CONTINUOUS IN SITU MEASUREMENTS OF ATMOSPHERIC O2 AND CO2
Description: Simultaneous
and continuous measurements of O2 and CO2 made in
the air around terrestrial ecosystems have the potential to improve our
understanding of the biogeochemistry of the ecosystem, and may reduce
uncertainties in estimates of terrestrial carbon uptake derived from
atmospheric O2 measurements. Following the
design of Stephens et al. [2001], we
have constructed an instrument that performs continuous in situ measurements of atmospheric O2 and CO2
concentrations. We present design and performance data, along with preliminary
results from a deployment at the Environmental Measurement Site at Harvard Forest
in central Massachusetts.
Author's Names: M.O. Battle, R. Perry, E. Sofen, J. Carpenter, B.B. Stephens
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Added on: 25-Jul-2005 Downloads: 39
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CROSS-COMPARISON OF THE DECADAL TRENDS IN CARBON BUDGET OF TERRESTRIAL ECOSYSTEMS ESTIMATED BY DIFFE
Description:
There remain large uncertainties in our model estimations of
terrestrial CO2 budget at broad scales. We used two terrestrial
carbon cycle models (Sim-CYCLE and SASAI) and three climate datasets
(NCEP/NCAR, NCEP/DOE, and ERA40) for the period from 1982 to 2001 and performed
cross-comparison, aiming at clarifying the source of uncertainties. Using the
same model, different carbon budgets were obtained by the three climate
datasets, globally due to the difference in solar radiation and locally due to
precipitation. The two models, which differ in canopy processes, estimated
different temporal trends and spatial patterns of CO2 budget during
the experimental period. This study exemplified the necessity of developments
in both models and datasets.
Author's Names: Akihiko Ito and Takahiro Sasai
Filesize: 68.69 Kb
Added on: 29-Jul-2005 Downloads: 27
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DETERMINING SOIL CO2 EFFLUX FROM SOIL AIR CO2 CONCENTRATION PROFILES
Description:
In this study,
soil CO2 effluxes determined from CO2 concentration
gradients were compared to effluxes obtained with automated chamber
measurements. The CO2 concentrations showed a diurnal pattern following
the soil temperature the concentrations increasing with increasing soil depth.
Both methods gave comparable CO2 effluxes indicating that the
gradient method provides an alternative method for monitoring soil CO2
effluxes.
Author's Names: J. Pumpanen, L. Kulmala, E. Siivola C. Helenelund, et al
Filesize: 70.71 Kb
Added on: 03-Aug-2005 Downloads: 20
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DIAGNOSING CONTROLS OVER GPP AND ECOSYSTEM RESPIRATION USING FLUX DATA AND ASSIMILATION MODELING
Description: We used data assimilation to estimate the
contributions of GPP, heterotrophic (Rh) and autotrophic (Ra) respiration to
Net Ecosystem Exchange at the Niwot Ridge long-term eddy covariance site using
5 years of data. The assimilation problem is solved by optimizing state and
parameter values in a version of the PnET ecosystem model by minimizing the
misfit between modeled and observed NEE, subject to Bayesian prior estimates of
the model parameters and initial state. Seventeen free parameters, about half
of the total, are estimated, with the remaining parameters defined from other
studies. The model computes GPP, Rh and Ra fluxes for each day and night, and
thus produces an estimate of the separation of NEE into its components. We
checked the model’s partitioning of the NEE into GPP and total respiration by
comparing the modeled and observed diurnal NEE cycle, and evaluated the Rh-Ra
partitioning by comparing modeled and observed Net Primary Productivity, which
constrains this partitioning since GPP- Ra=NPP. While some discrepancies exist,
overall the assimilation model had considerable skill on diurnal to interannual
timescales.
Author's Names: W. Sacks, D. Schimel, R. Monson, G. Churkina
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Added on: 05-Aug-2005 Downloads: 20
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DIRECT COMPARISON OF EDDY COVARIANCE AND BOWEN RATIO ENERGY BALANCE MEASUREMENTS OF CO2 FLUXES ...
