Improvements in Circumpolar Southern Hemisphere Extratropical Atmospheric Circulation in CMIP6 Compared to CMIP5
One of the major globally relevant systematic biases in previous generations of climate models has been an equatorward bias in the latitude of the Southern Hemisphere (SH) mid‐latitude tropospheric eddy driven westerly jet. The far reaching implications of this for Southern Ocean heat and carbon upt...
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American Geophysical Union
2020
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Online Access: | http://nora.nerc.ac.uk/id/eprint/527792/ https://nora.nerc.ac.uk/id/eprint/527792/1/2019EA001065.pdf https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019EA001065 |
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ftnerc:oai:nora.nerc.ac.uk:527792 2023-05-15T13:24:10+02:00 Improvements in Circumpolar Southern Hemisphere Extratropical Atmospheric Circulation in CMIP6 Compared to CMIP5 Bracegirdle, T.J. Holmes, C.R. Hosking, J.S. Marshall, G.J. Osman, M. Patterson, M. Rackow, T. 2020-06 text http://nora.nerc.ac.uk/id/eprint/527792/ https://nora.nerc.ac.uk/id/eprint/527792/1/2019EA001065.pdf https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019EA001065 en eng American Geophysical Union https://nora.nerc.ac.uk/id/eprint/527792/1/2019EA001065.pdf Bracegirdle, T.J. orcid:0000-0002-8868-4739 Holmes, C.R. orcid:0000-0002-3134-555X Hosking, J.S. orcid:0000-0002-3646-3504 Marshall, G.J. orcid:0000-0001-8887-7314 Osman, M.; Patterson, M.; Rackow, T. 2020 Improvements in Circumpolar Southern Hemisphere Extratropical Atmospheric Circulation in CMIP6 Compared to CMIP5. Earth and Space Science, 7 (6), e2019EA001065. 12, pp. https://doi.org/10.1029/2019EA001065 <https://doi.org/10.1029/2019EA001065> cc_by_4 CC-BY Publication - Article PeerReviewed 2020 ftnerc https://doi.org/10.1029/2019EA001065 2023-02-04T19:50:43Z One of the major globally relevant systematic biases in previous generations of climate models has been an equatorward bias in the latitude of the Southern Hemisphere (SH) mid‐latitude tropospheric eddy driven westerly jet. The far reaching implications of this for Southern Ocean heat and carbon uptake and Antarctic land and sea ice are key reasons why addressing this bias is a high priority. It is therefore of primary importance to evaluate the representation of the SH westerly jet in the latest generation of global climate and earth‐system models that comprise the Coupled Model Intercomparison Project Phase 6 (CMIP6). In this paper we assess the representation of major indices of SH extratropical atmospheric circulation in CMIP6 by comparison against both observations and the previous generation of CMIP5 models. Indices assessed are the latitude and speed of the westerly jet, variability of the Southern Annular Mode (SAM) and representation of the Amundsen Sea Low (ASL). These are calculated from the historical forcing simulations of both CMIP5 and CMIP6 for time periods matching available observational and reanalysis datasets. From the 39 CMIP6 models available at the time of writing there is an overall reduction in the equatorward bias of the annual mean westerly jet from 1.9° in CMIP5 to 0.4° in CMIP6 and from a seasonal perspective the reduction is clearest in austral spring and summer. This is accompanied by a halving of the bias of SAM decorrelation timescales compared to CMIP5. However, no such overall improvements are evident for the ASL. Article in Journal/Newspaper Amundsen Sea Antarc* Antarctic Sea ice Southern Ocean Natural Environment Research Council: NERC Open Research Archive Antarctic Southern Ocean Austral Amundsen Sea Earth and Space Science 7 6 |
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Open Polar |
collection |
Natural Environment Research Council: NERC Open Research Archive |
op_collection_id |
ftnerc |
language |
English |
description |
