P. Kuipers Munneke

A new, high-resolution surface mass balance map of Antarctica (1979–2010) based on regional atmospheric climate modeling

A new, high resolution (27 km) surface mass balance (SMB) map of the Antarctic ice sheet is presented, based on output of a regional atmospheric climate model that includes snowdrift physics and is forced by the most recent reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF), ERA-Interim (1979–2010). The SMB map confirms high accumulation zones in the western Antarctic Peninsula (>1500 mm y!1) and coastal West Antarctica (>1000 mm y!1), and shows low SMB values in large parts of the interior ice sheet (

Explaining the presence of perennial liquid water bodies in the firn of the Greenland Ice Sheet

Recent observations have shown that the firn layer on the Greenland Ice Sheet features subsurface bodies of liquid water at the end of the winter season. Using a model with basic firn hydrology, thermodynamics, and compaction in one dimension, we find that a combination of moderate to strong surface melt and a high annual accumulation rate is required to form such a perennial firn aquifer. The high accumulation rate ensures that there is pore space available to store water at a depth where it is protected from the winter cold. Low-accumulation sites cannot provide sufficiently deep pore space to store liquid water. However, for even higher accumulation rates, the total cold content of the winter accumulation becomes sufficient to refreeze the total amount of liquid water. As a consequence, wintertime or springtime observations of subsurface liquid water in these specific accumulation conditions cannot distinguish between a truly perennial firn aquifer and water layers that will ultimately refreeze completely.

Validation of the summertime surface energy budget of Larsen C Ice Shelf (Antarctica) as represented in three high-resolution atmospheric models

We compare measurements of the turbulent and radiative surface energy fluxes from an automatic weather station (AWS) on Larsen C Ice Shelf, Antarctica with corresponding fluxes from three high-resolution atmospheric models over a 1 month period during austral summer. All three models produce a reasonable simulation of the (relatively small) turbulent energy fluxes at the AWS site. However, biases in the modeled radiative fluxes, which dominate the surface energy budget, are significant. There is a significant positive bias in net shortwave radiation in all three models, together with a corresponding negative bias in net longwave radiation. In two of the models, the longwave bias only partially offsets the positive shortwave bias, leading to an excessive amount of energy available for heating and melting the surface, while, in the third, the negative longwave bias exceeds the positive shortwave bias, leading to a deficiency in calculated surface melt. Biases in shortwave and longwave radiation are anticorrelated, suggesting that they both result from the models simulating too little cloud (or clouds that are too optically thin). We conclude that, while these models may be able to provide some useful information on surface energy fluxes, absolute values of modeled melt rate are significantly biased and should be used with caution. Efforts to improve model simulation of melt should initially focus on the radiative fluxes and, in particular, on the simulation of the clouds that control these fluxes.

A modeling study of the effect of runoff variability on the effective pressure beneath Russell Glacier, West Greenland

Basal sliding is a main control on glacier flow primarily driven by water pressure at the glacier base. The ongoing increase in surface melting of the Greenland Ice Sheet warrants an examination of its impact on basal water pressure and in turn on basal sliding. Here we examine the case of Russell Glacier, in West Greenland, where an extensive set of observations has been collected. These observations suggest that the recent increase in melt has had an equivocal impact on the annual velocity, with stable flow on the lower part of the drainage basin but accelerated flow above the Equilibrium Line Altitude (ELA). These distinct behaviors have been attributed to different evolutions of the subglacial draining system during and after the melt season. Here we use a high-resolution subglacial hydrological model forced by reconstructed surface runoff for the period 2008 to 2012 to investigate the cause of these distinct behaviors. We find that the increase in meltwater production at low elevation yields a more efficient drainage system compatible with the observed stagnation of the mean annual flow below the ELA. At higher elevation, the model indicates that the drainage system is mostly inefficient and is therefore strongly sensitive to an increase in meltwater availability, which is consistent with the observed increase in ice velocity.

A new, high resolution surface mass balance map of Antarctica (1979-2010) based on regional climate modeling

A new, high resolution (27 km) surface mass balance (SMB) map of the Antarctic ice sheet is presented, based on output of a regional atmospheric climate model that includes snowdrift physics and is forced by the most recent reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF), ERA-Interim (1979–2010). The SMB map confirms high accumulation zones in the western Antarctic Peninsula (>1500 mm y!1) and coastal West Antarctica (>1000 mm y!1), and shows low SMB values in large parts of the interior ice sheet (

The K-transect on the western Greenland Ice Sheet: Surface energy balance (2003–2016)

ABSTRACT We present thirteen years (2003–2016) of surface energy balance calculations from automatic weather stations (AWS) along the K-transect in west Greenland. Although short in a climatological sense, these time series start to become long enough to provide valuable insight into the interannual variability and drivers of melt in this part of Greenland and into trends in certain components of the surface energy balance. For instance, the data clearly reveal that albedo variations explain most of the interannual melt variability at the higher stations in the accumulation zone. Sensible heat becomes a major heat source for melt in the lower ablation zone, while latent heat modulates annual melt by up to 20 W m−2. Also, at two locations with the longest uninterrupted time series, we see a decreasing trend of incoming longwave radiation (−1.2 to −1.4 W m−2 y−1, p < 0.10) concurrent with an increase in incoming shortwave radiation (+2.4 to +3.8 W m−2 y−1, p < 0.10) during the observation period. This suggests that decreasing cloud cover plays a role in the increased availability of melt energy (+0.7 to +2.2 W m−2 y−1, not statistically significant at p < 0.10). At the AWS situated around the equilibrium line altitude (ELA), the observed negative trend in albedo is strongest of all stations (−0.0087 y−1), as the ELA moves upward and bare ice becomes exposed. These insights are important for modeling the future response of the ice sheet to continued global warming, which is expected to be dominated by surface processes.

