Geological Survey of Denmark and Greenland Bulletin 23, 2011, 73–76 73 The Greenland ice sheet is reacting to climate change. Yet, mass-budget estimates differ considerably, partly due to climatic variability and partly to uncertainties in the tech- niques of assessing mass change (IPCC 2007). Nevertheless, all recent estimates agree that the ice sheet is losing mass (e.g. 286 Gt/yr; Velicogna 2009) at an accelerating rate (Rignot et al. 2011). On top of this, the area with a negative mass budget is expanding rapidly (Khan et al. 2010). The mass loss is at- tributed equally to increases in both iceberg production and melting of the ice sheet (Van den Broeke et al. 2009). The increasing mass loss in recent years has caught public attention and given rise to concern worldwide due to its poten- tial impact on sea level. In the light of this, the Programme for Monitoring of the Greenland Ice Sheet (PROMICE) was ini- tiated in 2007 (Ahlstrøm & PROMICE project team 2008), lead by the Geological Survey of Denmark and Greenland (GEUS). PROMICE undertakes surface mass-budget mea- surements using automatic weather stations, quantifies the mass loss by iceberg calving using remotely sensed data from satellites and airborne surveys and tracks changes in the extent of glaciers. In this paper, we focus on weather station measure- ments, which are crucial in calculating the energy exchange between the atmosphere and the ice sheet, and in validating model calculations of the surface mass budget. In particular, we present the observed temperatures and investigate how their high 2010 values affected ablation in southern Greenland. PROMICE automatic weather stations The PROMICE weather station network started with five stations in 2007 and by summer 2010 consisted of seven sta- tion pairs (Fig. 1; Table 1). Typically, one of the stations in a pair is located in the upper ablation zone near the equi- librium line and the other at a lower elevation well into the ablation zone. The weather stations are equipped with the instruments shown in Fig. 2 which undergo continuous 10-minute measurement cycles. In summer, data are trans- mitted once per hour; in winter, transmissions are daily to reduce power consumption when solar power is limited. PROMICE weather station data can be downloaded at no charge at www.promice.dk. In spite of the stations being placed in inhospitable places where strong winds, severe cold, icing as well as melting and highly uneven terrain are com- mon, there was a success rate of 77–86% for the period up to February 2011. Not all data have been transmitted with success, so the success rate may reach 86% when also locally Programme for Monitoring of the Greenland Ice Sheet (PROMICE): first temperature and ablation records Dirk van As, Robert S. Fausto and the PROMICE project team* *Andreas P. Ahlstrøm, Signe B. Andersen, Morten L. Andersen, Michele Citterio, Karen Edelvang, Peter Gravesen, Horst Machguth, Faezeh M. Nick, Søren Nielsen and Anker Weidick. 80°N 75°N 70°N 65°N 60°N 80°W 60°W 40°W 50°W 40°W 20°W 20°W 0°W 2250 3000 2750 2500 1000 1500 1750 20 0022 50 27 5025 00 22 50 17 50 1500 1 2 5 0 2000 Greenland 500 km QAS NUK UPE THU KPC SCO TAS Fig. 1. Map of Greenland with the locations of the PROMICE automatic weather stations in 2010. Each dot represents a pair of stations. Station ab- breviations as in Table 1. Dotted lines: elevation contours. © GEUS, 2011. Geological Survey of Denmark and Greenland Bulletin 23, 73–76. Open Access: www.geus.dk/publications/bull 7474 stored data have been collected. Strikingly, only few values are missing due to harsh climatic conditions such as wind damage. A prime cause of data gaps is data logger malfunc- tion. Temperatures over the ice sheet In Fig. 3 we show the monthly mean near-surface air temper- atures at those PROMICE stations for which data cover at least half a month. A clear annual cycle is present in the tem- perature records of all weather stations, and we see that the amplitude of the annual signal increases with latitude. This is explained by the fact that during summer the solar radia- tion increases with latitude due to the midnight sun, while the opposite is true during winter when central and north- ern Greenland experiences polar night. During the ‘warm’ season the presence of a melting ice surface at the stations does not allow near-surface temperatures to increase well above freezing. In southern Greenland, where day-time, free atmospheric temperatures can exceed 20°C during summer, the melting ice surface dampens