HR: 1340h
AN: A13A-0096    [Abstracts]
TI: Will Satellite CO$_{2}$ Measurements Experience a Clear-Sky Bias?
AU: * Corbin, K
EM: kdcorbin@atmos.colostate.edu
AF: Colorado State University, Department of Atmospheric Science, Fort Collins, CO 80523-1371 United States
AU: Denning, A S
EM: denning@atmos.colostate.edu
AF: Colorado State University, Department of Atmospheric Science, Fort Collins, CO 80523-1371 United States
AB: Satellite measurements of CO$_{2}$ can help enhance our understanding of the carbon cycle; however, retrieval of near-surface CO$_{2}$ from satellites will require cloud-free conditions. Using continuous CO$_{2}$ measurements from tower sites in Wisconsin and Harvard Forest, we investigated the systematic bias that could occur from retrieving CO$_{2}$ concentrations only in clear-sky conditions. The clear-sky bias in near-surface CO$_{2}$ at each site was defined by detrending the CO$_{2}$ concentration timeseries, creating a clear-sky subset from mean daytime CO$_{2}$ concentrations by comparing photosynthetically active radiation (PAR) measurements taken at both towers to the top-of-the-atmosphere solar radiation, fitting two harmonics to both the clear-sky subset as well as all the mean daytime CO$_{2}$ measurements, and subtracting the fit for the daytime CO$_{2}$ measurements from the clear-sky fit. At both towers, clear-sky measurements experienced a negative bias relative to the mean of all daytime measurements: Wisconsin had a mean surface bias of -1.1 ppm while Harvard Forest had a mean surface bias of -2.85 ppm, with a larger bias in the winter due to fossil fuel combustion compared to a smaller bias in the summer. We obtained similar results investigating the bias at 1pm rather than using mean daytime measurements. These results indicate that satellite measurements will have a systematic negative bias, underestimating the total column CO$_{2}$ concentration by as much as .6 ppm at some locations and times of the year. Quantitative interpretation of satellite CO$_{2}$ retrievals will require accurate modeling of cloud radiative forcing of ecosystem carbon exchange.
UR: http://biocycle.atmos.colostate.edu
DE: 1610 Atmosphere (0315, 0325)
DE: 1615 Biogeochemical processes (4805)
DE: 0315 Biosphere/atmosphere interactions
DE: 0322 Constituent sources and sinks
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting