Surface layer climate and turbulent exchange in the ablation zone of the west Greenland ice sheet

2009 ◽  
Vol 29 (15) ◽  
pp. 2309-2323 ◽  
Author(s):  
Michiel van den Broeke ◽  
Paul Smeets ◽  
Janneke Ettema
Keyword(s):  
Surface Layer ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Turbulent Exchange ◽  
Ablation Zone ◽  
The West ◽  
West Greenland

scholarly journals Characteristics of the lower ablation zone of the West Greenland ice sheet for energy-balance modelling

1996 ◽  
Vol 23 ◽  
pp. 160-166 ◽  
Author(s):  
Michiel van den Broeke
Keyword(s):  
Heat Flux ◽  
Energy Balance ◽  
Global Radiation ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Longwave Radiation ◽  
Turbulent Fluxes ◽  
Ablation Zone ◽  
The West ◽  
West Greenland

In this paper, we present the summer-time energy balance for a site in the lower ablation zone of the West Greenland ice sheet. The summer climate of this part of Greenland is sunny and dry. The energy that is available for melting (on average 174 W m−2or 4.5 cm w.e.d−1) is mainly provided by net global radiation two-thirds and sensible-heat flux (one-third). The contribution of the sub-surface heat flux, the latent-heat flux and the net longwave radiation to the energy balance are small. We tested some parameterizations to calculate energy-balance components that are currently used in general circulation models, energy-balance models and mesoscale meteorological models. For the area and time period under consideration, parameterizations that use screen-level temperature for the calculation of incoming longwave radiation systematically underestimate this quantity by 10 W m−2owing to the proximity of the melting-ice surface that restricts temperature increase of the lowest air layers. The incoming global radiation was predicted correctly. Simple explicit schemes that calculate the stability corrections for turbulent fluxes as a function of the bulk Richardson number tend to underestimate the turbulent fluxes by 15 W m−2. The aerodynamic roughness lengthz0derived from wind-speed profiles appears to be erroneously small, leading to underestimation of the fluxes by 30 W m−2. Probably, the wind profile is distorted by the rough terrain. An estimate ofz0biased on microtopographical survey yielded a more realistic result. Because all errors work in the same direction, the use of some of the parameterizations can cause serious underestimation of the melting energy.

scholarly journals Partitioning of melt energy and meltwater fluxes in the ablation zone of the west Greenland ice sheet

2008 ◽  
Vol 2 (2) ◽  
pp. 179-189 ◽  
Author(s):  
M. van den Broeke ◽  
P. Smeets ◽  
J. Ettema ◽  
C. van der Veen ◽  
R. van de Wal ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Snow Accumulation ◽  
Ablation Zone ◽  
The West ◽  
Near Surface ◽  
Surface Mass ◽  
West Greenland ◽  
Ice Melt ◽  
June July

Abstract. We present four years (August 2003–August 2007) of surface mass balance data from the ablation zone of the west Greenland ice sheet along the 67° N latitude circle. Sonic height rangers and automatic weather stations continuously measured accumulation/ablation and near-surface climate at distances of 6, 38 and 88 km from the ice sheet margin at elevations of 490, 1020 and 1520 m a.s.l. Using a melt model and reasonable assumptions about snow density and percolation characteristics, these data are used to quantify the partitioning of energy and mass fluxes during melt episodes. The lowest site receives very little winter accumulation, and ice melting is nearly continuous in June, July and August. Due to the lack of snow accumulation, little refreezing occurs and virtually all melt energy is invested in runoff. Higher up the ice sheet, the ice sheet surface freezes up during the night, making summer melting intermittent. At the intermediate site, refreezing in snow consumes about 10% of the melt energy, increasing to 40% at the highest site. The sum of these effects is that total melt and runoff increase exponentially towards the ice sheet margin, each time doubling between the stations. At the two lower sites, we estimate that radiation penetration causes 20–30% of the ice melt to occur below the surface.

scholarly journals Surface radiation balance in the ablation zone of the west Greenland ice sheet

2008 ◽  
Vol 113 (D13) ◽  
Author(s):  
Michiel van den Broeke ◽  
Paul Smeets ◽  
Janneke Ettema ◽  
Peter Kuipers Munneke
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Radiation ◽  
Radiation Balance ◽  
Ablation Zone ◽  
The West ◽  
West Greenland

scholarly journals Partitioning of melt energy and meltwater fluxes in the ablation zone of the west Greenland ice sheet

2008 ◽  
Vol 2 (4) ◽  
pp. 711-736 ◽  
Author(s):  
M. Van den Broeke ◽  
P. Smeets ◽  
J. Ettema ◽  
C. Van der Veen ◽  
R. Van de Wal ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Snow Accumulation ◽  
Ablation Zone ◽  
The West ◽  
Near Surface ◽  
Surface Mass ◽  
West Greenland ◽  
Ice Melt ◽  
June July

Abstract. We present four years of surface mass balance data from the ablation zone of the west Greenland ice sheet along the 67° N latitude circle. Sonic height rangers and automatic weather stations continuously measured accumulation/ablation and near-surface climate at distances of 6, 38 and 88 km from the ice sheet margin at elevations of 490, 1020 and 1520 m a.s.l. Using a melt model and reasonable assumptions about snow density and percolation characteristics, these data are used to quantify the partitioning of energy and mass fluxes during melt episodes. The lowest site receives very little winter accumulation, and ice melting is nearly continuous in June, July and August. Due to the lack of snow accumulation, little refreezing occurs and virtually all melt energy is invested in runoff. Higher up the ice sheet, the ice sheet surface freezes up during the night, making summer melting intermittent. At the intermediate site, refreezing in snow consumes about 10% of the melt energy, increasing to 40% at the highest site. The sum of these effects is that total melt and runoff increase exponentially towards the ice sheet margin, each time doubling between the stations. At the two lower sites, we estimate that radiation penetration causes 20–30% of the ice melt to occur below the surface.