One of the major globally relevant systematic biases in previous generations of climate models has been an equatorward bias in the latitude of the Southern Hemisphere (SH) mid‐latitude tropospheric eddy driven westerly jet. The far reaching implications of this for Southern Ocean heat and carbon uptake and Antarctic land and sea ice are key reasons why addressing this bias is a high priority. It is therefore of primary importance to evaluate the representation of the SH westerly jet in the latest generation of global climate and earth‐system models that comprise the Coupled Model Intercomparison Project Phase 6 (CMIP6). In this paper we assess the representation of major indices of SH extratropical atmospheric circulation in CMIP6 by comparison against both observations and the previous generation of CMIP5 models. Indices assessed are the latitude and speed of the westerly jet, variability of the Southern Annular Mode (SAM) and representation of the Amundsen Sea Low (ASL). These are calculated from the historical forcing simulations of both CMIP5 and CMIP6 for time periods matching available observational and reanalysis datasets. From the 39 CMIP6 models available at the time of writing there is an overall reduction in the equatorward bias of the annual mean westerly jet from 1.9° in CMIP5 to 0.4° in CMIP6 and from a seasonal perspective the reduction is clearest in austral spring and summer. This is accompanied by a halving of the bias of SAM decorrelation timescales compared to CMIP5. However, no such overall improvements are evident for the ASL. |
format |
Article in Journal/Newspaper |
author |
Bracegirdle, T.J. Holmes, C.R. Hosking, J.S. Marshall, G.J. Osman, M. Patterson, M. Rackow, T. |
spellingShingle |
Bracegirdle, T.J. Holmes, C.R. Hosking, J.S. Marshall, G.J. Osman, M. Patterson, M. Rackow, T. Improvements in Circumpolar Southern Hemisphere Extratropical Atmospheric Circulation in CMIP6 Compared to CMIP5 |
author_facet |
Bracegirdle, T.J. Holmes, C.R. Hosking, J.S. Marshall, G.J. Osman, M. Patterson, M. Rackow, T. |
author_sort |
Bracegirdle, T.J. |
title |
Improvements in Circumpolar Southern Hemisphere Extratropical Atmospheric Circulation in CMIP6 Compared to CMIP5 |
title_short |
Improvements in Circumpolar Southern Hemisphere Extratropical Atmospheric Circulation in CMIP6 Compared to CMIP5 |
title_full |
Improvements in Circumpolar Southern Hemisphere Extratropical Atmospheric Circulation in CMIP6 Compared to CMIP5 |
title_fullStr |
Improvements in Circumpolar Southern Hemisphere Extratropical Atmospheric Circulation in CMIP6 Compared to CMIP5 |
title_full_unstemmed |
Improvements in Circumpolar Southern Hemisphere Extratropical Atmospheric Circulation in CMIP6 Compared to CMIP5 |
title_sort |
improvements in circumpolar southern hemisphere extratropical atmospheric circulation in cmip6 compared to cmip5 |
publisher |
American Geophysical Union |
publishDate |
2020 |
url |
http://nora.nerc.ac.uk/id/eprint/527792/ https://nora.nerc.ac.uk/id/eprint/527792/1/2019EA001065.pdf https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019EA001065 |
geographic |
Antarctic Southern Ocean Austral Amundsen Sea |
geographic_facet |
Antarctic Southern Ocean Austral Amundsen Sea |
genre |
Amundsen Sea Antarc* Antarctic Sea ice Southern Ocean |
genre_facet |
Amundsen Sea Antarc* Antarctic Sea ice Southern Ocean |
op_relation |
https://nora.nerc.ac.uk/id/eprint/527792/1/2019EA001065.pdf Bracegirdle, T.J. orcid:0000-0002-8868-4739 Holmes, C.R. orcid:0000-0002-3134-555X Hosking, J.S. orcid:0000-0002-3646-3504 Marshall, G.J. orcid:0000-0001-8887-7314 Osman, M.; Patterson, M.; Rackow, T. 2020 Improvements in Circumpolar Southern Hemisphere Extratropical Atmospheric Circulation in CMIP6 Compared to CMIP5. Earth and Space Science, 7 (6), e2019EA001065. 12, pp. https://doi.org/10.1029/2019EA001065 <https://doi.org/10.1029/2019EA001065> |
op_rights |
cc_by_4 |
op_rightsnorm |
CC-BY |
op_doi |
https://doi.org/10.1029/2019EA001065 |
container_title |
Earth and Space Science |
container_volume |
7 |
container_issue |
6 |
_version_ |
1766377810082922496 |