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Download or read book UAV Investigation Into Surface and Tidewater Mass Loss Processes of the Greenland Ice Sheet written by and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Jonathan Ryan
Publisher :
ISBN 13 :
Total Pages : 250 pages
Book Rating : 4.:/5 (111 download)
Download or read book UAV Investigation Into Surface and Tidewater Mass Loss Processes of the Greenland Ice Sheet written by Jonathan Ryan and published by . This book was released on 2018 with total page 250 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Jonathan Ryan
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (16 download)
Download or read book UAV Investigation of Surface and Tidewater Mass Loss Processes Across the Greenland Ice Sheet written by Jonathan Ryan and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Matthew Cooper
Publisher :
ISBN 13 :
Total Pages : 230 pages
Book Rating : 4.:/5 (119 download)
Download or read book Bare Ice Hydrologic Processes on the Greenland Ice Sheet Ablation Zone written by Matthew Cooper and published by . This book was released on 2020 with total page 230 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Greenland Ice Sheet is a major contributor to global sea level rise, with recent mass loss dominated by meltwater runoff from the ablation zone, i.e. areas of the ice sheet where annual mass losses exceed gains. In this zone, the winter snowpack melts entirely each summer exposing bare glacier ice. Observations of Greenland's ablation zone suggest the exposed bare ice surface is comprised of low-density ice termed "weathering crust" that may store meltwater, potentially reducing meltwater runoff export to surrounding oceans. Climate models are the primary tools used to forecast future Greenland mass loss, but these models treat the ablation zone as impermeable high-density ice with no meltwater retention capacity. Recent evidence suggests that climate models overpredict meltwater runoff from the ablation zone, which may be linked to weathering crust presence, but diagnosing climate model predictions is difficult because observations of meltwater runoff on the ice sheet surface are extremely rare and weathering crust presence is undocumented. This dissertation presents the results of four investigations that address this problem by pairing field observations of hydrologic and radiative properties of bare ice collected in Greenland's ablation zone with numerical modeling and analysis of climate model output. The results of these investigations reveal the presence of low-density weathering crust on Greenland's bare ice ablation zone surface and the potential for non-trivial meltwater runoff retention within weathering crust on Greenland's bare ice ablation zone surface. New estimates of spectral radiation attenuation coefficients are quantified and directly applied to a numerical model of spectral and thermodynamic heat transfer in bare ice. This model successfully simulates meltwater runoff from a supraglacial catchment on Greenland's southwest ablation zone surface. Model results suggest that nocturnal refreezing of meltwater stored within weathering crust occurs in Greenland's ablation zone, potentially reducing runoff up to 32% on annual timescales. These findings imply a reinterpretation of refreezing on bare ice as an important control on Greenland's ablation zone surface mass balance and the need to represent this process in climate model predictions of future Greenland mass loss.
