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Late-season melt spike
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A strong weather pattern from August 21 to 24 caused widespread melting across Greenland. This unusually late summer melt event was caused by a high and low air pressure configuration known as an omega pattern because of its jet stream shape. The 2023 cumulative melt area is currently the second largest in the 45-year satellite record, trailing the extreme melt year of 2012.
Overview of conditions
Figure 1a. The top left map illustrates the cumulative melt days on the Greenland Ice Sheet for the 2023 melt season through August 27. The top right map illustrates the difference from the 1981 to 2010 average melt days for the same period. The bottom graph shows daily melt area from April 1 to August 27, 2023, with daily melt area for other high melt years, plus the record high year of 2012. The thick gray line depicts the average daily melt area for 1981 to 2010.
Credit: National Snow and Ice Data Center/T. Mote, University of Georgia
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Figure 1b. This graph shows the daily melt area for Greenland from late July through the end of August for 2023 and longer for several other years with late-season melt area peaks. All 45 years in the satellite record of melt area are shown.
Credit: National Snow and Ice Data Center/University of Colorado Boulder
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Figure 1c. These maps show Melt area on August 21 through 24 showing the progression of the melt event.
Credit: T. Mote, University of Georgia
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Beginning on August 20, surface melt extent on the ice sheet increased rapidly, following a period when only 10 to 20 percent of the ice sheet melted in the second half of July (Figure 1a). Melt area peaked at nearly 730,000 square kilometers (282,000 square miles) on August 22, covering about 45 percent of the ice sheet (Figure 1b). Melting began in the southwest and spread toward the higher central areas of the ice sheet and northward on August 22, and then eastward on August 23 and beyond (Figure 1c).
Cumulative melt-day area is the second highest in the 45-year satellite record with over 30 million square kilometers (11.5 million square miles). This can be compared to the extreme record year of 2012, which accumulated over 45 million square kilometers (17.4 million square miles) by late August. Note that 2010 finished the year with a higher total than the current date for 2023 because of a very late melt event in early September.
Conditions in context
Figure 2. The top plot illustrates average surface air temperature as a difference from the 1991 to 2020 average from August 1 to August 26, 2023, for Greenland and surrounding areas. Above average temperatures are present across nearly the entire ice sheet, but particularly high temperatures exist across the northern third of the ice sheet. The bottom plot shows the height of the 700 millibar level (about 3,000 meters or 10,000 feet above sea level) for Greenland from August 1 to August 26, as a difference from average. On a near-monthly average, all of Greenland had above average air pressure, especially in the southwest and southern areas.
Credit: National Centers for Environmental Prediction (NCEP) Reanalysis data
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Warm conditions have persisted over all of Greenland through August, and particularly in the northern third of the island, where temperatures averaged 2 to 4 degrees Celsius (4 to 7 degrees Fahrenheit) above the 1991 to 2020 average. High temperatures are often associated with high air pressure over the island, which has been the case with all of Greenland experiencing above average air pressure for the month. Both these trends contrast sharply with conditions on Baffin Island, west of Greenland, where cool conditions and near-average air pressure persisted for most of August.
The omega
![Figure 3. Figure 5. Wind speed (color, scale is in knots, or nautical miles per hour) and height contours (tens of meters) of the 500 hPa level in the upper atmosphere (about 18,000 feet), at the level of the jet stream, showing the ‘omega pattern’ [Ω] surrounding Greenland on August 22. Credit: Climate Reanalyzer, University of Maine Climate Change Institute, https://climatereanalyzer.org](http://nsidc.org/greenland-today/files/2023/08/OmegaPattern.png)
Figure 3a. This map shows wind speed in nautical miles per hour and height contours as tens of meters of the 500 hPa level in the upper atmosphere (about 5,500 meters or 18,000 feet), in the middle atmosphere, showing the omega pattern [Ω] surrounding Greenland on August 22.
Credit: Climate Reanalyzer, University of Maine Climate Change Institute
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Figure 3b. The graph depicts air temperature at the Tunu station in northeastern Greenland, showing the sharp warming trend to above-freezing temperatures on August 21, 22, and 23.
