Errors and improvements in the use of archived meteorological data for chemical transport modeling: an analysis using GEOS-Chem v11-01 driven by GEOS-5 meteorology
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Published:2018-01-23
Issue:1
Volume:11
Page:305-319
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ISSN:1991-9603
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Container-title:Geoscientific Model Development
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language:en
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Short-container-title:Geosci. Model Dev.
Author:
Yu KarenORCID, Keller Christoph A., Jacob Daniel J., Molod Andrea M., Eastham Sebastian D.ORCID, Long Michael S.
Abstract
Abstract. Global simulations of atmospheric chemistry are commonly conducted with
off-line chemical transport models (CTMs) driven by archived meteorological
data from general circulation models (GCMs). The off-line approach has
the advantages of simplicity and expediency, but it incurs errors due to temporal
averaging in the meteorological archive and the inability to reproduce the
GCM transport algorithms exactly. The CTM simulation is also often conducted
at coarser grid resolution than the parent GCM. Here we investigate this
cascade of CTM errors by using 222Rn–210Pb–7Be chemical tracer
simulations off-line in the GEOS-Chem CTM at rectilinear
0.25∘ × 0.3125∘ (≈ 25 km) and
2∘ × 2.5∘ (≈ 200 km) resolutions and
online in the parent GEOS-5 GCM at cubed-sphere c360 (≈ 25 km) and
c48 (≈ 200 km) horizontal resolutions. The c360 GEOS-5 GCM
meteorological archive, updated every 3 h and remapped to
0.25∘ × 0.3125∘, is the standard operational product
generated by the NASA Global Modeling and Assimilation Office (GMAO) and used
as input by GEOS-Chem. We find that the GEOS-Chem 222Rn simulation at
native 0.25∘ × 0.3125∘ resolution is affected by
vertical transport errors of up to 20 % relative to the GEOS-5 c360 online
simulation, in part due to loss of transient organized vertical motions in
the GCM (resolved convection) that are temporally averaged out in the 3 h
meteorological archive. There is also significant error caused by operational
remapping of the meteorological archive from a cubed-sphere to a rectilinear
grid. Decreasing the GEOS-Chem resolution from
0.25∘ × 0.3125∘ to
2∘ × 2.5∘ induces further weakening of vertical
transport as transient vertical motions are averaged out spatially and
temporally. The resulting 222Rn concentrations simulated by the
coarse-resolution GEOS-Chem are overestimated by up to 40 % in surface air
relative to the online c360 simulations and underestimated by up to 40 %
in the upper troposphere, while the tropospheric lifetimes of 210Pb and
7Be against aerosol deposition are affected by 5–10 %. The lost
vertical transport in the coarse-resolution GEOS-Chem simulation can be
partly restored by recomputing the convective mass fluxes at the appropriate
resolution to replace the archived convective mass fluxes and by correcting
for bias in the spatial averaging of boundary layer mixing depths.
Publisher
Copernicus GmbH
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