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 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 Annual Greenland accumulation rates (2009–2012) from airborne snow radar

2016 ◽  
Vol 10 (4) ◽  
pp. 1739-1752 ◽  
Author(s):  
Lora S. Koenig ◽  
Alvaro Ivanoff ◽  
Patrick M. Alexander ◽  
Joseph A. MacGregor ◽  
Xavier Fettweis ◽  
...  
Keyword(s):  
Mass Balance ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Cores ◽  
Snow Accumulation ◽  
Ultra Wideband ◽  
The Arctic ◽  
Surface Mass Balance ◽  
Accumulation Rates ◽  
Surface Mass

Abstract. Contemporary climate warming over the Arctic is accelerating mass loss from the Greenland Ice Sheet through increasing surface melt, emphasizing the need to closely monitor its surface mass balance in order to improve sea-level rise predictions. Snow accumulation is the largest component of the ice sheet's surface mass balance, but in situ observations thereof are inherently sparse and models are difficult to evaluate at large scales. Here, we quantify recent Greenland accumulation rates using ultra-wideband (2–6.5 GHz) airborne snow radar data collected as part of NASA's Operation IceBridge between 2009 and 2012. We use a semiautomated method to trace the observed radiostratigraphy and then derive annual net accumulation rates for 2009–2012. The uncertainty in these radar-derived accumulation rates is on average 14 %. A comparison of the radar-derived accumulation rates and contemporaneous ice cores shows that snow radar captures both the annual and long-term mean accumulation rate accurately. A comparison with outputs from a regional climate model (MAR) shows that this model matches radar-derived accumulation rates in the ice sheet interior but produces higher values over southeastern Greenland. Our results demonstrate that snow radar can efficiently and accurately map patterns of snow accumulation across an ice sheet and that it is valuable for evaluating the accuracy of surface mass balance models.

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 Impact of updated radiative transfer scheme in RACMO2.3p3 on the surface mass and energy budget of the Greenland ice sheet

2020 ◽  
Author(s):  
Christiaan T. van Dalum ◽  
Willem Jan van de Berg ◽  
Michiel R. van den Broeke
Keyword(s):  
Radiative Transfer ◽  
Energy Budget ◽  
Climate Model ◽  
Regional Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Snow Melt ◽  
Transfer Scheme ◽  
Surface Mass ◽  
The Impact

Abstract. This study evaluates the impact of a new snow and ice albedo and radiative transfer scheme on the surface mass and energy budget for the Greenland ice sheet in the latest version of the regional climate model RACMO2, version 2.3p3. We also evaluate the modeled (sub)surface temperature and snow melt, as subsurface heating by radiation penetration now occurs. The results are compared to the previous model version and are evaluated against stake measurements and automatic weather station data of the K-transect and PROMICE projects. In addition, subsurface snow temperature profiles are compared at the K-transect, Summit and southeast Greenland. The surface mass balance is in good agreement with observations, and only changes considerably with respect to the previous RACMO2 version around the ice margins and in the percolation zone. Snow melt and refreezing, on the other hand, are changed more substantially in various regions due to the changed albedo representation, subsurface energy absorption and melt water percolation. Internal heating leads to considerably higher snow temperatures in summer, in agreement with observations, and introduces a shallow layer of subsurface melt.

scholarly journals A daily, 1 km resolution data set of downscaled Greenland ice sheet surface mass balance (1958–2015)

2016 ◽  
Vol 10 (5) ◽  
pp. 2361-2377 ◽  
Author(s):  
Brice Noël ◽  
Willem Jan van de Berg ◽  
Horst Machguth ◽  
Stef Lhermitte ◽  
Ian Howat ◽  
...  
Keyword(s):  
Mass Balance ◽  
Climate Model ◽  
Regional Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Mass Balance ◽  
Data Set ◽  
Surface Mass ◽  
Ice Caps ◽  
Elevation Model

