scholarly journals Southeast Greenland high accumulation rates derived from firn cores and ground-penetrating radar

2013 ◽  
Vol 54 (63) ◽  
pp. 322-332 ◽  
Author(s):  
Clément Miège ◽  
Richard R. Forster ◽  
Jason E. Box ◽  
Evan W. Burgess ◽  
Joseph R. McConnell ◽  
...  
Keyword(s):  
Ground Penetrating Radar ◽  
Climate Model ◽  
Regional Climate ◽  
Elevation Gradient ◽  
Greenland Ice Sheet ◽  
Snow Accumulation ◽  
Internal Layers ◽  
Accumulation Rates ◽  
High Accumulation ◽  
Ground Penetrating

AbstractDespite containing only 14% of the Greenland ice sheet by area, the southeastern sector has the highest accumulation rates, and hence receives ∼30% of the total snow accumulation. We present accumulation rates obtained during our 2010 Arctic Circle Traverse derived from three 50 m firn cores dated using geochemical analysis. We tracked continuous internal reflection horizons between the firn cores using a 400 MHz ground-penetrating radar (GPR). GPR data combined with depth-age scales from the firn cores provide accumulation rates along a 70 km transect. We followed an elevation gradient from ∼2350 to ∼1830m to understand how progressive surface melt may affect the ability to chemically date the firn cores and trace the internal layers with GPR. From the firn cores, we find a 52% (∼0.43 m w.e. a-1) increase in average snow accumulation and greater interannual variability at the lower site than the upper site. The GPR profiling reveals that accumulation rates are influenced by topographic undulations on the surface, with up to 23% variability over 7 km. These measurements confirm the presence of high accumulation rates in the southeast as predicted by the calibrated regional climate model Polar MM5.

scholarly journals Reconstruction of historical surface mass balance, 1984–2017 from GreenTrACS multi-offset ground-penetrating radar

2020 ◽  
pp. 1-10
Author(s):  
Tate G. Meehan ◽  
H. P. Marshall ◽  
John H. Bradford ◽  
Robert L. Hawley ◽  
Thomas B. Overly ◽  
...  
Keyword(s):  
Mass Balance ◽  
Ground Penetrating Radar ◽  
Greenland Ice Sheet ◽  
Snow Accumulation ◽  
Surface Mass Balance ◽  
Snow Density ◽  
Surface Mass ◽  
Age Model ◽  
Ground Penetrating ◽  
Good Agreement

Abstract We present continuous estimates of snow and firn density, layer depth and accumulation from a multi-channel, multi-offset, ground-penetrating radar traverse. Our method uses the electromagnetic velocity, estimated from waveform travel-times measured at common-midpoints between sources and receivers. Previously, common-midpoint radar experiments on ice sheets have been limited to point observations. We completed radar velocity analysis in the upper ~2 m to estimate the surface and average snow density of the Greenland Ice Sheet. We parameterized the Herron and Langway (1980) firn density and age model using the radar-derived snow density, radar-derived surface mass balance (2015–2017) and reanalysis-derived temperature data. We applied structure-oriented filtering to the radar image along constant age horizons and increased the depth at which horizons could be reliably interpreted. We reconstructed the historical instantaneous surface mass balance, which we averaged into annual and multidecadal products along a 78 km traverse for the period 1984–2017. We found good agreement between our physically constrained parameterization and a firn core collected from the dry snow accumulation zone, and gained insights into the spatial correlation of surface snow density.

scholarly journals Evaluation of the updated regional climate model RACMO2.3: summer snowfall impact on the Greenland Ice Sheet

2015 ◽  
Vol 9 (5) ◽  
pp. 1831-1844 ◽  
Author(s):  
B. Noël ◽  
W. J. van de Berg ◽  
E. van Meijgaard ◽  
P. Kuipers Munneke ◽  
R. S. W. van de Wal ◽  
...  
Keyword(s):  
Large Scale ◽  
Climate Model ◽  
Regional Climate ◽  
Elevation Gradient ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Cores ◽  
Detailed Comparison ◽  
Ablation Zone ◽  
Surface Mass

Abstract. We discuss Greenland Ice Sheet (GrIS) surface mass balance (SMB) differences between the updated polar version of the RACMO climate model (RACMO2.3) and the previous version (RACMO2.1). Among other revisions, the updated model includes an adjusted rainfall-to-snowfall conversion that produces exclusively snowfall under freezing conditions; this especially favours snowfall in summer. Summer snowfall in the ablation zone of the GrIS has a pronounced effect on melt rates, affecting modelled GrIS SMB in two ways. By covering relatively dark ice with highly reflective fresh snow, these summer snowfalls have the potential to locally reduce melt rates in the ablation zone of the GrIS through the snow-albedo-melt feedback. At larger scales, SMB changes are driven by differences in orographic precipitation following a shift in large-scale circulation, in combination with enhanced moisture to precipitation conversion for warm to moderately cold conditions. A detailed comparison of model output with observations from automatic weather stations, ice cores and ablation stakes shows that the model update generally improves the simulated SMB-elevation gradient as well as the representation of the surface energy balance, although significant biases remain.

