Surface Conditions

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The map illustrates how the surface of the Greenland Ice Sheet gains and loses mass on a daily basis. This is known as the surface mass balance. It does not include the mass that is lost when glaciers calve off icebergs and melt as they come into contact with warm seawater.

By holding the mouse over the circles, you can see the day’s weather observations from meteorological stations that are used to monitor the melting processes.

The graph below the map shows the total daily contribution from all points on the ice sheet.

The blue curve shows the current season’s surface mass balance measured in gigatonnes (1 Gt is 1 billion tonnes and corresponds to 1 cubic kilometre of water).

The dark grey curve traces the mean value from the period 1981-2010.

The light grey band shows differences from year to year. For any calendar day, the band shows the range over the 30 years (in the period 1981-2010), however with the lowest and highest values for each day omitted.

Read more.

The map illustrates what the ice sheet’s total surface gains and losses have been over the year since 1 September compared to the period 1981-2010. It does not include the mass that is lost when glaciers calve off icebergs and melt as they come into contact with warm seawater.

The animation shows one frame every seven days going back to the previous 1 September.

The blue curve shows the current season, whilst the red curve shows the corresponding development for the 2011-12 season, when the degree of melting was record high.

The dark grey curve traces the mean value from the period 1981-2010.

The light grey band shows differences from year to year. For any calendar day, the band shows the range over the 30 years (in the period 1981-2010), however with the lowest and highest values for each day omitted.

Read more.

The map shows how much light is reflected from the Greenland Ice Sheet – on a day-to-day basis. This is also known as the albedo.

Light areas reflect more sunlight than dark areas. Dark areas are thus warmed up more than light areas.

Red areas on the map show where the surface of the ice is darker than normal, while the blue areas indicate where the surface of the ice is lighter than normal. The map is shown as deviation from the average, i.e. the average of the albedo measured during the period 2000-2009 has been subtracted.

The animation shows the past 50 days’ satellite images available

Read more.

 

 

 

The map shows where on the Greenland Ice Sheet there has been melting over the previous day. This is defined as minimum 1 mm of melting at the surface.

The curve under the map shows how large a percentage of the total area of the ice sheet has seen melting. The blue curve shows this year’s melt extent while the dark grey curve traces the mean value over the period 1981-2010. The light grey band shows differences from year to year. For any calendar day, the band shows the range over the 30 years (in the period 1981-2010), however with the lowest and highest values for each day omitted.

Note, when comparing with the surface mass balance under ”Daily change”, that melting can occur without surface mass loss since the meltwater can refreeze in the underlying snow. Likewise, surface mass loss can occur without melting due to sublimation.

Read more.

Yearly updated end of melt season snowline. The snowline integrates the competing effects of melt (increasing snowline elevation) and snow accumulation (decreasing snowline elevation).

Thus snowline provides a key holistic variable indicating climate change.

Read more.

Melting at the surface is different from surface mass balance

 

The Greenland Ice Sheet evolves throughout the year as weather conditions change. Precipitation increases the mass of the ice sheet, whilst greater warmth leads to melting, which causes it to lose mass. The term surface mass balance is used to describe the isolated gain and loss of mass of the surface of the ice sheet – excluding the mass that is lost when glaciers calve off icebergs and melt as they come into contact with warm seawater.

Melting does not in itself necessarily give rise to mass loss, however. Much of the meltwater will refreeze in the surface snow layers rather than running off the ice sheet, and this process is included in the calculations of surface mass balance which is why the melt area plot may differ from the areas of negative mass balance seen on the map “Daily change”. Likewise, sublimation does not count as melting and surface mass balance can therefore occur with the surface temperature being far below the melting point. See further discussions of the difference between surface mass balance and melting here.

 

 

 

Day-to-day development of the Greenland Ice Sheet with the weather

 

The Greenland Ice Sheet evolves throughout the year as weather conditions change. Precipitation increases the mass of the ice sheet, whilst greater warmth leads to melting, which causes it to lose mass. The term surface mass balance is used to describe the isolated gain and loss of mass of the surface of the ice sheet – excluding the mass that is lost when glaciers calve off icebergs and melt as they come into contact with warm seawater.

The figures above are updated on a daily basis and show how much mass in terms of snow, ice or water is lost or gained on the surface of the Ice Sheet.