Credit: Jason Box, Denmark and Greenland Geological Society (GEUS) and PROMICE GC-NET
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Figure 3c. This animation map shows near-surface air temperature as a difference from average temperatures for August 20 to 26 from the climate model MARv3.12.
Credit: X. Fettweis, University of Liège and MARv3.12
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The late-season melt event was induced by a recognizable and potentially more frequent weather pattern that brings unseasonably warm conditions. The pattern develops when high pressure that is centered over Greenland is flanked by low air pressure off the western and eastern coasts. The resulting shape of the jet stream resembles the uppercase Greek letter omega (Ω) (Figure 3a). Winds near the surface and in the lower atmosphere flow northward along the western Greenland coast, over the northern flank of the ice sheet, and then downhill and southward on the eastern side. The downhill flow can further warm the air through a chinook or foehn effect, known as dry adiabatic compression.
In this case, the pattern was associated with high air temperatures at altitude over the island (700 millibar level, or 10,000 feet above sea level), far above average for this time of year. Surface air temperatures were up to 16 degrees Celsius (29 degrees Fahrenheit) above average, with foehn-effect warming along the eastern Greenland coast during the latter part of the event. Two periods of melting were observed at the Tunu automatic weather station, located in northeastern Greenland on the ice sheet at 2,079 meters above sea level (over 6,821 feet) (Figure 3b). On August 22, the National Oceanic and Atmospheric Administration (NOAA) Observatory at Summit Station had a series 1-minute air temperature readings of about -0.6 degrees Celsius (30.9 degrees Fahrenheit) (Figure 3c). Those data will be further detailed in the seasonal wrap-up report.
Ice art II
Figure 4. Asperitas clouds linger over the southern Greenland town of Narsaq on August 22, 2023.
Credit: J. Box, Denmark and Greenland Geological Society (GEUS)
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On August 22, glaciologist Jason Box took a photo of an ominous sky over Greenland. At this coastal town of Narsaq, conditions were rainy and very warm at 17 degrees Celsius (63 degrees Fahrenheit).
Further reading
Hanna, E., T. E. Cropper, R. J. Hall, R. C. Cornes, and M. Barriendos. 2022. Extended north Atlantic oscillation and Greenland blocking indices 1800–2020 from new meteorological reanalysis. Atmosphere, 13(3), 436, doi:10.3390/atmos13030436.
Mattingly, K.S., J. V. Turton, J. D. Wille, B. Noël, X. Fettweis, Å. K. Rennermalm, and T. L. Mote. 2023. Increasing extreme melt in northeast Greenland linked to foehn winds and atmospheric rivers. Nature Communications, 14(1), 1743, doi:10.1038/s41467-023-37434-8.
Wachowicz, L. J., J. R. Preece, T. L. Mote, B. S. Barrett, and G. R. Henderson. 2021. Historical trends of seasonal Greenland blocking under different blocking metrics. International Journal of Climatology, 41, E3263, doi:10.1002/joc.6923.
Sudden shift to southern heat
Late June ushered in a significant shift in weather and melting for Greenland, particularly for the southern portion of the ice sheet, known as South Dome, where melting is currently on a record pace. Melting along the northern rim of the ice sheet is also greater than average. These changes are a result of a shift in the air circulation, associated to negative North Atlantic Oscillation (NAO) index values. High air pressure now covers the island, bringing warm winds from the southwest and favoring sunnier condition enhancing the surface melt in the ablation zone, for which the extent is now close to the previous records in the summers of 2012 and 2019.
Overview of conditions
Figure 1. The top left map illustrates cumulative melt days on the Greenland Ice Sheet for the 2023 melt season through July 12. The top right map illustrates the difference from the 1981 to 2010 average melt days for the same period. The bottom graph shows the daily melt area for Greenland from April 1st through August 6th for 2023 and several of the near-record melt years in this century. The gray lines and bands depict the average daily melt area for 1981 to 2010, the interquartile range, and the interdecile range.