scholarly journals Accumulation rates (2009–2017) in Southeast Greenland derived from airborne snow radar and comparison with regional climate models

2020 ◽  
Vol 61 (81) ◽  
pp. 225-233 ◽  
Author(s):  
Lynn Montgomery ◽  
Lora Koenig ◽  
Jan T. M. Lenaerts ◽  
Peter Kuipers Munneke
Keyword(s):  
Spatial Data ◽  
Climate Models ◽  
Layer Structure ◽  
Accumulation Rate ◽  
Regional Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Regional Climate Models ◽  
Internal Layers ◽  
Accumulation Rates

AbstractSince the year 2000, Greenland ice sheet mass loss has been dominated by a decrease in surface mass balance rather than an increase in solid ice discharge. Southeast Greenland is an important region to understand how high accumulation rates can offset increasing Greenland ice sheet meltwater runoff. To that end, we derive a new 9-year long dataset (2009–17) of accumulation rates in Southeast Greenland using NASA Operation IceBridge snow radar. Our accumulation dataset derived from internal layers focuses on high elevations (1500–3000 m) because at lower elevations meltwater percolation obscured internal layer structure. The uncertainty of the radar-derived accumulation rates is 11% [using Firn Densification Model (FDM) density profiles] and the average accumulation rate ranges from 0.5 to 1.2 m w.e. With our observations spanning almost a decade, we find large inter-annual variability, but no significant trend. Accumulation rates are compared with output from two regional climate models (RCMs), MAR and RACMO2. This comparison shows that the models are underestimating accumulation in Southeast Greenland and the models misrepresent spatial heterogeneity due to an orographically forced bias in snowfall near the coast. Our dataset is useful to fill in temporal and spatial data gaps, and to evaluate RCMs where few in situ measurements are available.

scholarly journals Annual Greenland accumulation rates (2009–2012) from airborne Snow Radar

2015 ◽  
Vol 9 (6) ◽  
pp. 6697-6731 ◽  
Author(s):  
L. S. Koenig ◽  
A. Ivanoff ◽  
P. M. Alexander ◽  
J. A. MacGregor ◽  
X. Fettweis ◽  
...  
Keyword(s):  
Large Scale ◽  
Climate Model ◽  
Regional Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Cores ◽  
The Arctic ◽  
Accumulation Rates ◽  
Surface Mass ◽  
Automated Method

Abstract. Contemporary climate warming over the Arctic is accelerating mass loss from the Greenland Ice Sheet (GrIS) through increasing surface melt, emphasizing the need to closely monitor surface mass balance (SMB) in order to improve sea-level rise predictions. Here, we quantify accumulation rates, the largest component of GrIS SMB, at a higher spatial resolution than currently available, using Snow Radar stratigraphy. We use a semi-automated method to derive annual-net accumulation rates from airborne Snow Radar data collected by NASA's Operation IceBridge from 2009 to 2012. An initial comparison of the accumulation rates from the Snow Radar and the outputs of a regional climate model (MAR) shows that, in general, the radar-derived accumulation matches closely with MAR in the interior of the ice sheet but MAR estimates are high over the southeast GrIS. Comparing the radar-derived accumulation with contemporaneous ice cores reveals that the radar captures the annual and long-term mean. The radar-derived accumulation rates resolve large-scale patterns across the GrIS with uncertainties of up to 11 %, attributed mostly to uncertainty in the snow/firn density profile.

scholarly journals Recent accumulation variability in northwest Greenland from ground-penetrating radar and shallow cores along the Greenland Inland Traverse

2014 ◽  
Vol 60 (220) ◽  
pp. 375-382 ◽  
Author(s):  
Robert L. Hawley ◽  
Zoe R. Courville ◽  
Laura M. Kehrl ◽  
Eric R. Lutz ◽  
Erich C. Osterberg ◽  
...  
Keyword(s):  
Ground Penetrating Radar ◽  
Spatial Scales ◽  
Ice Core ◽  
Greenland Ice Sheet ◽  
Accumulation Rates ◽  
Density Profiles ◽  
Direct Measurements ◽  
Point Data ◽  
Ground Penetrating ◽  
Key Parameter