Author : Tristan A. Rhodes
Publisher :
ISBN 13 :
Total Pages : 174 pages
Book Rating : 4.:/5 (8 download)
Download or read book Measuring Recent Ice Mass Loss from the Margin of the Greenland Ice Sheet Using Aster-derived Digital Elevation Models written by Tristan A. Rhodes and published by . This book was released on 2009 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Yun Xu
Publisher :
ISBN 13 :
Total Pages : 138 pages
Book Rating : 4.:/5 (871 download)
Download or read book Subaqueous Melting of Greenland Tidewater Glaciers written by Yun Xu and published by . This book was released on 2013 with total page 138 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Greenland Ice Sheet has been experiencing accelerating mass loss in the past two decades, due to enhanced surface melting and accelerated ice discharge into the ocean through tidewater glaciers. Many tidewater glaciers accelerated as anomalous warm water intruded into their glacial fjords. Subaqueous melting of the glaciers in the ocean is a potential trigger of glacier acceleration. However, the processes of subaqueous melting are not well understood. In this dissertation, we modify an ocean general circulation model, MITgcm, to include the melting/freezing processes on the vertical calving face of tidewater glaciers. We simulate the subaqueous melting using 2D and 3D configurations of the numerical model at high resolution (20-m to 1-m grid spacing). The model well represents the turbulent buoyant plume we simulate in a laboratory tank, and is then applied to a glacial fjord domain configured from oceanographic data we collected in several Greenland tidewater glacier fjords in August 2010 and 2012. The rate and distribution of subglacial freshwater discharge is estimated and used to force model simulations. The numerical simulations show the turbulent upwelling and expansion of subglacial freshwater plumes, which induce high rates of subaqueous melting along their routes. Average rates of subaqueous melting of Greenland tidewater glaciers could be several meters per day in summer and an order of magnitude smaller in winter. The melt rate increases less than linearly with subglacial freshwater discharge and more than linearly with ocean thermal forcing. The uncertainty of the distribution of subglacial freshwater discharge leads to ±15% error on the melt rate. We derive a sensitivity relationship between the melt rate and ocean thermal forcing and subglacial water discharge for Store Glacier, and calculate the daily melt rate of Store Glacier between 2008 and 2011. The simulated melt rate in August 2010 compares well with the melt rate derived from the oceanographic data. This study provides simple guidelines for interpreting recent changes in glacier fronts as a result of climate warming and the inclusion of ice-ocean interactions along the calving fronts of Greenland glaciers in ice sheet numerical models.
Author : Soroush Rezvanbehbahani
Publisher :
ISBN 13 :
Total Pages : 102 pages
Book Rating : 4.:/5 (845 download)
Download or read book Temporal History of Ice Dynamics Contribution to Volume Changes of the Southeast Greenland Ice Sheet written by Soroush Rezvanbehbahani and published by . This book was released on 2013 with total page 102 pages. Available in PDF, EPUB and Kindle. Book excerpt: Current estimations of the contribution of ice sheets to future sea level rise are solely based on changes in Surface Mass Balance (SMB) of Antarctic and Greenland Ice Sheets. However, the reported SMB changes over the Greenland Ice Sheet explain only about 50% of the observed total mass loss of the Greenland Ice Sheet (GrIS). The other 50% is caused by ice dynamic processes, which have not been included in most sea level rise predictions. The goal of this study was to investigate surface elevation changes of the entire GrIS in 2003-2009. In addition to the total elevation changes, elevation changes due to ice dynamics were also estimated by computing the difference between surface elevation changes measured by laser altimetry and those caused by SMB processes. I applied the Surface Elevation And Change Detection (SERAC) approach to derive surface elevation changes from laser altimetry observations. By fusing satellite laser altimetry (Ice, Cloud, and land Elevation Satellite (ICESat)) and airborne laser altimetry (Airborne Topographic Mapper (ATM) and Land, Vegetation, and Ice Sensor (LVIS)) data, I have reconstructed the elevation and volume change history of the GrIS at more than 55,000 locations. To estimate elevation changes due to SMB, SMB anomalies from RACMO2/GR were converted into height changes using a simple firn-densification model. To facilitate the visualization of elevation changes and the computation of volume changes I interpolated the irregularly distributed observations of ice sheet elevation changes into regular grids. Finally, I partitioned the ice sheet elevation and volume changes into SMB-related and ice dynamics-related changes and computed the contributions of major drainage basins. I have shown that the southeast GrIS was the main contributor of ice loss in Greenland inx2003-2009. The Kangerlussuaq Glacier drainage basin exhibited the largest ice-dynamics related volume loss from the twelve major drainage basins of southeast Greenland. The regions below 2000 m elevation, despite constituting only about 28% of the southeast GrIS, contribute to more than 92% to its ice-dynamics related volume loss. Ice sheet elevation changes, as well as annual volume changes of the twelve major southeast Greenland drainage basins, show a complex spatial and temporal pattern. Finally, the effect of ocean and air temperature changes as external forcing mechanisms on the observed volume change patterns is also discussed. I have shown that the trend of ocean temperatures anomalies along the southeast coast of the GrIS shows a close similarity to the estimated ice-dynamics related volume change pattern.