the amplitude of the tem- perature cycle by about 10°C. The smallest amplitude and highest winter temperatures occur at the Tasiilaq stations (TAS_L and TAS_U), and the lower Qassimiut station (QAS_L; Fig. 1; Table 1). These stations are located at lower elevations close to the ice-sheet margin, and are exposed to the relatively warm wintertime atmospheric conditions of the Atlantic Ocean. The largest amplitude in the tempera- ture cycle is seen at the upper Kronprins Christian Land sta- tion (KPC_U), where melting occurs in summer, but where mean temperatures drop below –30°C in winter. The lowest daily mean temperature recorded at this station was –40.6°C on 9 January 2010. Mid summer (July) monthly mean tem- peratures are above freezing at all stations, but never exceed 6°C. Temperatures in Greenland have been rising since the 1980s, prior to which there was almost half a century of cooling (Box 2002). Still, 2010 was exceptionally warm over large parts of Greenland. It was the warmest year in Green- land on record at most of the land-based weather stations operated by the Danish Meteorological Institute. The only exception was seen in the north-east. Individual months and seasons showed record setting temperatures, with the longest instrument records in Greenland dating back to the 1870s (John Cappelen, personal communication, 2011). The PROMICE weather station network was not fully estab- lished until 2010 and thus comparison with previous years is limited. However, for our westerly and southerly stations we can confirm that the monthly mean temperatures in 2010 were mostly higher than those of previous years (Fig. 3). Record-setting 2010 in southern Greenland The longest running GEUS measurement series on ice start- ed in 2001 on the Qassimiut lobe in southern Greenland. This locality was incorporated in the PROMICE network by establishing station QAS_L in 2007. The nearly 10 years 1 2 3 4 5 7 8 5 9 7 6 10 11 Fig. 2. PROMICE automatic weather station UPE_L photographed on 17 August 2009. 1: radiometer. 2: inclinometer. 3: satellite antenna. 4: anemometer. 5: sonic height rangers. 6: thermometer and hygrometer. 7: pressure transducer. 8: solar panel. 9: data logger, barometer and GPS. 10: battery box with 4 × 28 Ah batteries. 11: 8-level thermistor string. Station Latitude Longitude Elevation Start date name (°N) (°W) (m) KPC_L* 79°55´ 24°05´ KPC_U 79°50´ 25°10´ SCO_L 72°14´ 26°49´ SCO_U 72°24´ 27°15´ TAS_L 65°38´ 38°54´ TAS_U 65°42´ 38°52´ QAS_L 61°02´ 46°51´ QAS_U 61°11´ 46°49´ NUK_L 64°29´ 49°32´ NUK_U 64°30´ 49°16´ UPE_L 72°54´ 54°18´ UPE_U 72°53´ 53°32´ THU_L 76°24´ 68°16´ THU_U 76°25´ 68°09´ Table 1. PROMICE automatic weather station metadata (status 2010) *L: Lower station, U: upper station. 17 July 2008 17 July 2008 21 July 2008 21 July 2008 23 August 2007 15 August 2007 24 August 2007 7 August 2008 20 August 2007 20 August 2007 17 August 2009 17 August 2009 9 August 2010 9 August 2010 380 870 470 1000 270 580 310 890 560 1140 230 980 570 770 75 of data from this locality provide an opportunity to put 2010 into a longer temporal perspective and assess how extra- ordinary 2010 was at this place. Figure 4A shows all avail- able monthly mean temperatures measured at the QAS_L site. The Qaqortoq temperature record from 56 km south- east of QAS_L are included to help interpret the months in 2010 with data gaps due to logger failure (values are reduced by 3°C to facilitate comparison). The climate at QAS_L is mild in terms of temperature compared to most other regions on the ice sheet (Fig. 3). The lowest winter values do not drop much below –10°C; typical monthly mean winter temperatures during the past decade were in the –10 to –3°C range. Summer (June–Au- gust) temperatures are predictable in that their mean value is within 2°C of all other years. The presence of ice limits the near-surface air temperature to about 5°C even during warm summers such as 2003. We therefore assume that the August 2010 temperature did not greatly exceed this value, even though the Qaqortoq value for this month is the high- est ever recorded value (10.6°C). In our records (supported by Qaqortoq data), we see that 2010 had the highest on-ice mean temperatures for all months of the year compared to earlier values, with the exception of April (warmer in 2008), July (warmer in 2003, 2005 and 2009) and October (warm- er in 2003). This is in full agreement with the values from Qaqortoq, which show above-decade average temperatures for all months except July. The most extreme values (in order of excess) were November, May, August, December and Sep- tember, which exceeded the two standard deviation ranges for the 2000–2009 averages. Qaqortoq was on average an astonishing 2.0°C warmer in 2010 than in the second (2003) and third (2005) warmest years on record, 4.5 standard de- viations above the 2000–2009 average (which is the warmest decade on record). Fig. 3. Monthly mean temperatures measured at seven weather station pairs. The upper stations of each pair record the lower temperatures, and vice versa. For locations see Fig. 1. 