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Abstract There is great uncertainty in the atmospheric circulation response to future Arctic sea ice loss, with some models predicting a shift towards the negative phase of the North Atlantic Oscillation (NAO), while others predicting a more neutral NAO response. We investigate the potential role of systematic model biases in the spread of these responses by modifying the unperturbed (or ‘control’) climate (hereafter referred to as the ‘basic state’) of the Canadian Earth system model version 5 (CanESM5) in sea ice loss experiments based on the protocol of the Polar Amplification Model Intercomparison Project. We show that the presence or absence of the stratospheric pathway in response to sea ice loss depends on the basic state, and that only the CanESM5 version that shows a weakening of the stratospheric polar vortex features a strong negative NAO response. We propose a mechanism that explains this dependency, with a key role played by the vertical structure of the winds in the region between the subtropical jet and the stratospheric polar vortex (‘the neck region winds’), which determines the extent to which anomalous planetary wave activity in response to sea ice loss propagates away from the polar vortex. Our results suggest that differences in the models’ basic states could significantly contribute to model spread in the simulated atmospheric circulation response to sea ice loss, which may inform efforts to narrow the uncertainties regarding the impact of diminishing sea ice on mid-latitude climate.
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Intermodel Spread in the Northern Hemisphere Stratospheric Polar Vortex Response to Climate Change in the CMIP5 Models
Abstract This study investigates the intermodel spread of the Northern Hemisphere winter stratospheric polar vortex change to anthropogenic greenhouse gas increase in Coupled Model Intercomparison Project Phase 5 (CMIP5) models. Previous proposed mechanisms for the polar vortex response to climate change, based on analysis of atmosphere‐only models, are found inadequate to explain the intermodel spread in the coupled models in CMIP5. It is further found that resolved stationary wave driving in the polar vortex region accounts for less than 30% of the intermodel spread, and intermodel differences in both the vertical and meridional wave propagation contribute to differences in the wave driving. The results call for a detailed budget analysis of the stratospheric circulation response by including both the resolved and parameterized processes through the Dynamics and Variability Model Intercomparison Project. The results also highlight a need for an improved theoretical understanding of future projected polar vortex change and intermodel spread.
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- Award ID(s):
- 1734760
- PAR ID:
- 10448430
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 46
- Issue:
- 22
- ISSN:
- 0094-8276
- Page Range / eLocation ID:
- p. 13290-13298
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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