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Long-term monitoring of sensible and latent heat fluxes using eddy covariance at a high Arctic permafrost site in Svalbard, Norway

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Westermann, S. , Boike, J. , Piel, K. and Lüers, J. (2008): Long-term monitoring of sensible and latent heat fluxes using eddy covariance at a high Arctic permafrost site in Svalbard, Norway , 9th International Conference on Permafrost, June 29 - July 3, University of Alaska, Fairbanks, USA .
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Abstract:

Land-atmosphere interactions are an important element in the energy and water budget in permafrost regions. We present long-term measurements of sensible and latent heat fluxes at a high-arctic continuous permafrost site in Svalbard, Norway, using the eddy covariance method. The site is situated in hilly tundra at the foot of two major glaciers, and is characterized by sparse vegetation altering with exposed soil and rock fields. The study was performed from April to September 2007, thus covering a period from late winter until the end of the summer season.During April, temperatures ranged from 20°C to +5°C, with an average of 11°C. Sensible heat fluxes were mostly negative, corresponding to an energy transfer from the atmosphere to the snow pack. Highest values were associated with increasing air temperature in combination with high wind speed, which can be interpreted as a cooling effect of the near surface air due to a much colder snow surface. The latent heat flux was generally positive, but remained low most of the time. With a temperature remaining rather constant between 5°C and +5°C and predominantly neutral atmospheric exchange conditions during most of May and June, both measured fluxes were comparatively insignificant. The appearance of large snow free patches around June, 26th, triggered a strong increase of sensible and latent heat fluxes. Hereby, the latent heat flux was approx. twice as large as the sensible heat flux, most likely due to very wet soil conditions directly after snow melt. This situation reversed during July, when the tundra increasingly dried up in most of the potential fetch area of the eddy system. The immediate surrounding of the measurement site could then be characterized as moderately moist tundra. Both sensible and latent heat fluxes remained largely positive, but displayed a strong diurnal course, with peak fluxes associated with maxima of solar radiation. During periods with moderately high wind speeds (5m s-1 to 10 m s-1), the maximum sensible heat fluxes were up to a factor of two higher than during periods with low wind speeds (0 m s1 to 2 m s1).In relation with recordings of the radiative parts of the energy budget, eddy covariance measurements have proven to be a valuable tool to capture a more complete picture of energy fluxes at this maritime permafrost site.

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