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  • 1.
    Charalampidis, Charalampos
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Geological Survey of Denmark and Greenland (GEUS).
    van As, Dirk
    Geological Survey of Denmark and Greenland (GEUS).
    Box, Jason E.
    Geological Survey of Denmark and Greenland (GEUS).
    van den Broeke, Michiel R.
    Institute for Marine and Atmospheric Research in Utrecht (IMAU).
    Colgan, William T.
    Geological Survey of Denmark and Greenland (GEUS).
    Doyle, Samuel H.
    Aberystwyth University.
    Hubbard, Alun L.
    University of Tromsø.
    MacFerrin, Michael
    Cooperative Institute for Research in Environmental Sciences (CIRES).
    Machguth, Horst
    Geological Survey of Denmark and Greenland (GEUS).
    Smeets, C. J. P. Paul
    Institute for Marine and Atmospheric Research in Utrecht (IMAU).
    Changing surface-atmosphere energy exchange and refreezing capacity of the lower accumulation area, West Greenland2015In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 9, no 6, p. 2163-2181Article in journal (Refereed)
    Abstract [en]

    We present 5 years (2009-2013) of automatic weather station measurements from the lower accumulation area (1840 m a.s.l. - above sea level) of the Greenland ice sheet in the Kangerlussuaq region. Here, the summers of 2010 and 2012 were both exceptionally warm, but only 2012 resulted in a strongly negative surface mass budget (SMB) and surface meltwater run-off. The observed run-off was due to a large ice fraction in the upper 10 m of firn that prevented meltwater from percolating to available pore volume below. Analysis reveals an anomalously low 2012 summer-averaged albedo of 0.71 (typically similar to 0.78), as meltwater was present at the ice sheet surface. Consequently, during the 2012 melt season, the ice sheet surface absorbed 28% (213 MJ m-2) more solar radiation than the average of all other years. A surface energy balance model is used to evaluate the seasonal and interannual variability of all surface energy fluxes. The model reproduces the observed melt rates as well as the SMB for each season. A sensitivity analysis reveals that 71% of the additional solar radiation in 2012 was used for melt, corresponding to 36% (0.64 m) of the 2012 surface lowering. The remaining 64% (1.14 m) of surface lowering resulted from high atmospheric temperatures, up to a + 2.6 degrees C daily average, indicating that 2012 would have been a negative SMB year at this site even without the melt-albedo feedback. Longer time series of SMB, regional temperature, and remotely sensed albedo (MODIS) show that 2012 was the first strongly negative SMB year, with the lowest albedo, at this elevation on record. The warm conditions of recent years have resulted in enhanced melt and reduction of the refreezing capacity in the lower accumulation area. If high temperatures continue, the current lower accumulation area will turn into a region with superimposed ice in coming years.

  • 2.
    Charalampidis, Charalampos
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Geol Survey Denmark & Greenland GEUS, Oster Voldgade 10, DK-1350 Copenhagen K, Denmark.
    van As, Dirk
    Geol Survey Denmark & Greenland GEUS, Oster Voldgade 10, DK-1350 Copenhagen K, Denmark.
    Colgan, William T.
    Geol Survey Denmark & Greenland GEUS, Oster Voldgade 10, DK-1350 Copenhagen K, Denmark.; York Univ, Dept Earth & Space Sci & Engn, 4700 Keele St, Toronto, ON M3J 1P3, Canada.
    Fausto, Robert S.
    Geol Survey Denmark & Greenland GEUS, Oster Voldgade 10, DK-1350 Copenhagen K, Denmark.
    MacFerrin, Michael
    Univ Colorado, CIRES, 216 UCB, Boulder, CO 80309 USA.
    Machguth, Horst
    Geol Survey Denmark & Greenland GEUS, Oster Voldgade 10, DK-1350 Copenhagen K, Denmark.; Tech Univ Denmark, Arctic Technol Ctr ARTEK, Byg 118, DK-2800 Lyngby, Denmark.
    Thermal tracing of retained meltwater in the lower accumulation area of the Southwestern Greenland ice sheet2016In: Annals of Glaciology, ISSN 0260-3055, E-ISSN 1727-5644, Vol. 57, no 72, p. 1-10, article id 6000021Article in journal (Refereed)
    Abstract [en]