Credit: National Snow and Ice Data Center/T. Mote, University of Georgia
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Beginning around June 23, the areal extent of Greenland’s surface melting and runoff increased significantly. Several widespread melting events covering about 800,000 square kilometers (302,000 square miles) or up to 50 percent of the ice sheet occurred on June 27, July 6 to 7, and July 11, as several pulses of warm air swept across the southern portion of the ice sheet and northward around the northern coast. The total number of days with melting are now well above average throughout the southern and southwestern portions of the ice sheet by up to 5 to 15 days, and along its northern flank by about 10 days. Total melt-day extent, the sum of daily melt extents for the season so far, is now sixth highest overall. Melt-day extent over the southern portion of the ice sheet is now at a record high for the 45-year satellite record.
A significant increase in the estimated (modelled) run-off has occurred in the South Dome and Zachariæ Isstrøm Glacier regions, exacerbated by the below-average net accumulation in the southern and northeastern portions of the ice sheet at the end of spring. Moreover, at least some melting has now occurred over most of the ice sheet, even at high elevations, and this preconditions the snow for further melting by warming and darkening the upper layers.
We have in part corrected the parameters for determining melt from the satellite data by adjusting the baseline reference period used to characterize the pre-melting springtime snowpack. However, somewhat unusual conditions in the upper Jakobshavn Gletscher region, inferred to be due to a heavy surface frost event sometime earlier in the spring, prevent a complete removal of the anomalous early-melt area. This remaining possible inaccuracy is now a small fraction of the total melt-day mapping for the year (less than 5 percent).
Conditions in context
Figure 2a. The above plot illustrates average surface air temperature as a difference from the 1991 to 2020 mean for the period of June 21 to July 12, 2023, for Greenland and the surrounding areas. Warmer-than-average conditions are now present across nearly all of the ice sheet.
Credit: National Centers for Environmental Prediction (NCEP) Reanalysis data
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Figure 2b. This plot shows the difference from average of the height of the 700-millibar level (about 3 kilometers or 10,000 feet above sea level), an indication of the mean air pressure, for Greenland and the surrounding areas for June 21 to July 12. High pressure to the southwest of Greenland drove warm air along the western coast and across the ice sheet.
Credit: National Centers for Environmental Prediction (NCEP) Reanalysis data
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Figure 3. The top graph shows melt run-off and the bottom graph shows daily surface melt total from the Modèle Atmosphérique Régional (MAR) model for May 1 through July 18. The last few days are based on a forecast.
Credit: X. Fettweis, University of Liège and MAR3.12
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Air temperatures across Greenland have been above average over the past several weeks, by up to 1.5 to 2 degrees Celsius (3 to 4 degrees Fahrenheit) in the south and over 3 degrees Celsius (5 degrees Fahrenheit) in the north-central area. Air pressure patterns have changed markedly since the May-June period, with higher-than-average pressure both to the southwest and the northeast of the island. This pattern has brought a series of warm air pulses across the island from the southwest.
Both melt volume and surface meltwater run-off have increased since the weather pattern change. Daily estimated totals of melt have been about 15 billion tons per day for the first half of July, and estimated melt run-off about 10 billion tons per day. These anomalies have been two standard deviations above average since the end of June. Negative NAO conditions are expected to continue through the end of July, and we expect the total July runoff at South Dome to exceed the previous record years of 2002, 2007, 2012, and 2019. Given the below-average snowfall in the southern and northeastern areas, and the frequent occurrence of rainfall this July, the surface is pre-conditioned for further melting, exposing more ice-covered ablation areas especially near the coast. Further melting in July and early August will be enhanced by sunnier conditions as a result of negative NAO condition and will lead to high melt run-off.
Record pace of melting at South Dome
Figure 4. At top left, melting degree days total for 2023 up to July 14 for 2006 through 2023 for the Northeast Eemian (NEM) automatic weather station (AWS) site; at top left melting degree days up to July 14 for 1996 through 2023 for South Dome (SDM) AWS. Melting degree days are the sum of the number of degrees above melting at the peak daily temperature for days with melt in a summer season. The bottom graph is a plot of hourly air temperature for the SDM AWS for 2023 showing the persistent period of melting during July 6 to 12.
Credit: J. Box and the Geological Survey of Denmark and Greenland (GEUS), PromIce GC-Net
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Figure 5. This graph shows surface mass balance, the sum of snow and rainfall minus evaporation and run-off, difference from the 1981 to 2010 average for the South Dome area for the 2022 to 2023 hydrological year and several recent years through mid-July.
