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| Titel |
Heat storage in forest biomass improves energy balance closure |
| VerfasserIn |
A. Lindroth, M. Mölder, F. Lagergren |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 7, no. 1 ; Nr. 7, no. 1 (2010-01-21), S.301-313 |
| Datensatznummer |
250004381
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| Publikation (Nr.) |
 copernicus.org/bg-7-301-2010.pdf |
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| Zusammenfassung |
| Temperature measurements in trunks and branches in a mature ca. 100 years-old mixed
pine and spruce forest in central Sweden were used to
estimate the heat storage in the tree biomass. The estimated heat flux in
the sample trees and data on biomass distributions were used to scale up to
stand level biomass heat fluxes. The rate of change of sensible and latent
heat storage in the air layer below the level of the flux measurements was
estimated from air temperature and humidity profile measurements and soil
heat flux was estimated from heat flux plates and soil temperature
measurements. The fluxes of sensible and latent heat from the forest were
measured with an eddy covariance system in a tower. The analysis was made
for a two-month period in summer of 1995. The tree biomass heat flux was the
largest of the estimated storage components and varied between 40 and −35 W m−2
on summer days with nice weather. Averaged over two months the
diurnal maximum of total heat storage was 45 W m−2 and the minimum was
−35 W m−2. The soil heat flux and the sensible heat storage in air
were out of phase with the biomass flux and they reached maximum values that
were about 75% of the maximum of the tree biomass heat storage. The
energy balance closure improved significantly when the total heat storage
was added to the turbulent fluxes. The slope of a regression line with sum
of fluxes and storage as independent and net radiation as dependent
variable, increased from 0.86 to 0.95 for half-hourly data and the scatter
was also reduced. The most significant finding was, however, that during
nights with strongly stable conditions when the sensible heat flux dropped
to nearly zero, the total storage matched the net radiation very well.
Another interesting result was that the mean energy imbalance started to
increase when the Richardson number became more negative than ca. −0.1. In
fact, the largest energy deficit occurred at maximum instability. Our
conclusion is that eddy covariance measurements can function well during
stable conditions but that the functioning under strong instabilities might
be a so far unforeseen problem. |
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