    We present in situ firn temperatures from the extreme 2012 melt season in the southwestern lower accumulation area of the Greenland ice sheet. The upper 2.5 m of snow and firn was temperate during the melt season, when vertical meltwater percolation was inefficient due to a c. 5.5 m thick ice layer underlying the temperate firn. Meltwater percolation and refreezing beneath 2.5 m depth only occurred after the melt season. Deviations from temperatures predicted by pure conductivity suggest that meltwater refroze in discrete bands at depths of 2.0–2.5, 5.0–6.0 and 8.0–9.0 m. While we find no indication of meltwater percolation below 9 m depth or complete filling of pore volume above, firn at 10 and 15 m depth was respectively 4.2–4.5 degrees C and 1.7 degrees C higher than in a conductivity-only simulation. Even though meltwater percolation in 2012 was inefficient, firn between 2 and 15 m depth the following winter was on average 4.7 degrees C warmer due to meltwater refreezing. Our observations also suggest that the 2012 firn conditions were preconditioned by two warm summers and ice layer formation in 2010 and 2011. Overall, firn temperatures during the years 2009–13 increased by 0.6 degrees C.

  • 3.
    Citterio, Michele
    et al.
    Geological Survey of Denmark and Greenland (GEUS).
    van As, Dirk
    Geological Survey of Denmark and Greenland (GEUS).
    Ahlstrøm, Andreas P.
    Geological Survey of Denmark and Greenland (GEUS).
    Andersen, Morten L.
    Geological Survey of Denmark and Greenland (GEUS).
    Andersen, Signe B.
    Geological Survey of Denmark and Greenland (GEUS).
    Box, Jason E.
    Geological Survey of Denmark and Greenland (GEUS).
    Charalampidis, Charalampos
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Geological Survey of Denmark and Greenland (GEUS).
    Colgan, William T.
    Geological Survey of Denmark and Greenland (GEUS).
    Fausto, Robert S.
    Geological Survey of Denmark and Greenland (GEUS).
    Nielsen, Søren
    Geological Survey of Denmark and Greenland (GEUS).
    Veicherts, Martin
    Geological Survey of Denmark and Greenland (GEUS).
    Automatic weather stations for basic and applied glaciological research2015In: Geological Survey of Denmark and Greenland Bulletin, ISSN 1811-4598, E-ISSN 1604-8156, Vol. 33, p. 69-72Article in journal (Refereed)
    Abstract [en]

    Since the early 1980s, the Geological Survey of Denmark and Greenland (GEUS) glaciology group has developed automatic weather stations (AWSs) and operated them on the Greenland ice sheet and on local glaciers to support glaciological research and monitoring projects (e.g. Olesen & Braithwaite 1989; Ahlstrøm et al. 2008). GEUS has also operated AWSs in connection with consultancy services in relation to mining and hydropower pre-feasibility studies (Colgan et al. 2015). Over the years, the design of the AWS has evolved, partly due to technological advances and partly due to lessons learned in the field. At the same time, we have kept the initial goal in focus: long-term, year-round accurate recording of ice ablation, snow depth and the physical parameters that determine the energy budget of glacierised surfaces. GEUS has an extensive record operating AWSs in the harsh Arctic environment of the diverse ablation areas of the Greenland ice sheet, glaciers and ice caps [...].

    The GEUS AWS model in use now is a reliable tool that is adapted to the environmental and logistical conditions of polar regions. It has a proven record of more than 150 stationyears of deployment in Greenland since its introduction in 2007–2008, and a success rate of c. 90% defined as the fraction of months with more than 80% valid air-temperature measurements over the total deployment time of the 25 stations in the field. The rest of this paper focuses on the technical aspects of the GEUS AWS, and provides an overview of its design and capabilities.

