Improvements in Circumpolar Southern Hemisphere Extratropical Atmospheric Circulation in CMIP6 Compared to CMIP5
Abstract 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 c...
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ftdoajarticles:oai:doaj.org/article:dcc43c816582418a8aa884db988f4887 2023-05-15T13:23:57+02:00 Improvements in Circumpolar Southern Hemisphere Extratropical Atmospheric Circulation in CMIP6 Compared to CMIP5 T. J. Bracegirdle C. R. Holmes J. S. Hosking G. J. Marshall M. Osman M. Patterson T. Rackow 2020-06-01T00:00:00Z https://doi.org/10.1029/2019EA001065 https://doaj.org/article/dcc43c816582418a8aa884db988f4887 EN eng American Geophysical Union (AGU) https://doi.org/10.1029/2019EA001065 https://doaj.org/toc/2333-5084 2333-5084 doi:10.1029/2019EA001065 https://doaj.org/article/dcc43c816582418a8aa884db988f4887 Earth and Space Science, Vol 7, Iss 6, Pp n/a-n/a (2020) CMIP6 CMIP5 Antarctic Southern Ocean westerly jet Amundsen Sea Low Astronomy QB1-991 Geology QE1-996.5 article 2020 ftdoajarticles https://doi.org/10.1029/2019EA001065 2022-12-31T13:30:36Z Abstract 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 data sets. 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 Directory of Open Access Journals: DOAJ Articles Amundsen Sea Antarctic Austral Southern Ocean Earth and Space Science 7 6 |
institution |
Open Polar |
collection |
Directory of Open Access Journals: DOAJ Articles |
op_collection_id |
ftdoajarticles |
language |
English |
topic |
CMIP6 CMIP5 Antarctic Southern Ocean westerly jet Amundsen Sea Low Astronomy QB1-991 Geology QE1-996.5 |
spellingShingle |
CMIP6 CMIP5 Antarctic Southern Ocean westerly jet Amundsen Sea Low Astronomy QB1-991 Geology QE1-996.5 T. J. Bracegirdle C. R. Holmes J. S. Hosking G. J. Marshall M. Osman M. Patterson T. Rackow Improvements in Circumpolar Southern Hemisphere Extratropical Atmospheric Circulation in CMIP6 Compared to CMIP5 |
topic_facet |
CMIP6 CMIP5 Antarctic Southern Ocean westerly jet Amundsen Sea Low Astronomy QB1-991 Geology QE1-996.5 |
description |
Abstract 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 data sets. 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 |
T. J. Bracegirdle C. R. Holmes J. S. Hosking G. J. Marshall M. Osman M. Patterson T. Rackow |
author_facet |
T. J. Bracegirdle C. R. Holmes J. S. Hosking G. J. Marshall M. Osman M. Patterson T. Rackow |
author_sort |
T. J. Bracegirdle |
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 (AGU) |
publishDate |
2020 |
url |
https://doi.org/10.1029/2019EA001065 https://doaj.org/article/dcc43c816582418a8aa884db988f4887 |
geographic |
Amundsen Sea Antarctic Austral Southern Ocean |
geographic_facet |
Amundsen Sea Antarctic Austral Southern Ocean |
genre |
Amundsen Sea Antarc* Antarctic Sea ice Southern Ocean |
genre_facet |
Amundsen Sea Antarc* Antarctic Sea ice Southern Ocean |
op_source |
Earth and Space Science, Vol 7, Iss 6, Pp n/a-n/a (2020) |
op_relation |
https://doi.org/10.1029/2019EA001065 https://doaj.org/toc/2333-5084 2333-5084 doi:10.1029/2019EA001065 https://doaj.org/article/dcc43c816582418a8aa884db988f4887 |
op_doi |
https://doi.org/10.1029/2019EA001065 |
container_title |
Earth and Space Science |
container_volume |
7 |
container_issue |
6 |
_version_ |
1766376564466909184 |