HR: 11:35h
AN: A12B-06    [Abstracts]
TI: The Constraint on Surface CO₂ Fluxes Provided by OCO Column CO₂ Measurements: a Realistic Assessment
AU: * Baker, D F
EM: dfb@ucar.edu
AF: Woods Hole Atmospheric Institution, Marine Chemistry & Geochemistry, Woods Hole, MA 02543, United States
AU: Boesch, H
EM: hartmut.boesch@le.ac.uk
AF: University of Leicester, Department of Physics & Astronomy, Leicester, LE1 7RH, United Kingdom
AU: Doney, S C
EM: sdoney@whoi.edu
AF: Woods Hole Atmospheric Institution, Marine Chemistry & Geochemistry, Woods Hole, MA 02543, United States
AB: The current network of in situ CO₂ monitoring sites lacks the spatial coverage to provide regional estimates of the sources and sinks of CO₂ over most of the globe. NASA's soon-to-be-launched Orbital Carbon Observatory (OCO), a sun synchronous satellite specially designed to be sensitive to near-surface CO₂ concentrations, should soon furnish such coverage. Here we use a variational data assimilation method in a simulation framework to estimate how well OCO's column-CO₂ measurements can constrain the surface sources and sinks. We start with new estimates of the measurement uncertainties for a single column measurement, given by an analysis of the instrument's inversion procedure as a function of surface type, aerosol optical depth, and solar zenith angle . Next, we examine cloud and aerosol statistics derived from MODIS and other satellites to determine the likely correlations in measurement error (including modelling errors) along the OCO trajectory. These are used to obtained the effective number of independent measurements inside each 2°x5° atmospheric model grid box that the satellite passes over, from which effective multi-shot measurement errors are calculated. These are then used in the simulation study to determine how much of the error in the prior flux estimate can be removed by assimilating the OCO data. The merits of OCO's nadir- and glint-viewing modes are assessed. Spatial discretization errors due to the atmospheric model are quantified and considered. Our analysis highlights the importance of aerosols in the problem: not only do thick aerosol optical depths preclude useful retrievals, but aerosols at lower levels will bias the column measurements; we simulate the impact of such aerosol levels globally to quantify their importance. This study is the first to realistically consider the impact of clouds and aerosols in the problem, and hopefully will help the mission operations personnel decide when to operate in nadir versus glint mode, and which retrievals to process first.
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0322 Constituent sources and sinks
DE: 0428 Carbon cycling (4806)
DE: 3260 Inverse theory
DE: 3315 Data assimilation
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting