Departmental Seminar: The Wind-Driven Ocean Circulation: Bifurcations, Simulations and Observations by Dr. Michael Ghil

January 12, 2017, 3:30 pm, Burnside Hall 934

Dr. Michael Ghil, Distinguished Research Professor, Atmospheric & Oceanic Sciences, UCLA

Title:  The Wind-Driven Ocean Circulation: Bifurcations, Simulations and Observations

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 physical 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 low-frequency variability (LFV) 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 analytical and numerical methods of dynamical systems theory are applied to the models of interest. Recent work has focused on the application of non-autonomous and random forcing to  double-gyre models. We discuss the associated pullback and random attractors and the non-uniqueness of the invariant measures that are obtained. The effects of the oceanic LFV 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. This talk reflects collaborative work with a large and still increasing number of people.

Please visit

https://dept.atmos.ucla.edu/tcd for their names, affiliations, and respective contributions.

References

1. H. A. Dijkstra and M. Ghil, 2005: Low-frequency variability of the
large-scale ocean

circulation: A dynamical systems approach, Rev. Geophys., 43, RG3002,
doi:10.1029/2002RG000122.

2. M. Ghil, 2016. The wind-driven ocean circulation: Applying dynamical
systems

theory to a climate problem, Discr. Cont. Dyn. Syst. – A, 37(1), 189–228,
doi:10.3934/dcds.2017008.