scholarly journals The importance of insolation changes for paleo ice sheet modeling

2014 ◽  
Vol 8 (1) ◽  
pp. 337-362
Author(s):  
A. Robinson ◽  
H. Goelzer
Keyword(s):  
Temperature Anomaly ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Climatic Forcing ◽  
Near Surface ◽  
Ice Volume ◽  
The Past ◽  
Ice Sheet Modeling ◽  
Surface Melt ◽  
Continental Ice Sheets

Abstract. The growth and retreat of continental ice sheets in the past has largely been a response to changing climatic forcing. Thus, the calculation of surface melt is an important aspect of paleo ice sheet modeling. Changes in insolation are often not accounted for in calculations of surface melt, under the assumption that the near-surface temperature transmits the majority of the climatic forcing to the ice sheet. To assess how this could affect paleo simulations, here we investigate the importance of different orbital configurations for estimating melt on the Greenland ice sheet. We find that during peak Eemian conditions, increased insolation contributes 20–50% to the surface melt anomaly. However, this percentage depends strongly on the temperature anomaly at the time. Furthermore, the spatial pattern of surface conditions in terms of temperature and albedo exert a strong influence on the relative importance of insolation in the melt calculations. In coupled simulations, the additional insolation-induced melt translates into up to threefold more ice volume loss, compared to output using a model that does not account for insolation changes. We also introduce a simple correction factor that allows reduced complexity melt models to account for changes in insolation.

scholarly journals The importance of insolation changes for paleo ice sheet modeling

2014 ◽  
Vol 8 (4) ◽  
pp. 1419-1428 ◽  
Author(s):  
A. Robinson ◽  
H. Goelzer
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Principal Component ◽  
Climatic Forcing ◽  
Near Surface ◽  
Ice Sheet Modeling ◽  
Higher Temperature ◽  
Surface Melt ◽  
Continental Ice Sheets

Abstract. The growth and retreat of continental ice sheets in the past has largely been a response to changing climatic forcing. Since ablation is the principal component of mass loss for land-based ice sheets, the calculation of surface melt is an important aspect of paleo ice sheet modeling. Changes in insolation are often not accounted for in calculations of surface melt, under the assumption that the near-surface temperature transmits the majority of the climatic forcing to the ice sheet. To assess how this could affect paleo simulations, here we investigate the importance of different orbital configurations for estimating melt on the Greenland ice sheet. We find that during peak Eemian conditions, increased insolation contributes 20–50% to the surface melt anomaly. However, this percentage depends strongly on the temperature anomaly at the time. For higher temperature anomalies, the role of insolation changes is less important. This relationship is not homogenous over the ice sheet, since the contribution of insolation to melt is modulated by the local surface albedo. In coupled simulations, the additional insolation-induced melt translates into up to threefold more ice volume loss, compared to output using a model that does not account for insolation changes. We also introduce a simple correction factor that allows reduced-complexity melt models to account for changes in insolation.

scholarly journals The modelled liquid water balance of the Greenland Ice Sheet

2017 ◽  
Author(s):  
Christian R. Steger ◽  
Carleen H. Reijmer ◽  
Michiel R. van den Broeke
Keyword(s):  
Water Balance ◽  
Liquid Water ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Special Focus ◽  
Southeastern Part ◽  
Upward Migration ◽  
Near Surface ◽  
Surface Mass ◽  
Surface Melt

Abstract. Recent studies indicate that the surface mass balance will dominate the Greenland Ice Sheet's (GrIS) contribution to 21st century sea level rise. Consequently, it is crucial to understand the liquid water balance (LWB) of the ice sheet and its response to increasing surface melt. We therefore analyse a firn simulation conducted with SNOWPACK for the GrIS and over the period 1960–2014 with a special focus on the LWB and refreezing. An indirect evaluation of the simulated refreezing climate with GRACE and firn temperature observations indicate a good model performance. Results of the LWB analysis reveal a spatially uniform increase in surface melt during 1990–2014. As a response, refreezing and runoff also indicate positive trends for this period, where refreezing increases with only half the rate of runoff, which implies that the majority of the additional liquid input runs off the ice sheet. However, this pattern is spatially variable as e.g. in the southeastern part of the GrIS, most of the additional liquid input is buffered in the firn layer due to relatively high snowfall rates. The increase in modelled refreezing leads to a general decrease in firn air content and to a substantial increase in near-surface firn temperature in some regions. On the western side of the ice sheet, modelled firn temperature increases are highest in the lower accumulation zone and are primarily caused by the exceptional melt season of 2012. On the eastern side, simulated firn temperature increases more gradually and with an associated upward migration of firn aquifers.

