Mapping parameters updated

Mapping parameters for the 2020 Greenland melt season have been updated, and new results are available since April 1. The adjustment slightly reduces the mapped daily area of surface melt. A discussion of the early melt season and Greenland climate in 2020 will be posted in early June.

A modest beginning to the Greenland melt season

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Spring melting over Greenland was near the long-term average, and concentrated along the southern coast, where extent was slightly above average. Although snowfall contribution to the ice sheet was below average early in the year, a significant snowfall event in early to mid-June brought the ice sheet close to balance, delaying the rapid early surface mass loss seen in recent years. A large melt event began on June 21, 2020, which will be discussed in a future post.

Overview of conditions

Figure 1. The top right map shows the total number of days of surface melt days for the Greenland Ice Sheet for the 2020 melt season from April 1 through June 20, 2020. The top right map shows the difference between 2020 total melt days and the 1981 to 2010 average number of melt days for the same period. The lower panel shows daily area of surface melting from April 1 to June 20, 2020, with daily melt extent trends for the preceding four years. This also includes 2012, the year with the record for total melt area. ||Credit: National Snow and Ice Data Center/T. Mote, University of Georgia|High-resolution image

Figure 1. The top left map of the Greenland Ice Sheet shows the total number of surface melt days from April 1 through June 20, 2020. The top right map shows the difference between total 2020 melt days and the number of 1981 to 2010 average melt days for the same period. The lower graph shows daily area in square kilometers of surface melting from April 1 to June 20, 2020, with daily melt extent trends for the preceding four years, including 2012, the record year for total melt area.

Credit: National Snow and Ice Data Center/T. Mote, University of Georgia
High-resolution image

The total aerial extent of surface melting through June 20, 2020, was slightly above the 1981 to 2010 average, particularly along the southeastern coast. Total melt-day extent was 3.60 million square kilometers (1.39 million square miles) for 2020, versus 3.30 million square kilometers (1.27 million square miles) for the 1981 to 2010 average. Most of the melt-day area accumulated during a moderate 10-day-long spike in melt area beginning around June 2, 2020. Areas on both coasts north of 65 degrees N had fewer melt days. Near Nuuk, on the southern tip of the island, 30 out of 81 days were melt days, and there were around 25 melt days near the Helheim Glacier region.

Conditions in context 

Figure 2. The top plot shows average air temperature difference from average, relative to 1981 to 2010, for the period of April 1 through June 20, 2020. This is shown as the height difference from average of the 700 mb pressure level (about 10,000 feet), in meters. The bottom plot shows air temperature difference from average at the same altitude, in degrees Celsius. ||Credit: NCEP Reanalysis data, National Center for Atmospheric Research |High-resolution image

Figure 2. The top plot shows air temperature as a difference from average, relative to 1981 to 2010, for the period of April 1 through June 20, 2020, in degrees Celsius. The bottom plot shows air pressure difference from average, relative to 1981 to 2010. This is shown as the height difference from average of the 700 mb pressure level (about 10,000 feet), in meters.

Credit: National Centers for Environmental Prediction (NCEP) Reanalysis data, National Center for Atmospheric Research
High-resolution image

Figure 3. This graph shows the surface mass balance (SMB) for the Greenland Ice Sheet for the 2019 to 2020 autumn through spring season (red line) through June 20, 2020, relative to the 1981 to 2010 average. It also includes several recent years for comparison. SMB is the sum of snowfall and rainfall, minus any evaporation or runoff. The estimates come from a model based on daily weather measurements. ||Credit: X. Fettweis, Université de Liège, Belgium|High-resolution image

Figure 3. This graph shows the surface mass balance (SMB) for the Greenland Ice Sheet for the 2019 autumn to 2020 spring season (red line) through June 20, 2020, relative to the 1981 to 2010 average. It also includes several recent years for comparison. SMB is the sum of snowfall and rainfall, minus any evaporation or runoff. The estimates come from a model based on daily weather measurements.

Credit: X. Fettweis, Université de Liège, Belgium
High-resolution image

Figure 4. The left map shows total net snowfall and rainfall, minus runoff or evaporation, which is the Surface Mass Balance (SMB) for the Greenland Ice Sheet, from September 1, 2019, through June 20, 2020. The right map shows the difference from average net snowfall for the same period. Numbers are shown in centimeters (0.4 inches) of water equivalent. ||Credit: X. Fettweis, Université of Liège, Belgium |High-resolution image

Figure 4. The left map shows total snowfall and rainfall, minus runoff or evaporation, which is the surface mass balance (SMB) for the Greenland Ice Sheet, from September 1, 2019 through June 20, 2020. The right map shows the difference from average net snowfall for the same period. Numbers are shown in centimeters (0.4 inches) of water equivalent.

Credit: X. Fettweis, Université of Liège, Belgium
High-resolution image

Temperatures in the Greenland region were generally higher than average over the April 1 to June 20, 2020 period, except for highest elevations of the ice sheet where temperatures were near-average to slightly below average (Figure 2). The western coastline was about 1 degree Celsius (2 degrees Fahrenheit) higher than the 1981 to 2010 average, while other coastlines were about 0.5 degrees Celsius (1 degree Fahrenheit) above average. Air pressure was generally slightly higher than the 1981 to 2010 average. This pattern, low pressure to the southwest and high pressure to the southeast, brought more frequent warm winds from the south throughout the late spring.

Total snowfall and rainfall over Greenland since September 1, 2019  shows that the beginning of 2020 was drier than the 1981 to 2020 average (Figure 3). However, increased snowfall in late April and especially mid-June has increased the surface mass balance (SMB), which does not include glacier outflow, to above average (Figure 4). The additional snowfall is in the southeast. Much of the southern and western side of the ice sheet has less snow cover than average. With summer melt, this can mean that the albedo, or reflectivity, of the Greenland surface will drop quickly, leading to more heat absorption and more intense surface melting. In recent years, intense melting and runoff at the beginning of June have removed hundreds of billions of tons of snow relative to Greenland’s 1981 to 2010 net accumulation, resulting in about half of the total ice lost from the ice sheet each year. A more intense melting event occurred in late June, and runoff is increasing for the year.

Wearing white in June

Figure 5. These maps show NASA MODIS-derived albedo, or reflectivity, for the Greenland Ice Sheet in mid-May (left) and early June (right) after a snowfall event as compared to the same period in 2000 to 2009. ||Credit: NASA|High-resolution image

Figure 5. These maps show NASA MODIS-derived albedo, or reflectivity, for the Greenland Ice Sheet in mid-May (left) and early June (right) after a snowfall event as compared to the same period in 2000 to 2009.

Credit: Polar Portal
High-resolution image

An expansive snowfall event in early June added to the net mass of the ice sheet relatively late in the melt season and brightened the surface, reducing the impact of later warm weather in mid-June by allowing the surface to reflect heat. However, the snow cover over much of the western side of the ice sheet is thin, and further warm events will re-expose the dark bare ice and dustier snow below the fresh layer, accelerating melt and run off.

Further reading

The Greenland Ice Sheet SMB simulated by MARv3.5.2 in real time

Polar Portal’s Greenland surface conditions

Programme for Monitoring of the Greenland Ice Sheet