Title: Climate Change and the Wind-driven Ocean Circulation
Speaker: Professor Michael Ghil, Ecole Normale Supérieure, Paris & University of California, Los Angeles.
Abstract: The large-scale, near-surface flow of the mid-latitude oceans is dominated by the presence of a larger, anticyclonic and a smaller, cyclonic gyre. The two gyres share the eastward extension of western boundary currents, such as the Gulf Stream or Kuroshio, and are induced by the shear in the winds that cross the respective ocean basins. This phenomenology is described by a hierarchy of models — quasi-geostrophic, shallow-water and primitive equations — with an increasing horizontal resolution and number of vertical levels. We study the interannual variability of this wind-driven, double-gyre circulation in mid-latitude ocean basins, subject to time-constant, purely periodic, and more realistic forms of time-dependent wind stress, both deterministic and random.
Analytical and numerical methods of dynamical systems theory are applied to the models of interest. We discuss the associated pullback and random attractors and the non-uniqueness of the invariant measures that are obtained. The effects of the oceans’ variability on the atmosphere above are explored and compared to observations. Finally, connections are made with the highly topical issues of climate change and climate sensitivity.