scholarly journals Importance of Orography for Greenland Cloud and Melt Response to Atmospheric Blocking

2020 ◽  
Vol 33 (10) ◽  
pp. 4187-4206 ◽  
Author(s):  
L. C. Hahn ◽  
T. Storelvmo ◽  
S. Hofer ◽  
R. Parfitt ◽  
C. C. Ummenhofer
Keyword(s):  
High Pressure ◽  
Cloud Cover ◽  
Large Scale ◽  
Climate Model ◽  
Model Simulation ◽  
Regional Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Atmospheric Blocking ◽  
Circulation Anomalies

AbstractMore frequent high pressure conditions associated with atmospheric blocking episodes over Greenland in recent decades have been suggested to enhance melt through large-scale subsidence and cloud dissipation, which allows more solar radiation to reach the ice sheet surface. Here we investigate mechanisms linking high pressure circulation anomalies to Greenland cloud changes and resulting cloud radiative effects, with a focus on the previously neglected role of topography. Using reanalysis and satellite data in addition to a regional climate model, we show that anticyclonic circulation anomalies over Greenland during recent extreme blocking summers produce cloud changes dependent on orographic lift and descent. The resulting increased cloud cover over northern Greenland promotes surface longwave warming, while reduced cloud cover in southern and marginal Greenland favors surface shortwave warming. Comparison with an idealized model simulation with flattened topography reveals that orographic effects were necessary to produce area-averaged decreasing cloud cover since the mid-1990s and the extreme melt observed in the summer of 2012. This demonstrates a key role for Greenland topography in mediating the cloud and melt response to large-scale circulation variability. These results suggest that future melt will depend on the pattern of circulation anomalies as well as the shape of the Greenland Ice Sheet.

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 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 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 Climate of the Greenland ice sheet using a high-resolution climate model – Part 2: Near-surface climate and energy balance

2010 ◽  
Vol 4 (2) ◽  
pp. 603-639 ◽  
Author(s):  
J. Ettema ◽  
M. R. van den Broeke ◽  
E. van Meijgaard ◽  
W. J. van de Berg
Keyword(s):  
High Resolution ◽  
Large Scale ◽  
Climate Model ◽  
Regional Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Katabatic Wind ◽  
Surface Cooling ◽  
Near Surface ◽  
Surface Climate

Abstract. The near-surface climate of the Greenland ice sheet is characterized by persistent katabatic winds and quasi-permanent temperature deficit. Using a high resolution (11 km) regional climate model allows for detailed study of the spatial variability in these phenomena and the underlying atmospheric processes. The near-surface temperature distribution over the ice sheet is clearly affected by elevation, latitude, large scale advection, meso-scale topographic features and the occurrence of summer melt. The lowest annual temperatures of −30.5 °C are found north of the highest elevations of the GrIS, whereas the lowest southern margins are warmest (−3.5 °C). Over the ice sheet, a persistent katabatic wind system develops due to radiative surface cooling and the gently slope of the surface. The strongest wind speeds are seen in the northeast where the strong large scale winds, low cloud cover and concave surface force a continuous supply of cold air, which enhances the katabatic forcing. The radiative cooling of the surface is controlled by the net longwave emission and transport of heat towards the surface by turbulence. In summer this mechanism is much weaker, leading to less horizontal variability in near-surface temperatures and wind speed.

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 Liquid Water Flow and Retention on the Greenland Ice Sheet in the Regional Climate Model HIRHAM5: Local and Large-Scale Impacts

2017 ◽  
Vol 4 ◽  
Author(s):  
Peter L. Langen ◽  
Robert S. Fausto ◽  
Baptiste Vandecrux ◽  
Ruth H. Mottram ◽  
Jason E. Box
Keyword(s):  
Regional Climate Model ◽  
Water Flow ◽  
Liquid Water ◽  
Large Scale ◽  
Climate Model ◽  
Regional Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet

scholarly journals Modelling of large-scale melt parameters with a regional climate model in south Greenland during the 1991 melt season

2002 ◽  
Vol 35 ◽  
pp. 391-397 ◽  
Author(s):  
Filip Lefebre ◽  
Hubert Gallée ◽  
Jean-Pascal Van Ypersele ◽  
Philippe Huybrechts
Keyword(s):  
Regional Climate Model ◽  
Large Scale ◽  
Climate Model ◽  
Regional Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Temperature Deviation ◽  
Degree Day ◽  
Positive Degree ◽  
Snow And Ice

