Bifurcation of potential vorticity gradients across the Southern Hemisphere stratospheric polar vortex
The wintertime stratospheric westerly winds circling the Antarctic continent, also known as the Southern Hemisphere polar vortex, create a barrier to mixing of air between middle and high latitudes. This dynamical isolation has important consequences for export of ozone-depleted air from the Ant...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-06-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/18/8065/2018/acp-18-8065-2018.pdf |
| _version_ | 1819138617657786368 |
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| author | J. Conway G. Bodeker C. Cameron |
| author_facet | J. Conway G. Bodeker C. Cameron |
| author_sort | J. Conway |
| collection | DOAJ |
| description | The wintertime stratospheric westerly winds circling the Antarctic
continent, also known as the Southern Hemisphere polar vortex, create a
barrier to mixing of air between middle and high latitudes. This dynamical
isolation has important consequences for export of ozone-depleted air from
the Antarctic stratosphere to lower latitudes. The prevailing view of this
dynamical barrier has been an annulus compromising steep gradients of
potential vorticity (PV) that create a single semi-permeable barrier to
mixing. Analyses presented here show that this barrier often displays a
bifurcated structure where a double-walled barrier exists. The bifurcated
structure manifests as enhanced gradients of PV at two distinct latitudes –
usually on the inside and outside flanks of the region of highest wind speed.
Metrics that quantify the bifurcated nature of the vortex have been developed
and their variation in space and time has been analysed. At most isentropic
levels between 395 and 850 K, bifurcation is strongest in mid-winter and
decreases dramatically during spring. From August onwards a distinct
structure emerges, where elevated bifurcation remains between 475 and 600 K,
and a mostly single-walled barrier occurs at other levels. While bifurcation
at a given level evolves from month to month, and does not always persist
through a season, interannual variations in the strength of bifurcation
display coherence across multiple levels in any given month. Accounting for
bifurcation allows the region of reduced mixing to be better characterised.
These results suggest that improved understanding of cross-vortex mixing
requires consideration of the polar vortex not as a single mixing barrier
but as a barrier with internal structure that is likely to manifest as more
complex gradients in trace gas concentrations across the vortex barrier
region. |
| first_indexed | 2024-12-22T11:09:37Z |
| format | Article |
| id | doaj.art-31b89245e5574206b18aaa7fc4962764 |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-12-22T11:09:37Z |
| publishDate | 2018-06-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-31b89245e5574206b18aaa7fc49627642022-12-21T18:28:12ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242018-06-01188065807710.5194/acp-18-8065-2018Bifurcation of potential vorticity gradients across the Southern Hemisphere stratospheric polar vortexJ. Conway0G. Bodeker1C. Cameron2Bodeker Scientific, 42 Russell Street, Alexandra, 9320, New ZealandBodeker Scientific, 42 Russell Street, Alexandra, 9320, New ZealandBodeker Scientific, 42 Russell Street, Alexandra, 9320, New ZealandThe wintertime stratospheric westerly winds circling the Antarctic continent, also known as the Southern Hemisphere polar vortex, create a barrier to mixing of air between middle and high latitudes. This dynamical isolation has important consequences for export of ozone-depleted air from the Antarctic stratosphere to lower latitudes. The prevailing view of this dynamical barrier has been an annulus compromising steep gradients of potential vorticity (PV) that create a single semi-permeable barrier to mixing. Analyses presented here show that this barrier often displays a bifurcated structure where a double-walled barrier exists. The bifurcated structure manifests as enhanced gradients of PV at two distinct latitudes – usually on the inside and outside flanks of the region of highest wind speed. Metrics that quantify the bifurcated nature of the vortex have been developed and their variation in space and time has been analysed. At most isentropic levels between 395 and 850 K, bifurcation is strongest in mid-winter and decreases dramatically during spring. From August onwards a distinct structure emerges, where elevated bifurcation remains between 475 and 600 K, and a mostly single-walled barrier occurs at other levels. While bifurcation at a given level evolves from month to month, and does not always persist through a season, interannual variations in the strength of bifurcation display coherence across multiple levels in any given month. Accounting for bifurcation allows the region of reduced mixing to be better characterised. These results suggest that improved understanding of cross-vortex mixing requires consideration of the polar vortex not as a single mixing barrier but as a barrier with internal structure that is likely to manifest as more complex gradients in trace gas concentrations across the vortex barrier region.https://www.atmos-chem-phys.net/18/8065/2018/acp-18-8065-2018.pdf |
| spellingShingle | J. Conway G. Bodeker C. Cameron Bifurcation of potential vorticity gradients across the Southern Hemisphere stratospheric polar vortex Atmospheric Chemistry and Physics |
| title | Bifurcation of potential vorticity gradients across the Southern Hemisphere stratospheric polar vortex |
| title_full | Bifurcation of potential vorticity gradients across the Southern Hemisphere stratospheric polar vortex |
| title_fullStr | Bifurcation of potential vorticity gradients across the Southern Hemisphere stratospheric polar vortex |
| title_full_unstemmed | Bifurcation of potential vorticity gradients across the Southern Hemisphere stratospheric polar vortex |
| title_short | Bifurcation of potential vorticity gradients across the Southern Hemisphere stratospheric polar vortex |
| title_sort | bifurcation of potential vorticity gradients across the southern hemisphere stratospheric polar vortex |
| url | https://www.atmos-chem-phys.net/18/8065/2018/acp-18-8065-2018.pdf |
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