scholarly journals Evaluation of surface and near-surface melt characteristics on the Greenland ice sheet using MODIS and QuikSCAT data

2009 ◽  
Vol 114 (F4) ◽  
Author(s):  
Dorothy K. Hall ◽  
Son V. Nghiem ◽  
Crystal B. Schaaf ◽  
Nicolo E. DiGirolamo ◽  
Gregory Neumann
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Near Surface ◽  
Surface Melt

scholarly journals Improved representation of the contemporary Greenland ice sheet firn layer by IMAU-FDM v1.2G

2021 ◽  
Author(s):  
Max Brils ◽  
Peter Kuipers Munneke ◽  
Willem Jan van de Berg ◽  
Michiel van den Broeke
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Liquid Water Content ◽  
Climate Forcing ◽  
Air Content ◽  
The Past ◽  
Meltwater Runoff ◽  
Surface Elevation Change ◽  
Increased Sensitivity ◽  
Surface Melt

Abstract. The firn layer that covers 90 % of the Greenland ice sheet (GrIS) plays an important role in determining the response of the ice sheet to climate change. Meltwater can percolate into the firn layer and refreeze at greater depths, thereby temporarily preventing mass loss. However, as global warming leads to increasing surface melt, more surface melt may refreeze in the firn layer, thereby reducing the capacity to buffer subsequent episodes of melt. This can lead to a tipping point in meltwater runoff. It is therefore important to study the evolution of the Greenland firn layer in the past, present and future. In this study, we present the latest version of our firn model, IMAU-FDM (Firn Densification Model), with an application to the GrIS. We improved the density of freshly fallen snow, the dry-snow densification rate and the firn's thermal conductivity using recently published parameterizations and by calibrating to an extended set of observations of firn density, temperature and liquid water content at the GrIS. Overall, the updated model settings lead to higher firn air content and higher 10 m firn temperatures, owing to a lower density near the surface. The effect of the new model settings on the surface elevation change is investigated through three case studies located at Summit, KAN-U and FA-13. Most notably, the updated model shows greater inter- and intra-annual variability in elevation and an increased sensitivity to climate forcing.

scholarly journals Future projections of the Greenland ice sheet energy balance driving the surface melt, developed using the regional climate MAR model

2012 ◽  
Vol 6 (4) ◽  
pp. 2265-2303 ◽  
Author(s):  
B. Franco ◽  
X. Fettweis ◽  
M. Erpicum
Keyword(s):  
Energy Balance ◽  
Cloud Cover ◽  
Surface Albedo ◽  
Regional Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Heat Fluxes ◽  
Near Surface ◽  
Global Circulation Models ◽  
Surface Melt

Abstract. In this study, 25 km-simulations are performed over the Greenland ice sheet (GrIS) throughout the 20th and 21st centuries, using the regional climate model MAR forced by four RCP scenarios from two CMIP5 global circulation models, in order to investigate the projected changes of the surface energy balance (SEB) components driving the surface melt. Analysis of 2000–2100 melt anomalies compared to melt results over 1980–1999 reveals an exponential relationship of the GrIS surface melt rate simulated by MAR to the near-surface temperature (TAS) anomalies, mainly due to the surface albedo positive feedback associated with the extension of bare ice areas in summer. On the GrIS margins, the future melt anomalies are rather driven by stronger sensible heat fluxes, induced by enhanced warm air advections over the ice sheet. Over the central dry snow zone, the increase of melt surpasses the negative feedback from heavier snowfall inducing therefore a decrease of the summer surface albedo even at the top of the ice sheet. In addition to the incoming longwave flux increase associated to the atmosphere warming, MAR projects an increase of the cloud cover decreasing the ratio of the incoming shortwave versus longwave radiation and dampening the albedo feedback. However, it should be noted that this trend in the cloud cover is contrary to that simulated by ERA-INTERIM-forced MAR over current climate, where the observed melt increase since the 1990's seems rather to be a consequence of more anticyclonic atmospheric conditions. Finally, no significant change is projected in the length of the melt season. This timing highlights the importance of solar radiation in the melt SEB.

