Description and Evaluation of the specified-dynamics experiment in the Chemistry-Climate Model Initiative

Clara Orbe (1) , David A. Plummer (2) , Darryn W. Waugh (3) , Huang Yang (4, 3) , Patrick Jöckel (5) , Douglas E. Kinnison (6) , Béatrice Josse (7) , Virginie Marecal (7) , Makoto Deushi (8) , Nathan Luke Abraham (9) , Alexander T. Archibald (9) , Martyn P. Chipperfield (10) , Sandip Dhomse (11, 10) , Wuhu Feng (10) , Slimane Bekki (12)

1 GISS - NASA Goddard Institute for Space Studies
2 CCCma - Canadian Centre for Climate Modelling and Analysis
3 Morton K. Blaustein Department of Earth and Planetary Sciences [Baltimore]
4 AOS - Department of Atmospheric and Oceanic Sciences [Los Angeles]
5 IPA - DLR Institut für Physik der Atmosphäre
6 ACOML - Atmospheric Chemistry Observations and Modeling Laboratory
7 CNRM - Centre national de recherches météorologiques
8 MRI - Meteorological Research Institute [Tsukuba]
9 Department of Chemistry [Cambridge, UK]
10 ICAS - Institute for Climate and Atmospheric Science [Leeds]
11 SEE - School of Earth and Environment [Leeds]
12 STRATO - LATMOS

We provide an overview of the REF-C1SD specified-dynamics experiment that was conducted as part of phase 1 of the Chemistry-Climate Model Initiative (CCMI). The REF-C1SD experiment, which consisted of mainly nudged general circulation models (GCMs) constrained with (re)analysis fields, was designed to examine the influence of the large-scale circulation on past trends in atmospheric composition. The REF-C1SD simulations were produced across various model frameworks and are evaluated in terms of how well they represent different measures of the dynami-cal and transport circulations. In the troposphere there are large (∼ 40 %) differences in the climatological mean distributions , seasonal cycle amplitude, and trends of the merid-ional and vertical winds. In the stratosphere there are similarly large (∼ 50 %) differences in the magnitude, trends and seasonal cycle amplitude of the transformed Eulerian mean circulation and among various chemical and idealized trac-ers. At the same time, interannual variations in nearly all quantities are very well represented, compared to the underlying reanalyses. We show that the differences in magnitude, trends and seasonal cycle are not related to the use of different reanalysis products; rather, we show they are associated with how the simulations were implemented, by which we refer both to how the large-scale flow was prescribed and to biases in the underlying free-running models. In most cases these differences are shown to be as large or even larger than the differences exhibited by free-running simulations produced using the exact same models, which are also shown to be more dynamically consistent. Overall, our results suggest that care must be taken when using specified-dynamics simulations to examine the influence of large-scale dynamics on composition.

Domains: Atmospheric and Oceanic Physics [physics.ao-ph]; Climatology

Clara Orbe, David A. Plummer, Darryn W. Waugh, Huang Yang, Patrick Jöckel, et al.. Description and Evaluation of the specified-dynamics experiment in the Chemistry-Climate Model Initiative. Atmospheric Chemistry and Physics, 2020, 20 (6), pp.3809 - 3840. ⟨10.5194/acp-20-3809-2020⟩. ⟨insu-02525775⟩