Wood, T orcid.org/0000-0002-6049-5805, McKenna, CM orcid.org/0000-0002-9677-4582, Chrysanthou, A orcid.org/0000-0002-8670-5436 et al. (1 more author) (2020) Role of sea surface temperature patterns for the Southern hemisphere jet stream response to CO2 forcing. Environmental Research Letters. ISSN 1748-9326
Abstract
The Southern Hemisphere eddy-driven jet stream has been shown to move poleward in climate models in response to greenhouse gas forcing, but the magnitude of the shift is uncertain. Here we address the fact that the latest Coupled Model Intercomparison Project phase 6 (CMIP6) models simulate, on average, a smaller jet shift in response to an abrupt quadrupling in CO2 than the predecessor models (CMIP5), despite producing larger global average surface warming. We focus on the response in the first decade when the majority of the long-term jet shift occurs and when the difference between CMIP5 and CMIP6 models emerges. We hypothesise the smaller poleward jet shift is related to the weaker increase in the meridional sea surface temperature (SST) gradient across the southern extratropics in CMIP6 models. We impose the multi-model mean SST patterns alongside a quadrupling in CO2 in an intermediate complexity general circulation model (IGCM4) and show that many of the regional and seasonal differences in lower tropospheric zonal winds between CMIP5 and CMIP6 models are reproduced by prescribing the SST patterns. The main exception is in austral summer when the imposed SST patterns and CO2 increase in IGCM4 produce weaker differences in zonal wind response compared to those simulated by CMIP5/6 models. Further IGCM4 experiments that prescribe only Southern Hemisphere extratropical SSTs simulate a weaker jet shift for CMIP6 SSTs than for CMIP5, comparable to the full experiment. The results demonstrate that Southern Hemisphere SST patterns are an important source of uncertainty for the shift of the midlatitude circulation in response to CO2 forcing. The study also provides an alternative explanation than was proposed by Curtis et al. (2020), who suggested model improvements in jet biases could account for the smaller jet shift in CMIP6 models in the extended austral winter season.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Inst for Climate & Atmos Science (ICAS) (Leeds) |
Funding Information: | Funder Grant number NERC (Natural Environment Research Council) NE/M018199/1 EU - European Union 820829 Leverhulme Trust PLP-2018-278 |
Depositing User: | Symplectic Publications |
Date Deposited: | 27 Nov 2020 14:27 |
Last Modified: | 27 Nov 2020 14:27 |
Status: | Published online |
Publisher: | Institute of Physics (IoP) |
Identification Number: | 10.1088/1748-9326/abce27 |
Related URLs: | |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:168242 |