Inclusion of CO2 fluxes in a coupled mesoscale land surface and ...€¦ · fluxes in a coupled...
Transcript of Inclusion of CO2 fluxes in a coupled mesoscale land surface and ...€¦ · fluxes in a coupled...
Inclusion of CO2 fluxes in a coupled mesoscale land surface and atmospheric model
Markus Uebel, Prabhakar Shrestha, Mauro Sulis and Andreas Bott
University of Bonn, Meteorological Institute, email: [email protected]
1) Motivation
An essential part of numerical weather prediction models is the accurate simulation
of the interaction of the land surface with the lower atmosphere. We use a fully
coupled model system (COSMO-CLM-ParFlow) that comprehensively calculates
the exchange processes between the soil, the vegetation and the atmosphere.
Field measurements on the regional scale indicate distinct spatio-temporal
heterogeneities in the distribution of atmospheric carbon dioxide (CO2). This
variability of CO2 induces a direct response on the stomatal resistance of plants
resulting in a modified transpiration that influences the near surface atmospheric
moisture. Thus, for a consistent modeling of latent and sensible heat fluxes the net
CO2 flux between the land surface and the atmosphere will be included in our
coupled model system. This flux consists of the photosynthesis rate A as an atmos-
pheric sink as well as plant and soil respiration, Rplant and Rsoil as sources for the
atmospheric CO2 concentration (see Fig. 1). Now, the atmospheric CO2 is no longer
a constant value but a prognostic variable used for calculating canopy processes.
Figure 1: CO2 fluxes between the land surface and the atmosphere
2) Coupling of CO2
The atmospheric CO2 distribution
is initialized in the atmospheric
model COSMO and sent to the
external coupler OASIS which
organizes the downscaling to the
finer grid resolution of the
Community Land Model (CLM)
and unit conversions of all
variables and fluxes that are
exchanged between the models.
The CLM receives the CO2
partial pressure and uses this for
the calculation of the CO2 fluxes
(see Fig. 1). The determined net
CO2 flux is sent to the OASIS
coupler to be upscaled to the
atmospheric grid. The atmospheric
CO2 content is updated by this net
CO2 flux and the COSMO model
performes the atmospheric
transport. This coupling cycle is
repeated every coupling time step.
The coupling frequency can also
be varied with the OASIS coupler. Figure 2: Coupling cycle of CO2 with the OASIS coupler
for the coupling option COSMO – CLM
3) Model simulations
The selected day (8th of May 2008) was dominated by fair weather conditions with unattenuated
solar radiation over the western part of Germany. All model simulations with the coupled model
system COSMO – CLM were initialized with 390 ppmv of CO2 in all atmospheric model layers:
Reference run: no coupling of CO2 fluxes (standard model coupling)
Turbulence run: coupling of photosynthesis rate A and vertical turbulent mixing of CO2 in
the COSMO model (no advection)
analysis of the direct effects of plant type depending photosynthesis rates
Real run: coupling of photosynthesis rate A, influence of all transport processes on CO2
analysis of expected 3D-patterns of CO2 in the atmosphere
4) Atmospheric CO2 transport
The atmospheric model of our coupled model system is the non-hydrostatic, incompressible local
weather prediction model COSMO provided by the German Meteorological Service (DWD).
With this model we perform mesoscale weather forecasts with a grid resolution of 1km. For the
atmospheric transport of the specific CO2 content qCO2 a passive tracer has been included.
5) Canopy processes
6) Summary and outlook
The simulations show that the coupling of the photosynthesis rate A with the COSMO model results
in a reduction of the near surface atmospheric CO2 content and in a diurnal vertical variation of the
CO2 distribution due to vertical turbulence and advection with the wind field. This decrease of
atmospheric CO2 leads to a reduced photosynthesis rate and as a direct consequence to an increase
of plant transpiration compared with the reference run (Fig. 7 and 8). Plants react on the modified
availability of CO2 with opening their stomata to take up more CO2 for producing photosynthesis.
In our future research the plant respiration as well as the soil respiration will be included in our
model system to calculate the accurate net CO2 flux which will be exchanged between the CLM
and the COSMO model. We will perform sensitivity studies both for idealized cases and for
different real weather conditions. Different atmospheric CO2 distributions will be used in order to
assess the response of the stomatal resistance and the moisture and heat fluxes on these variations.
Modifications in the atmospheric moisture distribution and their possible impact on the simulation
results will be analyzed. Further, we will validate our model results with field and remote sensing
measurements performed by other working groups of the TR32 project.
The photosynthesis rate A as well as the plant
transpiration TP is controlled by the stomatal
resistance rst which describes the permeability
of the stomata of leaves:
ei* water vapor saturation pressure inside the leaf
b minimum stomatal conductance
Standard model coupling:
atmospheric pressure Patm(lat,lon,t)
water vapor pressure at leaf surface es (lat,lon,t)
CO2 partial pressure at leaf surface cs constant (every time step)
Coupling of CO2 fluxes:
atmospheric pressure Patm(lat,lon,t)
water vapor pressure at leaf surface es (lat,lon,t)
CO2 partial pressure at leaf surface cs (lat,lon,t)
prognostic
(atmospheric forcing variables)
prognostic
(atmospheric forcing variables)
Figure 6: Transpiration and CO2 uptake through stomata
(leaf cross section)
Figure 7: Difference of photosynthesis rate [μmol(CO2)m-2s-1]
between standard coupling and CO2 coupling
(reference – real): 05/08/2008, 09 UTC
Figure 8: Difference of transpiration [Wm-2] between standard
coupling and CO2 coupling (reference – real):
05/08/2008, 09 UTC
After the coupling with the CLM the tracer becomes active (influence on other variables).
local tendency advection sources/sinks subgrid scale processes
Figure 3: Specific CO2 content qCO2 [g kg-1] in the lowermost model layer of the COSMO model: 05/08/2008, 09 UTC
(a) turbulence run, (b) real run (red cross: position of the vertical profile, dashed line: position of the cross-section)
Figure 5: Vertical profiles of specific CO2 content qCO2 [g kg-1]
in the PBL at different times (real run): 05/08/2008
Figure 4: Vertical cross-section of the specific CO2 content qCO2
[g kg-1] in the PBL (real run): 05/08/2008, 10 UTC
Budget
equation
The spatial patterns in Fig. 3a) are mainly the result of different photosynthesis rates depending on
the plant type whereas in b) also advective transport occurs. The red regions in a) are urban areas
or bare soil without photosynthesis so that the initial concentration remains.
(a) (b)
Acknowledgements: The authors thank the German Meteorological Service (DWD) for providing the COSMO model
and the analysis data needed for driving the model. We gratefully acknowledge financial support
from SFB/TR32 “Patterns in Soil-Vegetation-Atmosphere Systems: Monitoring, Modelling and Data Assimilation” funded by the Deutsche Forschungsgemeinschaft (DFG). www.tr32.de
References: Baldauf, M. et al. (2011). “Operational convective-scale numerical weather prediction with the COSMO model: Description and sensitivities”. In: Mon. Wea. Rev., 139, pp. 3887-3905
Collatz, G.J. et al. (1991). “Physiological and environmental regulation of stomatal conductance, photosynthesis and transpiration: a model that includes a laminar boundary layer”. In: Agric. For. Meteorol. 54, pp. 107 –136.
Dolman, A.J. et al. (2006). “The CarboEurope regional experiment strategy”. In: University of Wollongong Research Online.
Shrestha P. et al. (2012). „Development of a Scale-Consistent Soil-Vegetation-Atmosphere Modeling System Using COSMO, Community Land Model and ParFlow“ (to be submitted)
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