  • 4.
    Fausto, Robert S.
    et al.
    Geological Survey of Denmark and Greenland (GEUS).
    van As, Dirk
    Geological Survey of Denmark and Greenland (GEUS).
    Antoft, Jens A.
    Box, Jason E.
    Geological Survey of Denmark and Greenland (GEUS).
    Colgan, William T.
    Geological Survey of Denmark and Greenland (GEUS).
    Andersen, Signe B.
    Geological Survey of Denmark and Greenland (GEUS).
    Ahlstrøm, Andreas P.
    Geological Survey of Denmark and Greenland (GEUS).
    Andersen, Morten L.
    Geological Survey of Denmark and Greenland (GEUS).
    Citterio, Michele
    Geological Survey of Denmark and Greenland (GEUS).
    Charalampidis, Charalampos
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Geological Survey of Denmark and Greenland (GEUS).
    Edelvang, Karen
    Geological Survey of Denmark and Greenland (GEUS).
    Haubner, Konstanze
    Geological Survey of Denmark and Greenland (GEUS).
    Larsen, Signe H.
    Geological Survey of Denmark and Greenland (GEUS).
    Veicherts, Martin
    Geological Survey of Denmark and Greenland (GEUS).
    Weidick, Anker
    Geological Survey of Denmark and Greenland (GEUS).
    Greenland ice sheet melt area from MODIS (2000–2014)2015In: Geological Survey of Denmark and Greenland Bulletin, ISSN 1811-4598, E-ISSN 1604-8156, Vol. 33, p. 57-60Article in journal (Refereed)
    Abstract [en]

    The Greenland ice sheet is an excellent observatory for global climate change. Meltwater from the 1.8 million km2 large ice sheet influences oceanic temperature and salinity, nutrient fluxes and global sea level (IPCC 2013). Surface reflectivity is a key driver of surface melt rates (Box et al. 2012). Mapping of different ice-sheet surface types provides a clear indicator of where changes in ice-sheet surface reflectivity are most prominent. Here, we present an updated version of a surface classification algorithm that utilises NASA’s Moderateresolution Imaging Spectroradiometer (MODIS) sensor on the Terra satellite to systematically monitor ice-sheet surface melt (Fausto et al. 2007). Our aim is to determine the areal extent of three surface types over the 2000–2014 period: glacier ice, melting snow (including percolation areas) and dry snow (Cuff ey & Paterson 2010). Monthly 1 km2 resolution surface-type grids can be downloaded via the CryoClim internet portal (www.cryoclim.net). In this report, we briefly describe the updated classification algorithm, validation of surface types and inter-annual variability in surface types.

  • 5.
    Machguth, Horst
    et al.
    Department of Geography, University of Zurich.
    MacFerrin, Michael
    Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado at Boulder.
    van As, Dirk
    Geological Survey of Denmark and Greenland (GEUS).
    Box, Jason E.
    Geological Survey of Denmark and Greenland (GEUS), København, Denmark.
    Charalampidis, Charalampos
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Geological Survey of Denmark and Greenland (GEUS).
    Colgan, William
    Department of Earth and Space Science and Engineering, York University.
    Fausto, Robert S.
    Geological Survey of Denmark and Greenland (GEUS).
    Meijer, Harro A. J.
    Univ Groningen, Energy & Sustainabil Res Inst Groningen, Ctr Isotope Res CIO, NL-9747 AG Groningen, Netherlands.
    Mosley-Thompson, Ellen
    Ohio State Univ, Byrd Polar & Climate Res Ctr, Columbus, OH 43210 USA.; Ohio State Univ, Dept Geog, Columbus, OH 43210 USA.
    van de Wal, Roderik S. W.
    Univ Utrecht, Inst Marine & Atmospher Res Utrecht IMAU, NL-3584 CC Utrecht, Netherlands.
    Greenland meltwater storage in firn limited by near-surface ice formation2016In: Nature Climate Change, ISSN 1758-678X, E-ISSN 1758-6798, Vol. 6, no 4, p. 390-393Article in journal (Refereed)
    Abstract [en]

