Preprints
https://doi.org/10.5194/gmd-2022-277
https://doi.org/10.5194/gmd-2022-277
Submitted as: model experiment description paper
25 Nov 2022
Submitted as: model experiment description paper | 25 Nov 2022
Status: this preprint is currently under review for the journal GMD.

Understanding AMOC stability: the North Atlantic Hosing Model Intercomparison Project

Laura Claire Jackson1, Eduardo Alastrué de Asenjo2,9, Katinka Bellomo3,4, Gokhan Danabasoglu5, Helmuth Haak2, Aixue Hu5, Johann Jungclaus2, Warren Lee6, Virna L. Meccia10, Oleg Saenko6,8, Andrew Shao6, and Didier Swingedouw7 Laura Claire Jackson et al.
  • 1Met Office, Exeter, UK
  • 2Max Planck Institute for Meteorology, Hamburg, Germany
  • 3National Research Council of Italy, Institute of Atmospheric Sciences and Climate, Turin, Italy
  • 4Polytechnic University of Turin, Department of Environment, Land and Infrastructure Engineering, Turin, Italy
  • 5Climate and Global Dynamics Lab, National Center for Atmospheric Research, Boulder, CO 80307, USA
  • 6CCCma, Canada
  • 7University of Bordeaux, CNRS, Bordeaux, France
  • 8SEOS, University of Victoria, BC, Canada
  • 9International Max Planck Research School on Earth System Modelling, Hamburg, Germany
  • 10National Research Council of Italy, Institute of Atmospheric Sciences and Climate, Bologna, Italy

Abstract. The Atlantic meridional overturning circulation (AMOC) is an important part of our climate system. The AMOC is predicted to weaken under climate change, however there are theories that it may have a tipping point beyond which recovery is difficult, hence showing quasi-irreversibility (hysteresis). Although hysteresis has been seen in simple models, it has been difficult to demonstrate in comprehensive global climate models. Here we outline a set of experiments designed to explore AMOC hysteresis and sensitivity to additional freshwater input as part of the North Atlantic hosing model intercomparison project (NAHosMIP). These experiments include adding additional freshwater (hosing) for a fixed length of time to examine the rate and mechanisms or AMOC weakening, and whether the AMOC subsequently recovers once hosing stops.

Initial results are shown from eight climate models participating in the Sixth Coupled Model Intercomparison Project (CMIP6). The AMOC weakens in all models from the freshening, but once the freshening ceases, the AMOC recovers in half of the models, and in the other half it stays in a weakened state. The difference in model behaviour cannot be explained by the ocean model resolution or type, or by details of subgridscale parameterizations. Nor can it be explained by previously proposed properties of the mean climate state such as the strength of the salinity advection feedback. Instead the AMOC recovery is determined by the climate state reached when hosing stops, with those experiments where the AMOC is weakest not experiencing a recovery.

Laura Claire Jackson et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on gmd-2022-277', Wilbert Weijer, 16 Dec 2022
  • RC2: 'Comment on gmd-2022-277', Anonymous Referee #2, 23 Dec 2022

Laura Claire Jackson et al.

Data sets

NAHosMIP data Jackson, Laura; Alastue de Asenjo, Eduardo; Bellomo, Katinka; Danabasoglu, Gokhan; Hu, Aixue; Jungclaus, Johann; Lee, Warren; Meccia, Virna; Saenko, Oleg; Shao, Andrew; Swingedouw, Didier https://zenodo.org/record/7324394

Model code and software

NAHosMIP data Jackson, Laura; Alastue de Asenjo, Eduardo; Bellomo, Katinka; Danabasoglu, Gokhan; Hu, Aixue; Jungclaus, Johann; Lee, Warren; Meccia, Virna; Saenko, Oleg; Shao, Andrew; Swingedouw, Didier https://zenodo.org/record/7324394

NAHosMIP experimental protocol Jackson, Laura; Alastue de Asenjo, Eduardo; Bellomo, Katinka; Danabasoglu, Gokhan; Hu, Aixue; Jungclaus, Johann; Lee, Warren; Meccia, Virna; Saenko, Oleg; Shao, Andrew; Swingedouw, Didier https://zenodo.org/record/7225014

Laura Claire Jackson et al.

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Short summary
The Atlantic meridional overturning circulation (AMOC) has an important impact on the climate. There are theories that freshening of the ocean might cause the AMOC to cross a tipping point (TP) beyond which recovery is difficult, however it is unclear whether TP exist in global climate models. Here we outline a set of experiments designed to explore AMOC tipping points and sensitivity to additional freshwater input as part of the North Atlantic hosing model intercomparison project (NAHosMIP).