On the existence of an El Niño-type phenomenon in the Benguela System
Abstract:Since the early 1950s, although there have been several warm and cool periods in the Benguela region off southwestern Africa, e.g. the warm event in the southern part of the system during the austral summer of 1982/83, only two events which approximate to an El Niño-type situation have occurred, viz in 1963 and in 1984. During the 1963 event temperatures 2–4°C and salinities 0.1–0.2 × 10−3 above normal were recorded in the upper 50 m off Namibia up to at least 150 km offshore. The pressure adjusted sea level during 1963 was on average 4 cm above the mean. During early 1984 an intrusion of equatorial water moved southward along the coast of northern and central Namibia to 25S. This most recent Benguela Niño was preceded by an extended period of vigorous upwelling during 1982 and 1983. Higher than average pressure adjusted sea levels were recorded at Walvis Bay between October 1983 and September 1984 with maximum positive monthly anomalies of 7 cm during March and August 1984. Equatorward windstress was above average during both the 1963 and 1984 events. Although long time series in the Benguela are few, historic records indicate that in March 1950 the 27°C isotherm in the eastern Atlantic lay 600 km further south than normal, while there is evidence that a major El Niño-like event occurred here between February and August 1934, with sea temperatures 2–3°C above the long term average from March to July 1934. During the 1934 perturbation there was a reported slackening and reversal of the usual equatorward surface flow of the Benguela current and abnormally high rainfall occurred which resulted in extensive flooding of Namib Desert rivers. High rainfall over the Namib was recorded in 1950 and 1963 while some flooding occurred in 1984. Conditions were clearly anomalous in low latitudes in the Atlantic in 1934 and 1963, while there was a major perturbation in the equatorial Atlantic in 1984. This strongly suggests a nonlocal cause of the Benguela anomalies. It is suggested that there is a South Atlantic equivalent of the Pacific El Niño, but that in the Benguela region these events are less pronounced and less frequent. Their causal mechanism may also be different. The effect of these events on the southern Benguela is minimal.
Document Type: Research Article
Publication date: 1986-08-01
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