Observed Agulhas Current sensitivity to interannual and long-term trend atmospheric forcings

Of the interannual variance of the Agulhas Current transport, 29% can be linearly related to six modes of Southern Hemisphere atmospheric variability. Agulhas Current transport is quantified by a 24-yr proxy constructed using satellite altimetry and in situ data, while atmospheric variability is represented by two reanalysis products. The two leading modes of atmospheric variability, each explaining 5% of the variance of the Agulhas Current, can be described as a tropical Indo-Pacific mode, strongly correlated to ENSO, and a subtropical-subpolar mode, strongly correlated with the SAM. ENSO alone can explain 11.5% of Agulhas transport variance, yet SAM alone has no significant correlation. The remaining four atmospheric modes are not related to common climate indices and together they explain 19% of Agulhas variance, describing decadal oscillations. In previous studies using reanalyses and climate models it has been suggested that the Agulhas Current is intensifying in response to a strengthening and poleward shift of the westerlies, expressed by a positive trend in the SAM. Here, the authors find that, given its apparent weak sensitivity to the SAM, the increase in SAM over the past 24 years does not lead to a detectable trend in Agulhas Current transport.