Full Text Available
Note: Clicking the button above will open the full text document at the original institutional repository in a new window.
Intra-seasonal oscillations of convection over southern Africa
This work examines intra-seasonal rainfall variability over the summer rainfall region of South Africa. Spectral analysis of a precipitation minus evaporation index (P-E) compiled from 16 rainfall stations in the western Transvaal region of South Africa has shown that two dominant spectral peaks occ...
Saved in:
| Main Author: | |
|---|---|
| Other Authors: | |
| Format: | Thesis |
| Language: | English |
| Published: |
Department of Oceanography
2014
|
| Subjects: | |
| Tags: |
No Tags, Be the first to tag this record!
|
| _version_ | 1867613733139775488 |
|---|---|
| access_status_str | Open Access |
| author | Levey, Kevin M |
| author2 | Jury, Mark R |
| author_browse | Jury, Mark R Levey, Kevin M |
| author_facet | Jury, Mark R Levey, Kevin M |
| author_sort | Levey, Kevin M |
| collection | Thesis |
| description | This work examines intra-seasonal rainfall variability over the summer rainfall region of South Africa. Spectral analysis of a precipitation minus evaporation index (P-E) compiled from 16 rainfall stations in the western Transvaal region of South Africa has shown that two dominant spectral peaks occur in the water budget or convection as identified by an outgoing longwave radiation (OLR) index and P-E index. A longer 40-60 day oscillation or Madden Julian Oscillation (MJO) and a shorter 20-30 day ISO are identified. The interaction between the Rossby waves of the mid-latitudes and the MJO of tropics appears to be the main cause of the 20-30 day ISO operating over southern Africa. Hovmoller analysis at 10° S and 40° S has shown that four modes exist in the propagation and oscillatory characteristics of various anomalies. Eastward and westward propagation is noted as well as standing wave patterns and "flip-flop" modes where anomalies alternate between positive and negative across the latitude band with time. The composite analysis revealed a tropically initiated signal of the 20-30 day ISO in the water vapour flux (WVF) anomaly field where strong easterly WVF vectors are noted between the equator and 10°S and between 40° E and 80° E. Strong convergence of water vapour occurs during the wet phase of the 20-30 day ISO over the south-western Indian Ocean and together with strong ridging of the South Atlantic Anticyclone (SAA) causes the south-easterly advection of moisture from the southern Mozambique Channel and over the warm Agulhas Current into South Africa. Post-wet phase anomaly composites do not show much similarity with pre-cursor anomaly composites. This implies that the 20-30 day ISO may be a half cycle of 40-60 days which is consistent with the MJO. However, it is felt that 20-30 day ISO's affecting the southern African region alternate in intensity within the period of the MJO. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/8499 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:40:50.262Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2014 |
| publishDateRange | 2014 |
| publishDateSort | 2014 |
| publisher | Department of Oceanography |
| publisherStr | Department of Oceanography |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/8499 Intra-seasonal oscillations of convection over southern Africa Levey, Kevin M Jury, Mark R Ocean and Atmosphere Science This work examines intra-seasonal rainfall variability over the summer rainfall region of South Africa. Spectral analysis of a precipitation minus evaporation index (P-E) compiled from 16 rainfall stations in the western Transvaal region of South Africa has shown that two dominant spectral peaks occur in the water budget or convection as identified by an outgoing longwave radiation (OLR) index and P-E index. A longer 40-60 day oscillation or Madden Julian Oscillation (MJO) and a shorter 20-30 day ISO are identified. The interaction between the Rossby waves of the mid-latitudes and the MJO of tropics appears to be the main cause of the 20-30 day ISO operating over southern Africa. Hovmoller analysis at 10° S and 40° S has shown that four modes exist in the propagation and oscillatory characteristics of various anomalies. Eastward and westward propagation is noted as well as standing wave patterns and "flip-flop" modes where anomalies alternate between positive and negative across the latitude band with time. The composite analysis revealed a tropically initiated signal of the 20-30 day ISO in the water vapour flux (WVF) anomaly field where strong easterly WVF vectors are noted between the equator and 10°S and between 40° E and 80° E. Strong convergence of water vapour occurs during the wet phase of the 20-30 day ISO over the south-western Indian Ocean and together with strong ridging of the South Atlantic Anticyclone (SAA) causes the south-easterly advection of moisture from the southern Mozambique Channel and over the warm Agulhas Current into South Africa. Post-wet phase anomaly composites do not show much similarity with pre-cursor anomaly composites. This implies that the 20-30 day ISO may be a half cycle of 40-60 days which is consistent with the MJO. However, it is felt that 20-30 day ISO's affecting the southern African region alternate in intensity within the period of the MJO. 2014-10-17T07:35:14Z 2014-10-17T07:35:14Z 1993 Master Thesis Masters MSc http://hdl.handle.net/11427/8499 eng application/pdf Department of Oceanography Faculty of Science University of Cape Town |
| spellingShingle | Ocean and Atmosphere Science Levey, Kevin M Intra-seasonal oscillations of convection over southern Africa |
| thesis_degree_str | Master's |
| title | Intra-seasonal oscillations of convection over southern Africa |
| title_full | Intra-seasonal oscillations of convection over southern Africa |
| title_fullStr | Intra-seasonal oscillations of convection over southern Africa |
| title_full_unstemmed | Intra-seasonal oscillations of convection over southern Africa |
| title_short | Intra-seasonal oscillations of convection over southern Africa |
| title_sort | intra seasonal oscillations of convection over southern africa |
| topic | Ocean and Atmosphere Science |
| url | http://hdl.handle.net/11427/8499 |
| work_keys_str_mv | AT leveykevinm intraseasonaloscillationsofconvectionoversouthernafrica |