Author : Jessica Dawn Kromer
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.6/5 (625 download)
Download or read book Assessing the Impact in Using Reanalysis Products to Simulate Surface Mass Balance Over the Greenland Ice Sheet written by Jessica Dawn Kromer and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Greenland ice sheet (GrIS) surface mass balance (SMB), and processes which influence its behavior remain an active area of research, particularly for understanding the current sea-level budget and future projections of ice sheet mass loss. Currently, various methods are employed to model the surface mass balance of the contemporary GrIS, with methodologies ranging from the use of simple positive degree day models (PDD) to computationally intensive energy balance models (EBM's) and regional climate models (RCM's). Many of these methodologies rely on either direct forcing's (EBM's and PDD) or boundary conditions (RCM's) from atmospheric reanalysis products. Over time atmospheric reanalysis products have continued to improve with respect to horizontal resolution, allowing for direct use of fields critical for modeling and understanding the surface mass balance. Here we use a PDD model forced by temperature and precipitation from 3 atmospheric reanalysis products (ERA 5, Arctic System Reanalysis, and MERRA 2) at varying mesh resolution (30 km, 15 km, ~55 km respectively) to simulate the surface mass balance across the GrIS during the period 2000-2016. As higher resolution reanalysis products can help to better understand the contemporary GrIS surface mass balance, we highlight how variables important to the estimation of SMB vary amongst these reanalysis products and how these differences affect the SMB.
Author : Tyler Clark Sutterley
Publisher :
ISBN 13 : 9781339784113
Total Pages : 132 pages
Book Rating : 4.7/5 (841 download)
Download or read book Remote Sensing Observations of Modern-Day Regional Ice Sheet Change written by Tyler Clark Sutterley and published by . This book was released on 2016 with total page 132 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Earth's great ice sheets are losing mass at accelerating levels, rising global sea levels and posing a significant problem to society. The ice sheets contain enough water to raise sea level by 65 meters, and are the largest reservoirs of freshwater on the planet. Measurements of current ice sheet mass change are important in order to assess their current contribution to sea level rise, and to constrain future projections. There are three general approaches for measuring the current mass balance of ice sheets: the gravimetric method using time-variable gravity measurements, the altimetric method combining surface elevation change measurements with estimates of the density change, and the mass budget method combining rates of mass input from snow and rain with rates of mass output from meltwater runoff, ice discharge and other processes. In this dissertation, we use multiple independent measurements to assess the current uncertainties in mass balance efforts, and to create new estimates of current ice sheet mass change. We investigate key regions of Antarctica, where changes in the ice sheet velocity structure have led to accelerating mass losses. We compile new assessments of the mass change of the Greenland ice sheet, where increased rates of surface runoff and losses from ice sheet dynamics have dramatically shifted the mass balance regime. The work helps constrain estimation errors from GRACE, provides new constraints to ice sheet and glacial isostatic adjustment models, and helps improve our general understanding of the mechanisms driving current ice sheet mass change.
