CO2 flux estimation errors associated with moist atmospheric processes 1Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
24 Jul 2012
2Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado, USA
3NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
4Department of Statistics and Computer Science, University of Sri Jayawardenepura, Gangodawila, Nugegoda, Sri Lanka
Received: 03 Apr 2012 – Published in Atmos. Chem. Phys. Discuss.: 18 Apr 2012 Abstract. Vertical transport by moist sub-grid scale processes such as deep convection
is a well-known source of uncertainty in CO2 source/sink inversion.
However, a dynamical link between vertical transport, satellite based
retrievals of column mole fractions of CO2, and source/sink inversion
has not yet been established. By using the same offline transport model with
meteorological fields from slightly different data assimilation systems, we
examine sensitivity of frontal CO2 transport and retrieved fluxes to
different parameterizations of sub-grid vertical transport. We find that
frontal transport feeds off background vertical CO2 gradients, which
are modulated by sub-grid vertical transport. The implication for
source/sink estimation is two-fold. First, CO2 variations contained in
moist poleward moving air masses are systematically different from
variations in dry equatorward moving air. Moist poleward transport is hidden
from orbital sensors on satellites, causing a sampling bias, which leads
directly to small but systematic flux retrieval errors in northern
mid-latitudes. Second, differences in the representation of moist sub-grid
vertical transport in GEOS-4 and GEOS-5 meteorological fields cause
differences in vertical gradients of CO2, which leads to systematic
differences in moist poleward and dry equatorward CO2 transport and
therefore the fraction of CO2 variations hidden in moist air from
satellites. As a result, sampling biases are amplified and regional scale
flux errors enhanced, most notably in Europe (0.43 ± 0.35 PgC yr−1).
These results, cast from the perspective of moist frontal
transport processes, support previous arguments that the vertical gradient
of CO2 is a major source of uncertainty in source/sink inversion.
Revised: 25 Jun 2012 – Accepted: 01 Jul 2012 – Published: 24 Jul 2012
Citation: Parazoo, N. C., Denning, A. S., Kawa, S. R., Pawson, S., and Lokupitiya, R.: CO2 flux estimation errors associated with moist atmospheric processes, Atmos. Chem. Phys., 12, 6405-6416, doi:10.5194/acp-12-6405-2012, 2012.