent in the Bellingshausen/ Amundsen Seas region, such decline is more than compensated by increases in the extent of the sea ice cover in the Ross Sea region. The results of analysis of

Sea Ice Sensitivities in the 0.72 deg and 0.08 deg Arctic Cap Coupled HYCOM/CICE Models

DTIC Science & Technology

2014-09-30

1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Sea Ice Sensitivities in the 0.72°and 0.08° Arctic Cap...Arctic ice extent, which corresponds to the sea ice that remains during the summer minimum, has decreased over the years 1979–2007 by more than 10% per...Goosse et al. 2009) with the lowest observed sea ice extent in the satellite record (1979-present) occurring in September 2012 (Perovich et al. 2012

Simulation of the Greenland Ice Sheet over two glacial-interglacial cycles: investigating a sub-ice-shelf melt parameterization and relative sea level forcing in an ice-sheet-ice-shelf model

NASA Astrophysics Data System (ADS)

Bradley, Sarah L.; Reerink, Thomas J.; van de Wal, Roderik S. W.; Helsen, Michiel M.

2018-05-01

Observational evidence, including offshore moraines and sediment cores, confirm that at the Last Glacial Maximum (LGM) the Greenland ice sheet (GrIS) expanded to a significantly larger spatial extent than seen at present, grounding into Baffin Bay and out onto the continental shelf break. Given this larger spatial extent and its close proximity to the neighbouring Laurentide Ice Sheet (LIS) and Innuitian Ice Sheet (IIS), it is likely these ice sheets will have had a strong non-local influence on the spatial and temporal behaviour of the GrIS. Most previous paleo ice-sheet modelling simulations recreated an ice sheet that either did not extend out onto the continental shelf or utilized a simplified marine ice parameterization which did not fully include the effect of ice shelves or neglected the sensitivity of the GrIS to this non-local bedrock signal from the surrounding ice sheets. In this paper, we investigated the evolution of the GrIS over the two most recent glacial-interglacial cycles (240 ka BP to the present day) using the ice-sheet-ice-shelf model IMAU-ICE. We investigated the solid earth influence of the LIS and IIS via an offline relative sea level (RSL) forcing generated by a glacial isostatic adjustment (GIA) model. The RSL forcing governed the spatial and temporal pattern of sub-ice-shelf melting via changes in the water depth below the ice shelves. In the ensemble of simulations, at the glacial maximums, the GrIS coalesced with the IIS to the north and expanded to the continental shelf break to the southwest but remained too restricted to the northeast. In terms of the global mean sea level contribution, at the Last Interglacial (LIG) and LGM the ice sheet added 1.46 and -2.59 m, respectively. This LGM contribution by the GrIS is considerably higher (˜ 1.26 m) than most previous studies whereas the contribution to the LIG highstand is lower (˜ 0.7 m). The spatial and temporal behaviour of the northern margin was highly variable in all simulations

Sea Ice and Hydrographic Variability in the Northwest North Atlantic

NASA Astrophysics Data System (ADS)

Fenty, I. G.; Heimbach, P.; Wunsch, C. I.

2010-12-01

marginal ice zone is mainly ablated via large sustained turbulent ocean enthalpy fluxes. The sensible heat required for these sustained fluxes is drawn from a reservoir of warm subsurface waters of subtropical origin entrained into the mixed layer via convective mixing. Analysis of ocean surface buoyancy fluxes during the period preceding quasi-equilibrium reveals that low-salinity upper ocean anomalies are required for ice to advance seaward of the Arctic Water/Irminger Water thermohaline front in the northern Labrador Sea. Anomalous low-salinity waters inhibit mixed layer deepening, shielding the advancing ice pack from the subsurface heat reservoir, and are conducive to a positive surface stratification enhancement feedback from ice meltwater release. Interestingly, the climatological location of the front coincides with the minimum observed wintertime ice extent; positive ice extent anomalies may require hydrographic preconditioning. If true, the export of low-salinity anomalies from melting Arctic ice associated with future warming may be predicted to lead positive ice extent anomalies in Labrador Sea via the positive surface stratification enhancement mechanism feedback outlined above.

Summer 2007 and 2008 Arctic Sea Ice Loss in Context: OUTLOOK 2008

NASA Astrophysics Data System (ADS)

Overland, J. E.; Eicken, H.; Wiggins, H. V.

2008-12-01

The Arctic is changing faster than the publication cycle for new information. In response, the SEARCH and DAMOCLES Programs initiated an OUTLOOK 2008 to provide broad-based communication and assessment within the arctic science community on the causes of rapid summer sea ice loss, synthesizing information from Arctic observing networks and model simulations. The question for summer 2008 was whether the previous loss of multi-year sea ice and delay in sea ice formation in autumn 2007 would still allow sufficient winter growth of sea ice thickness to last through the summer 2008, potentially allowing for recovery from the 2007 minimum. The answer is no; summer 2008 was a second sequential year of extremely low minimum sea ice extent. To organize OUTLOOK 2008, respondents were asked in May, June and July to provide a rationale and semi-quantitative assessment of arctic sea ice extent anticipated for September 2008. OUTLOOK 2008 supplemented information maintained by ice centers, universities and other data providers. Using a range of methods, all of the approximately 20 groups responded that summer sea ice would not return to climatological mean conditions, with a median response near the 2007 extent. The range of responses depended on the relative weight given to "initial conditions," e.g., age and thickness of sea ice at the end of spring, versus whether summer winds in 2008 would be as supportive for ice loss as in 2007. Initial conditions turned out to be a primary factor for summer 2008, with implications for continued sea ice loss in future years. OUTLOOK 2008 highlighted aspects of the observation and modeling efforts that require further attention such as interpretation of summer microwave signatures, in situ buoy measurements, and data assimilation in models. We appreciate the contributions from respondents and reviewers who made OUTLOOK 2008 a success.

Development of global sea ice 6.0 CICE configuration for the Met Office global coupled model

DOE PAGES

Rae, J. . G. L; Hewitt, H. T.; Keen, A. B.; ...

2015-03-05

The new sea ice configuration GSI6.0, used in the Met Office global coupled configuration GC2.0, is described and the sea ice extent, thickness and volume are compared with the previous configuration and with observationally-based datasets. In the Arctic, the sea ice is thicker in all seasons than in the previous configuration, and there is now better agreement of the modelled concentration and extent with the HadISST dataset. In the Antarctic, a warm bias in the ocean model has been exacerbated at the higher resolution of GC2.0, leading to a large reduction in ice extent and volume; further work is requiredmore » to rectify this in future configurations.« less

Winter ocean-ice interactions under thin sea ice observed by IAOOS platforms during N-ICE2015: Salty surface mixed layer and active basal melt

NASA Astrophysics Data System (ADS)

Koenig, Zoé; Provost, Christine; Villacieros-Robineau, Nicolas; Sennéchael, Nathalie; Meyer, Amelie

2016-10-01

IAOOS (Ice Atmosphere Arctic Ocean Observing System) platforms, measuring physical parameters at the atmosphere-snow-ice-ocean interface deployed as part of the N-ICE2015 campaign, provide new insights on winter conditions North of Svalbard. The three regions crossed during the drifts, the Nansen Basin, the Sofia Deep, and the Svalbard northern continental slope featured distinct hydrographic properties and ice-ocean exchanges. In the Nansen Basin, the quiescent warm layer was capped by a stepped halocline (60 and 110 m) and a deep thermocline (110 m). Ice was forming and the winter mixed layer salinity was larger by ˜0.1 g/kg than previously observed. Over the Svalbard continental slope, the Atlantic Water (AW) was very shallow (20 m from the surface) and extended offshore from the 500 m isobath by a distance of about 70 km, sank along the slope (40 m from the surface) and probably shed eddies into the Sofia Deep. In the Sofia Deep, relatively warm waters of Atlantic origin extended from 90 m downward. Resulting from different pathways, these waters had a wide range of hydrographic characteristics. Sea-ice melt was widespread over the Svalbard continental slope and ocean-to-ice heat fluxes reached values of 400 W m-2 (mean of ˜150 W m-2 over the continental slope). Sea-ice melt events were associated with near 12 h fluctuations in the mixed-layer temperature and salinity corresponding to the periodicity of tides and near-inertial waves potentially generated by winter storms, large barotropic tides over steep topography, and/or geostrophic adjustments.

Surface Exposure Dating of the Huancané III Moraines in Peru: A Record of Quelccaya Ice Cap's Maximum Extent during the Last Glacial Period

NASA Astrophysics Data System (ADS)

Baranes, H. E.; Kelly, M. A.; Stroup, J. S.; Howley, J. A.; Lowell, T. V.

2012-12-01

The climatic conditions that influenced the tropics during the height of the last glacial period are not well defined and controversial. There are disparities in estimates of temperature anomalies (e.g., MARGO, 2009; Rind and Peteet, 1985; CLIMAP, 1976), and critical terrestrial paleotemperature proxy records in tropical regions are poorly dated (e.g., Porter, 2001). Defining these conditions is important for understanding the mechanisms that cause major shifts in climate, as the tropics are a primary driver of atmospheric and oceanic circulation. This study aims to constrain the timing of maximum glacier extents in the Cordillera Oriental in southern Peru during the last glacial period by applying surface exposure (beryllium-10) dating to the Huancané III (Hu-III) moraines. The Hu-III moraines mark the maximum extent of Quelccaya Ice Cap (QIC) (13.93°S, 70.83°W), the largest tropical ice cap, during the last ice age. The eight beryllium-10 ages presented here yield 17,056 ± 520 yrs ago as a minimum age for the onset of recession from the ice cap advance marked by the Hu-III moraines. Comparing this age to other paleoclimate records indicates that the ice cap advance marked by the Hu-III moraines is more likely associated with a North Atlantic climate event known as Heinrich I (H1; 16,800 yrs ago, Bond et al., 1992, 1993) than with global cooling at the Last Glacial Maximum (LGM; ~21,000 yrs ago, Denton and Hughes, 1981). This result suggests that climate processes in the North Atlantic region are linked to climatic conditions in the tropical Andes. A mesoscale climate model and an ice-flow model are currently being developed for QIC. The moraine data presented in this study will be used with these two models to test response of QIC to North Atlantic and global climate events.

What Governs Ice-Sticking in Planetary Science Experiments?

NASA Astrophysics Data System (ADS)

Gaertner, Sabrina; Gundlach, B.; Blum, J.; Fraser, H. J.

2018-06-01

Water ice plays an important role, alongside dust, in current theories of planet formation. Decades of laboratory experiments have proven that water ice is far stickier in particle collisions than dust. However, water ice is known to be a metastable material. Its physical properties strongly depend on its environmental parameters, the foremost being temperature and pressure. As a result, the properties of ice change not only with the environment it is observed in, but also with its thermal history.The abundance of ice structures that can be created by different environments likely explains the discrepancies observed across the multitude of collisional laboratory studies in the past [1-16]; unless the ices for such experiments have been prepared in the same way and are collided under the same environmental conditions, these experiments simply do not collide the same ices.This raises several questions:1. Which conditions and ice properties are most favourable for ice sticking?2. Which conditions and ice properties are closest to the ones observed in protoplanetary disks?3. To what extent do these two regimes overlap?4. Consequently, which collisional studies are most relevant to planetary science and therefore best suited to inform models of planet formation?In this presentation, I will give a non-exhaustive overview of what we already know about the properties of ice particles, covering those used in planetary science experiments and those observed in planet forming regions. I will discuss to what extent we can already answer questions 1-3, and what information we still need to obtain from observations, laboratory experiments, and modelling to be able to answer question 4.References:1. Bridges et al. 1984 Natur 309.2. Bridges et al. 1996 Icar 123.3. Deckers & Teiser 2016 MNRAS 456.4. Dilley & Crawford 1996 JGRE 101.5. Gundlach & Blum 2015 ApJ 798.6. Hatzes et al. 1991 Icar 89.7. Hatzes et al. 1988 MNRAS 231.8. Heißelmann et al. 2010 Icar 206.9. Higa et al. 1996 P

Numerical model of ice melange expansion during abrupt ice-shelf collapse

NASA Astrophysics Data System (ADS)

Guttenberg, N.; Abbot, D. S.; Amundson, J. M.; Burton, J. C.; Cathles, L. M.; Macayeal, D. R.; Zhang, W.

2010-12-01

Satellite imagery of the February 2008 Wilkins Ice-Shelf Collapse event reveals that a large percentage of the involved ice shelf was converted to capsized icebergs and broken fragments of icebergs over a relatively short period of time, possibly less than 24 hours. The extreme violence and short time scale of the event, and the considerable reduction of gravitational potential energy between upright and capsized icebergs, suggests that iceberg capsize might be an important driving mechanism controlling both the rate and spatial extent of ice shelf collapse. To investigate this suggestion, we have constructed an idealized, 2-dimensional model of a disintegrating ice shelf composed of a large number (N~100 to >1000) of initially well-packed icebergs of rectangular cross section. The model geometry consists of a longitudinal cross section of the idealized ice shelf from grounding line (or the upstream extent of ice-shelf fragmentation) to seaward ice front, and includes the region beyond the initial ice front to cover the open, ice-free water into which the collapsing ice shelf expands. The seawater in which the icebergs float is treated as a hydrostatic fluid in the computation of iceberg orientation (e.g., the evaluation of buoyancy forces and torques), thereby eliminating the complexities of free-surface waves, but net horizontal drift of the icebergs is resisted by a linear drag law designed to energy dissipation by viscous forces and surface-gravity-wave radiation. Icebergs interact via both elastic and inelastic contacts (typically a corner of one iceberg will scrape along the face of its neighbor). Ice-shelf collapse in the model is embodied by the mass capsize of a large proportion of the initially packed icebergs and the consequent advancement of the ice front (leading edge). Model simulations are conducted to examine (a) the threshold of stability (e.g., what density of initially capsizable icebergs is needed to allow a small perturbation to the system

Time-dependence of sea-ice concentration and multiyear ice fraction in the Arctic Basin

USGS Publications Warehouse

Gloersen, P.; Zwally, H.J.; Chang, A.T.C.; Hall, D.K.; Campbell, W.J.; Ramseier, R.O.

1978-01-01

The time variation of the sea-ice concentration and multiyear ice fraction within the pack ice in the Arctic Basin is examined, using microwave images of sea ice recently acquired by the Nimbus-5 spacecraft and the NASA CV-990 airborne laboratory. The images used for these studies were constructed from data acquired from the Electrically Scanned Microwave Radiometer (ESMR) which records radiation from earth and its atmosphere at a wavelength of 1.55 cm. Data are analyzed for four seasons during 1973-1975 to illustrate some basic differences in the properties of the sea ice during those times. Spacecraft data are compared with corresponding NASA CV-990 airborne laboratory data obtained over wide areas in the Arctic Basin during the Main Arctic Ice Dynamics Joint Experiment (1975) to illustrate the applicability of passive-microwave remote sensing for monitoring the time dependence of sea-ice concentration (divergence). These observations indicate significant variations in the sea-ice concentration in the spring, late fall and early winter. In addition, deep in the interior of the Arctic polar sea-ice pack, heretofore unobserved large areas, several hundred kilometers in extent, of sea-ice concentrations as low as 50% are indicated. ?? 1978 D. Reidel Publishing Company.