Author : Thomas Chudley
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (123 download)
Download or read book UAV-based Investigations Into the Hydrology and Dynamics of the Greenland Ice Sheet written by Thomas Chudley and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Mahdi Navari
Publisher :
ISBN 13 :
Total Pages : 189 pages
Book Rating : 4.:/5 (17 download)
Download or read book Improving a Priori Regional Climate Model Estimates of Greenland Ice Sheet Surface Mass Loss Through Assimilation of Measured Ice Surface Temperatures written by Mahdi Navari and published by . This book was released on 2015 with total page 189 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Greenland ice sheet has been the focus of climate studies due to its considerable impact on sea level rise. Accurate estimates of surface mass balance components - including precipitation, runoff, and evaporation - over the Greenland ice sheet would contribute to understanding the cause of the ice sheet's recent changes (i.e., increase in melt amount and duration, thickening of ice sheet interior, thinning at the ice sheet margins) and help to forecast future changes. Deterministic approaches provide a general trend of the surface mass fluxes, but they cannot characterize the uncertainty of estimates. The data assimilation method developed in this dissertation aimed to optimally merge the satellite-derived ice surface temperature into a snow/ice model while taking into account the uncertainty of input variables. Satellite-derived ice surface temperatures were used to improve the estimates of the Greenland ice sheet surface mass fluxes. Three studies were conducted on the Greenland ice sheet. The goal of the first study was to provide a proof of concept of the proposed methodology. A set of observing system simulation experiments was performed to retrieve the true surface mass fluxes of the Greenland ice sheet. The data assimilation framework was able to reduce the RMSE of the prior estimates of runoff, sublimation/evaporation, surface condensation, and surface mass loss fluxes by 61%, 64%, 76%, and 62%, respectively, over the nominal prior estimates from the regional climate model. In the second study, satellite-derived ice surface temperatures were assimilated into a snow/ice model. The results show that the data assimilation framework was capable of retrieving ice surface temperatures with a mean spatial RMSE of 0.3 K which was 69% less than that of the prior estimate without conditioning on satellite-derived ice surface measurements. Evaluation of surface mass fluxes is a critical part of the study; however, it is limited by the spare amount of independent data sets. Several data sets were used to investigate the feasibility of verification of results. It was found that predicted melt duration is in agreement with melt duration from passive microwave measurements; however, more efforts are needed to further verify the results. In the third study, the feasibility of microwave radiance assimilation was investigated by characterizing the error and uncertainty in predicted passive microwave brightness temperature from the radiative transfer model. We found significant uncertainty between the predicted measurement and satellite-derived passive microwave brightness temperature due to error in snow states, coarse resolution of the passive microwave and also an imperfect coupled snow/ice and radiative transfer model. Based on our findings, radiance assimilation requires more accurate snow grain size parameterization to take into account temporal and spatial variability of snow grain size. Furthermore, coarse resolution of both passive microwave brightness temperature and snow/ice model and attribute uncertainties of both predicted and measured brightness temperature make the radiance assimilation unattractive. This research demonstrates that ice surface temperature measurements have valuable information that can be extracted by a data assimilation technique to improve the estimates of the Greenland ice sheet surface mass fluxes.
Author : Gail Ruth Gutowski
Publisher :
ISBN 13 :
Total Pages : 96 pages
Book Rating : 4.:/5 (865 download)
Download or read book Effect of Modeled Pre-industrial Greenland Ice Sheet Surface Mass Balance Bias on Uncertainty in Sea Level Rise Projections in 2100 written by Gail Ruth Gutowski and published by . This book was released on 2013 with total page 96 pages. Available in PDF, EPUB and Kindle. Book excerpt: Changes to ice sheet surface mass balance (SMB) are going to play a significant role in future sea level rise (SLR), particularly for the Greenland ice sheet. The Coupled Model Intercomparison Project Phase 5 (CMIP5) found that Greenland ice sheet (GIS) response to changes in SMB is expected to contribute 9 ± 4 cm to sea level by 2100 (Fettweis et al 2013), though other estimates suggest the possibility of an even larger response. Modern ice sheet geometry and surface velocities are common metrics for determining a model's predictability of future climate. However, care must be taken to robustly quantify prediction uncertainty because errors in boundary conditions such as SMB can be compensated by (and therefore practically inseparable from) errors in other aspects of the model, complicating calculations of total uncertainty. We find that SMB calculated using the Community Earth System Model (CESM) differs from established standards due to errors in the CESM SMB boundary condition. During the long ice sheet initialization process, small SMB errors such as these have an opportunity to amplify into larger uncertainties in GIS sensitivity to climate change. These uncertainties manifest themselves in ice sheet surface geometry changes, ice mass loss, and subsequent SLR. While any bias in SMB is not desirable, it is not yet clear how sensitive SLR projections are to boundary condition forcing errors. We explore several levels of SMB forcing bias in order to analyze their influence on future SLR. We evaluate ensembles of ice sheets forced by 4 different levels of SMB forcing error, covering a range of errors similar to SMB biases between CESM and RACMO SMB. We find that GIS SMB biases on the order of 1 m/yr result in 7.8 ± 3.4 cm SLR between 1850 and 2100, corresponding to 100% uncertainty at the 2[sigma] level. However, we find unexpected feedbacks between SMB and surface geometry in the northern GIS. We propose that the use of elevation classes may be incorrectly altering the feedback mechanisms in that part of the ice sheet.
