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Coupled Stratospheric Chemistry–Meteorology Data Assimilation. Part II: Weak and Strong Coupling
Open AccessArticle

Coupled Stratospheric Chemistry–Meteorology Data Assimilation. Part I: Physical Background and Coupled Modeling Aspects

1
Air Quality Research Division, Environment and Climate Change Canada, 2121 Transcanada Highway, Montréal, QC H9P 1J3, Canada
2
Royal Belgian Institute for Space Aeronomy, BIRA-IASB, 1180 Brussels, Belgium
3
Meteorological Research Division, Environment and Climate Change Canada, Montréal, QC H9P 1J3, Canada
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Department of Physics, University of Toronto, Toronto, ON M5S 1A7, Canada
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Data Assimilation and Quality Control Section, Canadian Center for Meteorological and Environmental Prediction, Montréal, QC H9P 1J3, Canada
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Institute of Geophysics, Polish Academy of Sciences, 01-452 Warsaw, Poland
*
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Current affiliation: PROUD Program Universidad de Puerto Rico - Humacao, PR-908, Humacao, PR 00792 USA.
§
Current affiliation: Shared Services Canada, HPC (High Performance Computing) Division, 2121 Transcanada Highway, Montréal, QC H9P 1J3, Canada.
Atmosphere 2020, 11(2), 150; https://doi.org/10.3390/atmos11020150
Received: 19 October 2019 / Revised: 17 January 2020 / Accepted: 21 January 2020 / Published: 30 January 2020
(This article belongs to the Special Issue Air Quality Prediction)
A coupled stratospheric chemistry–meteorology model was developed by combining the Canadian operational weather prediction model Global Environmental Multiscale (GEM) with a comprehensive stratospheric photochemistry model from the Belgian Assimilation System for Chemical ObsErvations (BASCOE). The coupled model was called GEM-BACH for GEM-Belgian Atmospheric CHemistry. The coupling was made across a chemical interface that preserves time-splitting while being modular, allowing GEM to run with or without chemistry. An evaluation of the coupling was performed by comparing the coupled model, refreshed by meteorological analyses every 6 h, against the standard offline chemical transport model (CTM) approach. Results show that the dynamical meteorological consistency between meteorological analysis times far outweighs the error created by the jump resulting from the meteorological analysis increments at regular time intervals, irrespective of whether a 3D-Var or 4D-Var meteorological analysis is used. Arguments in favor of using the same horizontal resolution for chemistry, meteorology, and meteorological and chemical analysis increments are also presented. GEM-BACH forecasts refreshed by meteorological analyses every 6 h were compared against independent measurements of temperature, long-lived species, ozone and water vapor. The comparison showed a relatively good agreement throughout the stratosphere except for an upper-level warm temperature bias and an ozone deficit of nearly 15%. In particular, the coupled model simulation during an ozone hole event gives better ozone concentrations than a 4D-Var chemical assimilation at a lower resolution. View Full-Text
Keywords: coupled chemistry–meteorology model; dynamical–photochemical–radiation interactions in the stratosphere; comparison between online model and offline CTM approach coupled chemistry–meteorology model; dynamical–photochemical–radiation interactions in the stratosphere; comparison between online model and offline CTM approach
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Ménard, R.; Chabrillat, S.; Robichaud, A.; de Grandpré, J.; Charron, M.; Rochon, Y.; Batchelor, R.; Kallaur, A.; Reszka, M.; Kaminski, J.W. Coupled Stratospheric Chemistry–Meteorology Data Assimilation. Part I: Physical Background and Coupled Modeling Aspects. Atmosphere 2020, 11, 150.

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