Antarctic firn compaction rates from repeat-track airborne radar data : II. Firn model evaluation

Abstract The thickness and density of the Antarctic firn layer vary considerably in time and space, thereby contributing to ice-sheet volume and mass changes. Distinguishing between these mass and volume changes is important for ice-sheet mass-balance studies. Evolution of firn layer depth and density is often modeled, because direct measurements are scarce. Here we directly compare modeled firn compaction rates with observed rates obtained from repeat-track airborne radar data over a 2 year interval (2009–11) in West Antarctica. Spatially, the observed compaction rates exhibit significant variability, but when averaged to scales comparable to the model resolution (20–50 km), the measurements and model results qualitatively agree. A colder and drier period preceding the 2009 survey led to lower compaction rates during the 2009–10 interval, when compared to 2010–11, which is partly captured by the firn model. Spatially, higher compaction rates are observed and modeled in warmer regions with higher accumulation.

The Impact of Föhn Winds on Surface Energy Balance During the 2010-2011 Melt Season Over Larsen C Ice Shelf, Antarctica

We use model data from the Antarctic Mesoscale Prediction System (AMPS), measurements from automatic weather stations and satellite observations to investigate the association between surface energy balance (SEB), surface melt, and the occurrence of fohn winds over Larsen C Ice Shelf (Antarctic Peninsula) over the period November 2010 to March 2011. Fohn conditions occurred for over 20% of the time during this period and are associated with increased air temperatures and decreased relative humidity (relative to nonfohn conditions) over the western part of the ice shelf. During fohn conditions, the downward turbulent flux of sensible heat and the downwelling shortwave radiation both increase. However, in AMPS, these warming tendencies are largely balanced by an increase in upward latent heat flux and a decrease in downwelling longwave radiation so the impact of fohn on the modeled net SEB is small. This balance is highly sensitive to the representation of surface energy fluxes in the model, and limited validation data suggest that AMPS may underestimate the sensitivity of SEB and melt to fohn. There is broad agreement on the spatial pattern of melt between the model and satellite observations but disagreement in the frequency with which melt occurs. Satellite observations indicate localized regions of persistent melt along the foot of the Antarctic Peninsula mountains which are not simulated by the model. Furthermore, melt is observed to persist in these regions during extended periods when fohn does not occur, suggesting that other factors may be important in controlling melt in these regions.

Intense Winter Surface Melt on an Antarctic Ice Shelf

The occurrence of surface melt in Antarctica has hitherto been associated with the austral summer season, when the dominant source of melt energy is provided by solar radiation. We use in situ and satellite observations from a previously unsurveyed region to show that events of intense surface melt on Larsen C Ice Shelf occur frequently throughout the dark Antarctic winter, with peak intensities sometimes exceeding summertime values. A regional atmospheric model confirms that in the absence of solar radiation, these multiday melt events are driven by outbreaks of warm and dry fohn wind descending down the leeside of the Antarctic Peninsula mountain range, resulting in downward turbulent fluxes of sensible heat that drive sustained surface melt fluxes in excess of 200 W/m2. From 2015 to 2017 (including the extreme melt winter of 2016), ∼23% of the annual melt flux was produced in winter, and spaceborne observations of surface melt since 2000 show that wintertime melt is widespread in some years. Winter melt heats the firn layer to the melting point up to a depth of ∼3 m, thereby facilitating the formation of impenetrable ice layers and retarding or reversing autumn and winter cooling of the firn. While the absence of a trend in winter melt is consistent with insignificant changes in the observed Southern Hemisphere atmospheric circulation during winter, we anticipate an increase in winter melt as a response to increasing greenhouse gas concentration.

Clear‐sky Atmospheric Radiative Transfer: A Model Intercomparison for Shortwave Irradiances

This study consists of an intercomparison of clear-sky shortwave irradiances calculated by the Doubling Adding model of KNMI (DAK) and the Simple Model of the Atmospheric Radiative Transfer of Sunshine (SMARTS). The DAK and SMARTS models are run with identical input (state profiles, water vapour, ozone, aerosols, etc.) and the differences between the models are examined in terms of broadband shortwave irradiances as a function of solar zenithangle. The DAK and SMARTS models agree very well. For a pure Rayleigh atmosphere the differences in the irradiances are less than 5 W/m2. For cases with aerosols the differences of the irradiances are within 10 W/m2.