Observation of the cosmic-ray shadow of the Moon with IceCube

NASA Astrophysics Data System (ADS)

Aartsen, M. G.; Abbasi, R.; Abdou, Y.; Ackermann, M.; Adams, J.; Aguilar, J. A.; Ahlers, M.; Altmann, D.; Auffenberg, J.; Bai, X.; Baker, M.; Barwick, S. W.; Baum, V.; Bay, R.; Beatty, J. J.; Bechet, S.; Becker Tjus, J.; Becker, K.-H.; Bell, M.; Benabderrahmane, M. L.; BenZvi, S.; Berdermann, J.; Berghaus, P.; Berley, D.; Bernardini, E.; Bernhard, A.; Bertrand, D.; Besson, D. Z.; Binder, G.; Bindig, D.; Bissok, M.; Blaufuss, E.; Blumenthal, J.; Boersma, D. J.; Bohaichuk, S.; Bohm, C.; Bose, D.; Böser, S.; Botner, O.; Brayeur, L.; Bretz, H.-P.; Brown, A. M.; Bruijn, R.; Brunner, J.; Carson, M.; Casey, J.; Casier, M.; Chirkin, D.; Christov, A.; Christy, B.; Clark, K.; Clevermann, F.; Coenders, S.; Cohen, S.; Cowen, D. F.; Cruz Silva, A. H.; Danninger, M.; Daughhetee, J.; Davis, J. C.; De Clercq, C.; De Ridder, S.; Desiati, P.; de With, M.; DeYoung, T.; Díaz-Vélez, J. C.; Dunkman, M.; Eagan, R.; Eberhardt, B.; Eisch, J.; Ellsworth, R. W.; Euler, S.; Evenson, P. A.; Fadiran, O.; Fazely, A. R.; Fedynitch, A.; Feintzeig, J.; Feusels, T.; Filimonov, K.; Finley, C.; Fischer-Wasels, T.; Flis, S.; Franckowiak, A.; Franke, R.; Frantzen, K.; Fuchs, T.; Gaisser, T. K.; Gallagher, J.; Gerhardt, L.; Gladstone, L.; Glüsenkamp, T.; Goldschmidt, A.; Golup, G.; Gonzalez, J. G.; Goodman, J. A.; Góra, D.; Grandmont, D. T.; Grant, D.; Groß, A.; Ha, C.; Haj Ismail, A.; Hallen, P.; Hallgren, A.; Halzen, F.; Hanson, K.; Heereman, D.; Heinen, D.; Helbing, K.; Hellauer, R.; Hickford, S.; Hill, G. C.; Hoffman, K. D.; Hoffmann, R.; Homeier, A.; Hoshina, K.; Huelsnitz, W.; Hulth, P. O.; Hultqvist, K.; Hussain, S.; Ishihara, A.; Jacobi, E.; Jacobsen, J.; Jagielski, K.; Japaridze, G. S.; Jero, K.; Jlelati, O.; Kaminsky, B.; Kappes, A.; Karg, T.; Karle, A.; Kelley, J. L.; Kiryluk, J.; Kislat, F.; Kläs, J.; Klein, S. R.; Köhne, J.-H.; Kohnen, G.; Kolanoski, H.; Köpke, L.; Kopper, C.; Kopper, S.; Koskinen, D. J.; Kowalski, M.; Krasberg, M.; Krings, K.; Kroll, G.; Kunnen, J.; Kurahashi, N.; Kuwabara, T.; Labare, M.; Landsman, H.; Larson, M. J.; Lesiak-Bzdak, M.; Leuermann, M.; Leute, J.; Lünemann, J.; Madsen, J.; Maruyama, R.; Mase, K.; Matis, H. S.; McNally, F.; Meagher, K.; Merck, M.; Mészáros, P.; Meures, T.; Miarecki, S.; Middell, E.; Milke, N.; Miller, J.; Mohrmann, L.; Montaruli, T.; Morse, R.; Nahnhauer, R.; Naumann, U.; Niederhausen, H.; Nowicki, S. C.; Nygren, D. R.; Obertacke, A.; Odrowski, S.; Olivas, A.; Olivo, M.; O'Murchadha, A.; Paul, L.; Pepper, J. A.; Pérez de los Heros, C.; Pfendner, C.; Pieloth, D.; Pinat, E.; Pirk, N.; Posselt, J.; Price, P. B.; Przybylski, G. T.; Rädel, L.; Rameez, M.; Rawlins, K.; Redl, P.; Reimann, R.; Resconi, E.; Rhode, W.; Ribordy, M.; Richman, M.; Riedel, B.; Rodrigues, J. P.; Rott, C.; Ruhe, T.; Ruzybayev, B.; Ryckbosch, D.; Saba, S. M.; Salameh, T.; Sander, H.-G.; Santander, M.; Sarkar, S.; Schatto, K.; Scheel, M.; Scheriau, F.; Schmidt, T.; Schmitz, M.; Schoenen, S.; Schöneberg, S.; Schönwald, A.; Schukraft, A.; Schulte, L.; Schulz, O.; Seckel, D.; Sestayo, Y.; Seunarine, S.; Sheremata, C.; Smith, M. W. E.; Soldin, D.; Spiczak, G. M.; Spiering, C.; Stamatikos, M.; Stanev, T.; Stasik, A.; Stezelberger, T.; Stokstad, R. G.; Stößl, A.; Strahler, E. A.; Ström, R.; Sullivan, G. W.; Taavola, H.; Taboada, I.; Tamburro, A.; Tepe, A.; Ter-Antonyan, S.; Tešić, G.; Tilav, S.; Toale, P. A.; Toscano, S.; Usner, M.; van der Drift, D.; van Eijndhoven, N.; Van Overloop, A.; van Santen, J.; Vehring, M.; Voge, M.; Vraeghe, M.; Walck, C.; Waldenmaier, T.; Wallraff, M.; Wasserman, R.; Weaver, Ch.; Wellons, M.; Wendt, C.; Westerhoff, S.; Whitehorn, N.; Wiebe, K.; Wiebusch, C. H.; Williams, D. R.; Wissing, H.; Wolf, M.; Wood, T. R.; Woschnagg, K.; Xu, C.; Xu, D. L.; Xu, X. W.; Yanez, J. P.; Yodh, G.; Yoshida, S.; Zarzhitsky, P.; Ziemann, J.; Zierke, S.; Zoll, M.; IceCube Collaboration

2014-05-01

We report on the observation of a significant deficit of cosmic rays from the direction of the Moon with the IceCube detector. The study of this "Moon shadow" is used to characterize the angular resolution and absolute pointing capabilities of the detector. The detection is based on data taken in two periods before the completion of the detector: between April 2008 and May 2009, when IceCube operated in a partial configuration with 40 detector strings deployed in the South Pole ice, and between May 2009 and May 2010 when the detector operated with 59 strings. Using two independent analysis methods, the Moon shadow has been observed to high significance (>6σ) in both detector configurations. The observed location of the shadow center is within 0.2° of its expected position when geomagnetic deflection effects are taken into account. This measurement validates the directional reconstruction capabilities of IceCube.

Observations of Martian ice clouds by the Mars Global Surveyor Thermal Emission Spectrometer: The first Martian year

NASA Astrophysics Data System (ADS)

Pearl, John C.; Smith, Michael D.; Conrath, Barney J.; Bandfield, Joshua L.; Christensen, Philip R.

2001-06-01

Successful operation of the Mars Global Surveyor spacecraft, beginning in September 1997 (Ls=184°), has permitted extensive observations over more than a Martian year. Initially, thin (normal optical depth <0.06 at 825 cm-1) ice clouds and hazes were widespread, showing a distinct latitudinal gradient. With the onset of a regional dust storm at Ls=224°, ice clouds vanished in the southern hemisphere, to reappear gradually after the decay of the storm. The zonally averaged cloud opacities show little difference between the beginning and end of the first Martian year. A broad low-latitude cloud belt with considerable longitudinal structure was present in early northern summer. Apparently characteristic of the northern summer season, it vanished between Ls=140° and 150°. The latitudinal extent of this feature is apparently controlled by the ascending branch of the Hadley circulation. The most opaque clouds (optical depth ~0.6) were found above the summits of major volcanic features; these showed spatial structure possibly associated with wave activity. Variety among low-lying late morning clouds suggests localized differences in circulation and microclimates. Limb observations showed extensive optically thin (optical depth <0.04) stratiform clouds at altitudes up to 55 km. Considerable latitude and altitude variations were evident in ice clouds in early northern spring (Ls=25°) near 30 km, thin clouds extended from just north of the equator to ~45°N, nearly to the north polar vortex. A water ice haze was present in the north polar night (Ls=30°) at altitudes up to 40 km. Because little dust was present this probably provided heterogeneous nucleation sites for the formation of CO2 clouds and snowfall at altitudes below ~20 km, where atmospheric temperatures dropped to the CO2 condensation point. The relatively invariant spectral shape of the water ice cloud feature over space and time indicates that ice particle radii are generally between 1 and 4 μm.

Arctic and Antarctic Sea Ice Changes and Impacts (Invited)

NASA Astrophysics Data System (ADS)

Nghiem, S. V.

2013-12-01

The extent of springtime Arctic perennial sea ice, important to preconditioning summer melt and to polar sunrise photochemistry, continues its precipitous reduction in the last decade marked by a record low in 2012, as the Bromine, Ozone, and Mercury Experiment (BROMEX) was conducted around Barrow, Alaska, to investigate impacts of sea ice reduction on photochemical processes, transport, and distribution in the polar environment. In spring 2013, there was further loss of perennial sea ice, as it was not observed in the ocean region adjacent to the Alaskan north coast, where there was a stretch of perennial sea ice in 2012 in the Beaufort Sea and Chukchi Sea. In contrast to the rapid and extensive loss of sea ice in the Arctic, Antarctic sea ice has a trend of a slight increase in the past three decades. Given the significant variability in time and in space together with uncertainties in satellite observations, the increasing trend of Antarctic sea ice may arguably be considered as having a low confidence level; however, there was no overall reduction of Antarctic sea ice extent anywhere close to the decreasing rate of Arctic sea ice. There exist publications presenting various factors driving changes in Arctic and Antarctic sea ice. After a short review of these published factors, new observations and atmospheric, oceanic, hydrological, and geological mechanisms contributed to different behaviors of sea ice changes in the Arctic and Antarctic are presented. The contribution from of hydrologic factors may provide a linkage to and enhance thermal impacts from lower latitudes. While geological factors may affect the sensitivity of sea ice response to climate change, these factors can serve as the long-term memory in the system that should be exploited to improve future projections or predictions of sea ice changes. Furthermore, similarities and differences in chemical impacts of Arctic and Antarctic sea ice changes are discussed. Understanding sea ice changes and

Weddell-Scotia sea marginal ice zone observations from space, October 1984

NASA Technical Reports Server (NTRS)

Carsey, F. D.; Holt, B.; Martin, S.; Rothrock, D. A.; Mcnutt, L.

1986-01-01

Imagery from the Shuttle imaging radar-B experiment as well as other satellite and meteorological data are examined to learn more about the open sea ice margin of the Weddell-Scotia Seas region. At the ice edge, the ice forms into bandlike aggregates of small ice floes similar to those observed in the Bering Sea. The radar backscatter characteristics of these bands suggest that their upper surface is wet. Further into the pack, the radar imagery shows a transition to large floes. In the open sea, large icebergs and long surface gravity waves are discernable in the radar images.

CLaMS-Ice: Large-scale cirrus cloud simulations in comparison with observations

NASA Astrophysics Data System (ADS)

Costa, Anja; Rolf, Christian; Grooß, Jens-Uwe; Spichtinger, Peter; Afchine, Armin; Spelten, Nicole; Dreiling, Volker; Zöger, Martin; Krämer, Martina

2016-04-01

Cirrus clouds are an element of uncertainty in the climate system and have received increasing attention since the last IPCC reports. The interactions of different freezing mechanisms, sedimentation rates, updraft velocity fluctuations and other factors that determine the formation and evolution of those clouds is still not fully understood. Thus, a reliable representation of cirrus clouds in models representing real atmospheric conditions is still a challenging task. At last year's EGU, Rolf et al. (2015) introduced the new large-scale microphysical cirrus cloud model CLaMS-Ice: based on trajectories calculated with CLaMS (McKenna et al., 2002 and Konopka et al. 2007), it simulates the development of cirrus clouds relying on the cirrus bulk model by Spichtinger and Gierens (2009). The qualitative agreement between CLaMS-Ice simulations and observations could be demonstrated at that time. Now we present a detailed quantitative comparison between standard ECMWF products, CLaMS-Ice simulations, and in-situ measurements obtained during the ML-Cirrus campaign 2014. We discuss the agreement of the parameters temperature (observational data: BAHAMAS), relative humidity (SHARC), cloud occurrence, cloud particle concentration, ice water content and cloud particle radii (all NIXE-CAPS). Due to the precise trajectories based on ECMWF wind and temperature fields, CLaMS-Ice represents the cirrus cloud vertical and horizontal coverage more accurately than the ECMWF ice water content (IWC) fields. We demonstrate how CLaMS-Ice can be used to evaluate different input settings (e.g. amount of ice nuclei, freezing thresholds, sedimentation settings) that lead to cirrus clouds with the microphysical properties observed during ML-Cirrus (2014).

Scaling Properties of Arctic Sea Ice Deformation in a High‐Resolution Viscous‐Plastic Sea Ice Model and in Satellite Observations

PubMed Central

Losch, Martin; Menemenlis, Dimitris

2018-01-01

Abstract Sea ice models with the traditional viscous‐plastic (VP) rheology and very small horizontal grid spacing can resolve leads and deformation rates localized along Linear Kinematic Features (LKF). In a 1 km pan‐Arctic sea ice‐ocean simulation, the small‐scale sea ice deformations are evaluated with a scaling analysis in relation to satellite observations of the Envisat Geophysical Processor System (EGPS) in the Central Arctic. A new coupled scaling analysis for data on Eulerian grids is used to determine the spatial and temporal scaling and the coupling between temporal and spatial scales. The spatial scaling of the modeled sea ice deformation implies multifractality. It is also coupled to temporal scales and varies realistically by region and season. The agreement of the spatial scaling with satellite observations challenges previous results with VP models at coarser resolution, which did not reproduce the observed scaling. The temporal scaling analysis shows that the VP model, as configured in this 1 km simulation, does not fully resolve the intermittency of sea ice deformation that is observed in satellite data. PMID:29576996

The Leipzig Ice Nucleation chamber Comparison (LINC): An overview of ice nucleation measurements observed with four on-line ice nucleation devices

NASA Astrophysics Data System (ADS)

Kohn, Monika; Wex, Heike; Grawe, Sarah; Hartmann, Susan; Hellner, Lisa; Herenz, Paul; Welti, André; Stratmann, Frank; Lohmann, Ulrike; Kanji, Zamin A.