scholarly journals Improving surface boundary conditions with focus on coupling snow densification and meltwater retention in large-scale ice-sheet models of Greenland

2009 ◽  
Vol 55 (193) ◽  
pp. 869-878 ◽  
Author(s):  
Robert S. Fausto ◽  
Andreas P. Ahlstrøm ◽  
Dirk Van as ◽  
Sigfús J. Johnsen ◽  
Peter L. Langen ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Large Scale ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Boundary ◽  
Snow Layer ◽  
Near Surface ◽  
Surface Mass ◽  
Surface Boundary Conditions ◽  
Surface Melt

AbstractSnowpack changes during the melt season are often not incorporated in modelling studies of the surface mass balance of the Greenland ice sheet. Densification of snow accelerates when meltwater is present, due to percolation and subsequent refreezing, and needs to be incorporated in ice-sheet models for ablation calculations. In this study, simple parameterizations to calculate surface melt, snow densification and meltwater retention are included as surface boundary conditions in a large-scale ice-sheet model of Greenland. Coupling the snow densification and meltwater-retention processes achieves a separation of volume and mass changes of the surface layer, in order to determine the surface melt contribution to runoff. Experiments for present-day conditions show that snow depth at the onset of melt, mean annual near-surface air temperature and the mean density of the annual snow layer are key factors controlling the quantity and spatial distribution of meltwater runoff above the equilibrium line on the Greenland ice sheet.

scholarly journals Brief communication: Firn data compilation reveals the evolution of the firn air content on the Greenland ice sheet

2018 ◽  
Author(s):  
Baptiste Vandecrux ◽  
Michael MacFerrin ◽  
Horst Machguth ◽  
William T. Colgan ◽  
Dirk van As ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Sea Level ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Retention Capacity ◽  
Near Surface ◽  
Air Content ◽  
Data Compilation ◽  
Surface Melt ◽  
Firn Core

Abstract. The firn covering the Greenland ice sheet interior can retain part of the surface melt, buffering the ice sheet’s contribution to sea level, but its characteristics are still little known. Using remote-sensing observations from 2000–2017, we estimate that firn covers 1,405,500 ± 17,250 km2 of the ice sheet. We present 344 firn-core-derived observations of the top 10 m firn air content (FAC10), indicative of the firn’s meltwater retention capacity. FAC10 remained stable in the coldest 74 % of the firn area during 1953–2017, while FAC10 decreased in the warmest and driest 12 % of the firn area between 1997–2008 and 2011–2017, resulting in a loss of 180 ± 78 km3 (−26 ± 11 %) of air from the near-surface firn.

scholarly journals The modelled liquid water balance of the Greenland Ice Sheet

2017 ◽  
Vol 11 (6) ◽  
pp. 2507-2526 ◽  
Author(s):  
Christian R. Steger ◽  
Carleen H. Reijmer ◽  
Michiel R. van den Broeke
Keyword(s):  
Water Balance ◽  
Liquid Water ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Special Focus ◽  
Near Surface ◽  
Surface Mass ◽  
Run Off ◽  
Surface Melt ◽  
Western Side

Abstract. Recent studies indicate that the surface mass balance will dominate the Greenland Ice Sheet's (GrIS) contribution to 21st century sea level rise. Consequently, it is crucial to understand the liquid water balance (LWB) of the ice sheet and its response to increasing surface melt. We therefore analyse a firn simulation conducted with the SNOWPACK model for the GrIS and over the period 1960–2014 with a special focus on the LWB and refreezing. Evaluations of the simulated refreezing climate with GRACE and firn temperature observations indicate a good model–observation agreement. Results of the LWB analysis reveal a spatially uniform increase in surface melt (0.16 m w.e. a−1) during 1990–2014. As a response, refreezing and run-off also indicate positive changes during this period (0.05 and 0.11 m w.e. a−1, respectively), where refreezing increases at only half the rate of run-off, implying that the majority of the additional liquid input runs off the ice sheet. This pattern of refreeze and run-off is spatially variable. For instance, in the south-eastern part of the GrIS, most of the additional liquid input is buffered in the firn layer due to relatively high snowfall rates. Modelled increase in refreezing leads to a decrease in firn air content and to a substantial increase in near-surface firn temperature. On the western side of the ice sheet, modelled firn temperature increases are highest in the lower accumulation zone and are primarily caused by the exceptional melt season of 2012. On the eastern side, simulated firn temperature increases are more gradual and are associated with the migration of firn aquifers to higher elevations.

