Atmospheric transport model LMDz
The transport model is an essential component of the CCDAS that relates the surface
fluxes to the atmospheric CO2 concentrations.
1) Overall model description
It follows the configuration of the General Circulation Model LMDz model (Hourdin et
al., 2006) as implemented in the coupled climate simulations for the IPCC AR4 report
(IPCC, 2007). The dynamical part of the GCM is based on a finite-difference formulation
of the primitive equations solved on a 3D Eulerian grid with a typical horizontal
resolution of 3.75° (longitudes) x 2.5° (latitudes) and 19 sigma-pressure layers up to
3hPa. This corresponds to a vertical resolution of about 300-500 m in the planetary
boundary layer (first level at 70 m height) and to a resolution of about 2 km at the
tropopause (with 7-9 levels located in the stratosphere). The calculated winds (u and v)
are relaxed to ECMWF analyzed meteorology with a relaxation time of 2.5h (nudging) in
order to realistically account for large scale advection (Hourdin et al., 2000). The
advection of tracers is calculated based on the finite-volume, second-order scheme as
described by Hourdin and Armengaud (1999). Deep convection is parameterized
according to the scheme of Tiedtke (1989) and the turbulent mixing in the planetary
boundary layer is based on a local second-order closure formalism.
Representation of vertical and
horizontal grids of LMDZ
Colors represent simulated surface
and air temperatures, arrows
represent wind’s direction.
© L. Fairhead (IPSL/LMD)
The model has been widely used to model climate (IPCC, 2001, 2007) as well as
transport and chemistry of gas and particles (Peylin et al., 2005, Bousquet et al. 2005,
2006, Rivier et al., 2006, Hauglustaine et al., 2004, Folberth et al., 2005). LMDz-INCA is
running operationally since 2006 and calculates every day a 5-day forecast of the main
atmospheric trace gases (http://www-lsceinca.cea.fr). For greenhouse gases, we have
been using LMDz since 2003 at LSCE in an offline mode named LMDZt (with precalculated transport fields) to save computational time compared to the full GCM.
Few main changes have occurred since the first use of LMDz in the CCDAS. The model
used for the first CARBONES re-analysis is based on LMDz version 3. Recent and ongoing
developments at the LMD laboratory have led to an improved version, LMDz version 4,
with the following changes:
 A more sophisticated parameterization of the planetary boundary layer has been
implemented by Hourdin et al. (2002) based on the representation of a dry
thermal in terms of mass fluxes, as in deep convection schemes. In this new
version we introduced the nudging of air temperature T with the same relaxation
time as for the wind (u and v).
 Several small inconsistencies have been cleared for the convection and advection
schemes.
The updated version has led to significant improvement in terms of simulated
atmospheric CO2 concentrations. An internal report that can be requested from Philippe
Bousquet at LSCE ([email protected]) compares the two LMDz versions together
with two other state of the art global transport models (TM3 and TM5) to atmospheric
CO2 data using a standard set of fluxes. Model skills for the simulation of i) large scale
atmospheric features (TRANSCOM-I experiment), ii) upper air CO2 data, iii) vertical
profile within the planetary boundary layer, and iv) continuous surface CO2 records are
on averaged improved with the new LMDz version. Within the continental PBL, the
standard LMDZ performances were limited by a too large diffusion that smoothes
gradients of concentrations too efficiently. The new version 4 with an improved PBL
scheme, presents equivalent capabilities to represent the synoptic variations of CO2
concentrations as other state-of-the-art models such as TM5. Such improvement is thus
crucial to properly assimilate all surface CO2 concentration data within the CCDAS.
2) Model Policy
The model is freely available under a free-software license: CECILL. It can be access
through: http://lmdz.lmd.jussieu.fr/
3) References
Bousquet P., Hauglustaine D.A., Peylin P., et al. (2005), Two decades of OH variability as
inferred by an inversion of atmospheric transport and chemistry of methyl
chloroform, Atmospheric Chemistry and Physics, 5: 2635-2656
Bousquet P., Ciais P., Miller J.B., et al. (2006), Contribution of anthropogenic and natural
sources to atmospheric methane variability, Nature, 443 (7110): 439-443
Folberth G., Hauglustaine D.A., Ciais P., et al. (2005), On the role of atmospheric chemistry
in the global CO2 budget, Geophysical Research Letters, 32(8): L08801
Hauglustaine D.A., Hourdin F., Jourdain L., et al. (2004), Interactive chemistry in the
Laboratoire de Meteorologie Dynamique general circulation model: Description and
background tropospheric chemistry evaluation, Journal of Geophysical Research Atmosphere, 109(D4): D04314
Hourdin F., Armengaud A. (1999), The use of finite-volume methods for atmospheric
advection of trace species. Part I: Test of various formulations in a general
circulation model, Monthly Weather Review, 127(5): 822-837
Hourdin, 2000
Hourdin, F. D., F. Couvreux, and L. Menut (2002), Parameterization of the dry convective
boundary layer based on a mass flux representation of thermals, J Atmos Sci, 59,
1105-1123
Hourdin, F., I. Musat, S. Bony, P. Braconnot, F. Codron, J. L. Dufresne, L. Fairhead, M. A.
Filiberti, P. Friedlingstein, J. Y. Grandpeix, G. Krinner, P. Levan, Z. X. Li and F.
Lott, (2006), The LMDZ4 general circulation model: climate performance and
sensitivity to parametrized physics with emphasis on tropical convection, Climate
Dynamics, 27, 787-813
IPCC (2001). Climate Change 2001: The Scientific Basis. Contribution of Working Group I
to the Third Assessment Report of the Intergovernmental Panel on Climate Change
[Houghton, J.T., Y. Ding, D.J. Griggs, M. Noguer, P.J. van der Linden, X. Dai, K.
Maskell, and C.A. Johnson (eds.)]. Cambridge University Press, Cambridge, United
Kingdom and New York, NY, USA, 881pp
IPCC, (2007). Climate Change 2007: The Physical Science Basis. Contribution of Working
Group I to the Fourth Assessment Report of the Intergovernmental Panel on
Climate Change [Solomon, S., D. Qin, M. Manning (eds.)]
Peylin P, Rayner PJ, Bousquet P, et al. (2005), Daily CO2 flux estimates over Europe from
continuous atmospheric measurements: 1, inverse methodology, Atmospheric
Chemistry and Physics, 5: 3173-3186
Rivier L., Ciais P., Hauglustaine D.A., et al. (2006), Evaluation of SF6, C2Cl4, and CO to
approximate fossil fuel CO2 in the Northern Hemisphere using a chemistry
transport model, Journal Geophysical Research-Atmosphere, 111(D16) - D16311.
Tiedtke M. (1989), A comprehensive mass flux scheme for cumulus parameterization in
large-scale models, Monthly Weather Review, 117(8): 1779-1800