2016-04-01

Mixed-phase clouds (MPCs) are found to be the most relevant cloud type leading to precipitation in mid-latitudes. The formation of ice crystals in MPCs is not completely understood. To estimate the effect of aerosol particles on the radiative properties of clouds and to describe ice nucleation in models, the specific properties of aerosol particles acting as ice nucleating particles (INPs) still need to be identified. A number of devices are able to measure INPs in the lab and in the field. However, methods can be very different and need to be tested under controlled conditions with respect to aerosol generation and properties in order to standardize measurement and data analysis approaches for subsequent ambient measurements. Here, we present an overview of the LINC campaign hosted at TROPOS in September 2015. We compare four ice nucleation devices: PINC (Portable Ice Nucleation Chamber, Chou et al., 2011) and SPIN (SPectrometer for Ice Nuclei) are operated in deposition nucleation and condensation freezing mode. LACIS (Leipzig Aerosol Cloud Interaction Simulator, Hartmann et al., 2011) and PIMCA (Portable Immersion Mode Cooling chamber) measure in the immersion freezing mode. PIMCA is used as a vertical extension to PINC and allows activation and droplet growth prior to exposure to the investigated ice nucleation temperature. Size-resolved measurements of multiple aerosol types were performed including pure mineral dust (K-feldspar, kaolinite) and biological particles (Birch pollen washing waters) as well as some of them after treatment with sulfuric or nitric acid prior to experiments. LACIS and PIMCA-PINC operated in the immersion freezing mode showed very good agreement in the measured frozen fraction (FF). For the comparison between PINC and SPIN, which were scanning relative humidity from below to above water vapor saturation, an agreement was found for the obtained INP concentration. However, some differences were observed, which may result from ice

Comparing a thermo-mechanical Weichselian ice sheet reconstruction to GIA driven reconstructions: aspects of earth response and ice configuration

NASA Astrophysics Data System (ADS)

Schmidt, P.; Lund, B.; Näslund, J.-O.

2013-12-01

In this study we compare a recent reconstruction of the Weichselian ice-sheet as simulated by the University of Main ice-sheet model (UMISM) to two reconstructions commonly used in glacial isostatic adjustment (GIA) modeling: ICE-5G and ANU (also known as RSES). The UMISM reconstruction is carried out on a regional scale based on thermo-mechanical modelling whereas ANU and ICE-5G are global models based on the sea-level equation. The Weichselian ice-sheet in the three models are compared directly in terms of ice volume, extent and thickness, as well as in terms of predicted glacial isostatic adjustment in Fennoscandia. The three reconstructions display significant differences. UMISM and ANU includes phases of pronounced advance and retreat prior to the last glacial maximum (LGM), whereas the thickness and areal extent of the ICE-5G ice-sheet is more or less constant up until LGM. The final retreat of the ice-sheet initiates at earliest time in ICE-5G and latest in UMISM, while ice free conditions are reached earliest in UMISM and latest in ICE-5G. The post-LGM deglaciation style also differs notably between the ice models. While the UMISM simulation includes two temporary halts in the deglaciation, the later during the Younger Dryas, ANU only includes a decreased deglaciation rate during Younger Dryas and ICE-5G retreats at a relatively constant pace after an initial slow phase. Moreover, ANU and ICE-5G melt relatively uniformly over the entire ice-sheet in contrast to UMISM which melts preferentially from the edges. We find that all three reconstructions fit the present day uplift rates over Fennoscandia and the observed relative sea-level curve along the Ångerman river equally well, albeit with different optimal earth model parameters. Given identical earth models, ICE-5G predicts the fastest present day uplift rates and ANU the slowest, ANU also prefers the thinnest lithosphere. Moreover, only for ANU can a unique best fit model be determined. For UMISM and ICE

Observation of Cosmic-Ray Anisotropy with the IceTop Air Shower Array

NASA Astrophysics Data System (ADS)

Aartsen, M. G.; Abbasi, R.; Abdou, Y.; Ackermann, M.; Adams, J.; Aguilar, J. A.; Ahlers, M.; Altmann, D.; Andeen, K.; Auffenberg, J.; Bai, X.; Baker, M.; Barwick, S. W.; Baum, V.; Bay, R.; Beattie, K.; Beatty, J. J.; Bechet, S.; Becker Tjus, J.; Becker, K.-H.; Bell, M.; Benabderrahmane, M. L.; BenZvi, S.; Berdermann, J.; Berghaus, P.; Berley, D.; Bernardini, E.; Bertrand, D.; Besson, D. Z.; Bindig, D.; Bissok, M.; Blaufuss, E.; Blumenthal, J.; Boersma, D. J.; Bohaichuk, S.; Bohm, C.; Bose, D.; Böser, S.; Botner, O.; Brayeur, L.; Brown, A. M.; Bruijn, R.; Brunner, J.; Carson, M.; Casey, J.; Casier, M.; Chirkin, D.; Christy, B.; Clark, K.; Clevermann, F.; Cohen, S.; Cowen, D. F.; Cruz Silva, A. H.; Danninger, M.; Daughhetee, J.; Davis, J. C.; De Clercq, C.; De Ridder, S.; Descamps, F.; Desiati, P.; de Vries-Uiterweerd, G.; DeYoung, T.; Díaz-Vélez, J. C.; Dreyer, J.; Dumm, J. P.; Dunkman, M.; Eagan, R.; Eisch, J.; Ellsworth, R. W.; Engdegård, O.; Euler, S.; Evenson, P. A.; Fadiran, O.; Fazely, A. R.; Fedynitch, A.; Feintzeig, J.; Feusels, T.; Filimonov, K.; Finley, C.; Fischer-Wasels, T.; Flis, S.; Franckowiak, A.; Franke, R.; Frantzen, K.; Fuchs, T.; Gaisser, T. K.; Gallagher, J.; Gerhardt, L.; Gladstone, L.; Glüsenkamp, T.; Goldschmidt, A.; Golup, G.; Goodman, J. A.; Góra, D.; Grant, D.; Gross, A.; Grullon, S.; Gurtner, M.; Ha, C.; Haj Ismail, A.; Hallgren, A.; Halzen, F.; Hanson, K.; Heereman, D.; Heimann, P.; Heinen, D.; Helbing, K.; Hellauer, R.; Hickford, S.; Hill, G. C.; Hoffman, K. D.; Hoffmann, R.; Homeier, A.; Hoshina, K.; Huelsnitz, W.; Hulth, P. O.; Hultqvist, K.; Hussain, S.; Ishihara, A.; Jacobi, E.; Jacobsen, J.; Japaridze, G. S.; Jlelati, O.; Kappes, A.; Karg, T.; Karle, A.; Kiryluk, J.; Kislat, F.; Kläs, J.; Klein, S. R.; Köhne, J.-H.; Kohnen, G.; Kolanoski, H.; Köpke, L.; Kopper, C.; Kopper, S.; Koskinen, D. J.; Kowalski, M.; Krasberg, M.; Kroll, G.; Kunnen, J.; Kurahashi, N.; Kuwabara, T.; Labare, M.; Landsman, H.; Larson, M. J.; Lauer, R.; Lesiak-Bzdak, M.; Lünemann, J.; Madsen, J.; Maruyama, R.; Mase, K.; Matis, H. S.; McNally, F.; Meagher, K.; Merck, M.; Mészáros, P.; Meures, T.; Miarecki, S.; Middell, E.; Milke, N.; Miller, J.; Mohrmann, L.; Montaruli, T.; Morse, R.; Nahnhauer, R.; Naumann, U.; Nowicki, S. C.; Nygren, D. R.; Obertacke, A.; Odrowski, S.; Olivas, A.; Olivo, M.; O'Murchadha, A.; Panknin, S.; Paul, L.; Pepper, J. A.; Pérez de los Heros, C.; Pieloth, D.; Pirk, N.; Posselt, J.; Price, P. B.; Przybylski, G. T.; Rädel, L.; Rawlins, K.; Redl, P.; Resconi, E.; Rhode, W.; Ribordy, M.; Richman, M.; Riedel, B.; Rodrigues, J. P.; Rothmaier, F.; Rott, C.; Ruhe, T.; Ruzybayev, B.; Ryckbosch, D.; Saba, S. M.; Salameh, T.; Sander, H.-G.; Santander, M.; Sarkar, S.; Schatto, K.; Scheel, M.; Scheriau, F.; Schmidt, T.; Schmitz, M.; Schoenen, S.; Schöneberg, S.; Schönherr, L.; Schönwald, A.; Schukraft, A.; Schulte, L.; Schulz, O.; Seckel, D.; Seo, S. H.; Sestayo, Y.; Seunarine, S.; Sheremata, C.; Smith, M. W. E.; Soiron, M.; Soldin, D.; Spiczak, G. M.; Spiering, C.; Stamatikos, M.; Stanev, T.; Stasik, A.; Stezelberger, T.; Stokstad, R. G.; Stössl, A.; Strahler, E. A.; Ström, R.; Sullivan, G. W.; Taavola, H.; Taboada, I.; Tamburro, A.; Ter-Antonyan, S.; Tilav, S.; Toale, P. A.; Toscano, S.; Usner, M.; van der Drift, D.; van Eijndhoven, N.; Van Overloop, A.; van Santen, J.; Vehring, M.; Voge, M.; Vraeghe, M.; Walck, C.; Waldenmaier, T.; Wallraff, M.; Walter, M.; Wasserman, R.; Weaver, Ch.; Wendt, C.; Westerhoff, S.; Whitehorn, N.; Wiebe, K.; Wiebusch, C. H.; Williams, D. R.; Wissing, H.; Wolf, M.; Wood, T. R.; Woschnagg, K.; Xu, C.; Xu, D. L.; Xu, X. W.; Yanez, J. P.; Yodh, G.; Yoshida, S.; Zarzhitsky, P.; Ziemann, J.; Zierke, S.; Zilles, A.; Zoll, M.; IceCube Collaboration

2013-03-01

We report on the observation of anisotropy in the arrival direction distribution of cosmic rays at PeV energies. The analysis is based on data taken between 2009 and 2012 with the IceTop air shower array at the south pole. IceTop, an integral part of the IceCube detector, is sensitive to cosmic rays between 100 TeV and 1 EeV. With the current size of the IceTop data set, searches for anisotropy at the 10-3 level can, for the first time, be extended to PeV energies. We divide the data set into two parts with median energies of 400 TeV and 2 PeV, respectively. In the low energy band, we observe a strong deficit with an angular size of about 30° and an amplitude of (- 1.58 ± 0.46stat ± 0.52sys) × 10-3 at a location consistent with previous observations of cosmic rays with the IceCube neutrino detector. The study of the high energy band shows that the anisotropy persists to PeV energies and increases in amplitude to (- 3.11 ± 0.38stat ± 0.96sys) × 10-3.

Reliable radiocarbon evidence for the maximum extent of the West Antarctic Ice Sheet in the easternmost Amundsen Sea Embayment during the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Hillenbrand, C. D.; Klages, J. P.; Kuhn, G.; Smith, J.; Graham, A. G. C.; Gohl, K.; Wacker, L.

2016-02-01

We present the first age control and sedimentological data for the upper part of a stratified seismic unit that is unusually thick ( 6-9 m) for the outer shelf of the ASE and overlies an acoustically transparent unit. The transparent unit probably consists of soft till deposited during the last advance of grounded ice onto the outer shelf. We mapped subtle mega-scale glacial lineations (MSGL) on the seafloor and suggest that these are probably the expressions of bedforms originally moulded into the surface of the underlying till layer. We note that the lineations are less distinct when compared to MSGLs recorded in bathymetric data collected further upstream and suggest that this is because of the blanketing influence of the thick overlying drape. The uppermost part (≤ 3 m) of the stratified drape was sampled by two of our sediment cores and contains sufficient amounts of calcareous foraminifera throughout to establish reliable age models by radiocarbon dating. In combination with facies analysis of the recovered sediments the obtained radiocarbon dates suggest deposition of the draping unit in a sub-ice shelf/sub-sea ice to seasonal-open marine environment that existed on the outer shelf from well before (>45 ka BP) the Last Glacial Maximum until today. This indicates the maximum extent of grounded ice at the LGM must have been situated south of the two core locations, where a well-defined grounding-zone wedge (`GZWa') was deposited. The third sediment core was recovered from the toe of this wedge and retrieved grounding-line proximal glaciogenic debris flow sediments that were deposited by 14 cal. ka BP. Our new data therefore provide direct evidence for 1) the maximum extent of grounded ice in the easternmost ASE at the LGM (=GZWa), 2) the existence of a large shelf area seawards the wedge that was not covered by grounded ice during that time, and 3) landward grounding line retreat from GZWa prior to 14 cal. ka BP. This knowledge will help to improve LGM ice

Ku/Ka band observations over polar ice sheets

NASA Astrophysics Data System (ADS)

Thibaut, Pierre; Lasne, Yannick; Guillot, Amandine; Picot, Nicolas; Rémy, Frédérique

2015-04-01

For the first time, comparisons between Ku and Ka altimeter measurements are possible thanks to the new AltiKa instrument embarked onboard the Saral mission launched on February 25, 2013. This comparison is of particular interest when dealing with ice sheet observations because both frequencies have different penetration characteristics. We propose in this paper to revisit the estimation of the ice sheet topography (and other related parameters) with altimeter systems and to present illustrations of the differences observed in Ku and Ka bands using AltiKa, Envisat/RA-2 but also Cryosat-2 measurements. Working on AltiKa waveforms in the frame of the PEACHI project has allowed us to better understand the impact of the penetration depth on the echo shape, to improve the estimation algorithm and to compare its output with historical results obtained on Envisat and ERS missions. In particular, analyses at cross-overs of the Cryosat-2 and Saral data will be presented. Sentinel-3 mission should be launch during 2015. Operating in Ku band and in delay/doppler mode, it will be crucial to account for penetration effects in order to accurately derive the ice sheet heights and trends. The results of the work presented here, will benefit to the Sentinel-3 mission.

