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  • 1
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    Observed eddy dissipation in the Agulhas Current
    American Geophysical Union (AGU) ; 2016
    In:  Geophysical Research Letters Vol. 43, No. 15 ( 2016-08-16), p. 8143-8150
    Details
    In: Geophysical Research Letters, American Geophysical Union (AGU), Vol. 43, No. 15 ( 2016-08-16), p. 8143-8150
    Kurzfassung: Eddies dissipate as they approach the Agulhas Current Eddies affect Agulhas Current velocities Eddies can cause meanders in the Agulhas Current
    Materialart: Online-Ressource
    ISSN: 0094-8276 , 1944-8007
    URL: Issue
    URL: Article
    DOI: 10.1002/grl.v43.15
    DOI: 10.1002/2016GL069480
    Sprache: Englisch
    Verlag: American Geophysical Union (AGU)
    Publikationsdatum: 2016
    ZDB Id: 2021599-X
    ZDB Id: 7403-2
    SSG: 16,13
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  • 2
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    Variability in the South Atlantic Anticyclone and the Atlantic Niño Mode*
    American Meteorological Society ; 2014
    In:  Journal of Climate Vol. 27, No. 21 ( 2014-11-01), p. 8135-8150
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 27, No. 21 ( 2014-11-01), p. 8135-8150
    Kurzfassung: Previous studies have argued that the strength of the South Atlantic subtropical high pressure system, referred to as the South Atlantic anticyclone (SAA), modulates sea surface temperature (SST) anomalies in the eastern equatorial Atlantic. Using ocean and atmosphere reanalysis products, it is shown here that the strength of the SAA from February to May impacts the timing of the cold tongue onset and the intensity of its development in the eastern equatorial Atlantic via anomalous tropical wind power. This modulation in the timing and amplitude of seasonal cold tongue development manifests itself via SST anomalies peaking between June and August. The timing and impact of this connection is not completely symmetric for warm and cold events. For cold events, an anomalously strong SAA in February and March leads to positive wind power anomalies from February to June resulting in an early cold tongue onset and subsequent cold SST anomalies in June and July. For warm events, the anomalously weak SAA persists until May, generating negative wind power anomalies that lead to a late cold tongue onset as well as a suppression of the cold tongue development and associated warm SST anomalies. Mechanisms by which SAA-induced wind power variations south of the equator influence eastern equatorial Atlantic SST are discussed, including ocean adjustment via Rossby and Kelvin wave propagation, meridional advection, and local intraseasonal wind variations.
    Materialart: Online-Ressource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-14-00202.1
    RVK:
    UA 4548
    Sprache: Englisch
    Verlag: American Meteorological Society
    Publikationsdatum: 2014
    ZDB Id: 246750-1
    ZDB Id: 2021723-7
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  • 3
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    Atmospheric and Climatic Drivers of Tide Gauge Sea Level Variability along the East and South Coast of South Africa
    MDPI AG ; 2021
    In:  Journal of Marine Science and Engineering Vol. 9, No. 9 ( 2021-08-26), p. 924-
    Details
    In: Journal of Marine Science and Engineering, MDPI AG, Vol. 9, No. 9 ( 2021-08-26), p. 924-
    Kurzfassung: Atmospheric forcing and climate modes of variability on various timescales are important drivers of sea level variability. However, the influence of such drivers on sea level variability along the South African east and south coast has not yet been adequately investigated. Here, we determine the timescales of sea level variability and their relationships with various drivers. Empirical Mode Decomposition (EMD) was applied to seven tide gauge records and potential forcing data for this purpose. The oscillatory modes identified by the EMD were summed to obtain physically more meaningful timescales—specifically, the sub-annual (less than 18 months) and interannual (greater than two years) scales. On the sub-annual scale, sea level responds to regional zonal and meridional winds associated with mesoscale and synoptic weather disturbances. Ekman dynamics resulting from variability in sea level pressure and alongshore winds are important for the coastal sea level on this timescale. On interannual timescales, there were connections with ENSO, the Indian Ocean Dipole (IOD) and the Southern Annular Mode (SAM), although the results are not consistent across all the tide gauge stations and are not particularly strong. In general, El Niño and positive IOD events are coincident with high coastal sea levels and vice versa, whereas there appears to be an inverse relationship between SAM phase and sea level.