Credit: J. Box and the Geological Survey of Denmark and Greenland (GEUS), PromIce GC-Net
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Figure 6. National Oceanic and Atmospheric Administration Global Monitoring Laboratory temperature data from the Summit Observatory, initially transmitted at 1-minute average resolution, are plotted here at 10-minute averages for the month of June (late June 2008 through 2023). The previous record high temperature for June was on June 12, 2019, briefly at 0.1 degrees Celsius (32 degrees Fahrenheit). On June 26, 2023, a temperature of 0.4 degrees Celsius (33 degrees Fahrenheit) was seen during a several-hour stretch of near or above freezing conditions at the Summit weather station.
Credit: Christopher A. Shuman, University of Maryland, Baltimore County at NASA Goddard Space Flight Center and Michael Schnaubelt, Johns Hopkins University, using data from NOAA’s Global Monitoring Laboratory
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Warm conditions in both the northern and southern sections of the island have led to a record high melt-degree-day index for weather stations in those areas for the periods when they have operated. For all days in a season where the maximum temperature is above freezing, the melting degree day index sums the total number of degrees above freezing for each day. At both the Northeast Eemian automatic weather station (NEM) and the South Dome automatic weather station (SDM), the total melting degree day index is ahead of the past record melt season, 2012 (Figure 4). At South Dome, an extended period of above-freezing temperatures occurred from July 6 to 12, pushing its total melting degree-days index rapidly higher (Figure 5). However, both 2019 and 2012 had very intense melting in the second half of July and in early August.
At Summit Station, we have been monitoring the reported air temperature, and on several occasions in June and into July the air temperatures have been very close to or slightly exceeding the melting point. The above freezing temperatures on June 26 (Figure 6) represents a record warm air temperature for June at Summit.
Greenland catches the wave
Figure 7. This figure shows example days of the mapping of air-flow waviness over the study area used in the Preece et al., 2023 study. The top map shows airflow contours with low sinuosity (waviness) on August 16, 2001. The bottom map shows a strong waviness pattern on July 11, 2012.
Credit: Modified from Preece et al., 2023, Nature Communications
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Air circulation in the Arctic is dominated by westerly winds that encircle the Pole, driven at a fundamental level by the difference in temperature between the tropics and the high latitudes. The boundary of these eastward-flowing winds is marked by the polar jet stream. As Arctic and Greenland air temperatures have warmed, with strongly decreased sea ice and springtime snow cover and increased surface melting, the notion has been forwarded that the jet stream could become more sinuous, or ‘wavier’, leading to weather extremes of persistent warmer or cooler than average conditions. This is one of the more debated potential aspects of Arctic Amplification, that is, the processes that seem to amplify the pace of warming in the high northern latitudes.
A new study supports this hypothesis based on the observed summertime waviness of the airflow over northern Canada, Greenland, and the North Atlantic for 1979 through 2022. During the months of June, July, and August there has been a small but statistically significant increase in the waviness of air circulation in the region of Greenland. Since the mid-2000s, waviness of the airflow has increased in concert with a strong decrease in the June snow cover for North America and Europe. Moreover, this is associated with high pressure over Greenland, creating a ‘blocking high’ that can remain fixed for extended periods (weeks to months). High pressure conditions in Greenland are associated with increased warmth and melting and increased solar energy input to the ice sheet. Given the low June snow cover for 2023, and the emergence of above average pressure over Greenland in June and the first half of July, there is a strong possibility that this pattern will persist through this year as well.
Ice Art
Figure 8. This digital image shows melting ice and ice mélange near Qaanaaq, Greenland.
Credit: Sebastian Copeland
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On June 26, photographer and explorer Sebastian Copeland captured this image of an ice cliff during the widespread melting event at that time.
Further reading
Preece, J. R., T. L. Mote, J. Cohen, L. J. Wachowicz, J. A. Knox, M. Tedesco and G. J. Kooperman. 2023. Summer atmospheric circulation over Greenland in response to Arctic amplification and diminished spring snow cover. Nature Communications, 14(1), 3759. doi:10.1038/s41467-023-39466-6
Acknowledgements: Greenland Ice Sheet Today is produced at the National Snow and Ice Data Center under funding from NASA Cryospheric Sciences.