Author : Laura A. Stevens
Publisher :
ISBN 13 :
Total Pages : 220 pages
Book Rating : 4.:/5 (1 download)
Download or read book Influence of Meltwater on Greenland Ice Sheet Dynamics written by Laura A. Stevens and published by . This book was released on 2017 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt: Seasonal fluxes of meltwater control ice-flow processes across the Greenland Ice Sheet ablation zone and subglacial discharge at marine-terminating outlet glaciers. With the increase in annual ice sheet meltwater production observed over recent decades and predicted into future decades, understanding mechanisms driving the hourly to decadal impact of meltwater on ice flow is critical for predicting Greenland Ice Sheet dynamic mass loss. This thesis investigates a wide range of meltwater-driven processes using empirical and theoretical methods for a region of the western margin of the Greenland Ice Sheet. I begin with an examination of the seasonal and annual ice flow record for the region using in situ observations of ice flow from a network of Global Positioning System (GPS) stations. Annual velocities decrease over the seven-year time-series at a rate consistent with the negative trend in annual velocities observed in neighboring regions. Using observations from the same GPS network, I next determine the trigger mechanism for rapid drainage of a supraglacial lake. In three consecutive years, I find precursory basal slip and uplift in the lake basin generates tensile stresses that promote hydrofracture beneath the lake. As these precursors are likely associated with the introduction of meltwater to the bed through neighboring moulin systems, our results imply that lakes may be less able to drain in the less crevassed, interior regions of the ice sheet. Expanding spatial scales to the full ablation zone, I then use a numerical model of subglacial hydrology to test whether model-derived effective pressures exhibit the theorized inverse relationship with melt-season ice sheet surface velocities. Finally, I pair near-ice fjord hydrographic observations with modeled and observed subglacial discharge for the Saqqardliup sermia–Sarqardleq Fjord system. I find evidence of two types of glacially modified waters whose distinct properties and locations in the fjord align with subglacial discharge from two prominent subcatchments beneath Saqqardliup sermia. Continued observational and theoretical work reaching across discipline boundaries is required to further narrow our gap in understanding the forcing mechanisms and magnitude of Greenland Ice Sheet dynamic mass loss.