    Materialart: Online-Ressource
    ISSN: 2077-1312
    URL: Article
    DOI: 10.3390/jmse9090924
    Sprache: Englisch
    Verlag: MDPI AG
    Publikationsdatum: 2021
    ZDB Id: 2738390-8
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 4
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    The Cape Town “Day Zero” drought and Hadley cell expansion
    Springer Science and Business Media LLC ; 2019
    In:  npj Climate and Atmospheric Science Vol. 2, No. 1 ( 2019-08-08)
    Details
    In: npj Climate and Atmospheric Science, Springer Science and Business Media LLC, Vol. 2, No. 1 ( 2019-08-08)
    Kurzfassung: In early 2018, Cape Town (population ~3.7 million) was at risk of being one of the first major metropolitan areas in the world to run out of water. This was due to a severe multi-year drought that led to the levels of supply dams falling to an unprecedented low. Here we analyze rainfall data from the city catchment areas, including rare centennial records from the surrounding region, to assess the severity of the 2015–2017 drought. We find that there has been a long-term decline in the number of winter rainfall days, but this trend has been generally masked by fluctuations in rainfall intensity. The recent drought is unprecedented in the centennial record and represents a combination of the long-term decline in rainfall days and a more recent decline in rainfall intensity. Cold fronts during the winter months are responsible for most of the rainfall reaching Cape Town and our analysis shows no robust regional trend in the number of fronts over the last 40 years. Rather, the observed multidecadal decline in rainfall days, which threatens to increase the occurrence of severe drought, appears to be linked to a decrease in the duration of rainfall events associated with cold fronts. This change in rainfall characteristics associated with fronts appears to be linked to Hadley Cell expansion seen across the Southern Hemisphere and an increasing trend in post-frontal high-pressure conditions that suppress orographically enhanced rainfall.
    Materialart: Online-Ressource
    ISSN: 2397-3722
    URL: Article
    DOI: 10.1038/s41612-019-0084-6
    Sprache: Englisch
    Verlag: Springer Science and Business Media LLC
    Publikationsdatum: 2019
    ZDB Id: 2925628-8
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 5
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    A classification of synoptic weather patterns linked to extreme rainfall over the Limpopo River Basin in southern Africa
    Springer Science and Business Media LLC ; 2019
    In:  Climate Dynamics Vol. 53, No. 3-4 ( 2019-8), p. 2265-2279
    Details
    In: Climate Dynamics, Springer Science and Business Media LLC, Vol. 53, No. 3-4 ( 2019-8), p. 2265-2279
    Materialart: Online-Ressource
    ISSN: 0930-7575 , 1432-0894
    URL: Article
    DOI: 10.1007/s00382-019-04829-7
    Sprache: Englisch
    Verlag: Springer Science and Business Media LLC
    Publikationsdatum: 2019
    ZDB Id: 382992-3
    ZDB Id: 1471747-5
    SSG: 16,13
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  • 6
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    The influence of southeastern African river valley jets on regional rainfall
    Springer Science and Business Media LLC ; 2021
    In:  Climate Dynamics Vol. 57, No. 9-10 ( 2021-11), p. 2905-2920
    Details
    In: Climate Dynamics, Springer Science and Business Media LLC, Vol. 57, No. 9-10 ( 2021-11), p. 2905-2920
    Materialart: Online-Ressource
    ISSN: 0930-7575 , 1432-0894
    URL: Article
    DOI: 10.1007/s00382-021-05846-1
    Sprache: Englisch
    Verlag: Springer Science and Business Media LLC
    Publikationsdatum: 2021
    ZDB Id: 382992-3
    ZDB Id: 1471747-5
    SSG: 16,13
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 7
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    April 2022 Floods over East Coast South Africa: Interactions between a Mesoscale Convective System and a Coastal Meso-Low
    MDPI AG ; 2022
    In:  Atmosphere Vol. 14, No. 1 ( 2022-12-30), p. 78-
    Details
    In: Atmosphere, MDPI AG, Vol. 14, No. 1 ( 2022-12-30), p. 78-
    Kurzfassung: Extreme rainfall occurred over the South African east coast during 10–12 April 2022, leading to over 500 deaths and massive damage. This study seeks to understand a key feature, namely the progression of the rainfall maxima from the northern KwaZulu-Natal (KZN) coast during the night of 10–11 April by ~550 km to the Eastern Cape coast about 48 h later. The large-scale circulation was dominated by a cut-off low over the South African interior with a strong ridging anticyclone southeast of the country in the South Indian Ocean. Satellite, rain gauge, and ERA5 reanalysis are used to show that the timing and location of the heaviest rainfall are closely tied to, firstly, the formation of a Mesoscale Convective System (MCS) at ~0300UTC April 11 on the northern KZN coast which tracked south and then offshore, and secondly, a meso-trough which formed a coastal meso-low by ~2100 UTC April 11. The meso-low tracked south over the warm waters of the Agulhas Current before strengthening into Subtropical Depression Issa. Mesoscale interaction between the MCS and coastal meso-low determined the positioning and timing of the strongest onshore low-level jet, moisture convergence and uplift, and hence the progression of the heavy rainfall down the coast. Such mesoscale interaction has not previously been documented in southern Africa or the Southern Hemisphere.