Description: The objectives of this study were to (1) compare
annual mass and energy fluxes of sensible carbon dioxide (CO2), heat
flux density (H), and latent heat flux density (LE) from Campbell Scientific,
Inc. (CSI) manufactured eddy
covariance (EC) and Bowen Ratio/energy balance (BREB) instrumentation in a
tallgrass prairie site and (2) make similar short term (5-14 d) comparison in
other grazing ecosystems throughout the western United States. The long-term
tallgrass prairie site was located in central Oklahoma
with measurements being made from August 2001- October 2004, while the
short-term sites were located in Oregon, Colorado, Idaho, North Dakota, and Arizona
during the summers of 2003 and 2005. Results from the long-term (< 36-month)
co-located EC and BREB units indicated that both systems demonstrated similar
seasonal patterns, yet the EC consistently failed to close the energy balance
by 25-35% when compared to the BREB.
Author's Names: G.L. Doyle, W.A. Dugas, and H. Mayeux
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Added on: 05-Aug-2005 Downloads: 18
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DIURNAL CHANGES IN CO2 EXCHANGE OF A TROPICAL RAIN FOREST IN PENINSULAR MALAYSIA
Description:
Understanding the energy/H2O/CO2
exchange processes is very important for evaluating the roles of tropical rain
forest in climate change. The sensible heat, latent heat, and CO2
fluxes above a tropical rain forest in Peninsular Malaysia were measured using
the eddy covariance method for the year 2003. The diurnal patterns of energy, H2O
and CO2 flux were investigated using a multi-layer model that
considered patchy stomatal closure. Both bimodal and homogeneous stomatal
opening distributions were simulated, and the results indicated that the
observed negative relationship between CO2 absorption under
light-saturated conditions and vapor pressure deficit were not sufficiently
explained by stomatal closure alone, for homogeneous stomatal opening
distributions. For bimodal stomatal opening distributions, however, a greater
depression in canopy photosynthesis was found with increased atmospheric vapor
pressure deficit. These results strongly suggested that the depression in
canopy photosynthesis was caused not only by stomatal closure limitation but
also by the patchy (bimodal) stomatal behavior response to the increased
atmospheric vapor pressure deficit. Thus, the midday depression in canopy photosynthesis was mainly
caused by patchy (bimodal) stomatal closure.
Author's Names: S. Takanashi, Y. Kosugi, M. Tani, N. Matsuo, et al
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Added on: 08-Aug-2005 Downloads: 22
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DOWN AND DIRTY: USING A CONTINENTAL, NOT-SO-TALL TOWER TO STUDY TRENDS...
Description: Precise CO2 concentration
measurements at marine stations and tall towers are crucial for quantifying
global trends in atmospheric CO2 concentrations.
We propose that measurements in the continental planetary boundary layer—the
poor cousin of the clean background stations—can be used to understand trends
in, and controls, of atmospheric CO2 concentrations
at local and regional scales as well as global scales. The key is choosing
appropriate time scales of integration for the data. In the US Southern Great
Plains, we are measuring precise CO2 concentrations
continuously at 2–60 m and weekly at 300 and 3300 m above ground level (agl). CO2 flux is measured in individual crop fields and pastures (4 m
towers) and at 60 m. The precise CO2 concentrations
show strong continental influence in both diurnal and seasonal cycles. In
continental regions, atmospheric CO2 profiles are
strongly influenced by atmospheric dynamics as well as ecosystem and
anthropogenic fluxes. Relating site level measurements or atmospheric profiles
to regional CO2 budgets requires methods to represent or evaluate these
influences. We observe inter-annual differences in the
climatology of diurnal cycles (seasonal average diurnal cycles). Using the several years’ data for
boundary layer concentrations, the annual trend in CO2
growth nearly matches the value estimated by National Oceanic and
Atmospheric Administration (NOAA) Climate Monitoring Diagnostic
Laboratory for our latitude band.