    Approximately half of Greenland's current annual mass loss is attributed to runoff from surface melt. At higher elevations, however, melt does not necessarily equal runoff, because meltwater can refreeze in the porous near-surface snow and firn. Two recent studies suggest that all or most of Greenland's firn pore space is available for meltwater storage, making the firn an important buffer against contribution to sea level rise for decades to come. Here, we employ in situ observations and historical legacy data to demonstrate that surface runoff begins to dominate over meltwater storage well before firn pore space has been completely filled. Our observations frame the recent exceptional melt summers in 2010 and 2012, revealing significant changes in firn structure at different elevations caused by successive intensive melt events. In the upper regions (more than similar to 1,900 m above sea level), firn has undergone substantial densification, while at lower elevations, where melt is most abundant, porous firn has lost most of its capability to retain meltwater. Here, the formation of near-surface ice layers renders deep pore space difficult to access, forcing meltwater to enter an efficient surface discharge system and intensifying ice sheet mass loss earlier than previously suggested.

  • 6.
    van As, Dirk
    et al.
    Geological Survey of Denmark and Greenland (GEUS).
    Fausto, Robert S.
    Geological Survey of Denmark and Greenland (GEUS).
    Colgan, William T.
    Geological Survey of Denmark and Greenland (GEUS).
    Box, Jason E.
    Geological Survey of Denmark and Greenland (GEUS).
    Ahlstrøm, Andreas P.
    Geological Survey of Denmark and Greenland (GEUS).
    Andersen, Signe B.
    Geological Survey of Denmark and Greenland (GEUS).
    Andersen, Morten L.
    Geological Survey of Denmark and Greenland (GEUS).
    Charalampidis, Charalampos
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Geological Survey of Denmark and Greenland (GEUS).
    Citterio, Michele
    Geological Survey of Denmark and Greenland (GEUS).
    Edelvang, Karen
    Geological Survey of Denmark and Greenland (GEUS).
    Jensen, Trine S.
    Geological Survey of Denmark and Greenland (GEUS).
    Larsen, Signe H.
    Geological Survey of Denmark and Greenland (GEUS).
    Machguth, Horst
    Geological Survey of Denmark and Greenland (GEUS).
    Nielsen, Søren
    Geological Survey of Denmark and Greenland (GEUS).
    Veicherts, Martin
    Geological Survey of Denmark and Greenland (GEUS).
    Weidick, Anker
    Geological Survey of Denmark and Greenland (GEUS).
    Darkening of the Greenland ice sheet due to the melt-albedo feedback observed at PROMICE weather stations2013In: Geological Survey of Denmark and Greenland Bulletin, ISSN 1811-4598, E-ISSN 1604-8156, Vol. 28, p. 69-72Article in journal (Refereed)
    Abstract [en]

    The Greenland ice sheet is losing mass (Barletta et al. 2012) and at least half of this loss is caused by an increase in surface melt (e.g. Tedesco et al. 2013). The other part is caused by increased dynamic mass loss, as marine-terminating glaciers lose resistive stresses (Nick et al. 2009) due to both retreat and meltwater lubrication at the bed (Sasgen et al. 2012).

    In 2007, the Programme for Monitoring of the Greenland Ice Sheet (PROMICE) was initiated with the aim of gaining an insight into the causes of the ice-mass budget changes based on quantitative observations. This is primarily done by assessing how much mass is gained as snow accumulation on the surface versus how much is lost by calving and surface ablation (Ahlstrøm et al. 2008). PROMICE monitors the surface mass balance by means of automatic weather stations (AWSs) designed to quantify accumulation and ablation, as well as the specific energy sources contributing to ablation. These observations are vital to interpreting the physical mechanisms for ice-sheet response to climate change and for the calibration and validation of both satellite observations and climate models.

