investigating representation errors in inversions of satellite co 2 retrievals
DESCRIPTION
Investigating Representation Errors in Inversions of Satellite CO 2 Retrievals. K.D. Corbin, A.S. Denning, N.C. Parazoo Department of Atmospheric Science Colorado State University. Transcom Meeting - Purdue University April 24-27, 2007. Motivation. - PowerPoint PPT PresentationTRANSCRIPT
Investigating Representation Errors in
Inversions of Satellite CO2 Retrievals
K.D. Corbin, A.S. Denning, N.C. Parazoo
Department of Atmospheric ScienceColorado State University
Transcom Meeting - Purdue UniversityApril 24-27, 2007
Transcom Meeting - Purdue UniversityApril 24-27, 2007
Motivation
OCO and GOSAT will retrieve total column XCO2 measurements beginning late 2008 Inverse modelers will use these measurements to help identify CO2 sources and sinks Using space borne XCO2 to represent a transport model grid-cell may introduce sampling errors into inversions XCO2 measurements will only represent clear conditions Investigate sampling errors using continuous data, a regional cloud-resolving model (SiB-RAMS), and a global transport model (PCTM)
Transcom Meeting - Purdue UniversityApril 24-27, 2007
CO2 continuous data from 3 towers: WLEF: 1995-2003 Harvard Forest: 1993-2002 Tapajos (km67): 2002-2005
Mid-day means from 1100-1600 LST Created clear-sky subset
Ranked PAR measurements from all years at each site Selected 20% of days per month with highest PAR
Fit separate harmonic functions to clear-sky subset and entire time-series Subtracted fits: CO2 fitCLEAR - CO2 fitTOTAL
Calculating Clear-Sky Errors at CO2 Towers
Transcom Meeting - Purdue UniversityApril 24-27, 2007
Clear-Sky Bias at Continuous CO2 Tower Sites
CO2 lower on clear days than on average Temperate sites have greatest bias in winter Tropical site shows biggest difference in rainy season[Corbin and Denning, 2006]
Transcom Meeting - Purdue UniversityApril 24-27, 2007
NEE Clear-Sky Bias at Tower Sites
[Corbin and Denning, 2006]
In mid-lats, enhanced uptake on clear days during summer, but negligible winter errors In tropics, enhanced uptake year-round on clear days NEE bias cannot account for CO2 errors
Transcom Meeting - Purdue UniversityApril 24-27, 2007
SiB2-RAMS Case DescriptionsNorth America South America
97 K
M450 KM
August 11-21, 2001 3 frontal passages
August 1-16, 2001 Dry season - calm conditions
Bulk microphysical parameterization to simulate clouds and precipitation explicitly
Emulatedsatellite
track
Transcom Meeting - Purdue UniversityApril 24-27, 2007
Spatial Representation Errors using SiB-RAMS
[Corbin et al., 2007]
Errors are unbiased and generally less than 0.5 ppm Spatial errors increase with domain heterogeneity and size
Transcom Meeting - Purdue UniversityApril 24-27, 2007
Clear-Sky Temporal Errors using SiB-RAMS
[Corbin et al., 2007]
Large errors at both sites Biased errors at temperate site due to CO2 anomalies associated with frontal systems that are masked by clouds
Transcom Meeting - Purdue UniversityApril 24-27, 2007
Clear-Sky Errors using PCTM Global 2003 simulation 1.25o longitude x 1.0o latitude Calculated clear-sky CO2 error for each land grid-cell
Used daytime mean total column CO2 concentrations Created clear-sky subset using downward shortwave radiation Fit 2 harmonics to clear-sky and total data Subtracted FitCLEAR - FitTOTAL
WLEF Tapajos
Transcom Meeting - Purdue UniversityApril 24-27, 2007
2003 PCTM Comparisons to Observations
Clear-sky bias from PCTM at tower locations match observed errors reasonably well
Transcom Meeting - Purdue UniversityApril 24-27, 2007
Annual Mean Clear-Sky Errors in PCTM
Errors vary regionally with spatially coherent patterns Underestimation of CO2 in South America and Alaska Overestimation of CO2 in Asia
Transcom Meeting - Purdue UniversityApril 24-27, 2007
Annual Mean Clear-Sky Errors by Latitude
Clear-sky errors larger in NH Underestimation of mean in sub-tropics
Transcom Meeting - Purdue UniversityApril 24-27, 2007
Seasonal Clear-Sky Errors in PCTM
Magnitude of errors varies with season
Transcom Meeting - Purdue UniversityApril 24-27, 2007
Seasonal Clear-Sky Errors by Latitude
Large underestimation of CO2 in NH land during winter Overestimation of CO2 in NH summer Underestimation of CO2 in SH spring
Transcom Meeting - Purdue UniversityApril 24-27, 2007
Conclusions
Spatial representation errors are small (< 0.5 ppm) Clear-sky (temporal) sampling errors are large and vary seasonally and regionally Satellite XCO2 cannot be used to represent temporal averages Transport must be modeled accurately and sampled at same time/location as satellite
Transcom Meeting - Purdue UniversityApril 24-27, 2007
Acknowledgements
Thanks to Steve Wofsy for the Tapajos Forest (km67) and Harvard Forest tower data and Ken Davis for the data from WLEF
Funding by NASA Earth System Science Fellowship 53-1970, NASA Contract NNG04GQ15H SUPP2, and NASA Subcontract (via Purdue University) 521-0438-01