AbstractLarge-scale positive degree-day based melt parameterizations for the Greenland ice sheet are highly sensitive to their parameters (standard temperature deviation, snow and ice degree-day factors). In this paper, these parameters are simulated with a coupled atmosphere–snow regional climate model for southern Greenland during summer 1991, forced at the lateral boundaries with European Centre for Medium-Range Weather Forecasts re-analyses at a high horizontal resolution of 20 km. the calculated (from net ablation, i.e. melt minus refreezing) snow and ice positive degree-day factors vary considerably over the ice sheet. At low elevations, the modelled snow degree-day factor closely approaches the generally accepted value of 3 mm w.e. d–1 ˚C–1.Higher up the ice sheet, large values up to 15 mm w.e. d– 1 ˚C– 1 are simulated. for ice melt, maximum values of 40 mm w.e. d–1 ˚C– 1 are found. the snow and ice positive degree-day factor distributions peak, respectively, at 3 and 8mm w.e. d–1 ˚C–1. Refreezing is of small importance close to the ice-sheet margin. Higher up the ice sheet, refreezing considerably lowers the amount of net ablation. the monthly simulated 2 m air-temperature standard deviation exhibits a strong seasonal cycle, with the highest (3.0–5.0˚C) values in May and June. July shows the lowest temperature fluctuations, due to the melting of the surface.

scholarly journals Sensitivity of Greenland Ice Sheet Projections to Model Formulations

2013 ◽  
Vol 59 (216) ◽  
pp. 733-749 ◽  
Author(s):  
H. Goelzer ◽  
P. Huybrechts ◽  
J.J. Fürst ◽  
F.M. Nick ◽  
M.L. Andersen ◽  
...  
Keyword(s):  
Regional Climate Model ◽  
Sea Level ◽  
Flow Model ◽  
Climate Model ◽  
Regional Climate ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Flow ◽  
Outlet Glacier ◽  
Glacier Dynamics

AbstractPhysically based projections of the Greenland ice sheet contribution to future sea-level change are subject to uncertainties of the atmospheric and oceanic climatic forcing and to the formulations within the ice flow model itself. Here a higher-order, three-dimensional thermomechanical ice flow model is used, initialized to the present-day geometry. The forcing comes from a high-resolution regional climate model and from a flowline model applied to four individual marine-terminated glaciers, and results are subsequently extended to the entire ice sheet. The experiments span the next 200 years and consider climate scenario SRES A1B. The surface mass-balance (SMB) scheme is taken either from a regional climate model or from a positive-degree-day (PDD) model using temperature and precipitation anomalies from the underlying climate models. Our model results show that outlet glacier dynamics only account for 6–18% of the sea-level contribution after 200 years, confirming earlier findings that stress the dominant effect of SMB changes. Furthermore, interaction between SMB and ice discharge limits the importance of outlet glacier dynamics with increasing atmospheric forcing. Forcing from the regional climate model produces a 14–31 % higher sea-level contribution compared to a PDD model run with the same parameters as for IPCC AR4.

scholarly journals Dependence of Eemian Greenland temperature reconstructions on the ice sheet topography

2013 ◽  
Vol 9 (6) ◽  
pp. 6683-6732
Author(s):  
N. Merz ◽  
A. Born ◽  
C. C. Raible ◽  
H. Fischer ◽  
T. F. Stocker
Keyword(s):  
Energy Balance ◽  
Surface Energy ◽  
Large Scale ◽  
Surface Energy Balance ◽  
Climate Model ◽  
Surface Wind ◽  
Sensible Heat Flux ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Lapse Rate

Abstract. The influence of a reduced Greenland ice sheet (GrIS) on Greenland's surface climate during the Eemian interglacial is studied using a comprehensive climate model. We find a distinct impact of changes in the GrIS topography on Greenland's surface air temperatures (SAT) even when correcting for changes in surface elevation which influences SAT through the lapse rate effect. The resulting lapse rate corrected SAT anomalies are thermodynamically driven by changes in the local surface energy balance rather than dynamically caused through anomalous advection of warm/cold air masses. The large-scale circulation is indeed very stable among all sensitivity experiments and the NH flow pattern does not depend on Greenland's topography in the Eemian. In contrast, Greenland's surface energy balance is clearly influenced by changes in the GrIS topography and this impact is seasonally diverse. In winter, the variable reacting strongest to changes in the topography is the sensible heat flux (SHFLX). The reason is its dependence on surface winds, which themselves are controlled to a large extent by the shape of the GrIS. Hence, regions where a receding GrIS causes higher surface wind velocities also experience anomalous warming through SHFLX. Vice-versa, regions that become flat and ice-free are characterized by low wind speeds, low SHFLX and anomalous cold winter temperatures. In summer, we find surface warming induced by a decrease in surface albedo in deglaciated areas and regions which experience surface melting. The Eemian temperature records derived from Greenland proxies, thus, likely include a temperature signal arising from changes in the GrIS topography. For the NEEM ice core site, our model suggests that up to 3.2 °C of the annual mean Eemian warming can be attributed to these topography-related processes and hence is not necessarily linked to large-scale climate variations.

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