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Title:
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Atmospheric transport and chemistry of trace gases in LMDz5B: evaluation and implications for inverse modelling
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Author(s):
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Locatelli, R.; Bousquet, P.; Hourdin, F.; Saunois, M; Cozic, A.; Couvreux, F.; Grandpeix, J.-Y.; Lefebvre, M.-P.; Rio, C.; Bergamaschi, P.; Chambers, S.; Karstens, U.; Kazan, V.; Laan, van der S.; Meijer, H.A.J.; Moncrieff, J.; Ramonet, M.; Scheeren, H.A.; Schlosser, C.; Schmidt, M.; Vermeulen, A.T.; Williams, A.G.
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Published by:
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Publication date:
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ECN
Environment & Energy Engineering
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12-12-2014
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ECN report number:
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Document type:
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ECN-W--14-039
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Article (scientific)
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Number of pages:
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30
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Published in: Geoscientific Model Development (European Geosciences Union), , 2015, Vol.8, p.129-150.
Abstract:
Representation of atmospheric transport is a major source of error in the estimation of
greenhouse gas sources and sinks by inverse modelling. Here we assess the impact on
trace gas mole fractions of the new physical parameterisations recently implemented in
5 the Atmospheric Global Climate Model LMDz to improve vertical diffusion, mesoscale
mixing by thermal plumes in the planetary boundary layer (PBL), and deep convection
in the troposphere. At the same time, the horizontal and vertical resolution of the
model used in the inverse system has been increased. The aim of this paper is to
evaluate the impact of these developments on the representation of trace gas trans10
port and chemistry, and to anticipate the implications for inversions of greenhouse gas
emissions using such an updated model.
Comparison of a one-dimensional version of LMDz with large eddy simulations
shows that the thermal scheme simulates shallow convective tracer transport in the
PBL over land very efficiently, and much better than previous versions of the model.
15 This result is confirmed in three dimensional simulations, by a much improved reproduction
of the Radon-222 diurnal cycle. However, the enhanced dynamics of tracer
concentrations induces a stronger sensitivity of the new LMDz configuration to external
meteorological forcings. At larger scales, the inter-hemispheric exchange is slightly
slower when using the new version of the model, bringing them closer to observations.
20 The increase in the vertical resolution (from 19 to 39 layers) significantly improves the
representation of stratosphere/troposphere exchange. Furthermore, changes in atmospheric
thermodynamic variables, such as temperature, due to changes in the PBL
mixing, significantly modify chemical reaction rates and the equilibrium value of reactive
trace gases.
25 One implication of LMDz model developments for future inversions of greenhouse
gas emissions is the ability of the updated system to assimilate a larger amount of highfrequency
data sampled at high-variability stations. Others implications are discussed
at the end of the paper.
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