Invited talk - Broadening not Strengthening: A 24-year altimeter proxy for Agulhas Current transport
Event: 2017 Ocean Surface Topography Science Team Meeting
Session: OSTST Opening Plenary Session
Western boundary currents—such as the Agulhas Current in the Indian Ocean—carry heat poleward, moderating Earth’s climate and fuelling the mid-latitude storm tracks. They could exacerbate or mitigate warming and extreme weather events in the future, depending on their response to anthropogenic climate change. Climate models show an ongoing poleward expansion and intensification of the global wind systems, most robustly in the Southern Hemisphere, and reanalyses suggest western boundary currents have intensified and shifted poleward as a result. Here we use an array of current meters combined with satellite altimetry to develop a proxy of Agulhas Current transport since the early 1990s. We show that the Agulhas Current has broadened, not intensified, as a result of more eddy activity. Recent analyses of other western boundary currents—the Kuroshio and East Australia currents—hint at similar trends. These results indicate that intensifying winds may be increasing the eddy kinetic energy of boundary currents, rather than their mean flow, and that broadening of currents must be take into consideration when interpreting sea surface topography and temperature changes from space.