Author's Names: M.S. Torn, M.L. Fischer, S.C. Biraud, W.J. Riley, et al
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Added on: 25-Jul-2005 Downloads: 38
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EDDY-COVARIANCE, CHAMBER AND BIOMETRIC BASED ESTIMATES OF ANNUAL CO2 EXCHANGE ABOVE TEMPERATE ...
Description:
In a temperate deciduous forest in Japan
situated complex terrain, net ecosystem CO2 exchange (NEE) was
estimated using micro-meteorological method, and net ecosystem products (NEP)
was estimated by measures of major carbon pools and fluxes using biometric and
chamber methods. In this study we evaluate the threshold value of u* for
interpolation in case stability was high using estimated NEP acquired by biometric
method. And the function which relate temperature to FCO2 for
interpolation was evaluated by the data acquired using automated chamber for
soil, CWD, trunk and foliage CO2 exchanges. Averaged net uptake of
CO2 measured by eddy covariance method from 1999 to 2002 was 3.4 tC
yr-1 ha-1 without compensation of nighttime underreport.
Increase of live under and above ground biomass from 1994 to 1999 was 1.56 tC
yr-1 ha-1. U* threshold values based on biometric and
chamber NEP were respectively 0.28 and 0.35 m sec-1
Author's Names: Y. Kominami, T. Miyama, K. Tamai, Y. Goto, et al
Filesize: 82.79 Kb
Added on: 01-Aug-2005 Downloads: 27
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EFFECT OF INCLUDING CO2 VERTICAL PROFILES ON PARTITIONING CARBON SOURCES AND SINKS BETWEEN ...
Description:
Understanding the geographical distribution of
carbon uptake by the terrestrial biosphere is critical for predicting future
trends of atmospheric CO2.
With inverse techniques, atmospheric CO2 measurements can be
used to estimate this uptake. The results from this approach, however, depend
on the accuracy of the transport model(s).
Because of the covariance between the seasonally-varying biosphere
exchange and the strength of vertical mixing (the rectifier effect), using only
the surface CO2 observations for this analysis yields an inferred
carbon flux that is highly sensitive to the details of the boundary-layer
dynamics in the transport model [Gurney
et al., 2004]. One possible way to reduce the sensitivity of these
inversions to poorly-represented boundary-layer dynamics is to use CO2
vertical profiles (and/or column CO2 measurements) in addition to
surface observations. In theory, multi-level aircraft CO2
measurements from several well-positioned sites are capable of improving the
estimate of the true annual mean inter-hemisphere CO2 gradient and
thereby improving the estimate of the partitioning of carbon sinks between the
two hemispheres.
Author's Names: Z. Yang, N. Krakauer, P. Wennberg, J. Randerson
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Added on: 09-Aug-2005 Downloads: 24
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EFFECT OF RESPIRATION AND CANOPY PARAMETERIZATIONS ON MODELED CARBON FLUX
Description: Simulations
of the global carbon cycle are strongly dependent upon model representations of
the exchange of carbon, energy, moisture and momentum between the atmosphere
and terrestrial biosphere. The carbon flux produced by these biophysical models
is subsequently dependent on the method used to produce respiration and
photosynthesis within the model on both spatial and temporal scales. We use an
updated version of the Simple Biosphere Model (SiB3) to simulate global carbon
flux between atmosphere and land surface, and compare model results to flux
tower and flask network observations. SiB3 assumes no annual net source or sink
of carbon in each gridcell, but the spatial pattern and seasonality of carbon
flux and atmospheric concentration can be strongly influenced by
parameterization of heterotrophic and autotrophic respiration and the
representation of vegetation phenology.
Author's Names: I.T. Baker, K.M. Schaefer and A.W. Philpott
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Added on: 25-Jul-2005 Downloads: 41
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