Evaluating the Impact of the Atmospheric “ Chemical Pump ” on CO 2 Inverse Analyses
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Transcript of Evaluating the Impact of the Atmospheric “ Chemical Pump ” on CO 2 Inverse Analyses
Evaluating the Impact of the Atmospheric “Chemical Pump” on
CO2 Inverse Analyses
P. Suntharalingam
GEOS-CHEM Meeting, April 4-6, 2005
Acknowledgements
J. Randerson, N. Krakauer (UCI/CalTech); D. J. Jacob, J. A. Logan, Y. Xiao, R. M. Yantosca (Harvard); A. Fiore (GFDL)
Suntharalingam et al. [2005], Global Biogeochemical Cycles, submitted.
APPLICATION OF GEOS-CHEM TO EVALUATE CHEMICAL PUMP EFFECT
QUESTION :
What is impact of accounting for realistic representation of
reduced carbon oxidation
1) on modeled CO2 distributions
2) on inverse flux estimates
APPROACH :
Use GEOS-CHEM simulations to estimate magnitude of effect
ATMOSPHERIC CARBON BUDGET
An outstanding question on global CO2 budget :
What is magnitude and distribution of net terrestrial biospheric flux ? (“missing sink”)
The “Top-down” approach uses Inverse Analyses of Atmospheric CO2
? Net Terrestrial Flux ?
CARBON FLUX FRAMEWORK UNDERLYING RECENT ATMOSPHERIC CO2 INVERSIONS
Fossil Seasonal Biosphere
“Residual Biosphere”
Land use change, Fires, Regrowth, CO2 Fertilization
Ocean
6 120 120
Units = Pg C/yr
Atmospheric CO2
9092
NET LAND UPTAKE
??
( 0-2 )
All surface fluxes
ymod - yobsConcentration residual
•Model prior distributions for fossil, seasonal biosphere, ocean ymod
•76 Surface CO2 observation stations (GLOBALVIEW-CO2) yobs
•Estimate “RESIDUAL” CO2 fluxes for 22 regions
Inference of Northern Hemispheric Carbon Uptake from Annual Mean Concentration Residuals
THE TRANSCOM 3 INVERSE ANALYSES (Gurney et al. 2002)
Residuals = ymod – y obsModel simulations (prior fluxes)
CO2 Observations
N. Hem. carbon uptake
OXIDATION OF REDUCED C SPECIES PROVIDES A TROPOSPHERIC SOURCE OF CO2
Fossil Biomass Burning, Agriculture, Biosphere Ocean
ATMOSPHERIC CO2
CO
0.9-1.3 Pg C/yr Non- CO pathways
CH4NMHCs
Distribution of this CO2 source can be far downstream of C
emission location
HOW IS REDUCED CARBON ACCOUNTED FOR IN CURRENT INVERSIONS ?
A : Emitted as CO2 in surface inventories
Fossil fuel : CO2 emissions based on carbon content of fuel and assuming complete oxidation of CO and volatile hydrocarbons.
(Marland and Rotty, 1984; Andres et al. 1996)
Seasonal biosphere (CASA) : Biospheric C efflux represents respiration (CO2) and emissions of reduced C gases (biogenic hydrocarbons, CH4,etc)
(Randerson et al. , 2002; Randerson et al. 1997)
Seasonal Biosphere : CASA
Fossil Fuel
MODELING REDUCED CARBON CONTRIBUTION AT SURFACE PRODUCES BIASED INVERSION ESTIMATES
Surface release of CO2 from reduced C
gases
Tropospheric CO2 source from reduced C oxidation
CO, CH4, NMHCs
VS.
Observation network detects tropospheric CO2 source from
reduced C oxidation
ymodsurf ymod3D yobs
VS.