Observations on the Growth of Roughness Elements Into Icing Feathers

NASA Technical Reports Server (NTRS)

Vargas, Mario; Tsao, Jen, Ching

2007-01-01

This work presents the results of an experiment conducted in the Icing Research Tunnel at NASA Glenn Research Center to understand the process by which icing feathers are formed in the initial stages of ice accretion formation on swept wings. Close-up photographic data were taken on an aluminum NACA 0012 swept wing tip airfoil. Two types of photographic data were obtained: time sequence close-up photographic data during the run and close-up photographic data of the ice accretion at the end of each run. Icing runs were conducted for short ice accretion times from 10 to 180 sec. The time sequence close-up photographic data was used to study the process frame by frame and to create movies of how the process developed. The movies confirmed that at glaze icing conditions in the attachment line area icing feathers develop from roughness elements. The close-up photographic data at the end of each run showed that roughness elements change into a pointed shape with an upstream facet and join on the side with other elements having the same change to form ridges with pointed shape and upstream facet. The ridges develop into feathers when the upstream facet grows away to form the stem of the feather. The ridges and their growth into feathers were observed to form the initial scallop tips present in complete scallops.

The Annual Glaciohydrology Cycle in the Ablation Zone of the Greenland Ice Sheet: Part 2. Observed and Modeled Ice Flow

NASA Technical Reports Server (NTRS)

Colgan, William Terence; Rajaram, Harihar; Anderson, Robert S.; Steffen, Konrad; Zwally, H. Jay; Phillips, Thomas; Abdalati, Waleed

2012-01-01

Ice velocities observed in 2005/06 at three GPS stations along the Sermeq Avannarleq flowline, West Greenland, are used to characterize an observed annual velocity cycle. We attempt to reproduce this annual ice velocity cycle using a 1-D ice-flow model with longitudinal stresses coupled to a 1-D hydrology model that governs an empirical basal sliding rule. Seasonal basal sliding velocity is parameterized as a perturbation of prescribed winter sliding velocity that is proportional to the rate of change of glacier water storage. The coupled model reproduces the broad features of the annual basal sliding cycle observed along this flowline, namely a summer speed-up event followed by a fall slowdown event. We also evaluate the hypothesis that the observed annual velocity cycle is due to the annual calving cycle at the terminus. We demonstrate that the ice acceleration due to a catastrophic calving event takes an order of magnitude longer to reach CU/ETH ('Swiss') Camp (46km upstream of the terminus) than is observed. The seasonal acceleration observed at Swiss Camp is therefore unlikely to be the result of velocity perturbations propagated upstream via longitudinal coupling. Instead we interpret this velocity cycle to reflect the local history of glacier water balance.

Evaluation of icing drag coefficient correlations applied to iced propeller performance prediction

NASA Technical Reports Server (NTRS)

Miller, Thomas L.; Shaw, R. J.; Korkan, K. D.

1987-01-01

Evaluation of three empirical icing drag coefficient correlations is accomplished through application to a set of propeller icing data. The various correlations represent the best means currently available for relating drag rise to various flight and atmospheric conditions for both fixed-wing and rotating airfoils, and the work presented here ilustrates and evaluates one such application of the latter case. The origins of each of the correlations are discussed, and their apparent capabilities and limitations are summarized. These correlations have been made to be an integral part of a computer code, ICEPERF, which has been designed to calculate iced propeller performance. Comparison with experimental propeller icing data shows generally good agreement, with the quality of the predicted results seen to be directly related to the radial icing extent of each case. The code's capability to properly predict thrust coefficient, power coefficient, and propeller efficiency is shown to be strongly dependent on the choice of correlation selected, as well as upon proper specificatioon of radial icing extent.

Ice phase in altocumulus clouds over Leipzig: remote sensing observations and detailed modeling

NASA Astrophysics Data System (ADS)

Simmel, M.; Bühl, J.; Ansmann, A.; Tegen, I.

2015-09-01

The present work combines remote sensing observations and detailed cloud modeling to investigate two altocumulus cloud cases observed over Leipzig, Germany. A suite of remote sensing instruments was able to detect primary ice at rather high temperatures of -6 °C. For comparison, a second mixed phase case at about -25 °C is introduced. To further look into the details of cloud microphysical processes, a simple dynamics model of the Asai-Kasahara (AK) type is combined with detailed spectral microphysics (SPECS) forming the model system AK-SPECS. Vertical velocities are prescribed to force the dynamics, as well as main cloud features, to be close to the observations. Subsequently, sensitivity studies with respect to ice microphysical parameters are carried out with the aim to quantify the most important sensitivities for the cases investigated. For the cases selected, the liquid phase is mainly determined by the model dynamics (location and strength of vertical velocity), whereas the ice phase is much more sensitive to the microphysical parameters (ice nucleating particle (INP) number, ice particle shape). The choice of ice particle shape may induce large uncertainties that are on the same order as those for the temperature-dependent INP number distribution.

Ice phase in altocumulus clouds over Leipzig: remote sensing observations and detailed modelling

NASA Astrophysics Data System (ADS)

Simmel, M.; Bühl, J.; Ansmann, A.; Tegen, I.

2015-01-01

The present work combines remote sensing observations and detailed cloud modeling to investigate two altocumulus cloud cases observed over Leipzig, Germany. A suite of remote sensing instruments was able to detect primary ice at rather warm temperatures of -6 °C. For comparison, a second mixed phase case at about -25 °C is introduced. To further look into the details of cloud microphysical processes a simple dynamics model of the Asai-Kasahara type is combined with detailed spectral microphysics forming the model system AK-SPECS. Vertical velocities are prescribed to force the dynamics as well as main cloud features to be close to the observations. Subsequently, sensitivity studies with respect to ice microphysical parameters are carried out with the aim to quantify the most important sensitivities for the cases investigated. For the cases selected, the liquid phase is mainly determined by the model dynamics (location and strength of vertical velocity) whereas the ice phase is much more sensitive to the microphysical parameters (ice nuclei (IN) number, ice particle shape). The choice of ice particle shape may induce large uncertainties which are in the same order as those for the temperature-dependent IN number distribution.

Antarctic Sea Ice Variability and Trends, 1979-2010

NASA Technical Reports Server (NTRS)

Parkinson, C. L.; Cavalieri, D. J.

2012-01-01

In sharp contrast to the decreasing sea ice coverage of the Arctic, in the Antarctic the sea ice cover has, on average, expanded since the late 1970s. More specifically, satellite passive-microwave data for the period November 1978 - December 2010 reveal an overall positive trend in ice extents of 17,100 +/- 2,300 square km/yr. Much of the increase, at 13,700 +/- 1,500 square km/yr, has occurred in the region of the Ross Sea, with lesser contributions from the Weddell Sea and Indian Ocean. One region, that of the Bellingshausen/Amundsen Seas, has, like the Arctic, instead experienced significant sea ice decreases, with an overall ice extent trend of -8,200 +/- 1,200 square km/yr. When examined through the annual cycle over the 32-year period 1979-2010, the Southern Hemisphere sea ice cover as a whole experienced positive ice extent trends in every month, ranging in magnitude from a low of 9,100 +/- 6,300 square km/yr in February to a high of 24,700 +/- 10,000 square km/yr in May. The Ross Sea and Indian Ocean also had positive trends in each month, while the Bellingshausen/Amundsen Seas had negative trends in each month, and the Weddell Sea and Western Pacific Ocean had a mixture of positive and negative trends. Comparing ice-area results to ice-extent results, in each case the ice-area trend has the same sign as the ice-extent trend, but differences in the magnitudes of the two trends identify regions with overall increasing ice concentrations and others with overall decreasing ice concentrations. The strong pattern of decreasing ice coverage in the Bellingshausen/Amundsen Seas region and increasing ice coverage in the Ross Sea region is suggestive of changes in atmospheric circulation. This is a key topic for future research.

Comparison of PARASOL Observations with Polarized Reflectances Simulated Using Different Ice Habit Mixtures

NASA Technical Reports Server (NTRS)

Cole, Benjamin H.; Yang, Ping; Baum, Bryan A.; Riedi, Jerome; Labonnote, Laurent C.; Thieuleux, Francois; Platnick, Steven

2012-01-01

Insufficient knowledge of the habit distribution and the degree of surface roughness of ice crystals within ice clouds is a source of uncertainty in the forward light scattering and radiative transfer simulations required in downstream applications involving these clouds. The widely used MODerate Resolution Imaging Spectroradiometer (MODIS) Collection 5 ice microphysical model assumes a mixture of various ice crystal shapes with smooth-facets except aggregates of columns for which a moderately rough condition is assumed. When compared with PARASOL (Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar) polarized reflection data, simulations of polarized reflectance using smooth particles show a poor fit to the measurements, whereas very rough-faceted particles provide an improved fit to the polarized reflectance. In this study a new microphysical model based on a mixture of 9 different ice crystal habits with severely roughened facets is developed. Simulated polarized reflectance using the new ice habit distribution is calculated using a vector adding-doubling radiative transfer model, and the simulations closely agree with the polarized reflectance observed by PARASOL. The new general habit mixture is also tested using a spherical albedo differences analysis, and surface roughening is found to improve the consistency of multi-angular observations. It is suggested that an ice model incorporating an ensemble of different habits with severely roughened surfaces would potentially be an adequate choice for global ice cloud retrievals.

Sea ice and pollution-modulated changes in Greenland ice core methanesulfonate and bromine

NASA Astrophysics Data System (ADS)

Maselli, Olivia J.; Chellman, Nathan J.; Grieman, Mackenzie; Layman, Lawrence; McConnell, Joseph R.; Pasteris, Daniel; Rhodes, Rachael H.; Saltzman, Eric; Sigl, Michael

2017-01-01

Reconstruction of past changes in Arctic sea ice extent may be critical for understanding its future evolution. Methanesulfonate (MSA) and bromine concentrations preserved in ice cores have both been proposed as indicators of past sea ice conditions. In this study, two ice cores from central and north-eastern Greenland were analysed at sub-annual resolution for MSA (CH3SO3H) and bromine, covering the time period 1750-2010. We examine correlations between ice core MSA and the HadISST1 ICE sea ice dataset and consult back trajectories to infer the likely source regions. A strong correlation between the low-frequency MSA and bromine records during pre-industrial times indicates that both chemical species are likely linked to processes occurring on or near sea ice in the same source regions. The positive correlation between ice core MSA and bromine persists until the mid-20th century, when the acidity of Greenland ice begins to increase markedly due to increased fossil fuel emissions. After that time, MSA levels decrease as a result of declining sea ice extent but bromine levels increase. We consider several possible explanations and ultimately suggest that increased acidity, specifically nitric acid, of snow on sea ice stimulates the release of reactive Br from sea ice, resulting in increased transport and deposition on the Greenland ice sheet.

How well can the observed Arctic sea ice summer retreat and winter advance be represented in the NCEP Climate Forecast System version 2?

NASA Astrophysics Data System (ADS)

Collow, Thomas W.; Wang, Wanqiu; Kumar, Arun; Zhang, Jinlun

2017-09-01

The capability of a numerical model to simulate the statistical characteristics of the summer sea ice date of retreat (DOR) and the winter date of advance (DOA) is investigated using sea ice concentration output from the Climate Forecast System Version 2 model (CFSv2). Two model configurations are tested, the operational setting (CFSv2CFSR) which uses initial data from the Climate Forecast System Reanalysis, and a modified version (CFSv2PIOMp) which ingests sea ice thickness initialization data from the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) and includes physics modifications for a more realistic representation of heat fluxes at the sea ice top and bottom. First, a method to define DOR and DOA is presented. Then, DOR and DOA are determined from the model simulations and observational sea ice concentration from the National Aeronautics and Space Administration (NASA). Means, trends, and detrended standard deviations of DOR and DOA are compared, along with DOR/DOA rates in the Arctic Ocean. It is found that the statistics are generally similar between the model and observations, although some regional biases exist. In addition, regions of new ice retreat in recent years are represented well in CFSv2PIOMp over the Arctic Ocean, in terms of both spatial extent and timing. Overall, CFSv2PIOMp shows a reduction in error throughout the Arctic. Based on results, it is concluded that the model produces a reasonable representation of the climatology and variability statistics of DOR and DOA in most regions. This assessment serves as a prerequisite for future predictability experiments.

Sea Ice Outlook for September 2015 June Report - NASA Global Modeling and Assimilation Office

NASA Technical Reports Server (NTRS)

Cullather, Richard I.; Keppenne, Christian L.; Marshak, Jelena; Pawson, Steven; Schubert, Siegfried D.; Suarez, Max J.; Vernieres, Guillaume; Zhao, Bin

2015-01-01

The recent decline in perennial sea ice cover in Arctic Ocean is a topic of enormous scientific interest and has relevance to a broad variety of scientific disciplines and human endeavors including biological and physical oceanography, atmospheric circulation, high latitude ecology, the sustainability of indigenous communities, commerce, and resource exploration. A credible seasonal prediction of sea ice extent would be of substantial use to many of the stakeholders in these fields and may also reveal details on the physical processes that result in the current trends in the ice cover. Forecasts are challenging due in part to limitations in the polar observing network, the large variability in the climate system, and an incomplete knowledge of the significant processes. Nevertheless it is a useful to understand the current capabilities of high latitude seasonal forecasting and identify areas where such forecasts may be improved. Since 2008 the Arctic Research Consortium of the United States (ARCUS) has conducted a seasonal forecasting contest in which the average Arctic sea ice extent for the month of September (the month of the annual extent minimum) is predicted from available forecasts in early June, July, and August. The competition is known as the Sea Ice Outlook (SIO) but recently came under the auspices of the Sea Ice Prediction Network (SIPN), and multi-agency funded project to evaluate the SIO. The forecasts are submitted based on modeling, statistical, and heuristic methods. Forecasts of Arctic sea ice extent from the GMAO are derived from seasonal prediction system of the NASA Goddard Earth Observing System model, version 5 (GEOS 5) coupled atmosphere and ocean general circulation model (AOGCM). The projections are made in order to understand the relative skill of the forecasting system and to determine the effects of future improvements to the system. This years prediction is for a September average Arctic ice extent of 5.030.41 million km2.

Petermann Glacier, North Greenland: Large Ice-Discharge Episodes from 20 Years of Satellite Observations

NASA Astrophysics Data System (ADS)

Babiker, M.; Johannessen, O. M.; Miles, M. W.; Miles, V. V.

