 |
| Titel |
The Annual Surface Energy Budget of a High-Arctic Permafrost Site on Svalbard, Norway |
| VerfasserIn |
Sebastian Westermann, Johannes Lüers, Moritz Langer, Konstanze Piel, Julia Boike |
| Konferenz |
EGU General Assembly 2010
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250039334
|
|
|
|
|
|
| Zusammenfassung |
| Energy balance models are highly capable tools to estimate the thermal conditions of
permafrost. Their successful application depends on a detailed understanding of the different
components of the surface energy budget and their seasonal variations, including snow cover
effects. We present independent measurements of all components of the surface
energy budget over a full seasonal cycle at a high-arctic permafrost site on Svalbard.
The sensible and latent heat fluxes are hereby measured with an eddy covariance
system. A detailed description of the effects of the snow cover is included in the
study.
The short-wave radiation is the dominant energy source during the snow-free summer
months, while well developed turbulent processes, the long-wave radiation and the heat flux
in the ground are the balancing components of the surface energy budget. The Bowen ratio
varies between 0.25 and 2, depending on water content of the uppermost soil layer. In the
months of July and August, the seasonal thawing of the active layer consumes about 15%
of the net radiation. During polar night conditions in winter, the net long-wave
radiation is the principal energy loss for the snow surface, while strong sensible heat
fluxes and the ground heat flux, which originates from the refreezing of the active
layer, lead to a warming of the surface. During the first half of the polar day season
from April to June, the surface energy budget resembles “winter-like” conditions,
since the long-lasting snow cover with its high albedo effectively reflects the short
wave radiation and thus reduces the energy input. The timing of the snow melt,
with its associated albedo change is therefore crucial for the annual surface energy
budget.
The strong positive sensible heat fluxes in July and August are compensated by negative
fluxes during the rest of the year, so that the average annual sensible heat flux is
negative with a value of -6.9Wm-2. Strong evaporation is found during the snow melt
period and particularly during the snow-free period in summer and fall. When the
ground is covered by snow, latent heat fluxes through sublimation of snow occur
regularly, but are on average negligible in the surface energy budget. With an annual
average of 6.8Wm-2, the latent heat flux more or less compensates the sensible heat
flux.
For snow-free ground, an unstable to neutral near-surface atmospheric stratification is found,
while stable to neutral conditions prevail for snow-covered ground. Long-lasting near-surface
inversions in winter lead to an average temperature difference of approximately 3K
between the air temperature at 10m height and the surface temperature of the snow. |
|
|
|
|
|
|