Role of sea surface temperature patterns for the Southern Hemisphere jet stream response to CO2 forcing
The Southern Hemisphere (SH) 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...
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IOP Publishing
2020-01-01
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Series: | Environmental Research Letters |
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Online Access: | https://doi.org/10.1088/1748-9326/abce27 |
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author | Tom Wood Christine M McKenna Andreas Chrysanthou Amanda C Maycock |
author_facet | Tom Wood Christine M McKenna Andreas Chrysanthou Amanda C Maycock |
author_sort | Tom Wood |
collection | DOAJ |
description | The Southern Hemisphere (SH) 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 CO _2 than the predecessor models (Coupled Model Intercomparison Project phase 5 (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 CO _2 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 CO _2 increase in IGCM4 produce weaker differences in zonal wind response compared to those simulated by CMIP5/6 models. Further IGCM4 experiments that prescribe only SH extratropical SSTs simulate a weaker jet shift for CMIP6 SSTs than for CMIP5, comparable to the full experiment. The results demonstrate that SH SST patterns are an important source of uncertainty for the shift of the midlatitude circulation in response to CO _2 forcing. The study also provides an alternative explanation than was proposed by Curtis et al (2020 Environ. Res. Lett. 15 64011), who suggested model improvements in jet biases could account for the smaller jet shift in CMIP6 models in the extended austral winter season. |
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language | English |
last_indexed | 2024-03-12T15:54:52Z |
publishDate | 2020-01-01 |
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series | Environmental Research Letters |
spelling | doaj.art-8a97fa6cf6b44c11823ced3c38472def2023-08-09T14:59:48ZengIOP PublishingEnvironmental Research Letters1748-93262020-01-0116101402010.1088/1748-9326/abce27Role of sea surface temperature patterns for the Southern Hemisphere jet stream response to CO2 forcingTom Wood0https://orcid.org/0000-0002-6049-5805Christine M McKenna1https://orcid.org/0000-0002-9677-4582Andreas Chrysanthou2https://orcid.org/0000-0002-8670-5436Amanda C Maycock3https://orcid.org/0000-0002-6614-1127School of Earth and Environment, University of Leeds , Leeds, United KingdomSchool of Earth and Environment, University of Leeds , Leeds, United KingdomSchool of Earth and Environment, University of Leeds , Leeds, United KingdomSchool of Earth and Environment, University of Leeds , Leeds, United KingdomThe Southern Hemisphere (SH) 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 CO _2 than the predecessor models (Coupled Model Intercomparison Project phase 5 (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 CO _2 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 CO _2 increase in IGCM4 produce weaker differences in zonal wind response compared to those simulated by CMIP5/6 models. Further IGCM4 experiments that prescribe only SH extratropical SSTs simulate a weaker jet shift for CMIP6 SSTs than for CMIP5, comparable to the full experiment. The results demonstrate that SH SST patterns are an important source of uncertainty for the shift of the midlatitude circulation in response to CO _2 forcing. The study also provides an alternative explanation than was proposed by Curtis et al (2020 Environ. Res. Lett. 15 64011), who suggested model improvements in jet biases could account for the smaller jet shift in CMIP6 models in the extended austral winter season.https://doi.org/10.1088/1748-9326/abce27climate changeatmospheric circulationjet streamsclimate modelssea surface temperatures |
spellingShingle | Tom Wood Christine M McKenna Andreas Chrysanthou Amanda C Maycock Role of sea surface temperature patterns for the Southern Hemisphere jet stream response to CO2 forcing Environmental Research Letters climate change atmospheric circulation jet streams climate models sea surface temperatures |
title | Role of sea surface temperature patterns for the Southern Hemisphere jet stream response to CO2 forcing |
title_full | Role of sea surface temperature patterns for the Southern Hemisphere jet stream response to CO2 forcing |
title_fullStr | Role of sea surface temperature patterns for the Southern Hemisphere jet stream response to CO2 forcing |
title_full_unstemmed | Role of sea surface temperature patterns for the Southern Hemisphere jet stream response to CO2 forcing |
title_short | Role of sea surface temperature patterns for the Southern Hemisphere jet stream response to CO2 forcing |
title_sort | role of sea surface temperature patterns for the southern hemisphere jet stream response to co2 forcing |
topic | climate change atmospheric circulation jet streams climate models sea surface temperatures |
url | https://doi.org/10.1088/1748-9326/abce27 |
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