CALCULATION OF CHEMICAL PUMP EFFECT
• Flux Estimate: x = xa + G (y - K xa)
• STEP 1 : Impact on modeled concentrations
Adjust ymodel to account for redistribution of reduced C from surface inventories to oxidation location in troposphere
ymodelyobs
• Adjustmentymodel = y3D – ySURF
ADD effect of CO2 source from reduced C oxidation
SUBTRACT effect of reduced C from surface inventories
EVALUATION OF THE CHEMICAL PUMP EFFECTGEOS-CHEM SIMULATIONS (v. 5.07)
Standard Simulation
CO2 Source from Reduced C Oxidation = 1.1 Pg C/yr
Distribute source according to seasonal 3-D
variation of CO2 production from CO
Oxidation
Distribute source according to seasonal SURFACE
variations of reduced C emissions from Fossil and
Biosphere sources
CO2SURF Simulation : ySURFCO23D Simulation : y3D
Simulations spun up for 3 years. Results from 4th year of simulation
GEOS-CHEM Model Configurationhttp://www-as.harvard.edu/chemistry/trop/geos/index.html
•Global 3-D model of atmospheric chemistry (v. 5.07)
•2ox2.5o horizontal resolution; 30 vertical levels
•Assimilated meteorology (GMAO); GEOS-3 (year 2001)
•CO oxidation distribution from tagged CO simulation using archived monthly OH fields
Reduced Carbon Emissions Distributions (spatial and temporal variability)
Fossil : Duncan et al. [2005] (annual mean)
Biomass Burning : Duncan et al. [2003] (monthly)
Biofuels : Yevich and Logan [2003]
NMVOCs : Duncan et al. [2005] ; Guenther et al. [1995]; Jacob et al. [2002]
CH4 : A priori distributions from Wang et al. [2004] (monthly)
REDUCED CARBON SOURCES BY SECTOR STANDARD SIMULATION : CO2 Source from Reduced C Oxidation = 1.1 Pg C/yr
• Sector breakdown based on Duncan et al. [2005]
• *Methane sources distributed according to a priori fields from Wang et al. [2004]
REDUCED CARBON SOURCES Pg C/yr
Fossil (CO,CH4,NMHCs) 0.27
Biomass Burning (CO,CH4,NMHCs) 0.26
Biofuels (CO,CH4) 0.09
Biogenic Hydrocarbons 0.16
Other Methane Sources* 0.31
TOTAL 1.1
SOURCE DISTRIBUTIONS : ANNUAL MEAN
Zonal Integral of Emissions
Latitude
CO23D: Column Integral of
CO2 from CO OxidationCO2SURF :CO2 Emissions from
Reduced C Sources
CO23D :Maximum in tropics, diffuse
CO2SURF : Localized, corresponding to regions of high CO, CH4 and biogenic NMHC emissions
CO23D
CO2SURF
gC/(cm2 yr)
-50 50
MODELED SURFACE CONCENTRATIONS : Annual Mean
CO2SURFCO23D
Surface concentrations reflect source distributions:
Diffuse with tropical maximum for CO23D and localized to regions of high reduced C emissions for CO2SURF
Largest changes in regions in and downstream of high reduced C emissions
TAP : - 0.55; ITN : - 0.35; BAL : - 0.35 (ppm)
REGIONAL VARIATION OF CHEMICAL PUMP EFFECT ymodel = CO23D – CO2SURF
ymodel : Zonal average
at surface
CO
2 (p
pm
)
CHEMICAL PUMP EFFECT : N/S DIFFERENCES
Mean Interhemispheric
difference = - 0.21 ppm
0.21 ppm
Latitude
Impact on TRANSCOM3 Systematic decrease in Northern Hemisphere
Residuals
50-50
IMPACT ON SURFACE FLUX ESTIMATESInverse analyses by Nir Krakauer
•Estimate effect by modifying concentration error vector as :
(y – (K xa + ymodel))
Then, ‘adjusted’ state estimate is:
xadj = xa + G(y – (K xa + ymodel))
• Evaluate with 3 transport models (MATCH, GISS-UCI, LSCE-TM2)
Q : What are the changes in estimates of ‘residual’ fluxes when we account for chemical pump adjustment ymodel
Evaluate impact using TransCom annual mean analysis (Gurney et al. 2002)
Relative impact of chemical pump adjustment on CO2 uptake varies across models.
0.22 0.25 0.26
Original Uptake
-19%-27%-9%
2.5 0.9 1.4
% Change
REDUCTION IN LAND UPTAKE (Northern extratropics) Systematic Reduction (0.22-0.26 Pg C/year)
Pg
C/y
r
SUMMARY
•Neglecting the 3D representation of the CO2 source from reduced C oxidation produces biased inverse CO2 flux estimates.
•Accounting for a reduced C oxidation source of 1.1 Pg C/yr gives a reduction in the modeled annual mean N-S CO2 gradient of 0.2 ppm (equivalent to a reduction of 0.2-0.3 Pg C/yr in Northern Hemispheric land uptake in an annual mean inversion.)
•Regional changes are larger; up to 0.6 ppm concentration adjustment in regions of high reduced C emissions.
•Impacts on seasonal inverse estimates may be significant and will be examined in future work (N/S y variation: –0.32 ppm (January) to –0.15 ppm (July)).
EXTRA SLIDES
SOURCE ESTIMATES FROM INVERSE ANALYSIS
Minimize cost function:
J(x) = (x – xa)T Sa –1 (x - xa) + (y – K x)T S –1 (y –K x)
Solution:
x = xa + G (y - K xa)
where, G = Sa KT (K Sa KT + S) -1
A posteriori errors : S = (KT S –1 K + Sa –1) -1
Observed concentrations
Modeled concentrations
x = state vector (sources)
xa = a priori source estimate
K = Jacobian matrix (model transport)
Sa = Error covariance matrix on sources
Se = Error covariance matrix on
concentration error
IMPACT ON SURFACE FLUX ESTIMATES Relative Reduction in N.Hemisphere Land Uptake Varies with Model
Reduction in Land Uptake : LSCE-TM2
Reduction in Land Uptake : MATCH
CHEMICAL PUMP FLUX ADJUSTMENTSZONALLY AGGREGATED LAND REGIONS
Relative impact of chemical pump adjustment varies across models, though magnitude of zonally aggregated flux adjustment relatively invariant
Sum N. extratrop. Land net flux (PgC/yr)
- 2.5
- 0.9
-1.4