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Discussion papers
https://doi.org/10.5194/acp-2019-1206
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-1206
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 22 Jan 2020

Submitted as: research article | 22 Jan 2020

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This preprint is currently under review for the journal ACP.

Hadley cell expansion in CMIP6 models

Kevin M. Grise1 and Sean M. Davis2 Kevin M. Grise and Sean M. Davis
  • 1Department of Environmental Sciences, Universityof Virginia, Charlottesville, VA 22904, USA
  • 2NOAA Earth System Research Laboratory Chemical Sciences Division, Boulder, CO 80305, USA

Abstract. In response to increasing greenhouse gases, the subtropical edges of Earth's Hadley circulation shift poleward in global climate models. Recent studies have found that reanalysis trends in the Hadley cell edge over the past 30–40 years are within the range of trends simulated by Coupled Model Intercomparison Project Phase 5 (CMIP5) models, and have documented seasonal and hemispheric asymmetries in these trends. In this study, we evaluate whether these conclusions hold for the newest generation of models (CMIP6). Overall, we find similar characteristics of Hadley cell expansion in CMIP5 and CMIP6 models. In both CMIP5 and CMIP6 models, the poleward shift of the Hadley cell edge in response to increasing greenhouse gases is 2–3 times larger in the Southern Hemisphere (SH), except during September–November. The trends from CMIP5 and CMIP6 models agree well with reanalyses, although prescribing observed coupled atmosphere-ocean variability allows the models to better capture reanalysis trends in the Northern Hemisphere (NH). We find two notable differences between CMIP5 and CMIP6 models. First, both CMIP5 and CMIP6 models contract the NH summertime Hadley circulation equatorward (particularly over the Pacific sector), but this contraction is larger in CMIP6 models due to their higher average climate sensitivity. Second, in recent decades, the poleward shift of the NH annual-mean Hadley cell edge is slightly larger in CMIP6 models. Increasing greenhouse gases drive similar trends in CMIP5 and CMIP6 models, so the larger recent NH trends in CMIP6 models point to the role of other forcings, such as aerosols.

Kevin M. Grise and Sean M. Davis

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Kevin M. Grise and Sean M. Davis

Kevin M. Grise and Sean M. Davis

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Latest update: 25 Feb 2020
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Short summary
As Earth's climate warms, the tropical overturning circulation (Hadley circulation) is projected to expand, potentially pushing subtropical dry zones further poleward. This study examines projections of the Hadley circulation from the latest generation of computer models and finds several notable differences from older models. For example, the Northern Hemisphere circulation expands northward at a greater rate in recent decades than would be expected from increasing greenhouse gases alone.
As Earth's climate warms, the tropical overturning circulation (Hadley circulation) is projected...
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