Tarfala research station

Systematic climatological measurements at Tarfala station exist since 1961 and are continued till today.

The valley is sometimes hit by katabatic winds, which can generate very high wind speeds. The Swedish record of measured wind speed is from Tarfala research station with 81 m/s (290 km/h) on 20 December 1992.

The mass balance of a glacier is the difference between accumulation and ablation (sublimation and melting). A glacier with a sustained negative balance is out of equilibrium and will retreat, while one with a sustained positive balance is out of equilibrium and will advance. The determination of the mass balance requires time consuming field work. The winter mass balance is taken in the end of winter by measuring and probing snowpack depth in snow pits at the accumulation zone. Thus the past winters residual snowpack is analysed by its depth and density. In the ablation zone, ablation measurements are made using stakes inserted vertically into the glacier, usually at the end of the previous melt season. At the end of the melt (ablation) season, the length of stake exposed by melting ice is measured. Most stakes must be replaced each year. Mass balance results have been regularly published by Schytt[7] and Holmlund.[8]

The climate in the Tarfala valley is quite continental, compared with the regions west of the Kebnekaise; the climate in western Norway is maritime. This steep climatic gradient influences also both the net balance gradients on glaciers and the glaciation level. The average annual precipitation is about 1000 mm at Tarfala Research Station. This is less than half of the precipitation in the Norwegian mountains to the west. The mean annual air temperature at the equilibrium line at about 1500 m a.s.l. is about -6 °C.

Regular glaciological measurements at Storglaciären were started in 1946.[2] In 1968, a new gauging station was built, and the International Hydrological Decade (IHD) spawned its hydrological activities also in the Tarfala valley. Today, the glacier mass balance program at Storglaciären is globally known as one of the most important glaciological records and supplies important data to climate change questions in subarctic mountain regions.[9][10][11]

Altitudinal zonation of mountain permafrost for Tarfala (Kebnekaise) and Jotunheimen (Norway) with corresponding mean annual air temperatures (MAAT)

Whereas permafrost occurrences in palsa bogs were well known already in the beginning of the 20th century[12] and many permafrost studies were done on Spitzbergen, it was doubted until the early 1980s that mountain permafrost is present in the Scandinavian mountains. Its widespread existence at Tarfala could be proved in 1976 with refraction seismic soundings. It was demonstrated clearly, that Tarfala valley belongs to the region of discontinuous mountain permafrost. The active layer thickness on protalus ramparts and other wind exposed ridges was up to two meters.[13] Four years of systematic permafrost research in the Tarfala valley followed during the years 1977 till 1980, applying different geophysical methods (seismic and DC-geoelectrical soundings in summer, continuous measurements of the ground temperatures in boreholes to get the mean annual ground temperature). In March 1980, measurement of the basal temperature of the snow cover[14] and snow distribution were used to secure the findings. The field studies allowed to sketch a reliable picture of the permafrost distribution in the Kebnekaise region. Detailed results were published in 1982 and later on.[15]

The studies were enlarged to the areas north of Tarfala (Abisko region, Lyngen Peninsula in Norway). Additional studies covered the mountain ranges in the south of the Scandinavian mountain range (Jotunheimen, Rondane, Dovre). The resulting habilitation thesis was dedicated to the memory of Valter Schytt.[16] A summary of the results was printed in Geografiska Annaler.[17] Thus, Tarfala station is located inmidst of the discontinuous permafrost zone, with a MAAT of -3.5 °C at 1130 m. At 1600 m a.s.l. the continuous permafrost zone will be reached.

Within the EU-sponsored project PACE (Permafrost and Climate in Europe), two boreholes in bedrock, 100 m and 15 m deep were drilled in March 2000.[18] The location is above the research station at an altitude of 1540 meters and near Tarfalaglaciären. The thermistor chain in the 100 m hole includes 30 thermistors. The depth of the Zero Annual Amplitude (ZAA) is 15 to 20 meters with a temperature of -3.2 °C in the year 2000. The ground temperature at a depth of 100 meters is -2.75 °C. The geothermal gradient of 1.17 °C /100 m allows to extrapolate a permafrost thickness of 330 meters, and thus confirms suggestions done with the results of earlier geoelectric soundings.[19]

Warming trend of the air temperatures due to climate change is reflected also in the ground temperatures. The geothermal gradient in the uppermost 50 meters hint to a significant temperature increase during at least 50 years.[20]