Frozen Ground

Temperature in 1 m depth, calculated with the GIPL permafrost model, which is driven at the surface by data from DMI’s run with the HARMONIE-AROME weather model for Greenland.

The curves show the average temperature in the boxes marked in the figure (Northwest and Southeast Greenland, respectively) at 20 cm and 1 m depth.

The map is updated on a daily basis.

The temperatures shown here are not observed, but rather a model product.

Read more.

 

Temperature calculations in subsurface ground layers

 

The temperature distributions and curves we present here are not observed, but rather a model product that is described in some detail below. We expect to add observed subsurface temperatures to the Polar Portal with one of the next updates. Observed ground temperatures can also be found via the Center for Permafrost (CENPERM) which maintains several field stations in Greenland.

The figures we show here are based on DMI’s run with the HARMONIE-AROME weather model for Greenland, coupled to a dedicated permafrost model, GIPL, which has been developed at the University of Alaska Fairbanks. GIPL is a numerical model that solves the one-dimensional heat conduction equation with phase changes in porous media, first formulated by the Slovenian scientist Josef Stefan in 1891.

GIPL simulates the temperature in the ground down to a depth of 100 m for 24 different ground types. These ground types represent a wide variety of soil properties, including peat-like or muddy soils, silt-rich, clayish or rock-rich types and even partially sealed urban grounds, that differ in the layering of soil textures, soil material, pore space, unfrozen water content and thermal properties. These ground properties strongly determine the heat flow in the ground and, ultimately, if permafrost is present. In addition, insulating layers of snow and vegetation that can change their properties over time are taken into account at the upper boundary.

GIPL receives temperature and precipitation fields from the weather model and outputs vertical temperature profiles so that we can determine the upper boundary of permafrost, which lies below the (seasonally thawed) active layer. The map shows the temperature in 1 m depth, and the curves show spatial averages at 20 cm and 1 m depth.

Since the exact layout of the ground is unknown in large parts of Greenland, we are presenting average temperatures across all typical ground types - if sufficient subsurface data was available, we would be able to compute the actual conditions. Therefore, the soil conditions shown here may deviate from the real conditions in some parts of Greenland.

Since the ground has a very long memory to previous atmospheric conditions, we have to "spin up" the temperature fields for each ground type in the model for several thousand years. For this we have taken atmospheric fields (temperature and precipitation) for present-day climate from our regional climate model HIRHAM and scaled them with temperature variations deduced from ice cores in Greenland to obtain a forcing covering the last 10000 years.