Author : National Aeronautics and Space Adm Nasa
Publisher : Independently Published
ISBN 13 : 9781729181614
Total Pages : 30 pages
Book Rating : 4.1/5 (816 download)
Download or read book Assessment of Climate Variability of the Greenland Ice Sheet: Integration of in Situ and Satellite Data written by National Aeronautics and Space Adm Nasa and published by Independently Published. This book was released on 2018-10-25 with total page 30 pages. Available in PDF, EPUB and Kindle. Book excerpt: The proposed research involves the application of multispectral satellite data in combination with ground truth measurements to monitor surface properties of the Greenland Ice Sheet which are essential for describing the energy and mass of the ice sheet. Several key components of the energy balance are parameterized using satellite data and in situ measurements. The analysis will be done for a ten year time period in order to get statistics on the seasonal and interannual variations of the surface processes and the climatology. Our goal is to investigate to what accuracy and over what geographic areas large scale snow properties and radiative fluxes can be derived based upon a combination of available remote sensing and meteorological data sets. Operational satellite sensors are calibrated based on ground measurements and atmospheric modeling prior to large scale analysis to ensure the quality of the satellite data. Further, several satellite sensors of different spatial and spectral resolution are intercompared to access the parameter accuracy. Proposed parameterization schemes to derive key component of the energy balance from satellite data are validated. For the understanding of the surface processes a field program was designed to collect information on spectral albedo, specular reflectance, soot content, grain size and the physical properties of different snow types. Further, the radiative and turbulent fluxes at the ice/snow surface are monitored for the parameterization and interpretation of the satellite data. The expected results include several baseline data sets of albedo, surface temperature, radiative fluxes, and different snow types of the entire Greenland Ice Sheet. These climatological data sets will be of potential use for climate sensitivity studies in the context of future climate change. Steffen, K. and Abdalati, W. and Stroeve, J. and Key, J. Unspecified Center NAGW-2158
Download or read book Greenland Ice Sheet Surface Mass-balance Modeling in a 131-year Perspective, 1950-2080 written by and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Fluctuations in the Greenland Ice Sheet (GrIS) surface mass-balance (SMB) and freshwater influx to the surrounding oceans closely follow climate fluctuations and are of considerable importance to the global eustatic sea level rise. SnowModel, a state-of-the-art snow-evolution modeling system, was used to simulate variations in the GrIS melt extent, surface water balance components, changes in SMB, and freshwater influx to the ocean. The simulations are based on the IPCC scenario AlB modeled by the HIRHAM4 RCM (using boundary conditions from ECHAM5 AOGCM) from 1950 through 2080. In-situ meteorological station (GC-Net and WMO DMI) observations from inside and outside the GrIS were used to validate and correct RCM output data before it was used as input for SnowModel. Satellite observations and independent SMB studies were used to validate the SnowModel output and confirm the model's robustness. We simulated a ≈90% increase in end-of-summer surface melt extent (0.483 x 106 km2) from 1950 to 2080, and a melt index (above 2,000-m elevation) increase of 138% (1.96 x 106 km2 x days). The greatest difference in melt extent occured in the southern part of the GrIS, and the greatest changes in the number of melt days was seen in the eastern part of the GrIS (≈50-70%) and was lowest in the west (≈20-30%). The rate of SMB loss, largely tied to changes in ablation processes, lead to an enhanced average loss of 331 km3 from 1950 to 2080, an average 5MB level of -99 km3 for the period 2070-2080. GrIS surface freshwater runoff yielded an eustatic rise in sea level from 0.8 ± 0.1 (1950-1959) to 1.9 ± 0.1 mm (2070-2080) sea level equivalent (SLE) y−1. The accumulated GrIS freshwater runoff contribution from surface melting equaled 160 mm SLE from 1950 through 2080.
Author : Guglielmo Maria Caporale
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (139 download)
Download or read book Trends and Persistence in the Greenland Ice Sheet Mass written by Guglielmo Maria Caporale and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This paper examines trends and persistence in the Greenland ice sheet mass by applying fractional integration methods to a dataset constructed by Mankoff et al. (2020) on ice discharge for seven different regions of Greenland. The adopted empirical framework encompasses a wide range of stochastic processes and is informative about their dynamic and long-run properties. The main finding is that significant changes have occurred in the behaviour of the series of interest in recent years; more specifically, although a deterministic trend is not present, ice discharge in the various regions of Greenland has become a non-stationary, explosive process, with shocks having permanent effects. It appears that, as a result of global warming, the ice mass loss in Greenland has already reached a tipping point and become an irreversible process.
Author :
Publisher :
ISBN 13 :
Total Pages : 236 pages
Book Rating : 4.:/5 (735 download)
Download or read book Vogel, Manfred, 1946- written by and published by . This book was released on 1961 with total page 236 pages. Available in PDF, EPUB and Kindle. Book excerpt: The folder may include clippings, announcements, small exhibition catalogs, and other ephemeral items.