2009-12-01

The major marine-terminating outlet glaciers of Greenland can undergo large mass losses through calving of icebergs and bottom melting from floating ice tongues. Recent observations of outlet glaiers around Greenland have shown that large and rapid changes in solid-ice fluxes are possible. The Petermann glacier in remote northern Greenland is the region’s largest floating-tongue glacier (~70 km by 10 km). In summer 2008 a large calving event was observed, as well as large cracks upstream of the remaining calving front, portending a more massive near-term loss. These observations may herald extraordinary and unprecedented change. However, the long-term variability of calving events and ice velocities are poorly known. Our research goal here is to identify the temporal variability and possible trends in solid-ice flux indicators - variability of the calving front and ice velocity - for Petermann glacier. The methodological approach is observational, based primarily on analysis of 20 years of repetitive satellite data over a period starting from 1990, together with sporadic earlier observations. The multisensor data range from high-resolution optical images from Landsat, SPOT and Terra ASTER and high-resolution synthetic aperture radar (SAR) images from ERS and ENVISAT. These disparate data have been imported, geo-registered and analysed within a Geographic Information System. The following measurements are made: (1) delineating changes in the calving front, (2) estimating the area of glacial ice loss during calving events, and (3) estimating the ice-surface velocity using sequential satellite images. We find evidence of a number of previous calving episodes of similar magnitude to the summer 2008. The ice-velocity estimates compare well with other estimates for particular years, and moreover are relatively consistent during the 20-year period. These findings suggest business-as-usual for Petermann glacier; however, a near-term calving event exceeding those observed

Ice Mapping Observations in Galactic Star-Forming Regions: the AKARI Legacy

NASA Astrophysics Data System (ADS)

Fraser, Helen Jane; Suutarinnen, Aleksi; Noble, Jennifer

2015-08-01

It is becoming increasingly clear that explaining the small-scale distribution of many gas-phase molecules relies on our interpretation of the complex inter-connectivity between gas- and solid-phase interstellar chemistries. Inputs to proto-stellar astrochemical models are required that exploit ice compositions reflecting the historical physical conditions in pre-stellar environments when the ices first formed. Such data are required to translate the near-universe picture of ice-composition to our understanding of the role of extra-galactic ices in star-formation at higher redshifts.Here we present the first attempts at multi-object ice detections, and the subsequent ice column density mapping. The AKARI space telescope was uniquely capable of observing all the ice features between 2 and 5 microns, thereby detecting H2O, CO and CO2 ices concurrently, through their stretching vibrational features. Our group has successfully extracted an unprecedented volume of ice spectra from AKARI, including sources with not more than 2 mJy flux at 3 microns, showing:(a) H2O CO and CO2 ices on 30 lines of sight towards pre-stellar and star-forming cores, which when combined with laboratory experiments indicate how the chemistries of these three ices are interlinked (Noble et al (2013)),(b) ice maps showing the spatial distribution of water ice across 12 pre-stellar cores, in different molecular clouds (Suutarinnen et al (2015)), and the distribution of ice components within these cores on 1000 AU scales (Noble et al (2015)),(c) over 200 new detections of water ice, mostly on lines of sight towards background sources (> 145), indicating that water ice column density has a minimum value as a function of Av, but on a cloud-by-cloud basis typically correlates with Av, and dust emissivity at 250 microns (Suutarinnen et al (2015)),(d) the first detections of HDO ice towards background stars (Fraser et al (2015)).We discuss whether these results support the picture of a generic chemical

Abrupt Shift in the Observed Runoff from the Southwest Greenland Ice Sheet?

NASA Astrophysics Data System (ADS)

Ahlstrom, A.; Petersen, D.; Box, J.; Langen, P. P.; Citterio, M.

2016-12-01

Mass loss of the Greenland ice sheet has contributed significantly to sea level rise in recent years and is considered a crucial parameter when estimating the impact of future climate change. Few observational records of sufficient length exist to validate surface mass balance models, especially the estimated runoff. Here we present an observation time series from 1975-2014 of discharge from a large proglacial lake, Tasersiaq, in West Greenland (66.3°N, 50.4°W) with a mainly ice-covered catchment. We argue that the discharge time series is representative measure of ice sheet runoff, making it the only observational record of runoff to exceed the 30-year period needed to assess the climatological state of the ice sheet. We proceed to isolate the runoff part of the signal from precipitation and identified glacial lake outburst floods from a small sub-catchment. Similarly, the impact from major volcanic eruptions is clearly identified. We examine the trend and annual variability in the annual discharge, relating it to likely atmospheric forcing mechanisms and compare the observational time series with modelled runoff from the regional climate model HIRHAM.

Recent Increases in Snow Accumulation and Decreases in Sea-Ice Concentration Recorded in a Coastal NW Greenland Ice Core

NASA Astrophysics Data System (ADS)

Osterberg, E. C.; Thompson, J. T.; Wong, G. J.; Hawley, R. L.; Kelly, M. A.; Lutz, E.; Howley, J.; Ferris, D. G.

2013-12-01

A significant rise in summer temperatures over the past several decades has led to widespread retreat of the Greenland Ice Sheet (GIS) margin and surrounding sea ice. Recent observations from geodetic stations and GRACE show that ice mass loss progressed from South Greenland up to Northwest Greenland by 2005 (Khan et al., 2010). Observations from meteorological stations at the U.S. Thule Air Force Base, remote sensing platforms, and climate reanalyses indicate a 3.5C mean annual warming in the Thule region and a 44% decrease in summer (JJAS) sea-ice concentrations in Baffin Bay from 1980-2010. Mean annual precipitation near Thule increased by 12% over this interval, with the majority of the increase occurring in fall (SON). To improve projections of future ice loss and sea-level rise in a warming climate, we are currently developing multi-proxy records (lake sediment cores, ice cores, glacial geologic data, glaciological models) of Holocene climate variability and cryospheric response in NW Greenland, with a focus on past warm periods. As part of our efforts to develop a millennial-length ice core paleoclimate record from the Thule region, we collected and analyzed snow pit samples and short firn cores (up to 20 m) from the coastal region of the GIS (2Barrel site; 76.9317 N, 63.1467 W) and the summit of North Ice Cap (76.938 N, 67.671 W) in 2011 and 2012, respectively. The 2Barrel ice core was sampled using a continuous ice core melting system at Dartmouth, and subsequently analyzed for major anion and trace element concentrations and stable water isotope ratios. Here we show that the 2Barrel ice core spanning 1990-2010 records a 25% increase in mean annual snow accumulation, and is positively correlated (r = 0.52, p<0.01) with ERA-Interim precipitation. The 2Barrel annual sea-salt Na concentration is strongly correlated (r = 0.5-0.8, p<0.05) with summer and fall sea-ice concentrations in northern Baffin Bay near Thule (Figure 1). We hypothesize that the positive

New Tools for Sea Ice Data Analysis and Visualization: NSIDC's Arctic Sea Ice News and Analysis

NASA Astrophysics Data System (ADS)

Vizcarra, N.; Stroeve, J.; Beam, K.; Beitler, J.; Brandt, M.; Kovarik, J.; Savoie, M. H.; Skaug, M.; Stafford, T.

2017-12-01

Arctic sea ice has long been recognized as a sensitive climate indicator and has undergone a dramatic decline over the past thirty years. Antarctic sea ice continues to be an intriguing and active field of research. The National Snow and Ice Data Center's Arctic Sea Ice News & Analysis (ASINA) offers researchers and the public a transparent view of sea ice data and analysis. We have released a new set of tools for sea ice analysis and visualization. In addition to Charctic, our interactive sea ice extent graph, the new Sea Ice Data and Analysis Tools page provides access to Arctic and Antarctic sea ice data organized in seven different data workbooks, updated daily or monthly. An interactive tool lets scientists, or the public, quickly compare changes in ice extent and location. Another tool allows users to map trends, anomalies, and means for user-defined time periods. Animations of September Arctic and Antarctic monthly average sea ice extent and concentration may also be accessed from this page. Our tools help the NSIDC scientists monitor and understand sea ice conditions in near real time. They also allow the public to easily interact with and explore sea ice data. Technical innovations in our data center helped NSIDC quickly build these tools and more easily maintain them. The tools were made publicly accessible to meet the desire from the public and members of the media to access the numbers and calculations that power our visualizations and analysis. This poster explores these tools and how other researchers, the media, and the general public are using them.

Low-frequency passive-microwave observations of sea ice in the Weddell Sea

NASA Technical Reports Server (NTRS)

Menashi, James D.; St. Germain, Karen M.; Swift, Calvin T.; Comiso, Josefino C.; Lohanick, Alan W.

1993-01-01

The microwave emission properties of first-year sea ice were investigated from the R/V Polarstern during the Antarctic Winter Weddell Gyre Project in 1989. Radiometer measurements were made at 611 MHz and 10 GHz and were accompanied by video and visual observations. Using the theory of radiometric emission from a layered medium, a method for deriving sea ice thickness from radiometer data is developed and tested. The model is based on an incoherent reflection process and predicts that the emissivity of saline ice increases monotonically with increasing ice thickness until saturation occurs.

A New Normal for the Sea Ice Index

NASA Technical Reports Server (NTRS)

Fetterer, Florence; Windnagel, Ann; Meier, Walter N.

2014-01-01

The NSIDC Sea Ice Index is a popular data product that shows users how ice extent and concentration have changed since the beginning of the passive microwave satellite record in 1978. It shows time series of monthly ice extent anomalies rather than actual extent values, in order to emphasize the information the data are carrying. Along with the time series, an image of average extent for the previous month is shown as a white field, with a pink line showing the median extent for that month. These are updated monthly; corresponding daily products are updated daily.

New details about the LGM extent and subsequent retreat of the West Antarctic Ice Sheet from the easternmost Amundsen Sea Embayment shelf

NASA Astrophysics Data System (ADS)

Klages, J. P.; Hillenbrand, C. D.; Kuhn, G.; Smith, J. A.; Graham, A. G. C.; Nitsche, F. O.; Frederichs, T.; Arndt, J. E.; Gebhardt, C.; Robin, Z.; Uenzelmann-Neben, G.; Gohl, K.; Jernas, P.; Wacker, L.

2017-12-01

In recent years several previously undiscovered grounding-zone wedges (GZWs) have been described within the Abbot-Cosgrove palaeo-ice stream trough on the easternmost Amundsen Sea Embayment shelf. These GZWs document both the Last Glacial Maximum (LGM; 26.5-19 cal. ka BP) grounding-line extent and the subsequent episodic retreat within this trough that neighbors the larger Pine Island-Thwaites trough to the west. Here we combine bathymetric, seismic, and geologic data showing that 1) the grounding line in Abbot Trough did not reach the continental shelf break at any time during the last glacial period, and 2) a prominent stacked GZW constructed from six individual wedges lying upon another was deposited 100 km upstream from the LGM grounding-line position. The available data allow for calculating volumes for most of these individual GZWs and for the entire stack. Sediment cores were recovered seawards from the outermost GZW in the trough, and from the individual wedges of the stacked GZW in order to define the LGM grounding-line extent, and provide minimum grounding-line retreat ages for the respective positions on the stacked GZW. We present implications of a grounded-ice free outer shelf throughout the last glacial period. Furthermore, we assess the significance of the grounding-line stillstand period recorded by the stacked GZW in Abbot Trough for the timing of post-LGM retreat of the West Antarctic Ice Sheet from the Amundsen Sea Embayment shelf.

There goes the sea ice: following Arctic sea ice parcels and their properties.

NASA Astrophysics Data System (ADS)

Tschudi, M. A.; Tooth, M.; Meier, W.; Stewart, S.

2017-12-01

Arctic sea ice distribution has changed considerably over the last couple of decades. Sea ice extent record minimums have been observed in recent years, the distribution of ice age now heavily favors younger ice, and sea ice is likely thinning. This new state of the Arctic sea ice cover has several impacts, including effects on marine life, feedback on the warming of the ocean and atmosphere, and on the future evolution of the ice pack. The shift in the state of the ice cover, from a pack dominated by older ice, to the current state of a pack with mostly young ice, impacts specific properties of the ice pack, and consequently the pack's response to the changing Arctic climate. For example, younger ice typically contains more numerous melt ponds during the melt season, resulting in a lower albedo. First-year ice is typically thinner and more fragile than multi-year ice, making it more susceptible to dynamic and thermodynamic forcing. To investigate the response of the ice pack to climate forcing during summertime melt, we have developed a database that tracks individual Arctic sea ice parcels along with associated properties as these parcels advect during the summer. Our database tracks parcels in the Beaufort Sea, from 1985 - present, along with variables such as ice surface temperature, albedo, ice concentration, and convergence. We are using this database to deduce how these thousands of tracked parcels fare during summer melt, i.e. what fraction of the parcels advect through the Beaufort, and what fraction melts out? The tracked variables describe the thermodynamic and dynamic forcing on these parcels during their journey. This database will also be made available to all interested investigators, after it is published in the near future. The attached image shows the ice surface temperature of all parcels (right) that advected through the Beaufort Sea region (left) in 2014.

United States Naval Academy Polar Science Program's Visual Arctic Observing Platforms; IceGoat and IceKids

NASA Astrophysics Data System (ADS)

Woods, J. E.; Rigor, I. G.; Valentic, T. A.

2013-12-01

The U.S. Naval Academy Oceanography Department currently has a curriculum based Polar Science Program (USNA PSP). Within the PSP there is an Arctic Buoy Program (ABP) student research component that will include the design, build, testing and deployment of Arctic Observing Platforms. Establishing an active, field-research program in Polar Science will greatly enhance Midshipman education and research, as well as introduce future Naval Officers to the Arctic environment. The Oceanography Department has engaged the USNA Engineering Departments, and in close collaboration with SRI International, developed the USNA Visual Arctic Observing Platforms. The experience gained through Polar field studies and data derived from these platforms will be used to enhance course materials and laboratories and will also be used directly in Midshipman independent research projects. The USNA PSP successfully deployed IceGoat1 (IG1) off the USCGC HEALY in September, 2012. IG1 suffered a malfunction to its solar powered webcam system upon deployment, but is still reporting via ARGOS SATCOM systems basic weather parameters of air temperature, pressure, and position. USNA PSP attempted to build a less robust, but more economical system integrating similar low power observing platforms housed in heavy duty coolers. This allowed for a streamlined process to get a complete system completed in one academic year. IceKids (IK) are similar observing platforms, just not designed to float once the sea ice melts. IK1 was deployed to Antarctica from October 2012 through January 2013 and captured over 11,000 web cam images in near real time of two remote environmental monitoring stations. IK2A and IK3T were built to be deployed at the Naval Academy Ice Experiment in Barrow, AK in March 2013. IK2A was unique in trying to collect and transmit underwater acoustic signals in near real time. The system integrated a passive hydrophone into the already developed low power data transport system

Nonthermal ice nucleation observed at distorted contact lines of supercooled water drops

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Fan; Cruikshank, Owen; He, Weilue

Ice nucleation is the crucial step for ice formation in atmospheric clouds and therefore underlies climatologically relevant precipitation and radiative properties. Some progress has been made in understanding the roles of temperature, supersaturation, and material properties, but an explanation for the efficient ice nucleation occurring when a particle contacts a supercooled water drop has been elusive for over half a century. Here, we explore ice nucleation initiated at constant temperature and observe that mechanical agitation induces freezing of supercooled water drops at distorted contact lines. Results show that symmetric motion of supercooled water on a vertically oscillating substrate does notmore » freeze, no matter how we agitate it. However, when the moving contact line is distorted with the help of trace amounts of oil or inhomogeneous pinning on the substrate, freezing can occur at temperatures much higher than in a static droplet, equivalent to ~1010 increase in nucleation rate. Several possible mechanisms are proposed to explain the observations. One plausible explanation among them, decreased pressure due to interface curvature, is explored theoretically and compared with the observational results quasiquantitatively. Indeed, the observed freezing-temperature increase scales with contact line speed in a manner consistent with the pressure hypothesis. Whatever the mechanism, the experiments demonstrate a strong preference for ice nucleation at three-phase contact lines compared to the two-phase interface, and they also show that movement and distortion of the contact line are necessary contributions to stimulating the nucleation process.« less

Nonthermal ice nucleation observed at distorted contact lines of supercooled water drops

DOE PAGES

Yang, Fan; Cruikshank, Owen; He, Weilue; ...

