Climatological Aspects of the Coastal Wind Field at Cape Town, Port Elizabeth and Durban

Schumann, E. H.; Martin, Jeff

doi:10.1080/03736245.1991.9713548

Cited by 39 publications

(29 citation statements)

References 11 publications

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“…3. The data was low-passed filtered which allowed for an illustration of longer-period (days to weeks) changes in temperatures that could have been caused by fluctuating (2-7 days) coastal winds Schumann and Martin, 1991;Schumann, 1999), Agulhas Currentdriven upwelling (as noted by Schumann et al, 1988) and Agulhas Current warm water intrusions into Algoa Bay as observed by Goschen and Schumann (1994).…”

Section: Resultsmentioning

confidence: 99%

“…Active upwelling is defined as the period between the start and end of upwelling. Seven days were chosen because wind-driven upwelling in the study area fluctuates at periods between 2 and 7 days Schumann and Martin, 1991), so any drop in temperature over a period of greater than 7 days could probably be attributed to Agulhas Current influences, if features of the Agulhas Current such as a Natal Pulse were present offshore during that time.…”

Section: Methods and Measurementsmentioning

confidence: 99%

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Coastal upwelling on the far eastern Agulhas Bank associated with large meanders in the Agulhas Current

Goschen

Bornman

Deyzel

et al. 2015

Continental Shelf Research

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a b s t r a c tSix large solitary meanders in the Agulhas Current, so-called Natal Pulses, propagated down the eastern coast of South Africa between 2009 and 2011. Their influence on the coastal waters between Port Alfred and Algoa Bay, on the far eastern Agulhas Bank, was measured by thermistor strings moored at 30-80 m bottom depths and two current metres (30 m bottom depth) located at both sides of Algoa Bay. During all events active upwelling lasting 1-3 weeks was observed over the inner shelf and in Algoa Bay. During upwelling the isotherms ascended at an average rate of 1.8 m day À 1 as the cold bottom layer increased in thickness to 40-60 m, although upwelled water did not break the surface in all cases. Cold water remained in the area for a further 2-3 weeks. During three Natal Pulses the water temperatures at the outer moorings initially increased as the plume of the leading edge (crest) of the meander moved onshore. During one Natal Pulse upwelling was recorded before the warm water plume impacted the moorings. At the onset of upwelling currents switched to the southwest in the case of Bird Island and southward at the Cape Recife inner-bay site and reached a maximum speed of 80 cm s À 1 . During all Natal Pulses cold bottom water (10-12°C) flooded over the 80 m bottom depth moorings as the crest of the meander moved onshore, but also around the same time the core of the Agulhas Current began to move offshore. In all cases upwelling was wide-spread.

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Section: Resultsmentioning

confidence: 99%

Section: Methods and Measurementsmentioning

confidence: 99%

Coastal upwelling on the far eastern Agulhas Bank associated with large meanders in the Agulhas Current

Goschen

Bornman

Deyzel

et al. 2015

Continental Shelf Research

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“…1982, Beckley 1983, 1988. The upwelling is caused by north-easterly or easterly winds, which increase in frequency and intensity during summer (Schumann and Martin 1991). For this preliminary investigation, opportunistic data are used to investigate the effect of changes in wind direction, which occur regularly on the spawning grounds of Loligo vulgaris reynaudii, and sea temperature on squid catches.…”

mentioning

confidence: 99%

A preliminary investigation of the effect of sea temperature fluctuations and wind direction on catches of chokka squidLoligo vulgaris reynaudiioff the Eastern Cape, South Africa

Sauer¹,

Goschen²,

Koorts³

1991

South African Journal of Marine Science

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“…The seasonal movement of this belt of about 4 ø to 6 ø latitude causes the South Atlantic anticyclone to ridge eastward over the southern tip of Africa during winter, but generally to lie further south in summer. The result is that northwesterly and southeasterly winds dominate conditions during winter and summer respectively at Cape Town (see Figure 1), westerly-component winds are most common at Port Elizabeth though there is a higher percentage of easterly winds in summer, and at Durban there is little seasonal variation in the direction of coastal winds [Schumann and Martin, 1991]. The southwestern Cape has a climate with winter rainfall, while the east coast has a typical subtropical climate with summer rainfall, and the Port Elizabeth region lies in an intermediate situation [Schulze, 1965].…”

confidence: 88%

“…The first wind roses (Figure 2a Schumann and Martin [1991]. Wind speeds at Durban are also much less than at the other two sites.…”

Section: Wind Variabilitymentioning

confidence: 99%

Interannual wind variability on the south and east coasts of South Africa

Schumann¹

1992

J. Geophys. Res.

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An analysis of 38 years of wind data from three sites along the South African east and south coasts is made to determine interannual variability. Different period bands are investigated, and it is found that the northernmost site (Durban, at about 30øS) differs markedly from the two southern sites (Port Elizabeth and Cape Town, at about 34øS). At the latter sites interannual trends exist in the yearly averaged wind directions, while for Port Elizabeth the principal axis orientations including winds lying within the "weather band" also show such a trend. It appears that a major readjustment occurred at the two southern sites during the very strong E1 Nifio Southern Oscillation (ENSO) event in 1982/1983, with abrupt changes of up to 30 ø in the wind directions being registered. On the other hand, there are no clearly identifiable trends in the wind speeds, and longer time series will be needed to establish correlations with weaker ENSO events. INTRODUCTION Interannual variability involves both long-term trends, and events which take place at intervals of years. Various parameters can be used to analyze this variability, and in particular air temperature records have proved very valuable [Hansen and Lebedeff, 1987]; on the other hand, the E1 Nifio Southern Oscillation (ENSO) was identified from a difference in air pressures across the Pacific Ocean [Philander, 1983]. Wind measurements are more complex, involving both speed and direction, and by comparison with air temperature there are limited data available. While many weather and climate parameters are closely correlated, it is nonetheless true that wind data can give a different perspective on climate variability. The ENSO events are associated with changes in global wind belts, but cause concomitant changes in precipitation and temperatures [Quinn et al., 1987; EnfieM, 1989]; it should be noted that there is not unanimity in deciding whether and when some ENSO events occurred, and how severe they were. The core ENSO interactions occur along the equator, and it is important to identify teleconnections with areas remote from the dominant effects in the Pacific region. Shannon et al. [1986] failed to find conclusive evidence for an ENSO effect off the southwest coast of southern Africa, and instead postulated that less frequent "Benguela Nifios" occur. In contrast, van Heerden et al. [1988] and Lindesay [1990] found positive correlations between South African summer rainfall and ENSO events, while Walker [1990] identified "Agulhas warm events" outside of the ENSO years.

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Climatological Aspects of the Coastal Wind Field at Cape Town, Port Elizabeth and Durban

Cited by 39 publications

References 11 publications

Coastal upwelling on the far eastern Agulhas Bank associated with large meanders in the Agulhas Current

Coastal upwelling on the far eastern Agulhas Bank associated with large meanders in the Agulhas Current

A preliminary investigation of the effect of sea temperature fluctuations and wind direction on catches of chokka squidLoligo vulgaris reynaudiioff the Eastern Cape, South Africa

Interannual wind variability on the south and east coasts of South Africa

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