Dynamics of the Southern Hemisphere extratropical atmospheric circulation
The Southern Hemisphere extratropical westerly winds are the strongest time-averaged surface winds on Earth, having a profound impact on weather systems, ocean circulation, Antarctic sea-ice as well as oceanic uptake of heat and carbon. The westerly winds have shown poleward intensification in the l...
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ftdatacite:10.26190/unsworks/2007 2023-05-15T13:24:19+02:00 Dynamics of the Southern Hemisphere extratropical atmospheric circulation Goyal, Rishav 2022 https://dx.doi.org/10.26190/unsworks/2007 http://hdl.handle.net/1959.4/100097 en eng UNSW Sydney Creative Commons Attribution 4.0 International https://creativecommons.org/licenses/by/4.0/legalcode cc-by-4.0 CC-BY Atmospheric circulation Southern Annular Mode Zonal wave 3 Zonally asymmetric circulation Climate Change Climate policy 370105 Atmospheric dynamics 370201 Climate change processes 370803 Physical oceanography Dissertation thesis Thesis doctoral thesis 2022 ftdatacite https://doi.org/10.26190/unsworks/2007 2022-04-01T18:42:29Z The Southern Hemisphere extratropical westerly winds are the strongest time-averaged surface winds on Earth, having a profound impact on weather systems, ocean circulation, Antarctic sea-ice as well as oceanic uptake of heat and carbon. The westerly winds have shown poleward intensification in the last few decades driven primarily by stratospheric ozone depletion with a secondary role played by increasing greenhouse gases. In recent years we have seen early signs of ozone recovery as a result of the Montreal Protocol. Part 1 of this thesis demonstrates that by curbing CFC emissions, the Montreal Protocol also played a critical role in mitigating future surface climate change, equivalent to approximately 25% reduction in global surface warming by 2050. A major feature of the Southern Hemisphere extratropical atmospheric circulation is its strong zonal coherence. However, there are notable zonal asymmetries embedded in the flow, with two important examples being the zonal wave 3 (ZW3) and Amundsen Sea Low (ASL). Although these features have received significant attention from the scientific community, the mechanisms responsible for their presence are still not clear. In Part 2, model experiments suggest that the ZW3 pattern is generated remotely by tropical deep convection and not by the presence of three extratropical landmasses as had previously been assumed. Quantification of ZW3 impacts requires a way to consistently characterize this variability. In Part 3, I formulate a new index for ZW3 which accounts for variability in the structure, phase and amplitude of ZW3. In Part 4, I provide evidence that in contrast to ZW3, the ASL is generated primarily by the interaction between westerly winds and Antarctic orography. Zonally asymmetric features are not only present in the mean circulation but also in the past and projected westerly wind changes in the Southern Hemisphere. These are characterized in Part 5 in reanalysis and models. Following on from this, I demonstrate in ocean model simulations that future projected zonally asymmetric atmospheric changes can drive substantial changes in the ocean circulation in the Pacific and Indian Oceans, accounting for more than 30% of the projected surface ocean warming around parts of Australia (Part 6). Doctoral or Postdoctoral Thesis Amundsen Sea Antarc* Antarctic Sea ice DataCite Metadata Store (German National Library of Science and Technology) Antarctic Amundsen Sea Pacific Indian |
institution |
Open Polar |
collection |
DataCite Metadata Store (German National Library of Science and Technology) |
op_collection_id |
ftdatacite |
language |
English |
topic |
Atmospheric circulation Southern Annular Mode Zonal wave 3 Zonally asymmetric circulation Climate Change Climate policy 370105 Atmospheric dynamics 370201 Climate change processes 370803 Physical oceanography |
spellingShingle |
Atmospheric circulation Southern Annular Mode Zonal wave 3 Zonally asymmetric circulation Climate Change Climate policy 370105 Atmospheric dynamics 370201 Climate change processes 370803 Physical oceanography Goyal, Rishav Dynamics of the Southern Hemisphere extratropical atmospheric circulation |
topic_facet |
Atmospheric circulation Southern Annular Mode Zonal wave 3 Zonally asymmetric circulation Climate Change Climate policy 370105 Atmospheric dynamics 370201 Climate change processes 370803 Physical oceanography |
description |
The Southern Hemisphere extratropical westerly winds are the strongest time-averaged surface winds on Earth, having a profound impact on weather systems, ocean circulation, Antarctic sea-ice as well as oceanic uptake of heat and carbon. The westerly winds have shown poleward intensification in the last few decades driven primarily by stratospheric ozone depletion with a secondary role played by increasing greenhouse gases. In recent years we have seen early signs of ozone recovery as a result of the Montreal Protocol. Part 1 of this thesis demonstrates that by curbing CFC emissions, the Montreal Protocol also played a critical role in mitigating future surface climate change, equivalent to approximately 25% reduction in global surface warming by 2050. A major feature of the Southern Hemisphere extratropical atmospheric circulation is its strong zonal coherence. However, there are notable zonal asymmetries embedded in the flow, with two important examples being the zonal wave 3 (ZW3) and Amundsen Sea Low (ASL). Although these features have received significant attention from the scientific community, the mechanisms responsible for their presence are still not clear. In Part 2, model experiments suggest that the ZW3 pattern is generated remotely by tropical deep convection and not by the presence of three extratropical landmasses as had previously been assumed. Quantification of ZW3 impacts requires a way to consistently characterize this variability. In Part 3, I formulate a new index for ZW3 which accounts for variability in the structure, phase and amplitude of ZW3. In Part 4, I provide evidence that in contrast to ZW3, the ASL is generated primarily by the interaction between westerly winds and Antarctic orography. Zonally asymmetric features are not only present in the mean circulation but also in the past and projected westerly wind changes in the Southern Hemisphere. These are characterized in Part 5 in reanalysis and models. Following on from this, I demonstrate in ocean model simulations that future projected zonally asymmetric atmospheric changes can drive substantial changes in the ocean circulation in the Pacific and Indian Oceans, accounting for more than 30% of the projected surface ocean warming around parts of Australia (Part 6). |
format |
Doctoral or Postdoctoral Thesis |
author |
Goyal, Rishav |
author_facet |
Goyal, Rishav |
author_sort |
Goyal, Rishav |
title |
Dynamics of the Southern Hemisphere extratropical atmospheric circulation |
title_short |
Dynamics of the Southern Hemisphere extratropical atmospheric circulation |
title_full |
Dynamics of the Southern Hemisphere extratropical atmospheric circulation |
title_fullStr |
Dynamics of the Southern Hemisphere extratropical atmospheric circulation |
title_full_unstemmed |
Dynamics of the Southern Hemisphere extratropical atmospheric circulation |
title_sort |
dynamics of the southern hemisphere extratropical atmospheric circulation |
publisher |
UNSW Sydney |
publishDate |
2022 |
url |
https://dx.doi.org/10.26190/unsworks/2007 http://hdl.handle.net/1959.4/100097 |
geographic |
Antarctic Amundsen Sea Pacific Indian |
geographic_facet |
Antarctic Amundsen Sea Pacific Indian |
genre |
Amundsen Sea Antarc* Antarctic Sea ice |
genre_facet |
Amundsen Sea Antarc* Antarctic Sea ice |
op_rights |
Creative Commons Attribution 4.0 International https://creativecommons.org/licenses/by/4.0/legalcode cc-by-4.0 |
op_rightsnorm |
CC-BY |
op_doi |
https://doi.org/10.26190/unsworks/2007 |
_version_ |
1766378730820730880 |