HR: 1340h
AN: A13A-0083    [Abstracts]
TI: Evaluating Model-Observation CO$_2$ Sampling Strategies: Implications for the Strength of the Latitudinal CO$_2$ Gradient.
AU: * Olsen, S C
EM: solsen@uci.edu
AF: UC Irvine, Dept of Earth System Science, Irvine, Ca 92697-3100 United States
AU: Randerson, J T
EM: jranders@uci.edu
AF: UC Irvine, Dept of Earth System Science, Irvine, Ca 92697-3100 United States
AU: Prather, M
EM: mprather@uci.edu
AF: UC Irvine, Dept of Earth System Science, Irvine, Ca 92697-3100 United States
AU: Krakauer, N
EM: niryk@caltech.edu
AF: Caltech, Dept. of Geological and Planetary Sciences, Pasadena, Ca 91125 United States
AB: In CO$_2$ source inversion studies, the combination of model-simulated and observed atmospheric CO$_2$ concentrations suggest that the Northern Hemisphere terrestrial biosphere is sequestering approximately 1-2 PgC/yr. However, in these studies the model simulated CO$_2$ concentrations are generally averaged over all times of day and meteorological conditions whereas most of the observations are made during daylight hours and subject to meteorological restrictions, e.g., wind speed and direction criteria. We investigated the effect of different sampling strategies on modeled CO$_2$ distributions in two different global chemical transport models driven with different meteorological inputs. In our analysis we used diurnally varying CO$_2$ fluxes from the terrestrial biosphere and focused on the stations used in the Transcom intercomparison. We found that annual mean CO$_2$ concentrations simulated in the models were sensitive to the time of day sampling and wind speed and direction. Failing to account for the diurnal cycle of CO$_2$ when sampling atmospheric models leads to an overestimate of CO$_2$ levels at a number of continental and coastal stations. In atmospheric inversions, this bias could lead to an overestimation of the size of the Northern Hemisphere carbon sink. As more observations in non-remote locations are incorporated into model-observation comparisons, extra care will be necessary to sample model simulations in the same manner that the observations were sampled.
DE: 1610 Atmosphere (0315, 0325)
DE: 0315 Biosphere/atmosphere interactions
DE: 0368 Troposphere--constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting