The Influence of the Lower Stratosphere on Ridging Atlantic Ocean Anticyclones over South Africa

The link between Rossby wave breaking and ridging Atlantic Ocean anticyclones in the South African domain is examined using NCEP–DOEAMIP-II reanalysis data .A simple composite analysis, which used the duration of ridging events as a basis of averaging, reveals that ridging anticyclones are coupled w...

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Bibliographic Details
Published in:Journal of climate 2018-08, Vol.31 (15), p.6175-6187
Main Authors: Ndarana, Thando, Bopape, Mary-Jane, Waugh, Darryn, Dyson, Liesl
Format: Article
Language:English
Subjects:
Anomalies
Anticyclones
Atmospheric boundary layer
Climate
Coupling
Cyclones
Data processing
Duration
High pressure
High pressure systems
Lower stratosphere
Oceans
Planetary waves
Pressure
Ridging
Rossby wave breaking
Rossby waves
Snow
Storm damage
Stratosphere
Tropopause
Wave breaking
Weather
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Summary:The link between Rossby wave breaking and ridging Atlantic Ocean anticyclones in the South African domain is examined using NCEP–DOEAMIP-II reanalysis data .A simple composite analysis, which used the duration of ridging events as a basis of averaging, reveals that ridging anticyclones are coupled with Rossby wave breaking at levels higher than the dynamical tropopause. Lower-stratospheric PV anomalies extend to the surface, thus coupling the ridging highs with the lower stratosphere. The anomaly extending from the 70-hPa level to the surface contributes to a southward extension of the surface negative anomaly over the Namibian coast, which induces a cyclonic flow, causing the ridging anticyclone to take a bean-like shape. The surface positive anomaly induces the internal anticyclonic flow within the large-scale pressure system, causing the ridging end to break off and amalgamate with the Indian Ocean high pressure system. Lower-stratospheric Rossby wave breaking lasts for as long as the ridging process, suggesting that the former is critical to the longevity of the latter by maintaining and keeping the vertical coupling intact.
ISSN:0894-8755
1520-0442
DOI:10.1175/JCLI-D-17-0832.1