2018-02-06

Ice nucleation is the crucial step for ice formation in atmospheric clouds and therefore underlies climatologically relevant precipitation and radiative properties. Some progress has been made in understanding the roles of temperature, supersaturation, and material properties, but an explanation for the efficient ice nucleation occurring when a particle contacts a supercooled water drop has been elusive for over half a century. Here, we explore ice nucleation initiated at constant temperature and observe that mechanical agitation induces freezing of supercooled water drops at distorted contact lines. Results show that symmetric motion of supercooled water on a vertically oscillating substrate does notmore » freeze, no matter how we agitate it. However, when the moving contact line is distorted with the help of trace amounts of oil or inhomogeneous pinning on the substrate, freezing can occur at temperatures much higher than in a static droplet, equivalent to ~1010 increase in nucleation rate. Several possible mechanisms are proposed to explain the observations. One plausible explanation among them, decreased pressure due to interface curvature, is explored theoretically and compared with the observational results quasiquantitatively. Indeed, the observed freezing-temperature increase scales with contact line speed in a manner consistent with the pressure hypothesis. Whatever the mechanism, the experiments demonstrate a strong preference for ice nucleation at three-phase contact lines compared to the two-phase interface, and they also show that movement and distortion of the contact line are necessary contributions to stimulating the nucleation process.« less

Nonthermal ice nucleation observed at distorted contact lines of supercooled water drops

NASA Astrophysics Data System (ADS)

Yang, Fan; Cruikshank, Owen; He, Weilue; Kostinski, Alex; Shaw, Raymond A.

2018-02-01

Ice nucleation is the crucial step for ice formation in atmospheric clouds and therefore underlies climatologically relevant precipitation and radiative properties. Progress has been made in understanding the roles of temperature, supersaturation, and material properties, but an explanation for the efficient ice nucleation occurring when a particle contacts a supercooled water drop has been elusive for over half a century. Here, we explore ice nucleation initiated at constant temperature and observe that mechanical agitation induces freezing of supercooled water drops at distorted contact lines. Results show that symmetric motion of supercooled water on a vertically oscillating substrate does not freeze, no matter how we agitate it. However, when the moving contact line is distorted with the help of trace amounts of oil or inhomogeneous pinning on the substrate, freezing can occur at temperatures much higher than in a static droplet, equivalent to ˜1010 increase in nucleation rate. Several possible mechanisms are proposed to explain the observations. One plausible explanation among them, decreased pressure due to interface curvature, is explored theoretically and compared with the observational results quasiquantitatively. Indeed, the observed freezing-temperature increase scales with contact line speed in a manner consistent with the pressure hypothesis. Whatever the mechanism, the experiments demonstrate a strong preference for ice nucleation at three-phase contact lines compared to the two-phase interface, and they also show that movement and distortion of the contact line are necessary contributions to stimulating the nucleation process.

Nonthermal ice nucleation observed at distorted contact lines of supercooled water drops.

PubMed

Yang, Fan; Cruikshank, Owen; He, Weilue; Kostinski, Alex; Shaw, Raymond A

2018-02-01

Ice nucleation is the crucial step for ice formation in atmospheric clouds and therefore underlies climatologically relevant precipitation and radiative properties. Progress has been made in understanding the roles of temperature, supersaturation, and material properties, but an explanation for the efficient ice nucleation occurring when a particle contacts a supercooled water drop has been elusive for over half a century. Here, we explore ice nucleation initiated at constant temperature and observe that mechanical agitation induces freezing of supercooled water drops at distorted contact lines. Results show that symmetric motion of supercooled water on a vertically oscillating substrate does not freeze, no matter how we agitate it. However, when the moving contact line is distorted with the help of trace amounts of oil or inhomogeneous pinning on the substrate, freezing can occur at temperatures much higher than in a static droplet, equivalent to ∼10^{10} increase in nucleation rate. Several possible mechanisms are proposed to explain the observations. One plausible explanation among them, decreased pressure due to interface curvature, is explored theoretically and compared with the observational results quasiquantitatively. Indeed, the observed freezing-temperature increase scales with contact line speed in a manner consistent with the pressure hypothesis. Whatever the mechanism, the experiments demonstrate a strong preference for ice nucleation at three-phase contact lines compared to the two-phase interface, and they also show that movement and distortion of the contact line are necessary contributions to stimulating the nucleation process.

Ocean Profile Measurements During the Seasonal Ice Zone Reconnaissance Surveys Ocean Profiles

DTIC Science & Technology

2017-01-01

repeated ocean, ice, and atmospheric measurements across the Beaufort-Chukchi sea seasonal sea ice zone (SIZ) utilizing US Coast Guard Arctic Domain...contributing to the rapid decline in summer ice extent that has occurred in recent years. The SIZ is the region between maximum winter sea ice extent and...minimum summer sea ice extent. As such, it contains the full range of positions of the marginal ice zone (MIZ) where sea ice interacts with open water

Modeling of cryoseismicity observed at the Fimbulisen Ice Shelf, East Antarctica

NASA Astrophysics Data System (ADS)

Hainzl, S.; Pirli, M.; Dahm, T.; Schweitzer, J.; Köhler, A.

2017-12-01

A source region of repetitive cryoseismic activity has been identified at the Fimbulisen ice shelf, in Dronning Maud Land, East Antarctica. The specific area is located at the outlet of the Jutulstraumen glacier, near the Kupol Moskovskij ice rise. A unique event catalog extending over 13 years, from 2003 to 2016 has been built based on waveform cross-correlation detectors and Hidden Markov Model classifiers. Phases of low seismicity rates are alternating with intense activity intervals that exhibit a strong tidal modulation. We performed a detailed analysis and modeling of the more than 2000 events recorded between July and October 2013. The observations are characterized by a number of very clear signals: (i) the event rate follows both the neap-spring and the semi-diurnal ocean-tide cycle; (ii) recurrences have a characteristic time of approximately 8 minutes; (iii) magnitudes vary systematically both on short and long time scales; and (iv) the events migrate within short-time clusters. We use these observations to constrain the dynamic processes at work at this particular region of the Fimbulisen ice shelf. Our model assumes a local grounding of the ice shelf, where stick-slip motion occurs. We show that the observations can be reproduced considering the modulation of the Coulomb-Failure stress by ocean tides.

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

NASA Astrophysics Data System (ADS)

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

2013-12-01

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

Observed Differences between North American Snow Extent and Snow Depth Variability

NASA Astrophysics Data System (ADS)

Ge, Y.; Gong, G.

2006-12-01

Snow extent and snow depth are two related characteristics of a snowpack, but they need not be mutually consistent. Differences between these two variables at local scales are readily apparent. However at larger scales which interact with atmospheric circulation and climate, snow extent is typically the variable used, while snow depth is often assumed to be minor and/or mutually consistent compared to snow extent, though this is rarely verified. In this study, a new regional/continental-scale gridded dataset derived from field observations is utilized to quantitatively evaluate the relationship between snow extent and snow depth over North America. Various statistical methods are applied to assess the mutual consistency of monthly snow depth vs. snow extent, including correlations, composites and principal components. Results indicate that snow depth variations are significant in their own rights, and that depth and extent anomalies are largely unrelated, especially over broad high latitude regions north of the snowline. In the vicinity of the snowline, where precipitation and ablation can affect both snow extent and snow depth, the two variables vary concurrently, especially in autumn and spring. It is also found that deeper winter snow translates into larger snow-covered area in the subsequent spring/summer season, which suggests a possible influence of winter snow depth on summer climate. The observed lack of mutual consistency at continental/regional scales suggests that snowpack depth variations may be of sufficiently large magnitude, spatial scope and temporal duration to influence regional-hemispheric climate, in a manner unrelated to the more extensively studied snow extent variations.

Air-Sea Interactions in the Marginal Ice Zone

DTIC Science & Technology

2016-03-31

Arctic Ocean has increased with the significant retreat of the seasonal sea-ice extent. Here, we use wind, wave, turbulence, and ice measurements to...which has experienced a significant retreat of the seasonal ice extent (Comiso and Nishio, 2008; Comiso et al., 2008). Thomson and Rogers (2014) showed

Microwave radiometric aircraft observations of the Fabry-Perot interference fringes of an ice-water system

NASA Technical Reports Server (NTRS)

Harrington, R. F.; Swift, C. T.; Fedors, J. C.

1980-01-01

Airborne stepped-frequency microwave radiometer (SFMR) observations of the Fabry-Perot interference fringes of ice-water systems are discussed. The microwave emissivity at normal incidence of a smooth layered dielectric medium over a semi-infinite dielectric medium is examined for the case of ice over water as a function of ice thickness and attenuation coefficient, and the presence of quarter-wavelength oscillations in emissivity as the ice thickness and frequency are varied is pointed out. Experimental observations of pronounced quarter-wavelength oscillations in radiometric brightness temperature due to the Fabry-Perot interference fringes over smooth sea ice and lake ice varying in roughness as the radiometer frequencies were scanned are then presented.

A review of sea ice proxy information from polar ice cores

NASA Astrophysics Data System (ADS)

Abram, Nerilie J.; Wolff, Eric W.; Curran, Mark A. J.

2013-11-01

Sea ice plays an important role in Earth's climate system. The lack of direct indications of past sea ice coverage, however, means that there is limited knowledge of the sensitivity and rate at which sea ice dynamics are involved in amplifying climate changes. As such, there is a need to develop new proxy records for reconstructing past sea ice conditions. Here we review the advances that have been made in using chemical tracers preserved in ice cores to determine past changes in sea ice cover around Antarctica. Ice core records of sea salt concentration show promise for revealing patterns of sea ice extent particularly over glacial-interglacial time scales. In the coldest climates, however, the sea salt signal appears to lose sensitivity and further work is required to determine how this proxy can be developed into a quantitative sea ice indicator. Methane sulphonic acid (MSA) in near-coastal ice cores has been used to reconstruct quantified changes and interannual variability in sea ice extent over shorter time scales spanning the last ˜160 years, and has potential to be extended to produce records of Antarctic sea ice changes throughout the Holocene. However the MSA ice core proxy also requires careful site assessment and interpretation alongside other palaeoclimate indicators to ensure reconstructions are not biased by non-sea ice factors, and we summarise some recommended strategies for the further development of sea ice histories from ice core MSA. For both proxies the limited information about the production and transfer of chemical markers from the sea ice zone to the Antarctic ice sheets remains an issue that requires further multidisciplinary study. Despite some exploratory and statistical work, the application of either proxy as an indicator of sea ice change in the Arctic also remains largely unknown. As information about these new ice core proxies builds, so too does the potential to develop a more comprehensive understanding of past changes in sea

Tropical pacing of Antarctic sea ice increase

NASA Astrophysics Data System (ADS)

Schneider, D. P.

2015-12-01

One reason why coupled climate model simulations generally do not reproduce the observed increase in Antarctic sea ice extent may be that their internally generated climate variability does not sync with the observed phases of phenomena like the Pacific Decadal Oscillation (PDO) and ENSO. For example, it is unlikely for a free-running coupled model simulation to capture the shift of the PDO from its positive to negative phase during 1998, and the subsequent ~15 year duration of the negative PDO phase. In previously presented work based on atmospheric models forced by observed tropical SSTs and stratospheric ozone, we demonstrated that tropical variability is key to explaining the wind trends over the Southern Ocean during the past ~35 years, particularly in the Ross, Amundsen and Bellingshausen Seas, the regions of the largest trends in sea ice extent and ice season duration. Here, we extend this idea to coupled model simulations with the Community Earth System Model (CESM) in which the evolution of SST anomalies in the central and eastern tropical Pacific is constrained to match the observations. This ensemble of 10 "tropical pacemaker" simulations shows a more realistic evolution of Antarctic sea ice anomalies than does its unconstrained counterpart, the CESM Large Ensemble (both sets of runs include stratospheric ozone depletion and other time-dependent radiative forcings). In particular, the pacemaker runs show that increased sea ice in the eastern Ross Sea is associated with a deeper Amundsen Sea Low (ASL) and stronger westerlies over the south Pacific. These circulation patterns in turn are linked with the negative phase of the PDO, characterized by negative SST anomalies in the central and eastern Pacific. The timing of tropical decadal variability with respect to ozone depletion further suggests a strong role for tropical variability in the recent acceleration of the Antarctic sea ice trend, as ozone depletion stabilized by late 1990s, prior to the most

The Role of Laboratory-Based Studies of the Physical and Biological Properties of Sea Ice in Supporting the Observation and Modeling of Ice Covered Seas

NASA Astrophysics Data System (ADS)

Light, B.; Krembs, C.

2003-12-01

Laboratory-based studies of the physical and biological properties of sea ice are an essential link between high latitude field observations and existing numerical models. Such studies promote improved understanding of climatic variability and its impact on sea ice and the structure of ice-dependent marine ecosystems. Controlled laboratory experiments can help identify feedback mechanisms between physical and biological processes and their response to climate fluctuations. Climatically sensitive processes occurring between sea ice and the atmosphere and sea ice and the ocean determine surface radiative energy fluxes and the transfer of nutrients and mass across these boundaries. High temporally and spatially resolved analyses of sea ice under controlled environmental conditions lend insight to the physics that drive these transfer processes. Techniques such as optical probing, thin section photography, and microscopy can be used to conduct experiments on natural sea ice core samples and laboratory-grown ice. Such experiments yield insight on small scale processes from the microscopic to the meter scale and can be powerful interdisciplinary tools for education and model parameterization development. Examples of laboratory investigations by the authors include observation of the response of sea ice microstructure to changes in temperature, assessment of the relationships between ice structure and the partitioning of solar radiation by first-year sea ice covers, observation of pore evolution and interfacial structure, and quantification of the production and impact of microbial metabolic products on the mechanical, optical, and textural characteristics of sea ice.

Modeling of Antarctic Sea Ice in a General Circulation Model.

NASA Astrophysics Data System (ADS)

Wu, Xingren; Simmonds, Ian; Budd, W. F.