The circles on the map correspond to the PROMICE meteorological stations that have been established to monitor the melting processes. Note that the circles on the map are slightly displaced from their actual positions in order for them to be distinguishable. On the large version of the map they are marked with small dots at their true positions.

The density of snow and ice is different to that of water, and the figures are therefore converted to water to ensure that the total mass is calculated.

 

The model on which “Daily change” and “Accumulated” are based

 

The figures are based in part on observations made by meteorological stations on the ice sheet and in part on DMI's research weather model for Greenland, Hirlam-Newsnow, and since 1 July 2017 the HARMONIE-AROME weather model. This data is used in a model that can calculate the total amounts of ice and snow. Snowfall, melting of snow and bare ice, refreezing of melt water and snow that evaporates without melting first (sublimation) are all taken into account in this model.

The model was enhanced in 2014 to take into account the fact that some of the melt water refreezes in the snow, and again in 2015 in order to also take into account the low reflection of sunlight on bare ice compared to snow. Finally, it has been updated again in 2017 with a more advanced representation of percolation and refreezing of meltwater. At the same time, we have extended the reference period to 1981-2010. The update means that the new maps, figures and graphs will deviate from previous examples that can be seen in earlier season reports. Everything that appears on this page, however, is calculated using the same model, such that all graphs and values are directly comparable.

Data from the meteorological stations may be missing due to problems with instruments or transmissions via satellite if the power of the solar-powered battery is low or if the meteorological station is covered in snow, or, in the worst case, has toppled over.

More information:

PROMICE

DMI’s page on surface mass balance

Surface mass balance and other model output from DMI's regional climate model HIRHAM5 as shown on the daily surface mass balance page is freely available for research purposes from the DMI research department. A selection of variables for the ERA-Interim period and future simulations driven by EC-Earth can be downloaded here. These simulations are documented in scientific publications by Langen et al. (2017) and Mottram et al. (2017).

The HIRLAM weather model

The HARMONIE-AROME weather model that since 1 July 2017 drives the melt model

How much light is reflected from the Greenland Ice Sheet?

 

The proportion of light that is reflected from the Greenland Ice Sheet is also known as the albedo.

Freshly fallen snow is very bright and reflects most of the sunlight that hits it. The snow becomes darker when it is warmed up or has been lying on the ground for a while. Dark areas absorb more energy from the sun, which leads to further warming and melting of ice. Changes in reflectivity are thus amplified via a positive feedback loop.

The red areas of the map indicate where the surface of the ice has become darker. This can be due to melting and in certain cases due to particles that have precipitated from distant forest fires, for example. Blue areas show where the surface of the ice has become lighter. This can be due to freshly fallen snow or perhaps simply more snow than normal.

The albedo provides a convenient indicator of the competing effects: ice mass gain from snowfall and ice mass loss from melting. Ice that melts is darker (has a lower albedo) because the melting process makes the ice crystals more rounded in shape, in addition to which the melt water also reduces the reflectivity of the snow and ice.

The albedo is thus a very sensitive climate indicator.

The map is based on NASA’s satellite measurements from the MODIS sensor, which measures the reflection of sunlight from the surface. The map is updated on a weekly basis. These measurements cannot be carried out during the winter season due to the lack of sunlight.

More information:

NASA MODIS

How to determine the snowline

 

The snowline is defined as the maximum elevation during the melt season where snow from the previous accumulation season remains (Cogley et al., 2011).

The snowline is a valuable climate indicator as its position integrates the competing effects of melt (increasing snowline elevation) and snow accumulation (decreasing snowline elevation). Thus snowline provides a key holistic variable indicating climate change.

The figure illustrates the location of remotely-sensed snowline plotted on top of the digital elevation model (DEM) from the Greenland Mapping Project (GIMP, Howat et al. (2014). The snowline is easily visible in the southern, western, and northern part of Greenland due to the relatively even terrain, while the snowline shows a more complicated pattern in mountainous East Greenland.

We developed a methodology that determines snowline elevation utilizing the moderate-resolution imaging spectroradiometer (MODIS) sensor on the Terra satellite. The MODIS sensor produces a global dataset on a daily basis, with a resolution varying between 250 m and 1 km, in 36 bands covering visible to thermal wavelengths.

We use normalized thresholds between visible and thermal wavelengths to derive the maximum snow line altitude around Greenland for the years 2000-2017. For more information about the snowline product, see Fausto et al. (submitted).