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 Temperatures at Qaqortoq (reduced with 3°C). –10 5 –5 0 –10 0 –2 –4 –6 –8 Month Month 5 6 7 8 9 100 2 4 6 8 10 12 T em pe ra tu re ( ºC ) A B Fig. 4. A: Monthly mean temperatures and B: cumulative net ablation at lower Qassimiut station (QAS_L). The ablation measurements are by pressure transducer; supported and validated by sonic ranger where available. The black dot in B shows the total ablation by November 2010. Variability in the pressure transducer output is caused by atmospheric pressure. –30 –20 –10 0 KPC SCO TAS QAS NUK UPE THU 2008 2009 2010 2011 T e m p e ra tu re ( ºC ) Year 7676 Even though QAS_L summer temperatures are damp- ened by the ice surface and on average do not exceed 5°C, this does not imply that melt rates are similar between years. The energy consumed by the ice surface to cool the near-surface atmosphere (sensible heat flux) will be larger during warmer periods, as will the down-welling longwave radiation, thus enhancing melting. However, there is only a relatively small amount of year-to-year variability in melt rates (given the slopes of the ablation curves from the pressure transducer in Fig. 4B) since solar radiation is the main contributor to melt energy (Van As et al. 2009). More important to net abla tion is the length of the ice-melt season, which largely depends on the duration of the period with positive temperatures and the amount of snow accumulation in the preceding winter. For instance, even though the melt rate in 2003 was above average due to high temperatures, the total ablation was near average because of the time it took to melt the relatively large amount of snow that had accumulated during the preceding winter. The year 2005 had lower summer temperatures, but a larger ablation total as there was very little snow accumula- tion the previous winter. The net ice ablation observations for the period 2001–2009 range from 5 m to 6.5 m of ice per year, which are the largest ablation totals measured anywhere on the Greenland ice sheet. For 2010 the extreme months of August and September are lacking from our data series, but spring values show that hardly any snow had accumulated in winter, and that the melt of the bare ice surface began in early May, 1–2 months earlier than in previous years. Melt rates were high in late summer and autumn, setting a new ablation record with a measured end-of-year total of about 9 m of ice (Fig. 4B, black dot). Similar record setting ablation is expected to have taken place in all of southern Greenland, as well as along the western margin of the Greenland ice sheet (Tedesco et al. 2011). Conclusions PROMICE has been successful in acquiring near-surface meteorological data over the Greenland ice sheet since 2007. Temperature measurements display distinct differences be- tween the locations due to solar influences, elevation and regional climate. The PROMICE temperature record con- firms that 2010 was an exceptionally warm year in the south- ern and western regions of Greenland, although a longer time series is needed to quantify the 2010 anomaly over the ice sheet. A record-setting net ablation of 9 m of ice in Green- land was measured on the southernmost part of the ice sheet in 2010. The enhanced down-welling longwave radiation and sensible heat flux due to the high atmospheric tempera- tures are not the main reason for the large ablation; low snow accumulation in the previous winter and a long melt season are. Acknowledgements The Programme for Monitoring of the Greenland Ice Sheet (PROMICE) is funded by the Danish Ministry of Climate and Energy, and is con- ducted in collaboration with the National Space Institute (DTU Space) and Asiaq (Greenland Survey). The Greenland Climate Research Centre (GCRC) co-finances the NUK stations through the FreshLink and Im- GlaCo projects. 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Authors’ address Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. E-mail: dva@geus.dk