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| Titel |
Application of a two-dimensional model to describe the CO2 exchange between a spatially non-uniform forest stand and the atmosphere |
| VerfasserIn |
Yulia Mukhartova, Alexander Olchev, Natalia Shapkina |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250092139
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| Publikation (Nr.) |
 EGU/EGU2014-6465.pdf |
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| Zusammenfassung |
| Within the framework of the study a two dimensional hydrodynamic high-resolution model of
the energy, H2O, CO2 turbulent exchange was developed and applied to describe effect of the
horizontal and vertical heterogeneity of a forest canopy on CO2exchange between
soil surface, forest stand and the atmosphere under different weather conditions.
Most attention in the study was paid to analyze the influence of forest clearing,
windthrow of different sizes, forest edges, etc. on turbulent exchange rate and CO2 flux
partitioning between forest overstorey, understorey and soil surface. The modeling
experiments were provided under different wind conditions, thermal stratification of the
atmospheric boundary layer, incoming solar radiation, etc. To quantify effect of spatial
heterogeneity on total ecosystem fluxes the modeling results were compared with
CO2 fluxes modeled for a spatially uniform forest canopy under similar ambient
conditions.
The averaged system of hydrodynamic equations is used for calculating the components
of the mean velocity -ăV = {V1, V2}:
( ( ) )
-Vi+ V -Vi= - 1--δP- - --– δ E - K -Vi-+ -Vj- + F, -Vi = 0,
-t j-xj Ï0 -xi -xj ij -xj -xi i -xi
where E is the turbulent kinetic energy (TKE), K is the turbulent diffusivity, δP is the
deviation of pressure from the hydrostatic distribution and Ï0-ăF is the averaged force of air
flow interaction with vegetation. F-ă was parameterized as -ăF = -cd -
LAD -
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||V-ă||-
-ăV, where
cd is the drag coefficient and LAD is the leaf area density. The turbulent diffusivity K can
be expressed by means of TKE and the velocity of TKE dissipation É as follows:
K = CμE2É-1, where Cμ is the proportionality coefficient.
One of the ways to obtain E and É is to solve the additional system of two differential
equations of diffusion-transport type:
( ) ( )
-E- --E- --- -K--E- --φ -φ– --- K–-φ -φ ( 1 2 )
-t +Vj-xj = -xi ÏăE -xi +PE - É, -t +Vj -xj = -xi Ïăφ-xi +E C φPE - CφÉ - Δ φ,
where ÏăE and Ïăφ are the Prandtl numbers, PE is the TKE production by shear, Cφ1 and
Cφ2 are the model constants. The term Δφ = φ-
E(C φ1 - Cφ2) -
12Cμ1-2c
dLAD||-ă ||
|V |E
describes the increase of TKE dissipation due to the interaction with vegetation
elements.
The function φ can be any of the following variables: É, É/ E, or El, where l is the
mixing length. Detailed analysis of these equations performed by Sogachev (Sogachev,
Panferov, 2006) showed that for φ = É/ E the model is less sensible to the errors of the input
data.
Transfer equation for CO2 within and above a plant canopy can be written as:
( )
-C- --C- --- -K--C-
-t + Vj-xj = -xi ÏăC -xi + FC,
where C is CO2 concentration, ÏăC is the Prandtl number, and the term FC describes the
sources/sinks of CO2 in the vegetation and soil. For parameterization of the photosynthesis
rate in the forest canopy the Monsi and Saeki approach (Monsi M., Saeki T., 1953)
was applied. Stem respiration was ignored in the study. The CO2 emission from
the soil surface into the atmosphere was assumed to be constant for entire forest
area.
This study was supported by grants of the Russian Foundation for Basic Research (RFBR
14-04-01568-a). |
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