AbstractAccumulation is a key parameter governing the mass balance of the Greenland ice sheet. Several studies have documented the spatial variability of accumulation over wide spatial scales, primarily using point data, remote sensing or modeling. Direct measurements of spatially extensive, detailed profiles of accumulation in Greenland, however, are rare. We used 400 MHz ground-penetrating radar along the 1009 km route of the Greenland Inland Traverse from Thule to Summit during April and May of 2011, to image continuous internal reflecting horizons. We dated these horizons using ice-core chemistry at each end of the traverse. Using density profiles measured along the traverse, we determined the depth to the horizons and the corresponding water-equivalent accumulation rates. The measured accumulation rates vary from ~0.1 m w.e. a–1 in the interior to ~0.7 m w.e. a–1 near the coast, and correspond broadly with existing published model results, though there are some excursions. Comparison of our recent accumulation rates with those collected along a similar route in the 1950s shows a ~10% increase in accumulation rates over the past 52 years along most of the traverse route. This implies that the increased water vapor capacity of warmer air is increasing accumulation in the interior of Greenland.

scholarly journals High-resolution study of layering within the percolation and soaked facies of the Greenland ice sheet

2011 ◽  
Vol 52 (59) ◽  
pp. 35-42 ◽  
Author(s):  
Joel Brown ◽  
Joel Harper ◽  
W. Tad Pfeffer ◽  
Neil Humphrey ◽  
John Bradford
Keyword(s):  
Ground Penetrating Radar ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Internal Reflection ◽  
Small Scale ◽  
Stratigraphic Correlation ◽  
Accumulation Rates ◽  
Ground Penetrating ◽  
The Relationship ◽  
Lower Site

AbstractWithin the percolation and soaked facies of the Greenland ice sheet, the relationship between radar-derived internal reflection horizons and the layered structure of the firn column is unclear. We conducted two small-scale ground-penetrating radar (GPR) surveys in conjunction with 10 m firn cores that we collected within the percolation and soaked facies of the Greenland ice sheet. The two surveys were separated by a distance of ~50 km and ~340m of elevation leading to ~40 days of difference in the duration of average annual melt. At the higher site (~1997ma.s.l.), which receives less melt, we found that internal reflection horizons identified in GPR data were largely laterally continuous over the grid; however, stratigraphic layers identified in cores could not be traced between cores over any distance from 1.5 to 14.0 m. Thus, we found no correlation between firn core stratigraphy observed directly and radar-derived internal reflection horizons. At the lower site (~1660ma.s.l.), which receives more melt, we found massive ice layers >0.5m thick and stratigraphic boundaries that span >15m horizontally. Some ice layers and stratigraphic boundaries correlate well with internal reflection horizons that are laterally continuous over the area of the radar grid. Internal reflection horizons identified at ~1997ma.s.l. are likely annual isochrones, but the reflection horizons identified at ~1660ma.s.l. are likely multi-annual features. We find that mapping accumulation rates over long distances by tying core stratigraphy to radar horizons may lead to ambiguous results because: (1) there is no stratigraphic correlation between firn cores at the 1997 m location; and (2) the reflection horizons at the 1660m location are multi-annual features.

scholarly journals Summer snowfall on the Greenland Ice Sheet: a study with the updated regional climate model RACMO2.3

2015 ◽  
Vol 9 (1) ◽  
pp. 1177-1208 ◽  
Author(s):  
B. Noël ◽  
W. J. van de Berg ◽  
E. van Meijgaard ◽  
P. Kuipers Munneke ◽  
R. S. W. van de Wal ◽  
...  
Keyword(s):  
Regional Climate Model ◽  
Large Scale ◽  
Climate Model ◽  
Freezing Point ◽  
Regional Climate ◽  
Elevation Gradient ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ablation Zone ◽  
Surface Mass

Abstract. We discuss Greenland ice sheet (GrIS) surface mass balance (SMB) differences between the updated polar version of the regional climate model RACMO2.3 and the previous version RACMO2.1. Among other revisions, the updated model includes an adjusted rainfall-to-snowfall conversion, producing exclusively snowfall under freezing conditions; this especially favours snowfall in summer when upper air temperatures reach the freezing point. Summer snowfall in the ablation zone of the GrIS has a pronounced effect on melt rates, affecting modelled GrIS SMB in two ways. By covering relatively dark ice with highly reflective fresh snow, these summer snowfall have the potential to locally reduce melt rates in the ablation zone of the GrIS through a snow-albedo-melt feedback. At larger scales, SMB changes are driven by differences in orographic precipitation following a shift in large-scale circulation, in combination with enhanced moisture to precipitation conversion for warm to moderately cold conditions. A detailed comparison of model output with long-term observations from automatic weather stations and ablation stakes in west Greenland shows that the model update generally improves the simulated SMB-elevation gradient as well as the representation of the surface energy balance, although significant biases remain.