Abstract. This study presents a data set of daily, 1 km resolution Greenland ice sheet (GrIS) surface mass balance (SMB) covering the period 1958–2015. Applying corrections for elevation, bare ice albedo and accumulation bias, the high-resolution product is statistically downscaled from the native daily output of the polar regional climate model RACMO2.3 at 11 km. The data set includes all individual SMB components projected to a down-sampled version of the Greenland Ice Mapping Project (GIMP) digital elevation model and ice mask. The 1 km mask better resolves narrow ablation zones, valley glaciers, fjords and disconnected ice caps. Relative to the 11 km product, the more detailed representation of isolated glaciated areas leads to increased precipitation over the southeastern GrIS. In addition, the downscaled product shows a significant increase in runoff owing to better resolved low-lying marginal glaciated regions. The combined corrections for elevation and bare ice albedo markedly improve model agreement with a newly compiled data set of ablation measurements.

scholarly journals Coupling of climate models and ice sheet models by surface mass balance gradients: application to the Greenland Ice Sheet

2012 ◽  
Vol 6 (2) ◽  
pp. 255-272 ◽  
Author(s):  
M. M. Helsen ◽  
R. S. W. van de Wal ◽  
M. R. van den Broeke ◽  
W. J. van de Berg ◽  
J. Oerlemans
Keyword(s):  
Mass Balance ◽  
Climate Models ◽  
Climate Model ◽  
Regional Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Lapse Rate ◽  
Surface Mass Balance ◽  
Surface Mass ◽  
Temperature Lapse Rate

Abstract. It is notoriously difficult to couple surface mass balance (SMB) results from climate models to the changing geometry of an ice sheet model. This problem is traditionally avoided by using only accumulation from a climate model, and parameterizing the meltwater run-off as a function of temperature, which is often related to surface elevation (Hs). In this study, we propose a new strategy to calculate SMB, to allow a direct adjustment of SMB to a change in ice sheet topography and/or a change in climate forcing. This method is based on elevational gradients in the SMB field as computed by a regional climate model. Separate linear relations are derived for ablation and accumulation, using pairs of Hs and SMB within a minimum search radius. The continuously adjusting SMB forcing is consistent with climate model forcing fields, also for initially non-glaciated areas in the peripheral areas of an ice sheet. When applied to an asynchronous coupled ice sheet – climate model setup, this method circumvents traditional temperature lapse rate assumptions. Here we apply it to the Greenland Ice Sheet (GrIS). Experiments using both steady-state forcing and glacial-interglacial forcing result in realistic ice sheet reconstructions.

Evaluation of a new snow albedo scheme in RACMO2 for the Greenland ice sheet

2020 ◽  
Author(s):  
Christiaan van Dalum ◽  
Willem Jan van de Berg ◽  
Stef Lhermitte ◽  
Michiel van den Broeke
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Regional Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Atmospheric Conditions ◽  
Surface Mass ◽  
Snow Albedo ◽  
In Situ Data ◽  
Snow And Ice

<p>Snow and ice albedo schemes in present day climate models often lack a sophisticated radiation penetration scheme and are limited to a broadband albedo. In this study, we evaluate a new snow albedo scheme in the regional climate model RACMO2 that uses the two-stream radiative transfer in snow model TARTES and the spectral-to-narrowband albedo module SNOWBAL for the Greenland ice sheet. Additionally, the bare ice albedo parameterization has been updated. The snow and ice albedo output of the updated version of RACMO2, referred to as RACMO2.3p3, is evaluated using PROMICE and K-transect in-situ data and MODIS remote-sensing observations. Generally, the RACMO2.3p3 albedo is in very good agreement with satellite observations, leading to a domain-averaged bias of only -0.012. Some discrepancies are, however, observed for regions close to the ice margin. Compared to the previous iteration RACMO2.3p2, the albedo of RACMO2.3p3 is considerably higher in the bare ice zone during the ablation season, as atmospheric conditions now alter the bare ice albedo. For most other regions, however, the albedo of RACMO2.3p3 is lower due to spectral effects, radiation penetration, snow metamorphism or a delayed firn-ice transition. Furthermore, a white-out effect during cloudy conditions is captured and the snow albedo shows a low sensitivity to low soot concentrations. The surface mass balance of RACMO2.3p3 compares well with observations. Subsurface heating, however, now leads to increased melt and refreezing in south Greenland, changing the snow structure.</p>