scholarly journals Characteristics of the lower ablation zone of the West Greenland ice sheet for energy-balance modelling

1996 ◽  
Vol 23 ◽  
pp. 160-166 ◽  
Author(s):  
Michiel van den Broeke
Keyword(s):  
Heat Flux ◽  
Energy Balance ◽  
Global Radiation ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Longwave Radiation ◽  
Turbulent Fluxes ◽  
Ablation Zone ◽  
The West ◽  
West Greenland

In this paper, we present the summer-time energy balance for a site in the lower ablation zone of the West Greenland ice sheet. The summer climate of this part of Greenland is sunny and dry. The energy that is available for melting (on average 174 W m−2 or 4.5 cm w.e.d−1) is mainly provided by net global radiation two-thirds and sensible-heat flux (one-third). The contribution of the sub-surface heat flux, the latent-heat flux and the net longwave radiation to the energy balance are small. We tested some parameterizations to calculate energy-balance components that are currently used in general circulation models, energy-balance models and mesoscale meteorological models. For the area and time period under consideration, parameterizations that use screen-level temperature for the calculation of incoming longwave radiation systematically underestimate this quantity by 10 W m−2 owing to the proximity of the melting-ice surface that restricts temperature increase of the lowest air layers. The incoming global radiation was predicted correctly. Simple explicit schemes that calculate the stability corrections for turbulent fluxes as a function of the bulk Richardson number tend to underestimate the turbulent fluxes by 15 W m−2. The aerodynamic roughness length z0 derived from wind-speed profiles appears to be erroneously small, leading to underestimation of the fluxes by 30 W m−2. Probably, the wind profile is distorted by the rough terrain. An estimate of z0 biased on microtopographical survey yielded a more realistic result. Because all errors work in the same direction, the use of some of the parameterizations can cause serious underestimation of the melting energy.

scholarly journals Topographic and Glaciological Controls on Holocene Ice-Sheet Margin Dynamics. Central West Greenland

1990 ◽  
Vol 14 ◽  
pp. 307-310 ◽  
Author(s):  
C.R. Warren ◽  
N.R.J. Hulton
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Glacial Maximum ◽  
Warm Climate ◽  
Short Term ◽  
The West ◽  
West Greenland ◽  
The Past

The retreat of the West Greenland ice sheet from its Sisimiut (Wisconsinan) glacial maximum, was punctuated by a series of Stillstands or small readvances that formed numerous moraines. These landforms have been interpreted in the past as the result of short-term, regional falls in ablation-season temperatures. However, mapping of the geomorphological evidence south of Ilulissat (Jakobshavn) suggests that retreat behaviour was not primarily governed by climate, and therefore that the former ice margins are not palaeoclimatically significant. During warm climate ice-sheet wastage, the successive quasi-stable positions adopted by the ice margin were largely governed by topography. The retreat of the inherently unstable calving glaciers was arrested only at topographically-determined locations where stability could be achieved.

scholarly journals Early Holocene history of the west Greenland Ice Sheet and the GH-8.2 event

2006 ◽  
Vol 25 (9-10) ◽  
pp. 904-922 ◽  
Author(s):  
A.J. Long ◽  
D.H. Roberts ◽  
S. Dawson
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Early Holocene ◽  
The West ◽  
West Greenland ◽  
History Of

scholarly journals The seasonal cycle and interannual variability of surface energy balance and melt in the ablation zone of the west Greenland ice sheet

2011 ◽  
Vol 5 (2) ◽  
pp. 377-390 ◽  
Author(s):  
M. R. van den Broeke ◽  
C. J. P. P. Smeets ◽  
R. S. W. van de Wal
Keyword(s):  
Energy Balance ◽  
Surface Energy ◽  
Interannual Variability ◽  
Seasonal Cycle ◽  
Surface Energy Balance ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Shortwave Radiation ◽  
Ablation Zone ◽  
The West

Abstract. We present the seasonal cycle and interannual variability of the surface energy balance (SEB) in the ablation zone of the west Greenland ice sheet, using seven years (September 2003–August 2010) of hourly observations from three automatic weather stations (AWS). The AWS are situated along the 67° N latitude circle at elevations of 490 m a.s.l. (S5), 1020 m a.s.l. (S6) and 1520 m a.s.l. (S9) at distances of 6, 38 and 88 km from the ice sheet margin. The hourly AWS data are fed into a model that calculates all SEB components and melt rate; the model allows for shortwave radiation penetration in ice and time-varying surface momentum roughness. Snow depth is prescribed from albedo and sonic height ranger observations. Modelled and observed surface temperatures for non-melting conditions agree very well, with RMSE's of 0.97–1.26 K. Modelled and observed ice melt rates at the two lowest sites also show very good agreement, both for total cumulative and 10-day cumulated amounts. Melt frequencies and melt rates at the AWS sites are discussed. Although absorbed shortwave radiation is the most important energy source for melt at all three sites, interannual melt variability at the lowest site is driven mainly by variability in the turbulent flux of sensible heat. This is explained by the quasi-constant summer albedo in the lower ablation zone, limiting the influence of the melt-albedo feedback, and the proximity of the snow free tundra, which heats up considerably in summer.

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