Journal cover Journal topic
Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
Geosci. Model Dev., 9, 1683-1695, 2016
https://doi.org/10.5194/gmd-9-1683-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Development and technical paper
03 May 2016
Sensitivity of chemistry-transport model simulations to the duration of chemical and transport operators: a case study with GEOS-Chem v10-01
Sajeev Philip1, Randall V. Martin1,2, and Christoph A. Keller3,a 1Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada
2Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, USA
3School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA
anow at: Universities Space Research Association/GESTAR, NASA GMAO Code 610.1, Greenbelt, Maryland, USA
Abstract. Chemistry-transport models involve considerable computational expense. Fine temporal resolution offers accuracy at the expense of computation time. Assessment is needed of the sensitivity of simulation accuracy to the duration of chemical and transport operators. We conduct a series of simulations with the GEOS-Chem chemistry-transport model at different temporal and spatial resolutions to examine the sensitivity of simulated atmospheric composition to operator duration. Subsequently, we compare the species simulated with operator durations from 10 to 60 min as typically used by global chemistry-transport models, and identify the operator durations that optimize both computational expense and simulation accuracy. We find that longer continuous transport operator duration increases concentrations of emitted species such as nitrogen oxides and carbon monoxide since a more homogeneous distribution reduces loss through chemical reactions and dry deposition. The increased concentrations of ozone precursors increase ozone production with longer transport operator duration. Longer chemical operator duration decreases sulfate and ammonium but increases nitrate due to feedbacks with in-cloud sulfur dioxide oxidation and aerosol thermodynamics. The simulation duration decreases by up to a factor of 5 from fine (5 min) to coarse (60 min) operator duration. We assess the change in simulation accuracy with resolution by comparing the root mean square difference in ground-level concentrations of nitrogen oxides, secondary inorganic aerosols, ozone and carbon monoxide with a finer temporal or spatial resolution taken as “truth”. Relative simulation error for these species increases by more than a factor of 5 from the shortest (5 min) to longest (60 min) operator duration. Chemical operator duration twice that of the transport operator duration offers more simulation accuracy per unit computation. However, the relative simulation error from coarser spatial resolution generally exceeds that from longer operator duration; e.g., degrading from 2°  ×  2.5° to 4°  ×  5° increases error by an order of magnitude. We recommend prioritizing fine spatial resolution before considering different operator durations in offline chemistry-transport models. We encourage chemistry-transport model users to specify in publications the durations of operators due to their effects on simulation accuracy.

Citation: Philip, S., Martin, R. V., and Keller, C. A.: Sensitivity of chemistry-transport model simulations to the duration of chemical and transport operators: a case study with GEOS-Chem v10-01, Geosci. Model Dev., 9, 1683-1695, https://doi.org/10.5194/gmd-9-1683-2016, 2016.
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Short summary
We assessed the sensitivity of simulation accuracy to the duration of chemical and transport operators in a chemistry-transport model. Longer continuous transport operator duration increases concentrations of emitted species. Chemical operator duration twice that of the transport operator duration offers more simulation accuracy per unit computation. The simulation error from coarser spatial resolution generally exceeds that from longer operator duration.
We assessed the sensitivity of simulation accuracy to the duration of chemical and transport...
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