scholarly journals Increased variability in Greenland Ice Sheet runoff from satellite observations

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Thomas Slater ◽  
Andrew Shepherd ◽  
Malcolm McMillan ◽  
Amber Leeson ◽  
Lin Gilbert ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Large Scale ◽  
Climate Models ◽  
Climate Model ◽  
Global Climate Model ◽  
Regional Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Model Simulations ◽  
Climate Model Simulations

AbstractRunoff from the Greenland Ice Sheet has increased over recent decades affecting global sea level, regional ocean circulation, and coastal marine ecosystems, and it now accounts for most of the contemporary mass imbalance. Estimates of runoff are typically derived from regional climate models because satellite records have been limited to assessments of melting extent. Here, we use CryoSat-2 satellite altimetry to produce direct measurements of Greenland’s runoff variability, based on seasonal changes in the ice sheet’s surface elevation. Between 2011 and 2020, Greenland’s ablation zone thinned on average by 1.4 ± 0.4 m each summer and thickened by 0.9 ± 0.4 m each winter. By adjusting for the steady-state divergence of ice, we estimate that runoff was 357 ± 58 Gt/yr on average – in close agreement with regional climate model simulations (root mean square difference of 47 to 60 Gt/yr). As well as being 21 % higher between 2011 and 2020 than over the preceding three decades, runoff is now also 60 % more variable from year-to-year as a consequence of large-scale fluctuations in atmospheric circulation. Because this variability is not captured in global climate model simulations, our satellite record of runoff should help to refine them and improve confidence in their projections.

scholarly journals Quantification of the Greenland ice sheet contribution to Last Interglacial sea level rise

2013 ◽  
Vol 9 (2) ◽  
pp. 621-639 ◽  
Author(s):  
E. J. Stone ◽  
D. J. Lunt ◽  
J. D. Annan ◽  
J. C. Hargreaves
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Climate Model ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Cores ◽  
The Arctic ◽  
Substantial Contribution ◽  
Interglacial Period ◽  
Last Interglacial

Abstract. During the Last Interglacial period (~ 130–115 thousand years ago) the Arctic climate was warmer than today, and global mean sea level was probably more than 6.6 m higher. However, there are large discrepancies in the estimated contributions to this sea level change from various sources (the Greenland and Antarctic ice sheets and smaller ice caps). Here, we determine probabilistically the likely contribution of Greenland ice sheet melt to Last Interglacial sea level rise, taking into account ice sheet model parametric uncertainty. We perform an ensemble of 500 Glimmer ice sheet model simulations forced with climatologies from the climate model HadCM3, and constrain the results with palaeodata from Greenland ice cores. Our results suggest a 90% probability that Greenland ice melt contributed at least 0.6 m, but less than 10% probability that it exceeded 3.5 m, a value which is lower than several recent estimates. Many of these previous estimates, however, did not include a full general circulation climate model that can capture atmospheric circulation and precipitation changes in response to changes in insolation forcing and orographic height. Our combined modelling and palaeodata approach suggests that the Greenland ice sheet is less sensitive to orbital forcing than previously thought, and it implicates Antarctic melt as providing a substantial contribution to Last Interglacial sea level rise. Future work should assess additional uncertainty due to inclusion of basal sliding and the direct effect of insolation on surface melt. In addition, the effect of uncertainty arising from climate model structural design should be taken into account by performing a multi-climate-model comparison.

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