    Materialart: Online-Ressource
    ISSN: 2073-4433
    URL: Article
    DOI: 10.3390/atmos14010078
    Sprache: Englisch
    Verlag: MDPI AG
    Publikationsdatum: 2022
    ZDB Id: 2605928-9
    SSG: 23
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  • 8
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    The ‘Day Zero’ Cape Town drought and the poleward migration of moisture corridors
    IOP Publishing ; 2018
    In:  Environmental Research Letters Vol. 13, No. 12 ( 2018-12-17), p. 124025-
    Details
    In: Environmental Research Letters, IOP Publishing, Vol. 13, No. 12 ( 2018-12-17), p. 124025-
    Materialart: Online-Ressource
    ISSN: 1748-9326
    URL: Article
    DOI: 10.1088/1748-9326/aaebc7
    Sprache: Unbekannt
    Verlag: IOP Publishing
    Publikationsdatum: 2018
    ZDB Id: 2255379-4
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  • 9
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    Relationships between NDVI , river discharge and climate in the Okavango River Basin region
    Wiley ; 2022
    In:  International Journal of Climatology Vol. 42, No. 2 ( 2022-02), p. 691-713
    Details
    In: International Journal of Climatology, Wiley, Vol. 42, No. 2 ( 2022-02), p. 691-713
    Kurzfassung: The Okavango River Basin (ORB) is a highly sensitive and biodiverse region in southern Africa whose climate, vegetation and river discharge characteristics are not well understood. This study investigated relationships between rainfall, temperature, Normalized Difference Vegetation Index (NDVI) and river discharge over the region as well as their trends and interannual variability. It is found that spatial patterns of NDVI are closely related to those of rainfall, but less so with temperature at monthly and seasonal time scales. The relationships between NDVI and rainfall/temperature differ north of 18.9°S where rainfall is higher than to its south. Typically, there are lags of 1–2‐months between NDVI and either rainfall or temperature. Also, there are large areas across the region that show significant warming trends in all seasons as well as wetting (mainly in the north). This increasing trend in surface temperature may act to worsen the impacts of extreme events such as severe drought and fire in the region. There is also pronounced interannual variability with significant correlations found with El Niño‐Southern Oscillation (ENSO), the subtropical South Indian Ocean Dipole and the Botswana High for rainfall and temperature, and for NDVI with ENSO. For the Southern Annular Mode, significant correlations were found with rainfall and temperature only in December and April. On longer time scales, focus was also placed on the wet 2006–2013 period relative to much drier 1999–2005 epoch for October–December. The wetter conditions during 2006–2013 appear related to La Niña Modoki conditions and warmer sea surface temperature near Angola as well as regional circulation differences.
    Materialart: Online-Ressource
    ISSN: 0899-8418 , 1097-0088
    URL: Issue
    URL: Article
    DOI: 10.1002/joc.v42.2
    DOI: 10.1002/joc.7267
    RVK:
    RA 1000
    Sprache: Englisch
    Verlag: Wiley
    Publikationsdatum: 2022
    ZDB Id: 1491204-1
    SSG: 14
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 10
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    The sensitivity of the Seychelles–Chagos thermocline ridge to large-scale wind anomalies
    Oxford University Press (OUP) ; 2009
    In:  ICES Journal of Marine Science Vol. 66, No. 7 ( 2009-08-01), p. 1455-1466
    Details
    In: ICES Journal of Marine Science, Oxford University Press (OUP), Vol. 66, No. 7 ( 2009-08-01), p. 1455-1466
    Kurzfassung: Hermes, J. C., and Reason, C. J. C. 2009. The sensitivity of the Seychelles–Chagos thermocline ridge to large-scale wind anomalies. – ICES Journal of Marine Science, 66: 1455–1466. The Seychelles–Chagos thermocline ridge (SCTR) in the southwest tropical Indian Ocean is important for regional climate, the Madden–Julian Oscillation, as well as upper-ocean nutrients and related phytoplankton and zooplankton densities. Subsurface variability in this region has been proved to influence the overlying sea surface temperatures, which in turn can influence eastern African rainfall. There is evidence that austral summers with a deeper (shallower) SCTR tend to have more (less) tropical cyclone (TC) days in the Southwest Indian Ocean. The importance of this relationship was underlined during the 2006/2007 austral summer, when areas of Madagascar and central Mozambique experienced devastating floods, because of ten named tropical storms, including several intense TCs, effecting on these areas. At the same time, the SCTR during this season was anomalously deep, partly because of a downwelling Rossby wave that propagated across the South Indian Ocean during the previous austral winter/spring. In this paper, a regional ocean model is used to investigate the effect of remote forcing on this region and to study the sensitivity of the SCTR to changes in the large-scale winds over the South Indian Ocean, with a particular focus on the events of the 2006/2007 austral summer.
    Materialart: Online-Ressource
    ISSN: 1095-9289 , 1054-3139
    URL: Article
    DOI: 10.1093/icesjms/fsp074
    Sprache: Englisch
    Verlag: Oxford University Press (OUP)
    Publikationsdatum: 2009
    ZDB Id: 2463178-4
    ZDB Id: 1468003-8
    ZDB Id: 29056-7
    SSG: 12
    SSG: 21,3
    Standort Signatur Einschränkungen Verfügbarkeit
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