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| Permafrost thermal state
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| Definition |
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The temperature of the permafrost layer at defined sampling points.
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| Rationale |
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Thermal conditions within permafrost at high latitudes and high altitudes are closely linked to changes in atmospheric and surface conditions. Corresponding changes in temperature distribution and vertical heat flow at depth takes place over time scales of decades to centuries, and the adjustment of permafrost thickness can take decades, centuries or even millennia depending on the original permafrost thickness and ice content. These memory and filter functions (and the long time scales involved in heat conduction in virtually impermeable ground) indicate that the recent warming of near-surface temperatures in permafrost is a key signal of climate change (with likely long-term effect). Pronounced disturbances of temperature profiles related to 20th century warming can be observed in the uppermost 200 m of sub-arctic boreholes.
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| Users |
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Change detection analysts, climate impact modellers, and regional analysts/planners (engineering, oil and gas prospection, natural hazards) in polar and high mountain areas.
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| Assessment method |
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Tiers 1-4: borehole temperature measurements (continuing or periodical).
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| Units of Measure |
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Temperature (˚C) at depth (m), heat flow/energy flux (W/m2, derived).
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| Frequency of measurement |
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Weekly to monthly in the uppermost 20 m below the permafrost table, annually to once every 10 years for depths greater than 20 m.
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| Spatial resolution |
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Tiers 1, 2, 3 and 4
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| Accuracy/precision required |
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0.1C for temperatures near to the surface and 0.05 to 0.1C for temperature profiles in deep boreholes.
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| Associated measurements |
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Snow cover, meteorological data, permafrost active layer, and vegetation/surface changes.
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| Present status |
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A number of sites in North America (Canada, Alaska), in the Russian Federation and in some high-altitude areas (Tibet Plateau, Tien Shan Mountains, European Alps) are presently monitoring. Efforts are being undertaken by the IPA to systematically rescue, collect and distribute such data. Within the same framework, a circumpolar/northern hemisphere permafrost map at a scale of 1:10,000,000 was prepared and could be used for GCM-validation in polar regions.
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| R and D needed |
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- Borehole installations must be designed for long-term monitoring of temperature and vertical/horizontal deformation (creep, thaw settlement/frost heave). Thermal characteristics of the investigated ground material need to be carefully determined using a combination of laboratory and in situ measurements (thermal adjustment after drilling, decay/lag of seasonal amplitudes with depth). Special emphasis should be placed on the effects of unfrozen water near melting/freezing temperatures.
- Develop criteria for the selection of key existing sites to recommend continuance;
- Establish new sites where geographic gaps exist, including in high-altitude areas;
- Temperature measurements at 15 cm depth and in boreholes greater than 20 m depth should both be implemented.
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