Pulsing of the Benguela upwelling region: large-scale atmospheric controls

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Abstract
Large-scale atmospheric mechanisms which control coastal sea temperatures, sea levels and alongshore currents in the southern Benguela region are investigated. The influence of upper atmospheric Rossby waves in the mid-latitude westerlies is transmitted to the shelf circulation via coastal trapped waves in the atmosphere/ocean, and the physical environment becomes pulsed. Autocorrelation statistics identify an irregular upwelling-downwelling cycle with periods of >20 days in winter; summers exhibit a faster 10-day pulsing. The average time between successive upwelling pulses is 23 days. Relationships between large-scale atmospheric Rossby wave structure and the local shelf response are analysed on the basis of selected hemispheric weather charts at the 500 hPa level. Cohesive hemispheric waves of length 8 000 km (Wave 4) contribute significant energy to the pulsing. The shorter westerly waves (5 and 6) induce rapid and less distinct oscillations.

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