[A-AS08] Stratosphere-troposphere interaction

[AAS08-14] The response of extreme variability in the Arctic stratosphere to 4xCO₂ concentrations in CMIP6 models

*Blanca Ayarzaguena¹, Andrew J. Charlton-Perez², Amy H Butler³, Peter Hitchcock⁴, Isla R. Simpson⁵, Lorenzo Polvani⁶, Neal Butchart⁷, Edwin Gerber⁸, Lesley Gray⁹, Birgit Hassler¹⁰, Pu Lin¹¹, François Lott¹², Elisa Manzini¹³, Ryo Mizuta¹⁴, Clara Orbe¹⁵, Scott Osprey⁹, David Saint-Martin¹⁶, Michael Sigmond¹⁷, Masakazu Taguchi¹⁸, Evgeny Volodin¹⁹, Singo Watanabe²⁰ (1.Departamento de Física de la Tierra y Astrofísica, Universidad Complutense de Madrid, Spain, 2.Department of Meteorology, University of Reading, UK, 3.Cooperative Institute for Environmental Sciences (CIRES)/National Oceanic and Atmospheric Administration (NOAA) Chemical Sciences Division, USA, 4.Department of Earth and Atmospheric Sciences, Cornell University, USA, 5.Climate and Global Dynamics Laboratory, National Center for Atmospheric Research, USA, 6.Columbia University, USA, 7.Met Office Hadley Centre, UK, 8.Courant Institute of Mathematical Sciences, New York University, USA, 9.NCAS-Climate, Department of Physics, University of Oxford, UK, 10.Deutsches Zentrum für Luft-und Raumfahrt (DLR), Oberpfaffenhofen, Germany, 11.Atmospheric and Oceanic Sciences Program, NOAA, USA,, 12.Laboratoire de Météorologie Dynamique, Ecole Normale Supérieure, France, 13.Max-Planck-Institut für Meteorologie, Germany, 14.Meteorological Research Institute, Japan, 15.NASA Goddard Institute for Space Studies, USA, 16.Centre National de Recherches Météorologiques (CNRM), Université de Toulouse, Météo-France, CNRS, Toulouse, France, 17.Canadian Centre for Climate Modelling and Analysis Environment and Climate Change, Canada, 18.Department of Earth Science, Aichi University of Education, Kariya, Japan, 19.Marchuk Institute of Numerical Mathematics, Russia, 20.Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Japan)

Keywords:sudden stratospheric warmings, climate change

Sudden stratospheric warmings (SSWs) and stratospheric final warmings (SFWs) are the most important phenomena of the wintertime Arctic stratosphere. They also constitute one of the clearest examples of stratosphere-troposphere coupling. Given their impact on the troposphere, several previous studies have focused on the possible impact of increasing CO₂ concentrations on these events, but without reaching a robust conclusion across them. Several factors might explain this lack of robustness in the results, notably the availability of short data record or the consideration of moderate CO₂ forcing. Part of these limitations may now be overcome thanks to the new simulations of the Coupled Model Intercomparison Project, Phase 6 and in particular, to the long daily data requirements of the DynVarMIP project in preindustrial and quadrupled CO₂ forcing simulations.



In this work, we use this new model output to investigate the response, if any, of extreme variability in the Arctic stratosphere to 4xCO₂ forcing. The results of many models predict that the SSW frequency is sensitive to increase in CO₂ loading, but there is a large disagreement across models on the sign of this change. Regarding the SSW impact on the troposphere, the response over the North Atlantic remain unchanged, but the signal over the Pacific is more uncertain, with some indications that there might be a larger mean response under 4xCO₂ scenario. Finally, the models show robust changes to the seasonal cycle in the stratosphere. Specifically, we find an earlier formation of the vortex in Autumn and a delay in the date of SFWs, resulting in a longer duration of the polar vortex and so, of the season of stratosphere-troposphere coupling.