1997-04-01

A dynamic-thermodynamic sea ice model is developed and coupled with the Melbourne University general circulation model to simulate the seasonal cycle of the Antarctic sea ice distribution. The model is efficient, rapid to compute, and useful for a range of climate studies. The thermodynamic part of the sea ice model is similar to that developed by Parkinson and Washington, the dynamics contain a simplified ice rheology that resists compression. The thermodynamics is based on energy conservation at the top surface of the ice/snow, the ice/water interface, and the open water area to determine the ice formation, accretion, and ablation. A lead parameterization is introduced with an effective partitioning scheme for freezing between and under the ice floes. The dynamic calculation determines the motion of ice, which is forced with the atmospheric wind, taking account of ice resistance and rafting. The simulated sea ice distribution compares reasonably well with observations. The seasonal cycle of ice extent is well simulated in phase as well as in magnitude. Simulated sea ice thickness and concentration are also in good agreement with observations over most regions and serve to indicate the importance of advection and ocean drift in the determination of the sea ice distribution.

Modeling of Antarctic sea ice in a general circulation model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Xingren; Budd, W.F.; Simmonds, I.

1997-04-01

A dynamic-thermodynamic sea ice model is developed and coupled with the Melbourne University general circulation model to simulate the seasonal cycle of the Antarctic sea ice distributions The model is efficient, rapid to compute, and useful for a range of climate studies. The thermodynamic part of the sea ice model is similar to that developed by Parkinson and Washington, the dynamics contain a simplified ice rheology that resists compression. The thermodynamics is based on energy conservation at the top surface of the ice/snow, the ice/water interface, and the open water area to determine the ice formation, accretion, and ablation. Amore » lead parameterization is introduced with an effective partitioning scheme for freezing between and under the ice floes. The dynamic calculation determines the motion of ice, which is forced with the atmospheric wind, taking account of ice resistance and rafting. The simulated sea ice distribution compares reasonably well with observations. The seasonal cycle of ice extent is well simulated in phase as well as in magnitude. Simulated sea ice thickness and concentration are also in good agreement with observations over most regions and serve to indicate the importance of advection and ocean drift in the determination of the sea ice distribution. 64 refs., 15 figs., 2 tabs.« less

Specific findings on ice crystal microphysical properties from in-situ observation

NASA Astrophysics Data System (ADS)

Coutris, Pierre; Leroy, Delphine; Fontaine, Emmanuel; Schwarzenboeck, Alfons; Strapp, J. Walter

2017-04-01

This study focuses on microphysical properties of ice particles populating high ice water content areas in Mesoscale Convective Systems (MCS). These clouds have been extensively sampled during the High Altitude Ice Crystal - High Ice Water Content international projects (HAIC-HIWC, Dezitter et al. 2013, Strapp et al. 2015) with the objective of characterizing ice particle properties such as size distribution, radar reflectivity and ice water content. The in-situ data collected during these campaigns at different temperature levels and in different type of MCS (oceanic, continental) make the HAIC-HIWC data set a unique opportunity to study ice particle microphysical properties. Recently, a new approach to retrieve ice particle mass from in-situ measurements has been developed: a forward model that relates ice particles' mass to Particle Size Distribution (PSD) and Ice Water Content (IWC) is formulated as a linear system of equations and the retrieval process consists in solving the inverse problem with numerical optimization tools (Coutris et al. 2016). In this study, this new method is applied to HAIC-HIWC data set and main outcomes are discussed. First, the method is compared to a classical power-law based method using data from one single flight performed in Darwin area on February, 7th 2014. The observed differences in retrieved quantities such as ice particle mass, ice water content or median mass diameter, highlight the potential benefit of abandoning the power law simplistic assumption. The method is then applied to data measured at different cloud temperatures ranging from -40°C to -10°C during several flights of both Darwin 2014 and Cayenne 2015 campaigns. Specific findings about ice microphysical properties such as variations of effective density with particle size and the influence of cloud temperature on particle effective density are presented.

Assessing deformation and morphology of Arctic landfast sea ice using InSAR to support use and management of coastal ice

NASA Astrophysics Data System (ADS)

Dammann, D. O.; Eicken, H.; Meyer, F. J.; Mahoney, A. R.

2016-12-01

Arctic landfast sea ice provides important services to people, including coastal communities and industry, as well as key marine biota. In many regions of the Arctic, the use of landfast sea ice by all stakeholders is increasingly limited by reduced stability of the ice cover, which results in more deformation and rougher ice conditions as well as reduced extent and an increased likelihood of detachment from the shore. Here, we use Synthetic Aperture Radar Interferometry (InSAR) to provide stakeholder-relevant data on key constraints for sea ice use, in particular ice stability and morphology, which are difficult to assess using conventional SAR. InSAR has the capability to detect small-scale landfast ice displacements, which are linked to important coastal hazards, including the formation of cracks, ungrounding of ice pressure ridges, and catastrophic breakout events. While InSAR has previously been used to identify the extent of landfast ice and regions of deformation within, quantitative analysis of small-scale ice motion has yet to be thoroughly validated and its potential remains largely underutilized in sea ice science. Using TanDEM-X interferometry, we derive surface displacements of landfast ice within Elson Lagoon near Barrow, Alaska, which we validate using in-situ DGPS data. We then apply an inverse model to estimate rates and patterns of shorefast ice deformation in other regions of landfast ice using interferograms generated with long-temporal baseline L-band ALOS-1 PALSAR-1 data. The model is able to correctly identify deformation modes and proxies for the associated relative internal elastic stress. The derived potential for fractures corresponds well with large-scale sea ice patterns and local in-situ observations. The utility of InSAR to quantify sea ice roughness has also been explored using TanDEM-X bistatic interferometry, which eliminates the effects of temporal changes in the ice cover. The InSAR-derived DEM shows good correlation with a high

Long-term observing system for the oceanic regime of Filchner-Ronne Ice Shelf, Antarctica

NASA Astrophysics Data System (ADS)

Østerhus, Svein; Schröder, Michael; Hellmer, Hartmunt; Darelius, Elin; Nicholls, Keith; Makinson, Keith

2014-05-01

Long term observations of the flow of dense waters from their area of formation to the abyss of the World Ocean, and the return flow of warm waters, are central to climate research. For the Weddell Sea an important component of such a system entails monitoring the formation of High Salinity Shelf Water (HSSW) on the continental shelf north of Ronne Ice Front, the transformation to Ice Shelf Water (ISW) beneath the floating Filchner-Ronne ice shelf, and the flux of ISW overflowing the shelf break to the deep Weddell Sea. Equally important is the return flow of warm water toward the Filchner-Ronne Ice Shelf system. AWI, BAS and UNI/UIB operate a number of monitoring stations in the southern Weddell Sea. The systems build upon techniques and methods developed over several decades and have a proven record of high data return. Here we present plans for extending, integrating and operating the existing long term observatories to increase our knowledge of the natural variability of the ocean-ice shelf system, and to allow early identification of possible changes of regional or global importance. The S2 observatory at the Filchner sill was established in 1977 and continues to deliver the longest existing marine time series from Antarctica. As a key site for monitoring the ISW overflow S2 is a part of the global net of monitoring sites under CLIVAR Southern Ocean Observing System (SOOS) and OceanSITES. The existing S2 observatory consists of a sub-surface mooring carrying sensors for current velocity, temperature, salinity and dissolved oxygen measurements. Observations at the Filchner sill also show a seasonal inflow of relatively warm water that is able to reach Filchner Ice Front. New model results indicate that this flow of water might increase in the future and we have deployed a number of instrumented moorings in the Filchner Depression to estimate the heat flux towards the ice shelf. In 1999 we established Site 5 on Ronne Ice Shelf using a hot-water drill to access

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

PubMed

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

2012-04-25

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

Seasonal reversal at Miryang Eoreumgol (Ice Valley), Korea: observation and monitoring

NASA Astrophysics Data System (ADS)

Byun, Hi-Ryong; Tanaka, Hiroshi L.; Choi, Pom-Yong; Kim, Do-Woo

2011-12-01

We investigate an anomalous phenomenon evident in the Miryang Eoreumgol (Ice Valley), Korea: The wind and water are cold during summer and warm during winter, and ice formation does not occur in winter but in summer. We have initiated observations and investigations into the origin of heat sources particularly with regard to the mechanism of ice formation in summer. Previous theories, e.g., concerning underground gravity currents, water evaporation, diurnal and seasonal respirations of the talus, effects of ground heat, radiation and topography, etc., are considered. After a calculation of heat sources, we propose two new concepts—a repetitious heat separation mechanism and a positive feedback mechanism of cold air generation—to demonstrate that the heat mechanism of the seasonal reversal of the ice valley may be controlled by the use of the phase change between ice and water vapor with only a small amount of additional unknown energy.

Isopycnal deepening of an under-ice river plume in coastal waters: Field observations and modeling

NASA Astrophysics Data System (ADS)

Li, S. Samuel; Ingram, R. Grant

2007-07-01

The Great Whale River, located on the southeast coast of Hudson Bay in Canada, forms a large river plume under complete landfast ice during early spring. Short-term fluctuations of plume depth have motivated the present numerical study of an under-ice river plume subject to tidal motion and friction. We introduce a simple two-layer model for predicting the vertical penetration of the under-ice river plume as it propagates over a deepening topography. The topography is idealized but representative. Friction on the bottom surface of the ice cover, on the seabed, and at the plume interface is parameterized using the quadratic friction law. The extent of the vertical penetration is controlled by dimensionless parameters related to tidal motion and river outflow. Model predictions are shown to compare favorably with under-ice plume measurements from the river mouth. This study illustrates that isopycnal deepening occurs when the ice-cover vertical motion creates a reduced flow cross-section during the ebbing tide. This results in supercritical flow and triggers the downward plume penetration in the offshore. For a given river discharge, the freshwater source over a tidal cycle is unsteady in terms of discharge velocity because of the variation in the effective cross-sectional area at the river mouth, through which freshwater flows.

Observing rotation and deformation of sea ice with synthetic aperture radar

NASA Technical Reports Server (NTRS)

Vesecky, J. F.; Samadani, R.; Daida, J. M.; Smith, M. P.; Bracewell, R. N.

1987-01-01

The ESA's ERS-1 satellite will carry SARs over the polar regions; an important component in the use of these data is an automated scheme for the extraction of sea ice velocity fields from a sequence of SAR images of the same geographical region. The image pyramid area-correlation hierarchical method is noted to be vulnerable to uncertainties for sea ice rotations greater than 10-15 deg between SAR observations. Rotation-invariant methods can successfully track isolated floes in the marginal ice zone. Hu's (1962) invariant moments are also worth considering as a possible basis for rotation-invariant tracking methods. Feature tracking is inherently robust for tracking rotating sea ice, but is limited when features are floe-lead boundaries. A variety of techniques appears neccessary.

Microwave Observations of Snow-Covered Freshwater Lake Ice obtained during the Great Lakes Winter EXperiment (GLAWEX), 2017

NASA Astrophysics Data System (ADS)

Gunn, G. E.; Hall, D. K.; Nghiem, S. V.

2017-12-01

Studies observing lake ice using active microwave acquisitions suggest that the dominant scattering mechanism in ice is caused by double-bounce of the signal off vertical tubular bubble inclusions. Recent polarimetric SAR observations and target decomposition algorithms indicate single-bounce interactions may be the dominant source of returns, and in the absence of field observations, has been hypothesized to be the result of roughness at the ice-water interface on the order of incident wavelengths. This study presents in-situ physical observations of snow-covered lake ice in western Michigan and Wisconsin acquired during the Great Lakes Winter EXperiment in 2017 (GLAWEX'17). In conjunction with NASA's SnowEx airborne snow campaign in Colorado (http://snow.nasa.gov), C- (Sentinel-1, RADARSAT-2) and X-band (TerraSAR-X) synthetic aperture radar (SAR) observations were acquired coincidently to surface physical snow and ice observations. Small/large scale roughness features at the ice-water interface are quantified through auger transects and used as an input variable in lake ice backscatter models to assess the relative contributions from different scattering mechanisms.

Evolution of a Greenland Ice sheet Including Shelves and Regional Sea Level Variations

NASA Astrophysics Data System (ADS)

Bradley, Sarah; Reerink, Thomas; van de Wal, Roderik S. W.; Helsen, Michiel; Goelzer, Heiko

2016-04-01

Observational evidence, including offshore moraines and marine sediment cores infer that at the Last Glacial maximum (LGM) the Greenland ice sheet (GIS) grounded out across the Davis Strait into Baffin Bay, with fast flowing ice streams extending out to the continental shelf break along the NW margin. These observations lead to a number of questions as to weather the GIS and Laurentide ice sheet (LIS) coalesced during glacial maximums, and if so, did a significant ice shelf develop across Baffin Bay and how would such a configuration impact on the relative contribution of these ice sheets to eustatic sea level (ESL). Most previous paleo ice sheet modelling simulations of the GIS recreated an ice sheet that either did not extend out onto the continental shelf or utilised a simplified marine ice parameterisation to recreate an extended GIS, and therefore did not fully include ice shelf dynamics. In this study we simulate the evolution of the GIS from 220 kyr BP to present day using IMAU-ice; a 3D thermodynamical ice sheet model which fully accounts for grounded and floating ice, calculates grounding line migration and ice shelf dynamics. As there are few observational estimates of the long-term (yrs) sub marine basal melting rates (mbm) for the GIS, we developed a mbm parameterization within IMAU-ice controlled primarily by changes in paleo water depth. We also investigate the influence of the LIS on the GIS evolution by including relative sea level forcing's derived from a Glacial Isostatic Adjustment model. We will present results of how changes in the mbm directly impacts on the ice sheet dynamics, timing and spatial extent of the GIS at the glacial maximums, but also on the rate of retreat and spatial extent at the Last interglacial (LIG) minimum. Results indicate that with the inclusion of ice shelf dynamics, a larger GIS is generated which is grounded out into Davis strait, up to a water depth of -750 m, but significantly reduces the GIS contribution to Last

Evolution of a Greenland Ice sheet Including Shelves and Regional Sea Level Variations

NASA Astrophysics Data System (ADS)

Bradley, S.; Reerink, T.; Vandewal, R.; Helsen, M.

2015-12-01

Observational evidence, including offshore moraines and marine sediment cores infer that at the Last Glacial maximum (LGM) the Greenland ice sheet (GIS) grounded out across the Davis Strait into Baffin Bay, with fast flowing ice streams extending out to the continental shelf break along the NW margin. These observations lead to a number of questions as to weather the GIS and Laurentide ice sheet (LIS) coalesced during glacial maximums, and if so, did a significant ice shelf develop across Baffin Bay and how would such a configuration impact on the relative contribution of these ice sheets to eustatic sea level (ESL). Most previous paleo ice sheet modelling simulations of the GIS recreated an ice sheet that either did not extend out onto the continental shelf or utilised a simplified marine ice parameterisation to recreate an extended GIS, and therefore did not fully include ice shelf dynamics. In this study we simulate the evolution of the GIS from 220 kyr BP to present day using IMAU-ice; a 3D thermodynamical ice sheet model which fully accounts for grounded and floating ice, calculates grounding line migration and ice shelf dynamics. There is few observational estimates of long-term (yrs) sub marine basal melting rates (mbm) for the GIS. Therefore we investigate a range of relationships to constrain the spatial and temporal parameterisation of mbm within IMAU-ice related to changes in paleo water depth, driven by changes in relative sea level and ocean temperature. We will present results of how changes in the mbm directly impacts on the ice sheet dynamics, timing and spatial extent of the GIS at the glacial maximums, but also on the rate of retreat and spatial extent at the Last interglacial (LIG) minimum. Initial results indicate that with the inclusion of ice shelf dynamics, a larger GIS is generated which is grounded out into Davis strait, up to a water depth of -750 m, but the total contribution to LIG ESL is reduced by up to 0.6 m.