scholarly journals Future projections of the Greenland ice sheet energy balance driving the surface melt

2013 ◽  
Vol 7 (1) ◽  
pp. 1-18 ◽  
Author(s):  
B. Franco ◽  
X. Fettweis ◽  
M. Erpicum
Keyword(s):  
Energy Balance ◽  
Positive Feedback ◽  
Cloud Cover ◽  
Surface Albedo ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Near Surface ◽  
Global Circulation Models ◽  
Recent Climate ◽  
Surface Melt

Abstract. In this study, simulations at 25 km resolution are performed over the Greenland ice sheet (GrIS) throughout the 20th and 21st centuries, using the regional climate model MAR forced by four RCP scenarios from three CMIP5 global circulation models (GCMs), in order to investigate the projected changes of the surface energy balance (SEB) components driving the surface melt. Analysis of 2000–2100 melt anomalies compared to melt results over 1980–1999 reveals an exponential relationship of the GrIS surface melt rate simulated by MAR to the near-surface air temperature (TAS) anomalies, mainly due to the surface albedo positive feedback associated with the extension of bare ice areas in summer. On the GrIS margins, the future melt anomalies are preferentially driven by stronger sensible heat fluxes, induced by enhanced warm air advection over the ice sheet. Over the central dry snow zone, the surface albedo positive feedback induced by the increase in summer melt exceeds the negative feedback of heavier snowfall for TAS anomalies higher than 4 °C. In addition to the incoming longwave flux increase associated with the atmosphere warming, GCM-forced MAR simulations project an increase of the cloud cover decreasing the ratio of the incoming shortwave versus longwave radiation and dampening the albedo feedback. However, it should be noted that this trend in the cloud cover is contrary to that simulated by ERA-Interim–forced MAR for recent climate conditions, where the observed melt increase since the 1990s seems mainly to be a consequence of more anticyclonic atmospheric conditions. Finally, no significant change is projected in the length of the melt season, which highlights the importance of solar radiation absorbed by the ice sheet surface in the melt SEB.

scholarly journals Greenland Ice Sheet Surface Melt and Its Relation to Daily Atmospheric Conditions

2018 ◽  
Vol 31 (5) ◽  
pp. 1897-1919 ◽  
Author(s):  
Richard I. Cullather ◽  
Sophie M. J. Nowicki
Keyword(s):  
Regression Analysis ◽  
Sea Level ◽  
Time Scales ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Radiative Flux ◽  
Near Surface ◽  
Synoptic Conditions ◽  
Surface Melt ◽  
Solar Radiative Flux

Melt area is one of the most reliably monitored variables associated with surface conditions over the full Greenland Ice Sheet (GrIS). Surface melt is also an important indicator of surface mass balance and has potential relevance to the ice sheet’s global sea level contribution. Melt events are known to be spatially heterogeneous and have varying time scales. To understand the forcing mechanisms, it is necessary to examine the relation between the existing conditions and melt area on the time scales that melt is observed. Here, the authors conduct a regression analysis of atmospheric reanalysis variables including sea level pressure, near-surface winds, and components of the surface energy budget with surface melt. The regression analysis finds spatial heterogeneity in the associated atmospheric circulation conditions. For basins in the southern GrIS, there is an association between melt area and high pressure located south of the Denmark Strait, which allows for southerly flow over the western half of the GrIS. Instantaneous surface melt over northern basins is also associated with low pressure over the central Arctic. Basins associated with persistent summer melt in the southern and western GrIS are associated with the presence of an enhanced cloud cover, a resulting decreased downwelling solar radiative flux, and an enhanced downwelling longwave radiative flux. This contrasts with basins to the north and east, where an increased downwelling solar radiative flux plays a more important role in the onset of a melt event. The analysis emphasizes the importance of daily variability in synoptic conditions and their preferred association with melt events.

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