Equatorward wind and atmospheric pressure spectra as metrics for primary productivity in the Benguela system

Abstract

Through its connection with upwelling, averaged longshore wind displacement is often invoked as a metric linearly related to productivity on timespans of months to seasons. In this paper, the linearity of such a relationship is questioned by analysing Ekman divergence against the modifying influence of freely propagating continental shelf waves. Both arise from common synoptic forcing events. Also considered is how the periodicity of the wind can be a more important factor in estimates of productivity than the integrated strength and duration of longshore wind. A suitable phase relationship between remotely generated coastal-trapped waves and local wind is a requirement for efficient upwelling. The theoretical concept of a metric for productivity, using a representation in an n-dimensional frequency space, is proposed.