Campuses:

Bifurcations and Pattern Formation in Earth's Fluid Envelope

Tuesday, September 25, 2001 - 2:00pm - 3:30pm
Keller 3-180
Michael Ghil (University of California, Los Angeles)
The global climate system is composed of a number of subsystems ­ atmosphere, biosphere, cryosphere, hydrosphere and lithosphere ­ each of which has distinct characteristic times, from days and weeks to centuries and millennia. Each subsystem has its own internal variability, all other things being constant. The nonlinearity of the feedbacks within each subsystem can result in the coexistence of stable equilibria, the presence of self-sustained oscillations, and the possibility of deterministic chaos. Multiple equilibria are discussed in the context of the radiation balance that dominates the thermodynamically open climate system, and the energy-balance and radiative-convective models that describe this balance.

Transitions between multiple equilibria may play a role in climate change on intraseasonal (10­100 days) and on multi-million-year time scales. On the interannual and interdecadal time scales of greatest interest to long-term socio-economic planning, it is oscillatory behavior ­ regular or irregular ­ that seems to be most important. Oscillatory behavior is illustrated in models of the oceans¹ thermohaline circulation. It is shown that the bifurcation-theoretical tools of nonlinear dynamics can be applied to fully three-dimensional general circulation models of the ocean with considerable spatial detail and even to coupled ocean-atmosphere models.

Given the complex behavior of the climate system on a full range of time scales, its predictability is discussed and conclusions drawn about the state of our knowledge. Possible approaches for expanding this knowledge and applying it wisely are explored.

References

Ghil, M., R. Benzi, and G. Parisi (Eds.), l985: Turbulence and Predictability in Geophysical Fluid Dynamics and Climate Dynamics, North-Holland Publ. Co., Amsterdam/New York/Oxford/ Tokyo, 449 pp.

uid Dynamics: Atmospheric Dynamics, Dynamo Theory and Climate Dynamics, Springer-Verlag, New York/Berlin/London/Paris/ Tokyo, 485 pp.

Ghil, M. (2001; PDF file): Natural climate variability, in Encyclopedia of Global Environmental Change, Vol. 1 (M. MacCracken & J. Perry, eds.), Wiley & Sons, Chichester/New York, in press.

Ghil, M. (2001) Revised version (PDF file). Hilbert problems for the geosciences in the 21st century, Nonlin. Proc. Geophys., in press.

Ghil, M., and A. W. Robertson (2001; Postscript file): Waves vs. particles in the atmosphere's phase space: A pathway to long-range forecasting?, Proc. Natl. Acad. Sci., submitted.

N.B. References #3­5 are available at http://www.atmos.ucla.edu/tcd/MG/mg_ref_preprints.html