Journal article
A quasi-geostrophic analysis of summertime southern African linear-regime westerly waves
- Abstract:
- Linear-regime westerly waves that propagate across the South African domain are often linked to well-known rainfall producing systems such as tropical temperate troughs and synoptic scale tropical low-pressure systems, and ridging South Atlantic Ocean anticyclones at the surface. It is accepted that the baroclinic waves that propagate across the domain provide the lifting mechanism that causes the required vertical motion for rainfall to occur. This study shows that there exists a jet streak embedded in these waves that is located downstream of the trough axis, to the east of which vertically upward motion is expected to occur. The entrance of the jet streak passes just south of the country, as the waves propagate past the domain. The study further shows that for this class of waves, the vertical motion that causes rainfall to occur is induced by the thermally direct transverse ageostrophic circulation that is located at this jet entrance. This is instead of the conventional upper air divergence that is located at the inflection point east of the trough axis. Using a method of decomposing the Q-vector into its transverse (Qn) and shear (Qs) components, the divergence fields of which are used to decompose the vertical motion into the corresponding components, i.e ωn and ωs respectively; it was shown that the vertical motion over South Africa is explained more by the former than the latter. Therefore, the uplift over the country and that located at the infection point east of the trough are dynamically distinct processes. Taking the limitations of the quasi-geostrophic framework into consideration, the study concludes that during the passage of linear-regime waves vertical motion that might lead to rainfall is caused by the circulation at the jet entrance and not the divergence in the baroclinic wave.
- Publication status:
- Published
- Peer review status:
- Peer reviewed
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(Preview, Version of record, pdf, 3.5MB, Terms of use)
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- Publisher copy:
- 10.1007/s00382-023-07067-0
Authors
+ UK Research and Innovation
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- Funder identifier:
- https://ror.org/001aqnf71
- Grant:
- MR/W011379/1
- Publisher:
- Springer
- Journal:
- Climate Dynamics More from this journal
- Volume:
- 62
- Issue:
- 5
- Pages:
- 3321–3336
- Publication date:
- 2024-01-18
- Acceptance date:
- 2023-12-09
- DOI:
- EISSN:
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1432-0894
- ISSN:
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0930-7575
- Language:
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English
- Keywords:
- Pubs id:
-
1605137
- Local pid:
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pubs:1605137
- Deposit date:
-
2024-01-23
Terms of use
- Copyright holder:
- Ndarana et al.
- Copyright date:
- 2024
- Rights statement:
- © The Author(s) 2024. Open Access. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.
- Licence:
- CC Attribution (CC BY)
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