scholarly journals Regional Greenland Accumulation Variability from Operation IceBridge Airborne Accumulation Radar

2016 ◽  
Author(s):  
Gabriel Lewis ◽  
Erich Osterberg ◽  
Robert Hawley ◽  
Brian Whitmore ◽  
Hans Peter Marshall
Keyword(s):  
Mass Balance ◽  
Sea Level Rise ◽  
Sea Level ◽  
Climate Models ◽  
Climate Model ◽  
Function Analysis ◽  
Greenland Ice Sheet ◽  
Northern Region ◽  
Snow Accumulation ◽  
Accumulation Rates

Abstract. The mass balance of the Greenland Ice Sheet (GIS) in a warming climate is of critical interest to scientists and the general public in the context of future sea-level rise. An improved understanding of temporal and spatial variability of snow accumulation will reduce uncertainties in GIS mass balance models and improve projections of Greenland's contribution to sea-level rise, currently estimated at 0.089 ± 0.03 m by 2100. Here we analyze 25 NASA Operation IceBridge Accumulation Radar flights totaling > 17 700 km from 2013–2014 to determine snow accumulation in the GIS dry snow and percolation zones over the past 100–300 years. IceBridge accumulation rates are calculated and used to validate accumulation rates from three regional climate models. Averaged over all 25 flights, the RMS difference between the models and IceBridge accumulation is between 0.037 ± 0.022 and 0.064 ± 0.033 m w.e. a−1, although each model shows significantly larger differences from IceBridge accumulation on a regional basis. In the central northern region, for example, the Regional Atmospheric Climate MOdel (RACMO2) underestimates by 26.9 ± 4.5 %, while in the southeast region the Modèle Atmosphérique Régional (MAR) overestimates by as much as 35.5 ± 6.8 %. Our results indicate that these regional differences between model and IceBridge accumulation are large enough to significantly alter GIS surface mass balance estimates. Empirical orthogonality function analysis suggests that the first two principal components account for 33 % and 18 % of the variance and correlate with the Atlantic Multidecadal Oscillation (AMO) and wintertime North Atlantic Oscillation (NAO), respectively. From 1976–2014 accumulation increased over most of the ice sheet's interior, consistent with the response to a positive AMO trend over this period. Regions that disagree strongest with climate models are those in which we have the fewest IceBridge data points, requiring additional in situ measurements to verify model uncertainties.

scholarly journals Thickening of the western part of the Greenland ice sheet

1998 ◽  
Vol 44 (148) ◽  
pp. 653-658 ◽  
Author(s):  
Robert H. Thomas ◽  
Beáta M. Csathó ◽  
Sivaprasad Gogineni ◽  
Kenneth C. Jezek ◽  
Karl Kuivinen
Keyword(s):  
Catchment Area ◽  
Regional Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Snow Accumulation ◽  
Ice Thickness ◽  
Accumulation Rates ◽  
Entire Area ◽  
Climate Assessment ◽  
Ice Velocity

Abstract NASA's Program for Arctic Regional Climate Assessment (PARCA) includes measurements of ice velocity and ice thickness along the 2000 m elevation contour line in the western part of the ice sheet. Here we use these measurements together with published estimates of snow-accumulation rates to infer die mass balance, or rate of thickening/thinning, of the ice-sheet catchment area inland from the velocity traverse. Within the accuracy to which we know snow-accumulation rates, the entire area is in balance, but localized regions inland from Upernavik Isstrom and Jakobshavn Isbra both appear to be thickening by about 10 cm a-1.

scholarly journals Thickening of the western part of the Greenland ice sheet

1998 ◽  
Vol 44 (148) ◽  
pp. 653-658 ◽  
Author(s):  
Robert H. Thomas ◽  
Beáta M. Csathó ◽  
Sivaprasad Gogineni ◽  
Kenneth C. Jezek ◽  
Karl Kuivinen
Keyword(s):  
Catchment Area ◽  
Regional Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Snow Accumulation ◽  
Ice Thickness ◽  
Accumulation Rates ◽  
Entire Area ◽  
Climate Assessment ◽  
Ice Velocity

AbstractNASA's Program for Arctic Regional Climate Assessment (PARCA) includes measurements of ice velocity and ice thickness along the 2000 m elevation contour line in the western part of the ice sheet. Here we use these measurements together with published estimates of snow-accumulation rates to infer die mass balance, or rate of thickening/thinning, of the ice-sheet catchment area inland from the velocity traverse. Within the accuracy to which we know snow-accumulation rates, the entire area is in balance, but localized regions inland from Upernavik Isstrom and Jakobshavn Isbra both appear to be thickening by about 10 cm a-1.

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