Snow Grain Size Retrieval over the Polar Ice Sheets with the Ice, Cloud, and land Elevation Satellite (ICESat) Observations

PubMed Central

Yang, Yuekui; Marshak, Alexander; Han, Mei; Palm, Stephen P.; Harding, David J.

2018-01-01

Snow grain size is an important parameter for cryosphere studies. As a proof of concept, this paper presents an approach to retrieve this parameter over Greenland, East and West Antarctica ice sheets from surface reflectances observed with the Geoscience Laser Altimeter System (GLAS) onboard the Ice, Cloud, and land Elevation Satellite (ICESat) at 1064 nm. Spaceborne lidar observations overcome many of the disadvantages in passive remote sensing, including difficulties in cloud screening and low sun angle limitations; hence tend to provide more accurate and stable retrievals. Results from the GLAS L2A campaign, which began on 25 September and lasted until 19 November, 2003, show that the mode of the grain size distribution over Greenland is the largest (~300 μm) among the three, West Antarctica is the second (~220 μm) and East Antarctica is the smallest (~190 μm). Snow grain sizes are larger over the coastal regions compared to inland the ice sheets. These results are consistent with previous studies. Applying the broadband snow surface albedo parameterization scheme developed by Garder and Sharp (2010) to the retrieved snow grain size, ice sheet surface albedo is also derived. In the future, more accurate retrievals can be achieved with multiple wavelengths lidar observations. PMID:29636591

Snow Grain Size Retrieval over the Polar Ice Sheets with the Ice, Cloud and Land Elevation Satellite (ICESat) Observations

NASA Technical Reports Server (NTRS)

Yang, Yuekui; Marshak, Alexander; Han, Mei; Palm, Stephen P.; Harding, David J.

2016-01-01

Snow grain size is an important parameter for cryosphere studies. As a proof of concept, this paper presents an approach to retrieve this parameter over Greenland, East and West Antarctica ice sheets from surface reflectances observed with the Geoscience Laser Altimeter System (GLAS) onboard the Ice, Cloud, and land Elevation Satellite (ICESat) at 1064 nanometers. Spaceborne lidar observations overcome many of the disadvantages in passive remote sensing, including difficulties in cloud screening and low sun angle limitations; hence tend to provide more accurate and stable retrievals. Results from the GLAS L2A campaign, which began on 25 September and lasted until 19 November, 2003, show that the mode of the grain size distribution over Greenland is the largest (approximately 300 microns) among the three, West Antarctica is the second (220 microns) and East Antarctica is the smallest (190 microns). Snow grain sizes are larger over the coastal regions compared to inland the ice sheets. These results are consistent with previous studies. Applying the broadband snow surface albedo parameterization scheme developed by Garder and Sharp (2010) to the retrieved snow grain size, ice sheet surface albedo is also derived. In the future, more accurate retrievals can be achieved with multiple wavelengths lidar observations.

Seasonal sea ice predictions for the Arctic based on assimilation of remotely sensed observations

NASA Astrophysics Data System (ADS)

Kauker, F.; Kaminski, T.; Ricker, R.; Toudal-Pedersen, L.; Dybkjaer, G.; Melsheimer, C.; Eastwood, S.; Sumata, H.; Karcher, M.; Gerdes, R.

2015-10-01

The recent thinning and shrinking of the Arctic sea ice cover has increased the interest in seasonal sea ice forecasts. Typical tools for such forecasts are numerical models of the coupled ocean sea ice system such as the North Atlantic/Arctic Ocean Sea Ice Model (NAOSIM). The model uses as input the initial state of the system and the atmospheric boundary condition over the forecasting period. This study investigates the potential of remotely sensed ice thickness observations in constraining the initial model state. For this purpose it employs a variational assimilation system around NAOSIM and the Alfred Wegener Institute's CryoSat-2 ice thickness product in conjunction with the University of Bremen's snow depth product and the OSI SAF ice concentration and sea surface temperature products. We investigate the skill of predictions of the summer ice conditions starting in March for three different years. Straightforward assimilation of the above combination of data streams results in slight improvements over some regions (especially in the Beaufort Sea) but degrades the over-all fit to independent observations. A considerable enhancement of forecast skill is demonstrated for a bias correction scheme for the CryoSat-2 ice thickness product that uses a spatially varying scaling factor.

Sub-daily sea ice motion and deformation from RADARSAT observations

NASA Technical Reports Server (NTRS)

Kwok, R.; Cunningham, G. F.

2003-01-01

We find a persistent level of oscillatory sea ice motion and deformation, superimposed on the large-scale wind-driven field, in May 2002 (spring) and February 2003 (mid-winter), in the high Arctic over a region centered at approx.(85degreeN, 135degreeW). At this latitude, the RADARSAT wide-swath SAR coverage provides 4??equential observations every day, for ice motion retrieval, with a sampling interval at the orbital period of approx. 101 minutes.

Vertical Distribution of Dust and Water Ice Aerosols from CRISM Limb-geometry Observations

NASA Technical Reports Server (NTRS)

Smith, Michael Doyle; Wolff, Michael J.; Clancy, Todd; Kleinbohl, Armin; Murchie, Scott L.

2013-01-01

[1] Near-infrared spectra taken in a limb-viewing geometry by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on board the Mars Reconnaissance Orbiter provide a useful tool for probing atmospheric structure. Specifically, the observed radiance as a function of wavelength and height above the limb enables the vertical distribution of both dust and water ice aerosols to be retrieved. More than a dozen sets of CRISM limb observations have been taken so far providing pole-to-pole cross sections, spanning more than a full Martian year. Radiative transfer modeling is used to model the observations taking into account multiple scattering from aerosols and the spherical geometry of the limb observations. Both dust and water ice vertical profiles often show a significant vertical structure for nearly all seasons and latitudes that is not consistent with the well-mixed or Conrath-v assumptions that have often been used in the past for describing aerosol vertical profiles for retrieval and modeling purposes. Significant variations are seen in the retrieved vertical profiles of dust and water ice aerosol as a function of season. Dust typically extends to higher altitudes (approx. 40-50km) during the perihelion season than during the aphelion season (<20km), and the Hellas region consistently shows more dust mixed to higher altitudes than other locations. Detached water ice clouds are common, and water ice aerosols are observed to cap the dust layer in all seasons.

Vertical thermodynamic structure of the troposphere during the Norwegian young sea ICE expedition (N-ICE2015)

NASA Astrophysics Data System (ADS)

Kayser, Markus; Maturilli, Marion; Graham, Robert M.; Hudson, Stephen R.; Rinke, Annette; Cohen, Lana; Kim, Joo-Hong; Park, Sang-Jong; Moon, Woosok; Granskog, Mats A.

2017-10-01

The Norwegian young sea ICE (N-ICE2015) expedition was designed to investigate the atmosphere-snow-ice-ocean interactions in the young and thin sea ice regime north of Svalbard. Radiosondes were launched twice daily during the expedition from January to June 2015. Here we use these upper air measurements to study the multiple cyclonic events observed during N-ICE2015 with respect to changes in the vertical thermodynamic structure, moisture content, and boundary layer characteristics. We provide statistics of temperature inversion characteristics, static stability, and boundary layer extent. During winter, when radiative cooling is most effective, we find the strongest impact of synoptic cyclones. Changes to thermodynamic characteristics of the boundary layer are associated with transitions between the radiatively "clear" and "opaque" atmospheric states. In spring, radiative fluxes warm the surface leading to lifted temperature inversions and a statically unstable boundary layer. Further, we compare the N-ICE2015 static stability distributions to corresponding profiles from ERA-Interim reanalysis, from the closest land station in the Arctic North Atlantic sector, Ny-Ålesund, and to soundings from the SHEBA expedition (1997/1998). We find similar stability characteristics for N-ICE2015 and SHEBA throughout the troposphere, despite differences in location, sea ice thickness, and snow cover. For Ny-Ålesund, we observe similar characteristics above 1000 m, while the topography and ice-free fjord surrounding Ny-Ålesund generate great differences below. The long-term radiosonde record (1993-2014) from Ny-Ålesund indicates that during the N-ICE2015 spring period, temperatures were close to the climatological mean, while the lowest 3000 m were 1-3°C warmer than the climatology during winter.

Current Status and Future Plan of Arctic Sea Ice monitoring in South Korea

NASA Astrophysics Data System (ADS)

Shin, J.; Park, J.

2016-12-01

Arctic sea ice is one of the most important parameters in climate. For monitoring of sea ice changes, the National Meteorological Satellite Center (NMSC) of Korea Metrological Administration has developed the "Arctic sea ice monitoring system" to retrieve the sea ice extent and surface roughness using microwave sensor data, and statistical prediction model for Arctic sea ice extent. This system has been implemented to the web site for real-time public service. The sea ice information can be retrieved using the spaceborne microwave sensor-Special Sensor Microwave Imager/Sounder (SSMI/S). The sea ice information like sea ice extent, sea ice surface roughness, and predictive sea ice extent are produced weekly base since 2007. We also publish the "Analysis report of the Arctic sea ice" twice a year. We are trying to add more sea ice information into this system. Details of current status and future plan of Arctic sea ice monitoring and the methodology of the sea ice information retrievals will be presented in the meeting.

Expanding Antarctic Sea Ice: Anthropogenic or Natural Variability?

NASA Astrophysics Data System (ADS)

Bitz, C. M.

2016-12-01

Antarctic sea ice extent has increased over the last 36 years according to the satellite record. Concurrent with Antarctic sea-ice expansion has been broad cooling of the Southern Ocean sea-surface temperature. Not only are Southern Ocean sea ice and SST trends at odds with expectations from greenhouse gas-induced warming, the trend patterns are not reproduced in historical simulations with comprehensive global climate models. While a variety of different factors may have contributed to the observed trends in recent decades, we propose that it is atmospheric circulation changes - and the changes in ocean circulation they induce - that have emerged as the most likely cause of the observed Southern Ocean sea ice and SST trends. I will discuss deficiencies in models that could explain their incorrect response. In addition, I will present results from a series of experiments where the Antarctic sea ice and ocean are forced by atmospheric perturbations imposed within a coupled climate model. Figure caption: Linear trends of annual-mean SST (left) and annual-mean sea-ice concentration (right) over 1980-2014. SST is from NOAA's Optimum Interpolation SST dataset (version 2; Reynolds et al. 2002). Sea-ice concentration is from passive microwave observations using the NASA Team algorithm. Only the annual means are shown here for brevity and because the signal to noise is greater than in the seasonal means. Figure from Armour and Bitz (2015).

Deciphering the evolution of the last Eurasian ice sheets

NASA Astrophysics Data System (ADS)

Hughes, Anna; Gyllencreutz, Richard; Mangerud, Jan; Svendsen, John Inge

2016-04-01

Glacial geologists need ice sheet-scale chronological reconstructions of former ice extent to set individual records in a wider context and compare interpretations of ice sheet response to records of past environmental changes. Ice sheet modellers require empirical reconstructions on size and volume of past ice sheets that are fully documented, specified in time and include uncertainty estimates for model validation or constraints. Motivated by these demands, in 2005 we started a project (Database of the Eurasian Deglaciation, DATED) to compile and archive all published dates relevant to constraining the build-up and retreat of the last Eurasian ice sheets, including the British-Irish, Scandinavian and Svalbard-Barents-Kara Seas ice sheets (BIIS, SIS and SBKIS respectively). Over 5000 dates were assessed for reliability and used together with published ice-sheet margin positions to reconstruct time-slice maps of the ice sheets' extent, with uncertainty bounds, every 1000 years between 25-10 kyr ago and at four additional periods back to 40 kyr ago. Ten years after the idea for a database was conceived, the first version of results (DATED-1) has now been released (Hughes et al. 2016). We observe that: i) both the BIIS and SBKIS achieve maximum extent, and commence retreat earlier than the larger SIS; ii) the eastern terrestrial margin of the SIS reached its maximum extent up to 7000 years later than the westernmost marine margin; iii) the combined maximum ice volume (~24 m sea-level equivalent) was reached c. 21 ka; iv) large uncertainties exist; predominantly across marine sectors (e.g. the timing of coalescence and separation of the SIS and BKIS) but also in well-studied areas due to conflicting yet equally robust data. In just three years since the DATED-1 census (1 January 2013), the volume of new information (from both dates and mapped glacial geomorphology) has grown significantly (~1000 new dates). Here, we present the DATED-1 results in the context of the

Arctic Sea Ice Simulation in the PlioMIP Ensemble

NASA Technical Reports Server (NTRS)

Howell, Fergus W.; Haywood, Alan M.; Otto-Bliesner, Bette L.; Bragg, Fran; Chan, Wing-Le; Chandler, Mark A.; Contoux, Camille; Kamae, Youichi; Abe-Ouchi, Ayako; Rosenbloom, Nan A.;

Airborne thickness and freeboard measurements over the McMurdo Ice Shelf, Antarctica, and implications for ice density

NASA Astrophysics Data System (ADS)

Rack, Wolfgang; Haas, Christian; Langhorne, Pat J.

2013-11-01

We present airborne measurements to investigate the thickness of the western McMurdo Ice Shelf in the western Ross Sea, Antarctica. Because of basal accretion of marine ice and brine intrusions conventional radar systems are limited in detecting the ice thickness in this area. In November 2009, we used a helicopter-borne laser and electromagnetic induction sounder (EM bird) to measure several thickness and freeboard profiles across the ice shelf. The maximum electromagnetically detectable ice thickness was about 55 m. Assuming hydrostatic equilibrium, the simultaneous measurement of ice freeboard and thickness was used to derive bulk ice densities ranging from 800 to 975 kg m-3. Densities higher than those of pure ice can be largely explained by the abundance of sediments accumulated at the surface and present within the ice shelf, and are likely to a smaller extent related to the overestimation of ice thickness by the electromagnetic induction measurement related to the presence of a subice platelet layer. The equivalent thickness of debris at a density of 2800 kg m-3 is found to be up to about 2 m thick. A subice platelet layer below the ice shelf, similar to what is observed in front of the ice shelf below the sea ice, is likely to exist in areas of highest thickness. The thickness and density distribution reflects a picture of areas of basal freezing and supercooled Ice Shelf Water emerging from below the central ice shelf cavity into McMurdo Sound.