    In the wake of several record-breaking warm summers – increasing surface melt rate and extent (Nghiem et al. 2012) – interest in Greenland’s surface mass balance has increased (Tedesco et al. 2013). Observations of net ablation at PROMICE stations provided in situ confirmation of extreme massloss events in 2010 (Fausto et al. 2012) and 2012, primarily documented by other workers through satellite data. In this paper, we present atmospheric temperatures and surface solar reflectivity (known as albedo) of the Greenland ice sheet in the PROMICE period. Albedo modulates the absorption of solar radiation, which is the primary source of melt energy. It is reported to be decreasing in Greenland in recent years (Box et al. 2012), causing the monitoring of albedo variability to be increasingly important. Air temperatures, besides being strongly correlated to surface melt rates, affect surface albedo by controlling the rate of snow-grain metamorphism and the fraction of summer precipitation falling as rain versus snow. To elucidate the so-called melt-albedo feedback, whereby increased melt darkens the ice sheet and further enhances melt, the relationship between albedo and air temperature, observed at PROMICE stations, is examined in this study.

  • 7.
    van As, Dirk
    et al.
    Geological Survey of Denmark and Greenland (GEUS).
    Fausto, Robert S.
    Geological Survey of Denmark and Greenland (GEUS).
    Steffen, Konrad
    Ahlstrøm, Andreas P.
    Geological Survey of Denmark and Greenland (GEUS).
    Andersen, Signe B.
    Geological Survey of Denmark and Greenland (GEUS).
    Andersen, Morten L.
    Geological Survey of Denmark and Greenland (GEUS).
    Box, Jason E.
    Geological Survey of Denmark and Greenland (GEUS).
    Charalampidis, Charalampos
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Geological Survey of Denmark and Greenland (GEUS).
    Citterio, Michele
    Geological Survey of Denmark and Greenland (GEUS).
    Colgan, William T.
    Geological Survey of Denmark and Greenland (GEUS).
    Edelvang, Karen
    Geological Survey of Denmark and Greenland (GEUS).
    Larsen, Signe H.
    Geological Survey of Denmark and Greenland (GEUS).
    Nielsen, Søren
    Geological Survey of Denmark and Greenland (GEUS).
    Veicherts, Martin
    Geological Survey of Denmark and Greenland (GEUS).
    Weidick, Anker
    Geological Survey of Denmark and Greenland (GEUS).
    Katabatic winds and piteraq storms: observations from the Greenland ice sheet2014In: Geological Survey of Denmark and Greenland Bulletin, ISSN 1811-4598, E-ISSN 1604-8156, Vol. 31, p. 83-86Article in journal (Refereed)
    Abstract [en]

    In 2007 the Programme for Monitoring the Greenland Ice Sheet (PROMICE) was initiated to observe and gain insight into the mass budget of Greenland ice masses. By means of in situ observations and remote sensing, PROMICE assesses how much mass is gained as snow accumulation on the surface versus how much is lost by iceberg calving and surface ablation (Ahlstrøm et al. 2008). A key element of PROMICE is a network of automatic weather stations (AWSs) designed to quantify components of the surface mass balance, including the energy exchanges contributing to surface ablation (Van As et al. 2013).

    The use of these AWS observations is not limited to studies of ice-sheet mass balance. PROMICE contributes to CryoNet (www.globalcryospherewatch.org/cryonet), the core network of surface measurement sites of the World Meteorological Organization (WMO) Global Cryosphere Watch. By real-time delivery through WMO, PROMICE observations contribute to improve both operational forecasting and climate analysis in the data-sparse Arctic. The Greenlandic population, highly dependent on accurate forecasting of weather conditions, benefits directly from these real-time observations. For instance, extreme surface wind speeds are a high-risk element in Greenland. The third-highest wind speed observed at the surface of the Earth (93 m/s or 333 km/h), was recorded in a 8–9 March 1972 storm at Thule in North-West Greenland (Stansfield 1972).

    In this paper, we discuss the extent to which the Greenland ice sheet generates its own near-surface wind field. We use PROMICE data to gain insight into the interaction between air temperature, radiation and gravity-driven katabatic winds. We focus on a particularly powerful spring storm in 2013 that contributed to a fatality on an ice-sheet ski traverse attempt (Linden 2013).

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